Hi,

I've got two 81SM6090 cross-hatch heads from an '82 and an '85 CVH.

Both heads are 1.3 casting (same intake valve dia, but smaller exhaust valve dia [1.3: 34mm/1.6: 37mm] than the 1.6 casting as stock)

According to pumaracing.co.uk, the cross-hatch heads are the best CVH ones for valve size upgrade and porting (due to thicker walls).

Do you reckon that despite being 1.3, a +2mm intake valve (from 42mm) upgrade can be done on these castings?



cheers

 

Is there any diff between pre '86 1.3 and 1.6 (carb) castings other than the exhaust valve size? Camshaft obviously, but port shape/size for instance?

 

doubtful, very doubtful.

 

The whole cumbustion chamber obviously will be different. There are also quite many different cross-hatch cvh heads; 1.3, 1.6 and even EFI. I doubt that the pumaracing statement is valid on all of these just because of the cross-hatch.

 

Thanks for the comment guys.

It's also the casting number that matches 81MS6090, but as I haven't seen a 1.6 of the same type to compare mine to, you might just be right.

However I think the combustion chambers are the same on 1.3 and 1.6 carb engines.

 

1.3 engines have smaller bores i believe so therefore small combustion chambers aswell.

The part number is only really relevant to the casting year (1981), hence the 1.3 casting, and some have letters such as BRA after

 

1.3s have the same bore as 1.6s, hence the head gasket compatibility. BKA it says on mine, and as I've got two of them, we'll possibly try how far we can go grinding-wise and with valve size.

The valve angles are the same too, I assume the radius of the hemispheric chamber dome is the same as well.

Would be interesting to know, as an engine swap is out of question at the mo. It all depends on my budget after the shell's repairs have been paid for.

 

just doubled checked after reading that and the bore size is the same yes!

Surely if the heads were the same they wouldnt bother to stamp 1.3 in the back though?