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Discussion Starter #1 (Edited)
So I know the throttle body is just a valve for the air and I've seen the stock 55 or 56mm throttle body be fine with around 300whp, but is there a limit? I would assume the throttle body would need to be enlarged if you try to cram more air in. Does anyone have a good way to measure the airflow into the engine and how restrictive a smaller throttle body would be? I know you can just go big, but then you would lose out on low-end power because the opening is too large. I'm mainly trying to find the perfect size for any setup. I currently have an OBD0 DOHC ZC intake manifold, so my only options are stock 55mm or 58mm B18A throttle body.
 

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\/Your Mom Was Here\/
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Discussion Starter #3
I think someone on here has done ITB on a DOHC ZC. That would be the only other thing i can think of. Or you can sen yours out to be bored/resized.
Yeah, but mainly just trying to find a way to see when the size starts becoming restrictive at certain pressure/air flow. I saw I could have it bored out to 60-62mm, but don't want to if I don't need to.
 

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you can bore the mani to 62 mm if you want and still keep the stock tb. this will not hurt the flow to my knowledge. most aftermarket mani's have a pretty large opening to begin with, so useing the stocker until you need to go larger wont hurt performance at all IMO.
 

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so your boosting your obd0 dohc zc (i'm assuming) and you want to know how big your tb should be to match your setup. what is your setup and what are your goals
 

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Discussion Starter #6
Well I mainly want to know for any setup I do, because I've built engines before and either went big or stock and had problems. I would usually go bigger until I found a sweet spot, which takes time and money. I've seen an equation before where you figure the airflow at WOT (also with the turbo airflow at certain boost levels), and intake size to figure what size throttle body is just the right size. I don't mind guessing and just getting a larger one, but I would rather have the perfect size.
 

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well as you stated lots of guy/gals have hit 300+ on stock Tb's it all depends on what your doing. if all you care about is top end then go like 70mm+ depending on power goals. knowing what turbo/Mani setup your using, exhaust size, if your planning on aftermarket cams, what pistons and how your inter-cooler is gonna be setup will help match up a suitable Tb size. where and how much power you want will definitely be a factor as well.
 

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B18A TB's use the 92 and up civic IM bolt pattern.
 

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the trick is to keep velocity of the intake air slower than the speed of sound. or something along those lines


so do some math to figure out how much your engine is breathing and at what RPM you will operate, then calculate the speed of the air by using the volume and the orifice size and take it from there!
 

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Discussion Starter #11
B18A TB's use the 92 and up civic IM bolt pattern.

The 90-91 B18A use the OBD0 or 91 and older bolt pattern, I've used them many times before, seems stupid to me to change in 92-93 but honda did it.


the trick is to keep velocity of the intake air slower than the speed of sound. or something along those lines


so do some math to figure out how much your engine is breathing and at what RPM you will operate, then calculate the speed of the air by using the volume and the orifice size and take it from there!
Okay, that's what I'm talking about^^ Thanks danz, at college I'm learning physics and whatnot so I wanna use some of it to figure out details for my engines. I wanna be a :smartass:
 

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The 90-91 B18A use the OBD0 or 91 and older bolt pattern, I've used them many times before, seems stupid to me to change in 92-93 but honda did it.
I was pretty sure the B18A TB I used on my Z6 IM was off a 91. Maybe it wasn't. Did 92-93' Integras still have firewall MAP sensors?
 

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the trick is to keep velocity of the intake air slower than the speed of sound. or something along those lines
Actually, it's physically impossible for the air not to be slower than the speed of sound. ;)

Like most things, this just requires testing. Throttle bodies and a little dyno time aren't terribly expensive.

Even if a 55mm throttle body is capable of flowing more air than the engine does at peak power, that doesn't mean it won't create a large pressure drop and a resulting power loss.
 

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Discussion Starter #14 (Edited)
Actually, it's physically impossible for the air not to be slower than the speed of sound. ;)

Like most things, this just requires testing. Throttle bodies and a little dyno time aren't terribly expensive.

Even if a 55mm throttle body is capable of flowing more air than the engine does at peak power, that doesn't mean it won't create a large pressure drop and a resulting power loss.
Oh, physics 101 :smartass: I guess flow isn't everything, I guess I might get a few sizes and try them out on the dyno to see how low and high end power are affected.

I was pretty sure the B18A TB I used on my Z6 IM was off a 91. Maybe it wasn't. Did 92-93' Integras still have firewall MAP sensors?
Yes from what I've seen all 90-93 integras have firewall mounted MAP sensors, but in 92-93 the bolt pattern changed. It might of been from a late 1991 (most wreaking yard see 10/91 and call it a 91), so technically it was a 1992.
 

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i didnt start getting into forums until after i did these mods and felt dumb but i have a 70mm throttle body on my d16y8 with a skunk2 intake mani and i just used a dremmel tool and honed out where it bolts up on the collection pipe and got it tuned and it runs fine... it just sucked getting my MAF sensor plugged in cus the throttle body was way bigger than stock...
 
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