Will a 52mm throttlebody give noticeable performance gains over stock? Is the stock size 48mm? Will the plenum need any porting if a 52mm is installed? I've seen them for sale for 200-300 dollars, and it's a rather large expense, so I want to know what the gains will be with one. I intend to use it with a K&N cone filter. Thanks

 

You won't see much of a gain without other mod's to increase the airflow. The plenum doesn't need to be ported for a 52mm, but at I would anyway, at least cut down the to ridges right behind the TB. There's also a post somewhere on here on how to bore a 48 MM to 52 MM yourself (with a little machine shop help) Might be able to save yourself some money, matter of fact I believe that's what TPIS does to get a 52 MM, that's why they want an exchange on it. Spend your money on exhaust mods and such first, you'll be happier.

 

The stock throttle body flows almost 750 cfm. Plenty for a very
healthy 350. Look at the intake of the plenum and you will see
the openings start out at 52mm then taper down to 48mm.
Open them up to the gasket size of 52mm then take out the two
EGR walls just inside of the openings and blend the floor between
the openings to get a nice smooth transition into the plenum.
This will help some but the real restriction is the runners between
the plenum and the base.

Look in the openings and you will see a lip from the tube that was
pressed into the headers. Use a drum sander to smooth them out
and match the openings to the gaskets on both ends.

You could also match the plenum outlets to the gaskets and
smooth the outlets quite a bit the help out the air flow.

The stock throttle body is plenty though. Use it as is and spend
the money on a mild cam or some headers that will really help.
That's about all you are going to get out of stock components
without pulling the intake base, then we get into siamesing
where the engine really comes to life.

 

How much HP can u get with the siamesing intake runners, ive seen long tube runners from a company called Arizona something, and they claim up 25HP with those. So i figure siamesing would be even more.

 

Thanx for the advice. I already have a 3" flowmaster catback that gives a nice healthy growl and lots of flow. I think I'm gonna buya 3.73 rear end and 2400 RPM torque converter with money instead of throttleody and K&N. The prices are about the same, cept I don't have the facilities or know how to install the transmission and rear end mods so it'll be more money out of pocket. Thanx guys!

 

https://www.thirdgen.org/techbb2/sho...hlight=siamese

Read this entire post. It goes into pretty good detail of what to do
and what to expect.