Rover V8 Lower Compression

[neal1980]

I have a 4.6 P38 engine with comp gaskets and 10 bolt 28CC heads giving the standard 9:35CR. Im going to be running a large single turbo and think I may need to lower the CR slightly, hoping to use about 10psi. Forged pistons are not really avilable off the shelf that I have seen anyway so can I drop the CR using earlier heads 34-36CC??? 14 Bolt.

Or failing that if anyone knows where there are Buick 300 Alloy heads :-P

Or any other options???

Thanks
Neal

[spend]

Early heads are fine (you can chemetal the extra holes if you want), but remember it changes the preload, adj pushrods would prob be the easiest solution.

Get the burr on the head chambers, if you are committed I took a fair bit out of heads I prepared for similar spec. Not measured but I guess about an extra 10cc could be gained easily. Thickest head gaskets you can get would help. Obviously if you could get LC pistons/rods that would be the ideal, but I think they were nearly all exported?

[GreenV8S]

In my case I was starting at a disadvantage because the block had already been decked to raise the CR. I used a decompression plate on mine (horrible, I know) as well as taking a bit out of the pistons and heads. You probably don't need anything that extreme, but the options are there if need be.

I've been told that the standard cast pistons are marginal at 10 PSI so I've kept a little below that just in case.

[neal1980]

I have 2 sets of late heads now then 28cc. Can these be opened up to save messing around with ealier heads as I know these heads are good. And whats the thickest head gasket you can get I will use comp I guess but does anyone make a thicker one.

The pistons will be out by the weekend so could machine them as well wont that weaken them too much??

Cheers
Neal

[stevieturbo]

9.35:1 CR + 10psi should not pose any problems with proper cooling and engine manaagement.

[Boosted LS1]

Don't machine the pistons because in doing so you'll weaken then, lose any squish effect the engine already had and unbalance the engine. I used to get away with 7 psi on a 9:1 compression ratio happily enough. You could use a little water injection if needed.

[neal1980]

I have fitted megasquirt to the car already to control ignition and fuel so should be fine there. Maybe need a set of new injectors though.

I was planning to use a front mount intercooler as well as maybe a simple snow performance water injection setup. Also an alloy rad :-)

Power predictions.........

[spend]

Buy a set of old heads to grind out anyway, its much easier to have a cheap set to destroy. By the time you've hacked a few chambers and measured the cc, you should be able to deduce what suits YOU the best. Some of us will do pretty aggressive things that we will tolerate failure with, thats for each to decide IYSWIM

You could also think out of the box and consider application of various thermal coatings?

[Boosted LS1]

Also, I've used the buick 300 heads before but they usually need a lot of work and bigger exhaust valves and seats etc. They also have a bigger chamber diameter then your bore diameter so I'd stick with modded stock heads or just stock heads. I have built a 5.1 with buick heads on it, the bores are 96mm, compression is about 9:1 iirc.