• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

12G295 question...Hap??

Share this page

64rocksprite

64rocksprite

Jedi Trainee
Country flag
Offline
Hello all.
I picked up a bare 12G295 head for my 1098, CG series engine (early 1098).
From what I have gathered, the intake and exhaust are improved in the 12G295 head vs 'stock'. (I bought Vizard's book...still in shipment!)

Can someone enlighten me as to what exact size the valves are and where I can find the parts to rebuild this head?
I am guessing most is the same...(rocker arms, pushrods, etc)?

I'm not planning anything wild..just a reliable engine with some flow improvement (and swap for unleaded gas!)

Thanks to all..
Devin
 
Devin, the intakes are 1.219" on the 295 head, exhausts are 1".
What head is on there now, a 202?
Parts are available from the usual suspects, but I would suggest if you are peformance oriented, to source them from APT.
I'll let Hap comment on the 28.3cc chamber volume of the 295 head vs the 26.1 of the 202.
Jeff
 
Jeff, pretty much covered it, most of my knowledge of the 295 heads is for SCCA GP racing and using dome pistons, we made alot of elaborate tooling to machine the combustion chambers to perfectly match the the custom domed piston we also machined ourselves, it worked great, we were the fastest GP 1098 Sprite at the runoffs for three years running. You can run the 1275 intake valve in the 1098 head, so that's option. When you get Vizards's book, just study his porting suggestions. As for combustion chamber volume differences, that can all be controled by running the numbers for compression ratio and then decking the head to get it where you want it to be.
 
You might be better off getting a decent 295 head that just needs a valve job and some new springs....and put hard seats in the exhaust.

The valves are not that expensive tho.....

You can run a 1/16" oversize intake but on a stock (or nearso) you wont realize much gain. You have to be careful with large valves on that very small bore , and there is no real locating dowels case to head.

Measure the chamber volume and calc the dish volume in the piston to se how much you have to cut off the head...probably .020" to about .035' to come up with about 9.25:1 Using the Vizard book and remembering it was written in the last century in the mid 80's , but SOME of the material still applies. You can clean up the ports and an inch in from the face as well as the intake manifold per his book.
 
Thanks all.
Jeff - I honestly don't know what is on the engine now. Engine runs OK (once I get her coolant passages cleaned out!) My current plan (changes weekly /bcforum/images/%%GRAEMLIN_URL%%/smile.gif is to rebuild the head so I can swap them out later.
Hap and Jerry, you're right, I'm not going for major performance on this engine. But the price for the head was dirt ($40 total shipped). I have not had it magnifluxed for cracks or checked it for true, but I'm guessing if its not cracked, I can fix any minor deck issues when it gets milled(?)
I doubt I'll go oversized on the valves.Honestly, I had seen a few mentions of the 295 and figured what the heck..even if its no improvement, it'll allow me to rebuild the head while I still drive the car. I am thinking of building a 'fast-road' 1098 in the future and figured that this head might come in handy then.
Again, appreciate the feedback and help.
Devin
 
Back
Top