Cylinder heads.

[Nova-Boy]

I am tuning up my 1.2 I have both a spare 1.2 head and a 1.3sr head complete with valves, springs etc. The heads both seem identicle apart from the 1.3sr head has slightly different area size in the cut away for the valves in the underside of the head and the valves etc are possibly different sizes??.

I am aware the 1.3 has smaller bore with bigger stroke but the 1.2 head gasket fits fine and when measured up there is not alot in it between the two heads.

Does the 1.2 have better gas flow than the 1.3sr??

Which one sould i use??

[mikeoxford]

well

different arguments here

use the 1.2 to maximise compression because as you said the raised bit in the head is grater in the 1.3 than the 1.2, so you will gain compression squeezing the petrol air into smaller space.

BUT the 1.3 has bigger valves etc like you said - SO depends how far you gonna take working on the head, you doing anything to them?

if not go with the 1.3

[Nova-Boy]

I was planning on skimming the head and porting it slightly for better matching of the inlet and exhaust. I thought i could re-gain the loss in compression due to the 1.3 head by skimming it down.

How much can you safely skim the head without it getting too close and damaging the valves :cry:

This would then have good compression and bigger valves.

[mikeoxford]

true.........

valve clearance shouldnt be a problem PROVIDED THE ENGINE IS TIMED CORRECTLY, i think you can aford one or two skims.......

[Nova-Boy]

1.3 it is then. I will do the work on my spare 1.2 head anyway and then maybe sell it when i have fitted the 1.3 head and got it running. If I fook it up i will go back and try again on the 1.2 head!!

[mikeoxford]

to be fair the 8v GM engine are VERY strong, unless you do something REALLY bad, there forgiving.........

[rgv_stu]

think you will find that the valves are the same size mate

[Nova-Boy]

Ok then. Still going to use the 1.3 thought cos the valves are in better condition and generally the head is in better nick. All the valves are going to be lapped in again with new valve seals.

[Will]

the heads are the identical :P

[Snowface]

the bigger the better:)

[Aragorn]

dont fit a 1300 head to a 1200

you'll lose power

since your swapping a head thats identical bar the compression ratio it will produce

u will lower the already stupidly low compression even further

stick with the 1200 head

[Nova-Boy]

Could I put the valves from the 1.3 into the 1.2 head if they are the same and I lap them in properly? How much is it for new valves?? Are the springs any different on the 1.3??

Arrgh which one should i use?

[mikeoxford]

Could I put the valves from the 1.3 into the 1.2 head if they are the same and I lap them in properly?

yes

[mikeoxford]

Are the springs any different on the 1.3??

no, unless it has had a performance cam fitted at some point, the springs may be shorter or a different profile, but if all standard then no there identical