Back to back fox versus 94-95 TB dyno results inside!!!

I agree I would really like to see 5.0 or MMFF pick this up and do some comparisons. As an Sn95 intake setup guy for me to do the conversion, I wanna know if the elbow behind the throttle body is a restriction or not. This is where I will make my decision. The throttle response argument isn't enough for me because I gained a lot of throttle response eliminating the 90 in front of the mass air meter. This is also accomplished with the fox thotttle body conversion. And I beleive alot of guys who do this conversion beleive that the thorttle response they just picked up was because of the elimination of that bend behind the throttlebody when in fact it was really do to the bend in front of the mass air meter.

With regards to throttlebody size I guess im in the other crowd because I beleve that you can go too big. I think theres a fine line between just the right amount of velocity and too much to the point where low end torque is affected. I've tried them all JMO.

I hope some see that this is a 360+ RWHP ride. It does not matter what top-end pieces, like the cylinder heads, that are on it. It is still putting out 360-370 RWHP.

It is the equivalent of a 328-338 RWHP 302.

I am very glad this test was done. Believe it or not, one of the most accurate I have seen. As has been stated, the difference is negligible and proves over and over the point a couple of us have been stating.

Bigger is not better when it comes to some select TB:Combo ratios, just more expensive.

Also, as Paul stated, an engine with some mileage on it shows how an engine loosens up. I have seen many before and after test run with 100 miles, then with 10,000 miles. Does anyone honestly think they are going to make the same HP/TQ? Of course not, but they claim gains from new parts they added.

Rick (the one who built Paul's engine) has said on several occasions that the fox set-up is less restrictive.

greenlantern said:

I agree I would really like to see 5.0 or MMFF pick this up and do some comparisons. .

Click to expand...

I shot an e-mail off to 5.0 Mustang and Modified Mustangs w/ a link to this thread. Who knows maybe they will have some interest in doing it.

There is a great discussion about TB sizing in which Jay Allen pitched in his thoughts here:

http://sbf_REMOVE-ME_tech.com/index.php/topic,9683.0.html

You'll have to edit the "_REMOVE-ME_" out of the link so it will work, I'm not sure why StangNet blocks other site URLs.

:SNSign:

Wes

And how about some datalogs? Dyno numbers are good but there are also a good many variables there!

Wes

greenlantern said:

With regards to throttlebody size I guess im in the other crowd because I beleve that you can go too big. I think theres a fine line between just the right amount of velocity and too much to the point where low end torque is affected. I've tried them all JMO.

Click to expand...

Remember, the throttle body is just a valve to let air in and out.

A larger throttle body blade has more area, and therefore if a 65 and 90 mm TB are depressed 10% (assuming 15% closed angle) , a 65 mm TB opens up to .32^2 inches, while a 90 mm TB opens up to .61^2.

Almost exactly double the open air area, and yet only 38% larger. This will:

A. Increase throttle response

or...

B. Create a touchier pedal

Depends on what one is willing to put up with.

Stanger007 said:

And how about some datalogs? Dyno numbers are good but there are also a good many variables there!

Wes

Click to expand...

Way more variables at a track Wes for daily driver, street and weekend warrior cars.

Also, many do not think about the upper intake tract after the throttle body. In many cases, the area is less than the throttle body area, even with the blade (.080" x 2.56" ) and shaft thickness.

5spd GT said:

Way more variables at a track Wes for daily driver, street and weekend warrior cars.

Click to expand...

Thinking datalogs of these dyno pulls...

Redline_351R said:

what we really need is the ability to compare TB to TB in controlled conditions, much of which is done in magazines.

Click to expand...

You are kidding, right?
The complete jokes of a magazine that we have offered to us are so biased it's not even funny. There may be some legit info in them but most is just

This is a cool thread, no doubt. Kudo's to Paul for stepping up. I still am 100 percent agreeing with Mike's statement:

WhiteCobra95 said:

I have to chime in on this one. I’ve calibrated a lot of TB air flow models and there are a couple big points being missed here.

Compare the areas of the two TB’s.

65mm: 3.14 * (65/2)^2 = 3316.625 mm^2
74mm: 3.14 * (75/2)^2 = 4415.625 mm^2

The relative difference in area is about 33%! This is like comparing apples to watermelons.

Don’t get me wrong; I still think that this comparison is interesting, but the only conclusion I can draw from the data is that the 65mm TB is somewhat restrictive when compared to the 75mm part.

Click to expand...

That little 331 is screaming pretty good. Throw another atmosphere at it and you are looking at 700rwhp... do you have that 9 second license yet???

Adam

I am gonna say this about throttle body size. A throttle body is not like a carb where it needs to create a vacumm in the venturi to pull the fuel out of the boosters. If you size a carb to large for a application it kills torque and throttle response due to decreased signal at the venturi's.

A too large throttle body is not going to hurt anything. It will just be more sensative to throttle inputs which can cause very touchy throttle response. On the same hand it will not help anything either unless your planning ahead for more signifigant mods down the road.

rj95svt said:

I am gonna say this about throttle body size. A throttle body is not like a carb where it needs to create a vacumm in the venturi to pull the fuel out of the boosters. If you size a carb to large for a application it kills torque and throttle response due to decreased signal at the venturi's.

A too large throttle body is not going to hurt anything. It will just be more sensative to throttle inputs which can cause very touchy throttle response. On the same hand it will not help anything either unless your planning ahead for more signifigant mods down the road.

Click to expand...

This is a good thread.

I wonder if the increased throttle response that Paul is feeling isn't due so much to the Fox switch, but is more due to the increased air let in by the larger throttle body, for the same amount of, for lack of a better phrase, "gas pedal pushed in."

To illustrate, say the Accufab flow 1000CFM (not the real number, just bear with me) and the FMS flows 600. If Paul depresses the pedal half way in with the 75, he gets around 500cfm flowing, but the same amount of pedal depression on the 65 nets him about 300, the 75mm will feel as though the throttle reponse is WAY better.

Take that a step farther, and I'll wager (5 bucks) that if Paul swapped on a 75mm throttle body in a 94/95 setup, there wouldn't be near a throttle response desparity between that and the fox. The only desparity would be in the superiority (more flow per "pedal push) of the accufab throttle body and the arc of the cable of the fox throttle body. I just heard about that difference recently though so I'll strike that and make it a constant for the purposes of this exercise.

Adam

I'm sure that the fox swap will be more responsive due to the differences in geometry of the the throttle linkage but your right the larger size will make some difference as well. Personally I would love to swap to a fox style throttle body because of the superior quality of the accufab throttle bodies over anything available for a 94-95 but because I have a cobra I'm not sure if I want to change the stock intake. If I ever upgrade to a holley intake I will install a accufab fox setup

The FRPP SVO 65 mm TB flows 540 CFM.
The Accufab 75 mm TB flows 924 CFM.

To find a solid estimate on how many cubic feet per minute an engine can inhale, use the following formula on a 347 being spun to 6,500 RPM at 100% volumetric efficiency:

347 x 6500 x 1.0/(1728/2) = 652.633 CFM

A 302 cubic inch engine flows 524.306 CFM at 6,000 RPM with 100% VE.
A 331 cubic inch engine flows 574.653 CFM at 6,000 RPM with 100% VE.
A 347 cubic inch engine flows 602.431 CFM at 6,000 RPM with 100% VE.
A 351 cubic inch engine flows 609.375 CFM at 6,000 RPM with 100% VE.
A 393 cubic inch engine flows 682.292 CFM at 6,000 RPM with 100% VE.
A 408 cubic inch engine flows 708.333 CFM at 6,000 RPM with 100% VE.
A 427 cubic inch engine flows 741.319 CFM at 6,000 RPM with 100% VE.

Compare this to the flow numbers from the throttle bodies. I realize that an engine does not see a pressure differential of 28” all the time, but it gives a baseline to compare all the throttle bodies. As the pressure differential increases (greater than 28”), the flow increases through the throttle body. As the pressure differential decreases (less than 28”), the flow decreases. Accufab scores a 75 mm throttle body at 924 CFM at 28” and 780 CFM at 20”. So if you flow that same throttle body at 36”, it will crest over 1000 CFM for a 75 mm throttle body. However I am aware that pressure differentials to flow ratios are not linear, but the CFM will be more linear than a cylinder head, due to the throttle body being a simple straight through design, with shape and design being a minimal issue.

Paul's ride is putting out 360-370 RWHP and look what it did with the sn-95 style set-up and the 65 mm TB. Again, Rick himself, has stated that that set-up is restrictive (sn-95).

Also, again, many do not realize that the upper intake restricts what a throttle body can do. The throttle body can show gains if the area after the throttle body is larger than the blade area - the TB valve obstructions.

Yes, the added "throttle response" (touchier throttle) is due to the larger surface area of the throttle body and the linkage angles.

Now, if you've got a throttle body that delivers 100% of the peak air requirements of your engine when the throttle plate is fully open, you have control of the air throughout 100% of the throttle position range. If you go to an oversized TB that delivers 100% of the air that your engine can consume while the throttle plate is only 60% open, you have given up usable throttle-control range for no advantage. Now I see this being a non-issue for track engines, because tip-in or throttle control is usually never thought about as a concern.

Take the well known LS1, with the 71.5 mm (back side measurement) throttle body. A couple measurements I have taken are 74.20 mm for the initial opening, and the minimum section was 73.14 mm.

Now even with a 71.5mm (75mm opening) TB from the factory, they include a throttle cam. Take the '98-'99 pulley system for opening the throttle, which has very close to the same cable pull to the angle of the blade. Now, what did GM do for the later years following 1999? They created a nautilus shell style throttle cam, where the part throttle portion of the cam requires more pull on the cable, with less degree angle actually being applied to the throttle body. As the blade gets closer to WOT, the radius of the cam shrinks and allows the blade to open up completely to WOT. So why would GM, do this?

Easy answer; it is to help with part throttle touchiness.

I have often said that more throttle response can be described in two ways:

1. More throttle response

2. Touchier throttle response

The area of a circle is PI x radius x radius. The radius is half of the diameter of the blade or circle.

Example: 60 mm/25.4 = 2.36. 2.36/2 = 1.18. Then 3.14 x 1.18 x 1.18 = 4.38” (squared).

58 mm - 4.09”
60 mm - 4.38”
65 mm - 5.14”
70 mm - 5.96”
75 mm - 6.84”
80 mm - 7.79”
85 mm - 8.79”
90 mm - 9.86”
95 mm - 10.98”
105 mm - 13.41”

The twin throttle bodies are a little different. You need to add the areas together of each individual blade, so the areas are:

57 mm - 7.90”
62 mm - 9.36”
65 mm – 10.28”

NASCAR is in the 125% VE with 358 cubic inches. They also run 750-830 CFM carburetors. Could they make more power with a larger carburetor? Very possible, but it shows you that the restriction is small, considering they are making near the 850 HP mark.

rj95svt said:

I am gonna say this about throttle body size. A throttle body is not like a carb where it needs to create a vacumm in the venturi to pull the fuel out of the boosters. If you size a carb to large for a application it kills torque and throttle response due to decreased signal at the venturi's.

A too large throttle body is not going to hurt anything. It will just be more sensative to throttle inputs which can cause very touchy throttle response. On the same hand it will not help anything either unless your planning ahead for more signifigant mods down the road.

Click to expand...

Good post.

5spd GT said:

The FRPP SVO 65 mm TB flows 540 CFM.
The Accufab 75 mm TB flows 924 CFM.

To find a solid estimate on how many cubic feet per minute an engine can inhale, use the following formula on a 347 being spun to 6,500 RPM at 100% volumetric efficiency:

347 x 6500 x 1.0/(1728/2) = 652.633 CFM

A 302 cubic inch engine flows 524.306 CFM at 6,000 RPM with 100% VE.
A 331 cubic inch engine flows 574.653 CFM at 6,000 RPM with 100% VE.
A 347 cubic inch engine flows 602.431 CFM at 6,000 RPM with 100% VE.
A 351 cubic inch engine flows 609.375 CFM at 6,000 RPM with 100% VE.
A 393 cubic inch engine flows 682.292 CFM at 6,000 RPM with 100% VE.
A 408 cubic inch engine flows 708.333 CFM at 6,000 RPM with 100% VE.
A 427 cubic inch engine flows 741.319 CFM at 6,000 RPM with 100% VE.

Compare this to the flow numbers from the throttle bodies. I realize that an engine does not see a pressure differential of 28” all the time, but it gives a baseline to compare all the throttle bodies. As the pressure differential increases (greater than 28”), the flow increases through the throttle body. As the pressure differential decreases (less than 28”), the flow decreases. Accufab scores a 75 mm throttle body at 924 CFM at 28” and 780 CFM at 20”. So if you flow that same throttle body at 36”, it will crest over 1000 CFM for a 75 mm throttle body. However I am aware that pressure differentials to flow ratios are not linear, but the CFM will be more linear than a cylinder head, due to the throttle body being a simple straight through design, with shape and design being a minimal issue.

Paul's ride is putting out 360-370 RWHP and look what it did with the sn-95 style set-up and the 65 mm TB. Again, Rick himself, has stated that that set-up is restrictive (sn-95).

Also, again, many do not realize that the upper intake restricts what a throttle body can do. The throttle body can show gains if the area after the throttle body is larger than the blade area - the TB valve obstructions.

Click to expand...

EXCELLENT POST.

does any body know if the race 75 mmm flows any better ?you know the one with the 90mm opening. it was made for the renegade cars because they were limited to 75mm tb.

The amt of power is only as high as the most RESTRICTIVE part of the flow allows. If the restricition is at some point other than the 65 mm TB, then the TB size after that is irrelevant. Or also stated....a "100mm" TB with all other things being equal does not make more power, so I dont think the size difference in this case is as important as people are making it seem, since I dont think the most restrictive part is the 65 mm TB.

RC