Tony D Posted April 16, 2015 Share Posted April 16, 2015 Coming back today and reading what I posted I went "WOW!" -- curious how that number off-idle (33%) coincides with the original Bosch-Licensed EFI "WOT Switch closing point!" What happens when you do a slow-roll-on to the throttle compared with a WOT Mash? What happens when you disconnect the Pump Plungers and try the same thing with both Mash and Slow-Roll-On? When you tune EFI, in similar manner, you disable all enrichments to get the base WOT curve, once that is dialed in...you start working on transients. Jetting for WOT takes 45 minutes on a Dyno. It can be 3-4 more hours to get transients and partial throttle dialed in. . . Come to think of it, you are running an appropriate rear end ratio, right? Not the 3.36? More like 3.9 or 4.11? N/A Carbbed engines need to twist to work well. Quote Link to comment Share on other sites More sharing options...
inline6 Posted April 16, 2015 Author Share Posted April 16, 2015 (edited) What happens when you do a slow-roll-on to the throttle compared with a WOT Mash? That makes a huge difference. If I squeeze the throttle, AFR on the screen of the LM-2 doesn't go as low, and the engine doesn't misfire. I have to squeeze slower in higher gears vs. lower (4th vs. 3rd specifically - I haven't even tried full throttle in the .745 overdrive in 5th anytime recently). I have to squeeze slower at lower RPMs vs. higher. Anything over around 4500 RPM right now, even in fourth, and I can snap the throttle open and I am ok, meaning I don't get the low to mid 10s and perceived misfire - the AFR still drops into the low 11's initially though. What happens when you disconnect the Pump Plungers and try the same thing with both Mash and Slow-Roll-On? Haven't done that yet. I can put it on the agenda for this weekend. Bummer is I have to travel about 6 miles through stop and go to get to my "test area" on the interstate. I could schedule another dyno session. Come to think of it, you are running an appropriate rear end ratio, right? Not the 3.36? More like 3.9 or 4.11? N/A Carbbed engines need to twist to work well. I've got an R200 4.11 in the car. Here is another plot from when I had the best set up in the car thus far. Because the tune was improved with the change I made for this run, I decided to snap open the throttle at lower RPM in third than I had been doing - to test that issue. I eased off until I was around 4k instead of 5k, and quickly went WOT. Edited April 16, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
inline6 Posted April 19, 2015 Author Share Posted April 19, 2015 (edited) I managed to get a few runs in despite the rain showers. One goal for today was to check to see if tightening down the intake manifold and header nuts changed anything. I saw essentially no change due to that. Next, I discovered that the front carb was being held to the manifold by only the top two nuts. It took me forever scrounging around my boxes of Nissan hardware to find a couple of 8 X 1.0 mm nuts for the carb isolator studs - what an uncommon size! I also changed out the pumps to 50's because I have seen that anything less causes a spike on full open throttle for the tuning runs I have been doing. Here is a comparison of 45's to 50's: The brief "jump" to lean at WOT, is essentially gone with the 50's. This is a run in both 3rd and 4th: It's not exactly easy to see, but the AFR curve is actually very consistent - just compare the same RPM in 3rd vs. 4th. As you can see with the stat markers I have, it doesn't matter what gear, the curve is essentially the same. I've logged a large number or 3rd and 4th gear pulls now, and I have overlayed them and compared the differences. Right now I have this combination in the car: Main 185 Air 250 Pilot 57.5 Pump 50 Choke 37 By looking at 3rd in this chart, all I am dealing with is revealed. Even with many main fuel and air correction jet combinations, the shape of this curve generally does not change. I have low 14's at steady state cruise 3100 RPM in 5th. I have low 13's at steady state 4600 RPM in 3rd. I can snap open the throttle at 4600 RPM in third without a lean spike. The AFR drops very briefly to low 12's, then climbs. It crosses over to the 13's around 5200 RPM. 5800 RPM is often the peak in lean AFR around and is about 14.4. Then AFR turns downward again. I don't see below 13 until about 6500 RPM. AFR keeps marching downward linearly from there until about 7000 RPM - where it hits low 11's. It does pretty much level off right at 11... I have rarely been going much above 7200 for now. Since low 12's for WOT through the power band of this cam is the goal, my next move will be to throw some 190 main jets in. 250 airs are as big as I own at the moment, but it looks like I'm going to need to buy something bigger. 300 airs is the largest size - I am at 250 now. Perhaps I need to start thinking about some larger outer venturis to reduce the "pull" on the aux venturi. Edited April 19, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
inline6 Posted April 21, 2015 Author Share Posted April 21, 2015 (edited) Spent the time to adjust the accelerator pump lever throws to the Mikuni manual spec. - 7.5 mm. They were about 4 to 5 mm prior to doing so. I went out after that change and got new baseline curves. That is the solid line in the plot below. Interestingly, my lean spike at WOT is back now. What I had in the carbs for the baseline: Main 185 Air 250 Pilot 57.5 Pump 50 Choke 37 Also in the plot are the dotted lines which is the change to 190 mains after recording new baselines (no other changes): No matter what jets I throw at this thing, I can't get that hump in the middle hammered down. Stepping up the size of the mains is making the curve richer for the entire RPM test range. While the bump in the middle shrinks, the AFR at the ends - just after WOT and full throttle above 7000, also descends. Combo in the car is now: Main 190 Air 250 Pilot 57.5 Pump 50 Choke 37 I am pretty far outside any other jet combo for Mikuni 44's than I have seen for any other 6 cyl. Z engine. Seems like I have something weird going on... wish I could identify it. Need to start thinking outside the box. Maybe I should revisit my cold air intake system... or maybe I have some weird fuel pressure fluctuations as RPMs change... Edited April 25, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
Lazeum Posted April 21, 2015 Share Posted April 21, 2015 Your study is interesting! You should plot the AFR vs. Rpm. It would be easier to compare data. Quote Link to comment Share on other sites More sharing options...
inline6 Posted April 21, 2015 Author Share Posted April 21, 2015 Your study is interesting! You should plot the AFR vs. Rpm. It would be easier to compare data. I just rediscovered this suggestion from you last night while reading back through this thread - it helps to have all of this info in one place to see where I have been and to hopefully inform where to go next. I am playing with AFR vs. RPM. Will see if I can get some plots together. Quote Link to comment Share on other sites More sharing options...
inline6 Posted May 3, 2015 Author Share Posted May 3, 2015 (edited) I've been trying to lean out the top end as of late. But, I have found that even substantial size increases has little to no effect in AFR at the high RPM range. For example, here is an AFR vs. RPM plot of the following jet combinations - the dotted line is the run with a 250 air jet: Main 190 Air 250 Pilot 57.5 Pump 50 Choke 37 vs. Air 270 I bought the 270's this past week and tested them this weekend. It seems no matter how high I go, I can't change the AFR at the high end. Here is another plot. This one shows a comparison of a much earlier run when I had 180 Mains and 220 Airs (dotted line), and everything else is the same vs. the latest 190 Mains 270 Airs that are in the car now. This is the problem... I can't get the upper range to lean out. What could be the problem? Are the carbs somehow not getting enough air? Edited May 3, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
inline6 Posted May 10, 2015 Author Share Posted May 10, 2015 (edited) Decided I would try 195 Mains to see what the change in AFR would look like. Obviously, I'd like to lower that hump in the AFR in the 5400-6400 territory if at all possible. So, I figured I see what the 195s would do. It was a pretty substantial change. And, as expected, AFR got richer where I didn't need it to also. I haven't had any luck getting airs to lean out the top in, so I am hesitant to order something bigger than 270's - I don't think it will make a difference. So, now the question is, which of those two plots is better? Should I stick with the 195's, or go back to the 190's. Edited October 7, 2017 by inline6 Quote Link to comment Share on other sites More sharing options...
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