[NBF823]

Interesting. I was expecting higher numbers also. Guess that can sort of teach me just how much the valve size can matter.

I know that most of these heads ran with a blower. Just out of curiosity, of the Hemi, and chamber/port designs in general. I won't be upset if nobody awnsers, but I got a rare opportunity here to get a motor man's opinion of the hemi. So;

Do you think the hemi head design would promote better scavanging in the overlap to the point where a wedge head with similar flow numbers would make less power on a running motor?

With a lack of a quench, and the port being so straight, would much be lost due to the lack of a quench area on an N/A gas combo?

Do you also think that would cause more reversion problems in a motor that saw time out side of it's peak power range?

[BruceWilkie]

Originally Posted by NBF823

Interesting. I was expecting higher numbers also. Guess that can sort of teach me just how much the valve size can matter.

I know that most of these heads ran with a blower. Just out of curiosity, of the Hemi, and chamber/port designs in general. I won't be upset if nobody awnsers, but I got a rare opportunity here to get a motor man's opinion of the hemi. So;

Do you think the hemi head design would promote better scavanging in the overlap to the point where a wedge head with similar flow numbers would make less power on a running motor?

Scavenging is dependent on lower lift flows and the headers and proper cam timing. You cant move the intake charge until pressure in the cylinder is lower than the intake pressure. If the exhaust timing is correct the high pressure wave from back when the ex valve first opens will be somewhere down the pipe. Behind this high pressure wave is a lower pressure which when it becomes less than manifold pressure allows the intake charge to begin moving into the cylinder and purging the chamber before the piston starts downward. This occurs even in a mild driver style motor and can be enhanced with header and manifold tuning.

With a lack of a quench, and the port being so straight, would much be lost due to the lack of a quench area on an N/A gas combo?

Depends on how well the mixture disburses as it leaves the intake valve. Mopars Hemi's liked a bunch of advance NA but they still ran good.

Do you also think that would cause more reversion problems in a motor that saw time out side of it's peak power range?

Reversion is more related to the intake closing event(far too early) and poor exhaust timing(open too late)/intake timing(open too soon)

[Jack Gifford]

Originally Posted by Jim Robertson

... turbulence that could in all likelihood be "tuned" with a bit of work around the seats...

I'll be talking to you in that regard, Jim...

On the data sheet- I assume the next-to-last column is the flow at pressure differentials greater than 28" of water (44.25" & 42.2")? If so- why wouldn't turbulence have a greater effect on these numbers?

[Jim Robertson]

Jack,
Yes to the first question

And I think I understand your 2nd question...
The flowbench software reports the blower capacity...in other words with the fan motors operating at 100% blower capacity I read a pressure differential of 44.25 and 42.2 respectively. Turbulence was noted as a surging or slightly non-steady sound and probably hurt the hemi's flow 5-8%. My reasonably good dports flowing in the 280-285 range will flow 390 - 400cfm at 100% blower capacity with a smoother "sound". Its all subjective but flowing enough restrictive heads (Pontiac's) a trend has begun to take shape, in my feeble mind at least. It is interesting at least to me, that most iron Pontiac heads (Ram Air Vs excluded) develop a sound change at about .500" -.550" lift and flow drops 10-20 cfm and sometimes more. Fixing that is delicate. Accurate sizing and correct shaping .5" before and after the seat is critical. So Jack I guess that is what we will be talking about.

[Tom Vaught]

Originally Posted by Jim Robertson

Jack,
Yes to the first question

And I think I understand your 2nd question...
The flowbench software reports the blower capacity...in other words with the fan motors operating at 100% blower capacity I read a pressure differential of 44.25 and 42.2 respectively.

The 44.25 and 42.2 is INCHES OF WATER COLUMN DEPRESSION across the orifice.

Ford historically has tested heads for years at different depressions. The 427 High Riser heads were developed with the use of a very high capacity flow bench. In 1964, Ford tested the High Riser heads for the Le Mans Ford GT-40s at 67" of depression.

Today we look for exactly the same issues that Jim pointed out: Unstable Flow.
Ford tests at 10", 20.4", 25", 28", 40.75", and 67" of water test depression.

10" and 25" cover the old Superflow test pressures

20.4" covers the old Holley and Rochester 4 bbl pressure (1.5" Hg)

40.75" covers the old Holley and Rochester 2 bbl pressure (3.0" Hg)

67" was the max test pressure of the bench and is approximately 5.0" Hg.

Tom Vaught

ps if you are interested in learning more about flow benches and how to build one, this site is excellent: http://www.flowbenchtech.com/forum/

[steve25]

Is that guide boss as huge as it looks in the pictures, or is it just a shadow or something?

If that boss is as big as it looks, its forcing a bunch more of the air mass then need be to try and rap its way around the short turn and likely making your turbulence issue I might think.
Have you velocity probed it at the crown of the short turn?

In general what I have found is that the roof flow path width needs to be 94% of the valve bowl throat, and that 100% of the throat width needs to be taken right back down the lenght of the short turn/ floor to the Intake flange if possible. Turbulence issues, the putt putt sound of the bench and the flow regression seen can only be cured with the right geometric floor radius in regards to the throat diameter and width and or added short turn height.

Fords 60s testing at 65" gave them the notion that those massive 351 C 4 BBL heads could work on 302 cid motor below 5000 rpm, how wrong they where!!
I wonder to this day if someone at Ford lost their job from that mis-development blunder!

[Jim Robertson]

Thanks Tom. Lots of good info on that site and in Harold Bettes's book Engine Airflow.

Port mold pics attached.

[Jim Robertson]

Yes guide boss is huge compared to what is seen today. The flow numbers are roughly the same give or take a bit. Note the similar size and shape within .5" of the seat and we used the same valve for both ports. Enlarging the straight section of the port did not increase the flow volume proportionately to the cross section increase...thus slowing the air down. On the positive side we have found blowers like big ports.

Pics compare with an Alan Johnson Top Fuel head from the late 1990s. Notice the straight port section within .75" of the seat. It is like a tube straight into the back of the valve. Small "short turn" radius (.3125") where the port turns...yes 5/16" radius.

[steve25]

Well since you will always have a positive pressure due to boost the flutter will be a moot point and the choke point/venturi should be at the throat in the bowl.

[Jim Robertson]

We try hard to fix any surging/turbulence/non-steady flow no matter the application. Some efforts are more successful than others.

Pics of exhaust port molds...Jack's Hemi on the ends and Alan Johnson Top Fuel in the middle. Not much difference after 35-40 years on the exhaust side of a blown hemi. AJ valve size was 1.900".

So it appears Jack's exhaust ports will support about +7000HP...now if we can just get a bit more past that intake valve. :-)

[Jim Robertson]

Jack,
What seat angles and widths did you use in the head and on the valves

[steve25]

Jim, where did you get that blue valve opening tool you use in one of the shots on the flow bench,did you make or buy it?

[Jim Robertson]

SteveI believe that one is from Powerhouse. Fairly common and a few are making similar products.

[Steve Barcak]

I had the idea years ago to mill the intake surface as far back as is possible- even to the guide area. Once that area is cut off, it will be easier to build up the side of the ports with weld. Then, after milling flat, install a peice to alum plate to replace the area milled off.
Smaller, thinner guides too are an obvious direction to go. 3/8" stems are huge and cumbersom.
This opens up a lot of possibilities to increase the efficency of the port. However, I still feel these heads in stock form can get a center steered car in nitro in the 5s. So, will not do this for awhile.

Jim, do you know what 392, 354 and AJ 392 heads flow? I do not think they flow impressive #s either but, they run well into the 5s with them at around 400 inches and no trans.

The rocker system i am designing will allow for push rod clearance with these new dimensions.

These mods are remiscent of the early to mid 70s pro stock days when NHRA let you do neat stuff like that. It was done with Fords, AMCs and others too.

Neat stuff.

Thanks for your efforts. Do you have plans to play with it further? or just basic flow work?

I have one set of ported/polished HEMI heads on my running M/T engine in my red boat. Also have ontouched ones as well.

[Jack Gifford]

Jim- I believe the valve faces and seats are all 45 degrees. I don't think I noted the seat widths. I'm sure they're pretty narrow, since I'll only be making fairly brief (and infrequent) runs on alcohol. The exhaust seats are full-radius, aren't they?

[Don Chapman]

Jack, Are you going to have your Hemi engine at Norwalk this Year?? And will you have a head not on engine we could take a look at?

[Jim Robertson]

Trying to post the last flow sheet. File too big...still working on it.

Exhaust flowed 243 at .600" and 248 at .650" on a 4.060" bore without a pipe.
With pipe exhaust ports went up to 264 at .600" and 267 at .625".
On a 4.310" bore with a pipe exhaust port flowed 274.7 at .600" and 277.1 at .625".
Pipe and a larger bore was worth nearly 30 cfm.

Bore pic is of the head mounted on the 4.310" bore fixture.

Close up pic of intake seat. I think there would be some additional flow in the intake seat work. Intakes flowed 274 at .600" and 290.9 at .700" on the 4.310" bore. Larger bore might have been worth about 5-7 cfm at the upper lifts but results show a bit of a loss in the mid lift range.

[R 70 Judge]

Originally Posted by Jim Robertson

Trying to post the last flow sheet. File too big...still working on it.

If you don't figure it out just email it to me and I'll upload it to my webspace and post a link. (or I'll shrink it)


Cool stuff btw

[BruceWilkie]

96% exhaust flow to intake flow balance at .600 lift is outstanding and very desirable on a supercharged motor. I suspect those heads NA could out hp some bigger flowing intake port heads on a mid 400 ci motor with the right cam timing.

IMO these heads need to be reproduced.

[Jack Gifford]

Originally Posted by Don Chapman

... you going to have your Hemi engine at Norwalk... have a head not on engine we could take a look at?

Yes and yes.

Jim- will you be in Linder's lot Thursday? Hoping I can "borrow" my head for the duration of the event?