Anyone ever flow bench verified the benefit of notched bore?

[CantedTexan]

I wish I had time to give you hard data based upon 351C heads. I plan to flow: a no-notch block, a factory notched block, and what I do which is notch within reason of what the head gasket allows.

A factory notched 4V block bored .030 renders a tremendous amount of factory notch remaining.......on intake and exhaust. As the bore increases from .030 over, the notching begins to go away noticeably in increments as fine as .010.

I have been building Clevelands and Boss 302's since 1972.

I have never seen factory notches disappear with a .........030 overbore!

My.....OPINION.....Notch the crap out of it.....until cylinder sealing, gasket restraints, and compression compromises are reached.



Quote: "One of my impressive attributes is that.....a lot of people don't like me.....or the horse I rode in on"

[Bob Hollinshead]

Is it better to machine cut a notch like the high performance BBC or just do a 45 degree eyebrow by hand with a file or burr bit? Anyone seen Vizard's new Bigblock book that supposedly has a lot of this info in it?

[MadBill]

He discusses it in detail but as far as the actual process, just says to scribe the block to the gasket fire ring contour and grind from there down to 1/16" above the upper limit of ring travel.

[wyrmrider]

gasket bore is too big
combustion chamber
for the MOPAR I have stainless shim gaskets for the 361 and 413 (4 3/16 bore) trucks
they scribe about right for an open chamber or 915 closed chamber 440 head

[BradH]

For anyone who has flow-tested the standard vs. notched bore, I'd be interested to know if the flow improvement was seen across the entire lift curve, or only in a certain range.

I had the same two heads flowed on a friend's bench using the same bore adapter size as mine -- only as I recall his had a notch for intake valve clearance added -- and his #s for both heads were higher in the .200-.300" range (maybe a tad higher?), but basically the same at lower and higher (.500"+) lifts. I always wondered if that was due to different benches & calibration, or because of his adapter...

[zums]

For anyone who has flow-tested the standard vs. notched bore, I'd be interested to know if the flow improvement was seen across the entire lift curve, or only in a certain range.

I had the same two heads flowed on a friend's bench using the same bore adapter size as mine -- only as I recall his had a notch for intake valve clearance added -- and his #s for both heads were higher in the .200-.300" range (maybe a tad higher?), but basically the same at lower and higher (.500"+) lifts. I always wondered if that was due to different benches & calibration, or because of his adapter...

There will ALWAYS be a difference between even identical bench,s take your friends adapter and try it on your bench

[Adger Smith]

For the fun of it flow a head with a 4.44 chamber size on a 4.625 flow adapter and then on a 4.5. It is interesting where the numbers pick up on the big adapter and fall back. Did those tests a long time ago. Never put a head that hangs more than about .060 over in the bore on the intake side. If the head is bigger than the bore, notch it. I had a SS NHRA engine pick up both MPH and ET by that change and one other small change(oil pump)