atb

Doable?

Assuming you are using a different intake and mill the pistons to make room for the extra pair of valves.

I feel like I'm missing something major here.

LightStriker

And what would be the point?
Aren't 32v on a 5L already? Why downgrade?

BC

Are you thinking about the liter scales for the new race classes?

hacker-pschorr

Maybe his block is shot and a used 4.5 or 4.7 is a hell of a lot cheaper then a 5.0.

atb

I was asked by Ken Osage about the possiblity of a boosted 4.5L with 32v S heads.
And Sterling and Brendan, you guys - of all people, myself included - we've got no business asking why any 928 owner want's to build a particular configuration of a 928 motor....
I can't think of a reason why the 32v S heads wouldn't physically wouldn't bolt up, but just wasn't sure I wasn't missing something obvious.

Alia, the owner has parts to spare for this combo, no 5L bottom end though.

atb

That's it Hacker, plenty of the 16v bottom ends floating around his garage.

He and local racer John Davis got stuck in the GT1 class in Portland this past weekend. An outing like that on the track with an otherwise pretty much stock 4.5L changes a man... he's ready to get serious in the HP dept.

hacker-pschorr

16V heads fit just fine on the 5.0 block....so as long as the pistons do not smack the valves you should be fine.

Assuming the resulting compression ratio is where you want it.

BC

Hey, I'm here with the guy whoever it is saying "cool" - trust me. My point was that I read the PCA racing rules for GT1 and GT2 and GT3 and GT4 and the 32V would be interesting on the 4.5L if you could make it like a 9000rpm motor.

That said, doing a 2V is easier in some ways, as its easier to make it a solid tapet motor, and then stick a huge cam in it that can be made by anybody because there is no cogs in the middle. And the spring seats can be cut out so you can use chevy or ford springs and big domestic valves.

Anyway - Cool.

hacker-pschorr

Did you have to go and tell everyone about the engine Todd is building for me??

Lizard928

32V S heads on a 4.7L bottom end would result in a very lowe CR I would imagine just due to the displacement in the heads.

hacker-pschorr

The 85/86 and S4/GT have different size combustion chambers.

I poked around and found my old thread on this:

https://rennlist.com/forums/928-forum/175136-16v-heads-valve-and-combustion-chamber-size.html

Some confusion in there, but it looks like somwhere in the 50's for combustion chamber size with the 16V heads.

Kibort just cc'd the heads on his S4, they came out to 37cc. So you would have higher than stock S4 compression with this setup.

largecar379

my initial thought is that you can not use the Euro pistons (M28/09/10 10:1 high dome), due to the dome poking up above the deck. The dome will not match up to the 32V chamber. A low compression US piston may be necessary.

Pistons from:

M28/13,14,19,20 will work (USA, Canada, Japan CR 9:1)

M28/11,12 possibly (can't tell if how high the dome is from pic in FWM)

M28/21,22 will work (FWM shows 2 CR's, 10.4:1 and 9.3:1)

you can check with the FWM to see what would work best for your application. compression ratios might still be pretty good, due to the smaller chamber in the 32V head vs the 16V head.

then you would also need to cut 4 valve reliefs in the pistons tops.

Maybe this will help-----


--Russ

Lizard928

I didn't realise that the 16V heads were so deep, but the 23V S heads have much more combustion chamber than the S4 heads.

mark kibort

euro heads flow probably as good as the 4 valve S4 heads and have cams that are very close to the Gt cams. no real reason to go 4 valve, especially since the inake is pretty restrictive. the easiest thing to do is just bore out the 4.7 to 5 liter and just buy 85US pistons. (scot did this) better yet, save the machining cost, just buy a 5.0 85 bottomend and bolt it to any 2 valve set up and upgrade to euro when you can

mk

atb

Yeah, but I know you were THINKING it.