How much CSA will be ideal

General engine tech -- Drag Racing to Circle Track

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swampbuggy
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How much CSA will be ideal

Post by swampbuggy » Tue May 22, 2018 11:53 am

SBC--371 C.I.--Dart 9 degree head--4.185" X 3.375"--46.375 C.I. per hole--8500-9000 RPM target RPM--290 to 310 F.P.S. air speed target--6.250" rod--55MM cam core--.937" lifter w/.850" wheel. I don't think i left out anything critical. Thanks for comments, Mark H. :)

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Re: How much CSA will be ideal

Post by swampbuggy » Tue May 22, 2018 11:55 am

Edit to the above 2.200" min. intake valve size.

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Re: How much CSA will be ideal

Post by mag2555 » Tue May 22, 2018 12:07 pm

The CSA goes hand in hand with the expansion rate of the full Intake tract.
Assuming a 91% Throat below that 2.200" valve then your minimum port circumference should be in the ball park of 6.286".

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Re: How much CSA will be ideal

Post by Scotthatch » Tue May 22, 2018 12:40 pm

How are they going to be used ?

I am assuming .800 valve lift shooting for like 420 cfm number .... 50 degree seat?

NA? Turbo?

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Re: How much CSA will be ideal

Post by Rick360 » Tue May 22, 2018 4:07 pm

swampbuggy wrote:
Tue May 22, 2018 11:53 am
SBC--371 C.I.--Dart 9 degree head--4.185" X 3.375"--46.375 C.I. per hole--8500-9000 RPM target RPM--290 to 310 F.P.S. air speed target--6.250" rod--55MM cam core--.937" lifter w/.850" wheel. I don't think i left out anything critical. Thanks for comments, Mark H. :)
What do you mean by "air speed target"? Flowbench? Port Average? I've seen it used to mean different things and want to be clear about your meaning.

I think you will want the mcsa to be around 2.9-3.0sqin for peak hp in that range. If you want 8500-9000 as max rpm and not peak then I'd want it smaller.

Rick

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Re: How much CSA will be ideal

Post by swampbuggy » Tue May 22, 2018 7:59 pm

850 to 900 net valve lift 50° seats naturally aspirated carburetor I hope for 300 feet per second roughly with it running at Full Tilt

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Re: How much CSA will be ideal

Post by Headguy » Tue May 22, 2018 8:32 pm

swampbuggy wrote:
Tue May 22, 2018 7:59 pm
850 to 900 net valve lift 50° seats naturally aspirated carburetor I hope for 300 feet per second roughly with it running at Full Tilt
I think you are asking a lot. 300ft/sec is top fuel stuff.

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Re: How much CSA will be ideal

Post by MTENGINES » Wed May 23, 2018 6:47 am

Headguy wrote:
Tue May 22, 2018 8:32 pm
swampbuggy wrote:
Tue May 22, 2018 7:59 pm
850 to 900 net valve lift 50° seats naturally aspirated carburetor I hope for 300 feet per second roughly with it running at Full Tilt
I think you are asking a lot. 300ft/sec is top fuel stuff.
I think he means air speed. not car acceleration.

If this is your first time building a setup like this, good luck. it will take some time to refine the build. a drag car with a 8000rpm converter is different from a dirt track car. YOUR BENCH can show you a different FPS if its HAPPY or SAD compared to others. if your bench shows 470cfm vs mine that shows 430, that is a big deal. why not 52,55,58 degree seats?

Someone posted a CSA range, and i can agree to that, take that advice from the start. a 2.200 valve should flow 430-440 speeding it up or slowing it down may not effect the flow number.

You should mention application and induction. because tunnel ram vs single plane will be drastically different at that range

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Re: How much CSA will be ideal

Post by Amilcar » Wed May 23, 2018 8:09 am

MTENGINES wrote:
Wed May 23, 2018 6:47 am
Headguy wrote:
Tue May 22, 2018 8:32 pm
swampbuggy wrote:
Tue May 22, 2018 7:59 pm
850 to 900 net valve lift 50° seats naturally aspirated carburetor I hope for 300 feet per second roughly with it running at Full Tilt
I think you are asking a lot. 300ft/sec is top fuel stuff.
I think he means air speed. not car acceleration.

If this is your first time building a setup like this, good luck. it will take some time to refine the build. a drag car with a 8000rpm converter is different from a dirt track car. YOUR BENCH can show you a different FPS if its HAPPY or SAD compared to others. if your bench shows 470cfm vs mine that shows 430, that is a big deal. why not 52,55,58 degree seats?

Someone posted a CSA range, and i can agree to that, take that advice from the start. a 2.200 valve should flow 430-440 speeding it up or slowing it down may not effect the flow number.

You should mention application and induction. because tunnel ram vs single plane will be drastically different at that range
Care to expand on this?

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Re: How much CSA will be ideal

Post by swampbuggy » Wed May 23, 2018 11:37 am

Question, if it is determined on the F. B. With pitot that one has an airspeed of xxx, is it not safe to think that is what the air speed will be in a max. Effort engine at max. H.P. RPM ??? Mark H.

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Re: How much CSA will be ideal

Post by swampbuggy » Wed May 23, 2018 11:46 am

App. Drag car, wgt. 3000, 4 spd. With appx. 5.57 gear, Dart 9 deg. Single plane. Thx. Guys, Mark H.

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Re: How much CSA will be ideal

Post by Scotthatch » Wed May 23, 2018 11:57 am

swampbuggy wrote:
Wed May 23, 2018 11:37 am
Question, if it is determined on the F. B. With pitot that one has an airspeed of xxx, is it not safe to think that is what the air speed will be in a max. Effort engine at max. H.P. RPM ??? Mark H.



No .... what you do on the flow bench is on the bench you don't control airspeed in a running dynamic engine what you change on the bench shows up as a change in rpm in the motor

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Re: How much CSA will be ideal

Post by swampbuggy » Thu May 24, 2018 2:51 am

Ok, Scott......what. airspeed do you think i want to see on the F.B. for my engine in your opinion ???

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Re: How much CSA will be ideal

Post by steve316 » Thu May 24, 2018 8:00 am

At 400 cfm on on 3" csa head if you have 380 to 440 fps your good. the more it flows at the same size port the faster it will be.

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Re: How much CSA will be ideal

Post by Rick360 » Thu May 24, 2018 9:12 am

swampbuggy wrote:
Thu May 24, 2018 2:51 am
Ok, Scott......what. airspeed do you think i want to see on the F.B. for my engine in your opinion ???
Where are you measuring the airspeed?

Why do you think there should be a "target" flowbench airspeed? Flowbench airspeed doesn't tell you anything about the suitability of a port size for a particular engine.

Rick

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