Volume and psi? March 04, 2017 12:53PM
Trying to figure out how much psi I would gain by reducing exhaust header size. Had 55 psi before if I reduced volume by 25 percent but stay same flow what would I gain in psi. If there is an equation for this I would use any help appreciated.
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Re: Volume and psi? March 05, 2017 03:18AM
PSI is nothing more than restriction. Do you want psi numbers, or flow and power numbers? Yes, you can go too big and too small on piping size. Don't let psi be the determining factor. Raising psi makes everything work harder for flow. You want to make sure you can flow enough to fill cylinder and then see what psi will do. Why do you think guys are going to fuel heads on the alky motors? More flow first, then psi. Try it on the dyno. Go from a 3" pipe to a 2 3/4" pipe. See what the numbers do for you. You can even do it on a flow bench if set up for it.
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Re: Volume and psi? March 05, 2017 03:33AM
I'm actually looking to turn turbo harder not so much as fill cylinder not turning charger hard enpugh oem exhaust manifold is square on inside wanted to switch to round. By doing so I can maintain same flow by reducing volume 25 percent was just trying figure out how much psi that would gain which in turn drive turbo harder..
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Re: Volume and psi? March 05, 2017 01:37PM
My experience don't amount to much but I have ran stock manifolds and headers on three different engines and other than the sound it made no noticeable difference .But on a dino it may .if you want to drive the turbo harder change cams or re degree and change the timing on the cam you have you can advance or retard depending on were you need it to turn harder at or change the exaust housing
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Re: Volume and psi? March 06, 2017 10:21AM
As others have already said, you dont need to worry about pressure. The more pressure you have in your exhaust manifold, the more you need in your intake to over come it. Heat energy/gas expansion is what turns the charger. Retard your injection timing and get the fire out there to it, wont have a problem turning it hard. Cam timing moves the power curve up or down in the rpm range, but then you have to watch valve/piston contact.
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Re: Volume and psi? March 06, 2017 11:43AM
That will definitely help switching from square to round. What you will gain is velocity more than psi. Air gets lazy, keep it moving.
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Re: Volume and psi? March 06, 2017 12:49PM
I am probably totally wrong and probably am and that's fine .my question is if your making 60 psi boost on the compressor side of the turbo and 60 on the exaust side of the turbo wich mean theres 60 pound of backpressure from the turbo flange all the way back to the valve seat how can it be free flowing there is no velocity at that point square or round is going to do the same at that point I no a good flowing head makes a difference especially on a naturally aspirated wich is how your flow bench is checking the head add some equel back pressure or resistance on the flow bench on the same head and my opinion there is no way you will se any difference in square or round because its not free flowing natural aspirated yes turbo no
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Re: Volume and psi? March 06, 2017 04:03PM
Simple answer: air doesn't like corners or friction and square tubing/ports have more friction than round. Most of that friction is skin friction or surface friction (some is turbulence)

Here's a more detailed explanation:
Let's take two equal cross-sectional areas (Exact same size (area) holes), one is square and one is round:

Square cross-section area = (w * w) = w^2
Circle cross-section area = (π * r * r) = π*r^2
Set the areas equal:
w^2 = π*r^2
w^2/r^2 = π
w/r = sqrt(π)
Solving for w:
w = sqrt(π)*r

Sum of sides of square = Surface area of square = 4w = 4*sqrt(π)*r
Circumference of a circle + Surface Area of circle = 2*π*r

Ratio of Surface Areas:
Square / Circle surface area =
(4*sqrt(π)*r) / (2*π*r) =
2*sqrt(π) / π =
2 / sqrt(π) = 1.128

Meaning there's 1.128 times more surface area in a square pipe for friction losses per unit of length.

This also shows that square tube/ports etc... uses more material in its construction than a circular pipe with the same cross-sectional area. More surface area (material) per cross-sectional area means more skin friction (surface friction). Therefore square tube will require more energy to pump fluid (air) through it than circular pipe.

Hope it helped.
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Re: Volume and psi? March 06, 2017 03:05PM
It sounds like what you are trying to do is keep the turbo spinning and developing boost as you lug the engine to a lower rpm. As some others have suggested, you are probably better off either changing the exhaust housing to a smaller one, or trying adjusting the cam and/or pump timing. If you don't have enough exhaust volume to keep the charger lit at X rpms, it's going to stop making boost. You need the gas velocity right at the exhaust wheel. If you constrict the flow before the exhaust housing you may even make the problem worse.

Do you have a gauge or a datalogger tracking your exhaust gas pressure to know what it's doing?
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Re: Volume and psi? March 06, 2017 03:58PM
This project consists of a 504ci case with a gt42 with a 101 housing. Have been told case exhaust is to big so just looking for ways to improve. Only have psi gauges a little green on lot of the tuning. Cam degree at 98 pump timing at 38 the manifold is two inch square internally was going to switch to two inch doing cut out the corners and drag to sppe
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Re: Volume and psi? March 06, 2017 05:00PM
Sorry got cutoff was hoping to speed up air plus reducing volume by switching to 2 inch round by doing so i was hoping to gain a few psi which in My theory has to leave through turbo hence drive it better. Thanks for opinions. New ideas never hurt.
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Re: Volume and psi? March 07, 2017 05:56PM
mhf,-- you think that higher psi is more air,--opposite in reality,listen to the guys trying to explain and help,higher psi is "RESTRICTION" !!!!!!!!!! A system that flows better means much more power and more volume at the lower pressures.
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Re: Volume and psi? March 08, 2017 09:52AM
You want as little pressure before turbo as you can. Otherwise you will not completely empty cylinder, intake has to overcome. Plus, more psi equals less air getting to the turbo.
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Re: Volume and psi? March 07, 2017 11:44PM
get a manifold off of a 451 . they are smaller internaly. I searched the junkyard for a good one that is sealed real good. cam timing should be at 95 or 96 depending on your centerline. case does not like a tight housing. I would recommend a 115 in place of 101. also use a 2090 0r 2290 head or case industrial head as they use 45 degree valves instead of 30 degree valves. to make a good pulling case engine you need to take the best of 3 different engines.
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Re: Volume and psi? March 08, 2017 12:42PM
Your going to get all confused without changing fuel settings ,injectection pump timeing,turbo ex housing cam timing or something your not going to se any difference round square or whatever if you do it will be so little you will never notice it and all cams have overlap on them so you never clean the cylinders out and the more pressure you can through at a bad flowing head the better it will run .If your running 30 psi boost now which is 30 psi pressure put some fuel to it and put a turbo on it that blows hard enough to put 60 pounds of boost to that same engine se what you got that 30 pounds of pressure will wake it up a couple hundred horses or more
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Re: Volume and psi? March 09, 2017 02:52AM
Quote
eagle
get a manifold off of a 451 . they are smaller internaly. I searched the junkyard for a good one that is sealed real good. cam timing should be at 95 or 96 depending on your centerline. case does not like a tight housing. I would recommend a 115 in place of 101. also use a 2090 0r 2290 head or case industrial head as they use 45 degree valves instead of 30 degree valves. to make a good pulling case engine you need to take the best of 3 different engines.

Ive never heard of those heads having different valve angles. How much of a difference does that make?
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Re: Volume and psi? March 11, 2017 10:28AM
Are you talking 451 turbo or a 451 NA manifold?
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Re: Volume and psi? March 08, 2017 12:46PM
Interesting I just assumed all the turbo manifolds were the same. As far as ex housing I have 101 on one but I've got a 98 perscision I might should try. I was told its less restrictive than the 101. I never have tried it thought it might not turn as well.
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Re: Volume and psi? March 08, 2017 01:02PM
Don't you need more exhaust psi than boost psi to keep boost psi from trying to turn turbo backwards.
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Re: Volume and psi? March 08, 2017 02:27PM
A little more ex press helps keep the turbo turning the closer the pressures are intake and ex the longer the turbo will last if one side is making a lot mere pressure than the other it will wear hard on that side of the thrust because the wheals are pushing against each other every engines different one may like that 101 the other may like the 98 the camshaft has a lot to do with how hard the engine drives the turbo.And all these head flow numbers and good flowing heads are great but the head neads to be built to match the class you can get that lazy air that head flow mentioned in other words if your pulling a stock 3lm class you don't want a hogged out high flowing head on it
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