If you don't know or are guessing please don't post. Keep the mindless chatter for the voices in your head :shock:

QUESTION/INVESTIGATION:

How much headroom does the stock ECU have for a larger bore TB or multiples etc, with a larger cross section flow? Is there enuf ceiling in the airflow maps to compensate for the TPS outputs being identical despite more air passing the butterfly?

I believe members have ran upto 68-69mm units on stock ecus?

For Eg: Including the shaft in the calculation the following results occur:

67mm 6.5% increase in cross sectional area
68mm 10%
70mm 16.88%

Twin 47mm give 0.2%
2x 48mm 4.8%
2x 50mm 14.5%

Anyone?

i reckon the only person that would know the ceiling and what the reading is at wot and full revs would be Heath Young. He seems to know a lot about the electrical systems on our cars. The rest of us are guessing dude.

Given the bolt spacing I was considering a rectangular butterfly - dragster style. I imagine throttle response would be tremendous and probably undrivable. But a handy addition for a track day or 1/4 run.

I think a 68-70mm unit still has potential. I will see what oversize butterflies I have lying around and check an old TB out. Might need to weld a busted one up :think:

the butterfly is just a round disc with a couple of holes for screws and a champhered edge so it seals right? wouldnt be too hard to make one would it? i might have a some 1.6mm aluminium at mum and dads place.

The way I see it the car reads how much air is going into the motor, and also maybe the manifold pressure. So I don't think a larger throttle body is going to upset the car to much as it bases the fuel injection off the measured air flow sensor and also the O2 sensor, not throttle position.

The way I see it the car reads how much air is going into the motor, and also maybe the manifold pressure. So I don't think a larger throttle body is going to upset the car to much as it bases the fuel injection off the measured air flow sensor and also the O2 sensor, not throttle position.

actually a big equation that is also used, is throttle position VS engine revs. Not so much at 0% (idle) or 100% (WOT) but at all the points of undulation between these zones. Such as in an auto, when say you go up gears and into the torque range of the enigne better you back off the throttle and the engine revs still increase (such as coming off the stall point going from 40-60 in 3rd/overdrive)

An increase of 10% as you say of cross sectional area of a NA car isnt that much, on a turbocharged car (where i used to fiddle) it can be quite a drastic change. Id still give it a go, but id just chuck it on the dyno for a run or 2.

the butterfly is just a round disc with a couple of holes for screws and a champhered edge so it seals right? wouldnt be too hard to make one would it? i might have a some 1.6mm aluminium at mum and dads place.

Brass is used for good reason. I do have some stainless ones approx 71mm I can turn down a bit. The expansion of various metals and alloys when heated may cause problems with sticking butterflies etc, I guess some trial and error and a little research.

I have FULL intentions of fitting one to my car for evaluation :D That's what I do.

I suspect it will work without a problem. I believe it's been done several times before on stock ecu.

Would be good to throw a wideband on it and see the differences, before and after.

i'm unsure how the magna ecu will compensate, but i've had some experience with both MAP sensored cars and AFM cars with larger throttle bodies..

MAP sensor was a toyota 4AGZE (supercharged engine) years ago when i was tweaking mine.. i fitted a 4AGE T/B (the NA motor).. the s/c version has a 46mm tb, and the na version has a 55mm tb.. same bolt spacing, same TPS fitting, you can even use a Gen 2 (MR2) 3SGE t/b and use the factory Idle speed controller.. noticeable increase in response, and less drop off at 7500 rpm..

AFM nissan SR20DET.. i don't know anyone that hasn't fiddled with one of these :cool: simply bolting on the NA throttle body (a little bit larger) and using an RB25DET AFM (doesn't bottle neck down) can see as much as 15kw at the wheels peak increase, with alot nicer curve top end..

Both instances the factory computer had plenty of fuel and compensated perfectly..

although the mitsubishi unit is completley different to the nissan's hot wire unit.. in theory i belive that if the larger throttle body is allowing a greater volume of air coming in, the MAF would obviously read this as needing more fuel..

in most toyota's the TPS can be unplugged and you can drive the car around with next to no issues.. as long as you keep it on WOT.. lol.. it's just a little rough but not as bad as you think with it unplugged in open loop mode..

on a side note.. on my 20v 4age corolla hatch circut basher i actually fitted a larger AFM from a 3SGTE (GT4/mr2 turbo).. the 20v comes factory with tapered 43mm quad throttle bodies.. yet toyota decided to use an AFM measuring 46x46mm square.. RESTRICTION?? the 3SGTE one was about 30% bigger.. i borrowed a mates laptop and wide band.. did some street testing and data logging.. compared it to the stock setup.. and it was fine on WOT.. i just had to increase the fuel pressure a tiny bit for cruise and open loop.. i did this with a simple hammer and socket on the face of the FPR.. a few gentle massages gave an extra 4psi rail pressure.. i prolly didn't need to when i look back.. but i did it to be on the safe side..