08/25/2026
We have been porting and flowing cylinder heads for over 45 years.
"We have learned a thing or two, because we have blown up a thing or two".
We built heads based on religious flow bench results. The bench "asked" that we build a big radius short turn, so that the flow would "stay attached to the short turn radius".
This action produced nice "quiet" flow and did flow 30 cfm more on a 300 cfm port. We were so excited to get this head back on the engine dyno and see the power gained.
But we were very disappointed with the results!! We were down at least 20 hp on a 300 hp engine (4 cylinder). We were so confused.
I decided to to pull the induction system off to look in and see if I could see what was going on. First thing I noticed was that much of the back of the valve and the cylinder wall, when the valve was open, was blocked from view, because of the nice big gentle radiused hump in the floor, over the short turn.
In my typical GB3 fashion, l decided to mow the hump right out of there, right then and there!
So we put a little air psi into the spark plug hole, stuck a small vacuum cleaner hose into the intake port, and with a 4 inch long burr, and we mowed all four floors out in an hour at the most, right on the dyno, with head bolted on the engine.
We cleaned up and fired it back up and gained all the power back and a couple more...So, I said, the flow bench cant be wrong....cant be. Let’s look again!
I decided we needed more cross section, with the big high flowing hump back installed. We used the green Marine repair epoxy.
We removed the head and carefully rebuilt the nice gentle short turn radius back to its high flowing stature.
Then we raised the roof and opened up the port above the hump, beside the guides and guide runners to regain the same cross section we had with the big power, hump removed, version.
Down 25 HP!!!!!!!!!!!!
Disgusted and defeated, I pulled the induction and looked in the ports again. There it was again, blocked view of the back of the valve and very little cylinder wall cross hatch to be seen..
SO, we MOWED it all out again!!!!! Right on the engine, right on the dyno. I was sure we had ruined a great performing cylinder head. I am certain we had successfully ended any ability to enhance production output in my shop for a few days.
With a new clear view into the cylinder, we ran the engine again and we gained all the power back, AGAIN.
After this experience and for sure wrecking the velocity producing potential of the head, we learned a lot!
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Take this story, experience, this opinion and share your thoughts and comments please.
We still like to see into the cylinder to win and set records, regardless of "test bench" results.
"If it was easy, it would be in a box, for sale, on the shelf at Walmart."
"I know enough to know I dont know enough."
StarRacing.com
P.S. Just so you know. This cylinder head has a 2.75 intake valve and it flows on the flow bench. (1020) over 650 CFM and it feeds a 5.144 bore.
