GunnerGTA

...ARE DISSAPOINTING!

254hp/360tq. I will get the graphs later, but hp peaked just before 5000rpm, and torque was around 3200rpm. It was pretty hot in the shop, 80+ degrees. It looks like the power was curbed by a really rich air/fuel mix. The wide band held rock solid at 10.3:1 for 2 pulls. I am going to look at the plugs, and check the heat range, check the timing. Is there an easy way to test the fuel pressure? What else do you think I should look at?

Specs: 383ci, 5spd, Edelbrock TPI runners/baseplate, 58 mm tb, 200cc Dart Iron heads, 1.6 roller rockers, comp 264hr cam, 13/4 slp headers, catless dual ypipe, 3" flowmaster crossflow catback, pcm4less chip, crane/msd ignition, 24lb injectors, 10:1 compression.
I
I will appreciate any help and advice, thanks.

Kennerz

You can buy a FP gauge at an autoparts store. You need to see what it does (fuel pressure wise)on a run under a load. The static pressure may be good, but your pump may be tired. Check timing, valves adjusted correctly? Air leak making it dump fuel. What kind of vaccum you pulling? I've run a XE264HR, on a 355 with ported stock heads and intake, it ran pretty strong. As you know your Giving up a lot of power with that fat AFR. What shape are the injector's in? How does it run with the chip? Things happen when programming, maybe something is off there..

Good luck Also TPS set correctly, IAC set right? EGR hooked up? THese cars do not run up to potential if they are not set up & on the money with the basic stuff first.

VincentZ28

iTrader: (2)

Your specs will not support a 383. It is sucking up the moving air way too soon. You would have made more power with a 350. Your combo needs a lot of porting.

1989GTATransAm

iTrader: (3)

"The wide band held rock solid at 10.3:1 for 2 pulls"

Your car is running pig rich and desperately needs a tune. You need to find someone who can tune your car. After that is done then we can see what else needs to be done.

NowhereFast

That's definitely your biggest issue. Fix that, and you'll be much happier.

Street Lethal

iTrader: (16)

Check and make sure your Initial timing is set in conjunction with where they have the spark reference set, and once that checks out, and all else is good in terms of fuel pressure, no leaky fuel pressure regulator, and the injectors aren't leaking or stuck open, then send the chip back to them for another burn based on your dyno readings...

Orr89RocZ

iTrader: (20)

They jacked up the pe vs rpm i believe. That needs adjusted again. With wideband reading and dyno rpms they can dial it in. You'll be pulling alot of fuel tho

TPIVette

If you're not interested in tuning it yourself , I would look for someone in your area that can dyno tune an OBD1 car. If your area is like my area, you'll find that its nearly impossible to find anyone that messes OBD1 cars anymore. What I did, after building my 383 TPI was get PCMforless to do an initial tune . I then bought the stuff to datalog the car. I sent PCMforless the data logs and dyno graphs and had them touch up my tune. Although I'm sure I still have some power left on the table, it runs pretty well now (11.82 @ 114). It point down 325/460 at the wheels with smaller heads then yours (ported 113s) and an LPE 219 cam. Of course this is in a Y-body, so its not exactly apples to apples.

Copperhead

I ran similar numbers (290/370) with a similar combo (except an XFI 280 cam, Patriot aluminum heads) and a buddy of mine suggested I advance the cam (per his desktop dyno program.) It is currently installed straight up. I was happy with RWTQ of 370 (Time Attack build) and not too concerned about peak HP, but if changing the cam timing would net some gains for free, why not?

Any thoughts on this?

85Iroc-Z

iTrader: (4)

I got 331rwhp and 411rwtq out of my set up. Mods in sig just without the blower.

GunnerGTA

Could you elaborate a bit on what you said here and how I would verify this. I have looked into the process to set and check the base timing, but I am not hip to what the spark reference is that you mentioned. Thanks.

GunnerGTA

Thanks for the advice guys. I spoke to pcmofnc today and they confirmed that they can pull the file for the chip they burned for the PO and modify it to my needs for a nominal fee. I have made a checklist to rule out any issues prior to tuning.

1. Verify fuel pressure and rule out injector issues. For this I will get something like the accel gauge for the schrader valve.

2. Change plugs, car was sitting for years and I should have done this already anyways

3. Check base timing, and do whatever Street Lethal suggested

4. Datalog the car, I need a cable and software for the laptop

5. If no issues present send dyno info and datalogs to pcmofnc for a updated tune

6. I have seen on here a few members claim the flowmaster 80 series can actually rob horsepower. Do you believe this? I am now curious after hearing the car in the upper rpm on the dyno. It may be something, or may be something else. I'll upload the video.

1989GTATransAm

iTrader: (3)

"I have seen on here a few members claim the flowmaster 80 series can actually rob horsepower. Do you believe this?"

I do and so do a lot of other people.

GunnerGTA

BadSS

Here’s an 80 series. Note how small the actual “internal” muffler is. While the 5” thick case 80 is a little better than the 4” case, I’d never run either – there’s just not enough room around the baffles for decent flow.


Here’s a 40 series muffler. Note how much more room there is between and around the baffles. There’s little question that it can flow better than the 80. In one of the last muffler "shootouts" I've seen, this series 3” muffler only flowed 392cfm compared to 878cfm for a 3” straight pipe.


With the typical 20% drop in flow for the bends in a typical exhaust system, the SINGLE 3” pipe is good for around 325HP (700cfm) - assuming a “zero loss” exhaust system (650HP for dual 3” pipes). This doesn’t mean you can’t make more power, just that the single 3” 40-series is only good for around 183HP before it starts rolling off some power (the 80 series can’t help but be worse).

If you want to keep the stock dual exit system, I’d replace that 80 series with a DynoMax welded UltraFlow. I did a lot of research in 2004 and at that time, it was the highest flowing 3" in / 2.5" out “cross-flow” dual exit muffler I could find - should be little to no loss over the 3" pipe. If you do, I’d replace the muffler before I did the data log for the new chip. I’d expect you would see a noticeable seat of the pants increase in power since it’s running so rich.

Fast355

iTrader: (2)

All flowmaster hurt hp. Straight through designs are much better.

Copperhead

Any thoughts on advancing the cam?

BadSS

Copperhead, most off the shelf Comps are "cut" with 4-degrees advancement "built in" - meaning if you didn't degree the cam and lined up the timing chain marks dot-to-dot (no advancement by the timing chain), more than likely it is already 4-degrees advanced. Desktop dyno does a good job at estimating peaks, but can be more than a little optimistic on power output below peak torque. I wouldn't have a problem using it to determine whether or not rocking the cam timing up or down was worth it based on what the peaks showed though.

As far as the original poster, with the cam being so small to begin with, I sure wouldn't advance it.