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12G295 Head - What To Do?


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#1 luismx123

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Posted 29 October 2019 - 09:01 AM

Hey all,

Got myself an untouched 12g295 head, no cracks, no skimming done - completely untouched - unfortunately no valves or studs in place. 

 

I'd love to put it on my 998 soon( will probably do a complete overhaul: rebore +60 and sw5 cam, lightened internals) which would mean cleaning it up, but until then I'm interested in doing some porting/cleaning up of the casting marks and some basic flow optimisation via david vizard. 
I know the 295 casting is already very good and Ive read the posts from russel on modifying a small bore head and I am aware that the 295 head has some more critical areas to be wary of, but what I would like to know from the experienced guys here is if it is worth it on a 295 head to do extensive work or should I just get a 60 grit cone and clean up the insides and remove casting marks?

How much more "value"/flow/power can be achieved by doing a top job on a 295 head vs a "clean up" and is it worth it? I'd like to do as much as possible myself, but the guy who will install larger valves for me COULD do some proper porting at a cost - hence value vs. reward?
 

Since the valves are out and I will be converting it to an unleaded head, I was thinking of increasing the valve sizes to something close to what keith calver does. 33.3 REC121 inlets and 27.2 exhaust valves. Any thoughts on this or other recommendations?

 

Anything else worth mentioning?
Anyone have some good articles to read  about 295 castings and porting them?
 

Cheers



#2 mini13

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Posted 29 October 2019 - 09:20 AM

for a fairly rare head like the 295, i wouldnt touch it myself, I would get turbophil to sort it, he does great head work at sensible prices, and is good to deal with. certanly he'll point you in the right direction if nothing else.

 

his website is  http://www.turbo-mini.com/ but he's often on here or other forums as TurboPhil or on facebook.



#3 DomCr250

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Posted 29 October 2019 - 09:55 AM

In all reality you are probably not going to make that much more extra HP with a DIY job. 

 

I'd go for unleaded exhaust seats, clean off the casting marks and then decide what you want to do about CR - standard pistons and a big chunk off the head or flattops and much less.



#4 nicklouse

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Posted 29 October 2019 - 09:59 AM

I would sell it on and get a ready modded standard head that is suitable for the current fuel.



#5 luismx123

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Posted 29 October 2019 - 09:59 AM

In all reality you are probably not going to make that much more extra HP with a DIY job. 

 

I'd go for unleaded exhaust seats, clean off the casting marks and then decide what you want to do about CR - standard pistons and a big chunk off the head or flattops and much less.

oh yea forgot to say i have flattops in there. its a 1990 High compression 998 so it wont need that much skimming from my understanding.



#6 mini13

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Posted 29 October 2019 - 10:17 AM

its worth pointing out that there is a market for these  unskimmed as they are ideal for people doing turbo'd 998's



#7 luismx123

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Posted 29 October 2019 - 10:29 AM

its worth pointing out that there is a market for these  unskimmed as they are ideal for people doing turbo'd 998's

yea I am aware, but Its not worth reselling it as I paid around 150€ for it and the price of them seems to be going up quite a lot lately so not sure if I want to flip it and get something else...



#8 Turbo Phil

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Posted 29 October 2019 - 12:29 PM

The biggest gains will come from improving the valve seat/throat area. Unfortunately the 295 has ridiculously thin seats and the port throat is almost at a 90deg angle to it, this makes it impossible to get a multi angle seat without going to a larger valve.
Regarding the ports just clean up the inlet, 60grit is fine, the exhaust benefits from having the boss ground away a bit. Fitting hardened seats is a good idea.
When done properly they’re certainly a vast improvement over the standard smallbore heads.

Phil.

#9 luismx123

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Posted 29 October 2019 - 02:08 PM

The biggest gains will come from improving the valve seat/throat area. Unfortunately the 295 has ridiculously thin seats and the port throat is almost at a 90deg angle to it, this makes it impossible to get a multi angle seat without going to a larger valve.
Regarding the ports just clean up the inlet, 60grit is fine, the exhaust benefits from having the boss ground away a bit. Fitting hardened seats is a good idea.
When done properly they’re certainly a vast improvement over the standard smallbore heads.

Phil.

Hey phil thanks for the reply.
Does it not make any sense increasing the size of the ports/matching the ports to the manifold gasket? The exhaust manifold holes on my maniflow cooper freeflow are way larger than the exhaust ports of the head, the inlet are fairly similar except for the locating ring step. Would you advice removing some material there?



#10 luismx123

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Posted 31 October 2019 - 10:42 AM

cheeky self bump:

as turbophil didnt answer, the question goes for the head modders. do I match the exhaust and inlet ports on the head to the ports on the manifolds? I have a maniflow alloy inlet and Cooper freelow. the exhaust port differences between the head and exhaust is pretty large... should I blend them?

#11 nicklouse

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Posted 31 October 2019 - 11:29 AM

exhaust nope.

 

make sure the inlet one is not too big. not sure if the Maniflow one is suitable I know Minispares do two different sizes and one is better for small bore engines.



#12 Cooperman

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Posted 31 October 2019 - 12:17 PM

When fitting a 12G295 head it is important to get the compression ratio correct.

The 295 was intended to be used on the 998 Cooper which had raised D-top pistons.

To get it right now you need flat-top pistons with the block decked to bring the pistons right to the top of the bores.



#13 luismx123

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Posted 31 October 2019 - 05:59 PM

exhaust nope.

 

make sure the inlet one is not too big. not sure if the Maniflow one is suitable I know Minispares do two different sizes and one is better for small bore engines.

for some reason i cannot seam to find one of the "smaller" versions. they only sell one atm i think... maybe im stupid and cant find 

 

When fitting a 12G295 head it is important to get the compression ratio correct.

The 295 was intended to be used on the 998 Cooper which had raised D-top pistons.

To get it right now you need flat-top pistons with the block decked to bring the pistons right to the top of the bores.

oh yes definitely. Will either get the head skimmed as little as possible - as its still unskimmed, or drop the deck height. didnt think about that one to be honest!

it!



#14 Cooperman

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Posted 31 October 2019 - 11:55 PM

 

exhaust nope.

 

make sure the inlet one is not too big. not sure if the Maniflow one is suitable I know Minispares do two different sizes and one is better for small bore engines.

for some reason i cannot seam to find one of the "smaller" versions. they only sell one atm i think... maybe im stupid and cant find 

 

When fitting a 12G295 head it is important to get the compression ratio correct.

The 295 was intended to be used on the 998 Cooper which had raised D-top pistons.

To get it right now you need flat-top pistons with the block decked to bring the pistons right to the top of the bores.

oh yes definitely. Will either get the head skimmed as little as possible - as its still unskimmed, or drop the deck height. didnt think about that one to be honest!

it!

 

Make sure you have flat-top pistons or you will really struggle to get the right CR.






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