Larger throttle body discussion...pros and cons

[GNSCOTT]

Yes, all that and what Ormand said. One thing that is also forgotten is the mention of stock or near stock heads at the beginning of the thread. They're only going to flow so much, and adding that 70mm throttle body isn't going to do a thing (but probably slow you down and add drivability issues).

The heads are part of what causes the blockage causing boost. It was kinda mentioned . I think the stock heads can flow more than the tb with just a big turbo and efficient intercooler, but your absolutly right that it becomes more necessary with better flowing heads.

 

[Syclone Dude]

this thread started to get really good when ormand talked about what cooler air actually does/requires. I'd like to add to that by mentioning that the turbo outlet and IC inlet/outlet I beleive (I don't own a GN) are probably smaller than the TB. (kinda follows the weakest link theory) So you could probably install a 10inch TB and not see any difference considering all of the other restrictions.

just my .02 worth.

BigAl...

 

[GNSCOTT]

Most front mounts are 70mm inlets and outlets. Its been so long since i've had a stock IC though. That is why you can keep the ic inlet pipe the same size as the turbo outlet because the air has not yet been cooled and expanded in the intercooler. The stock intercooler i think is around the same size as the tb though. Also you have to remember that there is a butterfly taking up some of the inlet space in the tb so with a more efficient turbo/ intercooler, maybe there is some justification to going to a modified 62mm tb.

 

[JDEstill]

GNSCOTT, air doesn't expand in the intercooler, it contracts. Air going into the compressor might be 650 acfm, coming out and going into the IC it might be 380 acfm, and coming out of the IC and going into the intake it might be 310 acfm. The magic of compression and cooling! Raise the boost and the compressor inlet and outlet volume flows might go up, but the IC outlet will still be the same, because that is the volume of air that a 231 can ingest. That's why bigger throttle bodies don't do a whole lot for us.

Similar vein, if you think you need bigger pipes, increasing the size of the compressor inlet pipe will give you the most gain, then the size of the IC inlet piping is next, and you'll get the least out of going bigger on the IC outlet piping.

But let's not forget our '84/'85 brothers, a hot air car with the throttle body on the compressor inlet will probably see some real nice gains with a bigger throttle body. Their throttle bodies do see a big volume flow jump when running more boost.

John

 

[Syclone Dude]

GNSCOTT, you need to re read Ormand's post "cooler, denser air coming out of the IC actuall needs LESS flow area, because it is cooler and denser"

BigAl...

 

[GNSCOTT]

Damn , trying to think of an easy way to explain my thinking (not a guru by any stretch)..Ok kinda hot air goes from the turbo to intercooler, intercooler cools air, you are right, dense air does contract, more cooler denser air fills that void, air exits the intercooler and now starts to contract becase it is not being cooled in the intercooler anymore. If the up pipe is the same size as the inlet pipe, or tb. there is no room for expansion causing a blockage at the up pipe and tb?? That is where my bigger turbo I mentioned comes in. I beleive the stock turbo in conjunction with the stock tb is fine, but as I mention above, a bigger turbo would have the power to push more air to take up the void that the cooler denser air that has contracted, and fill that void.

 

[GNSCOTT]

The air going into the ic is heated because the turbo compresses it (some think its because a turbo is hot, but the compressor side never runs that hot and air isn't in it long enough to be heated) The best an intercooler can do is cool it to ambient (that would be the best intercooler made) but it can't do that because heat is always being generated by compression, and a bigger turbo will have more compression and can heat up quickly. I think if you took air temps at the intercooler and temps at the tb there would be a bigger difference if you used the same size outlet pipe as the inlet pipe. That is why most have said ( I rememberMike at Ramchargers saying this) is that they found a 2-1/2 inlet along with a 3" outlet worked best with a fm.

Its kinda like an exhaust system. As exhaust leaves the motor it begins to cool, but there are bends and mufflers in exhaust systems that cause the exhaust to become hotter because they are packed together and can't flow efficiently, that is why a bigger exhaust system could help performance, with the other thinking, you could run a smaller exhaust system than the AR outlet because it is becoming more dense. Most people measure IC acfm at the two pipes, but give that air time to expand in the uppipe and measure it there, and it will be worse if there is a tb blockage..


Keep in mind though, I dropped out of physics in HS.

 

[Syclone Dude]

Originally posted by GNSCOTT
a bigger turbo will have more compression and can heat up quickly.

Dude, you realllllllly need to read a book on turbocharging!

BigAl...

 

[GNSCOTT]

Syclone, instead of a smart *** response, why not give an answer. The more air a turbo pushes into an intercooler where there is a blockage, the tigher the air will be packed causing heat? is that wrong??

 

[GNSCOTT]

I gave a VERY detailed reason why i think air expands going back up the up pipe, if I am wrong and it is explained to me why, I will say oh yea, that makes sense, thanks , not give a smart a** reply. I know your new here, but most come here to try to learn and share their theories and experiences to help their cars, and in this case help our wallets. This thread has meaning to me because my intake came with a 90mm TB and I was contemplating weather or not to buy a 70mm one.

 

[Syclone Dude]

Originally posted by GNSCOTT
Syclone, instead of a smart *** response, why not give an answer. The more air a turbo pushes into an intercooler where there is a blockage, the tigher the air will be packed causing heat? is that wrong??

I'm sorry if it sounded like a smart ass response (I enjoy good threads aswell and hate to see them go to s**t)

But, lets stay on the TB issue we'll deal with the IC on another thread. If you have a restriction whether it be the IC inlet or outlet a bigger TB will NOT help! Theoretically your TB doesn't need to be bigger or flow more than the smallest restriction

BigAl...

 

[GNSCOTT]

NP Al..I know things get a little heated . I'm just thinking that if the air is expanding going up the up pipe, the uppipe and tb can be the restricor causing the air coming out of the intercooler to further heat up and expand.

 

[UNGN]

The larger outlet has to do with the static pressure and the conservation of momentum through the the intercooler.

Desity*Area*velocity is constant through the intake system.

The Velocity is relatively constant from the outlet of the IC core to the TB (it decreases slightly as the air cools in the up pipe due to the density increase).

A smaller outlet/up pipe could be used at the expense of a slighlty larger pressure drop in the system.

Too large an outlet/UP pipe reduces velocity and promotes lag.

 

[Syclone Dude]

GNSCOTT, once the air leaves the IC it is not recompressed or reheated. theoretically it shouldn't get any hotter (unless of course your up pipe is resting on your header) your TB does not need to flow more than your smallest restriction on a turbo car!

The reason folks use bigger intercoolers is not because they cool more. It's because the bigger the IC the smaller the pressure loss!!! According to Corky Bell (just a guy who's tested a few IC's in his time):

Does one style core cool better than another?
No, almost no difference. With three decades of testing intercooler’s, we have found no appreciable difference between any core style or manufacturer. Keep in mind, that the merit of a core is it’s efficiency versus its internal drag characteristics. When sized for a tolerable flow loss, virtually all cores will produce essentially the same efficiency results. Perhaps a core with slightly less flow area per linear inch, or one with longer tubes, will need perhaps 5% more tubes to equal the best of intercooler’s with regard to flow loss and efficiency. Not a very important difference.

A little food for thought.

BigAl...

 

[UNGN]

Originally posted by GNSCOTT
NP Al..I know things get a little heated . I'm just thinking that if the air is expanding going up the up pipe, the uppipe and tb can be the restricor causing the air coming out of the intercooler to further heat up and expand.

The air is contracting in the uppipe. It contracts as it cools. It cools in the uppipe.

Air expands when heated/contracts when cooled. The static pressure is less on the TB side of I/C core. Any expansion due to reduced static pressure would happen there and not in the up pipe.

 

[GNSCOTT]

I shoulda stayed in Physics I gotta think about this one for a little while

 

[Syclone Dude]

Originally posted by UNGN
The air is contracting in the uppipe. It contracts as it cools. It cools in the uppipe.

I hate to split hairs BUT the air isn't actually cooling in he upipe. All the cooling is done in the IC, more often than not the up pipe is probably at around 160-200 degs cause of the air being blown on it by the radiator and fans.

but the upipe still isn't hot enough to heat the air inside since there isn't anything obstructing the air

BigAl...

 

[GNVAIR]

Posts like this remind me of the K.I.S.S. (Keep It Simple Stupid) methodology. I have loads more respect and admiration for the guys who make their cars fast using the bare minimum of aftermarket parts. I have been building my car along those same lines. All too many times you see guys with the performance part of the week running near stock times. Why?
I think too many people fall in love with the looks or the status of having a certain part. Front mount intercoolers on near stock cars comes to mind. Like someone else mentioned, spend the money if it is burning a hole in your pocket or if you cant sleep at night.
I honestly dont think anything bigger than a bored stock throttle body is going to net any gains unless you have a car that is DEEP into the 9's.

 

[Syclone Dude]

Originally posted by GNVAIR
Posts like this remind me of the K.I.S.S. (Keep It Simple Stupid) methodology. I have loads more respect and admiration for the guys who make their cars fast using the bare minimum of aftermarket parts. I have been building my car along those same lines. All too many times you see guys with the performance part of the week running near stock times. Why?
I think too many people fall in love with the looks or the status of having a certain part. Front mount intercoolers on near stock cars comes to mind. Like someone else mentioned, spend the money if it is burning a hole in your pocket or if you cant sleep at night.
I honestly dont think anything bigger than a bored stock throttle body is going to net any gains unless you have a car that is DEEP into the 9's.

Preach on Brotha, can I get an Amen!!!

BigAl...

 

[UNGN]

Originally posted by Syclone Dude
I hate to split hairs BUT the air isn't actually cooling in he upipe. All the cooling is done in the IC, more often than not the up pipe is probably at around 160-200 degs cause of the air being blown on it by the radiator and fans.

but the upipe still isn't hot enough to heat the air inside since there isn't anything obstructing the air

BigAl...

Maybe in your up pipe but in my up pipe its hot from the inside, meaning heat is transferred, meaning something is giving off that heat.

My underhood never gets more than 150 degrees at the track. per the dangling ATC.