Whats the ups and downs of getting a throttle body ported to 52mm and buying a new one that comes at 52mm. Thanks

 

This may not help you very much, but it seems to me that the effectiveness of one over the other has a lot to do with the competency of whoever is porting the stock TB

 

The stock TB on the LT1 is fine. However, I do believe that the LS1, putting a different TB in there WILL give you gains. A lot of people use their stock TB up to 400 RWHP, same goes with the MAF.

 

Honestly, with my limited experience with these things, if I had the choice to make all over again, I'd opt for the ported to 52mm stock TB.

Reason being:

A: EVERY aftermarket throttle body being sold does NOT have the IAC bleed hole (little hole that looks straight through the IAC intake and exit passages) drilled. This can cause problems with bigger cammed cars and the IAC's ability to maintain a stable idle. The stock unit has a 11/64" bleed hole from the factory.

B: The IAC exit passage on the BBK and ASM (not sure of the Holley) isn't isolated from the main intake plenum. This allows air that should be going through the IAC passages escape directly into the intake. By products of this are split fuel trims at idle. The stock unit has the passage leading directly to the IAC passages in the intake, with no leaks.

C: My BBK was junk when I bought it brand new. I had to nearly disassemble the entire thing, and clean/clearance/polish various areas just to ensure smooth operation.

 

Ported TBs are OK, but your car may not need a larger TB. (it can actually reduce the power if it doesn't need it) I would borrow one from a friend or local board member and test it on the dyno with and without it.

 

Would I be correct in assuming that it matters less on a engine with a centrifugal supercharger?


Would I also be correct in assuming that it matters less, but only up to a point?


Finally, at what point in either airflow or HP does the TB need to be bigger, even with a supercharger?

 

I'm wondering the same. I don't think having my mods would benefit with a larger TB, but you never know. Would it?

 

Ion,
just out of curiosity, how would a motor lose power due to a larger tb? i am by no means calling you out. ive just never heard that a larger port in your tb could cause you to lose power and curious as to how that would work against you.

 

My BBK 52mm TB (purchased in 1996) came with the idle "sidestream hole" drilled to the factory size.

 

good points. i would like to point out that it is fairly simple (or was in my case) to seal up the iac exit passages going from the throttle body to the iac passages on the intake.

not that i am recommending you to invest in a larger aftermarket tb. i too would probably recommend the ported stock tb as opposed to the aftermarket 52mm tb. and i doubt at the moment that you would even really see any benefit to the increase in tb port size.

 

I'm not speaking on behalf of Ion, or anybody else. I don't know if I AM correct though..But I think a larger TB may cause turbulence because of its large size compared to the rest of the system. I'm not totally sure, but I think it's a turbulence issue or something of the sort. Don't quote me on any of that :P

 

thanks for the info. that idea had crossed my mind. but i thought that the intake passages and head ports are what created the proper turbulence for mixing the a/f. i wouldnt see how a less restrictive (not that stock is restrictive, just for example) tb on a mostly stock motor would inhibit performance.

 

If i was gonna get a 52mm i'd get a stocker for the better IAC system listed above. I wanted a 58mm tb so i had to get an aftermarket one.

 

Its not really a question whether i need one or not. I am doing heads/cam package so i know it would help to increase the size of the TB to a 52mm. I have also heard that it is pretty much a waste of money to buy a larger TB on a car that doesnt have any internal motor work. I just needed to know if its actually worth it to buy a ported TB over an aftermarket one. Someone has offered me a ported TB to buy and i just needed to know your guys opinions. How much are these usually going for? Thanks. -Matt

 

Turbulence may be an explanation, but I do not have a deep enough understanding of the airflow and how it affects this engine to give you a thorough explanation. Plus, it seems as though some cars with less horsepower may benefit from it and some with more horsepower may lose, so I think intake duration/lift may play a role in this too. All I know is that on my cam only/headers engine, it lost about 10 RWHP and 20 RWTQ and it's throughout the whole range, not just peak. Both runs were done on the same dyno, but a week or two in between. I'll try it again sometime during the same day, but considering the numbers are SAE corrected, I don't think it will make much of a difference.