Scott 87 IROC-Z

After getting a good amount of break-in miles on my new motor, I am starting to give it more throttle and get on it more. It pulls hard until about 4000 rpm and then it seems to lay down and not really want to accellerate as fast after that. The solid roller cam should pull to about 7000rpm. I checked the valve lash and gone over everything from the scan tools. The only thing I reused from the old motor was the distributor, but it has a new ignition module and MSD coil. The fuel filter is new and the pump was replaced with a Walbro 255 ltr/hr pump. The trans was rebuilt last year and the catalytic converter was new last year when the headers were put on.

I don't know if it is the distributor, the transmission slipping already or something else. Any suggestions on what to look at?

More info on my motor that might me relevant:
377, miniram, 242/248 .570/.576" 112ls solid roller, SVO #30, MSD 8.5mm wires, 58MM TB, Yank 3500 stall, 3.73 gears, 215cc Brodix heads fully ported,
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87 IROC-Z
Minirammed Solid Roller 377

[This message has been edited by Scott 87 IROC-Z (edited September 05, 2001).]

JohnnyIROC-Z

what's your fuel pressure

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1987 IROC-Z T-Tops No mods yet... Oh wait !MAF!

Scott 87 IROC-Z

It is set to 48psi with the vacuum line unplugged.

Z28DJP1987

Your running too rich at 48 psi thats why
you are bogging at 4000 rpm's. Try 42 psi.

Scott 87 IROC-Z

I'll give it a try and see how it is.

five7kid

iTrader: (14)

Knock sensors don't like solid cams, either.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" cat-back, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

Scott 87 IROC-Z

I am not getting any knock retard.

Ed Maher

I'd bet you are running into the upper limits of the MAF around 4k rpms, and from there the default PE settings are probably way too lean.
Witha combo that radical, if you're not into PROM tuning, you are now (at least if you want to make power and keep your engine in one piece.) Also, that combo is far beyond what a MAF system wants to deal with, and since you seem to be starting from scratch, might as well convert to SD no as well.
...ed

Scott 87 IROC-Z

I have burned probably over 50 chips for the new setup. All my BLM' are 128 +/- 3 and I increased the acceleration enrichment for the upper rpm's. The MAF is about 200 g/s at 4000 under about 30% throttle and it still happens.

I plan on switching to SD this winter but just wanted to get it better now. I am just wondering if is is something mechanical or maybe the PROM just needs more work.

afgun

What kind of O2 sensor voltage are you seeing as you get on it in the upper RPMs?

Ed Maher

Hmmmm...really it could be either. If you are feeling a hard drop off at 4k rpms, even under part throttle as you describe i'd really lean towards a mechanical problem first, like the distributor pick up coil or something moving around on you.
I don't know much about MAF tuning, but is it possible that just the high end areas of your tables need more work (as in the 4k rpm, >200g/s area, + the AE that MAF uses past max airflow, which is basically your entire powerband probably, lol) It sure can't hurt to try increasing your fuel in that area. With your engine combo 4k is where it is just coming alive, and no doubt it will need ridiculously more fuel than a stock engine would, so your fuel tables should reflect that

Scott 87 IROC-Z

I bumped the fuel pressure up 5psi and added more fuel across the entire rpm range along with more above 4000 rpm. It seemed to have helped a lot. It looks like I just need more tuning. However, I am maxing out the MAF sensor so it looks like I'll have to switch over to Speed Density and start tuning from scratch. Thanks for your help everyone.

EDGE

I had the holley/Walbro pump in my car. It was Sh*t. I could not pull past 4000rpm. It would just run out of rpm right there all the time. Not to mention the horrible noise. And the price. I put a carter OEM pump in it. Now the bastard pulls right up to redline in all the gears (700-R4) It goes real strong. See you can have fuel preassure but no volume. My Holley pump was less than a year old when it bought the farm. So dont be mislead by thinking your fuel preassure is good so the pump is good. you need the flow. The GM manual has specific numbers concerning gallons per hour. Basically you disconnect the fuel line up fron and pump the fuel into a container of a known size and you should get so many litres in a given amount of time. Just an Idea...cause my car was doing the same thing. Good luck

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

Scott 87 IROC-Z

I will have to look into that. I burned another 8 chips tonight but the car is just not making the power in the upper rpm's.