Compression ratio
Turbo Mini Forums

Evening all, bit of advice I have a 1293 block with 10 cc pistons, the block face has been skimmed as there was a few imperfections init. What head would you recommend to use for right ratio? Would a standard a series head work ?

What's your deck height? What crank? What head gasket?

Evening,
How far do the pistons sit down the bore?
What head gasket do you intend to use?

From memory/ off the top of my head pistons .020" down the bore (not ideal).
Bk450 Head gasket , 3.3 compressed volume.
.4cc ringlands.
10cc dished pistons.
28cc in the head gave a CR of around 8.5:1

would have to double check the maths to be 100%

Shane

Would it be better to get the machine shop to machine nthe block down so pistons bait flush?

Sorry sit not bait

6581 crank

Having the pistons flush with the deck I believe is better for squish but the compromise is you'll need to gain CC's from somewhere to reduce the CR back down.
You can have the dishes of the pistons opened out to gain a couple of CC's (dependant on your piston choice) or upgrade to 18cc Forged Acculites £££.
Use a Cometic head gasket which have a greater compressed volume.
Im not sure what the max CC's you can have chambers taken out to, this may be one for Phil to answer.

There is some good content in the yellow Vizzard book worth looking at for this sort of stuff.

Shane

28cc in the head is common, ( 21cc as standard)

32cc upwards has been done but it gets specialist above that, you can lose the beak, and take the chamber deeper which means cutting the valve seats in deeper, which compromises flow (screws with the shorst side radius?), obvioulsy the risk of breaking into the waterway increases, and you have to start picking the castings.

If the block hasn't been decked severely, you'd get round 8.4/8.2:1 with 28cc chambers on 10cc pistons. A lot depends on what boost you want and how you're fuelling it too.

Edited by Steve220 on 1st Dec, 2020.

There’s a video I made on my YouTube channel for working the static compression ratio out, super easy.
https://youtu.be/9Lp-1Rbb4Yo

Phil.

WWW.TURBO-MINI.COM

Thank you everyone much appreciated!
Phil iv sent you a message
George

Never knew this

Own the day

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