Those are totally different than an L98. Headers for those cars are mostly full length and the heads on those cars are way better than ours

 

Yeah,but its not so much the intakes on those cars, its the heads,cam. What good is a bigger intake (a mouth) without the stomach(guts) to back it up

 

You can only flow so much air in and then the heads and cam become the restriction. You see?Otherwise u have a mismatch of parts and the early guys that tried modifying TPI always went slower. We now know better nowadays.

 

This thread is about Bolt-Ons. Read the thread title. Not about heads/cam gains.

A full exhaust is the single greatest set of upgrades you can do to a TPI car. LT1 and LS1 cars make more power stock, so the percentage they gain from these mods is greater as well.

On average cars gain the most power from a full exhaust over other mods.

And an L98 will still gain more power from a full exhaust than from the intake side.

 

Ah I see. Sounds like I may get more gains from upgrading the intake when I do a head swap.

 

Best to start from the back. Do your exhaust first. You'll gain more power.

Runners + Base + time spent porting plenum vs a full exhaust. Full exhaust is cheaper too.

Good runners are expensive, almost the same cost as a base.

 

I've got 1 5/8'' ceramic hooker headers, 3''inch high flow cat, and 3'' flowmaster cat-back exhaust. The only intake mods I have done is open up the intake box, some k&n filters and a 52 mm throttle body. Everything else on the engine is stock.

I was wondering if it was worth it to upgrade the intake runners and base now or wait until later. I may do a head and cam swap at some point but not now. I am satisfied with the way the car performs now after the exhaust work.

 

why dont u now get an adjustable fuel pressure regulator?

 

Yes he is! If you look at my youtube page, All those cars on the Dyno has Dyno Don Headers except for my car. It has SLP's.

Well I tell y'all this, If somebody on this board will try the exact same setup as ItsMikey, lets us know how it turned out. The proof is in the pudding. The problem is that no one has ever tried this combo. That's why their are doubts. Everyone has tried the other ways and going with that.

I was at Dyno Don's shop 2 weeks ago and we put one of my SLP header next to his header and we notice that his header is about 2 inches longer that mine. Does that make a difference? Don't know.

Look at my SLP headers in the video and tell me what you think?
http://www.youtube.com/watch?v=JDX6r...1&feature=plcp

 

you lean it out most of the time u mod your car, if you richen it back up sometimes u get even more power cause u are correcting the air/fuel mix

 

Completely unnessesary. Thats the hammer method of adjusting your AF ratios. Best to do it in the chip.

A higher pressure DOES make for a better spray pattern though in most situations. But for a stock car it won't help much unless you alter the Injector Constant in the chip to match the new flow rate.

L98 injectors have a flow rate of 22lb/hr @ 43psi. If you bump the pressure up to 48psi then the effective flow rate becomes 24.5lb/hr. So you'd have to alter the chip so the constant read 24.5lb/hr to maintain the current AF ratios. I had 24lb/hr injectors on my old build once before the chip was altered to match. Fuel economy was terrible to say the least. I drove it about 100 miles to a guy who could burn a chip for me and do some datalogging and on the way up there I got 12mpg. On the way back I got 20mpg. I never got a real tune on it though and it was never happy with the mostly stock tune. Had some bad surging issues at idle.

 

I've seem that video before. One of then had 2.77 gears and the other one had 3.27 gears. I think the one that made 207whp had 3.27 gears. Now with that in mind if that car made 207whp bone stock and some of you might say a full exhaust will be about 25hp gain, well add 207 + 25 = 232whp. Now how much more will a tune be? After that then add the possible hp of a gutted airbox with K&N filters. What will you get? Whoop there it is! Oh yea, This 88 L98 was rated at 230fwhp. 90-92 rated at 245fwhp and a 89 240fwhp.

 

I see what you are saying, i am not talking stock, i am talking bolt-on car where the o2 signal is now reading leaner due to mods. Tuning is better of course,but an AFPR can be a band-aid. IIRC, raising the fuel pressure to 50 psi is like having 24lb injectors. Check out an article in chevyhighperformance magazine,where they added a set of dynomax headers and exhaust on a tpi Firebird they named "Blue thunder". Then they bumped up the fuel pressure and made more hp and torque. Yes, i do agree that fuel should be taken care of in the chip though. I just burned a custom SAUJP and mine runs much smoother and better performance all around.

 

Incorrect. There is an actual formula for determining actual flow rate vs pressure.

Divide base flow rate @ FP rating, then multiply it by the new fuel pressure.

(INJ Flow / base pressure ) * new pressure = new flow rate.

Ford injectors, at least the SVO injectors are all rated at 38psi. So a 24#/hr SVO injector on a stock thirdgen will flow 27.1#/hr @ 43psi.

Stock 22lb/hr L98 injectors at 50psi flow 25.5#/hr.

 

If u had 24lb injectors in your 350 TPI the correct injector constant setting is 24.02 lb at 43.5 psi of fuel pressure ,even Ford 24lb SVO injectors!

 

Injectors are rated at #/hr @ ?psi. You need to know the fuel pressure the injector was flowed at before you can set the Injector constant in the chip. Otherwise any tune changes you make will be wrong.

TPI/LT1 injectors are 43psi.
LS1 injectors are 58psi
SVO Ford injectors are 38psi.

 

Nope I just tested that theory! I have Ford 24's in mine. I have found them to be truly rated at 24LBS! I thought the same as u before. So i bumped up the inj constant and tried 25.81 as my new constant and burned the chip. It was so lean i lost hp and the car pinged. Setting it to 24.02 at the same stock 43.5 psi fuel pressure and it ran like it should!

 

No one can't dispute my last post. Wow!

 

While I guess its possible to add 25whp with full exhaust, I'm not sure I've seen that. I'd say 15-20whp seems most likely with good headers/catback. These cars just dont pick up as much as say an LS1 car will. Tune will likely get 5-15hp as well, depending. Maybe not as much peak but more in the midrange with some timing adjustments. I never got a chance to dyno my car and tune it properly. I just know I dyno'd 254whp/315wtq running lean as can be and still picked up alot of performance over the stock TPI intake.

But like many said, most L98 typically dyno 200-220whp stock, as it depends on the dyno as all vary to some degree. I think the 91-92's should have advantage as they supposively got the flat top pistons instead of dished. This should have more compression and make more power, 5-10hp more.

My car with stock TPI with headers/catback put down 204whp with the EST wire disconnected. I adjusted timing and forgot to put it back together!!! I ran 14.0 at 94mph like that when I normally was doing high 13's at 97 so 204whp was about 94mph traps, I'd say 97 was 230whp. Stealth ram bolted on, with no tuning I made 246whp, ran 99-100mph consistantly in abit warmer air so power was definately there. I'd say intake mods are worth just as much as exhaust mods. 15-20whp is possible with tune. Even tho the heads arent great and the cam is tiny, these cars still pick up good power with intake mods.

 

I've got a question about the dual cat exhaust. I've got headers and cat back. I've got an '88 so I only have the single cat. If I upgraded to dual cats how much of a gain in power would I see? Would it be worth the hassle?

 

Well a dual cat car 90-92 is rated at 245hp. A single cat car same years are rated 230hp. A dual cat car also was restricted with two 2 1/4in pipes and restricted Y-Pipe. We change that to 2 1/2in pipes and a Flowmaster Y-Pipe for a smoother merging flow.

 

Thanks for the info on the exhaust. I still think I'm going to work on the intake some more. I may come back to the exhaust later and put on the dual cats

 

Dual cat cars are not really restricted, that N10 dual cat option was worth 13% more hp. It is equal to a single 3" ypipe

 

Why dont you get better gears first

 

I don't mind the freeway gears for now. This is my primary car and I have to travel 120 miles round trip to work and back. The 2.77 keeps my rpms around 1900-2000 on the freeway at 70mph.

 

I said that cause for a better intake u may want better gears first. Cause u will be moving your powerband up higher and you will need to get up into the rpms quicker now, where that power is going to now be

 

do exhaust first

 

Yeah I understand what you are saying. At some point in the future I will upgrade to 3.27 gears.

 

I guess no one can really dispute the possible HP.