SR+74219 = slower E.T!?

Last year I upgraded my 91 Vette with Hooker 1 ¾” headers, dual 3” exhaust, AFPR and ported the plenum. The E.T dropped from 14.40 to 13.91@98mph. I was satisfied with that. Then I installed a B&M shift kit, the car felt faster but my new best time (same track, almost the same weather) was only 14.10. I was disappointed… But it could perhaps be explained with traction problems, it was not a dramatically deterioration. I should add that I have 2,59:1.

This winter I upgraded with a Super Ram (base, plenum) and a 74219 camshaft. New valve springs. I also had to replace the head gaskets since I discovered water in #7 cylinder. I grinded the heads so that the surface was good again.

I also removed the air pump and all that goes with it.

At first the idling was very bad but after some tuning it was good again at 800rpm. For different reasons we couldn’t tune the car at WOT so we only tuned the idle and cruise speed, apprx. 3000rpm. above that we let the engine run rich to be on the safe side.

When I went to the track this weekend I got very disappointed. Same track again, almost the same weather conditions. I had a hard time to run faster than 14.40!!! Back to the E.T that I had when it was stock. The trap speed was around 98mph so no improvement there either. After I adjusted down the fuel pressure a little I could finally run 14.09 @ 97mph. Any ideas?

The car feels slower out of the pit but faster on the highway in high speeds.

I also should add that I couldn’t really adjust the TV cable after the SR installation; the tranny doesn’t shift as hard as before.

Thanks in advance for all ideas and inputs.

BR

 

I think you answered your own questions. You went from a more low end oriented combo, with a high axle ratio (that needs low end), to a higher RPM combo. Then you stated that you couldnt tune WOT, but lowering the FP resulted in quicker times- I think you need a WOT tune. Last, adjust the TV cable before you ruin the transmission. Low line pressures can burn clutches and bands.

 

something doesnt sound right... i also have a 91 but with a 6spd 3.33 gears. i did tpis headers, 1.6 rr's, ported plenum, tpis big mouth, large tube runners and ran 20 passes at 13.1 at 106 on stock tune.it was lean.15/1 afr

but i had dr's and has 1.8 60ft's.

what were your 60 ft times?

who resurfaced your heads for you? your self?

always!!!! replace the head gaskets when heads are off....

you should go to the dyno and see what you put down and your afr at wot.get a new tune and bring new chip to the dyno with you. make 2 passes with the old chip then run a few with the new and compare. then you can do some fine tuning from there.

your car should run low 13's even with bad 60 ft times. i was running 2.2's and still was getting 13.4 s'. and i still have my stock cam and head in...

there was a guy at the track sunday that had a 383 superram firebird on dr's with 3.90 gears. he also ran stock tune. he could only turn 12.9's he should be at low low 12,s if not 11's with that combo
just to get it running he had to bypass the maf sensor and tune idle with the t/b screw. he was not happy it didnt help that i rubbed it in...

 

ask ski_dwn_it if he will do a tune for you...

 

You need to get to a shop with a dyno near you who can do a real tune on your car in person. Are the 2.59s still in the car?

 

I'm assuming that with the SR and cam on a speed density car that you've had a custom prom burned (i know you mentioned some tuning, but I wasn't sure if you meant a custom chip or just adjusting the AFPR). With this setup you should be deep into the 12s. Something is amiss and I'd suspect tuning. I couldn't get my SD car to run right with 24 lb injectors without a custom prom, so with a cam and SR I think you'd be in real trouble with a chip.

 

doesn't sound right to me....

 

Thanks for all the inputs.


My 60 ft times were 2,3-2,4, same as before SR and cam.

I had a shop resurface the heads and I replaced the gaskets.

I still have the 2.59 gears.

The tuning I did was not adjusting the AFPR. I friend of mine connected his laptop to the car and we did some serious low end and idle tuning and burned a new chip. For different reasons we couldn't do the high rpm and WOT tuning so we chose to let it be on the rich side just to be safe. I don't know how rich. We are going to connect a broadband lambda to try to get a proper tuning at the high rpm when my friend got time.

 

There is no substitute for a proper tune.

Don't let peak numbers fool you either. I helped tune an 86 with a supercharger. It only picked up about 30 horses at the peak, but at 6000 RPM's we picked it up 110! Talk about driving like a whole different car.

 

www.fasterproms.com did my tuning. They will burn a chip to your specs. They are very familiar with the 74219/SR combo. They did mine and it made a world of difference. You can borrow their datalogging software and it will let them fine tune your car.

 

It's the tune. Don't go with a mailorder chip . Unless they can hook up a wideband a/f meter through the mail.

Use the wideband to lean out WOT. Put the lower rpms to 12.3 and the upper rpm to 12.9(for a base) and it will FLY!!

 

Now I feel a little better, thanks

Problem is to find someone that is good at tuning Corvettes here in Sweden. I can just hope that my friend knows what he is doing. I hope that we can do a proper tune with his wideband and that the car will be a lot faster after that. I don't want to change gears, not yet. Seems like a vaste of money to do that now since I probably going to have to change to a D44 in the future.

 

Have you had any other head work done besides the resurfacing? You'd be really limiting that combination with a set of stock heads. I agree that the tuning is also an issue, but you're not going to see maximum potential without a good set of heads whether ported D-Ports or aftermarket.

As a comparison, scorp508's car has a worked set of L98 D-Ports and he laid down 320+HP at the rear wheels and was still in the process of tuning his car. I believe that he was in the 12.80s somewhat untuned.

Ron

 

:I hope so to.. I think your car will fly..

 

My friend's car has l98 heads(ported & stock valves). I tuned his car and it now runs 122mph+ at the local track. With the junk custom mail order chip it trapped a best of 112mph. I'm really impressed with the stock l98 heads

 

No head works besides the resurfacing. I am saving to buy some aftermarket heads so I didn't want to spend money on a good port work on my stock heads.

Yesterday I adjusted the Tv-cable that was out of position and I think that got it right this time, I didn't have time for a test drive. Hopefully I will feel a difference now already.

Devilfish - you don't have time to be here, you should work on my tuning