skipgresham

I would like to create what the factory never did, a 3.0L 8 valve NA engine. I have the ingredients: a good 2.7L engine and an S2 crankshaft. The plan would include having the reciprocating items all balanced and lightened, perhaps with knife-edging and boat-tailing along the way. I figure the output should fall somewhere in the same range as the 2.5L 944S or better, but with superior low end torque. Questions:

What compression ratio will I end up with (I assume the S2 crank will pull the stroke range a little lower in the cylinder)?

Any possible clearance problems - and if not, will I have comfort room for a slight head shave to bump the compression?

Are the 2.7L con rods compatible with the 3.0L crank journals? I would want to use the 2.7L's rods...

Any other problems with this concept?

TIA Skip

nine-44

I definately could be wrong, but, I'm thinking you need the 3L rods as well. BTW, welcome to the forums, I see this is your second post. Sounds like a good idea, I'm wondering if the intake and exhaust ports are up to the task tho? I'd wait for some other replies before getting into the project. Good luck.

Bhj0887

Sounds like a good idea, I think there would be some clearance issues though, doesn't the 2.7L block have a longer stroke and longer rods. So i'm assuming that you'd actually have to use a thicker headgasket. And since you already have the ideas of building a performance engine, you might want to think of upgrading the valvetrain, and get a normal idling cam.

Zero10

You would probably have to get shorter rods.
I always thought the 2.7L and 3.0L shared a crank, but perhaps they share a bore instead?
I think the 8V head would have some flow issues at around 6000+rpm, I don't think it could support 3.0L of displacement.

Although if you had custom rods, you could get them just the right length to up your compression.

PorscheG96

I think it's a great idea! With a 3 liter crank you have 9mm more stroke so you will need 4.5mm shorter rods to keep the pistons at the same position at the top of their compression/intake strokes. 2.7 engines have the same 104mm block as the 944 S2 so the addition of an S2 crank will make a 3 liter motor, but with 8 valve head and pistons.

The 8 valve head will easily support 3 liters...besides, 6k RPM performance isn't a big deal on the street. Folks use the 2.7 head on 3 liter turbos all the time so it will have NO PROBLEM flowing 3 liters of NA displacement. It should make great torque and be a blast on the street!

Good luck with it!!

Danno

"With a 3 liter crank you have 9mm more stroke so you will need 4.5mm shorter rods to keep the pistons at the same position at the top of their compression/intake strokes."

Uhhh, due to the longer stroke, if you place the piston-tops back at the same location as before, you'd raise the compression up to 12.0:1 from the previous 10.9:1. Not sure if the non-optimal shape of the 2V combustion chambers would allow you to run that much compression.

Better off with using 11.0:1 compression which would entail getting rods that are actually 5.4mm shorter than what you have now.

Wrecksimple03

i dont know anything about doing it, but it sounds like a great idea, i'd like to know how it turns out

Fishey

Why? I would think a 3.0L engine would be fine.. Leave it 16valve.. I never heard of anyone wanting 8v vs 16v.. I mean the maintance isnt that hard for the 16v and you gain alot of benifits... Lighter and stronger block..

Sach951

I really like the idea.

skipgresham

>>I would think a 3.0L engine would be fine.. Leave it 16valve.. I never heard of anyone wanting 8v vs 16v<<

It's an 8 valve 2.7L engine, I happen to have a 3L crank FROM a 16V car...

Seems like some debate on the CR issue - will have to call some shops and see if anyone knows the final word on that...Thanks Skip

Tom Carson

or possibly 5.4 shorter as Danno says...whatever with a shorter stroke you will not have 3 litre displacement anymore

the 3.0L 104mm 4v pistons are a lot shorter than the stock 2.7L 104mm 2v pistons and have wrist pins relocated to allow use of the same rods and thus the same stroke to make 3.0 litres...true?

PorscheG96

Tom the rods have nothing to do with stroke...even if your rods were 5 feet long the stroke would be the same. The issue is that using 2.7 rods with a 3 liter crank would have the piston traveling too high in the bore, actually OVER the top of the bore and it will not work.

Danno, I did not get so far to calculate compression. My 4.5mm suggestion was not carved in stone, it was to present the idea that shorter rods will be needed and he cannot use the ones he has with a longer stroke.

Now that compression has been brought up I didn't know Porsche ever ran 11:1 with an 8 valve head. The 16 valve designs run 10.9>11 compression and I thought the 2.7 had the same compression as a late NA car [10.2:1?]. Definitely a good point about compression, though. If the 2.7 has 10.9:1 compression then definitely get as close to that as you can.

You'll have to do a little math to find out what length of rods are needed to place the piston correctly at the top of the stroke and give you the compression you want as well but it should be a great project.

Mike Buck

the 2.7L was 10.9:1 . . . I used to have one. Also, IIRC, the 2.7L uses the same lighter and stronger block from the S2.

Hasn't Anderson Motorworks built some montser 8v NA motors?

skipgresham

I do wonder if the 3L crank will result in the pistons protruding above the deck at TDC, if using the 2.7L rods/pistons. I also wonder about the contribution of the 16V vs. 8V head volumes to the displacement figures of the two stock engines.

I wish I had a reference book listing the part numbers for the S2 pistons and rods vs. the 2.7L's. I guess my hope has been that the psitons and rods were the same on the two engines. Unfortunately, the Parts and Technical Reference book appears to end before these cars were manufactured. And there are so few 2.7L cars out there, not a lot of folks are familiar with them.

Sach951

Well hey there's one way to find out... Act now think later!

Cheers,
Sach