What are you running for a throttle body? (and what else is done to your car)

[jonnymopar]

Last week I cleaned up, bored, and half-shafted a 58mm throttle body for my 2.4L. I recently upgraded the stock SRT-4 turbo to a Forward Motion Enforcer, so I figured maybe I can take advantage of some more air flow. I put it on last week and drove it to work every day with some high-speed shenanigans mixed in.

Well, last night I ducked out to the garage and put the stock Neon 52mm back on. I was trying to convince myself that it was just me, but I swear, with the 58mm, I got the same top end power, less mid-range, and much worse gas mileage. I drove it to work today and the car is back to life! My nice big midrange is back, and it really doesn't feel any different at redline. As far as gas mileage, time will tell.

Thinking more about it, if I remember correctly, a lot of 2.2/2.5's reacted the same way to throttle body upgrades. Maybe 58mm is just too big? I have a 2.4 that's essentially stock internally, Neon DOHC intake, Enforcer turbo, and for the moment I've got the boost manually controlled at 16psi.

What's everybody using on their cars?

[Ondonti]

If its not a restriction at your current flow level its not gonna help much. Not sure what you are running it with so I don't know how the computer compensates when it sees more air than it should at the same throttle opening when you go bigger.

[Reaper1]

As Brent said, your throttle body is not a restriction in your system at this point. Your description of how the engine behaved with the 58mm throttle body is the perfect characterization.

Your mid range and fuel millage went to pot because there was no velocity to help the engine breathe in those load conditions, so your torque suffered. You add more throttle than you think you do to compensate, the computer sees the throttle position and the load from the MAP and dumps fuel, so your millage suffers.

With tuning you could probably get rid of all of that, but why? If top end didn't get better, then you don't need it anyway.

[thedon809]

When I was in college building a 2.2 for my daytona my buddy was rebuilding his stock engine in his integra. I remember how massive his throttle body was and how much better designed the intake was compared to my neon.

[jonnymopar]

Yeah, the ol' butt dyno didn't really see any difference in top end. I did some calculations and the 58mm throttle body with the half-shaft mod, the flow area at the shaft is closer to what a 61mm non-modified throttle body would be. So that was actually a pretty big jump in size and flow (and apparently one that wasn't necessary).

I'm running a Turbonator SMEC with a cal that Rob made me based on my specifications. What he sent me needed only very little tweaking to run really nicely.

Turbo cars sure are different in this regard. I've had a 60mm throttle body on my SOHC Neon for 10+ years now with excellent throttle response, even power through the band, and great gas mileage as long as I've owned it.

[thedon809]

You would probably see better gains with the big TB if you had a box intake. The stock dohc intake is doodoo.

[Reaper1]

When I was in college building a 2.2 for my daytona my buddy was rebuilding his stock engine in his integra. I remember how massive his throttle body was and how much better designed the intake was compared to my neon.

The small Honda engines use a different train of thought for their intakes. If you try to apply what you see them doing blindly to our normal intakes you will get crap results. Honda's use small plenum intakes. We use large (-ish) plenums. As a very loose rule, most of the time you will see large throttle bodies on a small engine if they have a small intake plenum and/or if the engine is tuned more for upper rpm operation. Smaller throttle bodies are used with larger plenums and engines that are more "pedestrian" and are geared more for torque. That isn't a steadfast "rule", but it's pretty darn consistent.