Port volume vs flow vs velocity

General engine tech -- Drag Racing to Circle Track

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Re: Port volume vs flow vs velocity

Post by fordified »

travis wrote: Wed Jun 16, 2021 4:10 am
Walter R. Malik wrote: Tue Jun 15, 2021 6:31 pm Maximum horsepower at Wide Open Throttle has little to do with street driving. Keep it all in perspective.
And I think, yet again, that this is where my confusion comes from.

I’ve found a large number of posts on here that state that anything over 330-350fps is too high and you start getting more pumping losses, more possibility of the port going turbulent, etc.

Larry’s posts are highly informative, no doubt about that. But…I don’t build SS engines. I primarily build stuff that needs to perform well in a 4000+ pound daily driver with highway friendly gears, or needs to lug up a rough mountain trail, or needs to pull a trailer full of hay out of the back 40. Cam timing is a lot of it, but not all of the picture. So…if I am interpreting correctly, 350+ FPS port velocity in the stuff I build isn’t a bad thing, especially when part throttle performance is more important that WOT performance.

I’ve never really driven a 6.0 LS powered truck, but spent plenty of time with 5.3 powered GM trucks and the Coyote based 5.0 in ford trucks, and to me they just don’t seem to be a good truck engine. I think they are more tolerable because of lower rear gears and multi speed transmissions, and they certainly get better fuel economy than anything I’ll ever build with ancient technology, but IMO they just don’t have the low end and part throttle grunt that I like…especially in a truck. I guess that’s why diesels have become so popular
One critical thing missing in this thread is intake manifold. For performance in general, people spend way too much time talking about heads and not nearly enough time talking about the manifold. Manifolds make a huge difference in overall performance. Don’t forget headers either.

If you want a puller or a climber, nothing beats a diesel. There’s no comparison between gas and diesel when it comes to truck performance. You can improve gas engine truck performance but diesels will always come out on top.
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Re: Port volume vs flow vs velocity

Post by mag2555 »

A Diesel really can’t be used as a comparison here since there at the max VE for any given rpm it happens to be at.
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Re: Port volume vs flow vs velocity

Post by Steve.k »

9B6E2B5A-15A1-47DF-8D60-26D93BD5173D.png
mag2555 wrote: Wed Jun 16, 2021 5:29 pm Lets put some needed details to that last post ok?

Port velocity goes up at max lift being applied only when the percentage of air flow gain exceeds that of the percentage of area gain in the port choke / minimum port area location if it was reworked.

Steve, so it looks like you picked up some 75 hp, that’s not unheard of and looks like that would be achieved with a 22 cfm gain per cylinder.

How many CCs where added to those ports to attain that flow level of flow gain?

How much bigger did the minimum port area get or was this power gain had by just making other areas more efficient?
Here is flow chart. Typical 4v heads flow 290-300 area. Usually around 241-244cc
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Re: Port volume vs flow vs velocity

Post by Steve.k »

Think these heads are around 248cc I’ll try and dig up paperwork.
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Re: Port volume vs flow vs velocity

Post by RW TECH »

digger wrote: Wed Jun 16, 2021 6:00 pm
RW TECH wrote: Wed Jun 16, 2021 3:15 pm
digger wrote: Tue Jun 15, 2021 10:50 pm Every post 2000 oem NA Chevy, just look at tq/cube it’s not in the impressive range at the stock power level.
Compared to what?
to something with the size and flow that is closer to what what the engine actually requires/consumes.
Specifically, which existing production engine, past or present, outproduces torque of the Gen III/Gen V small block GM?

A specific requirement for LS7 in Corvette involved rolling off the clutch in 6th gear, and flooring the gas with no bucking or stalling. Is this one an exception?
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Re: Port volume vs flow vs velocity

Post by digger »

RW TECH wrote: Thu Jun 17, 2021 6:54 pm
digger wrote: Wed Jun 16, 2021 6:00 pm
RW TECH wrote: Wed Jun 16, 2021 3:15 pm

Compared to what?
to something with the size and flow that is closer to what what the engine actually requires/consumes.
Specifically, which existing production engine, past or present, outproduces torque of the Gen III/Gen V small block GM?

A specific requirement for LS7 in Corvette involved rolling off the clutch in 6th gear, and flooring the gas with no bucking or stalling. Is this one an exception?

An LS3 head flows north of 300 , a 376CI engine doesn't need anywhere that near much flow for 430hp/424lbft unless you want it to do it with a baby cam and pass emissions, be real smooth etc. a slightly smaller port (but just as efficient) and slightly bigger cam to make the same peak hp number would slaughter the OEM setup through the middle.

OEM have been using small cam, big size and flowing heads for years.
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Re: Port volume vs flow vs velocity

Post by Elroy »

digger wrote: Thu Jun 17, 2021 7:59 pm a slightly smaller port (but just as efficient) and slightly bigger cam to make the same peak hp number would slaughter the OEM setup through the middle.
=D>
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Re: Port volume vs flow vs velocity

Post by Steve.k »

With camshaft tec where it is now I’d take big Cleveland ports over windsor offerings all day everyday!
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Re: Port volume vs flow vs velocity

Post by FPV_GTp »

Darin Morgan is another great contributor on ST ... have a listen/watch his youtube channel & SUBSCRIBE to it, plus many interviews Darin has done on YT.

As Darin states it's all about managing the air speed of the whole induction system for the application the motor is intended for.

Darin Morgan youtube_channel -
https://m.youtube.com/channel/UCJv1SDdwEMhcl5n_dkvdKng

Air speed limitations in 2 valve IC engines

https://m.youtube.com/watch?v=qhsTQn0uUOQ&t=15s

De-atomization in intake tract in IC racing engines PART 1

https://m.youtube.com/watch?v=f8XG9T8v-ng

De-atomization of air fuel mixture in intake tract of IC racing engines PART 2 of 3
F/S - CAST IRON FILLER WELDING RODS 5mm X 700mm Ship Australia & New Zealand wide.
http://speedtalk.com/forum/viewtopic.php?f=31&t=54136&p=758284#p758284
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Re: Port volume vs flow vs velocity

Post by blackford »

travis wrote: Tue Jun 15, 2021 4:35 am I’m trying to better understand the relationship between the items in the subject line and the overall effect on power output and rpm range. This is related more to street performance builds rather than racing applications although I’m sure there is some crossover there.

On a small port OEM head, if you concentrate on blending and smoothing but try to limit actually increasing the port size, you can see some pretty sizable gains on the flow bench with very minimal increases in port size…but it comes at a cost of much higher port velocity. My question is…does the increased flow increase power at the bottom end but hurt top end more because of the much increased velocity? An example head that I have memorized…

Stock D0OE head w/1.84” intake valve. 183cfm peak at .400” lift, 145cc port

Bowl hogged only D0OE with 1.94”, 193 cfm at .400, 320 fps at peak flow, 148cc port

Bowl hogged and blended/smoothed D0OE w/1.94”, 229 cfm@.500”, 152cc port, 415 cfm at peak

Another question…in this situation of better cylinder head flow but velocity being too high, would it be a good move to try to increase the port volume a bit even if no more flow is gained?
I am no expert with this subject, but I have an example that uses the same DOOE head. The heads were ported fully to 160cc and they use 1.94 intake valves. The port roof was raised over 1/8" and the pinch area was taken to the point where the pushrod hole thickness is pretty scant. Bowl work, throat work and port work so the entire port was massaged. Intakes were unshrouded also.

The heads went on a 327 Ford. It's a street engine. SFT with 236@.050 and .528 lift and just a tad under 10:1 compression. Peak power is north of 430 HP at 6500 and calculated air speed is 370 fps port velocity. HP is down about 30 HP at 7000 (shift point) and port velocity is just under 400 fps. Peak HP is with all accessories (flex fan, PS pump, alternator and stock water pump).

Naysayers said that you can't make very good power with those heads (even ported), but the engine is not radical by any means and it produces power rivaling similar engines with larger aftermarket heads. I never had the heads flowed.
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported Maxx 180s, T5z, 9" 3.89 gears. ~460HP@6500

2013 Corvette 427 Convertible daily driver
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Re: Port volume vs flow vs velocity

Post by mag2555 »

Your intake flow numbers to make 430 hp would in the 218 cfm range at .500”.
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Re: Port volume vs flow vs velocity

Post by mag2555 »

Your intake flow numbers to make 430 hp would in the 218 cfm range at .500”.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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Re: Port volume vs flow vs velocity

Post by blackford »

mag2555 wrote: Sat Jun 19, 2021 2:01 pm Your intake flow numbers to make 430 hp would in the 218 cfm range at .500”.
Sounds about right. I've always assumed flow was 220-225 cfm. Accessories (water pump, flex fan, PS pump and alternator) are probably eating up at least 10-15 HP.
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported Maxx 180s, T5z, 9" 3.89 gears. ~460HP@6500

2013 Corvette 427 Convertible daily driver
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