Weber jets??All who live for their triples please read this

[240zip]

Second ... have you hooked an AFM up and checked AFR across the RPM range?

[luke240z]

Second ... have you hooked an AFM up and checked AFR across the RPM range?

 

Advance and AFM are next on the list to get confirmed, should get a chance shortly when work slows down a bit. Will be sure to keep the thread updated.

 

Cheers

Luke

[zredbaron]

Been awhile since I've visited the Weber thread.

 

I wanted to chime in again for the purpose of sharing an extreme example; over the years many of us have accepted poor tunes as a consequence of triple carburetion, myself included. It took years for me to assemble the requisite knowledge and collection of jets for a proper tune, but in the end it took me about five years to realize that I didn't have to accept a tune where the carbs fall flat on their face if you didn't work the pedal properly.

 

Most say that the 40 DCOEs aren't enough carburetors for 2.8L+ engines. The book agrees, and I'm of that opinion as well. The difference is, the 40 DCOE will still run just fine, you'll just cap your high rpm flow / power production. My 3.1L race motor, for example, at this point is more or less all out in every aspect of the motor EXCEPT my 40DCOEs which severely restrict flow. The point is that with the right fuel, the right ignition and the right tune, even a severely restricted intake can be smooth and produce a ton of power.

 

A video is worth a thousand words. It's not exciting from a driving perspective per se, but it demonstrates my point just fine. Tuned via butt-dyno (vice AFR), too. It can be done.

[For those new to Webers, do *NOT* attempt to duplicate my jet selection as indicated in the video; this is not a typical setup. This is just a demo.]

 

Unfortunately the car is now in storage, so I won't be able to dyno the car to compare numbers, AFR, etc. For now, this is all I've got...but I'm happy to bring back the data at some point.

 

Cheers,

Mark

[duragg]

Great video.

 

I did relocate my progression holes via CNC drilling and closing off the old "first" hole for a relocated new first hole closer to the engine side.

THe difference in the throttle Tip-In response is now perfect.

 

Getting them to respond nicely on the street through tip-in, progression and transition is the trick.

 

MASSIVE ignition power helps a lot.

 

Tj

[30 ounce]

Holy crap, Mark, that sounds like a BEAST! So your saying that you have no bog at throttle tip in? That is the only reason I have not got triples yet! Your changing my mind...

[zredbaron]

Holy crap, Mark, that sounds like a BEAST! So your saying that you have no bog at throttle tip in? That is the only reason I have not got triples yet! Your changing my mind...

 

Sort of. The bog / "fall flat on it's face" aspect is presumably circumvented by a combination of tune, cam overlap and exhaust scavenging from tuned race headers. In all fairness, most of the video is above 4k rpm, which is past typical street driving rpm and into the air correction circuit of the carburetors.

 

This same cam used to bog fairly dramatically before I went to the race headers. I also used to be able to break the tires loose by stomping on the gas whenever in 1st or 2nd, and now I can't; I have to let the power do it at higher rpm vice the torque being able to do it whenever. This surprised me. It's more squirrely, but at less predictable times, making it harder to utilize the power efficiently.

 

The engine is not built for under 4k. It's been balanced for 10k, though I will set my rev limit to 7.6k (the video's rev limit was at 7k until I get it dynoed). There are a few points in the video where I offer a little pedal before the cam kicks in, 4:57 is a decent example of it. It sounds like the familiar unhappy race motor / retarded gurgling sound (not in the same league of course, but akin to F1 cars when they need to downshift). It does not hunt and surge like my car used to years ago, but feels more like a steady pull right before it pulls hard. I can floor it, but nothing happens; it neither falls flat nor pulls harder.

 

You can also see a few seconds before that point (at 4:51) in the video that I can also blip the throttle from idle to 3k without having to be ginger with the pedal. It responds quite nicely, but once in gear it's another matter. The motor as a whole simply doesn't want to be under load at that rpm.

 

This isn't a fair motor to compare. I'm sharing more in the sense of "look how far the smaller 40 DCOEs can go" than anything else. And to demonstrate that even with an extreme motor, the engine can run clean with no popping, even outside it's power band.

 

Keep in mind that with carburetors, you can either have low-rpm driveability, or higher rpm power. You cannot have both until you go fuel injection, and even then, you give up one for the other (just not as much as you would with carbs).

 

In my case, I have tuned the carbs for high rpm power, but the venturis are so small that I get some extra driveability down low. How much, I'll never know... but I do know that with ITBs I can minimize the tradeoff.

Edited October 4, 2011 by zredbaron

[Lazeum]

The car definitely sounds quite healthy.

 

I'm surprised how big are the mains! Since I started to post of this thread I moved from stock N42 head with mild off the shelf cam (schneider) to P79 head port/polished with Rebello Street cam. At first, I did not change anything on my carbs (40DCOE also), venturi/chokes are 32 - way too small. As a result, I had to move from 140 with the N42 to 120 with P79 and the engine still ran super rich (11:1 AFR)

Since your setup looks nowhere near like mine, it would be hard to compare but the effect of the new head/cam was quite interesting, I have much more vaccum at idle with the more extrem setup

 

Regarding Air jets, they are also huge. Is it because of AFR being rich at high RPM? If such, it seems too small carbs (= out of air at high RPM) still push gas inside engine without sufficient air coming. This is what happens with mine.

 

I'm the first one to state 40DCOE are NOT too small for L28 applications even if 45DCOE seems more suitable as soon as you start changing stuffs. In europe, I see 45DCOE being sold by pair for 400€ everyday - very tempting I have to admit but I need to tweak the intake manifold to do it properly since intake runners are Ø40mm (there's material to be removed anyway).

[cygnusx1]

Sounds great Mark. It definitely wants to rev, and it seems to kick you in the pants when you hit the powerband. On a slight counterpoint, it's easier to make carbs that are too small run smoothly, than the reverse. A carbs worse enemy is slow air.

[zredbaron]

Thanks guys! Only took 13 years to get here... haha.

 

On a slight counterpoint, it's easier to make carbs that are too small run smoothly, than the reverse. A carbs worse enemy is slow air.

 

Agreed. It was easier to tune the power band of this iteration of my motor than any previous version. I credit the headers. (My butt-dyno insists that the scavenging so effectively cleared remaining exhaust gases from the cylinders that varying intake mixtures were more dramatic/noticeable.)

 

That said, before the power band, with such a cam overlap -- below 4k does not flow well at all; the air will be slow regardless of venturi diameter. In this case (in my opinion) it's more a question of 'how slow' when comparing venturi sizes. (i.e. how crappy vice crappy or not crappy).

Edited October 7, 2011 by zredbaron

[zredbaron]

I'm surprised how big are the mains!

[...]

Regarding Air jets, they are also huge. Is it because of AFR being rich at high RPM? If such, it seems too small carbs (= out of air at high RPM) still push gas inside engine without sufficient air coming. This is what happens with mine.

 

My jet selection is definitely atypical. First, my cam is literally profiled to exactly match the peak flow characteristics of my head. Second, my fuel (VP 109) is oxygenated, meaning O2 is delivered in liquid form via the jets (in addition to the air drawn normally through the air filter).

 

Therefore, the mains are large to send O2 along with the fuel (less dense as a result) and also the air correctors are large because AFR graphs often richen up above 5000 rpm since the venturi usually cannot support the demand. Air correctors help.

 

It should be noted that my previous engine iteration (before tuned race headers) used about 140 mains and 175 airs (with the same fuel) last time I tuned it (about 20F colder, about 1300' elevation lower) with the same oxygenated fuel and same camshaft / head.

 

I believe the dramatic difference to be caused from exhaust scavenging leaving the cylinders cleaner (less remaining exhaust gases) when the exhaust valve closes.

[Lazeum]

I would not have expected a header to bring such changes.

Your story about oxygenated gas makes sense also. Now I'm waiting for AFR analysis to see exactly where you stand

 

It makes also me feel my library of jets might not even be complete also My engine is in rebuild stage but as soon as it would be back in my car, I'll have to start again from scratch since I'll change the chokes with bigger units.

[zredbaron]

I didn't expect it to be so dramatic, either. Then again, I expected more of a dramatic change in 2008 when I went to 12.5:1, race cam, etc, but that iteration only bumped up the mains by about 10 and the air correctors by about 20. I guess that's what happens when you chase around choke points and then finally open up a big one...

 

My tackle box of jets is about 12 of each type (main, airs, idles). It fell short this time, which really surprised me. That's the problem with triples; if you upgrade the motor enough times, the cost of a diverse jet selection costs as much as the carbs themselves. And that's just silly.

Edited October 6, 2011 by zredbaron

[240zip]

how is everyone handling vacuum advance with triples? I have a manifold that has three vacuum ports that go into a collector and then to the vacuum advance on the distributor. this improved the low RPM bog, didn't fix it all together.

[Leon]

how is everyone handling vacuum advance with triples? I have a manifold that has three vacuum ports that go into a collector and then to the vacuum advance on the distributor. this improved the low RPM bog, didn't fix it all together.

 

I noticed that low rpm running was much improved (practically no bog and overall smoother running) with static advance at about 15 degrees, however my 260Z distributor has a terrible timing curve for my application (26 degrees of mechanical) so I have to keep it at 10 degrees static. I have a spare E12-80 ZX dizzy, but instead of spending precious time playing with distributors and still ending up with a compromise I opted for a programmable EDIS setup!

 

I installed Derek's trigger wheel and sensor mount yesterday and will be getting the EDIS and Megajolt controller wired in soon, hopefully. Using Megajolt lets me keep the triples yet provides a relatively economical way to have a fully programmable, powerful ignition system. Load sensing (vacuum) advance will be provided via the built in MAP sensor. I know that I am missing out on a lot of "power under the curve" with my current dizzy. Once I'm done, I can punch buttons on a laptop while having a snack, instead of taking apart distributors and messing with all that crap. Hell, Megajolt lets me make temperature correction curves and allows two timing maps, switched with a flick of a finger! Try doing that with a distributor...

[Lazeum]

You better do a full report of your feelings with MJL I plan on doing it in the future.

 

I'm running a Mallory Mnilite dizzy with Mallory 6AL CDI box. It allows me to get good idle and total advance but it is a pain to tune right and very time consuming...

 

And I have no vacuum advance, I think it is bad, there's probably tons of torque to get back at part throttle & better economy during cruising.

 

 

[zredbaron]

I am running Elecromotive's XDI2 direct ignition. I ran direct ignition with no MAP sensor for years.

 

I later dyno tuned my race motor (oxygenated fuel) utilizing a MAP sensor that altered the programmed advance proportional to the MAP sensor's output.

 

After tuning the motor, I didn't particularly notice a difference in mid-throttle positions, particularly in the trouble areas below 4k rpm. WOT loved the tune, but mid-throttle didn't make a difference.

 

I even unplugged the MAP sensor to see what a difference it would make. It didn't make much of one. I could tell, sure, but it wasn't enough of a difference to affect my standings in an autocross race.

 

Did I not get much of a difference because of my cam's overlap? Is it because of my oxygenated fuel? Perhaps, but in my case I didn't notice much difference. I still run with a MAP sensor just for the hell of it...

 

[EDIT - I believe having a programmable advance curve (i.e. Electromotive ignition) is the most significant factor as to why the MAP sensor doesn't do much for me. With a mechanical distributor, you don't have the varied timing to begin with, so any input that varies the timing will have a much more dramatic effect.]

 

Not a typical setup, but that's my experience. For what it's worth.

Edited October 6, 2011 by zredbaron

[240zip]

OK ... that explains a ton. I'm not sure I'll spring $1,200 for the XDI-2 crank fire system. Of course it's only money right? It seems what you have is almost a mechanical EFI. It would almost make sense to just go with ITBs and skip the DCOEs at that point.

[240zip]

So I re-read the post. I guess you'd need a different unit to run EFI. It seems the XDI and XDI-2 differences are the MAP sense and you stated that it's not much of a difference. Did you have to custom make the crank sense wheel? I have one that for SDS. I'm going to guess that it's a different wheel for the XDI set-up.

[zredbaron]

Having a programmable advance curve will work wonders with getting the most out of carbs. Tuning is tuning, whether AFR or timing, flow matching, etc. It all has to work together of course. You could say it was a mechanical EFI if you are referring to the ignition half EFI, so sure, I'd agree with that.

 

I've been with Electromotive since the HPV-1 in 1999. The only improvement I've actually noticed as their technology has evolved has been easier starts, smoother rev limits, and more reliable sensors (the early model would crap out after about 2 years). They claim better spark energy since then, but as the driver, I didn't noticed that until I went to race fuel, and it's hard to separate the two variables. (Using both high end spark and fuel, it will burn no matter what the AFR is!) I personally am unwilling to consider any other brand of EFI controller; I've been that pleased with Electromotive's design and spark energy.

 

Unless you're a carb purist, I agree it's a better investment to go with ITBs from the start. Electromotive's TEC-3r / TEC-GT products + ITBs (such as Extrudabody, which I've been eyeing) will likely be about a $5000 setup. I have as much cash in my ignition, carbs, jets, manifold porting, etc., which is absurd when you compare the amount of tuning possible with ITBs to that of a mechanical device (carbs).

 

Vendors of Electromotive's products also supply the appropriate crank trigger wheel, and some offer an adapter plate (2 bolts) to mount the sensor itself to the block. Top End and Rebello are two vendors I know of that are familiar selling/using these products with L6s (I personally find Top End to be incompetent salesmen). Rebello makes their own custom (weight relieved) crank trigger wheel to mount with their high end dampers. If you want performance (i.e. are paying for Electromotive), do NOT go cheap on the damper. Call Rebello and buy their parts. If you want it to rev, then go have the damper, crank, and flywheel assembly balanced, otherwise I'd recommend setting your rev limit no higher than 7k.

 

It's only money, after all....

[Leon]

My complete programmable ignition system cost about $400, and there are ways to do it cheaper. I didn't have the time to fabricate the sensor mount and press on a trigger wheel so I went to the easier solution. I got Derek's EDIS mount kit (~$170), Megajolt Light Jr. (~$170), and an EDIS 6 set (module, sensor, 2nd gen coil pack, plug wires) from ebay (~$60). It is possible to economize on the EDIS mounting by making your own sensor bracket and pressing on a generic 36-1 trigger wheel which brings those costs down to materials and your labor. If you have time to go junkyard shopping the EDIS may be cheaper as well, so you can have a fully programmable system for maybe $250 or so. That's damn good for what you get if you ask me!