Hello everyone.

Over the course of the next few years im going to be pulling the 350TPI out of my car to either redo it or replace it.

I was just wondering what everyone thinks is the most efficient (fuel wise) way to pull 325-350 horse? Swap out the intake on my TPI and do some top end work? Or I have been strongly looking at swaping in a GN 3.8 turbo. My dad's friend has one I could pick up. With both motors making that horse the 6 would knock down some better mileage correct? I dont think a 4cyl is really going to do it for me since the car is relatively heavy for that, or am I wrong? Im considering all motor platforms. It doesnt have to be domestic, preferably though, for ease of swapping.

I realize that the LSx platform offers that power level and decent mileage, but I cant really afford one of those just yet. It is a possibility though as I will be building the motor over the next 5 years while im at college. What about the Ltx platform? Id really prefer an SFI setup, is the LT sfi or bank-fire?

Ive been looking at all sorts of swaps, 3.8turbos, 3800 S II, LSx, LTx, Stealthram, but Id just like your input. Id prefer to have a turbo, because, hey, they are just cool!

Thanks for your time in advance.

 

I'd think sticking with the 350 TPI and doing some work to it, would be the easiest and cheapest way to go

 

well ,your not going to get good gas milage with 350hp.

the best you could hope for would be18city /27 hiway the average milage would probably about 22 .

if you wanted less hp,like 250,then you could gte some decent milage to a point.

the best milage with gasoline is about 35hiway, 25city. and thats with only 80hp



but a diesel engine could could get you up 35hiway 30city and have more then 350hp,and gm makes diesel engines that should fit[ the fbody WAS designed to fit ANY gm crate motor] ,and you could have a switch to dial up 200+ extra hp when you want to go fast ,and dial it down when you want milage.

but its not going to be cheap to do it right. even with used parts its going to be expensive.

but do whatever you can afford.

 

Both the LSx and LTx based engines are SFI not bank fired, and with the LSx platform, you can push over 400hp and still get close to 30mpg on the interstate. Friend of mine with a '98 Trans Am has close to 440 at the wheels and on the trip to Fbody 9 was getting 28 on the interstate driving down there, and that's with 4.30's in a 12 bolt rear.

My LT1 had the stock tune on it when I got it and probably was about 280 or so at the wheels and was getting 26-27 on the highway and around 22 around town, that's normal driving, not gouging it alot.

This is also with a 6-speed, you may drop 2-3mpg with an auto.

 

Im not necessarily looking for 'good mileage' just the best mileage I can get @ that HP range.

Why is it that the LSx is much more efficient then the LTx? More compression?

 

The LSx design has a totally different style of head, intake ports, exhaust ports....it's a totally different engine.

 

I'd say do stuff that frees up power, before stuff that 'adds' power...

Replace the whole exhaust system with a set of 1-5/8 (minimum) headers, and a 3" catback, clean up the intake and heads, get a cold air induction setup, maybe some computer tuning (?).

After that, I'd say then replace the cam, and possibly and ignition upgrade.

Just my 0.02

 

Hi Adam.

Currently I have 1 5/8 hedmans, hooker 3" catback, CAI, Tb bypass, airfoil, ported plen, intake and heads. I also have a blaster coil and all new rotor/cap/wires/plugs. Still stock bumprod though. I just dont like the TPI. It doesnt take boltons too well, and the intake is really limiting. Sure... its the best looking, but I think its time for me to move on to bigger, better LT1 things