Don Terrill’s Speed-Talk

I got a set of CNC yates heads that I'm putting on a 315 CID drag racing engine. The heads supposably flowed 355 CFM at .750 and then fell off. They came with a new 55 degree valve job to help the high lift number but not put back on the bench. One of the bowls was blended but it looks like there is more work to be done.

I measured the base of the bottom cut on the seat and there is a 92 percent bowl to valve ratio. Below the bottom cut the bowl diameter gets smaller as it tapers down.

How much should I blend the bowl before I go to far and have to weld the head?

I also have a question about the port angle. The roof has a steep angle from the start of the short turn to the bowl. There is plenty of room to raise the entry by .100 or more and blend down to make the transition more smooth. I would add epoxy to the floor to compensate for the taller roof.

Is it worth it to do that? I think that it may help downdraft but have been told that port entry doesn't make a big difference. I'm going to cut and weld an intake manifold anyway. I could angle mill the flange to get it to match the port angle.

Don't blend the angle on the intake valve job. radius valve seat on exhaust.

Blend it!

The harder you blend into the 3rd cut, the more low lift flow will leave and the more the high flow will gain.

Blending is part of a good valve job.

cspeier wrote: ↑Thu Nov 02, 2017 7:18 pm Blend it!

The harder you blend into the 3rd cut, the more low lift flow will leave and the more the high flow will gain.

Blending is part of a good valve job.

Let the flaming begin. Most guys I know lose sleep, won't eat, beat their dog and do other malicious things when the lose a bit of low lift flow. I almost never get excited if I lose some low lift and and the mid and high lift goes up. Especially if it helps reverse flow.

I think I would find a flow bench an start doing some testing before I started blending an grinding anything that cannot be replaced.
Mitch

mitch wrote: ↑Thu Nov 02, 2017 7:48 pm I think I would find a flow bench an start doing some testing before I started blending an grinding anything that cannot be replaced.
Mitch

Without a doubt. I'm almost done building one and will not do anything without flowing first. I'm going to do a little at a time and check each change before doing any more.

cspeier wrote: ↑Thu Nov 02, 2017 7:18 pm Blend it!

The harder you blend into the 3rd cut, the more low lift flow will leave and the more the high flow will gain.

Blending is part of a good valve job.

I know that you're a very respected port developer and I thank you for the advice. Would you be concerned about the ratio being 92% of the valve right now?

steve316 wrote: ↑Thu Nov 02, 2017 7:04 pm Don't blend the angle on the intake valve job. radius valve seat on exhaust.

I was only going to blend under where the cutter went into the bowl. It was started but it looks like it needs some fine tuning. The bowl is not round. The side walls are almost straight in all the bowls. I plan on leaving them like that and just blending the front part of the bowl where the cutter dug in.

I'm concerned about taking to much material out. I don't know how far I should go down to taper the cut.

It has to be pretty solid there. The seat was bored out to its OD as deep as your lip is and that didn't go through.

fordified wrote: ↑Thu Nov 02, 2017 8:21 pm

cspeier wrote: ↑Thu Nov 02, 2017 7:18 pm Blend it!

The harder you blend into the 3rd cut, the more low lift flow will leave and the more the high flow will gain.

Blending is part of a good valve job.

I know that you're a very respected port developer and I thank you for the advice. Would you be concerned about the ratio being 92% of the valve right now?

Not at all. Two things. One, it's a 315 so RPM is your friend. And two, that is a reason your go with a 55 degree anyway.

The problem is it stalling early in the flow curve/

cgarb wrote: ↑Thu Nov 02, 2017 8:59 pm It has to be pretty solid there. The seat was bored out to its OD as deep as your lip is and that didn't go through.

I'm going to sonic check it but I think it is pretty thick.

cspeier wrote: ↑Thu Nov 02, 2017 9:26 pm

fordified wrote: ↑Thu Nov 02, 2017 8:21 pm

cspeier wrote: ↑Thu Nov 02, 2017 7:18 pm Blend it!

The harder you blend into the 3rd cut, the more low lift flow will leave and the more the high flow will gain.

Blending is part of a good valve job.

I know that you're a very respected port developer and I thank you for the advice. Would you be concerned about the ratio being 92% of the valve right now?

Not at all. Two things. One, it's a 315 so RPM is your friend. And two, that is a reason your go with a 55 degree anyway.

The problem is it stalling early in the flow curve/

Thank you again. I'm going to take my time and post up my progress.

Do you have any pointers about the port entry that you would be willing to give? There's a lot of room to raise the port and fill the floor some more. The angle on the roof from the short side to the bowl is pretty steep and I don't know if raising the roof will help any. Seems logical to me to make it as straight a shot as possible and just follow the angle into the manifold right to the plenum.

I would not do a thing without the aid of a flow bench , but not for air flow concerns at first , but to first get a base line on the port velocity you have now with the Manifold you will be running bolted on.

You do not want a radius valve job on the Intake side, although they flow more air at times the lack of defended angles do not shread balled up wet fuel flow back into the air stream!

The Intake seat angles are many times even in wedge type chambers your last chance to atomize the fuel, and in a Hemi forget about using the chamber shape to do that!