blueprinting v8 engine (for Porsche 944 - goal: 400 rwhp but still maintain 35mpg)

[some_other_dave]

The later Vettes use a transaxle and a torque tube like the 944 does, I think. And they definitely bolt right up to the LS motor. Might be worth a look to see if that can reasonably be mounted? You know it's strong enough for at least a moderate LS motor, and it definitely has a tall top gear.

-soD

[drmiller100]

No worries - I didn't know what you were starting with, and where you were headed.

I did some quick research. I have NOT played with the 944 transaxles, but the 911 transaxles from that era you can swap the drive and driven gears for pretty easy overdrive.
It MIGHT be possible you swap the fifth gear sets into the fourth gear for 1:1 in fourth gear, then take the fourth gear pair, swap shafts, and have a pretty massive overdrive for fifth.

This DOES mean a pretty big jump from third gear to fourth gear. But My bet is for road racing you will only use first through third gear.

Another option is leave first through fourth alone, and turn fifth into a huge overdrive. On the 911 gear boxes, you usually can't change first gear which is fixed to the main shaft. Don't know if this is true of the trans you are using.

[2000mc]

any ls engine with an aluminum block, 5.7 might be the easiest to find. whichever engine, if you use one out of a car you're more likely to be able to use more existing parts if you wanted to, thinking oil pan and intake for clearance. then just build for low end / torque.

- before you build, price out what gm has, standard engine in the corvette now is an all aluminum 6.2 making 430hp

[mcrews]

I like that 944 body...alraedy has that flared look that the 924 SOOOO desperately needed.
I say (from a non-engine point of view) that is all in the tires.
I rised a 99 Mazda RX7 in showroom stock SCCA. I rode on the steel 15 rims with 70 series tires.
When OI raced I ran 50 series on the 14 alloy rims. Made a world of difference in the 0-40mph start.
On my current dd I run 245/50/18 instead of 245/45 on the stock rims. really helps keep the rpms down on the highway cruise

[drmiller100]

Originally Posted by 2000mc

any ls engine with an aluminum block, 5.7 might be the easiest to find. whichever engine, if you use one out of a car you're more likely to be able to use more existing parts if you wanted to, thinking oil pan and intake for clearance. then just build for low end / torque.

- before you build, price out what gm has, standard engine in the corvette now is an all aluminum 6.2 making 430hp

you can get there with the old 5.7, but once you play with a 5.3 or a 6.0, you will NEVER look back......

[2000mc]

Originally Posted by drmiller100

you can get there with the old 5.7, but once you play with a 5.3 or a 6.0, you will NEVER look back......

yes... referring to gen3 / LS engines, there were 5.7s in corvettes firebirds, camaros and gto's. i assumed the OP was refering to those 5.7s, not the old iron boat anchor

[drmiller100]

Originally Posted by 2000mc

yes... referring to gen3 / LS engines, there were 5.7s in corvettes firebirds, camaros and gto's. i assumed the OP was refering to those 5.7s, not the old iron boat anchor

So was I. Even the ls1 is pretty crude compared to the 5.3.

[bp944]

First of all, thanks for all the replies and please keep them coming. It is amazingly helpful especially in the aspect that most v8 forums have no regard for mpg.

A fellow on another forum brought up a point I hadn't thought about. There is VVT and AFM on generation 4 GM engines which also can be retrofitted to most LS engines. That gives me a lot better chance at reaching my goal. Has anyone tinkered with what can be done with VVT and AFM?

Drmiller100, a few clarifications.
-Why 5.3 and the 6.0 over the 5.7? They're aluminum blocks with the same design just difference size bores or am I wrong?

-Also, I will check into the 911 gearbox but I'm pretty sure it won't work. There's been a lot of discussion on the 944 ls conversion forum about this and nothings turned upso far.

-Could you pass the hot rod article on to me please? I would love to take a look at it. Also, are you sure a set of ls3 heads can work on a 5.3 block?

-I think I will be rebuilding the internals since I have some of the parts and it'll make it more efficient. I have lighten rods that will fit a ground down crankshaft. So lighten all the internals and up the compression. Also, honing the engine and putting in new pistons and rings will clean up some of the tolerance allowing for a more efficient cycle. I also simply want to build up an engine for the experience.

mcrews
-You are absolutely right. I love the 944's looks especially compared to the 924. I wouldn't mind to get the turbo front nose on it but that can wait until I get the new engine in.

One question still stands. What would get better mpg, a 400hp 5.3L engine or 5.7L?

[some_other_dave]

Originally Posted by drmiller100

I did some quick research. I have NOT played with the 944 transaxles, but the 911 transaxles from that era you can swap the drive and driven gears for pretty easy overdrive.

It was very possible to do with the 901 boxes, but those were only used from 1963 through 1971 in the 911, and through 1976 in the 914. The 1972-88 911s used the 915 gearbox, and I have not heard of people flipping the gears around on those.

On the 911 gear boxes, you usually can't change first gear which is fixed to the main shaft.

The five-speed 901-based gearboxes had second gear fixed to the main shaft. Unless you get a 904 main shaft, which is serious cubic dollars, even in Porsche terms. The 915 did not have any gears fixed to the main shaft.


None of the 911 transaxles will work easily in a 924/944/968 or in a 928, for that matter. And none of them will hold up to 400+ HP (with a healthy big-V8 torque curve at least!) under heavy use. The 901s tend to detonate when you put more than about 250 lb-ft through them; the 915s are better but still not great. The 930 gearbox could be an option to hold up to the power, but it needs work to flip it around for use behind the engine. Machining of the diff housing so you can flip the ring and pinion, for example. Or run it upside down.

It may be worth looking into the later 928 transaxles. They are set up to run off a torque tube, and they can hold up to a reasonably healthy V8 motor. I don't know what, if any, alternate gear sets are available. The early 928 boxes are not well regarded as far as shifting and durability, so I'd probably avoid those.

The 968 might also prove a reasonable donor for the transaxle, but again I don't know what alternate gears are available.

Some Google searching will turn up info about the existing gearsets in different years of 924/944/968 cars. In general, the later ones will be stronger and the turbocharged cars will have stronger ones. And I'd be worried about the strength if the thing is hooked up to a healthy V8.

-soD

[bp944]

The AOR transmission in the 944 turbo S has been holding up for a lot of guys running v8's. There's a few running 500hp to the wheels and haven't had any problems. They say not to drop the clutch and you'll be fine. There's a reinforcement plate for the AOR that some guys make that does help the cause. There was one car I found that detonated his gearbox but he took a bet to try and wheelie. I think I'm going to be fine as far as the transmission goes. I'm more concerned about the engine setup for now.

Doing some scratchwork, I think I should be running 2600rpm at 70mph if I run 235/17/50's. That seems to be better than most ls1 engines but I'm going to see if anyone's fit taller wheels in the rear.