I'm sure it's been discussed before but I just can't seem to find much relevant info. How do you know when you're TB is choking your engine? My info: Ported plenum STOCK throttle body AS&M runners TPiS Bigmouth base AFR 195 Eliminators I believe upgrading my throttle body will help. Opinions? Thoughts?

How do you drive your engine? Mostly racing, daily driver, weekend cruiser?

From when I was punching numbers, it only seemed to help at very top end around 3000+ rpms.

My number crunching showed a hp increase as well.
I'm curious how you use the flow numbers of the individual pieces to determine when say a 1000 cfm TB is needed over 650 cfm.

This car is a street legal drag car. Most of the driving will be cruising around only on nice dry days.

I also believe in being ready for any "worthy" opponents if the situation is right.

You will know by the manifold air pressure or the kpa of the plenum. You want it as close to atmospheric pressure as possible.

I have had 48mm, 52mm, 58mm and now a monoblade throttle body on my car. I see very little difference in day to day driving. Now having a 3600rpm stall on my car may mask some of the quick opening problems. I think that is something you would get used to right away.

IMHO if the price is the same I would go for the larger throttle bodies. Won't hurt a thing.

I have about 98 kpa at WOT. Is that what you're looking for or maybe the fact that at idle I have around 40-45kpa?

Have you gotten any good dyno numbers yet with your mono?

98KPA is not bad at wide open throttle. However a little more can be had. What has to be determined is if you want to chase the minor restriction you are getting. Then is it the throttle body or maybe the airfilter or maybe the intake tube?

I'm trying to get into the 99+ to 100KPA range myself. I think I'm there with my monoblade. However I'm getting some reversion at the moment so it is hard to tell. But my overall average is up with the monoblade.

I believe the restriction to be the TB due to the fact that I haven't fabbed my 4" intake tube yet so all I have is the K&N RC-5000 mounted directly to the TB.

You'll definitely beat me to the dyno. Mine's on storage insurance until spring.

Two main reasons to replace the throttle body and one of them is when the stock throttle spring stops closing all the way and the other is for performance. You have a modified 383 and a larger throttle body will only help you. Above 3000rpm or so is when i would expect the biggest gains. A 52mm is sufficent for a lot of power but you will have trouble ever outflowing the 58 so might as well just go with the 58. The 52 flows around 900cfm if i rememeber correctly. Also those front mounted cones pull in all that hot air from the engine so fabbing up a 3.5 in tube to the throttle body is a good idea.

It all depends on your engines ability to flow air.
I have a 52mm and a 3 1/2" air tube with a large area K&N feeding a 355.
I have 99-100 kpa @WOT

I have a 383 with a LT1 intake and AFR 195's.
I have the stock throttle body(48mm)
My results are in the sig.

Notice the huge difference I got with a 50hp shot of nitrous(8 tenths). That tells me that I need a bigger throttle body. The nitrous provided me with the extra air that I needed.

I am getting a 58mm TB for next spring, so I'll tell you the results then.

But to answer your question, yes a bigger TB would help you. If you can, please post results.

Thanks for the info so far.
One final question.
The 58 i'm looking at right now flows 980 (benched). Would porting it to flow 1100 be beneficial or just a waste of time and money?

I'll try results but still in the tuning stage and the car being on storage insurance will make that difficult.

the 48mm flows 650cfm dry flow, the 52mm flows 900cfm dry flow, and the 58mm flows over 1000cfm. thats the general consensus, theres no way that 58mm is flowing 980, thats kinda low. by any chance wat is the 58mm TB?

the 48mm TB is good for 400hp before it becomes a restriction. for your setup i would recomend a 52mm since u wont be pulling enough air (since idk if its the 355 or the 383 in ur sig) or what your peak power will be/RPM.

383's run 650-750 carbs and thats wet flow, a 52mm 900cfm dry flow TB will flow over 1000cfm wet flow. you have a very good TPI setup but im not sure if its gona flow enough to take advantage of the AFR 195's. still it would be a strong motor.

What I have seen throttle body cfm's are usually measured at 28" h2o and carb's are measured at 1.5" hg=20.39" h20,which makes 750cfm carb(at 1.5"hg)flow 878 cfm at 28" h20.And that 1000cfm tb(at 28" h2o)flows 853 cfm at 1.5"hg.

It's a Professional Products throttle body.
The engine is the 383.
My peak AND useable hp is 6000 rpm.

You had your engine dynoed? Hard to imagine a longtube runner 383 making peak horsepower as high as 6000rpm. 5600 is probably more likely. just my two cents. Either way a larger than stock throttle body will benifit your motor.

1100 cfm though would be overkill?

Not officially dynoed yet. Just DD2000.

I've set my rev limiter to 5900 due to the AFR springs only being good for 6K.

If its designed to go that high, then yes you need a larger TB. However, some of your low end will suffer.

Edit, also if you have DD, you should beable to swap the CFM numbers around and find your results and see if you feel it is worth the cash.

"If its designed to go that high, then yes you need a larger TB. However, some of your low end will suffer."

How so?

It is my opinion that the idea is the keep the plenum as close to 100kpa at wide open throttle as possible.

I agree and I don't think there will be any hurt in perfomrance either, especially on a 383 since you are changing the volume of air the motor needs. Check the simulaterto see what it says. Should be worth some power at least in the upper half of the rpm band. It would be over kill on a stock 305 or 350 but not a heavily modded 383.

Plus when you decide to add more power later it won't be a restriction.

When I was running numbers, you lost torque at low RPMs when going to a larger TB. On a fairly stock motor, going to I think it was a 54mm, it lost 6'ish tq. But gained 3'ish hp, and extended the breathing room out another 300'ish rpms. This was all a year ago, so I may be off on my numbers.

Now, he may have so much power, that it wouldnt be noticeable. Im guessing it would also depend on cam, heads, etc.

Main thing, he has DD. He can run the numbers and see what it says. Althought that program isnt always right.

Lol especially with TPI or long tube runners, the horespower numbers for good heads and cams are always off, can't compute the huge torque and lack of horsepower.

I've run the numbers through DD and found a hp gain of 20 up top. Considering it's over 500 tq nearly throughout, I wouldn't be to worried about losing a little of it which actually didn't happen. I gained torque throughout. But it bumped my 510hp peak at 6k to 530hp at 6k. AND pushed my peak to 6500 (too far) at 541hp. So by going to 1100 cfm from 630cfm, I only gain a useable 20hp peak and 12lb-ft to 546 at 4K.
I've heard DD2K is accurate and i've also heard otherwise. That's why I figured i'd ask for real-world thirdgenners opinions.

I was calculating on a much weaker motor.

I can simulate factory motors quite easly on DD. But when I throw someones built motor on it, I can not duplicate what a dyno machine says(adding the drivetrain loss as well).

If DD shows you gained everywhere, then I would spend the money.

Okay. I'm sold.
Thanks for all the help.

i got the proffesional products TB 58mm and i think on your 383 it wouldnt be a prob.

i can tell u right now that your long runner TPI 383 isnt going to rev to 6k. ur peak power will be at 5200-5400, you gotta remember that your 383 is sucking a butt load more air than a 350-355. on a 350 the bigmouth/runners/ported plenum or aftermarket TPI intakes like edelbrock will only increase the 4200-4800 peak hp to about 5200. yes the AS&M runners are large and the bigmouth is the largest base avaible. but your long runner design will not support 6K peak power without heavily porting everything or fully siamesing the SLP runners and aftermarket base... even then a shorter runner design will make more power. my guess is your 383TPI will be making peak power at 5200-5400 if that(due to increasing stroke and cubes/sucking more air). so dont match your cam /heads to a motor that will be peaking at 6k.

your gona be making alot of tq at low RPM and your gona be making low RPM HP as well. i might even think your AFR195 are alil too large for your setup. a higher reving intake would take advantage of the heads flow... even tho i dont kno there numbers. 180cc heads are better off on a TPI setup. your not making 510hp with a TPI... thats really hard to do.

im prob only gona be making 480hp 383 even tho my goal is 500hp. im going wiht a fully ported HSR, portmatched to 1206felpros, portmatched to PATRIOT 195cc aluminum heads that are ported and have roller spring upgrade, compcams XFI280 230/236 .567/.571 113 lobe, 58mm TB, 1.6 RR, 30lb ford SVO injectors, billet adjustable fuel reg, grannelli MAF, ram air, walbro 255lph pump yadda yadda.... and ive been told 480hp and my HSR is flowing alot more than the TPI and i have a higher RPM range, peak power will be 5500-5600 with my HSR bc its on a 383 and not a 350 where it would rev to 6000 wit no prob.

as i said i believe your peak power is 5200-5400... not saying it wont rev to 6k bc it will but u wont be making peak power there. and i would be careful wit your head choice and to match your cam accordingly. just my .02 still its gona be a torquey and fast lil motor