Larger throttle body worth the cost?
 

I am building a new intake manifold for my Miata, and I want to hear some opinions on larger throttle bodies. The general consensis on m.net is that the OEM 55mm TB is large enough especially on turbo'ed miatas where the air is already compressed. But 55mm is 2.165 in...The closest normal TB size to my 2.5" I/C plumbing is 65mm. Oh look, plenty of 65mm "Acura" aftermarket TB's to choose from (look easier to package than mustang TB's).

So is it worth the cost and effort to go to a larger throttle body? Has anyone here done this? What kind of negative effect does larger TB's actually have on part throttle control?

Anyone know the actual differences between the 94-01 Acura Integra GSR TB and the 97-01 Acura Integra Type R TB?

how much power are you after? stock dsm is 60mm there's been plenty 400+ motors. I think the miata crowd is afraid to explore cams and that is the real power difference in small displacement motors.

If anything, there will be less flow loss and easier chamber filling with a larger TB. Probably help the benefit of gradulally tapering the runners at the block, to accerlate the airflow into the chamber.

Phil: there's no doubt that when I build my motor there will be cams in there....I don't see a reason not to build a motor and at least try to eliminate the torque drop at 5.5K, especially if I decided to increase the revs substainally.

also with a bigger throttle body at any given point of it being opened up, since it will allow more air in at a more closed position will be a bit more twitchy ... or so I hear. Might make launch control a bit tougher

From what I have heard, a larger TB only helps a SC'd car since they suck the air through it (starves the SC when you have a "small" TB). Doesn't make much difference with a turbo since you are blowing pressurized air through it.

That not true, coming from the DSM world. The TB is still a bottle neck.

Tim, if you already making you own manifold, I would swap TB. Remove an bottle necking of the system, this way you get a cleaning air way. On the 2g DSM when swaping over to just the 1gen TB, there was a small increase of spool time,(i tapped my boost gauge from the manifold) and others saw the same game. It was maybe 100rpm nothing to write home about. The biggest gain is if your flowing some nice cfm do to the lack of bottle neck

That's not what I was trying to say. Yes, getting a larger TB (if it is a restriction) will give you more power, getting a larger turbo (if it is a restriction) will get you more power, getting a larger exhaust/dp (if it is a restriction) will get you more power. What I am saying is if you spend $300 on a new TB you might get 100rpm faster spool on your turbo (your real world example). If you have an M62 SC and spend $300 on a larger TB you will see "real" gains since it is a restriction on the upstream side of the forced induction. This is why you see the 200-300 HP SC crowd all buying TBs but you never see the 200-300 HP turbo guys buy them. But, by all means, get a larger TB and let us know what gains you see.

understandable rmcelwee.

My thoughts are that if you are building a new intake manifold may as well upgrade at the same time. I would not spend an arm or a leg on the new TB Tim, but look around at cars that have OEM TB that you could use.

Tim...? If your building the manifold throw a Mustang TB on it then you don't have to question it. ;) On the other hand... it might be a bit snappy under boost. My '94 had that progressive TB where the first 50% pedal was 25% throttle then the other 50% was the other 75%. This made my boost throttle response really touchy compaired to the '97 linear TB I put on there. I like to drift to I enjoy the control I have now with the '97 TB. That's my suggestion to you is go with that. Any restriction in the TB can be easily overcome with another 1/4lb of boost. As far as spool I dont know if it would really help much since you should be comming on by 3000 and the original TB can flow plenty of air for 3000. For NA guys it would show up in the higher RPM.

Yes...? hehe

Interesting what you said about the progressive throttle linkage. I have a '94 engine/TB and thought the progressive TB was a benefit, with the smooth throttle control at low throttle openings. I never thought about the accompanying twitchiness at larger throttle openings. Thanks. I had to lessen the wastegate spring pressure to ~6 and use the EMS to control boost per throttle percent to get smooth boost control. Never thought it could have been due to the progressive linkage quickly ramping up the throttle at larger throttle openings. Hmmmmmm.

Acura TB's are the same price as mustang TBs (low $100's), at least in the company I'm looking at. Mustang TB's (foxbody style) have a linkage while the acura's have a cable/wheel setup like the later mustangs and the Miata. Later mustang TB's are longer and more money. Hence the 65mm (smallest) acura TB in consideration.

Thanks for the input everyone, keep them coming!

Money is a little tight now so I think I'll use the OEM TB and cutoff/modify the TB flange in the future. Plus I'll know if any HP gain is due directly to the new intake and intercooler piping. I'm going thru the fender on both sides with the I/C pipes. I want to stay away from the radiator. Over the radiator pipes would be much, MUCH easier and smarter. But I have to teach myself aluminum welding sometime. :)

All GSR (B18c/c1) = 60mm Type Arrrrr (B18c5) = 62mm

62mm is the biggest 4 cyl OE honda throttle body you will find. I believe even the new K20's use 62mm.
HTH

is the 80mm q45 tb i have that i was gonna use on my build to big?

15psi at the manifold is 15psi at the manifold. If it took the turbo 18psi to get it there then eliminating the restrictions could lower the strain on the turbo to sat 16psi. Other then that you won't see gains from the TB alone. Follow?

Yep.