70mm TB questions

[gizmotectegs]

Hey All,

just have a question about replacing my standard TB with a 70mm aftermarket job. My Stock B18C will have the following bits added in the next couple of weeks:

Skunk2 intake manifold
Simota Cold Air Intake
Headers (not sure what yet)
Apexi NEO

If I was to add the TB, what sort of gains do you think I'll see over the stock 125kw with a good tune

[workhackSIR]

ITR TB upgrade will be better 70mm would be pretty big for that setup. A reasonably stock motor can only flow so much air.

[Horny_Devil]

i wouldnt think ud need something that big, thats 30% bigger than stock. ull probably end up loosing intake velosity with something that big. maybe consider a type R one or have ur current one bored bigger to say 63mm?

also the skunk 2 manifold only has a 64mm throttle body opening so ud have to do a bit of port matching to make the 70mm one fit.

[gizmotectegs]

cheers guys

not worth the dosh at $400, better spent elsewhere :wink:

[BTLF3D]

thought about searching HT about them? some guys over there have most likely used/tested them.

[HITAIL]

63mm is a good upgrade for a 1600 mivec..theres a small write up on the forums, 63mm throttle body with a fuel pressure reg got another 13hp atw and peak power was held for longer instead of dropping off

[[QUIKdc2]]

What cams are you running?? I'd expect to lose power with a big throttle body and that intake manifold on a stock engine, It can pnly flow so much... then you start losing alot of intake air speed

[Coupe-R]

64-65mm is MORE than enough for N/A street motor, or probably a very worked b Series also!

[tianporn]

A spoon one might be ok as it tapers down from 70mm anyway.

[Mac]

How on earth would you lose power?

An enlarged throttle body seldom affects intake velocity as it's not normally the lowest common denominator. It also has too-smaller volume to drastically change intake air speed. Typically the restriction of the air filter and resonators is far more prominent when determining air velocity. Air velocity in *most* cars is created by suction within the engine - not by a massive amount of pressure sitting right at the intake mouth waiting to be utilised.

There may be a case when the extra size yields no additional benefit, especially when the next part in the equation - the intake manifold - cannot use such volume because of either the bore size where it connects to the throttle body or the volumetric size of the intake runners. Also, with regards to the first paragraph if your intake (filter, arm, bell mouth etc) is not able to feed enough air to the throttle body to make it's extra size effective then it's not going to be a worth while investment.

It's certainly a worthy upgrade for those who have a good intake system, and who can utilise a bored intake manifold. It's also beneficial to those looking to replace their stock TB because of stickage or shift linkage problems. It's definitely worth while if your future plans are to continue to build a more powerful engine.

And if it is $400 it's a heap cheaper than competitors!

[Horny_Devil]

Originally Posted by Mac

How on earth would you lose power?

An enlarged throttle body seldom affects intake velocity as it's not normally the lowest common denominator. It also has too-smaller volume to drastically change intake air speed. Typically the restriction of the air filter and resonators is far more prominent when determining air velocity. Air velocity in *most* cars is created by suction within the engine - not by a massive amount of pressure sitting right at the intake mouth waiting to be utilised.

think of it as a garden hose. keep the same amount of water flowing down it and then alter the diameter. larger diameter the water can spread over a wider aera meaning it doesnt have to flow as fast to get the same amount to the end, where as the smaller diameter hose the water has to flow faster.

and as u said the engine is sucking in the air so the faster it sucks it in the better the power it will make. slow down the intake velosity and u end up loosing power.

70mm is fine for turbo engines as the air is being pushed into the cylinders. na id tend to go with something smaller

also u have to have ur intake manifold bored out(matched) to the throttle body, which is also an extra expense to consider.

• High Flowing Large Bore Capable Of Supporting 1000 HP

dont quiet know if i would want something on my NA honda that is capiable of flowing that much air

[Horny_Devil]

http://www.honda-tech.com/zerothread?id=2009175

about the best i could find

in those setups the size of the throttle body isnt harming the preformance. and ur only wanting about 170whp (125wkw)

[Mac]

Exactly - it doesn't harm performance. Like I said the lowest common denominator isn't the throttle body - so making it the size of an elephant isn't really going to do much - IF you haven't allowed for the greater flow in the manifold or intake. However if it is then you'd benefit greatly.

I suppose the leason is, buying one now with a stock intake set up isn't beneficial, but if the goal is to make plenty more power down the road it's not going to harm you.

The hose isn't a good example either as pressure in fluids is consistent - so making it large won't affect the flow (I believe). Air is different and actually providing a chamber for air to flow into (this is how weather works -> High pressure flows towards low pressure, hence wind) that is volumetrically larger than the feeding pipe should accelerate the air. I get the point however.

[Horny_Devil]

cant mention pressure at all, in a NA setup, as there is none.

but the engine can only suck in so much air, the quicker it does it the more power it makes, make the throttle body bigger u slow this air down and u dont fill the cylinders as quick. yes it can harm performance, as ive mentioned above about the velosity of the intake slows down.

when u have say a skunk2 intake manifold the runner speed is also increased due to the size and legnth. yes getting a bigger throtle body will help like has been said, but there is a thing as too big and i believe that 70mm one will be to big for u setup seeing as u only plan on running stage 1 cams. even with stage 3 cams u probably wouldnt wanna go that big.

a 70mm throttle body is more for a boosted motor.

[Mac]

Of course there's pressure in a N/A car - mostly negative (vaccuum) which is why the engine is relied on to start drawing in air. Definately more suited to Turbo.

Edit - actually technically I'm not correct. It's not vaccuum, it's just a lack of positive pressure at the intake filter (or bell mouth, etc).

[Deanis]

Originally Posted by Horny_Devil

yes it can harm performance.

bullshit.
after your air goes through your "higher velocity 64mm throttle" where does it go? into a 70mm intake plenum, slowing it down again. you dont need a 70mm throttle for this application. 64mm is plenty. but it will in NO WAY harm the performance of the motor and you WILL pick up some throttle response. if anyone has a 70mm lying around you can happily put it on my ef9 and chuck it on the dyno to prove this.

[NAspirated]

so does reversion only occur on the exhaust side of the head?

[Horny_Devil]

Originally Posted by NAspirated

so does reversion only occur on the exhaust side of the head?

doug: u cant say that and not explain urself

dean: i said it can harm performance not that it will.

[Deanis]

no it works on the intake as well. down the intake runners size matters but when you are talking about the throttle body in this application, going from a 64 to a 70mm throttle isnt going to make any difference to the power output as the air will just slow down again in the plenum before it speeds up in the runners.

[NAspirated]

im just interested as to why some people would say run the largest TB you can but im sure they would change their tune when it came to port design...


yet another argument of velocity vs flow volume...


my reference to reversion is is exactly that. what would cause intake air to "turn around"??.....

[Mac]

Originally Posted by Deanis

no it works on the intake as well. down the intake runners size matters but when you are talking about the throttle body in this application, going from a 64 to a 70mm throttle isnt going to make any difference to the power output as the air will just slow down again in the plenum before it speeds up in the runners.

Yep. Match it with a Skunk2 Pro manifold which can be taken out to 75mm =]

[Deanis]

if your plenum was smaller than 70mm you wouldnt be making it bigger to put a 70mm on as that would be slowing down the intake air but if you have a certain size plenum then that is as slow as its going to be so a same size throttle body is not going to matter.

[Mac]

Yep, yep, I know. Wouldn't have written all that above if I didn't!

[NAspirated]

Originally Posted by Deanis

if your plenum was smaller than 70mm you wouldnt be making it bigger to put a 70mm on as that would be slowing down the intake air but if you have a certain size plenum then that is as slow as its going to be so a same size throttle body is not going to matter.

so with that thinking id want my manifold port diameter to be exactly the same as the port diameter in my cylinder head, correct?

[Deanis]

haha, no. you want to accellerate the air all the way into the back of the valve. like take my quads, they start with a 50mm hole in the trumpet down through a 45mm throttle into a 43mm (equivalent area) port in the head where it joins the manifold and then down to an even smaller valve diameter. as the air travels down the ever de creasing sized hole it accellerates. what you do not really want to do is speed air up a lot and slow it down. having a 64 or 70mm throttle on this motor does not really matter as the engine will not be sucking enough air for it to matter. if you had a higher spec motor thats sucking more air it will.