Head work, worth it on c1j?

[gttjames]

Iv searched the boards and was expecting to get alot of threads come back, but tbh got very little back. People in the no how good is the OE head? And what is it limited to. Does the 'port/polish, multi angle seats, shortened valve guides' give alot of gains and worth the money?

Main reason im asking is im looking like im going to have to be replacing most my engine and working out the best route. Im not after 250bhp etc just after a decent figure for a quick fast road car. Aiming for circa 20psi - is head work really going to be worth the gains at this level or will a well built standard head be good enough maybe with some valve springs thrown in there? Or any other worth while mods?

discuss:)

[J$£5GTT]

imo head work is only good if and IF you have everything gas flowed,inlet etc all matched then you will see gains worthwhile,free the flow up baby,free the flow..
:)

[rs250nut]

I think most people will agree that the c1j head is pretty poor, being from the 1940-50's its not excatly new technology, on the other hand anything you can do to improve an engines efficency is a worth while mod, the only thing being that you will never see gains like you would if you turned the boost up a psi or two:)

[Ian S]

And that is exactly the point.

A £400 spend might give you a few more BHP and maybe a smoother engine and maybe a few more useful rpm, but in terms of 'get up and go' power it's pales beside a few more PSI.

Anyway, your chambers can only be so full, head work helps to fill and empty them better so you may have to run less boost.

But the advantage of that is a bit lower exhaust manifold pressure and so better efficiency and better breathing and a bit more power for that less boost.

I would suggest new valve springs. I lost two engine through a valve dropping into a cylinder. After that I had longer firmer custom springs in lowered seats with custom caps. The springs length was calculated to be suitable for the lift of the Piper 285.

As they (CTM) were doing that, I also had them do three angle seats and the valve backs 'smoothed'.

Also had the throats done, as there are narrowings that can be removed, and the inlet manifold matched to to head.

If your changing to a taller cam, it also might be a good idea to have the rocker faces that rub on the valve tops ground to remove the wear edges as the taller cam will move the rocker faces past those edges and make a very loud tapping noise.

CTM stopped cutting back the valve guides for their own 5GTTs and their pals, as they felt there was too little guide left.

[gttjames]

some good replies, what i thought though doesnt really seem to be worthwhile unless going all out on a big setup. A good condition cylinder head with some better valve springs should do the job. I dont think il try anything else as without the proper tools etc just make a mess.

What is the deal with multi angle valves, im not clear on that whole setup?

[Ian S]

multi angle valve SEATS.

CTM assured me that it helps with the torque.

It's just a rounder shape to the valve seat. But three slopes instead of round. Compared to one slope in the normal way.

Helps the gas to flow, I expect mainly during the valve overlap period when both inlet and exhaust valves are only a little bit open.

[DaveL485]

multi angle valve SEATS.

CTM assured me that it helps with the torque.

It's just a rounder shape to the valve seat. But three slopes instead of round. Compared to one slope in the normal way.

Helps the gas to flow, I expect mainly during the valve overlap period when both inlet and exhaust valves are only a little bit open.

Quote from 21toc:



It's not about the 'biggest' ports. It's about airspeed around the valves...i'll make more power with small tweaks to the port than you will by grinding it out to the max. It's about using the port chamber to maximise the usage of the entire valve radius, specifically the short side radius, of the inlet valve. Gas speed in the valve throat just as the inlet valve is closing. Good 3 angle valve seats of which ive seen some fantastic info lately over on PH- certainly made me think anyway.

Lots of science. More than us mere mortals will ever understand.

From PH:


Having spent 20 years studying the effect of cylinder head modifications on my flowbench all I can tell you is it's far too complicated to summarise into simple rules like "more cut angles = better".

A completely smooth radiused seat will not necessarily flow more (usually less) than one with discrete seat angles and sharp edges between them. Sharks have rough skin (in fact most fish have scales) because the discontinuities actually reduce surface friction and drag. Golf balls have dimples because that lets them fly further than a ball with a smooth surface. "Smooth" does not always equate to friction free or higher flow.

The choice of seat width and bottom cut angle are far more important than just the number of cut angles which tell you bugger all about the knowledge of the person doing the job. Most places just have a small range of standard cutters which can't possibly be right for every valve size and nearly everyone cuts the main seat too narrow. A nice wide seat conducts heat away much better. The OE seat width is usually spot on because the person who designed the engine knew a lot more than the idiot with the Serdi who thinks 1mm wide valve seats are "race seats" or somehow better than what was there to start with.

Seat concentricity is more important than just about everything else combined and the commonly used Serdi machines are awful at achieving that unless the guides are in perfect condition. In fact most places with Serdis will try and tell you they need to either replace the guides first or at least hone them out (which of course buggers them) until they fit their next larger seat cutting pilot just to get the machine to work properly (they won't actually admit it's to get the crappy machine design to work properly of course). Far better are machines with fixed pilots which lock into the guides like the Sunnen system than rotating pilots like the Serdi where any play between guide and pilot translates straight into seats with poor concentricity.

Seats that flow well at high valve lift don't always flow well at low valve lift and vice versa. Seats that flow the absolute most might not last very long. Everything is a compromise and every seat I've ever cut has been tailored to the exact engine spec, cam lift, its intended use and the valve sizes.

If you want some simple rules for general use the 45 degree seat should be about 4.5% of the inlet valve diameter wide and use the same width on the exhaust seats which will usually translate to about 5.5% of their diameter seeing as they are smaller. So a 50mm inlet valve will want a 2.25mm wide seat and so on.

A 70 degree bottom cut always outflows the normally used 60 degree cut because it better splits the transition from 90 degree throat to 45 degree seat. A 60 degree bottom cut means a 30 degree transition from the throat and only 15 degrees from the seat angle which is a stupid way of trying to minimise the change of flow direction. Obviously the ideal would be to split the 45 degree difference and use a 67.5 degree bottom cut.

So why does everyone use cutters with 60 degree bottom angles? Because that's what the seat machine manufacturers list as stock items and hardly anyone out there is smart enough to question it. Actually OE heads usually have the correct 70 degree or similar bottom cut angle which your local engine reconditioner will happily and cluelessly bugger up when he refurbishes the head for you.

Similarly the top cut should split the difference between seat angle and chamber roof angle, i.e. with a flat chamber roof use a 22.5 degree top cut. With hemi heads or other heads with angled roofs use a bigger angle like 30 or 35 degrees.

So phone up a few people and ask them some searching questions because you now already know more than they do. Ask them what seat width they suggest and why. When they say they use 1.5mm on everything because that's the cutter they bought with the machine or that wide seats are good for road heads and narrow seats are good for race heads you can put the phone down. Ask them what bottom cut angle they use and why. When they say they've never given it much thought or they use 60 degrees because that's how the cutters are made you can put the phone down. Same for top cut angle.

Ask them how much time they've spent testing different seat widths and angles for flow on a flowbench. When they say "what's a flowbench?" you can put the phone down.

Ask them what concentricity level they strive for. They'll probably say their seat machine has a vacuum tester built in and they test every seat for leakage - at which point you can put the phone down. The trouble is a 45 degree valve and a 47 degree (or any other angle) seat will still touch at one point all the way round so it'll seal against vacuum but be worse than useless and burn straight out in service. I've watched a Serdi machine test every seat as perfect for leakage but then none of them would actually lap in and it all had to be redone. Only the fact that I was standing there glowering at people meant it got redone properly! I glower very well when the occasion requires it.

You have about as much chance of getting a set of valve seats cut perfectly (well what in my view is perfect) as of winning the lottery. In fact it is a lottery. If you can find someone who can answer all the above questions without you having to put the phone down first please let us know.

Get your teeth around that one :eek: :)

[gttjames]

:eek: cheers dave