4 replies to this topic

[dgear1984]

Hi,

 

Ok built up the block, spec below. Rob walker will machining the head, just need to let him know a cc.

 

cooper s 1275s thin flange block +60

21253 pistons

12g940 1805 head flowed and ported by Rob Walker

35.7 and 31mm unleaded valves with 3 angle hard seats and bronze guides

piper billet cross drilled bp270 with 1.3 forged rockers

97 fuel

 

Checked the deck height to pistons and I am getting 

cyl 1 = 10.5 thou

cyl 2 = 9 thou

cyl 3 = 8 thou

cyl 4 = 8.5 thou.

 

I burette the block and got 9.7cc per cylinder with 8.4cc of that being the dish of the piston.

 

Wrote a excel spread sheet and that worked out the cc per cylinder to be between 9.23 and 9.48cc (allowing for the slightly different deck heights). What I have no allowed for is the gap around the side of the piston and the top of the top ring, was unsure what this figure would be with the +60 21253. A 0.22cc and 0.47cc difference between the theoretical and burette figure.

 

For the excel sheet I have used the bore at 72.124 (1275 +60) and the stroke to be 81.33mm

 

Assuming I go for a 10.5:1 ratio, with cylinder 1 being the lowest compression due to the largest deck height (10.5thou) and cylinder 3 being the highest ratio due to the smallest deck height (8 thou). I have allowed 3.4cc for the gasket.

 

With a head of 22.2cc excel gives me a comp ratio of 10.53:1 (cylinder 3) and 10.47:1

 

Look about right, anything I have missed

 

Thanks Dave

 

ps. I am happy to upload my excel spread sheet for others to use, maybe someone can message me and tell me how is best to post it.

 

 

 

 

 

 

 

 

 

[grumpy dad]

HI 

I think the head gasket is 2cc

but you should wate for AC Dodd to come along and comforme 

[ACDodd]

I make that 10.15:1 with a bk450 gasket on cylinder no.3. I would run 10:1 cr with that cam and rocker combo. Therefore I would use a 22.8cc chamber.

Ac

[dgear1984]

I make that 10.15:1 with a bk450 gasket on cylinder no.3. I would run 10:1 cr with that cam and rocker combo. Therefore I would use a 22.8cc chamber.

Ac

 

Hi thanks for the reply. I am using a minispares GEG300 gasket which claims to have 3.4cc rather than a bk450 which gives 4cc.

 

I have done some research and it looks like the ring land is around 0.5cc. Have added the ring land to my calculations.

 

Does this look correct, what have I got wrong as I am still getting slightly different figures to what AC quoted. With a 22.8cc head and changing the head gasket to 4cc, I still get 10.1:1 rather than 10:1 which AC says

 

 

 

Thanks Dave

 

 

 

 

Edited by dgear1984, 03 February 2014 - 06:35 PM.

[ACDodd]

Ok using your figures I get 23.8cc to get 10:1.

Ac