Anyone had any experience with the 50mm up 52mm bored/polished throttle bodies for 5.2/5.9? Any truth to the ads that say more torque, more hp?

 

most of the time the throttle body size is increased the power gains aren't really noticable but they are real. i wouldn't spend that much $ unless u got to have it.

 

Well I bought a used 5.2 throttle body from ebay for $29 bucks and did the modifications myself. The two barrels are now a constant diameter top to bottom, basically I followed the pictures of the modified bodies on ebay to remove the lip around intakes mouth, trim butterfly rod, etc. Bolted everything up and everything sounds OK except for about 150 rpm increase at idle in P or N. May be some air leaking around the butterflies. Good news is there are no codes or lights blinking on the dash! Been raining all day so I won't be able to do much testing for mid and high end increases in HP, if any.

 

I was thinking about buying a mod. TB from "TheFastman" the few post I have seen on this mod. say next to the cold air intake and exhaust it was the be mod. they had done for HP and fuel economy so I am waiting to see how it goes for you I would imagine the 5.2 would not be much diff than the 4.7......

 

the fastman TB's are the way to go... I had a 52mm on my 5.9 motor and it was one of the best mods I'd done to my 2000... that and the 1.7 crower rollers.

edit: oh yeah, the boost was across the whole rpm range, mileage did go up some too. .75~1.0 mpg when i could keep my foot out of it.

 

Helped my newphew move to his new house today. Pulled a loaded 16' trailer and could really tell a difference with the new throttle body. I didn't need as much pedal as usual to get going with the load and I noticed more torque at lower rpms. Mileage seems to be better, too, but I need more miles of normal driving without a trailer. I'm wondering why the manufacturers haven't figured this out. The throttle body I modified is a Holley from 98 Grand Cherokee 5.2. Could it be the one size fits all (v6, 5.2, 5.9) limits fine tuning for individual engine requirements?

 

the 5.2's and the 5.9's are the same TB. the 3.9's get a different one. I'm told that just swapping over to a v8 TB on a 3.9 motor will get you 8~10 hp.

 

for a 3.9, would the 5.2 tb or 5.9 tb be a better fit, or fit at all? do you mean just an off-the- shelf larger throttle body?

 

they are the same TB. 5.2's & 5.9's have the same TB, the only difference is when you go aftermarket... 52mm for a 5.9 is better but too much for a 5.2 (unless it's a wild motor), 50 mm works best for the 5.2 motor.

 

Would that also help with gas milage do you think? Do you know if it's a direct bolt on part or does it need to be modified to make it fit the 3.9. I have the 3.9 and I am interested in this.