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[Mini30BVA]

Hello there,

First time posting on here, so here it goes! I'm looking to potentially putting a 12g202 head on my 998 engine and was wondering if its a good idea or not...

The current setup is this:
998cc with flat top pistons, full stage one kit (keeping airbox but with better flowing air filter) and currently has a 12g940 head on it. Not sure if the cam has been done to a fast road type cam and still has the traditional Lucas 59d4 points distributor.

My current problem is the horrendous bog in low RPM which is characteristic of putting a 12g940 head on a 998, and yes it has been skimmed and done properly by whoever owned it before me!!

So, the bog is getting annoying to drive with and was curious to know if a 12g202 head would be better. I've looked into a 12g295 head, but is a bit expensive and from my understanding, benefits the 998 better when pushing the revs.

I'm not wanting to build a super fast road car that goes out on track days, just wanting to keep it simple and a normal road car, just with a little extra punch and go compared to the stock 998.

Hopefully someone could shed some light onto this with experiences of having a 998 with a 12g202, or just simply some advice would be great!

Please ask any questions if you need more info.

Thank you!!

[timmy850]

Your engine might just need a really good tune up, correct the air fuel ratio across the rpm and load range & make sure the timing curve is suitable

Bogging tends to be a symptom of too lean ok acceleration or too little timing. The air speed will be slower on a 940 head due to the larger ports but it should still run OK

If you have a skimmed 12G940 head and flat top 998 pistons, my calculator says your compression ratio is very high - over 11:1

Changing to a standard 12G202 head will drop that down to approx 9.5:1

If you can find a 12G295 head it’ll need a large skim to get the compression ratio right for a 998.