Throttle Body Size

[WhiteDevil]

Carnut: My set up is pretty street only. Sound just like what your lookin at except for the heads. I daily drive my car and have for the past few months without issue.

 

[BlackVert]

Thats odd because according to uneducated internet racers, he shoulda lost a lot of low end

note to self: ignore inflammatory comments

He GAINED low end, GAINED mid range and GAINED up top

it seems pretty clear that that was a bona-fide restriction. even a high school drop out can see that. if you try to breathe through a straw, you will die.

what i have been talking about is the case where you have 2 different sized throttle bodies, neither of which is a restriction to the air flow. in that case, the engine is still getting enough air, but the air is moving at different speeds. in this case, which would be better, slower air, or faster air?

of course, when you push the air flow requirements to the max, as one would in a racing app where the rpms are high, then the increased air flow potential provided by the larger throttle body can become a positive because the smaller one may in that case be a restriction.

 

[wytstang]

Car nut, you need a 75mm tb for your 347.

Black95GTS, you da man!!

Im too lazy to do it but someone should look up Ernie302's stock tb vs 75mm tb dyno results on his little 302. The results may suprise you, but im NOT at all suprised. He GAINED low end, GAINED mid range and GAINED up top Thats odd because according to uneducated internet racers, he shoulda lost a lot of low end

Thats the only thing it shows is he needed a larger then stock TB, NOT that a 75mm gained his all the extra hp/tq. Who's to say a 65mm or 70mm couldn't have done the same.
Car nut-You need to find out what CFM *your* entire induction system can handle at your desired RPM then match it with a TB that flows with in that spec. If your heads flow X amount of CFM and your intake set up flow X amount of CFM whats the point of spending more on a TB that flows twice that amount?
Accufab has post countless times (on hardcore50) that TB's should be purchased based on CFM not on the size of the opening of the whole.

 

[wytstang]

Matter of fact I saved what Accufab posted on hardcore50 for a base line or ballpark figure

Here are some CFM ratings on "an engine", based on displacement and RPM's, but without any "CFM losses" due to heads, intakes, exhaust, etc.

Disp. (in cu. in.)..........CFM @ 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....... ..........790....................851
430.....................................747....... ..........809....................871

These CFM ratings are all "naturally aspirated" of course. I'm not suggesting that you only use a TB or a carb that is equal to these ratings, but (a), it won't hurt if you do, and (b), it won't help if you use one much bigger than what the engine can use.

 

[Black95GTS]

Thats the only thing it shows is he needed a larger then stock TB, NOT that a 75mm gained his all the extra hp/tq. Who's to say a 65mm or 70mm couldn't have done the same.

10-1 says he loses HP and TRQ with a 70mm unit.

I can definately your logic, but I'm gonna have to step in for the practical crowd. How does Joe street/strip builder test his entire induction system for CFM flow?

I could do it because I took fluid mechanics in college and can manipulate Bernoulli's equations. Then I would have to get coefficients of all the materials in the tract, sizes, rates of expansion/contraction for heat, etc etc etc.

Would I do it when selecting TB size for garage build up? Hell no! I'm not bringing that kind of crap into selecting a throttle body when I can do an internet search for 5 minutes and see that people here with "too big" TBs go faster and don't experience this loss of "low end grunt" that I keep hearing about.

You might ask why I'm so passionate about this... well look at my sig, I'm the dumbazz who bought a 65mm TB cause everyone said anything else was too big. It's a great unit and works awesome... but now I will have to buy the same part twice.

Adam

 

[wytstang]

Manufacures(sp?) have there specs listed on what heads/intake flow or will give you the specs if you give them a call. So lets see a cobra intake (upper and lower) has an average flow of 190 cfm per runner. So how is 800+ cfm going to make it's way through it?

 

[wytstang]

If want to find out how much minimum CFM is needed for X amount of bore/stroke/Cylinder/RPM here you go http://www.slowgt.com/Calc2.htm#Intake
Your right a 5 min search on the internet can get you the right answer

 

[final5-0]

Good discussion by all

I'm glad we are not only sharing our view point .......
We are also sharing the reasons why we have come to believe it.

While Adam has told us about his formal education ......
I can say I got most of mine from UHK

For those of you not familiar with that schooling institution
That is ..... University of Hard Knocks

I learned several important lessons from that great place. The ones
that IMHO, seem to pertain to this discussion are .......

1) Keep an open mind
2) Listen to those who have done what I seek to do
3) Gather all research to form a plan
4) Put that plan in place
5) Analyze the results

I'll go ahead and say the obvious here ...........
Steps 1-5 pertain to an unknown
and
After I've done 1-5 ... the unknowns are vanquished

I have not done a valid test to compare a 65mm tb to a 75mm tb
for BOTH max power and ... well lets call it ... street drivability

That means to me ... I'm still in the research mode here!

however

My Common Sense or Reasoning Ability tells me ........
the larger size should make more wot power.

Heck ... I got dlogs showing more wot air flow between
my oem 60mm tb and my current 65mm Ford 65mm tb

My view point of my current Street Car is ........
wot is NOT the only criteria I use to judge if my choices have been
successful or not.

One last thought here

I can also say this about unknowns
If you test something just to see what happens and you have good results ...
thats great

True ... Your lack of understanding how you got those good results does not
change the fact you had a good outcome with your test

however

You might not always be correct in thinking your outcome is gonna be
valid for everybody else under all different kinds of conditions

Again ... Great Discussion!

I'm done ............... at least for now

Grady

 

[5spd GT]

The smart way to chose a TB is based on CFM and how much CFM can the entire induction system handle. I have yet to see a 302-347 N/A needed/used 800+ CFM...

He hit the nail on the head

Size in millimeters means zilch in optimizing. You only get a ballpark.

Unfortunately many people think X millimeters gives X performance.

I believe BlackVert has got a good representation of how it works

Velocity is not affected at WOT but it is part throttle.

The gas becomes more "touchy" with the bigger blade, and is kind of a nuisance in and around town traffic.

The notion of matching your throttle body to the inlet and the inlet alone of an intake is silly. There are more factors than that.

In the vast majority of cases the throttle body on these cars (aftermarket) aren't even close to a bottleneck.

Time to look somewhere else...

 

[Grn92LX]

10-1 says he loses HP and TRQ with a 70mm unit.

I can definately your logic, but I'm gonna have to step in for the practical crowd. How does Joe street/strip builder test his entire induction system for CFM flow?

I could do it because I took fluid mechanics in college and can manipulate Bernoulli's equations. Then I would have to get coefficients of all the materials in the tract, sizes, rates of expansion/contraction for heat, etc etc etc.

Would I do it when selecting TB size for garage build up? Hell no! I'm not bringing that kind of crap into selecting a throttle body when I can do an internet search for 5 minutes and see that people here with "too big" TBs go faster and don't experience this loss of "low end grunt" that I keep hearing about.

You might ask why I'm so passionate about this... well look at my sig, I'm the dumbazz who bought a 65mm TB cause everyone said anything else was too big. It's a great unit and works awesome... but now I will have to buy the same part twice.

Adam

Yet again...

 

[Killercanary]

Grady, had I not hurt my engine when I did I had all intent on borrowing my cousin's 75mm setup from his '94GT and use it on the dyno and track to see the results. Alas, that won't happen now...

 

[Black95GTS]

If want to find out how much minimum CFM is needed for X amount of bore/stroke/Cylinder/RPM here you go http://www.slowgt.com/Calc2.htm#Intake
Your right a 5 min search on the internet can get you the right answer

Point taken! That doesn't account for an air filter though, does it? And that is a great site BTW.

If someone shows me real proof that they actually got faster and made more power by switching to a smaller TB, then I'll shut up. Slips, dyno charts, etc.

I'm loving this thread by the way, seems like we're actually trying to sift out some BS instead of arguing if 2300 RPMS in a 4.10 rear end is "too high for cruisin."

Keep it comin!:SNSign:

Adam

 

[BlackVert]

If someone shows me real proof that they actually got faster and made more power by switching to a smaller TB, then I'll shut up. Slips, dyno charts, etc.

lol you won't be shutting up then, because it seems your only focus is on the WOT case (racing and making maximum dyno numbers) where a larger throttle body (and a larger carb for that matter) is more suitable.

but as grady so eloquently put it:

My view point of my current Street Car is ........
wot is NOT the only criteria I use to judge if my choices have been successful or not.

i am more of grady's point of view. i rarely drive WOT and i never go to the track, so maximizing that case does not make sense for me. i will be extremely happy if my torque is 450 (or more!) from 3000-5000 rpm. max hp as 6000 rpm means nothing to me.

i have to say though, i am a little surprised by your stance, since you profess to have an understanding of fluid dynamics and are an engineer where an understanding of physics is really helpful. i would think that based on that you, of all people, would understand why velocity can make a difference.

please don't slam me because i said "you profess to" ... i am not doubting that you took the class or that you are an engineer. i do not mean any dis-respect. but i would think you would understand that the purpose of this thread is discuss when and why different sized throttle bodies might make sense, and use this as an opportunity to share some of the great info you have learned in school and in life.

are you saying that there is no case where a smaller throttle body might be more appropriate?

 

[WhiteDevil]

I switched from 65mm tbody to 75mm with a full 75mm inlet and the hard numbers i got were from Tweecer data logs. I picked up air flow throughout the whole rpm range. Lower rpms were near the same and slightly higher but in the peak area i saw several kg/hr if someone searches the tech i posted about it. Was like two years ago though.

 

[final5-0]

As said I said in the beginning post of this thread ...
Tom Moss said some things that got me to thinking

This is that thread
and
I cut & pasted the main points here for convenience

http://forums.stangnet.com/showthread.php?t=680089&highlight=velocity

Some info that is not focused around max or peak power

Cam specs are 555 lift intake 565 lift exhaust 114 lsa, with 1.6rr. I dont have the cam card in front of me but i'll find it if you would like the rest. I havnt tried a 75mm tb on this set up yet, But make no mistake I WILL.....Grady I didnt get it printed out, however when I get it redone I will get it printed. My a/f stayed right between 12 and 14 also, mostly right at 13. I have to get it retuned after the addition of the rpm2 and the introduction of nitros. i'm looking at 2 to 3 weeks before I do that stuff though The 98 cobra hasnt sold yet, so I dont have overflowing pockets right now.

Originally Posted by WHITE94COBRA View Post
I haven't tried a 75mm tb on this set up yet, But make no mistake I WILL.....

all i can say is, wow that is one well matched setup you have there. some people with 331s would be happy with that kind of power.

how is the driveability?

is the inlet on the rpm ii 70mm or 75mm?

and how about your elbow? 70mm or 75mm?

Originally Posted by WHITE94COBRA View Post
I havnt tried a 75mm tb on this set up yet, But make no mistake I WILL.....

Smart choice, you'll make more power with the 75. Just make sure the elbow and inlet match 75mm but you already know this

What is the rpm powerband on the cam card? Duration?

Originally Posted by BlackVert View Post
all i can say is, wow that is one well matched setup you have there. some people with 331s would be happy with that kind of power.

how is the driveability?

is the inlet on the rpm ii 70mm or 75mm?

and how about your elbow? 70mm or 75mm?

Driveability is pretty good, it bucks below 1200 rpm, but other than a pretty stiff clutch it's not too bad.
I'm not sure on the rpm2 opening, but it will be 75mm since my elbow is already a 75mm, I'm using the 70mm because of my old setup it ran better with the 70mm, And when I say better I dont mean faster, I mean better driveability. To be honest I dont know why it ran better with the 70mm, but with the 75mm it would buck like hell anything under 2k rpm's, with the 70mm it wouldnt do that.

I should have taken pics of my heads after Sid ported them. Sid is my fathers old buddy who in his hayday worked heads over for numerous manufacturers, I cannot explain what he did to them accept he said the intake ports didnt match up very well, and he would be making them line up to the intake, as well as some minor bowl and other port work. They looked the same to me accept they were soooo clean, and the ports were gleaming. I think most of my success with this combo is because of this. Nothing else on my setup is much different from others combo's but i'm putting up great numbers, with good driveability, so we'll see what it puts down after the intake and tb, i'll post results and dyno sheet after.

power band on the cam card is 1500 - 6500 rpm, And i'm having a hell of a time finding the cam card; Can I call Ed for a new cam card??? Cause i'm going crazy trying to locate it.

I'm also upping to the #30 injectors, with nitros the #24's will be a little thin.

Originally Posted by WHITE94COBRA View Post
........To be honest I dont know why it ran better with the 70mm, but with the 75mm it would buck like hell anything under 2k rpm's, with the 70mm it wouldnt do that.

in one word - velocity

the air charge moves faster (for each degree of TB blade movement) when using a smaller TB and that fills the cylinder better at lower rpms.

Points to think about for sure

Tell me what ya'll think about them

Grady

 

[nazstang]

.................Just throwing this in. On a pretty stock cobra, 75mm gave me more power through the whole range(especially bottom end), but that was S.O.T.P. testing. I'm barely at WOT, so i can't compare that too well, but there was definitly a boost in "street" driven power.

In comparison, i slapped on a 75mm on my 88 lx when it was stock(just curious), and it ran like a dog(bottleneck city). And that car has always been pretty much pegged at WOT, so i can agree with "you can go too big", but just a few mods later my 70mm was perfect for it. and now with my RPM II , i bet the 75 will match up with it well. either way, my veiw is that for street driving, it's ok if it's a tad too big. For race and WOT driving, calculating what you induction system calls for, just makes normal sense to me. just my 2cents

 

[Black95GTS]

are you saying that there is no case where a smaller throttle body might be more appropriate?

Well, on my girlfriend's pontiac sunfire, I would agree that a smaller throttle body may be appropriate. Same as on my old man's Buick LeSabre. Not on a mustang modified for performance.

I doubt someone with a carb just sizes it for flow and throws it on there expecting it to be optimal. I'm pretty sure that lots of screw twisting and jet sizing occurs before it runs at peak. Now, I've only done points once but one of you old timers can chime in on that.

I think the age of "bolt ons" have in a certain sense softened the hardcore mechanic. Just like Grady used to do his tweaking with a flathead, he now does it with a laptop. More headaches, less elbow grease. It requires more time, but hey it starts up when the car is cold out!

IMO, if a combo is mechanically sound, there is no such thing as an uncureable driveability issue in a FI car.

Adam

 

[m0l0]

I am by no means any fluid dynamics knower at all , how ever i will throw my .02 on the matter :

The size of a carb vs size of a TB. is completely diferent, with a T.B. you are dealing with a upper intake that in most cases will have a "backup" air reserve, that will help with the low end tq. that why u usualy use spacers between the tb/upper intake to lower, so increasing the TB. size will not affect a lot this matter just increasing the upper intake breathing.

I can see this with the trottle felt at the skinny pedal, i was pressing the pedal at 20% on a stock t.b. with a bigger tb i will be pressing like 13% to fill the same qty. of air on the intake. ( just a perception and example ). I cant see air velocity on a F.I. upper intake affected by the TB blade size since the air is making the same travel through all the internal bend.

Contrary to the carbed the air passes directly from the ventury to the lower intake thus making the carbs more prone to looses with a bigger blade loosing the air velocity..

As i stated before i dont know ***** about fluid dynamics , but thats the most my little brain can pull as a " what if i am air passing through any vents on both cases"

Just a little note , the bigger tb on a stock intake will not help because the size on the TB size on the upper and making the air more turbulent, however on a ported upper intake matched to the size of the TB you will se gains , add this to the EEC programming and you will see gains , and no problems at all.

When i was first tweeking i missed the TB flow scalar ( i was learning just as today ) besides affecting the idle quality , i really gained a LOT of TB response by matching the flow to the real on the bigger TB. and i do mean really gained TB response on specially on the idle-3000 rpms.

Just trying to contribute with my thoughts and expecience with my car

 

[final5-0]

Well, on my girlfriend's pontiac sunfire, I would agree that a smaller throttle body may be appropriate. Same as on my old man's Buick LeSabre. Not on a mustang modified for performance.

I doubt someone with a carb just sizes it for flow and throws it on there expecting it to be optimal. I'm pretty sure that lots of screw twisting and jet sizing occurs before it runs at peak. Now, I've only done points once but one of you old timers can chime in on that.

I think the age of "bolt ons" have in a certain sense softened the hardcore mechanic. Just like Grady used to do his tweaking with a flathead, he now does it with a laptop. More headaches, less elbow grease. It requires more time, but hey it starts up when the car is cold out!

IMO, if a combo is mechanically sound, there is no such thing as an uncureable driveability issue in a FI car.

Adam

OK Mr. Adam!

I got your number
I catch your drift
I'm up to your little tricks

You knew very well I'd have to say something here

Flathead

I'm Old
but
I Ani't Ancient

Grady

 

[95Vert]

I just want to subscribe and give a standing ovation to all of you for the AWESOME discussion. Yet another reason why this place is bad ass!