Don Terrill’s Speed-Talk

Friend sent me his to just tune em up some nothing crazy

Numbers picked up nicely everywhere esp .400 and under picke up from .500-550 then stalled which I expected. gains were minimal
Stock AFR valve job

Wanted to keep the head small-
When going for more from .500 up & carry a little further what do you recommend withotu losing downstairs..guy was stuck on .400 and less getting most the work
Havent poured them but doubt if theres 3cc material removed

Share your thoughts, have an idea thought Id pick your brains.

How much valve lift is he running and how much spare rear gear does he have power band wise?

His average power will be strongly tied to his Heads air flow at a average 1/2 lift point.

If your air flow numbers are not backing up at high lift then your port area before the short turn and valve bowl are handling the velocity of the air mass passing thru them.

You did not state what the Heads current valve to bowl Throat percentage is , but if you make that let's say .040" bigger in diameter and the high lift flow does not pick up then your restriction is the port area at the start of the short turn.

If you do some bowl enlargement do not reduce the depth of the valve job bottom cut so your current low lift numbers will not drop off.
If you pick up higher lift flow and the numbers up there drop off instead of level off then you will need to lay back the short turn some from the mid point of the short turn on up to the crown of the short turn.

with where you are now I would confirm by flow testing the guys Manifold bolted to the Heads that it's not a choke point at his valve lift.

Was hoping youd pipe in mag
intake is a heavily ported superram, being bolted on the head today then reflowed just to see where things lie;its close to 290cfm now
Has a Jones cam, dont have the specs offhand. 1990 C4 6 spd 3.33 gear for now, that may change
Prior motor was a 383 with a 232ish HR jones cam stock 1040s, stock superram ;415hp 450tq to the tire

About 2 yrs ago did a set of old 190s which wound up almost identical (after one of Mamos valve jobs) with the 1040 head#s poured 193cc ..superram was 272cfm. 0 loss whern bolted together save for 2 cyls;one was down 1cfm, another 3 so called it a day;hoping this ones a little better. Not reaching for the sky

Amateur hour here dig this stuff though.

When you say it stalled above .5-.55" lift do you mean it gained no more flow above that, that it lost flow above that or that it gained but not much?

Gained but not much is okish, the other 2 indicate that the air is detatching from the turn & going turbulent (something I see all the time with AFR heads).

How's it sound above .550" - does the note change & become more harsh?

It's normal for a bit of a drop off in flow gain at the lift where curtain area = valve area, which is usually around .500-.550" lift, but you want it to recover & start gaining at a good rate again, if you look at the gain in .050" increments below the convergence point will it give you a hint as to how much the flow gain should recover after convergence.
If it does not recover after convergence you have a problem!

You want to see significant flow gains to *at least* .100" past the peak lift to be used, preferable .200", above that it's nice for it to keep gaining in smaller increments, but not always possible.

If you have stability issues below .100" past peak lift it will hurt power, improving stability even at the expense of flow where you think you need it will show gains on a running motor. The head can flow amazing numbers at .400" lift, but if flow becomes unstable at .550" & you're lifting the valve to .500-.600" then it's going to be a dog & not show the HP the flow figures make you think it should.
If you have to trade 20cfm at .400" lift in order to keep the port stable at .600" then you do it & don't look back. Yes I know it can hurt to look at lower flow figures, but learn to deal with it!

PS - many aftermarket heads (including AFR) have short turns that are too 'soft' with minimal layback, they do this to improve flow figures at lower lift, coz that's what the public thinks they want, then they just lie about higher lift figures.
It's also near impossible to cast or CNC cut a 23 deg chev head with the 'right' short turn accurately enough to be stable with mass production equipment. Hand finishing is often required to make them what they should be.

Until you get it out of your head that you need the low lift to stay, when trying to get it to not stall and go up stairs, YOU WILL NEVER make real power. Sorry to blunt, but, I am flat out am telling you, low lift flow DOES NOT gain low end torque, and everything you do to gain low lift flow, hurts the dynamics of the head that makes real power. I don't care who is telling you otherwise, you simply won't. Cut the appropriate seat, work the port and short turn the way it needs to be to make power, don't mess up the chamber by "unshrouding" to the limits, and you WILL lose low lift flow, period, end of story, and you will make more power. The low lift flow ends up what it is. under .300, not really important, even on lower lift stuff. Not saying you should kill it on purpose but, the things that actually make power, will lose low lift flow.

WHAT ???

LOW LIFT FLOW.. is....what?...... But, but, but I read somewhere that ?.. low lift flow,...but un-shrouding?,...and well uh ???? REALLY ??? You can't be serious !! ???

Come on you guys,......I suppose your gonna tell me Santa ain't real either ???

Randy

Another TRUE STORY-- A friend of mine got a Super Flow 600 bench, He spent about 100 hours reworking his already good heads, He was able to increase the high lift full very nicely, by about 30 CFM, BUT, he hurt the lower lift flow pretty bad. Even though he gained 30 CFM at 800 lift, his car was NO FASTER AT ALL ! This tells m,e there must be something to low and mid lift flow importance




JOE SHERMAN RACING

There is hope. Randy finally found another, he's no longer alone. There may be more out there.
What is this? The X-Files: "I Want To Believe"

bigjoe1 wrote:Another TRUE STORY-- A friend of mine got a Super Flow 600 bench, He spent about 100 hours reworking his already good heads, He was able to increase the high lift full very nicely, by about 30 CFM, BUT, he hurt the lower lift flow pretty bad. Even though he gained 30 CFM at 800 lift, his car was NO FASTER AT ALL ! This tells m,e there must be something to low and mid lift flow importance

JOE SHERMAN RACING

Or he made the port TOO BIG for the engine and or stall/rpm range.

Rick

Frankshaft wrote:Until you get it out of your head that you need the low lift to stay, when trying to get it to not stall and go up stairs, YOU WILL NEVER make real power. Sorry to blunt, but, I am flat out am telling you, low lift flow DOES NOT gain low end torque, and everything you do to gain low lift flow, hurts the dynamics of the head that makes real power. I don't care who is telling you otherwise, you simply won't. Cut the appropriate seat, work the port and short turn the way it needs to be to make power, don't mess up the chamber by "unshrouding" to the limits, and you WILL lose low lift flow, period, end of story, and you will make more power. The low lift flow ends up what it is. under .300, not really important, even on lower lift stuff. Not saying you should kill it on purpose but, the things that actually make power, will lose low lift flow.

Rick

You need a certain minimum amount of low lift Intake And exh flow to use the Cams overlap period to create as big a VE number as you can if the heads and or Intake Manifold on motor your dealing with is the choke.

If you have excess port area , and air flow that's not being tapped into and a narrow 1500 rpm wide power band , then poor low lift flow will not make much difference!

Mag, I didn't say you need zero low lift flow. The head is always going to flow something there. Like I said, it ends up flowing what it flows there. Bigjoe, your example of your friend, that gained 30 cfm up top and lost low lift, and the car went no faster, I am guessing he made no other change to take advantage of the new airflow/ port area. And, the engine was obviously using all the air it needed before and after the mods, lucky he didn't slow down. Just because a head flows 320, 240, 450 cfm, etc etc, doesn't mean the engine is using all that available air. It takes what it wants.

The .500 # was stronger than it was, held it to .550 didnt bother with any more you could hear the port wasnt liking it
I hear your agruemnts on both sides, know what I need to do now. Max rpm 6500 intakes done around 6ish
Owner is well aware not to pa much attention to # and may lose....heck they were off so why not type thing(doesnt expect much)
his intake will run out of steam before the cam/heads will

What did you do to "tune them up"? Also, how did they do on your bench compared to the flowz listed on AFR's website?

Just curious here. I'm considering a set for a 406 street/tow build.