15 replies to this topic

[TehMarchant]

So I havent really got the money to shell out £300-£400+ for a 12g295 for my 998,

So the question is could I get my standard head worked/ported to have the same proformance increase as a 12g295?

Cheers

[jakejakejake1]

In short - not really. The standard 998 heads are pretty terrible, and to get them even remotely close to a 12g295 would take a lot more effort and money than buying a 12g295. You could always use a 940 head as used on the large bore motors, but this may require either exhaust valves sinking of pockets in the block.

[TehMarchant]

Well I would rather not take the block out as she is a daily driver, but when you say sinking the exhaust valves can you modify the head in a way that will avoid changing the block?

[Turbo Phil]

You can recess the exhaust valves on the 940 head to provide clearance between valve & block face at full lift. Though not ideal, it does mean the block can remain in situ & without requiring pocketing.

[TehMarchant]

You can recess the exhaust valves on the 940 head to provide clearance between valve & block face at full lift. Though not ideal, it does mean the block can remain in situ & without requiring pocketing.

Okay thanks for that, What kind of placed would I take the head too to get that done? Would a car garrage to the job?

[cradley-heathen]

you would need to find a good engineer shop to do the job for you, most modern garages wont want to get involved in something like this, and wont have the machinery to do it anyway.

there was a keith calver write up on doing this to a 12g940 head a few years ago, i bet someone knows where you can find it on the net though?

there are some measurements you need to make before you can get it done though, so that you give yourself enough clearance at full lift.

[Vipernoir]

Recessing the valves always strikes me as being a bit like fitting a 12G295 and then bunging up the ports with plasticene - kinda defeats the object.

[MRA]

12G295 heads are on eBay all the time.. however you will need to get larger valves turned down to fit, as the 295 items are no longer available.

[Turbo Phil]

All the 295 heads I've ever come accross have been in desperate need of an overhaul. The valve seats are usually totally shot & as a result oversize valves need to be fitted in order to allow a decent seat to be cut.
Oversize valves are actually still available, Minispares sell an oversize exhaust valve for the smallbore heads here: http://www.minispare...|Back to search
And oversize 31.75mm inlet valves for the smallbore are available from Race engine components.

[MRA]

Does Paul still have the inlets, I last spoke to him a few years ago and he was not going to be making any more ? Personally I would always go for single groove collet unless the revs are going to be kept fairly low.

Phil, have you had much success with fitting seat inserts into a 295 ?

[Vipernoir]

Three of my 295s have had inserts fitted successfully (the ones I'm using).

[MRA]

Three of my 295s have had inserts fitted successfully (the ones I'm using).

Did that allow you to use a standard valve, I've machined valves down to fit, which works quite well, just make sure that the valves are NOT "tipped" of course.

[jaydee]

You need to smooth out the chamber sape on a CAM4180 cylinder head otherwise it will come out like a 202
A lot can be improved by porting and gas flowing
If you can get a 295 for cheap you still have to recon that (valve guides seats etc) but its a much better baseline, although it wont be cheap.

[Turbo Phil]

Phil, have you had much success with fitting seat inserts into a 295 ?

Hi
Yes I've done a few with no issues.
Phil.

[Vipernoir]

Depends if you put 4 or 8 inserts in - it's the oversize inlets that are the tricky bit iirc.

If I change the head on Betty for my full race 12G295 I may be tempted to part with the one thats on there at the moment - any idea what a refurbed 295 with 8 inserts would be worth ?