3 replies to this topic

[stevede]

Hi all

 

I received my block back from the machine shop today, with the shiny new pistons fitted to the rods.

 

Crank has been reground & balanced but I asked them not to skim the block as I wanted to measure & work out the CR ratio and then take it back for skimming, rather than guess and get it wrong.

 

I don't think the block has ever been touched until my work (it has a "B" stamped in the deck)?

 

• 0.040" overbore for 1310
• Minispares Mega pistons with 6cc dish
• Looking for 10.5:1CR

 

Working on Info from other posts (thanks Cooperman) I have the calculation, just would like someone to sense check please.

 

Cylinder head is 23cc

Pistons are currently 0.050" from deck 

 

Un swept volume if I am correct:

 

5.125 (+0.040" bore x 0.050" down) + 6cc (piston dish) + 23cc (head) + 4cc (Gasket) + 0.75cc (ring land) = 38.875

 

Swept volume = 327.5cc

 

CR  (SV+UV)/UV = 9.42:1

 

To achieve CR 10.5:1 I need to have .040" taken from the top of the block to give piston to deck height of 0.010"?

 

If anyone can verify or, point out my obvious error before I send the block back, it would be appreciated.

 

Thanks in advance

 

Steve

 

 

 

 

[ACDodd]

Thats correct, assuming 0.75cc ring land. Although what cam are you going to run? Are you sure 10.5 is not too high?

 

AC

Edited by ACDodd, 22 June 2013 - 07:22 PM.

[stevede]

Thanks for the reply AC.

 

I assumed the 0.75cc ring land as I have no other info to go on than the figures Cooperman had quoted in another post, although to be fair, that was relating to the 21253 pistons.

 

I have decided (long story) to go with the Kent 286 I purchased some time back and again, had read that around 10.5:1 was the way to go for this. 

 

Very happy (and at the moment have the ability to do so) to run a lower CR if you could offer advice.

 

Thanks in advance

 

Steve

[ACDodd]

10.5:1 is good for this cam, you must use 97Ron min fuel for this.

 

AC