I would always worry about welding a precipitation hardening alloy such as 2618. The Heat Affected Zone (HAZ) is likely to become overaged and if the precipitates may reach what is known as an equilibrium condition. Thisa means diffusion away from the precipitate is just as likely to ocuur as diffusion into the precipitate and it just won't dissolve.

Solution tratment needs all the precipitates to redissolve so that the material has single phase structure. This means the alloy is in its softest condition.

The precipitation stage of the heat treatment gives a significant improvement in strength.

Once the alloy is significantly overaged it will lose a great deal of strength and will become relatively brittle.

If you do weld pistons it may be agood idea to make a sample chop it up and do a few hardness tests through the HAZ as this will give a very good guide to the material condition and give some confidence that it won't fail.

Great thread...

If we had a blank sheet it would be likely we would indeed flatten the valve angles to use a flatter piston crown:

The chamber would no longer want to be anything near to a hemisphere..it would likely be designed around a nice venturi opening for the valves, with a big flat or almost flat squish zone effectively filling in with head metal much of the volume which is in the piston crown in the race pistons..

It would also be possible to help induce swirl to improve combustion , especially with single plugs..

I have seen major distortion from welding heads: as Chris implies this can always be machined out more or less but the structural weakness remains.

At some point it becomes more cost-effective to recast, or CNC from a lump..I do not know enough about production issues to guess where this point may be.

Kind regards
David

Walt:
Ferrea does sell valve 'blanks' that you can machine to your parameters. I was just looking for as close of a match from another stock application as possible. I'm not made of money yet :D. I have not been thru the whole cataloge yet, but most of the motors (other than the muscle car stuff) are 4 valve so the size typically peaks around 32-35mm for intakes. Ferrea also sells guides and there are several chevy applications that are real close in length, 7mm ID, and 'bigger' than stock p-car on the OD. I was thinking those could be chucked up in a lathe and cut to diameter.

As for head volume, I've actually gone so far as to chuck a head in the lathe and 'recontour' the chamber (with the seats removed!). The alloy actually machines pretty well. I didn't bother recutting for the valve seats as it was just a quick and dirty test.

Walt hits the nail on the head with the valve angle. I just can't see any way to fill the holes and then redrill at the 'new' angle. I agree with david that it would be smarter to just start with a new casting. For what a real set would cost I bet you could CNC from lump - 6 to 8k would buy a lot of machine time. Some soul just needs to CAD the head then someone covert to G-code. I just got proE on my work computer at work so maybe at some point I can give it a start. As I have never used any CAD program before, it will be a learning process first! I figured I start with a 2.2 head and go from there. It would be cool to do an 'open source' head. Then folks could just download the G-code and take that to there local shop and get a set made.

For the time being, the toyata valves seems really promising to get some of that top end back.

tadd

Tadd,

I know a guy in England that has recently set up a Company to CNC port heads and has all the right machinery.

He was responsible for port design at Mercedes Ilmor for 6 years and has the relevant flow benches and if pretty good at CFD Analysis. This guy's track record in F1 is excellent.

We have used this company to carry out some work on porting Lotus heads and the improvements they have made are quite worthwhile and the quality is excellent. We are currently paying about $2k to fully port a 4 cylinder 2.2 litre Lotus head for engines that produce 260 BHP and I think that this is a very reasonable cost by UK standards.

I am sure that someone in the States is already re-manufacturing heads and it must be possibe to buy blanks but if not there is a Company based in UK that are 90% of the way to producing a new forged billiet head from 4032-T6 and I would be happy to call and see where they are with production.

Let me know.

Chris,

Are these the Ninemeister's heads for early engines? Have they put the 930 head into production yet or are they still limited to the 993 head?

Does CMW produce a billet head for small bore spacing? I know this is not budget friendly, but you get to keep the short block and might make good use of the Ti rods.

Luke,

I am aware of the CMW heads but have not looked at Ninemeister.

Perfect Bore are threatening to manufacture heads but do seem to be taking quite a long time but from the last conversations I had with them it shouldn't be long now !!

Was Perfect Bore the guys the ones playing with the idea of threaded barrels into the heads to prevent them from lifting? Retro WWII style air cooled aircraft style no longer relying on the head studs to hold compression. I don't know if it was them or if it was the only design they had in the works, but I remember reading last year in a British Mag.

There was some debate on here about it and many were skepticle, but I figure they know more than me, so I'll wait and see.

Ninemeister's heads have showed promise, though it would seem a longtime before they consider small bore engines working backward from the 993.