Throttle Bodies... Come hither JT.

[Frank]

Found some information about flow, etc. According to Corkey Bell's book, throttle body velocity on a turbo motor should not exceed 300-ft/s. What good is this too you? Well I have equated the following together for more practical usage. This is done with a combination of data from common throttlebody sizes, hp levels, and maintaining close to a 300ft/s velocity. 300ft/s velocities were used to show the minimum size needed for that horsepower level efficently. Dont forget that the manifold has to be ported to the size of the throttle body also!

850cfm -> 75mm tb -> 298ft/s -> about 650chp
720cfm -> 70mm tb -> 289ft/s -> about 550chp
640cfm -> 65mm tb -> 298ft/s -> about 500chp
540cfm -> 60mm tb -> 296ft/s -> about 400chp
470cfm -> 58mm tb -> 276ft/s -> about 350chp
400cfm -> 52mm tb -> 290ft/s -> about 300chp
340cfm -> 48mm tb -> 291ft/s -> about 250chp



Frank

[B.A.P.]

Nice work Frank! Did Corky say why not to exceed 300 ft/s on a turbo motor? And did he give a minimum ft/s? And how many ft/s is a 52mm at 400 whp?

The 52mm is obviously good enough to make some power, just look at all those that have run good numbers with them. The question I always wondered is if a motor makes good HP on a 52mm, how much more could it make something larger? Well, I guess I was planning on making an intake anyways!

[Frank]

Those are exactly the questions Mike Mara and myself were discussing! I have my suspisions as to why not to exceed 300ft/s, however I was hopping someone had Corky Bell's book to explain that.

In answer to your question, you could expect around 443ft/s with that throttle body and hp level (470chp assuming manual transmission loss of 17%).


Frank

[russ jerome]

Have read and memorized Corkey's book (all text is directed to forced
induction) but it is dated. Look at the heavy hitter forced induction
racers, few of his 70's idea's hold up any more Most of book is directed
to drivability and not HP goals. There is suppose to be a re-release as
the book is dated by his own admission.

Good work none the less Frank!

[B.A.P.]

Since you got it memorized, why did he say 300 ft/s was the limit?

[Brian Putman]

Good info!!

[gasketmaster]

Quote:

Originally Posted by Frank Found some information about flow, etc. According to Corkey Bell's book, throttle body velocity on a turbo motor should not exceed 300-ft/s. What good is this too you? Well I have equated the following together for more practical usage. This is done with a combination of data from common throttlebody sizes, hp levels, and maintaining close to a 300ft/s velocity. 300ft/s velocities were used to show the minimum size needed for that horsepower level efficently. Dont forget that the manifold has to be ported to the size of the throttle body also! 850cfm -> 75mm tb -> 298ft/s -> about 650chp 720cfm -> 70mm tb -> 289ft/s -> about 550chp 640cfm -> 65mm tb -> 298ft/s -> about 500chp 540cfm -> 60mm tb -> 296ft/s -> about 400chp 470cfm -> 58mm tb -> 276ft/s -> about 350chp 400cfm -> 52mm tb -> 290ft/s -> about 300chp 340cfm -> 48mm tb -> 291ft/s -> about 250chp Frank

How did you figure the CFM?? I thought throttle bodies were flow tested like carbs are......at 10" of vacuum.I think they flow a whole bunch more when you add pressure

[Ondonti]

Hey, what about the bar that holds the throttle plate, that blocks a lot of airspace.

A good Carb modification when you have limited carb size is to flatten the bar and remove the bolts, then braze the plate on. Can increase the flow potencial 20%.
Not sure if a turbo would break that setup.

[Putter]

To move air 300ft/sec isn't even breaking a sweat of the speed of sound (roughly 1,100ft/sec). I am extremely curious to why such a low velocity, and what may even be more fun to figure is what manifold runner velocity at those same given power levels to compare TB velocity over intake runner velocity (which I would assume...you know how that goes... would be significantly higher than TB velocity). It may be a hard number to generate due to the actual duration of the intake cycle and account for manifold tuning....but I'm no engineer!

[russ jerome]

Quote:

Originally Posted by BadAssPerformance Since you got it memorized, why did he say 300 ft/s was the limit?

Was gonna cheat and re read it but I dont see his book...

Something about sonic speed air colliding and causing
turbulence. Along same lines as why given the choice you
would have an angle or convoluted end on your intake's rear
plenum, keeping air from smashing against stuff.

Today's 6,7 and 8 second cars are reverse engineered from
Corky's idea's:

Throttle bodies big enough to fit a grapefruit thru.
Intake plenums 100% the size of motors total cubic inch's.
Long tube headers with turbo's in headlight bucket.
Intercooler plumbing 3-4" inside diameter.
Compression ratio's equal to NA motor.

If Corky saw Stephan's car he would shake his head in
disbelief

[Ondonti]

Doesnt stephane have a big plenum, long headers, and turbo hear the headlights......

[russ jerome]

Quote:

Originally Posted by Ondonti Doesnt stephane have a big plenum, long headers, and turbo hear the headlights......

Yup, should be a lag monster and top end would be killed
by the loss of energy as expanding gass's soften before
turbo. Old school vs new idea's.

I built this intake for a Starlet owner, he used to run high 10's
with old setup. Called me last weak after first test run, wants
to know how we limit boost out of hole as he has never had
this much throttle response



Thats a GM 74mm throttle body I customized with a 3" inlet so
he could run his present plumbing on the huge TB I wanted
to make the plenum bigger (it's over 4" ID now) but he was
afraid of lag...LOL!

[Frank]

Quote:

Originally Posted by gasketmaster How did you figure the CFM?? I thought throttle bodies were flow tested like carbs are......at 10" of vacuum.I think they flow a whole bunch more when you add pressure

I calculated the required engine airflow to make that horsepower.


Frank

[Frank]

Quote:

Originally Posted by russ jerome Was gonna cheat and re read it but I dont see his book... Something about sonic speed air colliding and causing turbulence. Along same lines as why given the choice you would have an angle or convoluted end on your intake's rear plenum, keeping air from smashing against stuff. Today's 6,7 and 8 second cars are reverse engineered from Corky's idea's: Throttle bodies big enough to fit a grapefruit thru. Intake plenums 100% the size of motors total cubic inch's. Long tube headers with turbo's in headlight bucket. Intercooler plumbing 3-4" inside diameter. Compression ratio's equal to NA motor. If Corky saw Stephan's car he would shake his head in disbelief

Thought so! It not that the mean velocity of air is moving anywhere near sonic speeds, however air going around throttle body plates and where the TB meats the plenum. While turbulence is good for even air distrubution in the plenum, too much is very bad. I think that is the case on our cars.

Also remember we could through a huge tb on our car, but the car would be ugly on the street. (Well Russ knows that... just reminding other people)


Frank

[Shel-Game]

Quote:

Originally Posted by Putter To move air 300ft/sec isn't even breaking a sweat of the speed of sound (roughly 1,100ft/sec). I am extremely curious to why such a low velocity, and what may even be more fun to figure is what manifold runner velocity at those same given power levels to compare TB velocity over intake runner velocity (which I would assume...you know how that goes... would be significantly higher than TB velocity). It may be a hard number to generate due to the actual duration of the intake cycle and account for manifold tuning....but I'm no engineer!

I don't understand that either. The way a throttle works is by choking the airflow. By definition, that means the airspeed equals the speed of sound. If the throttle is only ~1/3 the speed of sound at WOT, then that means the last half (or so) of throttle movement does nothing.