i have a bone stock 90 vette with auto trans. i would like to do some bolt on mods. to gain 50-100 hp rockers ignition headers and duel exhaust. what have you guys had the best luck with .

 

Intake manifold = miniram, superram,. holley stealthram.
Headers/ full open exhaust
1.6 rr's
ud pulleys
heads
cam
tune

This could get you 100-125 with the right choice of parts.

Or just a 100 shot of nos.

 

I've had the best luck with 1) this forum, 2) figuring out it takes more than a couple of bolt-ons to make big power, and 3) learning to use the search function.

Even if you just troll backwards thru threads, you should find this question is asked a LOT! Lets just say around 100 times per year!!!

Oh yeah...one other thing. None of us have the same opinion!

 

You'll be hard pressed to get 100hp at the wheels from bolt-ons. You need to tell us exactly what you want, and how much money you have to spend here. Also how much of the work you can do yourself.

Read through my website to get some ideas of a plan, because you're not going anywhere til you plan it all out. Click my name.

 

What works to get the first 50 HP.

LT headers
dual outlet mufflers
delete pre cats
port the intake and runners
cut the filter lid (new filter)
remove frisbee
aluminum UD pulley set (3 piece)
1.6 full RR's and springs
performance tune(when all above is done)

 

thanks badduck. i wasnt trying to ask the same ? twice i just thought i made a mistake with my first post. sorry . at any rate iam pretty sure i can do all the work my self. ive built performance engines and trans. but i realy only know what ive read on here about the vette and the fuel injected l-98 engines. i dont realy want to go to over board with mods becouse i like the idea of driveabillity with this car and the milage you can acheive with this car. that and if i was going to go hot with this project i would like it to have had a manual trans . got her cheep so i will live with what i got ya know. besides i have a completly restored 70 big block nova with 4spees posi to scare me when i need to. well if i ever finnish the paint.

 

what are lt headers? which headers are the best and wich ones are the most cost effective . i want to conentrate on the exhaust first. as it has some issues. iam thinkin of fabin me up some duel exhaust out of some 2-1/4 mandel tube. can i elimminate the cats?

 

lt headers = long tube headers. Again, tons of threads on this. Best choice can depend on budget. Hedman Elites are cheapest and 1 5/8" tubes. EM Muscle/TPIS next @ 1.75" tubing, or Stainless Works for the stainless stuff.

You can dump the cats (and should for better flow). Getting some hi-flow bullets or a high-flow main cat (or both if inspected) for replacement is a good idea since this won't be a track car. Though some might vote for 2.25" exhaust, I like 2.5" better for stock. Or... 2.5" up front dropping to 2.25" by the rear wheels.

With bullet or main cats, you'd only need a light-duty mufflers to make it aggressive, yet not loud. Maybe glass-packs or cylindrical "can" mufflers. (Cats provide part of the muffling -- in addition to their "cleaning" ability.)

 

If you don't know how to make power with the L-98 stuff, don't rely on the internet. Use it as a reference point only. A tool that is helpful.
Building hot rods has evolved into constant regurgitation of flow numbers, dyno numbers and theory. To many pretenders, and it can be difficult to see who are the "do-er's" and who are the "talkers".

Simplest way is to find the ones that have done what you are wishing to do, and do what they did.
Most of these "do-er's can be found at you local dragstrip, autocross, or roadrace facility.

 

Building strong Horsepower with a long tube runner engine like the L-98 is difficult. People knock the tuned port design, but it is actually pretty good. Small, and better suited for a 305 engine, but pretty good in spite of it. Their BSFC numbers are quite good, showing how efficient they really are. Many spend time porting the base, porting the plenum, and porting or replacing the runner tubes. The runner length prevents huge gain. My advice, based on my experiences, is to invest nothing in the long tube runner set up, and replace the intake with one better suited to your car. Gear ration, torque converter stall speed etc should be factored in so you can pick the right one.

As far as intakes available that will bolt under a stock hood, the TPIS miniram is regarded as a great choice by many for big horsepower gains. It will make the car behave as if it is carburated as far as mid to higher rpm power. Expensive, and requires a good tuner to make it work right.

Decisions, decisions.....

 

LT= Long Tube headers. There are several makers but Hedman Elites seem to be the top overall choice for the L98. The 1 5/8" size is best unless you build a high output motor. Summit is a good source. When you install the LT's dump the precats. I kept my main cat but installed a Magnaflow (Carsound) hi flow unit. You can delete the main cat but your exhaust note may be annoying. Also install some dual outlet mufflers. I used Magnaflow but there are many out there. If you can fab and bend pipes fine, but I would stay with 2 1/4" toward the back.
Do the exhaust first then move on to the aluminum UD pulleys. I used the March Power & Amp set. Remove the Frisbee on the PS pump.
That will help to reduce rotating mass and parasitic loss.

Next install 1.6 full rocker arms and springs. You can use the self aligning type like you have now. I installed Scorpion narrow aluminum RR's to keep weight down. Your cam is not very big so RR's will help.

Once you have completed this you may want to get a performance tune. You can do that mail order for @ $150 - $200. By this time you will have added 50+ CHP.

 

I suspect some readers would find this post conflicting. On one hand, the TPI tubes are described as "efficient". On the other, not investing in the long tube runner setup followed. Both are valid statements which is indicitive of why opinions vary so much on the subject.

TPI tubes are efficient because they reach their maximum (volumetric) efficiency earlier in rpms than all other intakes. This happens because the tubes build pressure from reversion pulses.

Because a cam is a (relatively) slow-to-open/slow-to-close device, valve can't pop open/closed. When a piston sucks in air, you want the valve open. When it stops (at the bottom of the stroke), you want it to stop -- but that can't happen instantaneously. Because it takes time for the valve to "lower down off a cam lobe ramp", air gets pushed back into the intake as the piston begins it's trip back up the cylinder. Compared to the alternative of shutting the valve earlier which would lose some intake at the end of the intake stroke, this "intake reversion" is not such a bad thing.

Air forced backward thru an intake "compresses" against the air rushing in. The result is a mild form of "induction" where the intake charge increases in density. The variables on how this happens depend on lots to things like: intake tube size, tube length, engine rpm, etc.... For a TPI motor, it's the length of the tubes that build pressure faster (lower) in rpms. Those long tube create maximum efficiency at lower/mid rpms. (For a DD, this can be good and save fuel.) But, the tube length/size does something else. It's causes restriction at higher rpms. While it helps efficiency at lower rpms, it hurts power production at higher rpms.

People often talk about porting a stock intake to make improvement but the end result is minimal (and often impercievable). To effect real changes on intake performance, tubes need to be significantly enlarged or shortened. That's why high HP intakes are shorter and, usually, larger. While porting can flute tube openings, smooth flow, and increase the amount of air at the tube opening, that air still has to travel down a long, narrow opening. That means the motor's power characteristics will barely be altered.

For perspective, the superram which has tubes approximately half the length of a TPI, peak hp rpm is raised about 1000rpms. When you siamese or mega-port something like an SLP runner, the results are typically half that. It takes more than an inch/two to change rpm peak more than a couple hundred rpms. It also takes a good percentage increase in tubing diameter to accomplish the same. Because stock TPI runners can't be significantly siamesed or enlarged, peak hp RPM can't be significantly altered. Because the horsepower formula is a function of rpms, it's fairly easy to see why higher rpms (and shorter runners) are the best way to get more horsepower.

That's why Pete mentioned the miniram which is really the shortest-runner intake available as replacement for a TPI motor. The trade-off is a move upward in rpm peak (where reversion peaks it's efficiency). IOW, a short-runner intake motor isn't most "efficient" until higher rpms. But, it takes more fuel to run at higher rpms. Potential mpg can be somewhat lower for this reason. When you operate a motor close to peak efficiency, it does it's job the best and fuel comsumption (BSFC) is best. On the other hand, short-runner intakes don't really do that much worse (if any) on mpg. There are a lot of variables going into what a final build can accomplish. Most of the time, all the variables aren't explored because people just want power.

Since power depends on rpms, thats why you always see people saying the TPI stinks. It's also why you really need to consider removing it -- if great power is really what you're after -- even if you're only shooting for the lowest dollar improvement in the 50-100hp range.

 

experienced=no not with these L98s. But from all of my research I have done the most consistent proven bolt on mods and the best place to start is IMO and that of most of the articles I've read.

exhaust. ceramic LT headers with a free flow cat, or true duals, and an efficient catback.
An LT1 intake setup
K&N air filter and cut open the breather box or buy one of those expensive air breather setups
2400 stall converter if it's used mainly for the street or 2600 to 2800 stall for more aggressive cases
1.6 Roller rockers on the intakes and 1.5 on the exhuast
That will get you started for bolt ons. if that's not enough then into the engine you go with cams, rearends and such.

Speaking of rearends you may also go with 3.45 gears if you're not concerned with fuel mileage. But your top end will be effected.

If you have mucho experience as Petek has, or some of the others, you can do a lot to the L98. if you don't I recommend doing the bolt ons and accept peace with yourself and your car, because once you start all the other stuff you best know what's going on because you have limited yourself to what you can do hands on and will always have to have a professional diagnose and work on it.


the consitent thing I have reseached and everyone agrees is if you only do one thing to these L98's go with LT Headers and the exhaust.

There's tons of other stuff a person can bolt on but there is mucho controversy on whether it does anything or is worth the expense.

with these bolt ons I just mentioned, one of the article I read where they did these exact bolt ons, they also installed a 160 dgree therm.

JMO

Now I'm ready for the experts to tell me i'm wrong.

 

The problem with the L-98 long runner arrangement is greed.
Most want a few extra horsepower, get used to it, then want more. If you are one of the rare few that wants 50 extra ft lbs of torque and 50 extra hp, you can make them work pretty well.
Most of us greedy types that want more, and all the hard work, money and parts selection (previous purchases) may go out the window.
I am guilty of the above.

 

AGREED! Be careful! Once you start, it's very hard to stop.