Throttle Body Uprgade Worth It?

[streaknby]

Currently I have a 63mm tapered and polished NT TB bolted up to a JMFab Race SMIM. Up to the TB I have a 3" upper IC piping and narrows to 2.48" (63/25.4) at the TB. I have been told a number of times now tht I could see a noticeable airflow/power increase upgrading to a 3" throttle body. I'm looking to squeeze some more power out of my current setup without making any boost/timing advance increases or other significant part swaps as I am right on the edge of knock on pump as it is. For this reason I have had the thought and am starting to consider this TB upgrade as an option to get where I want to go. Would the swap from a ~2.5" to a 3" TB make a worth while difference?

[Ripper_XX]

Is it true that an oversized TB tends to make the car more sensitive to throttle input?

[Sean485]

That depends on what the rest of your setup looks like, a stock 60mm tb has gone 10's so they can flow the air required and money may be better spent elsewhere. I have never seen a test done where they measure pressure in the IC pipe pre-tb and then another measurement at the plenum and see the difference but if you did that would be a good indication of if your tb was actually limiting you much or not.

As for the more sensitive throttle, they can to a degree simply because your gas pedal only has 'X' amount of travel and you are changing the restriction in the intake system more per amount of movment of the pedal vs a stock tb. I have an accufab 75mm on my car and its definitely there but you get used to it quickly.

[MindBlowin03]

If you have 3" IC piping then you probably should upgrade but it also depends on the rest of your setup. Will you see a noticeable difference? Not sure on that. IMO, your money can be spent better elsewhere but it would make your intake slightly more efficient.

[scotthidley]

I think I'm missing something. Let me rephrase what I understand.

Your fuel system is maxed out, and you want to find out if putting a larger throttle body will increase your horsepower without you adding fuel for the additional air?

My hunch is you might get a slightly lower air temp at your intake manifold, but I don't think you'd be able to make any gains as you don't want to add more fuel.

[streaknby]

Yes I think you may have misunderstood a bit. My fuel system is not maxed out, I have lots of room in that area still. At 22psi on my HX40 and 10* of timing up top I'm at the limits if what 91 octane will allow. Another 1psi of boost or any more advance and I'm starting to get some knock. So my question is will the increase in airflow from a half inch diameter increase at the throttle body to match my 3" upper IC piping be a worthwhile upgrade.

Sean and Mindblowin, you both said it depends on the rest of my setup. What else are you referring to? The rest of the intake system is 4" FP straight to the 0.70a/r HX40 running speed density. 2.5" hot piping to a 3" in and out 24x12x3 IC with 3" short route UICP to a 63mm tapered and polished NT TB, JMFab Race SMIM, Buschur Stage 4 Head with Kelford 272's.

[Sean485]

With the fact you have significant flow upgrades with the head and cams as well as the 3" uicp (which I hadn't caught when I first read your post) and a sufficient turbo to supply the flow I would vote that a larger TB would give you a noticeable gain and you would likely do it at less boost.

[scotthidley]

Thanks for clarifying. I need to read things a few times as I still haven't caught up to my jet lag.

That swap could yield a gain. The area increase is ~40% neglecting the flappers. More than the area increase, you currently have a flow restriction right at the manifold. If you keep to your IC piping size and maintain steady flow into the manifold, you could eliminate a bit of turbulence and possibly save a bit on your intake temps.

Not the best turbo comparison, but years ago by opening up my 14b compressor housing, I was able to run another 2-3 PSI at the same intake temps as before the change.