2v forged internals in 4v

[ctdkid]

Hey guys,

Looking for some info. I have an option to pick up a 98 gt shortblock with an eagle 5.1 stroker kit, stock bore, 17cc dish pistons for a really good price. I have a 97 cobra that I am looking to install forged internals for a turbo build anyway. Would I be able to put the gt internals in my teksid?

 

[98fourvalve]

Yes, the only real difference is going to be the valve reliefs if they have some. If they do not then don't worry about it. If they do then I still wouldn't worry about it as long as the compression ratio is the same as most 4v cams don't have ptv clearance issues.

 

[deadernie]

The OP will also need a GT flywheel. IIRC.

 

[CJK440]

The OP will also need a GT flywheel. IIRC.

If it's a 6 bolt crank

Sent from my whiz bang pocket computer.

 

[ctdkid]

It has an 8 bolt crank. Would the valve reliefs make a difference with lower compression...pretty sure with the b heads and 17cc dish it comes to 8.5:1

 

[acth4347]

Isn't the need for valve relief determined by how aggressive the cams are? And on a 4v you don't really have a need for that kind of lift, right? Sorry if I'm missing something.

 

[SVT Rob]

Isn't the need for valve relief determined by how aggressive the cams are? And on a 4v you don't really have a need for that kind of lift, right? Sorry if I'm missing something.

Valve reliefs are mainly for total valve lift, this is correct. On a 4 valve engine, you don't have nearly as much lift as you do with a 2 valve engine, so it's a non-issue. But, having valve reliefs in the pistons could change the compression ratio. But it's usually negligible. You could probably get the same change by going to a thicker head gasket.

Rob

 

[na svt]

Valve reliefs are mainly for total valve lift, Rob

This is not true. As far as cams are concerned PTV clearance is determined by the intake lobe center, intake lobe duration, and intake lobe ramp rate. As a result, a stock lift cam may require valve reliefs while a .500" lift cam may not.

 

[SVT Rob]

This is not true. As far as cams are concerned PTV clearance is determined by the intake lobe center, intake lobe duration, and intake lobe ramp rate. As a result, a stock lift cam may require valve reliefs while a .500" lift cam may not.

And again. It's a non-issue with a 4-valve engine.

 

[na svt]

You would be looking at an 8.4:1 compression ratio with 17cc dish pistons and a stock size combustion chamber.

And again. It's a non-issue with a 4-valve engine.

If using stock cams there will be no issues, but if adding duration and a low ILC the PTV clearance can be reduced enough to where it can be an issue.