At some point I'm going to be grinding on a new pair of heads that are cast significantly undersize in the bowls, especially the intakes. I have a "done" set that I can use for reference measurements, but was also wondering if there any target #s (e.g., % of valve diam) that people use as a basic guideline.
Also... how big is "too big"? Is there is a typical indicator(s?) of having gone too big in the intake bowl (other than having broken through into the water jacket )?
Maybe this is always a trial-and-error effort that varies w/ the specific casting being worked on. Regardless, I wanted to ask. Thanks - Brad
The valve job SHOULD establish the bowl diameter. Ad a rough guideline, 87-88% for a 45, 92-94% for a 50 and over 94% a 55 or steeper. I've heard there are some 58 and even 60 degree valve jobs out there, but I haven't seen them.
As of late I've been researching the Newen Epoch and the Serdi equivelent. Was going to go to PRI but that didn't happen.
I'm a big fan of any single point cutting system for many reasons.
Just to clarify, I’m pretty sure Brad is asking about the “bowl” diameter...... not the “throat” diameter.
Much of the cnc stuff I’ve seen in the last several years has the bowl diameter at right about 100% of the valve diameter on the intake side.
I’m not saying that’s right or wrong, just what I have measured.
With heads like what he is working with, where the as cast bowl diameter is sitting at about 80% of the valve diameter, at some point you have to wonder how far can you go before you’ve comprised the casting?
I do have measurements from the CNC'd heads, as well as the heads I'm getting ready to reassemble and the Procomp clone "crash test dummy" that has the 3 test ports. I'll pull together all the data for my next post.
After thinking about it, the problem with that comparison is that the PC heads and the CNC head started out with much bigger bowls to begin with.
So, to end up with bowls the size of your hand ported version....... you would have to remove way less material to get there.
My guess is you’ll find the CNC heads you had will be very close to 100% of the valve diameter.
Any notes on what size the PC head bowl diameter was as cast?
Tell us about the engine, car, usage, HP goals, intended rpm range, cam, etc.
I find too many people blow out the bowls far too much, you get a wider power curve & more below peak with smaller bowls.
Larger bowls flow more on the bench, but fail when it comes to velocity ram.
KnightEngines wrote: ↑Tue Dec 17, 2019 7:12 pm
Tell us about the engine, car, usage, HP goals, intended rpm range, cam, etc.
I find too many people blow out the bowls far too much, you get a wider power curve & more below peak with smaller bowls.
Larger bowls flow more on the bench, but fail when it comes to velocity ram.
What Tony is saying makes sense to me, I can see the bowl area being an extension of the throat to speed up air/fuel after slowing down over the SSR, velocity through the valve seats and the best cfm/in2 as possible, I can see how steeper seat angles can help C/D through the venturi area.
SpeierRacingHeads wrote: ↑Tue Dec 17, 2019 8:19 pm
I like big bowls. I have one 23 degree CNC head that has a 2.200 wide bowl.
The mistake I see is they put a big bowl in a head AND a big throat.
Is there a % you use for your ssr/ bowl width to throat % or is it velocity gradients through that area??
Have to determine area/cc in the bowl area as well not just width.
Thinking out loud hear
SpeierRacingHeads wrote: ↑Tue Dec 17, 2019 8:19 pm
I like big bowls. I have one 23 degree CNC head that has a 2.200 wide bowl.
The mistake I see is they put a big bowl in a head AND a big throat.
Exactly why I said we need more info!
If it's a bigger cube drag racing engine that'll turn pretty hard then big bowls will be required.
But if it's a 350 cube streeter with a manual trans smaller bowls will be a bunch nicer.
I have read somewhere that a big bowl acts as a storage area for the positive waves coming down the port [DM I think], also I think it was larry M that said the bowl needs to be around the diameter of the valve [along the head] This has always worked for me.
I don;t know if this helps any. But I ask a guy to put 2.19 valves in place of my 2.06 and he said it was a waste of money if you did not bowl hog under the seat. So I did not do it. He said he did not have the tool to bowl hog. Not my greatest knowledge on these things. I am sure Chad Spier could tell you what to do. Its his expertise.
PRH wrote: ↑Tue Dec 17, 2019 4:52 pm
Just to clarify, I’m pretty sure Brad is asking about the “bowl” diameter...... not the “throat” diameter.
Much of the cnc stuff I’ve seen in the last several years has the bowl diameter at right about 100% of the valve diameter on the intake side.
I’m not saying that’s right or wrong, just what I have measured.
With heads like what he is working with, where the as cast bowl diameter is sitting at about 80% of the valve diameter, at some point you have to wonder how far can you go before you’ve comprised the casting?
Good catch...I was running full speed while still in the recliner!!!
I can post links to other threads that go into more details about the car, engine, etc. The quick overview is that it's a 3800# (with driver) street/strip car powered by a 452 ci BB Mopar. Old engine made a bit over 600 HP and the car ran mid-to-high 10s. New combination picked up 60+ HP with better heads and switching from .600" sft to .650" solid roller with same basic 266 at .050 duration and same 108 LSA.
Engine now has Edelbrock Victor heads with standard port size and 2.20" intakes. Measurements of max bowl diameter of same type of head, or a Procomp clone, prepped by different people / shops for reference to my original question. All the ported runners flow in the 340-360 range with MCSA of 2.6+" to about 2.8", and average CSA of 2.7" to 2.9". The port with the largest CSAs was not the best in terms of peak or average flow as tested up to .750" lift.
Procomp unported - 1.96"
Procomp ported by me - 2.04"
Procomp ported by PRH - 2.07"
CNC Victor from shop that specializes in Mopar (largest runner checked) - 2.05"
Latest version of Victor unported - 1.89"
Latest version of Victor ported by PRH - 2.07"
What I have in mind is to do the next set with more emphasis on stable high-lift flow, even if there is some tradeoff in low(er) lift. I was thinking this would be complimented by a cam of similar duration that had closer to .700" lift.
Last edited by BradH on Sat Dec 21, 2019 2:34 am, edited 1 time in total.
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