This is my first post

At what horsepower level does the 52mm become insufficient and an upgrade to the 58mm would be needed?

Any ideas?

Thanks in advance

 

For the most part the general theory is that unless u are making insane horsepower level such as 400+rwhp then it wont do a whole lot for u. Welcome to the boards.

 

Thanks for the welcome!

Right now the car is making 468rwhp, shutting it off at 5,000 RPM's due to lean conditions. I upgraded the in tank, and am having an inline bosch 420 installed. The inline will be installed and car will be tuned on January 5th and we are expecting it to make around 520RWHP (its a 355 with a custom turbo)

I have been thinking about upgrading to a 58mm but I was unsure it would help me. At these power levels do you have any idea how much power I could gain over the 52mm?

 

You make 468RWHP with a 52mm?? I usually heard those topping out at about 450 or so. If you have that much already you might want to consider a 58mm or a monoblade to go for higher HP. Have you been building this for a while or did you buy it like this?

 

This was a friend of mines car and I have been wanting to buy it for a while now, and for Christmas my wife surprised me with it

ANyways, I bought it the way it is, it was tuned last week and like I said shut off way early, the serious boost kicks in at about 4,000RPM's and above. They expect between 515 and 530 once the fuel issue is solved and with the rest of the tuning. Keep in mind this is on 9 lbs of boost....the turbo can go up to about 30, but my enging would be GONE

I was unsure if I would gain much, and the guys doing the tuning never mentioned me needing to upgrade the TB. If I end up with 520RWHP if I go up to a 58mm what do you think my RWHP improvement could be?

Also, are there any particular brands I should consider and/or stay away from?

 

If you have forced induction you might want to consider a 58 mm or monoblade. The trick to this is the intake manifold will need to be ported to accept either one. If you're going with an upgraded in tank and an inline combined with some heavy injectors you will have more potential with a TB upgrade.
BTW, you have a very nice wife to buy you a car like that for Xmas. Many women don't want their husbands to have sports cars.

 

Thanks Dave, I think I will be ordering one sometime soon, the upper is already ported so hopefully it will fit the 58mm, if not I will probably hold off a little while.

It was tough to convince her I needed a car, she made me sell my last one...I still miss it

Oh well, this car is faster

 

The Ramjet 502 uses a stock 48mm t/b. and its rated at 502 at the crank.

For a forced induction set-up the 58mm will help alot.

 

Rearwheel vs. flywheel he is making a whole lot more than 502 at the crank. The 502 using the 48mm is a weak argument at best GM is going to use whatever parts they have available, they have the 48mm available so they use it that does not mean it is not a restriction on the 502. That said the second fastest Impala in the land runs a 48mm on a TT383 think he has a best of 10.2. My thinking it that with forced induction the air is compressed thereby needing less area to flow through sort of the whole point of forced induction isn't it.

Personally I say instead of justthrowing theory and money around why not measure the pressure before and after the TB and see how much pressure drop there is. If there is 10psi in the intake tube and 8.5psi in the manifold then there is a restriction. Most vacuum gauges will read low pressures as well. I say run one in front and one behind at the same time then swap them to take gauge calibration out of the variables equasion.

 

well said, I have heard that theory regarding the throttle body's not performing as well on boosted cars because of the forced induction.

 

I have heard great reviews regarding the AS&M Monobalde.

 

No, forced induction doesn't actually compress the air making it smaller. The supercharger/ turbo moves more air into a given space. This would actually be the opposite of your theory. Trying to move more air intoa given space will cause a restriction.

I would borrow a 58 and try it. I've done the throttle body thing for a long time and feel a 58 is quite overrated in most cases. You are at the HP numbers now though where it may be applicable, the most important factor is to calculate how much air your engine is actually flowing. Thats what will awnser your question. I would not get a mono blade though for the simple fact it's not the best piece in the world for a street driven car.

-Shannon

 

Ah yes, forced induction does compress the air into a smaller space, and YES that is the point. 10# of boost will move more air thru smaller runners and TB's than total race ported heads and intakes working off vacum.

 

Shannon offers 52mm TB reboring if he is the Shannon I think he is so that might play into his assertion that 52mm is the best. In a well setup NA system the intake manifold will be near zero vacuum(or near atmospheric pressure if you prefer) at WOT the only way to get more air in would be to compress it.

 

Actually I advised him if you actually read my post that he is at the horsepower numbers now where it may be applicable to run a 58mm throttle body.

As stated before, It's hard to beat a 52mm throttle body on any application besides being boosted.

Air is still not compressed. More air is forced through the same size opening which it does not have the ability so do otherwise. You will still get a restriction and no matter how much boost you put down to it, it will not be as good as a properly sized intake tract. If he air was compresed before it reached the cylinders, then the compression stroke of the piston would be reduced. You are simpley forcing more air into the chambers. Any restriction is still a restriction. Nothing more, nothing less.


-Shannon