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Discussion Starter #1
So I know that I'll be needing a throttle body soon, well possibly. So I am trying to collect some information. I have found a variety of different bore sizes ranging from 58mm to 74mm. I know a bigger hole would let in more air, but is there more to know about this? Thanks.
 

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Bigger allows more potential air, but at a lower velocity. What are your plans for the car, that helps when sizing a TB.
 

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Discussion Starter #5
well i'm not looking for a crazy build or anything on this engine, just a little boost for a daily driver. I picked up a new y8 though, and the intake manny needs a throttle body, so I started looking...

I would say it would see some forced induction, but nothing crazy. Only looking for like 185 or so whp.
 

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i never saw flow testing to support that but i wouldn't be too surprised. most setups use 2.5" cold side IC piping. that equats to about 63mm. a smooth transition with no lips with a 63mm TB and bore matched IM would seem the best flow wise. if you run 2.5" piping with only a 56mm tb you run the risk of having a large step in the flow. if you can smooth that and still keep that 56mm tb that works too

-Luke
 

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Curious George
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60mm is a wise choice for our DD on a good n/a setup. On a b16a you can reach more than 200whp with oem 60mm on a built b16a engine. Bigger isn't always the best on a engine build.
 

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how much TB diameter recommend for up to 200-ish bhp , aggresive cam , 12-ish CR
port n polish head vtec

i put 60mm, is it too big ?
i use stock z6's IM anyway
 

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the biggest i would go is 60mm but thats only if i was cjanging the tb which you really dont need to. Your best bet is to just go to the junk yard and get another stock tb
 

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how much TB diameter recommend for up to 200-ish bhp , aggresive cam , 12-ish CR
port n polish head vtec

i put 60mm, is it too big ?
i use stock z6's IM anyway
swapping to a bigger TB and not boring out the IM does absolutely nothing. the air goes through the bigger TB and then smacks into the wall of the IM where it has to bottleneck through the smaller bore. if you want to run the 60mm TB take off the IM and bore out the hole to match it perfectly. eliminateing steps(disruptions in the path of the air) in air flow help improve it dramatically

-Luke
 

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Ideally, you'll want the intake manifold inlet diameter to be slightly larger than the throttle body diameter for an anti-reversion step. As stated, if the intake manifold inlet diameter is smaller than the throttle body diameter, you're going to hurt performance considerably.

The inlet diameter of a z6 manifold is 57mm, so I suggest using your 56mm throttle body.
 

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Ideally, you'll want the intake manifold inlet diameter to be slightly larger than the throttle body diameter for an anti-reversion step. As stated, if the intake manifold inlet diameter is smaller than the throttle body diameter, you're going to hurt performance considerably.

The inlet diameter of a z6 manifold is 57mm, so I suggest using your 56mm throttle body.
good point on the anti-reversion step

-Luke
 

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IIRC, liveforphysics spoke wisely of this in his long post a while back. I believe he said you always want your TB a little smaller than your IM b/c of the air velocity or vacuum it creates in the IM as opposed to creating it in the intake tube , thus creating less pressure in the mani. Of course, i'm not as smart as he, and i am just paraphrasing and its from memory, which isn't too good.

But, i know he said a smaller TB isn't always bad. I know it creates more velocity. You won't want too big of one especially if you've only got a stock IM, or stock bore size, which I think is around 58(or 57 someone said) mm.

On a build NA d series, i'd stay with a 60 mm. And thats only with higher CR and a cam. If you don't have a cam, higher CR or boost, the stock TB will supply more than enough air.

Think of it this way, a built d16 can put out anywhere from 140-160 whp, and a stock b16 lays down a little less than that and can handle (as stated above) 200 whp on stock tb.

Personally, i'll be running a 60mm TB on my Edlebrock IM, which has a 62mm opening. But, i'll be running a stg 2 cam and a bit higher CR.
 

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A smaller throttle body will act as an anti-reversion step and capture the pressure waves due to intake valve closing. Otherwise, the energy is lost, and efficiency will drop. If the pressure waves are captured and returned to the engine at the correct time, more air/fuel will be packed into the cylinders. Also, as stated, the cross sectional area and the air velocity are inversely proportional ( AvΔt = AvΔt ). If the flow rate of the engine has not changed enough to justify a larger throttle body, it will merely reduce air velocity and lower efficiency.

The stock intake manifold inlet diameter is 57mm (I hope I measured it correctly :-?), so any throttle body with a larger diameter will be counterproductive. An aftermarket manifold will have a larger plenum and a larger inlet diameter. Since it has the larger plenum, it is still beneficial to use the stock throttle body. Ideal throttle body diameter and intake manifold plenum volume also vary inversely. A smaller throttle body diameter will also create a larger boundary wall at the mating point between itself and the intake manifold (which establishes the aforementioned anti-reversion step).

Overall, there is no "ideal" throttle body diameter that can be applied to all setups. It must work in harmony with the other components in the system. Most often, 56mm is more than enough for our engines.
 

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Curious George
'99 LX Civic Sedan
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Ideally, you'll want the intake manifold inlet diameter to be slightly larger than the throttle body diameter for an anti-reversion step. As stated, if the intake manifold inlet diameter is smaller than the throttle body diameter, you're going to hurt performance considerably.

The inlet diameter of a z6 manifold is 57mm, so I suggest using your 56mm throttle body.
I got 56mm/y8 tb on my mildly built y7 setup, and I went to 60mm matched after, both setup dynoed, and 56mm has little bit more steady tq curves, and 60mm has a 4whp peaks at higher but tq curve was little bit more peaky. But not that much differences.
 
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