Just fuel shear ?

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steve cowan
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Re: Just fuel shear ?

Post by steve cowan »

Everyone should read that porting by the numbers thread,I have listened to the CD 100s of times,obviously DM works at the higher level and not cookie cutter crap 23 degree stuff I play with but there is a heap of things to think about.
In Eric's video he mentioned taper between the victor and Team G.
I think we have to consider how strong the reverse pulse is and what it does at the butterflies of carb.
Intake valve is opening 60 times per second @ 7000rpm approximately so what's happening in the induction tract,it must be crazy to say the least.
Apart from taper at the opening giving a better direction for the air and fuel to travel it must dampen the reversion pulses coming back up the runner due an increase in CSA .
Add in shear plates ,4 hole spacers,miss- matched spacers etc.
Have a think about Jon Kasse dyno video with the clear perspex and finger in the port deal.
All that fuel on the walls,JK says himself about not feeling much on the wall as in boundary layer.
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Re: Just fuel shear ?

Post by Tuner »

BLSTIC wrote: Mon May 22, 2023 5:48 am Wasn't there some Mercruiser big block with mismatched manifold/head combo that would lose an absolute crapton of low and mid range if you "fixed" the step?
That could have been the 460 Ford Marine Engine used in jet boats in the '70s that had Cobra Jet heads with a Super Cobra Jet cast iron 4150 Holley intake manifold. Joe Mondello was doing a lot with the Oldsmobile marine engine on Berkley pumps and got tangled in the Ford marine engine deal too.

The mismatch made people crazy and a lot of folks ported their heads to match the intake, which made a funnel like taper in the port.

Naturally, people were not happy when they lost power. Mondello did some dyno testing that showed matching the ports to the gasket by bellmouthing the port in the head lost some 30-40 HP. There was an article about this in Power Boat magazine.

If somebody has some Cobra Jet and Super Cobra Jet intake gaskets you could see the size difference and orientation of the misfit.

Interesting old film with flow visualization
https://www.youtube.com/watch?v=2JpKMbl ... N0&index=8
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Re: Just fuel shear ?

Post by BOOT »

There are other aspects people aren't considering. Keeping the plugs/other clean when not WOT(a small percentage of run time for engines). Injector, booster or rather fuel ratio/atomization at all times of engine operation. The cylinder and plenum are both large changes in area.

Ideal world perfectly straight and down, no lips/edges, no turns, no valve, no size changes and perfect amount of atomized fuel. Fuel never drops out or touches sides.

Real world, not all engines/combos are the same. Different solutions to same problems.
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Re: Just fuel shear ?

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Tom68 wrote: Mon May 22, 2023 4:56 am https://youtu.be/2sbICMpLiBI

So the 1275 is an excellent 550 to 600 Hp upper ci SBC manifold.
Yet again we see big runners feeding smaller ports making good power.
If you think about it, if it was the other way you'd have a small runner feeding a big head ( effectively reverse inlet runner taper) that'll always be crap.
An old combo I had was Sportsman II heads(1205) with a 1206 matched vic jr, big mismatch. The old X style runner(not torqer) weiand xcelerator intake was better but it cracked.

Two notes about Eric's recent vid
1) The track has the real final say, not that it wasn't interesting
2) Not all carbs need as much help as others
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Re: Just fuel shear ?

Post by BOOT »

3rd note, an after thought but always something most don't consider when comparing a single plane to dual plane. Part throttle driving. Some use the gas peddle as an on/off switch(even in their daily), while others use it progressively. So style of driving.
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Re: Just fuel shear ?

Post by RCJ »

Would be interesting to see somebody expoy an intake rather than grind out a head. If it was fuel sheer helping a motor shouldn't you be working on the carb , boosters etcc....
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Re: Just fuel shear ?

Post by BLSTIC »

Tuner wrote: Mon May 22, 2023 7:48 am
BLSTIC wrote: Mon May 22, 2023 5:48 am Wasn't there some Mercruiser big block with mismatched manifold/head combo that would lose an absolute crapton of low and mid range if you "fixed" the step?
That could have been the 460 Ford Marine Engine used in jet boats in the '70s that had Cobra Jet heads with a Super Cobra Jet cast iron 4150 Holley intake manifold. Joe Mondello was doing a lot with the Oldsmobile marine engine on Berkley pumps and got tangled in the Ford marine engine deal too.

The mismatch made people crazy and a lot of folks ported their heads to match the intake, which made a funnel like taper in the port.

Naturally, people were not happy when they lost power. Mondello did some dyno testing that showed matching the ports to the gasket by bellmouthing the port in the head lost some 30-40 HP. There was an article about this in Power Boat magazine.

If somebody has some Cobra Jet and Super Cobra Jet intake gaskets you could see the size difference and orientation of the misfit.

Interesting old film with flow visualization
https://www.youtube.com/watch?v=2JpKMbl ... N0&index=8
Yup that was it.

I wonder now if carving some super coarse texture into your "fixed" port and manifold would fix it properly and end up with a net gain, or "fix it again" and screw something up again?

There's no way the lip was gaining flow, so it must have been about mixture preparation, which an out of the box mass produced holley wouldn't usually be great at and an inwards lip would be helping
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Re: Just fuel shear ?

Post by Tom68 »

Thanks for the test Eric.

https://youtu.be/z5mVRZYL32w

s-l500.jpg


I think the Big Block cases where people have found improvement are probably low rise Qjet iron ovals to much better rec port manifolds and carbys ?

As well as the above mentioned Mercruisers.
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Re: Just fuel shear ?

Post by Tuner »

Tom68 wrote: Thu May 25, 2023 2:17 am Thanks for the test Eric.

https://youtu.be/z5mVRZYL32w


s-l500.jpg



I think the Big Block cases where people have found improvement are probably low rise Qjet iron ovals to much better rec port manifolds and carbys ?

As well as the above mentioned Mercruisers.
He just repeated the test Mondello performed 45 years ago that shows bellmouthing the port in the head kills the power. To make it a fair test the head should remain untouched with a sharp edge at the port entrance on the gasket flange.

Also, Mondello dyno tested Ford 460 marine engines which were used on jet pumps, Berkeley and others, not Mercruiser.

Also, the carburetors on those engines were 780 Holley VS and were calibrated by the Ford engineering department, they were not just generic replacement carbs. They were very similar to the Super Cobra Jet carbs and had the same modifications to the boosters to correct fuel distribution for sustained WOT such as was common in the marine applications.
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Re: Just fuel shear ?

Post by Tom68 »

Tuner wrote: Thu May 25, 2023 2:20 pm He just repeated the test Mondello performed 45 years ago that shows bellmouthing the port in the head kills the power. To make it a fair test the head should remain untouched with a sharp edge at the port entrance on the gasket flange.

Also, Mondello dyno tested Ford 460 marine engines which were used on jet pumps, Berkeley and others, not Mercruiser.

Also, the carburetors on those engines were 780 Holley VS and were calibrated by the Ford engineering department, they were not just generic replacement carbs. They were very similar to the Super Cobra Jet carbs and had the same modifications to the boosters to correct fuel distribution for sustained WOT such as was common in the marine applications.
He didn't use the bell mouthed iron head, just an unfortunate prop.
But he did use a performance oval port manifold.

Don't know why the iron heads have been bell mouthed, customer sent them in for evaluation I think. Eric doesn't grind iron.
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Re: Just fuel shear ?

Post by 1980RS »

The mis-match must work. My Vortec 406 I ran with the 062 heads were no port match at all. The S/V I used on it had the ports the same as a 1206 felpro gasket. I was going to epoxy the intake to match the heads but decided to try it the way it was with the intake hugely mis-matched on the sides of the ports. You know what? didn't matter, the car ran like crazy that day and made me a believer in what Joe Sherman said about intake manifolds.
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Re: Just fuel shear ?

Post by Chris_Hamilton »

steve cowan wrote: Mon May 22, 2023 6:18 am Everyone should read that porting by the numbers thread,I have listened to the CD 100s of times,obviously DM works at the higher level and not cookie cutter crap 23 degree stuff I play with but there is a heap of things to think about.
In Eric's video he mentioned taper between the victor and Team G.
I think we have to consider how strong the reverse pulse is and what it does at the butterflies of carb.
Intake valve is opening 60 times per second @ 7000rpm approximately so what's happening in the induction tract,it must be crazy to say the least.
Apart from taper at the opening giving a better direction for the air and fuel to travel it must dampen the reversion pulses coming back up the runner due an increase in CSA .
Add in shear plates ,4 hole spacers,miss- matched spacers etc.
Have a think about Jon Kasse dyno video with the clear perspex and finger in the port deal.
All that fuel on the walls,JK says himself about not feeling much on the wall as in boundary layer.
Is this the thread you are referring to?

viewtopic.php?t=4264
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Re: Just fuel shear ?

Post by Tom68 »

Chris_Hamilton wrote: Sun May 28, 2023 3:35 pm
Is this the thread you are referring to?

viewtopic.php?t=4264
Darin really can't take to a step down other than to label it a crude fix for too big a head. But he's done all the testing, maybe not that since he hates it though.

Still seems better to feed a small hole from a big one rather than a big one from a small one to me.
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Re: Just fuel shear ?

Post by Tom68 »

I have another theory (only) for step downs performing well in some instances..

If your pushrod pinch is somewhat smaller than the port opening at the head, you may at least not lose a lot of the flow from the dead pressure area created after the step and of course again the speed up at the edge would certainly pull some puddled fuel into the airstream.

895374.fig.007a.jpg
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