mike93eh2

one thing i have always wondered was how do you know what size throttlebody to go with your setup ??

i dynoed last year with my stock 56mm stock TB and 2.25" charge pipes and made 403whp and 310 ft lbs. (who knows what it is now, but plan to redyno tune once i get the intake mani and TB)

i bought a edelbrock manifold and am looking to buy a TB.. but what size? does it matter? does it make any sense for the TB being bigger than the charge pipe ? should i upgrade to a larger pipe on my setup?

Tippyman

Well, my stock throttle body had the exact same diameter as my charge piping so I kept it that way.

I don't know how much that hurts or helps me, but I didn't have to use a reducer coupling so I'm happy, lol.

mike93eh2

so what does the tb size mean then?? does it hurt to go big?

Tippyman

The way I thought about it was, the turbo is pushing air in right? Unless you're making so much power that the turbo is having a hard time pushing air through the hole, don't worry about it.

I figured that my throttle body wasn't the source of restriction. Every engine has sources of restriction, and I figured the throttle body was pretty low down on the list. My intercooler, turbo, and cam are probably more restrictive to my engines breathing than the tb.

boosstboy

i'm trying to find some info i had on this as far as velocity and flow amounts. i know on N/A cars you can hurt it bad by going to big (slows velocity of air down), on turbo cars it will hurt more on part and low throttle. an engine always has a component of most restriction, so upsizing on a tb may hurt or help hp depending on mods. i hope someone has some more info, cause this is a good Q.
i'm using this thanks to a post in the mustang forum, i still like my fords hope this helps

THE AIR PUMP UNDER YOUR HOOD
By George Klass
What size throttle body or carburetor do I need?
Good question but the real question should be “how many cubic feet per minute (CFM) of air will my engine require?”
An engine is an air pump. Based on the size of the engine (displacement) and how fast it will be spinning (RPM), it will pump out a certain amount of air. Works just like an air compressor. Of course, there are many variables to CFM requirements, such as cylinder head flow capabilities, intake and exhaust manifold flow capabilities, etc., but the basic engine block will pump a certain amount of air over a specified period of time, measured in cubic feet of air per minute.
If the engine is to be carbureted, it should be a relatively easy decision to pick out the correct sized carburetor. Carburetors are defined by CFM. If your engine calls for (or pumps out) about 664 CFM, the correct choice is probably a 650 CFM carburetor. Unfortunately, throttle bodies are rarely defined by CFM ratings. Instead, most throttle body manufacturers define their throttle bodies by the inside diameter of the unit, measured at or around the throttle blade, and usually in Millimeters (MM). Unless you have a direct correlation between the measurement in MM and the related CFM of that particular unit, the selection is going to be based on “best guess”.
And to further complicate the “guessing” process, all throttle bodies of the same dimension, do not have the same CFM rating. You might think that Brand A’s 75 MM throttle body would flow the same as Brand B’s 75 MM throttle body. Such is not the case, because all throttle bodies have a “major obstruction” in the middle of the air path, namely a throttle blade and shaft. How well the air flows over and under this obstruction will define the CFM a specific throttle body will flow. A big fat shaft with the attachment screws for the blade sticking up into the air stream will impact the CFM of that throttle body.
While most enthusiasts with EFI engines continue to purchase throttle bodies based on Millimeter size, caring little about the actual CFM ratings, the carb guys purchase carburetors based on CFM ratings, caring little about the size of the throttle plates. Score one for the carb guys.
But, back to the original question, “how much CFM do I need”?
Below is a chart with the CFM requirements, based on displacement (in cubic inches) and RPM. This chart will work for any piston engine with any number of cylinders. After you have determined the CFM for your specific engine combination, you can then choose the corresponding throttle body or carburetor size to best fit that combination.
DISPLACEMENT………….6000 RPM……….6500 RPM……….7000 RPM
280………..…………………486………………..527………………..567
290……..……………………503………………..545………………..587
300………..…………………521………………..564………………..608
310……..……………………538………………..583………………..628
320……..……………………556………………..602………………..648
330………..…………………573………………..621………………..668
340……………..……………590………………..639………………..689
350……..……………………608………….…….658………………..709
360………………..…………625………………..677………………..729
370………………..…………642………………..696………………..749
380………………..…………660………………..715………………..770
390………………..…………677………………..734………………..790
400………………..…………694………………..752………………..810
410………………..…………712………………..771………………..830
420………………..…………729………………..771………………..830
430………………..…………747………………..809………………..871
This chart should give you a general idea of the amount of air your combination will pump. Engines will pump less air because of the restrictions in the cylinder head or intake manifold design or valve lift, or all three. But, the chart still gives you a ball park starting point.
One other thing to know. A carburetor requires air speeding over the venturi to draw the gasoline into the mixture. Using too large a carburetor (high CFM rating) will usually cause derogatory performance in the lower or midrange. This is because the lower air velocity is inefficient in mixing the gasoline with the air. In general, and particularly for street use, a slightly smaller carb (less CFM) will give better overall performance.
With an EFI system, this is usually not a problem. The throttle body only controls air flow. A computer monitors the gasoline supply and the mixing of gasoline and air takes place inside the intake port, and not inside the carburetor. Using an oversize throttle body is not nearly as detrimental to low and midrange performance as is using an oversize carburetor.
So, to find the CFM ratings of a carburetor, all you need to do is to look in any catalog from Holley, Edelbrock, Barry Grant, etc. That’s how the carburetors are listed. To find the CFM ratings for a throttle body is going to be more difficult, unless you happen to choose an Accufab throttle body.
Below are the various throttle body sizes and corresponding CFM ratings for the Accufab throttle bodies. Because the Accufab throttle bodies are designed to “race engine specs”, the flow ratings are going to be greater than most of the other aftermarket throttle body designs, so don’t automatically expect a “75 MM Brand B” throttle body to flow as much as an Accufab 75 MM unit.
65 MM - 664 CFM
70 MM - 787 CFM
70 MM - 896 CFM (Race version)
75 MM - 924 CFM
75 MM - 1045 CFM (Race version)
80 MM - 1142 CFM
85 MM - 1322 CFM
90 MM - 1369 CFM
105 MM - 1550 CFM



Modified by boosstboy at 6:53 PM 1/2/2008

boosstboy

Modified by boosstboy at 4:31 PM 1/3/2008

mike93eh2

anyone else?

mike93eh2

i know but there has to be more to it then just run the biggest you can get... i think ill just stick with something small like 62,65, or 68mm

Tippyman

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">
Its all in the eye of the beholder really, I would use the same size that your inlet is on the intake mani </TD></TR></TABLE>

That's what I would do on an FI car. On an all motor car it may be more of a science, but I doubt it would really make a huge difference on an FI car.

mike93eh2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tippyman &raquo;</TD></TR><TR><TD CLASS="quote">

That's what I would do on an FI car. On an all motor car it may be more of a science, but I doubt it would really make a huge difference on an FI car.</TD></TR></TABLE>

yea but what kind of side effects would a larger tb on a turbo car have like with part throttle and such?

ExecutiveA

Bigger TB = Less Airspeed more Volume...

on any 4 banger 15/16/18/2000cc the biggest i would go is 70mm

mike93eh2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ExecutiveA &raquo;</TD></TR><TR><TD CLASS="quote">Bigger TB = Less Airspeed more Volume...

on any 4 banger 15/16/18/2000cc the biggest i would go is 70mm</TD></TR></TABLE>

well i have the air speed or velocity thanks to my 2.25" charge piping.. the TB is basically just the opening to the intake plenum. and my edelbrock plenum is larger than the TB.

thewrai6th

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">I would use the same size that your inlet is on the intake mani</TD></TR></TABLE>

Schister66

Your actual results may vary (ie when you add an IC) so just use my numbers as sort of a bench mark to compare different piping sizes. One thing you guys will notice is that none of the velocities go above 304 MPH or 0.4 mach. According to Corky Bell, Maximum Boost pg 61, 304 MPH or 0.4 mach is the point at which airflow meets increased resistance (drag) and flow losses are experienced.

**I'm not sure how to upload or link it, but i have a complete copy of Corky Bell's Maximum Boost on .pdf if anyone is interested**

Anyways here are the numbers I came up with. The velocities are in miles per hour and mach, and the flow rates are in cfm. Measurements for the piping are in inches.

****For those of you who dont want to figure out in CFM, the conversion to lb/min is this: 100cfm = 8.07 lb/min****

0.4 mach = 304 MPH

2" piping
1.57 x 2 = 3.14 sq in
300 cfm = 156 mph = 0.20 mach
400 cfm = 208 mph = 0.27 mach
500 cfm = 261 mph = 0.34 mach
585 cfm max = 304 mph = 0.40 mach


2.25" piping
3.9740625 sq in = 1.98703125 x 2
300 cfm = 123 mph = 0.16 mach
400 cfm = 164 mph = 0.21 mach
500 cfm = 205 mph = 0.26 mach
600 cfm = 247 mph = 0.32 mach
700 cfm = 288 mph = 0.37 mach
740 cfm max = 304 mph = 0.40 mach


2.5" piping
4.90625 sq in = 2.453125 x 2
300 cfm = 100 mph = 0.13 mach
400 cfm = 133 mph = 0.17 mach
500 cfm = 166 mph = 0.21 mach
600 cfm = 200 mph = 0.26 mach
700 cfm = 233 mph = 0.30 mach
800 cfm = 266 mph = 0.34 mach
900 cfm = 300 mph = 0.39 mach
913 cfm max = 304 mph = 0.40 mach


2.75" piping
5.9365625 sq in = 2.96828125 x 2
300 cfm = 82 mph = 0.10 mach
400 cfm = 110 mph = 0.14 mach
500 cfm = 137 mph = 0.17 mach
600 cfm = 165 mph = 0.21 mach
700 cfm = 192 mph = 0.25 mach
800 cfm = 220 mph = 0.28 mach
900 cfm = 248 mph = 0.32 mach
1000 cfm = 275 mph = 0.36 mach
1100 cfm max = 303 mph = 0.40 mach


3.0" piping
7.065 sq in = 3.5325 x 2
300 cfm = 69 mph = 0.09 mach
400 cfm = 92 mph = 0.12 mach
500 cfm = 115 mph = 0.15 mach
600 cfm = 138 mph = 0.18 mach
700 cfm = 162 mph = 0.21 mach
800 cfm = 185 mph = 0.24 mach
900 cfm = 208 mph = 0.27 mach
1000 cfm = 231 mph = 0.30 mach
1100 cfm = 254 cfm = 0.33 mach
1200 cfm = 277 mph = 0.36 mach
1300 cfm max= 301 mph = 0.39 mach

Based on these numbers you can get a good idea of what size charge piping you need. Also, the throttle body should be about the same size as the charge piping.

mike93eh2

ive decided to just stick with my 60mm h23 throttlebody. no point in getting an aftermarket except for bling. the inlet on the edelbrock is 62mm..

mike93eh2

anyone know what kind of tuning would be needed if any from switching froma stock z6 intake manifold to a edelbrock performer x ? ive got a dyno about 2 miles from my house but was just wondering.

Running925

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike93eh2 &raquo;</TD></TR><TR><TD CLASS="quote">anyone know what kind of tuning would be needed if any from switching froma stock z6 intake manifold to a edelbrock performer x ? ive got a dyno about 2 miles from my house but was just wondering.</TD></TR></TABLE>

my assumption is that it would be less restrictive up top (according to their advertising that says it makes more power 7k-10k).

so my guess is that you wouldn't see a whole lot of change down low, maybe slightly, but would expect to see your motor need more fuel added up top coz it would be flowing more air (less restricted air). It's probably not going to take a whole lot to adjust it for an intake manifold change but you should see a difference. Especially in the 400whp range.

mike93eh2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">I needed a bit more fuel when I put an aftermarket IM on a while back. You might as well get a new tune with some more boost haha</TD></TR></TABLE>

this 57 trim is pretty much pooped out at my 25psi..

and i hope i dont have to add too much more fuel because my injectors have been at 99% duty cycle (according to hondata) for the past year LOL...thats running about 42psi fuel pressure, should i raise the fuel psi up a little more you think?

well in the hot summer it doesnt need as much fuel but with these 5 degree temps lately it needs more fuel than normal so thats why its at 99% in the winter and about 95-96% in the summer.

stupid *** 780cc injectors

mike93eh2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rota92 &raquo;</TD></TR><TR><TD CLASS="quote">
Get a 60 trim and 1000cc's and call it a day! </TD></TR></TABLE>

that is sorta the plan later on down the road

i cant build a hot rod car in 2 months like you can...baby steps... lol j/k

SteamedRice

the only thing i've known to do when deciding TB/IM matching is to make sure the throttle body is slightly smaller than the IM opening to prevent reversion (at least while still in vacuum). some macine shops do a venturi effect on TB/IM port matching, so that last statement is more true, and you can retain flow rates (inlinefour.com). but this is definitely a gray area for me.

ej8

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike93eh2 &raquo;</TD></TR><TR><TD CLASS="quote">

this 57 trim is pretty much pooped out at my 25psi..

and i hope i dont have to add too much more fuel because my injectors have been at 99% duty cycle (according to hondata) for the past year LOL...thats running about 42psi fuel pressure, should i raise the fuel psi up a little more you think?

well in the hot summer it doesnt need as much fuel but with these 5 degree temps lately it needs more fuel than normal so thats why its at 99% in the winter and about 95-96% in the summer.

stupid *** 780cc injectors </TD></TR></TABLE>

Yeah bump the fuel pressure to 50psi, then you will be able to drop the duty cycle in your injectors when you retune. This will get you by until you get larger injectors

As far as throttle body sizes, FI guys have good luck with 70mm TBs. More power up top and better throttle response. Theroies and numbers aside, its real life results that matter. I would like to see a dyno comparison of a throttle body change.

ExecutiveA

****I would like to see a dyno comparison of a throttle body change. *****

That Would be Awsome!!!!!!

schwitzerT

1) Well the Fact that they Manufacture Larger TB, means they must work(Correct?) How well who knows.
2) What ever Power Figure you are aiming for the Stock TB WILL BE SUFFICENT! but the Carateristic of the Car will Change.

I upgraded from a 41mm - 70mm. i was looking for a 57 or 63 upgraded but only the 70mm was avalible so i took it. When installed a Recieved No Power Increase Just Better Throttle Response.

So did i do the Correct thing.
I do think the TB was a Restriction,now the Restriction has moved further down the line to the Unported Intake manifold and Un ported Cylinder head.so when im done porting both things should be 100%.

But now the Question is.for what aplication is which one better? whic Is better, Airspeed or Volume?

Now my next question is , if you look at the Pic you will see im using a Reducer, SHould i keep the Reducer or loose it ?

the Original Setup was TB 41mm Port on Intake manifold 56mm
now the aftermarket TB 70mm Port on Intake manifold 56mm(still)

I reckon i can port the whole Safely upto 66mm and make up a new reducer.
But i am yet to find any concreate fact's regarding TB' size.

Here is da pic

rudebwoy

iTrader: (1)

I run a edelbrock intake manifold with a edelbrock 65mm throttle body, with 2.5", I think thats a perfect balance, I've many people running 70mm + size TB , with similar parts, I don't understand why. because the 65mm tb is bigger than the 2.5" piping so why would you need more?
another thing I install all these parts and never had a chance to dyno to see if they are worth it.

Tony the Tiger

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Schister66 &raquo;</TD></TR><TR><TD CLASS="quote">Anyways here are the numbers I came up with. The velocities are in miles per hour and mach, and the flow rates are in cfm. Measurements for the piping are in inches.............

</TD></TR></TABLE>

Great post on the data...