Don Terrill’s Speed-Talk

Was doing some work tonight on Hemi and noticed the intake valve almost rides against the top of cylinder. Theres room for lower the eyebrow already there. Can not move ouward due to oring groove. I know theres flow to be gained.How much? Wondering if any have worked in this area reguardless of engine design I would like to here your results and thoughts.

A hemi typically does not have problems there. The valve angle and chamber shape allow the valve to move away from the walls as it opens toward the middle of the chamber and cylinder.
We use a small hemi engine, with a 3.4" bore size, and we have on occasion used a 2" valve in it, and achieved 308 cfm flow at 28" with a 1.767" MCSA upstream.
Ours also appears like the valve is right up against the bottom edge of the chamber, but it does not really shroud the flow like you might suspect.

Not a issue with a Hemi, but on a parallel valve motor it is! in fact in acting that mod may only sever to make for more reversion back up the Intake runner at overlap and then also effecting the amount of initial super charging that takes place at overlap!

mag2555 wrote:Not a issue with a Hemi, but on a parallel valve motor it is! in fact in acting that mod may only sever to make for more reversion back up the Intake runner at overlap and then also effecting the amount of initial super charging that takes place at overlap!

Mag2555,

Do you have any data for your assumptions concerning the enactment of this procedure?

With canted / poly angle valve arrangements utilized in 351C/Boss 302, 385 Ford series, BBC, and Hemi's........enough engines should have been built.......by enough sharp guys.....and testing of all conceivable situations...... should have by this time rendered conclusive facts.

Since the valve will open and move away from the outer borders of the chamber......using your same assumptions......would it also be a performance boo boo .....to unshroud the chamber borders closest to the valves? .....Would this also invite intake reversion during overlap?

Do these facts exist?

If they do.....I'm all ears concerning the detrimental effects to low lift flow and or.....intake reversion enhancement.

Where do we stop following this trail backwards? As we continue up the intake track do we need to develop seat characteristics that stress anti-reversion blockades?.....How about bowl designs while porting?.......


This is an interesting thread.......Has anyone actually beat this water till it foamed?




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

wideopen231 wrote:Was doing some work tonight on hemi and noticed the intake valve almost rides against the top of cylinder. There's room for lower the eyebrow already there. Can not move outward due to o-ring groove. I know there's flow to be gained. How much? Wondering if any have worked in this area regardless of engine design I would like to hear your results and thoughts.

mag2555 wrote:Not a issue with a hemi, but on a parallel valve motor it is! In fact enacting that mod may only serve to make for more reversion back up the intake runner at overlap and then also effecting the amount of initial supercharging that takes place at overlap!

Pretty broad statement which doesn't differentiate between stock, street, full race, cam timing, intake or header characteristics.

Several OEM engines have cylinder bore notches such as the one mentioned here and presumably the engineers found more positive than negatives to spend the machine time to put them there.

Just as some engines with some cam timing show an anti-reversion benefit from intake manifold smaller or header larger than the port served, many show no benefit, many show negative results.

Bottom line - it ain't that simple and while the +/- in enlarging/lowering the eyebrow in the cylinder is likely to be a yes/no/maybe, it depends.

mag2555 wrote:Not a issue with a Hemi, but on a parallel valve motor it is! in fact in acting that mod may only sever to make for more reversion back up the Intake runner at overlap and then also effecting the amount of initial super charging that takes place at overlap!

wouldn't you take the extra flow by relieving the cyl wall and minimize any reversion by screwing around with the o/l ?

Not saying there is huge gain here.Small gains make huge gains when added together. If I can push valve enough to drag cylinder (guides are not bad) there has to be a henderance to flow at that point.All of this done with head bolted down and no piston looking thru bottom. Pistons valve pocket sits appr. .165 below eyebrow in cylinder. 12.8:1 motor 13.2 with thinner gasket. My thought is lowering bottome edge of cut to where it is even with top of valve pocket.Can only remove about .040 to .050 at top due to o-ring groove. It occours from .110 off set to .230. Thats .120 of movement that it is almost touching and in all honseting almost the whole movement from seat to .250 before its actually fully open around the valve.Hard to believe its not hurting low lift flow.

Best thing would be ABA test.Pretty sure its easy to see difficulty in getting that done. May have to retool my homemade flow bench and test with old sleeve sitting agianst head using o-ring to center it and see if it shows much improvement. Man superflow would be nice.

On subject of others building these motors.No chance someone found same thing and figured hey I'll keep this to myself.Not exactly earthing shaking thing just a observation from a overly curious gearhead.

My bad on no specs. 4.250 bore with 2.375 intake.BAE fuel style heads.Cylinders have edge protruding into chamber but only on intake side.These heads also have a extra outter stud and dowel.Im wondering if they are shifted upward any. Seems unlikely with the number of studs.

4.190 valve .100 off seat more extreem than 4.25 bore but helps demonstrate what i was talking about.
4.310 .100 off seat.Not best pics but best one I had comeout. still gives idea how close valve is at .100 not lot better at .200 at cylinder

What is the valve stem angle on this engine?

would have to check to be sure.Same as factory engine these are early billet heads that where same except made of billet with larger valves.

wideopen231 wrote:would have to check to be sure.Same as factory engine these are early billet heads that where same except made of billet with larger valves.

The reason why I ask is that if it doesn't have a 45-degree valve angle(90 degree included angle), or somewhere near to that, like 40(80 included angle), then it isn't really a hemi and doesn't conform to the hemi non-shrouding discussion above. With a 45 degree valve angle, the valve moves equally away from the bore or walls as it opens, so no shrouding, typically.
I don't know the application, but from the appearance in the picture, it looks like you have too much intake valve in there for that bore. If you feel you must run an intake valve that overlaps the outside of the bore, maybe cutting the eyebrow is the solution.

Is a hemi.Just has all aftermarket parts. Its not a feel the need to run big valve thing.This is standard TA/FC,TA/D setup.If was BAE fat heads this would be less of issue since intake is laid over quite a bit. This combo has been 5.68 at 264 in 1/4 and that was 15 years ago. Valve will clear cylinder with gasket intalled. reason for post was for info on unshrouding valve for first .200 lift.It was not a issue with blower pushing 44 lbs of boost. Now using as NA motor and looking for anything extra. Opening eyebrow cut is possible. But only by opening it downward in center,still limited.Outward can not be done. Was wondering what gains with .030 or so more opening at that point and maybe little sooner would be possibly worth.Just have to check few piston combos to make sure not to grind to far down and mess cylinders up for other combo's I might want to switch to later.

As for pics.Its hard to get detail due to angle shooting down the sleeve. Cut away would be better.Not cutting 5500 set of heads for good pic.First pic is with a 4.190 and second is with 4.310 to demonstrat how much differance. Combo is 4.250 bores so its middle ground.

DO IT.

There aren't engines that come factory with this for no reason.

Maybe cut a small notch and radius the top edge there a little. The radius may help the air roll over there better. I don't see where it would hurt as long as it don't get into the top ring land.