Reducing C.R. On 2.2E

[copbait73]

I'm going the other way on C.R. :

1) Spec show 2.2E at 9.1:1 C. R. does anyone know from build experience how much the C.R. will drop with ADDing .5MM copper cylinder base spacer?

2) I've read of reducing head height by 1MM, conversely can the head be moved out 1MM without chain or seal problem?

All insights welcome.

[tadd]

Base gaskets are there to set piston to head height, and really shouldn't be used to set compression values. The additional space at the cylinder will not burn correctly - hence the spacing is set to squeeze that mix back into the main chamber. Detonation can result.

Why do you want to go down? That is throwing away combustion effiency, 9.1 is pretty low already.

If it's gas quality your worried about and want to future proof, twin plug. It's typically $400 to get the heads drilled and tapped. Put plugs in along with the stock covers and if you need/want them in the future, just wire them up.

[EBS_Don]

If all of the numbers work out and you are currently at 9.1:1 then a .5mm increase in deck height works out to 8.65:1. If you increase it by only .25mm it's 8.87:1. What ratio are you shooting for?

[304065]

Do not increase the deck height to reduce CR, you will cause detonation.

If you really must reduce CR from the 911E's wheezy 9,1 then I would mill some material off the piston top.

[copbait73]

Thank you all, I'm dropping to turbocharge.

Planning on 250HP so it will make a good showing for itself.

Don, if a go a full 1MM to approach my desired 8:1 will there will be stack-up issues with the chain length or cam seal/chain housing bore?

[tadd]

Use the spacers that supertec makes... They go between the cam tray and the heads. IIRC, the go up to 0.080".

[EBS_Don]

At 1mm over the stock deck clearance you will likely need to space the chain housings as well. There are some slightly thicker fiber gaskets available but you may have to use the 964/993 gaskets. You will have to measure everything out to be sure of your needs as your engine may have previous machine work done. With such a large deck clearance the quench area becomes less efficient and you could have a detonation issue as per the previous posts. Be careful with a turbo conversion!! You may want to consider machining pistons, going with 2.4S pistons, or a custom JE.

[copbait73]

All good leads, thanks.

I'll probably start a thread when I build this motor up. Plan to use MFI. Here is one for my 2.4T CIS Turbo at 8:1C.R.

73.5 911t cis turbo

Marty