cornracer

I have a Fiero that I'm looking at putting a gen III/IV LS engine in. I'd probably go with the 4T65E-HD which can't handle a ton of torque and neither can the CV shafts.

Since the drive-train can't handle a ton of torque, I'd like to maximize high RPM power rather than lower RPM lower. I don't think I could get low RPM power to hook up in a Fiero anyway.

I'd like to use an LS3 block, pistons and heads a LR4 crankshaft and connecting rods. That would result in a 4.065" bore and a 3.268" stroke with total displacement of 339 CID or 5.6L.

Is the deck height on a LR4 the same as an LS3? If not, the LR4 rods might be too short. Is the piston pin diameter on an LS3 piston the same as an LR4 piston pin? If not, the LR4 rods won't assemble to LS3 pistons.

I calculated the compression ratio (assuming the deck height matches) at 9.7:1. I'd like to run E85 and get the compression ratio really high and install a high lift / low overlap cam. What's the best way to increase compression ratio with LS3 pistons and heads, aftermarket pistons, shaved heads or aftermarket heads?

Assuming this is possible, I'm guessing this set-up would make about 410-420 hp and about 355-365 ft*lb of torque at the crank.

78novacaine

iTrader: (2)

If that is all for your power goals, you can probably get that with just a 5.3 and a cam, or even a 4.8 with cam and heads.

tb30570

LLT/LFX/LCS 3.6L weighs 35 less than a LS4 or LS3 and makes 300 hp 270 ftlb.

cornracer

I want to run this car in autocross, so I don't want very much valve overlap. Lots of lift should be fine though. Exhaust flow is going to be limited, long tube headers and cross-tubes aren't going to fit.

Maybe my 410-420 hp estimate is low for the LS3/LR4 hybrid, but I'm thinking this set-up will make substantially more power than the LS4 at a higher RPM. I'm not interested in the LR4 because of the iron block.

cornracer

The 3.6 is lighter, but the weight is in the wrong spot, on the top. That doesn't help the CG much. There have been a lot more LS swaps too, so more support out there.

rotor vs. piston

iTrader: (3)

Do you know anyone making a stand alone system for these engines? Last I checked I found one person and it was insane $$$.

psiconversion

iTrader: (5)

Standalone harness? We make them specifically for the GTMs which will be similar to what you are doing.

Jon
PSI

tb30570

If you are looking for a lower CG, the bowtie V6 (4.3L block) or aftermarket Buick V6 (3.8L block) might be a good options. Aluminum blocks, OHV and not too much torque for your transmission.

http://www.s-series.org/htm/tech/GMP...ts/136-139.pdf
http://www.taperformance.com/proddet...?prod=TA_V3800

Another option is the L26 4.9L. This engine probably doesn't have as many aftermarket performance parts though.

i r teh noobz

iTrader: (4)

The 4.9 Northstar? It was popular with the Fiero boys for a while. I recall seeing some with turbos a few years back.

Verz

iTrader: (21)

One issue youre going to have is the bellhousing bolt patterns are diff on the 4t65e and the ls3 block. Youll need an adaptor plate set up and with that you might as well find an alum 5.3 block and swap the internals from a ls4 to attain your weight loss goals. IMO though that work isnt worth the 85lbs or so that youll save especially since that weights over the rear wheels anyway.

cornracer

I think the Northstar is heavier than an LS engine. Not much for aftermarket anyway.

cornracer

how much do these engines weigh?

cornracer

weights are about the same between the LS3 and LS4. I'm more concerned about ripping the transaxle apart with too much torque.

LS3 V8 - 415 lbs
LS4 V8 - 419 lbs
LS7 V8 - 454 lbs

i r teh noobz

iTrader: (4)

Have you considered an Ecotec? I'm not sure how it works out with your goals, but it seems to be lighter than an LSx, even in supercharged trim, and I doubt they make enough torque to break anything. It might be a bit easier to fit in the car, too.

http://www.ecotecforum.com/forums/sh...y-Ecotec-Fiero

cornracer

I thought about it.

The supercharged LSJ has a pretty linear power curve which is good for autocross. The problem is the supercharger, inner-cooler, heat-exchanger, water pump and coolant add about 110 lb to the Ecotec. A higher powered aluminum block V6 probably weighs about the same.
I don't know as much about the weight on the LNF turbo version with it's air-to-air inner-cooler, but I'd guess it's less than the LSJ. The LNF's power curve isn't very linear, which is bad for autocross (or at least I don't like it).

oange ss

iTrader: (50)

FWIW, friend of mine put a supercharged Bonneville SSEI 3.8 into an 88 Fiero GT (?). It lloked like is was made for it.

tb30570