Holes on the exhaust is later head - better to support head gasket.

I have seen with my own eyes.

RS500 = no coscast, slits on exhaust side.
?? = coscast, slits.
?? = coscast, holes like later 4wd heads.

Not sure on numbers though.

Will check.

I don't think the numbers mean much.

Mate has seen identical numbers (86) with and without slits on exhaust side.

Maybe 89 is 4wd head but I have never taken notice.

Numbers does not seems to tell whether you have the closed in water jackets.

However all three bolt head housing have the larger head bolt surface I have seen.

Oops will check the yn numbers....

Lincoln the YN number tells all!!!
i just found out about all this.

your friends rs500 should have yn0627 no cos cast.

My EECIV head has YN1043 and Coscast on it I also have a 2wd Saff head which I will check and get back to you.

YN0635

3 bolt, coscast, holes on exhaust side.

cosworth made slight changes to the heads so i think its safe to say the higher the YN number the better design of the head and the "newer" the head?

it seems that its true that the YN0627 head with the coscast 3 bolt thermo and no dowel holes on the inlet and 2 bolt holes at the back of the head is a crate rs500 head.

and in determining what type of head you have. you use the YN0 numbers.

its just something i thought was interesting.... probably wasted my time but oh well... [:o)]
hope it might be usefull information?

Has anyone come across more of these numbers have now seen a yn0001

Ty, I have recently sold a YN1250 coscast.
I will have a look at my other heads.
Mark


As per Phils YN1043 coscast (YBP)and I think another coscast YN1250(YBT) but have to confirm as belt cover is in the way

Confirmed other head as coscast YN1250

My head is cast with YN0001 at the front...along with V86 HF 6090 AA

Now the engine No. is GBxxxxx and Cosworth No. YBBxxxx as per my receipt.

This will be a September 1986 Sierra Cosworth 3dr, right?!?!?!?