ViribusUnits

What are the diffrenced between the 968 block and the S4 block?

My understanding is the 968 is based on the 944, which is nearly identical do the 32v 928. According to 928sg.com the 968 head cover even bolts to the 928 head, with the same gasket.

Jim bailey - 928 International

I have never seen a 968 block open to compare but you are correct that heads are the same casting and we do use a modified 968 104 mm headgasket . The water flow path is slightly different . They share similar design features but a different block casting for the 4 cylinder

T_MaX

VU, Sterling G. is as far as I know is the only one to incorporate the V-cam technology onto a 928 and is planning to come to the 2nd annual Third Coast of Texas 928 Sharkfest Extravaganza. Should you attend, you could see it first hand.

Here's a link to his site. 1990 Cognac 6.4 liter w/VarioCam 928S4 5spd

Sterling, if you read this, we're all pulling for you to make it!


Jim, good info. I 'm glade to here a positive note on the 104.5 bore

BC

The 968 head gasket Jim - Are you saying that the coolant is let through in different areas? Where? How? What is the benefit?

Thanks,

Gary Quayle

jorj7 -
Rennlist changed the policy and you can have your custom avatar after 50 posts. Ask me how I know.

martin D

Jim
Just to clarify, does that mean that a nicasiled bore can run an unplated/coated piston ?
e.g. a forged Chevy/Ford/Mopar modified/custom piston (correct size/crown/pin etc.) ?

John Veninger

Jim,

Send it over to the East Coast. I'll abuse it for you

Jim bailey - 928 International

John we are into "self abuse" ?? or something like that ...... the nicasil block SHOULD be able to use " Chevy " pistons which is why we elected to build one this way rather than our usual Mahle 968 piston . The Mahle pistons are increasingly difficult to source and more difficult to PAY for !! Regarding coolant flow the 968 head gasket no plus or minus just slightly different due to using the same 968 gasket on the right side and lofted ; note that the 928 headgaskets are different side to side . We have had no problems with boring / honing to 104.5 when we start with a 100 mm 5 liter block . The GTS cylinder heads do have additional water passages to better cool the exhaust ports so the head gaskets have 4 small additional holes per side these heads work with ANY block . GTS block has the windows to allow the movement of air from under the piston to flow above the oil level to help control windage . And while we are in there the lower cradle main bear cap for a GTS uses bolts to attach it to the block rather than studs and nuts . The GTS engine also has forged connecting rods which are lighter weight .

Fastest928

The 928 block is a work or art, but like all art, its bueauty is balanced by its imperfections!

These imperfections and knowing how to treat them is how some engines make more power and are far more reliable than engine susing the exact same components. Contrary to popular beleif, it is not magic dust.

It is in the details.

To make a long story short, almost any block is borable to a limit. It is all about stress. The larger the bore, the greater the stress, and the greater the deformation of the cylinder under cylinder pressures.

As Jim mentioned, splitting is really not a concern, however, dynamic trumpheting, that is deformation of the top of the cylinder due to thin walls and pressure, is a concern...particularly if you want to make power and make it reliable. Even thoughthe Reynolds material is low elongation, it does move with increasing stress.

Remember, our test arena is open road racing whre you are at full throttle for 3-5 minutes, 5 second breat, then back on it for 37 minutes! So reliability and power are necesasry for success.

Back to the block....not all blocks are created equal, some are more equal than others . The distribution of Si in the bores is carefully controlled by the cooling process during manufacture. This can present issues.

Casting shift....another issue to deal with. Porosity in the casting....another issue...

Some recommendations:

1

Fastest928

...continued

1 if supercharging..go for the thickest walls possible
2 if boring..go for the thickest walls possible
3 if nickasiling - Lucky has a block done, but is concerned with Sulpher...John twin turbo will be a good test case...watch the fuel you are using
4 Mahle and Kolbenschmidt have sleeves for 944 that can be used in 928
5 maintain the recommended piston to bore dims tomaximize power
6 before doing any of the ablve look very carefully at the block, note and understand the imperfections and their effect on what you are doing......

anyways, good luck,

Marc

BC

So can a GTS crank fit into an S4 block?

Jim bailey - 928 International

Yes

BC

Thanks Jim. I'll assume some clearencing though, from a villhuller thread (or similar name). Hmmm.

FlyingDog

Will a GTS crank fit in a 4.7 block?

BC

I don't think so.