[Xf XR8 Ute]

Am looking to build a street engine (2000-6000 @ 350~400hp) and after reading a lot of posts on this topic, it seems that a 302 Clevo w/351 crank might be the go as its going to be straight gas (so no detonation issues?).

Was wondering what the deck height would be with this combo (if its even possible) and what comp would it be (roughly) with the 2v closed chamber heads?? If its possible, what about valve/piston clearances? Need a special cam? Or am i totally on the wrong track?

The reason for this is an engine builder once told me u can run really high comp on gas as it wont detonate (up to 14:1!! phew!)... Thanx guys!

Mik

 

[brenx]

With the special pistons required deck height should be zero. Gas does detonate. My had a 351 running 302 rods with the chambers opened up pinging it's guts out. Compression was 11:1 from memory. Gas has dropped octane wise. It's around 100 now where it used to be 110.

Short version:

Comp @ 11:1-11.5:1.
Special pistions required.
Cam's you can use any.
Clearance issues only become an issue when your getting close to 700thou lift.
Cam choice does affect combustion chamber pressures. Bigger cam = less pressure = no detonation.
350-400hp you won't have an issue achieving with the right cam. I'd suggest a Crane F238 or F246 solid but can be done with others.
Best bet is to try and stick around 10:1-10.5:1.

The engine your looking at building is a tried and tested combo built by many engine builders.

Brenden

 

[TyreToaster]

are you maybe confused? do you know that a 351 block and a 302 block are the same if you change the crank and rods to 351 you have a 351 not a stroker or long rod combo? your comp and everything else will be as stock 351.


no diffrence in deck heights etc

also lpg used to be good for anthing upto around 11.5to1 but is getting worse n worse, if you already knew what i put sorry.

 

[xdc351]

14:1 comp on LPG used to be possible but they have changed the propane/butane levels over the past few years, now its about 11:1 max unless your cam is massive and you'r not planning on doing a large amount of street driving.

302/351 cleveland use the same blocks but the heads can be different, if your looking at running straight LPG with a 351 crank, rods, pistons and 302 heads then you'd be best to have some material taken out of the combustion chambers to lower compression.

 

[Xf XR8 Ute]

Thanx guys! Yep, I'd planned 11:1 with a decent cam - really the only reason i wanted to go the 302 was the 2v closed chamber heads & pistons to get the comp up. But if i have to grind the chambers then whats the point? How hard is it to get 11:1 from a 351 & 2v open chamber heads? Know what im driving at (no pun intended)??

Mik

 

[clevo]

If you put 2v closed chamber heads on you'll have around 11:1. remember the 2v closed chamber heads varied from 56cc to I think 60cc. Have yours checked then you'll know your compression exactly.

To get 11.1 from open chambers you would need pop up pistons.