11 replies to this topic

[ejs-1995]

Hi guys! Sorry if i've posted in the wrong section im new!
I have been offered a brand new 12g295 cylinder head to fit to my 1985 Mayfair 998 that I will be rebuilding soon. My concern is that I would want to get it converted to unleaded. Are these heads suitible for unleaded conversion? Are heard that these engines have very thin valve throats? Would this be a problem in the future? Thanks All

[Shifty]

I had mine done a few years ago with no issues(to date)

[Vipernoir]

They can indeed be converted - I've had many done over the years, and tend to run one as a matter of course on a 998 or 1098.

If you have an unmolested one you will need to get a large lump skimmed off it as the standard combustion chamber is huge.

[The Otter]

I've had mine converted, its been running fine for over a year, so yes I'd say they are suitable.

[carbon]

Before doing the unleaded conversion to an old head would be worth balancing up conversion costs and fuel savings.

Unless you are doing a lot of miles per year the cost of converting a head to unleaded will probably keep you in additive for many years.

[ejs-1995]

thanks for the swift reply all! I do around 12,000 miles a year so being unleaded is a must. Now im in a bit of a split. I have found
a 12g202 head that has all ready been converted and is in new condition for a hell of a lot less! will this head give any gain compared to the standard a+ head? thanks

[Ethel]

Some, but nothing like as good as a 12g295.

[Vipernoir]

One of mine did exactly the same thing - exhaust seat all the way across the chamber roof and across the beak.

Given the success I've had using Castrol Valvemaster on other engines, I may or may not bother with converting the next head I use.

[jaydee]

Add me on the list of cracked 295..
mine had bigger valves fitted + unleaded seats.

[bmcecosse]

Do buy the 202 - it's almost as good -and can easily be fitted with the larger inlet valve. But will still need skimming if it hasn't been done. As for the 295 - great head, but will need a LOT of skimming if it hasn't been done. Just run it without the 'unleaded' conversion with 15 thou exhaust gaps - and check/reset every 3000 miles. Worst that can happen is a little bit of recession - so IF that happens - get it converted then. Could be many thousands of miles down the road...even at 12k per year. Personally - I wouldn't use either - I run a 940 head - no skimming required....

[ejs-1995]

Thanks all! Alot of useful info for me to think about! Doesnt the 940 need either ressessed valves or a modification to the block to prevent the valve contacting the block? I think im gunna go for the 202 head and might upgrade to stage 3 head when my budget can stretch to it! How much does the 202 normally need to be skimmed to give a good compression ratio?

[bmcecosse]

The 940 'may' need the exhaust valves sinking in to the head slightly - that's all - a 10 minute job with a 45 degree countersink in a pillar drill. It works well - but a 202 will give some improvement. If flat top pistons then 60 thou should do it - but check it hasn't already been skimmed. They all start at 2.750" .