Increasing Compression

[Dessertrunner]

As I understand it there are a number of ways to increase the compression,
Shave the heads to reduce the area around the valves,
Use different pistons that have a higher or larger top,

My question is can I also use longer rods to acheive the same thing,

If so then by how much would they need to be longer by?
Tony

[oab_au]

Originally Posted by Dessertrunner

As I understand it there are a number of ways to increase the compression,
Shave the heads to reduce the area around the valves,
Use different pistons that have a higher or larger top,

My question is can I also use longer rods to acheive the same thing,

If so then by how much would they need to be longer by?
Tony

No mate there is only 0.60" between the piston and the head, so you can't push them up any more. Shaving the heads is not the go as it will need adjustable cam pulleys to keep the timing right.
Higher comp pistons would be the best.

Harvey.

[svxfiles]

Originally Posted by oab_au

No mate there is only 0.60" between the piston and the head, so you can't push them up any more. Shaving the heads is not the go as it will need adjustable cam pulleys to keep the timing right.
Higher comp pistons would be the best.

Harvey.

Or a slightly larger diameter bore which would increase both displacement and compression ratio.
It still requires new pistons, but hey, boring is relatively cheap!
Its the pistons that are expencive.

[Dessertrunner]

No mate there is only 0.60" between the piston and the head, so you can't push them up any more. Shaving the heads is not the go as it will need adjustable cam pulleys to keep the timing right.
Higher comp pistons would be the best.

Are you saying .6 of a inch?
Tony

[dynomatt]

Harvey's right Tony...I shaved my heads and am having difficulty getting the timing right. Didn't realise that the poofteenth I took off would impact the timing as much as it has.

If you're interested in pistons, and you need some extras to get going, then I'll be interested in a set. Mike offered me a set a few years back, but I just wasn't in a position to do anything then. He may have the specs and contacts that could help?

What ratio are you thinking? And how did you work it out? Are you thinking E85 as well? So 13:1?

M

[Dessertrunner]

I was think of trying 14 to 14.5,
pretty sure the pistons I have in the motor from Mike were 13, I want to go higher.

[bazza]

Originally Posted by oab_au

No mate there is only 0.060" between the piston and the head, so you can't push them up any more. Shaving the heads is not the go as it will need adjustable cam pulleys to keep the timing right.
Higher comp pistons would be the best.

Harvey.

Can you please this number, is it from a tech manual or from your own measurements?

[oab_au]

Originally Posted by bazza

Can you please this number, is it from a tech manual or from your own measurements?

No mate that was a 'round about' measurement.

Harvey.

[bazza]

Originally Posted by oab_au

No mate that was a 'round about' measurement.

Harvey.

Hahah okay. Tony and I are just figuring out how much larger we can make the piston (up top) to bump up compression.

Also noticed a lot of cams are slightly open by up to 1mm ATDC... makes things tricky. A question we have to ask ourselves is do we go high compression or do you go for overlap or a mixture?

[dynomatt]

Admittedly it has direct injection, which allows a higher compression ratio, but the latest Subaru BRZ/Toyota 86 has a boxer Subaru engine with 12.5:1 compression. Might be a target for you Tony? Or are you already past 12.5?

Matt

[Dessertrunner]

I want to go higher Matt, good pice of info. You got to wonder if they can get away then would E85 or direction injection be more likly to be able to go higher compression.
Tony