Can you overdo it when it comes to throttle body size? The tiny 50mm stock one to a slightly larger 60mm doesn't seem to gain much. I was wondering if a dual 62mm Cobra TB could be retro fitted. If so would the ECU need to be re-programmed for the change? With headers and a 2.5" or 3" there should be a noticable power gain. Anyone have any sites or resources for info?

 

well tb doesnt FORCE the air into the intake just lets it trough....so if you have 2...when you step on the gas like half way...it will feel like say your gave it all the way cuz its letting trough twice as much air into the intake...just different throttle response...not much gain you will get...

 

What if you use higher output injectors and the TB with the exhaust upgrades? Would there be noticable gains?

 

A normally aspirated engine just sucks in air. It can only burn so much fuel for how much air it sucks in. The air is sucked in through the intake valves, not the throttle body. How much air it is capable of inhaling is determined by the displacement of the cylinder (bore and stroke), the size of the intake valve, and the lift and duration of the cam lobe that keeps the intake valve open. If you have six throttle bodies, one for each cylinder, the resistance to sucking in air will be less but it still won't suddenly let you pump out 300hp.

For your midrange power, the drop in intake manifold vaccume will actually hurt your torque. (with dual throttle bodies) Try driving a 240Z with stock SU's and then one with tripple Webbers.

Then on the top end, your cam duration will be too short to make use of your double throttle body setup.

I have mentioned before that on dyno tests of the 280Z and 280ZX (factory fuel injection) The top end goes rich, not lean. This is because the ECU continues to meter out the proper fuel and as the rpms increase the valves aren't open long enough to let in as much air. Less air, same fuel levels means too much fuel. That's why you lose power after 5200 rpm. (the oxygen sensor compensates only a small amount) A 60mm throttle body with a mildly ported intake is just fine. Port match the intake ports in the head and put in a long duration cam (280/.450lift) and then you'll see the power increase at higher rpms because now you can get more air in there to burn up the fuel that is already being delivered.

The point is, larger injectors will just run your NA engine more rich and give you less power and poor economy.

Don't forget to raise your compression when putting in a longer duration cam. This is a must!

 

ARRRRGHHH! So much to learn, so few places with good information.

I'm glad you're here to straighten me out. I did alot of searching for info on this and received so much information it just muddled the results. Ons site says this, and one site says that. Thanks for the info. I think I'll start with the 60mm and match the TB to intake bore. Then after getting a header I'll port match the intake and header to the head. That'll keep me busy while I gather more info from the rest of you guys that know what you're doing.