Port velocities

[106-1194218389]

I ran into quite a good discussion about port velocities on speedtalk.com that our own Larry Meaux was the main guru contributor. Larry Meaux, I always appreciate your input and guidance. Also from what the rest of you have said that the port velocity should never be above you test pressure. I am testing my Dart Iron Eagle 180 cc intake port heads and out of the box man do they need work. I guess if you never twisted you engine above 3500 - 4000 rpm they would be great. Velocities at the push rod, which is the tightest part of a SBC is as high as 392 fps or about 7.5" and I am testing at 6". I know it has been suggested to aim for 300 fps so I have some work to do. At least they have given me plenty of cast iron to play with. The roof at the SSR is 248 fps the middle at the SSR is 286 and the floor where it goes over the SSR is very turbulent and 392 fps and was hard to even hold the pitot still as it was bouncing all over the place. The port goes backwards badly at the convergence point which is about 512" lift on these heads as I am running 2.05 intake valves. But thanks to you guys I almost know where to attack now.

[WPH]

This quote might be from the same discussion and I'm running on the edge of these numbers although on a 4V head with quite strong downdraft.

Quote:

"350 FPS on the Short Turn apex is pushing it, but i've had Cyl Heads handle higher than 350 fps there and not loose HP/TQ,
and other times had Cyl Heads that had less than 350 fps show losses.

Anything around or above 400 FPS (36.5" Pitot press tested at 28") has always shown a HP/TQ Loss in a live running Engine,
depending upon overall Port Shape, around 350 fps to 400+ fps can show losses of 10 hp to 105+ hp on a V8 at approx 600 HP level."

It seems to me that I also have to reconsider my intake port size since I'm at 391FPS on port splitter entry.

[106-1194218389]

Yes that was from the same discussion. The biggest difference is I am running a 2 valve small block Chevy and they do not get away with the velocity that a good 4 valve engine can tolerate. The ports seem to be much better on most of the new 4 valve stuff. I think that you could tolerate the velocity much better than a small block Chevy. My highest velocity is right up against the wall at the pushrod and right at the SSR on the floor. My goal is to get the whole port as even as possible and around 300 feet per second. I think in that same discussion he also said that the choke in the port should really be right at the valve curtain area and the further up the port towards the intake mounting surface the worse it is. I hope I am correct in my interpretation.

[WPH]

That's the way I got it too. My port runner to valve dia ratio is 75% (as stock), a lot lower than in any of my previous heads.

It would have been great to do a comparison between actual dyno data vs. port flow on my previous headwork on this same engine
but we ran into ignition problems. No usable data above 6100rpm, power and torque were the same at this point, 205hp/205Nm/6050rpm.
Previous port work was done without flowbech and the head had an issue with SSR and the flow was only 129CFM@10".
With the manifold flow dropped further 9% so maybe those hp/tq numbers were the best we were going to get.

Measured intake port velocity on this head was in the 390's@15", after some SSR and bowl/guide area work it was above 400 with 171,5CFM@15"

[larrycavan]

[WPH]

Measured 394-404FPS, same as in splitter region. Probe was slightly off from the middle because of guide sticking out of the port roof.
In my scrap "development" head port whistles even though the splitter isn't knife edged .

When I opened up the port by 2.5mm to 27.5mm flow went up to 190-193CFM@15" but it didn't drop the velocity as much as I hoped.
I'll go to 28-28.5mm next and maintain the round shape.

[maxracesoftware]

[Dave W]

ya know it's funny how most of the magazine articles and books from the 80's and 90's said going after the pushrod area was not where the power was (SBC heads) it was somewhere else. Well I did a set of 180's and the pushrod was about in the 1.2 area. opened that up to 1.8 and lowered the ssr on top and like larry said it took off. The driver (circle track) would not believe me that i never touched the cam. His complaint was the engine was very snappy which I took as a narrow power band from the small cross section.

Dave

[larrycavan]

[maxracesoftware]

[larrycavan]

Am I ever grateful that you came along to reveal the results of our efforts and frustrations Larry.

[bruce]

I'll second that!!

[MMack]

Looks like I know what I will ask for on my birthday. My wife hates it when I give her some obscure part number and address to order something. Then it comes in and she has no idea what it is! But as long as I am happy, she is too. Great lady!

The slogan that the trainers used when i was taking Six Sigma Black Belt training was "questions lead, answers follow". We changed it to "Questions lead to more questions." I built this bench to learn, and I am learning, but I am learning that there is way more that I don't know than I ever could have imagined! But it is all great stuff!!!

Mike

[86rocco1]

[106-1194218389]

Well I feel that is where the wetflow bench comes in also. Fuel being heavier and harder to turn then air. I think, and I will stand to be corrected if I am wrong, when air speed gets to high then the fuel may be seperated from the air mixture and starts to puddle. This is much harder to ignite. If I remember correctly Larry Meaux mention in one of his discussions that the BSFC went way up on one of his tests where the velocity was too high and the horsepower dropped. Larry if you are monitoring, is that what happened?