First test 12G202 head

The first test of a 12g202 head . aka. Cooper 997 ( thanks TurboPhil for pointing out my synaptic misfire) .  Despite the famous/fancy name it is basically the same head that was used in the 1098 and a whole load of dull BL cars. It has very tiny valves and has a closed chamber design. The Cooper 998 had a 12G295 head that is more like a big bore head.  That head was to be used with raised D crown pistons that are NLA so you end up with a very low compression if you use normal flat top pistons, hence most of them are skimmed to death and have subsequently cracked.

the lesser cousin on the bench

the lesser cousin on the bench

This is a graph of the ported 12g940 (35.7/29mm valves) vs the stock (29.2/25.3mm) 12g202.

tested at 28′ depression with a manifold attached.

There is ample room for improvement as one can see.  The head hits the wall after 5mm lift and basically gives up. This is probably due to the closed chamber. CFM number roughly corresponds with the figures Vizards published (p.182) His numbers are at 25 inch depression though

The bore diameter I use for the adapter is about a +100 overbore (67.1068mm) . I see very little point in using a small overbore in a 998. The bigger the bore the squarer the whole lot becomes and minisport australia sells them at very reasonable prices. Upping the bore size this much makes it almost like a short stroke 1098 (1077cc). I always liked the 998 better than the 1275 as far as rev willingness goes ( it just sounds happier I think) and this way you can have a bit of both worlds… cheap.

ported big bore head vs untouched small bore head...

ported big bore head vs untouched small bore head…

On a different front: I bought a copy of EngMod4T. I must say that Dr Neels is keeping busy and it now does turbo’s as well ( not sequential). I have not gotten around to running some more sims but now I will have more  time to beaver away at it.

Tagged , , , , ,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: