Hi all

had my 1990 GTA on the rollers yesterday. It's a standard SD 5.7 TPI just with a K&N filter, headers (hooker I believe) and a 3" custom SS exhaust

Anyway, she made 195.5whp @4,400 rpm and 282.1 ft-lb (also at the wheels) @ 3,100. Does this sound about right?

tbh I was hoping for it to be in the low 200's hp wise (say 215-220) given the exhaust work but not overly dissapointed.

Next I noticed the AFR to be a bit rich. E.g. @ 2,600 rpm it gave a reading of 11.68 but this dipped into the 10s @ 2,800 (10.87) and again @ 3,800/ 3,900 rpm, otherwise lingering in the low 11's.

It also seems to spit a bit on overrun. Does this seem a bit rich for a TPI car. Wonder if the headers is causing the computer to dump more fuel in? Or perhaps something else?

Thoughts most welcome!

oh - and a pic of her on the dyno

 

Seems a bit low for a 350, but all dyno's are different. Next you need to get it on the dragstrip.

 

[QUOTE=spurgeon76;5136634]Seems a bit low for a 350, but all dyno's are different. Next you need to get it on the dragstrip.[/QUOTE

Those are about the correct numbers for a stock TPI 350. Also those are RWHP number with a 80% drivetrain lloss. I est his flywheel hP @ 245 with his add ons which are not big HP gainers.

 

thanks for the input both. Yep, I keep hearing about headers/ exhaust freeing about 15hp or so. Maybe that's when the intake has been changed and other bits so that the headers are the biggest restriction

thoughts about the Air/ Fuel reading. High 10's, low 11's sound a bit too rich for a TPI to hurt performance?

There's a fairly local quarter mile strip to me. Plan on taking it there in January. Given the heavy 'vette wheels, if I get a 14.xx I'll be happy

 

WITH 80% DRIVE TRAIN LOSS HE SHOULD ONLY BE AT40 RWHP

 

Yes you're right. You need to do some datalogging to see where your fuel trims are. Headers and open exhaust will often increase positive fuel trims, that then can result in added fuel at WOT. The factory calibration is often 10% - 15% too rich for best power from the start without any added fuel trims.

Once you determine what is going on with the fuel trims, and you rule out a mechanical issue like faulty injectors or O2 sensor, then you need to recalibrate your fueling a bit by PROM tuning.
If your AFR reading is correct, then you are much too rich for best power.

 

thanks for chiming in

I have no reason to doubt the AFR number from my time at the dyno but appreciate they could be out. Car does exhibit other 'rich' type behaviour such as a smell of petrol on cold days and sometimes stammering on take off.

I changed the 02 sensor quite recently (2 years ago) along with plugs, distributor and rotor arm and have only done about 10,000 since.

data-logging etc. is all out of my league at the moment but will start to read up on it. Is getting an AFR reading at the 02 sensor considered accurate? was thinking of wiring in a gauge.

In the meantime I may do some mechanical checks such as pull a few spark plus and see how they look

hey - hopefully I can break 200whp if the AFR is a bit more in line!

 

Stammering on take off is caused by misfires, which should not be the result of just a rich condition alone. Most engines can run quite rich without misfires. I would look for another cause. It is normal to run very rich on a cold-start, and without a CAT you will smell the fuel in the exhaust. Misfires will also cause unburned fuel to escape in the exhaust.


You will need to install a wideband O2 sensor just downstream of your factory O2 sensor in order to read the AFR correctly. The factory O2 sensor is of little use in that area, though once you are datalogging you can watch your fuel trims at part throttle to approximate the AFR. For WOT you need the WBO2.

I would check the fuel injectors for even flow. One clogged or leaking fuel injector can throw off your fuel trims for the entire engine. Misfires caused by other reasons can also do this. That's why I suggested eliminating mechanical issues first.

 

.. Yeah, AFR shouldn't be falling out of high 12's at WOT... although, as mentioned, one messed up injector could be skewing the readings... checking all 8 plugs for a light greyish/tan almost white color may indicate something... too bad some are so hard to get to...

.. What temp thermostat you using? A low temp one or no thermostat may be fooling the ECM into thinking the engine is still cold and needs a richer mixture...

.. 1 or 2 cats? If using any...

.. Yes, looks like an ECM tune could get you into the 200's HP...

.. Skim through the beginner's 'Performance Prom' 'sticky' above for some good understanding, if you haven't done so already...

.. Did you do a low HP 'cruise' dyno run to see if AFR in 14's - 15's?

 

thanks everyone

yep I've got some intake mods planned which include slightly bigger injectors so will hopefully eliminate a bad injector problem with that.

BuzzLOL
Its a 180 stat;
No cats;
No low cruise test unfortunately, was just a power run at WOT

have been reading a bit into prom tuning. My plan now is to get the intake / other mods all done and pick myself up an autoprom and get busy.

 

those numbers are pretty close to my stock 305 tpi.. but not bad for stock 350, your tq is way more then mine put out.. lol

 

Stock injectors on an L98 are 22#. Any chance somebody before you installed a (commonly available) set of 24# injectors? Is the fuel pressure setting stock (~43 PSI with vacuum regulator line disconnected and plugged)?

Running overly rich is not a really common problem on stock TPI engines.

ECM doesn't look at the O2 sensor at WOT since it's not shooting for stoich (14.7:1) during power enrichment mode. And TPI motors used narrow-band O2 sensors like many engines of that vintage.

 

really not sure Damon. Other than the headers and exhaust, car was stock when I got it. Being in the UK, I think its more been basic maintenance then upgrades by previous owners

Just pulled a sparkplug - drivers side, closest to the front of the car. It looked pretty sooty. By no means a definitive test, but I'm pretty sure the car is overfueling.

I'll pickup the datalogging (autoprom) bits soon and get reading. Off topic but sounds pretty cool running the car from a laptop...

thanks alll>>

 

Those DYNO numbers look exactly like mine when the car was stock, I have saved on my desktop, I can post it if you like, car was completely stock, it ran extremely lean at idle but I later found a vacuum leak in the right side runner.

 

Why put bigger injectors on it? Run the stock 22lb/hr. Bigger inj. will make you run overly rich and lose power.

 

Leave the injectors alone and get a custom tune. How was your A/F ratio measured? with a wideband right?

 

ITSMICKEY car is an GTA 5.7 G92. His car has a full aftermarket exhaust system only. with Dyno Don's headers, dual cats and 3in cat-back through a Magnaflow muffler and a chip tune. It dyno at 251whp and 35x wtq.

If you change the injectors, you need to reprogram the chip for 24's. You dont need them. Check the timing and give it a good tune up and a chip tune and the numbers will go up.

 

http://www.gmhightechperformance.com...all/index.html

read that article.

 

thanks - that's an interesting read. I do appreciate the benefits of a good tune. AFR was measured wideband with an exhaust probe I believe

VincentZ28 - exactly! I optimistically hoped my car would pull 210-220 with my exhaust mods, based on other people's reports.

I should elaborate that the larger injectors are to support intake work, a larger cam and better heads. This dyno run was performed as a baseline and health check on the engine before I proceeded to buy up the parts.

I was originally going to get the aforementioned done and close this session of 'hot-rodding' with a mail order tune. But your responses and further reading of the prom section have shown me that I'm better off spending the time and a little extra money to datalog and burn my own chips.

Perhaps that's the silver lining of finding my car is not running optimally!

 

An easier route to take would be to datalog, then email in your datalog to the chip burning company. That way they can actually see what you are working with and make a chip accordingly and also you can again datalog with the new chip and see what changes were made. Tunerpro is good for that.

 

You probably wont need bigger injectors for a while as most of the changes needed can be made in the chip. IIRC, 24lb injectors are not needed until you are closer or over 300hp.

 

I'm hoping for slightly north of 300 wheel horsepower with my new setup:

heavily ported TPI intake/ base with SLP runners < all matched and plenum end siamesed as recommended on this site. Ported L98 heads or after market heads 180/95 (AFR/ Profiler) and a cam to suite. And lastly a tune

Through my cursory research I understand 24lb injectors would be ideal for the above setup

Far too optimisitc? thoughts most welcome>>

 

"Far too optimistic".

 

Should beable to get to 300whp if you had a little bit of clean up work done to the heads. Even with stock heads I think its doable but need to cam up more and siamese the runners an inch or 2 more. Definately easier to just spend money on a good set of larger aftermarket heads. Profiler/AFR/Trickflow/Dart/Brodix in a 180-200cc runner can easily do 300whp with a mild cam. Most of those heads can support 400whp. SHould be easy to tune as well.

I like AFR or Profiler 195's with good hyd roller springs. comp 260XFI or 268XFI works well. 268 is capable of 350whp or so on a TPI based setup using aftermarket ported base/runners. Stock base thats been ported will restrict flow alittle bit more than aftermarket base but still make 300whp. Both are mild cams and easy to tune. Very EFI friendly. 24lb injectors will do 350+ whp so thats a good size for your goals.


IF you lean your current motor out to somewhere in the high 12's to 1 air fuel, you will pick up a good bit of hp. On a hotter motor (heads/cam L98), going from high 10's to 1 to mid 12's to 1 air fuel, i've seen 30hp

 

im not a fan of the mail order chips. you have the back and forth of trying to get it right. then if you make any changes to the motor, you go thru it all over.
then there are the little things you can do that will affect fuel mileage such as highway mode, TCC lockup speed, and part throttle timing.

if you do choose to tune it yourself, i feel its easier to learn chip tuning before you make very many mods.
when you start throwing intake work, heads and a cam in it, you add more variables.
once you get somewhat comfortable with tuning, then do the mods.
you can tune the chip with the stock O2 sensor, but you won't really know what the AFR is with it. a good wideband really helps.

i originally tuned my motor with the stock O2 sensor. i had even bought a new Delco sensor to tune with.
i thought my car was running pretty good, but my trip to the dyno was a bit of a disappointment.
torque was really good, ~306 average for 2 runs.
hp to the tires wasn't too good, around 180 average on 3 runs.
AFR was dipping into the 9s.
using my WB, im now at 12.8-13.0 across the RPM range.
after tuning with the stock O2 sensor, using a wideband kind of felt like cheating.
i have only 1 regret about buying my wideband, and that is not getting it sooner.

 

thanks guys.

Orr89 - that's really good to hear. Seeing what your car done with the HSR is very impressive stuff. Interestingly in the looks department by car could be your Camaro's cousin. Shame not so in the performance department! Thanks also for the cam recommendations.

DJP87Z28 - your mod list and your power output does conern me a little. I certianly don't have a freak factor performer. I do fear that once I get this all done and am about 2g's in, I'll dyno it @ 250whp or something.

Denn_Shah - cheers for chiming in. Yeah the intake bits are being custom done in the states and I haven't really spent any time properly researching the heads, let alone put an order through. My point? I may just get the autoprom first and troubleshoot and sort out my running rich problem first.

Tuning is just the sort of thing I could get into (I write macros etc. in my job all the time and generally am a logical, numbers kinda guy). Scene change to me writing the absolutely worst tune and cooking my engine!

 

That is why I posted my mod list. I was also hoping for more and did not get it. Everything was running good even my fuel ratio was 13:1... also a Prom from Fastchip for my set up. That was 10yrs ago and learned to live with it and since that time the car is still running well and looks good.

 

no two way's about it - that's a real looker.

I'm curious, what cam do you have and any port work to the TPI intake or other after market bits other than the SLP runners?

 

When I swapped from the 305TPI to the crate 350 I was mainly interested in having a streetable car that was a match for most 4th gen camaro/firebirds at the time.

1) No additional work was done to the SLP runners, but they did look good internally.
2) Heads were 67CC 9:6 to 1 comp ratio 1.940 int & 1.50 exh.
3) Cam Crane 272 hyd..110deg 450 lift 216 dur @50
4) Wells high flow MAF (750cfm)
It did turn out to be a very good driver with loads of low end torque.

Good luck on your project.......