Does a smaller bladed TB give a better throttle response? Like 75 mm inst of 80mm?

[Pokageek]

 

[5spd GT]

Better throttle response is in the eye of the beholder.

As I have explained it before, the larger throttle body will introduce more air in, at the same tip-in angle, but WOT air flow usually is the same.

"More throttle response" can be described in two ways and it is the same thing:

1. More throttle response
2. Touchier throttle

It is not the o.d. diameter change so much (ex. + 5 mm), but the area increase of nearly 33%.

I have more, but I will wait.

 

[Pokageek]

I'll take number 2 for $500 Alex.

 

[Killercanary]

It'll feel "snappier" with the larger TB due to the reason mentioned above of its area and the amount of air that is able to enter at the same throttle blade position.

 

[Zero Signal]

Yeah I'd like to know what people mean when they say better throttle response. Smoother power (i.e. better power modulation) or just touchy throttle as mentioned above.

I've always just imagined it like having an overall better feel between the power and where your foot is. For example, my Bronco has horrible throttle response. The first 1/4 inch is all I use. The middle of the pedal range doesn't do much more and the last inch or so has no effect, so mashing the pedal and holding it about 1/2 way has about the same feel. Then again, the 5L bronco only has something like 150hp.

I would think a GOOD throttle response would be one where you use the whole pedal and it maxes out at the last 1/4" or so of travel. But at the same time, have some touchiness to make the car feel nice and torquey.

 

[Pokageek]

I am looking for touchiness. Meaning I get power through the entire pedal pressdown. Not an on off switch.

 

[BlackVert]

Keith, there are at least 3 things going on here that you might be interested in:

(1) - differences between a SN95 style and a Fox style TB, both having the same blade size
(2) - differences between a 75 and 80mm TB of the same style
(3) - velocity of the air through the intake track

Given the way you worded the question, I suspect you are asking about (3) ... But ...

re (1) ... the pulley on a SN95 TB is elliptical, whereas a Fox TB pulley is more circular, such that for the same amount of throttle cable pull, a Fox throttle blade actually opens farther than does a SN95 one, which makes for ... take your pick ... (a) "better throttle response" nice or (b) a "touchier throttle" notnice. Ford changed the design for SN95 to give the driver more control over part throttle operation. I guess Ford looked at it as (b). Frankly, I'm with Ford on this one.

re (2) ... as the others have said, the larger diameter opening will mean that for the same blade angle, there will be a larger opening so more air should be able to get in, making it ... again ... (a) or (b).

At WOT, either one would probably be able to flow enough air to not be a restriction for your 414.

re (3) ... in a racing application like NASCAR, as you can imagine, they spend alot of time trying to squeeze the most power out of the engine as possible under the racing conditions, In that case, the velocity of the air going through the intake track is important, because the faster the air is moving when it hits the open intake valve, the more air will make it into the cylinder. To that end, they tailor the runner lengths and cam, and they size and taper the intake track to achieve the maximum velocity possible. Using these techniques, they can actually achieve a volumetric efficiency of over 100%, or in other words, a little boost without a blower! But remember, that is tuned for the fairly small RPM range that they want to maximize. At that level, it is the small stuff like this that makes the difference between winning and losing. That is cool stuff and neat to think about, but for street cars like ours, there are so many other inefficencies and variablilty in the RPM range and type of driving we do, that the velocity of the air in the intake track is not even on the radar as far as making a difference in the performance or the throttle response.

Does that help?

 

['94ChickStang]

I am looking for touchiness. Meaning I get power through the entire pedal pressdown. Not an on off switch.

My "touchiness" went away when I went from 65 to 70, which seems to be contradicting everyone's opinion up to this point in the thread. It felt snappier with the smaller unit until the pedal was about halfway down. Not in my head either, a real, noticable difference right away.

 

[BlackVert]

Yeah I'd like to know what people mean when they say better throttle response. Smoother power (i.e. better power modulation) or just touchy throttle as mentioned above.

I've always just imagined it like having an overall better feel between the power and where your foot is. For example, my Bronco has horrible throttle response. The first 1/4 inch is all I use. The middle of the pedal range doesn't do much more and the last inch or so has no effect, so mashing the pedal and holding it about 1/2 way has about the same feel. Then again, the 5L bronco only has something like 150hp.

I would think a GOOD throttle response would be one where you use the whole pedal and it maxes out at the last 1/4" or so of travel. But at the same time, have some touchiness to make the car feel nice and torquey.

I hear ya on this ... my Fairlane is what I would call touchy. From closed throttle to the slightest part throttle I can give it, it sort of lurches forward, which makes it kinda scary in close quarters like a parking lot. and by 1/2 throttle, it is done ... no noticeable difference between that and the pedal on the floor. To me, that means the throttle is "touchy" which has a negative connotation. I would like more control over it, especially at light throttle.

I am looking for touchiness. Meaning I get power through the entire pedal pressdown. Not an on off switch.

i think that to most people, "touchy"means not enough control at part throttle, especially from closed throttle to very light throttle. that has a negative connotation. but some people call that "better throttle response" because it responds more to less throttle movement. so i guess it depends on one's perspective.

so are you saying you have an on/off switch now and would like more control over part throttle conditions?

if so, that is probably more a result of the fox style TB as opposed to the SN95 style

 

[Black95GTS]

Dude you have an AFR headed custom cammed 410. Feed the beast. A stock LS1 has a 75mm from the factory with a 346. 80mm seems right for you.

To answer your question, no, it doesn't. My car was much easier to drive switching from a stock to a 65mm.

Adam

 

[Pokageek]

My "touchiness" went away when I went from 65 to 70, which seems to be contradicting everyone's opinion up to this point in the thread. It felt snappier with the smaller unit until the pedal was about halfway down. Not in my head either, a real, noticable difference right away.

This is what I prefer actually. I have done a terrible job of splaining it though. I like nice throttle respose. Like when I went from the stock 58mm tb to the 65mm ford racing TB. Anybody done this and can relate?

"i think that to most people, "touchy"means not enough control at part throttle, especially from closed throttle to very light throttle. that has a negative connotation. but some people call that "better throttle response" because it responds more to less throttle movement. so i guess it depends on one's perspective." - Yes this is what I prefer! So which TB? Bigger or smaller blade?

p.s. The 75mm accufab TB flows more than I would need. Now.. bbk or frpp? Not nearly enough...amazing the diff.

 

['94ChickStang]

These are all great points and the more I read, the more I'm understanding that it's more a perspective thing.

I have my larger TB in now and will make my final decision on 65 0r 70 once I finish up a few tasks I have left with the car. Truly the only way you will know what your preference is would be to have a friend let you use a 75mm unit to try out (or find some other avenue).

 

[BlackVert]

"i think that to most people, "touchy"means not enough control at part throttle, especially from closed throttle to very light throttle. that has a negative connotation. but some people call that "better throttle response" because it responds more to less throttle movement. so i guess it depends on one's perspective." - Yes this is what I prefer! So which TB? Bigger or smaller blade?

So you want it to be touchy and really jump at the slightest throttle movement, right? Sorry ... I'm probably having another senior moment, but I'm confused ... that seems to contradict a previous post of yours:

"I am looking for touchiness. Meaning I get power through the entire pedal pressdown. Not an on off switch. "

Or is it that you want both ... "jumpy" and power all through the throttle band? With the size of your engine, I think that means the smallest FOX TB that will be certain not to be a restriction. I think I would go with the larger TB in that case. Currently, do you notice a difference between 1/2 throttle and full throttle?

Also, with a manual tranny, doesn't that also contribute to how touchy it is (how fast you let the clutch out)?

Just be careful what you ask for ... as Daughtry says:

Be careful what you wish for,
'Cause you just might get it all.
You just might get it all,
And then some you don't want.

 

[Pokageek]

Right. I want like most or all throttle by 75% of the way down so it jumps. The bets way to describe it is when I went stock 5.0 TB to frpp 65mm. It made a jump off the line. Much more responsive. Turning these big blades, me don't think it is as cool a pedal feel.

Here's a better example:

One day after a change under the hood, my car took off like a ROCKET!! I didn't know what I did other than change an old vaccuum tube lol. Turned out the throttle cable was looped a bit around something. When I unlooped it...the car got slower. I then realized that the loop created the blade to be partially open and then open faster and that jerked me back in the seat right away ..RRROMP!

So I took a 2 zip tie and looped them around the throttle cable behind the pedal on the inside of the car and got an incredible rocket romp off the line! I kept it that way and loved the ride,lol.

 

[Chythar]

Well, you took the slack out of the pedal making it more responsive instead of a small delay. That's a nice tip I found on MustangWorld.com a while back - talk about a cheap "power" mod. The gas pedal doesn't get buried in the carpet so you definitely hit WOT.

 

[Pokageek]

I swear the car felt like it had 50 more rwhp and a alot of fun to drive!!

 

[Grn92LX]

Dude you have an AFR headed custom cammed 410. Feed the beast. A stock LS1 has a 75mm from the factory with a 346. 80mm seems right for you.

To answer your question, no, it doesn't. My car was much easier to drive switching from a stock to a 65mm.

Adam

Geez Adam, do you always have to make sense when you post

No negative issues here when I swapped from a 65 to a 75 on my 302 years ago as recommended by Ed C @ FTI.

 

[5spd GT]

Dude you have an AFR headed custom cammed 410. Feed the beast. A stock LS1 has a 75mm from the factory with a 346. 80mm seems right for you.

To answer your question, no, it doesn't. My car was much easier to drive switching from a stock to a 65mm.

Adam

An Ls1 has 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.

The minimum area I measured in my ls1 intake TB track was 73.14".

My car was easier to drive over a stock TB as well. The FRPP throttle body I had was much smoother. It had nothing to do with airflow, just the design and age.

 

[5spd GT]

As I have posted before...

Accufab:

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

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.

With the above information from Accufab's website, you can see that the aftermarket throttle bodies offered flow much more than your engine can breathe (302-347). Those CFM ratings are even given with no restrictions and of course engines all have restrictions, via our heads, cam, intake packaging. An actual running engine flows somewhere in the neighborhood of 70-90% from the factory. Some of the aftermarket throttle bodies flow two times this amount.

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.

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.

Throttle Body Blade Area:

One can figure out the area by a simple formula. Take the millimeter measurement and divide by 25.4 to get the inches across at the blade. Take that number and use it to find the area of the blade. We will use the area of a circle, which is roughly the shape of the throttle body blade and will give a good estimate.

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”

No wonder the Livernois 2000 HP drag car only runs a ~ 100 mm TB.

By the way, the intake tract (from plenum to cylinder) does not allow a straight shot into the cylinders.

First air SITS in the plenum first, and then it bounces back and forth between the higher pressure air in the plenum to the back of the intake valve several times.

Velocity is not an issue here, big or small.

Guys try to give you advice on "go big or go home" when they are having problems comprehending reality.

Also, keep in mind the intake you are working with. Many of them, just a couple inches after the throttle body, have much less area than the TB blade ( - blade thickness of .078-.080" and shaft thickness).

That is also known as a MCSA, minimum cross sectional area.

Think guys, think.

 

[Pokageek]

Thanks 5Spd! What abut going from a 4" cai pipe to a 70mm tb for example, to a 80mm intake opening. Will that screwup air flow enough to make a problem or decrease in hp? Thanks.