What valve can fit an Alloy 250 crossflow head

[Anonymous]

What are the biggest valves that people have fitted to the alloy head?

I searched the forums and found an old post suggesting 1.94" inlets and 1.65" exhaust. Can anyone confirm this? Seems like a decent jump in size.

Does anyone have suggestions for which valves are the best to buy for the right length to suit. I have heard of Clevo, Chev and Holden valves being used.

Also what brands of stainless valves are people using in them? Ferrea, Milodon, Manley?

 

[xctasy]

Unless its the earlier cast iron head, 1.96"and 1.65" is it, because the valve inserts get in the way, hurting duraility.

There is no overlap on valves unless there is a high lift cam, and a lot of vibration, so 2.07 and 1.65" is doable.

The point is, the restriction is the tiny port size of the HFx/Cx/Dx/Ex series castings...way too small for even a 1.96" valve.

Same size as the last versions of the compound vetex hemi heads in the AU I6. You can get the valve size going up till the annular area between the intake and exhast creates a long term durability problem. It happens with 351 4V's, and it happens earlier when you have valve inserts.

Technically, based on the valve centre spacings, the basic geometry of the head allows you to fit 2.07" and 1.65" valves. To do this, you have to create a small version of the old closed chamber 4V 302/351 heads, and its impossible to get to even 2V 351 port sizes in a 250.

If you take the oft repeated homologation premise of 2.25" and 1.79" for the 4 inch bore Boss 302, you find a 250 '4V' version of an Alloy Head has space for these bigger sizes without valve contact and without block cut-outs.

It's not size, its flow, and Ford downsized the intake valves with 2.19" for the 351 4V, and , according to work done by Australian gas flow technicinas, a perfectly shaped rim flow 2.05" inch valve on a 4" bore 351 4V is more than enough.

 

[Anonymous]

Xecute,

This is all good info.

Have you personally put bigger valves in one? My rough measurement of the head I had at home had 1.8" inlet and 1.49" exhaust and only about 0.160" between them.

My rough calc suggests that with say 1.65" exhaust that going to close the gap 0.080" leaving me 0.080" left to increase the inlet valve radius so 1.96" makes sense in theory. I just want to see if anyone else has actually done it?

I will eventually do a test head anyway, and I will try a bunch of valve sizes and see whether the head picks up flow on a flow bench as I go. might be easier and safer to stick with 1.9" x 1.6" as these sizes are easy to get in stainless.

 

[xctasy]

No, I haven't fitted anything other than a std valve in an XE head, but Dynoed 250 has.


I looked at the collision angles back in 1997. and there is no real reason why 351C 2V valves can't be fitted up. The static space is considerable. I've got a mate with some 302C heads. The Geelong head copies the Cleveland head in the wedge and cant angles,

Inlets valves are tilted 4 degrees 15 minutes forward to give short intake ports
Exhasts are tilted 3 degrees backwards to give short exhast ports

The valves are canted 9.5 degrees from the cylinder axis to create a semi spherical chamber.


The centre spacing differs from the Cleveland, all else is the same.

If you use the dot product, and some simple math, you can determine the amount of iron and seat material between the ports for any given valve combination, and get some idea on the amount of distance to a water jacket.

Alloy is repairable, and the seats are easily replaced, so the issue isn't that a 2.07" intake valve valve wont fit, it is how big can the port be?

 

[Anonymous]

XE cute. Those angles will be very handy. for starters I have to machine the rocker pedestals so those angles should get me pretty much spot first cut I hope.

I will draw something up now that I know that. The canted valve angles was really the only thing stopping me drawing them.

Are the valve only canted directly forward and back?

I don't suppose you know what axis they are canted on? Looks like I will have do do a heap more measurements.

Yeah the larger valve is a bit of a trial. My last head flowed 240 cfm @ 0.500" lift but then drop away to 220cfm by 0.550" (at 28" pressure). That head has 1.84" inlets and 1.54" exhausts.

When the head was ported it wasn't taken as far as it could be, there was still some gains to be made. The inlet port was at around 39mm but can only go another mm or so.

 

[xctasy]

By outside welding the inlet runners with at TIG, you can high port the intake port very effectively.

The index point is the piston centreline at 4.08" centres rather than 4.375"in the Boss 302 and 351C.

The basic cant is 9.5 degrees from vertical, and respective leads of 4 degrees 15 minutes and 3 degrees are easily seen by placing a couple of woodern dowels through the stock valve guides with the intake valves out. It shows this exactly.

The SVO heads used in AVESCO use the same angles, the Auroara Pontiac (Chev based with Holden part number) use another variation. Real simple once you see it. This is why the 396 Chev which the design is based on is called a porcupine head...its quills stick out radially like a Sex Pistols hair doo!