Hi all, I'm sure this has been done to death I did a search but couldn't find anything. So let me know if anyone is interested. I have an 1987 5.7 iroc with 28,000 miles totaly stock even ac/delco airfilters. I'm going to do some mods and see what the dyno says. My plan: This week I'm going to the local dynojet and get a base line then I'll install a test pipe with a new Dynomax 2-1/2 catback system, drive it a couple of days for the computer to adjust and do another pull trying to match weather conditions of the first (airtemp,humidity). Next I'll install the TPIS bigmouth intake,TPIS LTRS, ported plenum (from corvetteplenum) drive a few days and do another pull with weather conditions as close as poss. I have ordered but not received yet a Holly afpr and a TB by pass kit and the Mac's y-pipe when I get those items I'll do one more pull for the final hp/tq inprovement. If this has been done before and I just can't find it let me know and I won't waste anyone's time. If anyone has ideas about this that I have over looked please let me know. Robin Bailer

2.5" catback system is a waste of money....stock is 2.75 IIRC, get the 3" catback. Also you'd spend what $500 on different dyno days just to see a 25hp difference, I wouldn't bother. The dyno corrects to SAE conditions, so weather won't matter.

i'd be interested in seeing the baseline vs full bolt ons/tune.

I would estimate 215whp stock and 240 with the full bolt ons and tune. Possibly 250whp

But definately do the 3inch catback exhaust. headers/ypipe would be the biggest hp gainers tho. You probly wont see a whole bunch of power without the headers/ypipe combo

Fair enough..I won't waste anyone's time except with the base and final. Robin

Hi Robin,

I sort of ran out of money.
So my build up has come to a stop.
Not sure when I'll get started again.
My not so scientific record of my step by step
is at Cardomain.com & at Dragtimes.com

http://www.cardomain.com/ride/2175519

http://www.dragtimes.com/Chevrolet-C...slip-5874.html


All the items you mentioned are things
I was also hoping to install.
SO..
I'd also be interested to see what the
TPIS big mouth
Large tube runners
and Ported plenum
will do to improve performance.


Any chance you'll eventually install
Headers
A 52mm Throttle body
the tpis ZZ9 Cam
and a set of 180 cc AFR eliminator heads.

No, this is as far as I am willing to go with the mods. You did some great 1/4 mile runs with your mods.

If you want to do the dyno info and stuff, it will be GREAT resource for thirdgenners, but it will cost some money to dyno the car everytime. I know my shop charges 70 bucks for 3 pulls, and thats cheaper than most.

If you dont mind doing that then it be great to see some gains after a catback, then after the TPI mods. It be better that you plan to use some headers since thats where the biggest restriction is i feel

then possibly play with timing/tuning to see how much extra you can squeeze out the full bolt on car

Well in my opinion,
any information is always welcome.
Good luck.

Thanks that's the way I feel...More information the better!!

Well part 1: base line pull. Orr89RocZ You were right on target: 1st pull 209.6@4500,2nd 210.3 and 3rd 215.1. SAE. Next pull will be Monday with test pipe and Dynomax system installed. Temp 62deg and 50 % hum. Uncorrected 223@4400 Robin
----------
Also seems to me that GM WAY under rated the L-98 With the ZR-1 I've been told that a 16-18% drive line lost was normal I wonder what these are with the 4 sp auto?

i'd say 18-20% is normal loss. Glad to see that car making good power, thats about what i expected a L98 in good running condition do. The other mods should pick up some power but headers will definately do it

Also try advancing the timing from 6 degrees base to 8 degrees. you'll gain some torque and alittle hp

cool thread.

Suggestion, First, I love to see you install TPIS bigmouth intake,TPIS LTRS, ported plenum and make a pull, I think alot of us would love to see how much gain is made with these mods on a stock 350.

They say the LTRS is worth 25hp alone.

Update...Yesterday I had the test pipe and Dynomax cat-back installed..VERY quite not what I expected. Abit more rumble and vibration with it shifts into 4th but not bad. Will disconnect battery and make a few full throttle passes to reset the ecm. SLP-GTA good idea I'll do just that. Next pull Monday weather permitting. Robin

awesome good info here i'll be lurking and reading!

runners and base will net near 25hp but not with the runners alone. stock base would still be restrictive

Ok, went to the dyno today. Only change is no cat and 2 1/2 inch dynomax cat back exhaust. 228 hp and 308 fl-lbs torque. That's a 13 Hp peak increase with an avg of 10 hp all thru the curve. But the big increase is the TQ with an avg. of 20 ft-lbs and a peak of ...wait for it...24ft-lbs. Not bad for $189.00 and $50.00 install. next ..TPIS LTRS Ported plenum and TPIS loud moth intake. Robin

very nice, that should pick up with headers for sure. i'm thinking near 240whp or so with shorties and then another near 10 with the intake upgrades, but your rpm range should go up alittle

OK sorry for the delay but here is the lastest numbers..... From my last run peak HP 228 Peak TQ 308. Now with TPIS LTRs,Big moth intake,TPIS AFPR, TPIS plug wires....AVG HP gain 10-19 under the curve with a peak of 10Hp no where did it lose HP now peak is 238 . the peak BTW has moved 400 rpms up to 4800.TQ only went up 6-8ft-pounds. but lost at the peak to 302.Let me say abit about the company TPIS First the sent the wrong year intake (89 and newer no cold start injector) But Jim at TPIS was more then will to make it right he called my service tech and told him what to do to fix the problem. Then TPIS sent the wrong plug wires. Jim again called and had the tech measure the wires and sent custom made wires NEXT DAY at their expense. We all make mistakes it's how you handle them that marks a truly great person or company and TPIS is first rate in my book. Next and last upgrade is the MAC 2 1/2 Y-pipe and we'll see what the final numbers will be. Robin

Thanks for the update. It is always good to have back to back data like you did.

very nice numbers so far! Intake stuff looks to be worth near 15-20hp on motor which is near what i had in mind. 10whp peak is nice but 10-19 everywhere is what its all about

And to think this car has no headers right? just stock manifolds? And no real chip tuning. thats impressive. This car should run bottom 13's if setup right and in good weather

Stock manifold and stock chip.Chevy sure did under rate these engines, Robin

This is a great thread, I really appreciate you taking the time to post your results.

It would be extra special if you can scan the graft to show the power curve improvements.

Also what did you set your fuel pressure at?

I ran my car on the dyno a little while back and was suprised with the numbers. My car is an 89 L98 with edelbrock shorties, high flow cat, flowmaster cat back and K&N filters. Everything is bone stock. She put down 240 whp and 320 wtq. Not too bad. A set of headers and y pipe is going to be one of largest improvemenst you can do.

Just a little bookkeeping for those reading.

Stock: 215 HP
!cat & 2.5" Dynomax: 228 HP and 308 TQ*
TPIS LTR, Big Mouth, plug wires: 238 HP and 302 TQ**

Overall gain = 23 HP

* HP peak @ 4400 RPM
** HP peak @ 4800 RPM

I'd be interested to know how much changing the fuel pressure makes on the dyno.

Well I don't have the tech skill to scan and I don't have the equip. to do it if I knew how. Sorry I'm not a computer guy. BTW we got the best HP/TQ with only 43 for fuel pressure. We started with 47 went up and lost power on the dyno then started going down with psi and power went up until we dailed in at 43psi. Robin

many buy into the fuel pressure mod giving power but it doesnt if the car already runs rich from the factory.... more fuel will not make more power if its currently rich

my car was the same way. stock fuel pressure it was 12.3 to 1 air/fuel...abit rich. 1 full point leaner would have made some power. More fuel wouldnt have done much at all

Sorry to duplicate things, but
I sent you a PM a couple of days ago.
I was just curious......

I was asking about the TPIS big mouth intake you installed.
Did you port the runner entry’s ???
Or order it already ported???
Or did you just install one right out of the box???

Hey sorry I didn't see that I had a PM. I had the TPIS runners and TPIS intake installed right out of the box. BTW we tried advancing the timming to 8 deg. from the factory 6 but the computer kept pulling out 12 des. so we set it back to 6 and the computer still pulled a few degs. ANY ideas why?? I always run the 92-93 gas so that's not it,unless I have a bad tank full this time. Robin

my car did the same thing with timing.
I unhooked the knock sensor no more problems with that. I run 12-14degs
My car like 51 psi of fuel psi....
It picked up 2mph and a tenth or 2.
Higher fuel PSI tends to atomize the fuel better. The O2 helps with the rich lean thing. BTW my car didnt pick up power on the dyno with more psi but it does make a diff at the track...

could be a bad knock sensor or a rattle in the engine compartment that is acting like a knock. If its pulling 12 degrees then somethign is wrong. you can tune the ecm to pull less timing than factory's 10-15 degrees. I did this on my L98's tune. Seemed to help some

CMK-2 you need some headers on that car. You will see some good improvements.

This is great stuff. For comparison purposes also, here's my info. Brand new 355 , 9.6:1 CR (as close to a stock L98 as we could get). I have a STOCK ported base, SLP runners and ported plenum, everything is port-matched. AFR 180cc Eliminators (65cc chamber) and Comp Cams XR-276 HR. Also, 1 5/8" shorties and a 4" catback. I have a 2400 stall and 3.70 gears (which lowers the dyno whp number a bit I think). So far, best pull is 300whp, we are tuning through the ECM but it's not cooperating with timing changes atm so there may be more in it. Also, what floored me is that I made peak power at 5200 RPM.

Are you going to be doing heads and cam in the future as well?

Hey I have installed headers on my 1978 Trans Am about 2 months ago and I'm still fighting rattles,exhaust leaks (with stage 8 bolts,and the best header gaskets money could buy) and a starter that is dying b/c of header heat. I don't want to have to start the fight all over with the IROC. I am waiting for an up dated ESC that Gordin Kilibrew (C-4 Corvette factory tech) told me about That is going to take cake of my spark knock problems. I will then do the final dyno pull. Robin

Ok sorry for the long delay..Getting married is/was takking all my free time.
Latest dyno run. Yesterday temps and hum up in the 90's. Added a TPIS chip (stage 1) and a Mac's Y-pipe... 244hp @4800 and a BIG gain in TQ. 333ft lbs. That's only a dissapointing 6 hp but the TQ jumped by 31 points. I don't understand that I thought TQ was a product of HP How can HP go up by only 6HP but TQ goes WAY up? I guess as the saying goes..Don't look a gift horse in the mouth.
BTW Powerpluse sent me their spark plugs FREE to run a dyno test and post the results but they sent the wrong type. Next week I'll do the last run and A-B the new VERY high priced plugs and let you know the findings. Robin

Hmmm, something appears to be not right in my car then.

SuperRam (ported)
Accel manifold
descreen MAF, TB foil, TB bypass
high flow cat and catback (all 3")
AFPR set at 43 psi
PCMForLess chip
6° timing (pings at 8°)

Obviously with the SR, manifold, and cat/catback, the car is begging for headers. I just have the stock L98 manifolds at the moment.

I pulled 228 HP and 286 TQ.



Things I wonder about.

• Fuel pressure too low? (I seem to recall TPIS saying with the stock pressure and descreened MAF, that it leans out at 4200 RPM. That coincides with my dyno chart)
• My alternator is on the way out. I'm getting 13.5 volts at startup and then it will dip down into the 12's and sometimes 11's while driving.
• I bought a new battery a few weeks ago (after the dyno pull). My 690 CCA was only putting out 440 CCA.

The dyno chart was a lot flatter than I was expecting. But it sounded pretty good on the dyno.
http://smg.photobucket.com/albums/v2...t=MOV00626.flv

Does it matter where the spark plug probe gets installed? The AIR tubes on the manifolds were hot, so the clip got attached closer to where the distributor is.

sweet thread...some mods ive been thinking of are mentioned above. will keep an eye out.

BTW why did you not go w/ a 3" exhaust and chose a smaller that stock aftermarket one????

Hey Navy! I went with the Dynomax system for 2 reasons. First: at the time I ordered the system I did not realise that the stock system was 2.75 inches. But the MAIN reason was I did not want a bunch of noise in the cabin. I wanted to be able to hear the radio and talk to the passenger without yelling but still get a gain in power. The Dynomax did both for me the sound is low key ( just a bit louder then factory)but the HP went up 13 and the TQ jumped by 24 Foot-pounds. Robin

any new dyno runs

ya what ever happened with those high priced plugs?

Hey sorry for the long delay...I just (last week) had the new plugs installed I'll get the last dyno pull some time in Oct. As far as feeling any difference with idle or smoother cruising with the new plugs...nothing. I must say that my 1978 Trans Am with a close to stock Pontiac 400 ci did see a REAL improvement in idle and cruising with the new spark plugs. Robin

this thread was a fantastic read! thanx to cmk-2 for the time and effort he put into keeping us all informed to these results. btw, lt-5 motors are awesome! id also like to see a pic of this thirdgen. must be a nice one.

Thanks for taking the time to document your results on here.

BTW the dynomax system will get louder over time. When i first got it i thought it was too quiet. but after a year or so it sounds great now. Very nice deep rumble at idlebut when you get on it, it really opens up

That's good to read. It is almost too quiet right now. Robin

A friend of mine had a '92 Z28 with the following...

Stock motor
K&Ns
Headers w/ 3" exhaust no cat
Thermo Master chip
cut out airbox
MAT sensor mod
TB coolant line mod
Plenum "humps" ground down

It made 247HP and 345TQ

His car also had alot of the Corvette factory "hand-me-downs" identified by TB cover with no wording on it & the rough cast runners, so there may have been other unknown goodies on it.

I saved myself a lot of time and $$$ by purchasing one of the 'G-Tech' devices. They are extremely accurate and I measured & charted after each improvement, plus it gave me ongoing 1/4 mile info. If I had to do it over again, I would have done a dyno run first as the G-Tech's are measuring hp/tq as it's applied to the real world pavement, thus the initial numbers register lower than sitting on a Dyno.
Nitro-Nicky

OK everyone stay tuned Monday 11/3/08 I'm headed to the Dyno! This will be the last run the only difference will be the new plugs. We will be removing the A.I.R. pump belt after the first of three runs to see what if any difference the pump makes. This is an 1987 so the pump has a belt all it's own and will not need a delete pulley. This is weather dependent but the forecast is clear and cool (my kind of weather). Any guesses on the HP and TQ gain if any with the plugs and A.I.R. delete?

possibly a slight difference from the plugs if the old plugs were bad.. I'd make an estimate of nothing from the air pump..

I'm going to have to get back to the dyno one of these days. I just replaced the stock injectors with the Bosch III's from FIC. The car is a rocket now.

Old injectors were
9.7 ohms
11.2 ohms
14.1 ohms
14.5 ohms
16.5 ohms
16.5 ohms
16.6 ohms

They're supposed to be within half an ohm of each other and in the 16-17 range. 12 ohms is the dead zone. My measurements were done cold. (The ohms drop even farther when the engine is hot. So in reality the injectors were worse than what I measured them at)

Also replaced the alternator with a Powermaster 140 amp model a few months back. Volt readings are 1 volt higher using the same conditions mentioned in my above post.