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5 hours ago, bradyzq said:

Hopefully the dyno will have an air temp probe. I know my Dynapack does.


It's the famous orange wire that increases power if you put it under the hood.;) (Dynapack tuner in-joke)


Dynapack is king of chassis dynos as far as I'm concerned. A much more precise machine than any roller.

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Thanks guys. I'll try and have an IR gun on hand.


I had a chance to road tune the 38mm venturis this weekend. It has better mid-throttle response than it has had in years. 190 main jets, F9 Emulsion tubes, 220 Air Correctors. I can actually floor it under 3000 RPM! (Still have to gradually roll-on the throttle, though.)


This week's plan:

  • Monday (tonight)
    • Install 40mm venturis (with Weber long stacks) for dyno testing
    • Road tune 40mm venturis, write down jets, air temp, etc.
    • Get a feel for driveability of 40mm venturis with Weber long stacks (ready for baseline dyno data)
  • Tuesday
    • Order more main jets if 40mm venturis are thirsty (I have up to 205 main jets)
    • Fine-tune the throttle linkage synch for dyno testing
  • Wednesday
    • Road test and confirm the jetting again, if the synch was adjusted.
    • Swap to and road test the Weber short stacks, noting if the same jets can be used.
    • Rehearse velocity stack swaps, organize parts, etc.
  • Thursday
    • Backup day for final road testing
    • Stage trailer, fuel and parts
    • Finalize R&D flowchart
  • Friday, May 18 - Chassis Dyno @ 9am PST


I'm allowing myself to feel a little excitement. Trying to allow more.

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Excited for the results on this, will be following along closely. I'll be particularly interested to see heat gain on the gear-train over the course of several pulls. 


I did a little testing of my own with the T3 stacks and adding/removing a filter element on back to back runs, and did see a notable pickup. 


Good luck on the day!

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Thanks for being so upfront with the information sharing!

It's interesting that the XDi supports hall sensors, as I was under the impression that only the XDi2 and XDi200 did.  I've toyed with upgrading my XDi for just that reason, as the hall seems like a much more solid solution - zero chance of signal interference, and it's very difficult to avoid the spark plug wires, alternator and starter with our engine bay layout.  Do you recall the serial number it was to check to see if you're below?  I'm pretty sure mine will be too old as it's the same design as yours is...  

Have you considered upgrading to the newer XDi200 at all?  It has onboard datalogging with lots of input channels, which would certainly be really useful for backroad carb tuning I would think.  Some of the little extras like shift light control and the 3 programmable rev limiters might be useful as well.  More money though, and the basic functionality is unchanged. 

Hope you get big numbers and lots of useful data on Friday, good luck!!


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Thanks Ben! About the T3 stacks - I have both their 47mm and 49mm ID varieties. Do you know the ID of your setup? Since the (Weber) sleeves have an ID of 48mm, the T3 stacks are an exciting wild card to me, because I can also test with / without the inner (Weber) sleeve inserts that will be cut. When I have more time I'll post a table  of the impressive list of combinations I will be able to play with. More than I will have time. Fun!


Ryan - it's truly my pleasure to share. About the ignition upgrade - I will be calling their tech today. It's not an option for this week or maybe this summer... but I'd love to incorporate a throttle position sensor. I believe that means a TecS is a good option? Not sure. I owe the tech a call about the loaner unit anyway. Would allow software to map both throttle position (TPS) and manifold pressure (MAP). That'd be awesome to pair with carbs set up for WOT but retains driveability across a 5k+ RPM band.

I think it can be done. Between fancy fuel, fancy ignition and fancy head work... I think one can have their cake and eat it too. But they might have to have fancy intake and exhaust setups! LOL


Speaking of exhaust, I still haven't announced some of the other upgrades. The 3" mandrel exhaust now has two straight-through Magnaflow mufflers in series after the merge collector. The first is 14" and 1/2" thick(14x4), the second is 6" long and 3" thick (6x6). The sound is very balanced. The second muffler, since it is a different shape, attenuates a different sound frequency and it just-so-happened to work out the way I hoped: it didn't muffle the tough, but it did nip the high pitch resonance perfectly.


I still prefer it raw -- just remove the exhaust after the merge collector. No hood and no air filters, windows down. Just open air horns and a merge collector. That's my favorite sound. One day maybe late this summer I'll take the car to a drag strip without any exhaust attached... one milestone at a time.



Edited by zredbaron
Clarity about sleeves and stacks

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Also, I road tested the 40mm venturis last night... and they are not yet drivable or able to be dynoed. At first I was discouraged, but then I realized this might mean that they have more power potential than I realize. It must be tuned.


With 40mm venturis installed, it was way lean. I was afraid to touch the pedal to get past the "iffy" airflow and into the WOT performance where it was happier (but not happy). In the end, my largest main jets (205) aren't remotely close to being big enough. Choking the Air Corrector down to 145s still wasn't enough for an AFR that didn't make me nervous as all heck.


So... in my mind this means one or more of a few things:

  • Loss of aux venturi signal
    • The Weber book notes that jumping from 38mm to 40mm venturi will result in a loss of signal at the aux venturi.
    • I haven't read much carburetor theory about the aux venturi, so I'm not fully sure how this impacts WOT.
    • My impression is the aux venturi serves to assist mixtures at low RPMs and lesser throttle positions.
    • My impression is this is a less desirable drivability issue, but a drag or road race engine would like it just fine!
  • The main jets are just too damn small.
    • More air needs more fuel, duh.
    • More fuel means more power, duh.
    • I would love this to be the fix!
  • Emulsion tube experimentation is in order
    • See aux venturi notes... it's my understanding tubes are for mixing at low RPMs, not WOT.
    • I have 5 other tubes.
  • "Ram" tubes / velocity stacks are now crucial
    • That's the point of Friday, after all... but if I can't safely get on the throttle I have to test at the 38mm level.
    • Cleaning up this increase of air may clean up the signal loss at the aux. venturi.


Today I will order more main jets. I'll do more road testing as I'm able. Any experience with 40mm venturis out there?

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Hey gang. I haven't had much time for road testing the 40mm venturis yet (let alone stacks). Still not driveable, so at present, the forecast is testing via 38mm venturis tomorrow unless I pull off a good tune tonight. I have main jets up to 245 now (!) and with 6 sets of emulsion tubes one would think a solid setup is within grasp.


Attached is my tentative dyno flow chart:


It assumes unlimited time. I don't yet know if I'll be running 38mm venturis or 40mm venturis or both. At some point I will abandon broad data collection and proceed toward focused data collection. The results will navigate this flowchart, and so will the limited timeline. If half of those boxes have data at the end of the day I'd say that's a win. Any advice or thoughts here is always welcome.


Ryan - The electromotive hall effect upgrade instructions are attached. The XDI 200 ($895) would meet/exceed my needs for carburetors, but if I'm going to rewire my ignition... I might as well rewire everything under the hood and integrate all of my fan controllers, etc. into one computer: the GT200 ($1,695!), which would also be forward-compatible with sequential fuel injection one day (should ITBs ever occur on the car).




That's an $1,700 upgrade for a TPS at present. For now I'll save my cash and I'm buying the Electromotive loaner XDI unit from them, so I can get out there and race! I may have built a race motor (RIP, RIP...), but I'm a driver first and a builder/owner second. I'm already late to race season as it is!

Edited by zredbaron
Flow chart attachment; current Electromotive pricing
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Larger chokes will tip in the mains later so your mixture is showing lean due to that. Try tipping in at a higher RPM.  You shouldn't have to make an abnormally larger step-up in mains for a 2mm increase in choke size.


E-tubes affect both tip-in and the AFR curve when on the mains. The interaction between float level and emulsion tube is critical to both. Run what you got tomorrow and do your best to keep the tests controlled, otherwise it will be impossible to tell the difference between runs. Sounds like you did a pretty good job of preparing. Looking forward to hearing about what you find.

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Well,  I may have a decent handle on tuning Webers… But in general automotive proficiency… I couldn't get the 40 mm to run due to user error. I'm not sure what happened Monday night, but on Wednesday night I had a spark plug wire disconnected and didn't notice it. How embarrassing!   That's what I get  for checking the plugs late at night. 




I have really awesome jet presets for both the 38 mm and 40 mm venturis. 40 mms like the short stacks so far! Better AFR plot, but perhaps less peak horse power.


I've got about 2 1/2 hours of daylight for more testing this morning. Every minute I get done in preparation means more day that we get at the end of the day. 


More when I got it. Today is looking and feeling like it's going to be a solid day!


Video below, while still tuning 40mms last night. 3rd gear. So far it behaves identically to the 36mm venturis in the 40 mm carburetor body, which makes complete sense. Gargly until the cam kicks in... I think the reverb is allowed to travel outside the carb body with wide open venturis. I remember seeing fuel mist in person at the engine dyno. I'll capture it.


Cheers.... 🍻


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The Weber short stacks made the most power by about 270 whp.


I never swapped any parts. Frustrating day. Showed up with a singing car that refused to sing for the first hour, oddly, and ultimately broke on the dyno while tuning the timing for my initial baselines -- excessive vibrations above 35mph. Never even got a good initial baseline!  🙄


My new driveshaft was installed by a speed shop and my right rear CV axle was also removed and reinstalled in the offseason. They were found loose after I finally demanded to unstrap my Z, and two bolts on my bigger driveshaft lost their nuts today. So to speak.


I'll attach media when I am able.


I have my suspicions about the dyno itself, nothing but issues with ignition signal today (due to dyno? very odd day). The car was smooth as silk at the top of 4th on asphault... and on the dyno it not only shook itself apart but the ignition was so inconsistent I don't find tuning to be useful on their equipment and doubt I will return. Very cool shop though... just not for my car evidently? Weird.


I'll revisit this sometime this summer -- I still need to digest the day. It simply didn't add up from the beginning. For now, I am going to bed and still not attending my first race of the season tomorrow. I've literally made myself sick today. It was all I could do to get the car in the trailer in and out for the 4th time today as a shop with a lift helped me confirm my vibration issues. For now.


At least the motor remains stout and sings beautifully on road tests. 🍻



Edited by zredbaron
general grammar and typos

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Well it sounded great in that video! Sorry to hear but glad you caught the issues before tossing driveline bits all over the road (or track).


I highly recommend finding a shop with a Dynapack in your area, you can thank me later. ;)

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Man, I feel bad for you Mark. Every dyno session, with the latest iteration of the motor anyway, has been a clusterfuck. I hope you get it sorted.

I am pretty sure you're running the Porsche style CVs. I've heard of the bolts coming loose on quite a few different Datsuns. Might be a good idea to safety wire them. Could do the same with the driveshaft bolts too if you want.

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Love the information and feedback you are providing! Keep it up by all means! 

If you could answer a few quick questions in regards to some other details of your equipment I would really appreciate it. What diameter runners or brand of headers are you running and I know you mentioned you were running 65F8 idle jets, are you still running those when you were testing out the 38mm venturis? 

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Thanks Jon. I was pretty much in shock all day on Friday. I couldn't believe what was happening as it unfolded. Unreal. I agree, I'd be a lot more comfortable if the inner bolts were also safety wired.


rustler753, I'm running Stahl headers with 1 5/8" primaries, and 2.5" secondary collectors. The two 2.5" pipes are passed through a 20 degree merge collector, then expanded from 2.5" to 3" with 3" mandrel exhaust all the way back. Two straight through Magnaflow mufflers in series. I've been running 75F8 idle jets for the most part, with 70F8 and 80F8 also being used depending on the day and carb setup (venturis, horns, etc).


Edited by zredbaron
added jets info

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1946301743_KSDynoTightGraph5_18_2018.thumb.JPG.efd7fd75f97d776c2dec98cd26a70f8e.JPG05.18.2018 Dyno Day Report


  1. 630am - 815am
    • I arrive at my road testing location, and continue to prep for my dyno appt at 9am
    • I continue to refine the performance of the short stack webers
    • I achieve a near-constant 13.0 AFR from ~4000-7000 RPM
    • Car is smooth as silk at the top of 4th gear, 120ish?
    • I have known good jet settings for 38mm venturis with long stacks, and 40mm venturis with short and long stacks, and have swapped back to known good settings several time this week. Repeatable.
  2. 845am
    • Unload car at dyno shop
    • Car fires right up, I turn it off after driving it off trailer.
    • Tech wants to get in the car and put it on the dyno.
    • Against my better judgment, I allow a young tech to attempt to start my triple carbs (neither warm nor cold motor)
  3. 915am
    • At this point I kicked the tech out of the car and I'm trying to start it.
    • Flooded? Fouled plugs?
    • I decide to refuel, allowing time for the flooded carbs to clear.
    • Won't start
  4. 10am
    • New NGK plugs installed
    • Fires right up, I drive it onto dyno
    • Tech has me accelerate slightly to set the wheels.
    • I am already alarmed by dyno noises and vibrations, I am assured this is normal
    • It's not like I've never dynoed before
  5. 1030am
    • Car is NOT the same car that I've been tuning all week!
    • Making jet changes are having OPPOSITE effects then what happens roadside!
      • Example:  changing main jets 10 up or down DOES NOTHING!?
      • Example: changing air corrector jets now behave as if the main jet is being changed?
    • Additionally and separately, my ignition is being screwy
      • A few times, the rev limiter did not kick in AT ALL
      • Several times, the car wouldn't accelerate on the dyno, but would simply hesitate and chill out and get groceries
      • Several times, while getting groceries on the dyno, VTEC or something kicked in because the acceleration would suddently PULL VERY HARD.
    • Pulls back to back did NOT have the same performance.
      • We started to not trust the data, sometimes doing 3 pulls for every adjustment.
    • WTF is going on?
  6. 1130am
    • Despite that the rules of tuning are now unpredictable, despite that my known settings are now shit...
    • I finally find a good AFR again, very near my 13.0 AFR that was attained roadside that morning
    • Time to move to timing
      • Dyno is scheduled for another customer at 2pm!
      • At this point all I want is to capture data for the Weber short and long stacks
  7. 12pm
    • I start messing with 1000RPM timing
    • I get my triples idling very nicely with a screwdriver
    • I start messing with 3000RPM timing
    • Engine is hot, needs to cool
  8. 1230pm
    • Tech announces he is going to lunch
    • No other techs around
  9. 1pm
    • Pulls resume
    • I am less desensitized to the vibrations
    • I continue to express concerns and I am told all is normal
  10. 115pm
    • Eff this, I'm getting my car outta here
    • I drive off the dyno and onto the street, vibes are insane, loud at 35mph
    • Day is done
  11. 215pm
    • Drop my car off at a general auto place to investigate on a lift
    • They tighten the driveshaft and right CV axle (inner bolts)
  12. Evening
    • I pushed myself so hard this week that I start shaking and aching and getting sick
    • Straight to bed around 7pm
  13. Weekend
    • Saturday - rest. I skip the first race the car can actually enter... because the driver can't go physically.
    • Sunday - autocross. Car kicked my ass, in a good way. Couldn't get the rear to settle down, which was delightful.
    • Not sure if I had "fun." Big losses this week. That's sad.
  14. Ignition
    • My ignition was crippled by something that day.
    • The hall effect sensor is supposed to negate interference?
    • Haven't called Electromotive yet. Depressing. I will.
    • My theory: the dyno's ignition inductance pickup was near my hall effect sensor's harness, where the sensor wire is less shielded for a few inches to allow the sensor and XDI harness to clip together.
    • I suspect if this had been relocated, the issue would have cleared. (Some positions definitely made it worse!)
  15. Dyno Graphs
    • The way the dyno loaded up (very delayed)... it was very hard to scientifically produce consistent dyno runs.
    • You can see some really screwy dyno plots. The ignition pickup had a really hard time, clearly.
    • I attempted to attain WOT by 3500 and 4000 RPM as the engine tune allowed.
    • In most cases, if I rolled into WOT slowly, it worked out. If I rolled quickly, it would be a wasted dyno pull (delayed dyno loading).
    • A few times I forgot I was supposed to achieve WOT (for consistent analysis of what the change did) and throttled the carbs through the reverb RPM range.
    • Very interesting to look at the torque plots of the throttled runs! WOW! (Enter driver as a patch! Haha.)
  16. Summary
    • Phudge. What the crap, even?
    • I'm still going to mess with a few of the air horns for awhile.
    • I'll still come back... not at this dyno.
    • The staff, to me, was more interested in getting through their day than helping their customer accomplish anything.
    • They dismissed my concerns about ignition and vibrations. Not helpful.
    • Sigh...


A not-quite what we want to hear video:











KS Dyno Throttling Graph 5.18.2018.JPG

KS Dyno HP-TQ Graph 5.18.2018.jpg

KS Dyno AFR-TQ Graph 5.18.2018.jpg

Edited by zredbaron

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Sad to read this. I know stuff happens, but the shop should have reacted. If there was any doubt the RPM pickup might be causing an issue, then DUMP it! You don't need it anyways. I'm sure Dyno Dynamics have a sync tool for roller speed to engine RPM. Set it and forget it.

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I'm still here and making significant progress with my intake tuning.


At present, I can report that all aftermarket horns have outperformed the Weber straight horns, both short and tall. I have further invested in some custom machining solutions, one of which has really paid off (holy crap, I thought the car was singing before!) and is now very happy to quickly change engine speeds up and down with less resonance and gargling, even under 4k. I have another custom machining solution in the works, because well, my last three gut-instincts have been in the right direction and I'm still gaining lots of smoothly-delivered torque under the curve. And I still think I can have my peak power, too. No way I'm quitting while I'm ahead.


Why am I not sharing the actual details? Because I have another dyno date set and I'm tired of saying I'm going to deliver data. This might be my last foreseeable dyno visit. "Maybe I'll have data, maybe I won't." At a minimum I will share my qualitative comparisons as well as my jetting combinations (because the changes in jets reveal how the swapped intake part affected the AFR plot). Ideally this information will be accompanied by dyno plots, but I have abandoned my mission to have an R&D experience.


If I'm not already having an R&D experience then I should just give up my keys now. It's way past time to officially tune the engine timing and get an official, satisfactory baseline.


As always, I'll still share everything I have learned and I will post pictures of my custom machining solutions, whether they work or not.


EDIT - photos added showing some of the different air horns, mounted. (no I didn't ever fire it up this way)



Edited by zredbaron

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Really looking forward to the data you are willing to share. I am heading towards a new setup with 38mm or 40mm chokes on my weber 45s so I am very curious about all your jet settings. I asked early about a few things like your idle jets but I'd love a bigger picture to see the direction you went with each jetting option we have available. 

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