L98 Engine Mods - What works?
 

I am buying an early C4 Vette (86/87) soon, and I am planning to do something about the pretty paltry 230/240hp factory engine output.

I am very familiar with pushrod V8s, but not the L98 specifically, so I am wondering what people would usually do to extract a bit more power. I am not after anything crazy, it will be a street car, not a race car, around 350hp would be nice, any more is a bonus.

I am guessing that the usual stuff still works:

*Increase compression to around 10:1
*Head work/aftermarket heads (the Trickflow 195cc alloy heads look ok)
*Cam change - mid 220s duration, .500 or so lift, 112LSA
*Extractors and full exhaust
*Roller rockers
*Gear ratio change (3.45 ratio or similar)

Anything else?

350Hp , probably not with TPI. Aftermarket intake needed
Higher stall if auto before gears

Courtesy of Mr Vader
http://temp.corvetteforum.net/c4/vad...dstrategy.html

http://temp.corvetteforum.net/c4/vader86/minormods.html

So the stock intake won't cope with 350hp? That sucks....

What sort of power could the TPI support? Does anyone have any flow figures for the TPI intake?

What intake would you recommend?

A higher stall will be installed to match the chosen cam.

I just did a bit of a search, and Edelbrock actually does high flow runners for the TPI - would this be worth using?

I think to be in the 350 hp range, you will need a superram or miniram. Possibly a supercharger from blowerworks, their stage I kit is rated at 350 hp with an all stock motor. If you did a few mods like bigger runners and ported the base and plenum, heads,you could be in the 400hp ballpark.

Miniram: http://tpis.com/index.php?module=cat...niRam+Manifold

The Mini Ram, heads, and cam, is your most direct easy way to 350HP. It will take a good cam and heads to do it.

I'm using the Edelbrock Hi Flow intake and runners. Not sure of performance differences between them and the stock ones though.

you have to understand the early C4 corvette. These cars are all about torque. not horsepower. any maximizing of torque will drag along some horsepower as well. Try the torque route, and you will have a serious traction problem.
When they were designed, Chevrolet had decided to eliminate the 350 altogether and go with the 305, Which is the reason the TPI was designed for the 305, not the 350, and the limited RPM levels of the TPI engines. Originally, the problem was mileage.
The Government mileage standards deadline was getting close, and Chevrolet was attempting to comply by using the 305.
Understand as well that Chevrolet was facing this mileage constraint, and was running out of time. Since GM has a financial stake in Bosch, Chevrolet crated up a few 305 engines and all of their experimental manifolding and electronics and shipped them off to Germany for refining.
From what I have read, the 350 wasn't sent to Germany, just the 305 and a small bore experimental Monza engine known as the "littlest mouse" at 273 cubic inches.
Some engineers decided to try the TPI on a 350 since the engines are physically identical in dimension, and the 350 became the high torque mileage champ in 1985 through 1990 until they coud design the LT-1 intake and a supporting valvetrain to achieve mileage figures that would comply with the federal standards. In doing so, they came up with a manifold that was not so restrictive at upper RPM levels and sacrificed some torque down low, but made up for it with about 70 more HP.
If I could smoke the tires for a city block with 500 ft. Lbs of torque with 50 HP, I would do it, but it would probably not be able to go faster than 35 MPH.

The L98 is such a cool looking engine! Too bad you have to go away from runners to get the HP numbers up with even the base C5. I've been toying with uping my C4 HP as well. But, need to resolve where I'm going with the 86 4+3 tranny first.

Stroke it 383

ck out vader's site

http://temp.corvetteforum.net/c4/vad...dstrategy.html

Edelbrock claims that the high-flow runners and base plate are good up to 5500rpm and gain 18-20hp on their own, not sure how much power overall that would support though.

350hp is not alot of power, but even 300hp or so with max torque, converter and gears will make the car a whole lot more potent.

Stroking to 383 isn't a bad idea if I am going to rebuild the engine anyway. Does the block need to be clearanced for the longer stroke?

I think the TPI is a neat looking intake. Did my best to keep it and run 12s. Finally gave up and went with a Miniram. Does not look as cool but the ease of R&R makes it worth it.:cheers:

Lot of clearancing needs to be done for a stroker....including the connecting rod bolts.
Even if the machine shop clearances the block (which I advise having them do it) you will need to clearance the rod bolts yourself (if you are doing the assembly), and probably the pan rail.
I really really suggest you buy a good book on building strokers and read it 3 times prior to embarking on it.

Why must they make everything so difficult?? 5.7L is enough for what I need anyway, I don't want to spend a fortune on this engine.

OK, so if I use the following parts:

*Stock crank and rods
*Aftermarket pistons - SRP, Keith Black something like that - 10:1 comp
*TrickFlow 195cc alloy heads
*Edelbrock high-flow TPI runners and base plate
*Comp Cams XR270HR hyd roller cam - 224/230 .502/.510" lift, 110LSA
*2200rpm stall
*3.45 diff ratio (or something around that)
*Roller Rockers
*1.75" Tri-Y extractors with twin 2.5" exhaust

Surely that should make close to 350hp while maintaining a whole heap of low-mid range torque. If not, I might as well start looking at an LS3 conversion....

All I want is a nice street car with some extra punch. I have had an LS1 with over 500hp before, and have driven Ferrari's and Lamborghini's so I am used to fast cars. If I can make 300hp and 400ft/lbs then that sounds good too. I don't car if it runs 13s or 11s because it won't be out at the track too often. And I certainly don't want to have to explain myself to a Skyline or WRX driver because I lost at the lights.....erm.... track.... yes, track... :)

Trying to figure out how a 2200 rpm stall torque converter is gonna get you horsepower...along with a change in axle ratios.
Summit stickers have the same effect, and they are free.

That may get you 350 at the the crank, not the wheels. It will give you a car that is fun to drive. I really would not get too hung up on numbers. Dynos are a good tuning tool but the numbers do not mean a lot to me. A lot of variables. Ten dynos will get you ten different results. Drive the car for a while, you may be suprised how much fun 240 hp is when it comes with a ton of torque.:cheers::cheers:

I wasn't referring to the stall and gears giving me power, but they do give the perception of increased power with better seat-of-the-pants acceleration. I listed the whole combination, not just the stuff which will make power because getting the whole combination right is what is going to make the car good or crap to drive.

The increase in compression, intake mods, cam change, roller rockers and exhaust should definitely add power. I was talking about 350hp at the crank, not the wheels. Closer to 400 would be better, but by the sound of it, that will mean going a bit more aggressive than I would like for a street car - bigger cam, new intake etc which in turn means higher stall, stiffer gears etc.

I have never been one for getting hung up on dyno figures, and it will probably never see a dyno once it has been tuned.

I may be a newbie to Corvettes, but I am not a newbie to V8s.

Thanks for the info guys, gives me a bit to think about.

If you want a drag racer, buy a drag racer.
The vettes were never really designed for that.
If you want to go really fast and turn, a vette is a good choice.

:iagree: My stock `87 will outhandle my stock `00 Mustang GT `vert all day long, although the `stang feels faster in a straight line. Both cars are a lot of fun when driving them as they were intended to be driven.