FireDemonSiC

Do any of the guys with high lift, high duration and tight LSA cams (I understand the word "high" is perspective. Since there are a lot of bracket race and strip only guys the numbers I'm talking are 222/230, .534/.537 and 110* LSA) have trouble with the engine surging off dead cold starts? Gradually getting better and evening out as the engine warms up?


When the engine is started at full blown ambient temperatures (especially in the colder months), it will surge a bit (Rapidly between 3 - 500rpm) and even out as the car warms up. By 130F, it's pretty much all gone and idles/drives normal.


EFI motor and I've tried playing with both idle fueling and timing. Even tried cold start enrichment and gave it as much as I felt comfortable with (10.5:1). The one thing that seemed to make a difference was increasing the idle speed vs coolant temp settings to keep the motor at a higher idle speed when Temps are still cold. This improved the issue very noticeably but didn't 100% resolve it.


I'm wondering if this is something that can be rectified or if it's just the nature of the beast. It doesn't cause any problems and since I have 2618 forged pistons with the PTW clearance at .0055" I always let it warm up fully anyways before revving or driving any.


If it's just a mechanical trait of the motor I'm cool with it. But if it's something that needs addressing I'd like to know.


Details on the motor (I'll leave the cam specs out since I already listed them above).


334 cid sbc. 305 roller bored .030" over with a 3.75" crank (Yes you read that correctly). Frankenstein TPI setup. Superram base, SLP runners siamesed and opened way up. Plenum ported to match. 58mm TB. EBL flash ECM.


Everything else in the tune is PERFECT! This is just one of last small "Let's fix it because it isn't right" annoyances.


Upon cold startup, idle timing SHOULD be around 25* but it swings all over the place with the surging. Watching the WUD verifies this. Same thing with the vacuum, although once it's warmed up fully it pulls around 18hg at an 850RPM idle. Cold start idle speed can be as high as 1300rpm depending on temperature. Gradually settles down to 850 as the engine warms up.


Let me just get a few other things clarified to hopefully reduce redundant guesses.

- All sensors are verified working correctly and properly calibrated.
- Everything, and I mean everything including the AFPR and injectors are new or newish. BTW, FWIW I'm running bosch III 22/lb at 60psi.
- Narrowband oxygen sensor has been upgraded to a heated unit. Although I can't imagine it would even matter since it isn't even reading on a cold start and I have the EBL set to open loop idle.


This seems to be an issue isolated to something with this engine or tune in particular. The old motor, running off all the exact same parts with a much more EFI friendly cam, did not do this. FWIW it was a low compression, small cam POS, but it idled smoothly on cold starts.

Any ideas gurus?

RBob

iTrader: (1)

Surging is usually caused by a lean area in the VE table. At cold start the engine RPM and load will be using a different area of the VE table versus a warm start. Take a look at a data log and see where the engine does the upward surge (RPM and MAP).

That is likely the area (or near by) of the VE table that is on the lean side.

RBob.

FireDemonSiC

I will give that a go around this weekend. There is usually a brief period after it fires where it holds steady RPM and MAP before starting the surge.

Vanilla Ice

I'll go opposite and say try leaning it out first (assuming the table has been smoothed prior). I prefer to lean it and have been able to maintain 100% stock driveability with a cam exactly as described doing so.

Cam surge can and most of of the time will be tuned out with fueling regardless of which of us you listen to.

JP86SS

iTrader: (1)

I'm thinking it could be an air distribution issue at idle.
Superram with low cubes, low temp, and low RPM.
Try opening/closing the mechanical TB adjustment to put more/less air through the IAC passages. Low IAC count was making it worse, More IAC air is better IIRC (lookup "VernW" for some other background)

His superram was having similar issues and because of this you may be loading up on some cyls, while leaning out others.

If spark is jumping that doesn't help either. Reduce the SA vs RPM error values if that is one of the available variables.
Some things to try.

FireDemonSiC

Rob,

Started the car and let the EBL log during the surge. In the log, it seems that it starts up and holds steady for a few moments, with idle running off the 35 and 40 kPa cells. These areas in the tune were a bit lean since I tuned the running temp idle around 50-55kPa. The photo attached will show the first tune.

I made a second tune with the VE from 700 up raised by around 2-3 in all cells under 35 and 40 kPa and a small increase in the surrounding cells. Flashed it and started vehicle. Didn't appear to make any noticeable difference.

I DID have another test tune I created where I raised and smoothed/blended in the low RPM high kPa area, increased the 30-45 kPa cells even more and built a small "bowl" around my running temp cells to see if this would give me an even smoother idle. For whatever reason, TunerPro saved the file but it appears it didn't save the changes to the VE table, so I will be re-creating that tomorrow at work

Any recommendations in the meantime?