zredbaron

Nice! Well, not nice.... but nice to know! I was never very impressed with changing E tubes. Thought I was missing something. Probably still am. Hard to believe, I remember we used to get 20 emails a week on this thread. I have two updates, well, maybe they're sort of the same update: I will be engine-dynoing my new, rebuilt, new-rebuilt race motor (third time's a charm!) this spring / summer. I will be comparing 40 DCOEs (36mm venturis) to 45 DCOEs (36mm venturis) on the same motor, same day (two Cannon manifolds port-matched respectively). I don't know of such a comparison on the internet or in a book for any application. The comparison isn't fair to the 40 DCOEs, as my head outflows what the carbs can deliver. This is the whole point of the unfair experiment... to compare the dyno plots of a restricted intake (past the Weber flowcharts) to a more appropriate intake (within the charts). Appropriate being relative, of course, because 45 DCOEs are still a top-end compromise for a full race motor, and this is a deliberate compromise to maintain low-RPM torque and throttle response (autocross). This experiment is partly a result of painting myself into a corner in a discussion that came up on my engine thread, and partly out of my own curiosity and enjoyment of our mutual hobby. Weber debate begins here, which ultimately trails off with me citing a Weber chart and then saying I'll let the dyno settle the debate once and for all. My theory is that the draw of the pistons at a given RPM creates a given vacuum signal regardless of intake, drawing metered amounts of fuel set by the carburetor / jet combo. If under-carbureted, inadequate air matches fuel metered for adequate air, producing a rich condition. (The carburetor "feels" more airflow than is actually present.) This cannot be patched at high RPMs with air correctors, because what the engine needs is a more open intake, period. The thread has been pretty silent, not sure if I was too aggressive with my argument? Regardless, should be a fun experiment. We all expect HP and torque to rise... but what about the A/F graphs? What will those look like? And no, I'm not trying to send the debate to this thread. I've already typed too much on the subject as it is! Just completing the circle and replying to Steve. He's right, it's been a long time coming.

Thanks Ryan. Infinitely grateful the head and cam survived! I feel the same way! When I first started the engine and tinkered to synchronize the carbs (linkage), I was so intimidated by its sound that I cut the engine off several times, generally worried that it was about to damage itself. I was even so stressed that I asked my father and uncle to leave -- they were shouting their opinions over the engine, which didn't help. I brought that concern to the chassis dyno, where I hoped to confirm something one way or another. Men far more experienced than I smiled at the sound and said everything sounded just fine -- awesome, in fact. "I ain't ne'er heard a six-shooter sound like that, boy!" (--probably not the most technical reply available, but fully Arkansas! Haha.) It's really hard, and costly, having a strong instinct of the truth but lacking enough grasp to articulate it in a useful way -- even harder to tell if you're the only one that's right or if you're the only one being arrogant. Similar trend with my carb theories!

So where are we now? Joe uses a shop to repair catastrophic damage like this. Didn't get any pictures of the head damage, unfortunately. Evidently this shop uses a laser technology to map out another combustion chamber and duplicate it on the damaged cylinder. Neat! The head came back last week: Parts beyond repair: Valves, guides, spring retainers, block, bearings, pistons, 3 rocker arms Survived for another day: Camshaft, crank, rods, On order: New JE pistons via Rebello. As per Joe: .210" exh pocket depth, .190" intake pocket depth. Arrives January. 3 rocker arms and 12 titanium valve spring retainers via ZCCJDM. Arrive when they arrive. Competition oil pan via DP Racing. Arrives January. Or when it arrives. Planned but still pending: Send head, pistons and valves to SwainTech for thermal and friction coatings As per Swain: greatly increases engine longevity plus a guaranteed 2-5% hp gain for an NA engine if you do all coatings. Can thermal coat intake manifold, too. Not now. CC, exhaust port, valve face and radius side, and piston top all get a thermal barrier coating sides of the piston get a low-friction coating The technologies: http://swaintech.com/race-coatings/race-coating-descriptions/ The options: http://swaintech.com/race-coatings/automotive-coatings/automotive-coatings-price-sheet/ (Can you tell I want this engine to last?) Hah!

Way past time for an update. In April I pulled my engine, determined to have it open within a couple of weeks. After several phone calls and inquiries for an L6 engine builder in the pacific northwest, I chose to go with Joe Harlan of Top Tech Motorsports. Joe was very clear that I would wait for a while. Story of the industry, it was longer than we thought. My engine sat on the floor of my storage unit for about four months until he was able to receive it and open it up. When we spoke about what might have happened to the engine, Joe repeated the word "sad" more frequently than anything else. His conclusion is that the valve lash was set wrong across the head, every exhaust valve was coming into solid contact with the piston and to make matters worse, the twin idler pulley was evidently installed absurdly tight. He felt strongly that the build suffered from a lack of attention to detail throughout, and pointed to the valve reliefs being reversed (in/ex) for each cylinder, which is part of the problem lacking clearance (I don't see this reversal reflected in the pics). Lash was wrong, regardless. "Sad." Clearly only a matter of time before something gave. I still recall vividly how concerned I was when I was breaking it in--the engine sounded labored and unhappy from the beginning. Guess I was right. Wish I was wrong! The suspected sequence is rocker arm failure at the point of its largest weight relief (sparing camshaft damage?), valve collision into spark plug and compressed sideways between the piston and the combustion chamber of the head, piston and head both lose to the valve, throwing bits of metal into the intake plenum and into the next two cylinders, hence the oil going down those exhaust runners as well. Here are the pictures of the pistons:

+1 for me too, Gary! PM sent. Still marveling at the Li battery you sent me via your day job. Top notch, thanks again for the advice!

Somehow I don't think those are the specs theatriks is looking for. Nice build though! I like the Nissan pistons cast with reliefs. Hang onto those! As for the blue car... ironically, the green one edges it out in the race. Happens right before the guy walks in front of the camera. High-end NA L6s have radically different sounds from the ones I've heard, to include both in this video. The green sounds like a much higher pitch, really gargly. Sounds like it's more highly tuned up to the top of the RPM band, and the blue one sounds like it's the muscle car and has the grunt. But that's my ear. Is that why you like the blue one?

Ok, time for the Weber charts! Clearly not much of a social life at the moment. We don't know where the dotted lines are between successful and failing modes of operation, and the books can't talk about what's going on when I'm still running the same carbs from the stock 2.4L I had 17 years ago. They can't talk about it because it's literally off their "here's what is possible" chart, which is not something to brag about, but rather affirms that larger carburetors are needed. Since I'm off the flow chart, the high cfm demand isn't possible, so it fails to occur. This is BAD! [it "stalls?"] This is one of the worst things to happen to a carburetor. Not tunable. Jets and floats won't help you, because the pistons are too big and too fast. Wrong application. Fail. Pointing at venturis is not a mental attachment, it's an interpretation of the Weber charts. The attached chart only depicts the upper capability of flowrate (WOT), it does not tell us what happens when demand from a larger engine exceeds it. Note that chokes in a 40 DCOE perform wildly different than the same size chokes in a 45 DCOE body! (The exit of the body is a different diameter, which is clearly very influential.) If I were keeping the 40 DCOEs, I'd consider trying the 34mms chokes as per the aux venturi note in the book. I still might. It's my understanding the aux venturi helps more with mid-throttle positions at lower RPMs than WOT in the power band, but I'm not certain. You're right, we don't talk about it much! Based on the book, I'm guessing it would help my pre-4k RPM stagger and minimally cap peak hp even further. This chart shows us that a 45 DCOE might even be too small for me, but I'd like to see the 48 DCOE and 50 DCOE graphs for comparison. (I'd prefer to not be at the plateau range of operation.) The benchflow performance of my head was 205 cfm / 235 cfm, depending on some detail of their test that I don't recall. Not sure which number to go with, but both exceed the 40 DCOE's capabilities by a longshot.

By the way, when a turbine is stalled (again, a turbine is a glorified air pump), the solution is to slow it down until the stall clears (laminar flow restored), and then spool it back up. It will never, ever suck in laminar flow ever again until you slow it down below the speed in question. This is no different than power sliding; we must remove power until we regain performance, or traction. Adding or maintaining power will continue the lack of traction indefinitely. This is peeling out through our intake. I am submitting that If a turbine can be stalled, a carburetor can be stalled. All pumps are subject to cavitation, and a 4-stroke engine is a pump.

Steve - Fuel level? Do you mean the carburetor floats? Yes, precisely measured as per Weber guidance on plastic floats. I agree a bad float level can ruin an A/F graph, but I feel strongly this is not the issue. Again, the A/F graph responds to my jets very predictably, same as in 2008, just not enough since the venturis and are wrong and mains do what they can with what they've got. If it were floats, the A/F ratio would fall apart and my jets wouldn't affect it nearly as much. In my experience, the main jets raise/lower the whole A/F graph, but don't really change its shape much. Venturis, emulsion tubes, float levels and air correctors adjust shape. Anyone experience these differently? (In all objectivity, I really only have experience tuning "an undercarbureted stroker," so perhaps my experience is skewed?) No 02 sensor, the exhaust was never completed. The only data I have for either RIP motors is the 2015 dyno A/F graph. I agree with your point about high RPM ignition, but I really don't think that's a variable with Electromotive ignition. Very consistent, precise, powerful and long spark... so personally I for road tuning I turn exclusively to the carburetors once the timing is dialed in for a given build. madkaw - Thank you! Agreed. Too small, let the numbers do the talking and compare the tales of the tape. EDIT -- I do have a MAP sensor installed, after all. If a dyno could receive the signal from my sensor, we might actually get some data? I'm not following you. I've been talking about a lack of airflow, you previously presented that I wasn't rich from a lack of air but excess fuel... and when asked about the source of this excess fuel the answer is excess airflow? How did we get here? Where is this excess airflow coming from? The carburetors that are undersized? No, my quick summary is that fuel delivery rises consistently as a mechanical response to rising pressure differences, which is a crude approximation of pedal / demand. At some speed, air delivery isn't able to keep up with the rising demand, so increasingly inadequate air volume is paired with adequate fuel as RPM increases past the speed in question. The concept I point to, for the time being, is that the laminar airflow "stalls" on the way in and becomes turbulent, which drastically decreases air density and therefore total O2 available for combustion per unit volume. To your point, yes, I am suggesting if we had a MAP graph across the RPM range, instead of seeing a consistent shape as RPM rises, we would see a dip in MAP from the moment the carbs became restricted. This dip in pressure would send less fuel, yes, but would contain *significantly* less air density than that same pressure signal normally contains (when the intake isn't "stalled"). Remember, we can produce 1 atm of pressure with temperature, density, speed, and shape. The metered delivery of fuel in response to the pressure is only appropriate for one and only one air density. Combusting "less fuel" with "way less air" results in a rich condition, and the farther these two grow apart, the more rich we go. If we still see it differently, may I ask you to compare an ideal carb to a restricted carb in your mind? Perhaps our fog is here? Haha. If the 40 DCOEs are inadequate, what is the variable that is inadequate? What happens to the A/F ratio when this variable is inadequate and why? Would one carb would have limited adjustability with jets and why?

Hah! Round and round we go! Ok, let's try the simple route. Where is the excess fuel coming from then, if there isn't a lack of oxygen (air)? And if that were the only variable at play, then why can't I correct the condition with smaller jets? Are you proposing that 40 DCOEs are adequate for all applications?

We're definitely honing in the discussion, at the very least! I thought your descriptions were just fine, Brady. You and Steve are much better at being concise than I! 100% agree! This is where we diverge. Volumetric flow rate will be proportional to mass flow rate, yes, but I'm saying they will diverge farther and farther from one another with higher demand/restriction ratios (velocity continues to increase). You seem to indicate they are a given proportional relationship for given atmospheric conditions. From what I can tell, I have different conclusions because you and Steve are fixated on the tools we have and how to use them, and I'm fixated on the details of our physical limitations as a basis for engine design. (I just edited my last post and worded the phenomenon as more of "stall," if that changes anything.) I haven't measured vacuum, but I haven't observed anything that looks like measured vacuum would be a helpful direction, either. I have a vacuum canister to help with braking (it does nothing). I also have a MAP (manifold absolute pressure / vacuum) sensor hooked up to my ignition, so that it can vary advance with sensed load. I've dynoed it with and without the MAP sensor hooked, up, and it doesn't really affect the engine performance. Again, "good vacuum" can only be observed with proper carburetor and venturi selection, and not all camshafts are equal. If you're suggesting an experiment could be set up to observe where the "stall" occurs, I agree! I don't have any vacuum data for that, no. "Rich" is a condition involving combustion chemistry and nothing else. If the engine is rich, there is more fuel than there is available oxygen, period. There are no other variables such as volumetric efficiency, conditions, etc. -- those determine how we get there. The bottom line in combustion is chemistry, so only the balanced stoichiometric chemical equation matters. The carburetor parts and/or EFI are how we benefit from obeying the stoichiometric equation; the parts are not how we bend the laws of physics to our will. A carburetor is a "dumb" device that simply responds to pressure differentials, we agree. It has no idea what the composition of the "air" is, therefore it's up to the human to mechanically choose the appropriate jets, venturi, etc. Its purpose is to deliver a metered amount of fuel based on pressure difference. This pressure difference is a very crude approximation of engine demand, and it knows nothing about the air density. This approach is over 100 years old, let's not forget! Engine demand is responded to with a metered amount of fuel, and delivery is unverified. Too little or too much, Goldilocks, you get what you get. Enter EFI, and this entire conversation is now unobservable. We are still subject to the laws of physics, but now the symptoms are nearly invisible. An O2 sensor immediately senses that there is a shortage of O2 (or abundance) and adjusts how long the injector stays open on the next engine cycle, balancing the stoichiometric equation as per the computer's programming. When the car used to fall flat on it's face and say "choose a different venturi, I need more air, stoopid" now the computer smooths it out and I don't have to feather the throttle. I'm simply "not in my power band yet" because my cam is so aggressive. Wrong, but partially correct. The power band is still restricted, and the computer feathered the fuel delivery instead of my foot feathering the throttle plate. Neither the computer nor the jets addressed the physical limitation that the venturi is the wrong size or that VE was inadequate for engine demand! From what I can tell, you and Steve are talking about fluid flow like it's a "given day" type of static variable. Yes, that is a huge part of the foundation, but the science that's dedicated to it studies dynamics, not statics. I keep hearing "tune the carburetor, they're very tunable." I agree, but I don't hear anyone acknowledging that if we put a single SU carburetor on a big block V8, that carburetor wouldn't be tunable. They're only tunable on the right applications! VE isn't some subtle, in-the-weeds technotalk that can be left for the engineers. It's huge. Our Datsuns' OHC intake system is from the dark ages, and so are carburetors. We can't limit our thinking to the words printed in Weber books decades ago, technology moves way too fast these days for that. Let's not forget that Koenigsegg and Ferrari are all about intake VE via variable length manifolds: http://en.wikipedia.org/wiki/Variable-length_intake_manifold VE changes so much at different RPMs and different pedal positions, that intake manifolds themselves have been discovered to be one of the most significant areas for improvement in VE, which gives us both power and fuel economy. VTEC is another way that intake VE limitations are addressed. Multiple valves are another. ITBs vs. EFI is another. We mask our VE limitations with a vacuum advance distributor or vacuum sensor + pedal position for EFI, but both are simply patches to our gaps in fluid flow performance. Variable intake manifolds and VTEC address the limitations. Talking about tuning the carburetor or the computer is a patch; talking about carburetor selection or the intake system's design addresses the limitation. Do the old carburetor books talk about how important intake VE is? In the language of 1985's understanding of 1965's technology, they mention it, you bet. In the language of what Formula 1 and EcoBoost are doing in 2015, those books don't have any idea what we're talking about these days, and they'll guide us back to yesteryear if we let them. Wow, Weber DCOEs are over 50 years old! That's pretty crazy.

One or more of us are barking up the wrong tree, no doubt! Haha. Good stuff, learning is underway! [significantly edited for readability, this grew rather long! I made no assumptions about technical backgrounds.] No, I'm not saying the carburetors provide more fuel as the demand for air volume remains the same -- I'm saying the carburetors provide a constant amount of fuel, but when severely restricted, the *mass* flow rate of oxygen doesn't keep up with increasing demands for volumetric flow rate of air. I'm saying the more an intake system is restricted, the less laminar the airflow through a wider operating range. Less laminar fluid flow is less dense, which means less O2 is available for combustion. Same volume of "air" carrying less O2 mixed with the same amount of fuel, and the engine goes measurably rich. Let's take a step back. The carburetors come in different housing sizes (40, 45, 50) and offer different venturis. The manufacturing and performance industries both recognize that the airflow requirements to realize 150hp through 2.4L are different than realizing 300hp through 3.1L, both in terms of peak power and drivability. The airflow adjustments are with our intake shape and size, the venturis in the case of sidedraft carburetors, do we agree? None of us are talking about having to upgrade our fuel pumps or fuel lines, we only make fuel adjustments with jets. (The air corrector jet is not a "corrector" but the finest last-stage adjustment; it cannot provide adequate adjustment range if an improper venturi or main jet is selected.) Practically, if we had a fully-tuned race engine running 50 DCOEs and we were to then place 40 DCOEs on this engine and severely restrict it, I'm here to argue that there is no collection of jets that allow this 40 DCOE engine to have a remotely flat or stoichiometric A/F line ~5000 RPM and above, because the carburetor body does not allow proper venturi selection. It tapers way rich no matter what, making jet selection simply a matter of how early or late (RPM) you want to cross the stoichiometric line (main jet) and at what angle (air correctors). I choose to enter the region lean, and split the difference, knowing it will be going way rich unavoidably. Why this limit exists is another discussion, and here's my take. The short version: the air is "stalling" on the way into the engine. The detailed version: Fluid is of course any composition of gas and liquid, a good example being "air." Mixed composition fluid flow through an open system is very, very complex. It isn't simply water through a hose (same in, same out) and it isn't a wing moving through the fluid, or air. It's both and neither. In addition to its static variance in composition, pressure and temperature, fluid flow does all sorts of hard-to-control things: it can compress and expand, it can speed up and slow down, it can be laminar and dense or turbulent and unpredictable. In subsonic fluid flow, the faster a fluid travels, the more head loss or parasitic loss is encountered (drag or friction, essentially). As velocity and its associated losses continue to increase, the laminar layers of fluid flow are further separated from one another and the fluid flow becomes more and more turbulent and less dense. This means that above and below the one and only one ideal speed (the one speed with the fewest losses for a given set of conditions), as speed diverges further from the sweet spot, *mass* flow rate continues to decrease. For example, the reversion range might be for speeds too far below ideal, and the stalling range would of course be for speeds too far above ideal. What I don't know, is how far into the turbulent regions of fluid flow we are going. Reversion is a specific form of turbulence, and so is stalling. This discussion is much of why I would like to dyno the 40 DCOEs "fully tuned" and then 45/50 DCOEs fully tuned. ("Fully tuned" meaning the best I can do with the limitations of my jets, venturis, emulsion tubes, timing, etc.) The dyno plots would offer some of the data this discussion currently lacks. Similar fluid limitations are also present in propellers & pumps and wings & turbines. Cavitation occurs with propellers and pumps when a liquid can't move as fast as the conditions are asking it to (pressure difference is too great). Stalling occurs with aircraft wings and a turbines (an air pump comprised of thousands of tiny wings) when the pressure difference is too great, and the airflow goes from laminar to turbulent. I find it helpful to make the correlation that stalling is to gases what cavitation is to liquids; liquids and gases are both fluids, and both fluids respond unfavorably to excessive pressure differentials. The crankshaft and pistons are an air pump. Not quite a water pump, not quite a turbine. A piston-driven [compressible] air pump, like for inflating tires, is very crude in terms of fluid flow performance, or VE. The pulsing of fluid flow screws everything up bigtime, which is what centrifugal pumps and turbines were designed to overcome (but the rotary engine does not). Valvetrain and check-valves do not dampen pulsing, they only truncate or rectify it. I submit that with small enough straws and big enough slugs at a high enough RPMs, the airflow stalls (the pump cavitates if you like) as the flow goes from laminar to turbulent. This stall would be occurring I suppose in a toroid shape across the plane of the venturis or air horns or both and the stall would probably extend for several centimeters downstream before recovering to more laminar flow, but that's just theory of course. The molecules simply can't get into the hole fast enough, and since a gaseous mixture is compressible they end up fighting each other on the way in. This allows fewer total molecules through the door, just like a panicked room full of people relative to an orderly group. No really, it's for your health, people: try and stay calm. It's like the opposite end of peeling out, but through your air intake system (the first molecules from world to car) rather than mechanical power output (the first molecules from car to world). You tried to access/wield more force than physics would allow. "You suck too fast, you drive slow now." When fluid flow can't keep up, all bets are off. In supersonic fluid flow this manifests by all relationships becoming inverted (venturi principle is inverted). I'm not suggesting supersonic velocities are reached in our intake systems, I'm simply highlighting that you can't put fluid into a single conceptual box, or it will find a way to spring a leak and remind us that we're still figuring fluid out more and more every year. That's why fluid is also a verb; nothing else behaves like it. The moment we make a rule for it, we need to provide rules for its exceptions, which we normally haven't discovered yet. Sounds a lot like the laws of man, but let's leave the politics out of it! Haha! Cheers, fellas. However this fog lifts, let's clear the air!

I think we're talking about two different modes of operation. I have two separate RPM ranges with two separate breathing challenges, and they can't quite be interchanged. Below 4k RPM, as per Dan Baldwin's comments and several of our dyno plots, with big cam overlap the engine simply doesn't breathe well. Reversion is perhaps the issue at this in-between mode of operation where the intake system is very unhappy and VE is very low. This is a mainly a function of the camshaft duration and is worsened by running triple carburetors as opposed to EFI. I imagine the aux venturi of the DCOE exacerbates this issue relative to ITBs, since they have more of a straight-through design. Above 5k RPM (or so), for my engine specifically, I'm undercarbureted. The main venturis can't supply an adequate volume of air, and this is observed on my A/F graph as it tapers more rich as RPM increases. Said another way, since I'm running 36mm venturis, as RPM continues to increase past ~5000 rpm, my VE decreases. To the best of my knowledge, this will still occur with other venturi sizes and even ITBs, the graph shape will simply taper differently. Perhaps with ITBs this can be almost negligible if the correct sizes are chosen for a given application. But hey, this is a layman's understanding, and this layman doesn't have a very good track record at the moment...

bradyzq -- Thanks for the graph analysis! It's interesting that the curve shifted to the right. There are a lot of changes between these motors: outer-springs only, freshness of fuel, Stahl headers, no airbox, lightweight rocker arms and retainers, twin idler gear, and an adjustable cam pulley (which looks to be around 1 degree in my pictures, I think it was at 0 degrees in 2008?). Power doesn't really fade much at the 7500 RPM redline, either, which I didn't expect. Stahl headers, I suspect, allowing the head and cam to perform as they would. Yes, I'm running Electromotive's XDI ignition. I will be upgrading to their TEC-3R or whatever they'll call their current version when I get to ITBs. Currently my high RPM A/F ratio goes way rich because the 40 DCOEs with 36mm venturis can't supply the engine's air requirements above 4-5000 RPM. Oxygenated fuel helped! No air filter, no hood, just air horns. Exactly as shown in the video. At the time of the failure, I was driving behind traffic at about 10-15 mph @ 3k RPM, an easier speed for bouncing pebbles to have a fighting chance, perhaps even thrown up from the old slicks a couple feet away. Let's not forget I was in AR's Ozark Mountains, where more mud and rocks are flung around than just about anywhere else. Whoops? EDIT -- I'll have to get back with pics of the spark plug when able. I think the exhaust valve looks bent too, but I'm not experienced enough to pronounce it so. Yes, I suspect reversion between the intake manifold and the exit of the carburetor is the bulk of what we're experiencing under 4k, and I'm pretty sure that's what Dan Baldwin was describing as well. So did retarding the cam help driveability? I understand in theory it might, but how did it drive? That's why I have the adjustment available... After all, I'm not seeking a WOT high hp motor but a wide graph with power under the curve for autocross. ryant67 -- You're absolutely right about those airbox rivets! They don't last... the vibrations ream out the fiberglass and the rivets fall out. I drilled the problem-rivets out and replaced them with nuts and allen head screws in 2008. EDIT -- The airbox wasn't on the car when the incident occurred because it conflicts with my shock tower modifications for strut braces. The box is old and now it won't ever fit anyway, so I'm trying my hands at a fabrication experiment with it. It'll be a while before I return to it, but this is how much I ended up cutting out in order to use the box with a Canon manifold and my strut tower modifications. I cut rectangular shapes because I'm going to use sheet rubber so the box can "be flexible" when removing or installing, but pop back out into full shape once the maneuvering is complete, returning the air box to nearly the same performance characteristics. Leaning towards clenching the sheet rubber with fiberglass patches on both sides, but I'm not sure how that will hold up and will need to experiment first.

Thanks for the collective encouragement and support, guys. It isn't expected, but it sure does help. Thank you. Ouch! I still can't believe how fortunate I was to have a rocker arm break so cleanly. I think you're right, I think something got in there. When I put a flashlight into the exhaust port, I saw several very small, shiny dings (~.1mm thick, ~2mm long) in the otherwise very oily port, all concentrically parallel along the cored passageway toward the port. (Does that even make sense or is that technical nonsense? LOL!) It's really odd, actually. Maybe a piece of rock or nail found its way past the carburetor but found the valve seat, snapping the rocker arm and glancing the valve into the spark plug? Conjecture, but it's my running theory. EDIT -- Oh, and the broken rocker on an exhaust valve would explain the missing oil, right? If oil could enter the combustion chamber due to the damage, then it would have an open path out the exhaust leaving the headers quite oily? The missing oil was on the road behind me? Unfortunately I didn't have my USB boroscope to investigate the valve. I do remember seeing 3-4 black bits on top of the piston, next to the busted-up valve reliefs. The resolution and light didn't allow me to make out if they were just broken bits of the spark plug or if something else was present too. Yes, Brian's final design has significant weight reliefs. I don't suspect the rocker arms at this point, but who knows. I didn't touch any of the valvetrain; I snapped a pic exactly as I found it for this very reason. I always appreciate additional theories! I'll refer you to Dan Baldwin on this one: To dramatize it, I've accepted that the carburetors are basically telling us "Clatter all you want, I will not and can not rape that village." I've referred back to this VE limitation a number of times, both for tuning and the realization that this limitation is what makes the car all the more awesome when it's an "on" day and all the more classic / manual when it's an "off" day (still awesome). So for me, road-tuning a carbureted, aggressive L6 has two basic components: above 4k for AFR / power and below 4k to minimize feathering regardless of AFR so I can get back in the power band! Makes it much more driveable on course, too. [...case in point...] ...but FI is coming! Agreed.

Glad to hear all that typing wasn't just hot air! The art comment was unexpected, thank you. Super glad to hear you got lucky with your compression! Hmm, I'm surprised I missed the competition pan on DP Racing's website. Jon, you were referring to the AZC pan and not this pan, correct? Looks like the comparison is $300 cheaper for a cast-aluminum pan with potential pickup issues vs. an $800 forget-about-it solution. Hmmm. Negligible performance difference? I would think aluminum would transfer heat better, but I don't see it being an "issue." Any other experience is of course welcome! And in other news... the engine is out! I had a chance to pop off the valve cover and found #1 exhaust's rocker arm split in half at a minimum. I also found oil throughout the header runners for cylinders #1-3. Pics below. I wonder what the heck happened in that cylinder? Not knowing what caused the failure, it looks like the CNC rocker arm took one for the team in a very neat, let-everything-else-live sort of way. Maybe it was the failure, but then again maybe it saved the head and cam from further damage? Hopefully the engine builder will be able to make a determination.

Cheers to that! For a quick moment, my heartbreak wanted me to run away and pursue something safe that wouldn't risk failure or being disappointed again. And then after about half a second I grunted and plunged myself aggressively back into the arena. I knew I'd never stop longing for its pursuit.

Thanks Brady. That's my guess too. Again, great feedback with the tensioner Garrett, thank you. That's crazy! Did enough of a collision occur to lower / lose compression, or did you luck out? I can't quite make out your image. I didn't touch the tensioner, only the engine builder did. Slippage is possible I suppose. The chain was tight to the touch when I took the pic of the idler gear and since then the bolts haven't moved visually. I would think it would have to slip noticeably in order to jump a tooth, and would also think that all cylinders would be affected equally? Thanks for the oil pan suggestions, Jon. The Nissan Competition pan seems to be made of unobtanium, it didn't turn up on any of my internet searches, though it steered me to Kameari (again). Evidently the Kameari pan is > $1,500!? Haha! I might be one of the fools who's willing to sacrifice price if I feel I'll get what I pay for, but that's a ridiculous amount for a similar product. Looks like I'll be steering toward AZC. (Now that I think about it, I didn't think to check if Nissan still offers it. Too obvious?) I had a chance to dig out the copy of my dyno runs from a couple weeks ago. Evidently my memory with the numbers were a little generous! Haha, the poor sap was trying to make up for his heartbreak... The tale of the tape: 235 whp, 205 ft-lbs. Not shabby at all, however comma, the 2008 dyno was 264 whp, 249 ft-llbs with street headers and a lesser, non-oxygenated VP race gas. (Not that I think I had any oxygenation after 3 years, I simply mean that non-oxygenated fuel produced 264 in VA.) I went ahead and attached the 2008 dyno runs for comparison. As JohnC pointed out regarding my A/F ratio, it's awful. [below 3,500 RPM especially, which he called out predictably I might add!] As for the performance: fuel, friction, tune...? I'm not worried about the performance discrepancy at all, it drives like a totally different engine in the most intoxicating way. The purpose of the dyno pulls were to confirm all was well mechanically and timing-wise with the engine so I could confidently tune the carbs, order more jets, burn the fuel drum up and put more miles on the engine before ordering new tires, doing a full tune with fresh gas and competing. I was running the same race gas from 2011 ("fresh" from drum) and didn't have sufficient time to dial in either A/F or timing on the dyno, but certainly improved performance significantly. Sure, the ratio was ugly, but it drove like like a son-of-a-bitch to and from the taco stand. (Cue Al Bundy pose, living the glory days...) Carburetors: For me, the dyno is to dial in my timing curve so that I can productively be free to tune my carbs week-to-week before races. With timing locked in, I can road-tune the car to respond to the pedal better far than dyno pulls can. WOT doesn't help me for autocross, and leaves me with a car that doesn't drive in mid and low-pedal positions under 4k, not even with a feathered pedal. Butt-and-ears dyno? You bet. Yes, fuel injection is coming... but not for another year or two. I still want to progress via a *tuned* comparison from carbs, and I still plan on larger DCOEs as an interim comparison as well, simply because I want to enjoy competing with carburetors for a couple of seasons before spoiling myself as a driver and going to FI. WOT has never been possible until around 4k with this cam, so there is definitely some area under the curve to be had the day fuel injection arrives. Hanging onto carburetors is a product of my amateur perspective and my desires. If there are opinions out there that carburetors are *foolish,* I'm formally asking for them! There are reasons that I'm in the same boat again with this engine, but I don't know what the reasons are. I find it plausible that an "ok" carb tune under load might be fine, but the break-in moments when the engine has never turned over before and isn't under load... perhaps those moments are more crucial than I realize? (JohnC, were you holding back?) Perhaps: [amateur with carburetors] + [engine with tight tolerances] = [margin for damage/failure]? I don't think so, but I don't know. I keep referring to the first build in my memory and on YouTube. I was "more" of an amateur in 2011, and that engine purred from birth. The data points conflict, so a proper conclusion cannot be drawn. Productive criticism and debate aside, I'm particularly pleased with shapes of what the curves are trying to be. Despite the poor tune, I remain encouraged that VE has improved. Regardless, it's on! I'm in a new town all as a single guy staying in a hotel, but I found a storage unit for my Z that gave me permission to pull the engine out, keep a drum of fuel, etc. [side note -- in this case it was very challenging being an honest, responsible citizen in a free economy. I was judged and rejected by several owners because they have had "rif-raff" type tenants abuse their storage units in the past. I finally found a guy that appreciated my honesty so much he said yes. And a handshake. The way men used to shake hands. ] Very fortunate I brought my cherry picker with me in the front of the trailer! Zed willing, I'll have the block out this weekend...

Any while-I'm-at-it suggestions? Oil pan recommendations, for example?

Thanks for sharing your experience with the chain tensioner, Garrett. Yes, it was open exhaust. Here is the same idle from 2011: https://youtu.be/by_gtw18cLo?t=1m30s. The car was soooo much smoother last go-around, but I still think that the fancy fuel being fresh is the main difference. (The perceived friction in my mind, however, is a different matter.) I talked to two engine builders, Ray in VA who built the head and Dave Rebello since at a minimum I'll be needing to order some new forged piston(s) and valve(s). Both builders immediately discredited oil as the cause and fixated on "something happening" in cyl #1. A failure in the valvetrain, a rock bouncing into the intake... something. I didn't measure how much oil was in the system and that won't be possible. I drained it and filled it back up with clean oil before I removed the spark plug and discovered the damage (sigh). The dipstick was dry at the time of the event, so I assumed that meant >1.5 quarts were gone. Dave replied that a dry stick doesn't necessarily indicate the system lacked oil. I woke up this morning remembering something that might be a factor: When I was finished mounting the engine block to the transmission and chassis, as I lowered the car one of the wooden blocks that was being used split up the middle and my oil pan was dented from below (in the shallow region of the pan). I would think if it were a problem then oil pressure would indicate as such, but I figured I'd throw it out there. Lastly, I'm totally new to the pacific northwest... does anyone have any engine builder recommendations? I'm fine with hauling to Seattle, Portland or wherever I need to go. I'm not messing around this year, I'm getting this fixed pronto!

I keep asking myself too. I can confirm that I had oil at a full dipstick mark during initial break in and carb synchronization, added about a half quart to bring it up to the full line prior to road testing. Less than 100 miles total. Maybe 10 pulls on the dyno. Ran nicely after the adjustments, too. I don't see any other options either, Jon. I'm really confused and will probably remain confused for quite some time! Oh and I was hawking my gauges like it was my job. Constant 170-180 degree coolant temp and consistently high oil pressure, both of which remained true as it smoked and died.

Okay, it's time to fess up. I'm sure it was obvious from my tone that something happened. Another motor is toast under the most unexpected circumstances. Bottom line: cylinder #1 is at zero compression and the spark plug was clearly hit by a valve and busted into bits. Haven't pulled the valve cover yet, but I put my camera into the cylinder. Still runs, albeit like a dying dragon. [pours liquor on keyboard] The only media in existence: https://www.youtube.com/watch?v=YuEY8I0u6fs You can really hear the Kameari twin idler gear whine. Since the first time it turned over I was intimidated by this motor. I can't stress enough how unusual this is for my personality type. Part of me recognized that I was simply being cautious to not repeat yesteryear, but it sounded unhappy. I felt for every moment that this motor struggled to turn over (high friction?). Perhaps the twin idler pulley was too tight? Also, the car seemed louder this time (combustion, not the whine). It was also much, much smoother last time. The event occurred on Friday. I took the car out for some carb tuning, and after about 50 miles and confidence that WOT at higher rpms was ok, I took the car to a local dyno shop. The motor was fine above 2500 rpm, I was only concerned at low rpms when I could perceive the friction. To my surprise, the dyno tech wanted me to drive the car on the dyno, so I didn't get a video at WOT. He said he's only done that with two other cars, and he said he wanted to be able to sleep at night if something happened. I agreed wholeheartedly; if it breaks, please let me be at the controls! This wasn't a formal power-seeking run in my mind but a confirmation that the tune and A/F was safe and the engine was happy. I have about 30 gals of VP109 that's over 3 years old, so no doubt the oxygenation and peppiness left long ago. I wanted a safe indication that I can playfully use up this fuel and not worry about it. The car made about 240whp and 225 ft-lbs but I knew that I still needed a full tune on proper gas with an installed air box. The curve itself was very full and the torque band above 200hp was surprisingly wide (thank you JohnC and Jim T!). I'll take a picture of the printout when I can find it. Still on the road (IA at present). Immediately after the dyno pulls, I cruised to a local taco stand, and cruised back, just enjoying my Z moving again finally. I went about 2 miles, tops. About 1/4 mile from my trailer on the way back, I was in 2nd gear at about 2-3k rpm going with the flow of traffic and there was a slight hiccup and I could visibly see bluish smoke coming from my carburetors in general, but not from my exhaust behind me. The engine was still running but very rough and wanted to die without a little extra gas. I limped into the trailer as the thunderclouds approached and my intuition knew it was right. I found the car in an extremely low oil state for some reason. It was full of oil before my road test, but I didn't check it until the end of the day (80 miles on odometer). When I pulled the dipstick, smoke came out and it was dry! I don't understand where the oil went. The engine is new and dry externally. Cyl #1 spit some oil out, but it was ounces, not quarts. I didn't burn oil on the road or on the dyno (visibly or by smell). I knew the engine was in pain and it looks like the oil burnt up trying to help it out and no one noticed. I kept asking the shop owner and tech if they thought it sounded ok, but I should have asked the dipstick. I'm really, really confused. Part of me feels like this was my fault, I'm minimally experienced mechanically and I didn't have an expert with me during the first 15 minutes, perhaps one of the most important parts of race motor's life? Obviously everything is conjecture at this point... it's really hard to not want to understand in the meantime. Here are the pictures of the cylinders. Some were clean and brand new and some were oily as all heck (oil sucked across the intake manifold common plenum?). Cyl #1 had bits of the spark plug in the bottom and it clearly looks like a metal battlefield...

Update time -- successfully fired up the new motor! steve260z -- Yes, this is the RIP motor bebuilt. madkaw --Yes, I'm only running 40 DCOEs. Severely restricted indeed! 50s are likely necessary, research pending. I've been exceptionally busy with the car and the move, currently typing from a Panera's in Kansas City while hauling my truck, trailer and Z to begin life's next chapter in Richland, WA. I've a long ways to go! [if anyone lives along any of the routes that ultimately pass through Missoula, MT, PM me if you want to grab coffee or food in the next 3-4 days! Leaning towards traveling via Sioux Falls, SD -> Missoula, MT -> Richland, WA] There is much to update and unfold with the engine, but for now, here are pictures of the completed install. I also have a 3.5 min clip to upload to YouTube for discussion, but I'll have to wait until I have time and internet connection to upload a large file. EDIT -- Had to replace my battery, yay for improper storage yet again. Sigh. Luckily the damn thing only weighs 4.5 lbs now!

Perfect. Thank you both! (Sorry about the delay -- moving.)

Awesome, this is exactly the answer I was hoping for! I appreciate the reply, good sir. (Though I don't follow the "me thing" comment?) ryant67, yes the filter ends up being an oily filter, but I found that if the filter end of the hose is mounted in a climbing orientation, the hose seems to serve as the catch can. Perhaps this is sloppy? Just trying to keep it simple.