I posted this elsewhere but not getting many answers, so I'm trying here.

I'm upgrading my ECU which can use drive-by-wire throttle body so I have opportunity to do some meaningful modifications.

It would make my life little easier if I can move my throttle body away from the intake plenum about 1-2ft what effects will this have? or should I leave the TB on the intake plenum-the stock spot?

My current intake tube diameter going into plenum is 3.0 inches. I have a gt4202r turbo feeding 20b. My drive-by-wire throttle body is 4". I'm debating if I should upgrade my intake tube to 4", leave it at 3", or do 3.5, etc? Have no idea. What effect would it have to throttle response, driveability, peak power if I went larger intake tube diameter?

Thanks!

 

Tricky question. I do know extending the throttle body away from the plenum will increase plenum volume, and that's a pretty tricky thing to mess with. I think that could induce less response - hit the gas, then you wait until something happens. You have additional space to fill.

Dale

 

generally, increasing the plenum size trades response for top end. its really hard to say what moving the throttle body would do, but you could measure the stock plenum volume, and approximate the amount you would add, and come up with a percentage, if its under 10% you'd probably never notice.

for the IC pipe, bigger can be better on the cold side. the JDM tuners like to run a larger hot side pipe, the thinking is that the additional volume is good. some of the JDM tuners do a lot of testing too, so they don't do it to look cool, although it does.

 

cool thanks. just didn't want some gremlin to come out while tuning due to too small or too big of plenum volume after the throttle body. so bigger plenum=more high end power & smaller plenum=response. simple enough. thanks!

there have been mixed replies on size of charge tube.. one good guy said the flow limiting step is the intercooler, so the tube size doesn't matter all that much after 3". compiling all my replies, my overall thought is keep the turbo compressor housing outlet diameter 3.5" the same to the intercooler, then 3.5" until air intake temp sensor, then transition to 4" after AIT until throttle body. it technically would cool down the charge temp tiny bit by expanding after the AIT, which could help.

another pointer i got was to place BOV at the intercooler end tanks to keep flow as laminar as you can which makes sense to me.

 

i think the effect is probably pretty small, and not a lot of tuners test for just IC pipe size, so mixed answers isn't surprising.

 

Agree with that. It's mostly a bastard child of ongoing mental masturbation as the car sits disassembled.

About the plenum size, I was curious. When you're WOT, wouldn't your entire intake system act as plenum? I'm talking from the turbo inlet to the runners. so why wouldn't I make the plenum as small as possible to help with throttle response?

 

i think you're right, the S2000 has a tiny plenum.

Mazda has an SAE paper from when they went from a carb to EFI and they found that the rotary has this dynamic supercharging effect, DEI? its where the intake port closes, the incoming mixture hits the closed port and bounces back to the other rotor just in time for it to be open.

Mazda found that a smaller plenum made this effect bigger, and thus VE goes up. if you look at stock intakes, the GSL-SE has a big box, and as they progress it keeps getting smaller to the point with the Rx8 and FD where there almost isn't a plenum.

 

makes me want to chop my upper intake and get rid of plenum.. you're right with the chambered UIM, there is really no plenum volume....... what to do what to do

 

so are you thinking about the integration?

 

I can't with my current setup. I remade my firewall, and have barely enough space to pass a half pencil width on top and either side of the UIM. Idea was to keep a/c at the time, so I made it as tight as possible to put in an evap lol. oh well, live and learn i guess.

I've been reading about plenum sizes on rotary and it seems that smaller plenum = higher hp at cost of lower low end torque. I'm little torn, waiting for more solid info before I take hack saw to the manifold again.

Everything basically started because I decided to upgrade ecu with drive by wire control. I have to weld on the manifold anyway for the new TB flange, so I thought why not while I'm at it..

 

I wonder if moving the throttle farther away will make it harder to tune tip in fueling.

 

It's very possible. Unfortunately, most of the literature I can find on this issue is little beyond my comprehension. I'm just reviewing different design available on the web for various different engines. I don't know. I may go with smaller plenum size rather than extending the throttle body out. If anybody have any real understanding of the issue, i would really appreciate any meaningful input. Thank you