Port velocities

[maxracesoftware]

[larrycavan]

Larry,

What's your take on how to handle situations where there is no shurt turn height? I mean it's turn and righ to valve seat within .200"....

[106-1194218389]

Larry M.,

I think I unloaded the .550 lift again. I did unshroud the intake some in the chamber and it picked up a little from .050 to .500 but .550 dropped 20 cfm but is still better than it was originally. .600 and up it helped 2 - 3 cfm. I am going to play with the SSR some more thanks.

John

[maxracesoftware]

[106-1194218389]

Larry M.,
I laid the SSR back some more, not near the seat but closer to the top and I lowered the APEX height about .015 to .020" and it helped flow above .500" gained a couple but .550" up gained at least 10 cfm. I'll inch up on it. I am going to try raising the roof just a little and see what that will do. Everything you have suggested works. I am just going to ET bracket with these heads so I do not have to worry about class. I am getting really close to where I want to be. I am using Performance Trends Port Flow Analyzer software with their Black Box hooked up and it keeps track of some good stuff. One thing I like is it tracks stability of the port at each lift. It gives you a reading of depression bounce in percentage. So if you are flowing at 10" and have a 10% reading your depression is bouncing 1", let's say between 9.5 and 10.5". This seems to be a pretty good indication of turbulence. I am flowing at 6" and my average stability reading is under 1% usually aroun .7 -.5. Although .550" gained 10 cfm it's stability also jumped to 5.75% and the other lifts above .550" are around 1.7% and you can hear the port popping a little. Not as bad as some I have heard but still getting turbulence and separation.

[maxracesoftware]

back in Ancient Time,
when the best SBC Head out there was the #292 Turbo
casting .... that Head had a lower Short Turn Apex Height
and plenty enough metall in Chamber wall thickness to
lay back the Chamber wall if you wanted to,
sort of like a #990 BBC open-chamber look !

Porting Shops like Tim Cole/MadCap Racing use to lay
back that Chamber wall to its maximum.
it made it Flow everywhere because it worked with
the relatively low STPH,
and it had a ton of Swirl in that configuration !

Later GM/Chevy designed and came out with the newer
#034 Cast-Iron Bowtie Head.

This Head had a longer internal CenterLine Length than the 292

it also had a much higher STPH
(Short Turn Peak Height) above the Deck surface
it had no waterjacket above the Intake Ports
it also had smaller exhaust Ports

Here's where the Problems came in !!!! =>

All the HeadPorters were used to Porting the older
#292's #461's #462's , ETC.
with their lower Short Turns.
When they tried to Port the #034's the same way,
they were stopped by a few things GM-Chevy did=>

they could'nt get the Flow Numbers as good at first as the 292
so it turned some of them off.

then they couldn't lay back the Chamber Walls like they used
to because the waterjacket was so close, and besides,
when they did lay back the Chamber Wall it would hurt Flow
Numbers most times .

This was because GM-Chevy was using the
tighter Chamber Wall to keep pressure on the Short Turn,
(keep the LOAD on the Short Turn),
trying to force the Flow to use the entire Valve circumference
to flow from.

The next problems were since the Short Turn Peak was now
higher..the STPH were likewise faster causing Choke/Separation
on hi rpm Engines with hi lift Cams.
it looked good on a FlowBench, but wouldn't make the
HP Numbers...along with too much FPS at the Pushrods.

They couldn't also enlarge the Exh Ports like they were use to
because GM was trying to force them to think smaller Exh ports


Here's what i did=>

i made a Custom Caliper set at .080" thickness,
raised the entire Roof until it was .080 to .100 thick,
took the Load off the STP,
widened the STP CSA to slow the FPS,
laid back the Short Turn maxing it out,
used other Custom Calipers to measure Chamber wall thickness
so i could unshroud for the 2.085" Int Valve ( 1.585 Exh Valve),
widedned the pushrod area as much as i could without
breaking thru , or widening with Welding.
thinned the Port pair center divider all the way to the
common HeadBolt Hole,...pressed in a Tube into the
HeadBolt hole so i could max out the center divider more
and use the pressed in Tube to help steer the Flow
when it was around .500 to .650 Lift....that gain as
much as 3-4 percent flow in that Lift range with that Trick.

when it was done, the #034 Flowed 315's CFM

one of the #034 Heads i had Ported for a C/ED Racer
made its way into hands of legendary SS Racer
Bobby Warren


Bobby called me up out of the blue one day about
25 years ago...and told me he never saw at Bowtie Head
flow so much air ....the conversation was going
very nicely until i said i now had better flowing Heads than
that one ...around the mid 320's ...the phone went silent,
and i had to actually ask are you still there ?
..he replied yes, and that ended the conversation.
never heard anything from him again,
i guess he thought i was joking or lying ??
thats the first and last time i talked to him .
thats one of the strangest abrupt conversations i've had

so jfholm.. keep on trying things..but i'd advise you to test
them all on some junk Heads first !!!

one more thing about the #034 deal,
was at 320's CFM with unwelded pushrod area,
the FPS speed was way too high,
so that Head at 320's CFM would have made no more HP
than if it flowed 300 or 310 CFM.

[larrycavan]

Larry,

In heads where camshafts in the .400 to .488" lift range are to be used, how crucial is the short turn as compared to situations where the approach is to use cams in excess of .500" lift?

Lets use and example with an LD ratio of .294 - .325

That's a .417 lift cam with a 36mm intake [.294] and a .460 lift cam with same valve [.325]
The convergance lift is .354"

2 Valve / Hemi Chamber

This would also be a relatively no short turn height arrangement.



Edited By larrycavan on 1206976691

[maxracesoftware]

[larrycavan]

[106-1194218389]

This rough drawing is what I have been doing to my heads. The black lines are the original port and the thinner dark red lines are a rough representation of what I have done. I will try and upload some photos in a day or two.

John

[B]Sorry I don't know where the link to upload photos went so I could not do it.

[bruce]

Don't use the "Quick Reply" box use the button, it has the upload box

[106-1194218389]

Bruce that is what I do and I have been able to add images in the past but I am not seeing link to do it anymore. I did use add reply. The upload box is missing on my screen now. I tried logging off and logging back on and still no upload box

Thanks
John

[106-1194218389]

Bruce,
I checked some of the other threads, (subjects) and the ability is there for me to upload photos. It is just this subject that I do not see it in.

Thanks,
John

[bruce]

I had it turned off in the admin, should work now sorry bout that

[maxracesoftware]

the Brown Line is an example of what i call
"Laying Back the Short Turn"

the Black Line will make a little more very low RPM TQ,
most times where you won't use it or need it in Racing

the Brown line may or might not hurt Peak TQ,
tends to increase mid to high lift flow numbers, and
tends to shift the Power Curve higher.