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How big of a restriction is my 94rs's throttle body and how does it stack up to the gsr, and R's tb? If the gsr,r, or any other honda tb is larger, is it compatible w/ my obd1 94' non-vtec ecu? Will it bolt up?
 

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If what's in your profile is all you have done to your car don't worry about the TB. I'd only get a properly sized TB as a final step after big cams, headporting, and intake manifold upgrade.
 

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Every beginner wants the biggest possible size for their TB , like for instance. a 70 mm (on the plate side) TB...WHY?

Bigger is always better. Right?

Bigger bore = more air coming through with no restriction to the IM plenum. Simple. Right ?

WRoNG.

The TB is just 1 part of an induction SYSTEM. This system on the D series, B series and K series Honda engines is called a single stage (or dual stage for the gen 3 GSR), single plenum IM side draft design:




The TB size must be compatible to the other parts in this system's parts combination.

You can have a TB that is TOO BIG and INCOMPATIBLE for the system's size. Going too big on the TB is the most common beginner's mistake when they choose TB size.



There's more to it than just saying "go big or go home" in this case.




Professional import drag racer Chris Rado used to drag race a 800-1000 whp drag turbo GSR when he first started.


http://www.turbomagazine.com/features/0205tur_integra/









Back then Chris used a custom sheet metal , Kinsler - designed IM with an absolutely HUGE IM plenum on his 35 psi boost 800+ whp turbo B18C1, ...his TB size? 75 mm.





But why did he need a 75mm TB ?

Look at the size of the IM plenum.

PLUS , he's running 35-37 psi boost. That's when you need a 70-75mm TB.





Please remember this simple rule : The IM plenum size determines the TB bore size on the plate side .

A Big IM plenum with lots of flow capacity and resonance needs help with flow velocity and therefore a small to medium TB bore is better to get that flow speed started and going into the plenum, especially at part throttle.



A Small IM plenum has lots of resonance and flow speed but also has a lower flow capacity ((or the amount of air volume it can deliver) needs help with a larger TB bore (plate side) with more flow capacity or flow volume .


Every part in an engine works together with the other parts attached to it to form an overal system and that system creates an overall effect. The parts have to be compatible with one another. The size of one part in the system affects the sizes of the other parts. The same is true for a TB. The overall effect is how much overall air volume AND flow speed
can you deliver to the cylinder ?

These B series Honda engines run on fuel injection and aren't carbureted engines with dual plane open style IM in V8's and we aren't dealing with flow restrictor plates like you see in NASCAR V8's. Those kinds of conditions may need a huge TB bore. But not in our kinds of IM's.


The Realtime Racing ITR's in the SPeed World Challenge Touring Car Racing Series had to use a smaller 57mm bore TB and they still kicked everyone's ass powerwise.
It's not the TB that is the main player to restricting overall flow.

If the rule makers really wanted to penalize the Realtime Racing DC2 ITR guys, they'd make them use a smaller b16a IM instead of allowing them to use a stock ITR IM .



People fail to get that idea for some reason because they don't know about flow speed's importance. It is as important to how well you fill the cylinder as the amount of air volume you can stuff in.

Where did this misinfo all begin? oN THE HoNDA FORUM BOARDS!!! No fluid dynamics (physics and science..engineering) explanation...just an over simplified but wrong view that bigger must mean it's better...AND THEN EVERYoNE BUYS INTO IT AND BELIEVES IT BLINDLY!!....

They think the TB is a bottleneck when in fact it is a control point for the type of air flow behaviour into the plenum. It controls BOTH how fast and how much air gets into the IM plenum. They are BOTH equally important. If you neglect flow speed in your consideration of TB size choice, you will have an engine that doesn't rev as easily to the redline for acceleration. A big bore will make the butt dyno (throttle response) feel good but when you look at the stopwatch it will be disappointing because you killed flow speed with a TB that is too big for the IM plenum (or system).







A popular Honda web forum awhile back had a "know-it-all" promoted the use of a 75-80mm Infiniti Q45 TB on tegs....and everyone ignorantly complemented him on it endlessly post after post...IT WAS THE WRoNG ADVICE !!


Most people with 11.5-12mm lift , 245-255 duration @1mm cams shouldn't need more than 65-66 mm bore (plate side) on a 1.8L NA Bseries. The most common size max used is usually 64mm.



STOCK TB SIZES AT THE PLATE SIDE.


b16a 58mm

b18c1 60 mm

b18c5 62 mm

Remember that you can only overbore up to +4 mm on these stock sizes because of the stop screw on the TB which limits how far they can machine bore outwards.

Remember to portmatch the IM plenum port to the same size or 0.5 mm bigger to create an anti-reversion step.

Never bore the TB larger than the IM plenum port or you will kill flow volume and volume speed together into the IM plenum.


Notice lately that some of the newer IM's have the TB mounted to the plenum on an angle ? That's to reduce the formation of a separation bubble at the IM plenum port entrance and maximize the flow speed going to the IM runner furthest away from the plenum port at cylinder #1. This ensures that all 4 IM runners (or 4 tubes) get the same equal amount of air and flow volume. Usually the runner closer to the plenum port gets more flow .






That's pretty much most of the things you need to know or consider for discussion when you go out and shop for TB sizes. The good machine shops who bore out properly will do it precisely so that the plate won't stick open or be too loose to cause a vacuum leak. Te bad ones will have those problems and so, shop aroundwisely and ask around (I recommed RC Engineering in Southern California or King Motorsports in Wisconsin for example. I'm sure there are other reputable shops but those are 2 that have been doing it rigjht for a long time year after year).



Cheers
 

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This is where the butt dyno can fool you to perpetuate the myth...the story you see on many of the honda forum websites goes something like this:

" I just got a _____mm Overbore TB (you name the size that is too big). I drove my car afterwards and it feels amazingly better with lots of pull. The throttle response was crisper and it felt way better."

What the person posting doesn't tell you is the dyno numbers at full throttle on the upper rpm powerband and his acceleration times going from part throttle (driveability) to full throttle or his 1/4 mile or 0-60 mph times. Those will tell you the truth.

Going too big on the TB bore kills upper end rpm power through a loss of flow speed and flow quality. You won't see a gain after a certain size...it's the law of diminishing returns : you go bigger and bigger until eventually an increase in size nets no further gains in performance - it levels off or plateaus. The car at this overly big size accelerates much slower and the transient response of the engine after you shift up to the next gear is much slower if you go too big on a TB bore.


Explanation of Transient Response (article) on TI.net

For most of us with 1.8L all motor: 64-65 mm (on the plate side) is plenty.

There is some confusion out there on the forums about the 70 mm number.

There are some TB's that you can buy that are tapered and some shops that bore out the TB will taper the bore for you. This tapering helps produce more flow speed. So, if you get a 65mm bore job, some shops will bore 65mm where the intake attaches all the way to the plate side of the TB were it attaches to the IM. A tapered TB will have a 70 mm bore on the intake side and go down to 65mm on the plate side.

If you went 70 mm on both intake and plate side, that will be too big for most all motor 1.8L NA engine packages out there.
 

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MichaelDelaney on Sep/20/02 said:
If you went 70 mm on both intake and plate side, that will be too big for most all motor 1.8L NA engine packages out there.
just searching through about TB's.. Since you made it a point to specify NA when referring to 70mm being too big for our 1.8L cars, does that same rule apply to boosted applications? Say, a mildly boosted b18b with about 250whp? This is under the assumption that you're running a skunk2 IM?

-Johnson
 

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the idea here is that the bore can slow flow speed down. if you go too big on an NA motor...which fills the cylinder passively unlike boost,

you have to read the articles here to understand the idea of "flow volume" vs. "flow speed" (click) .

once you understand that, you then sort out WHY we say 70mm will kill part throttle driveability on an all motor car because although it delivers more flow volume, the flow speed to fill the plenum is torched and the acceleration is much less. With boost you aren't limited by flow speed because essentially you are pushing in at a high flow speed from the start. What you are more concerned with in FI is cavitation at the plenum-TB opening as shown. That's when going too big can begin to hurt your flow into the IM runners.

But you don't have to worry about that.


The performance forum here on TI is an all motor forum. We have a separate FI forum. Why the nitrous guys and turbo guys post here is beyond me. I always have to move the threads over to FI forum.

As I said before over and over: the TB isn't your choke point. It's easier to change than an IM, or doing cams/headporting which are the real choke points and so people do the easy way out and focus on it for the wrong reasons - affordability and expedience.
 

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So the people that are using the 68-70mm throttle bodies with matching size intake manifold opening on the 2.0L n/a hondas, they are all wrong or is it ok for that size motor. I have seen alot of 2.0L engines making close to 250whp using these big throttle bodies
 

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krayzielilsmoki on Aug/31/06 said:
So the people that are using the 68-70mm throttle bodies with matching size intake manifold opening on the 2.0L n/a hondas, they are all wrong or is it ok for that size motor. I have seen alot of 2.0L engines making close to 250whp using these big throttle bodies
2L is a different story. you can get away with 66-68 mm.

when you fill passively it's the pressure difference across the IM plenum that determines the suck when the piston drops on the intake stroke. Obviously with more displacement the pressure differential across the IM will be larger and has more pull.
 

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MichaelDelaney on Aug/31/06 said:
the idea here is that the bore can slow flow speed down. if you go too big on an NA motor...which fills the cylinder passively unlike boost,

you have to read the articles here to understand the idea of "flow volume" vs. "flow speed" (click) .

once you understand that, you then sort out WHY we say 70mm will kill part throttle driveability on an all motor car because although it delivers more flow volume, the flow speed to fill the plenum is torched and the acceleration is much less. With boost you aren't limited by flow speed because essentially you are pushing in at a high flow speed from the start. What you are more concerned with in FI is cavitation at the plenum-TB opening as shown. That's when going too big can begin to hurt your flow into the IM runners.

But you don't have to worry about that.


The performance forum here on TI is an all motor forum. We have a separate FI forum. Why the nitrous guys and turbo guys post here is beyond me. I always have to move the threads over to FI forum.

As I said before over and over: the TB isn't your choke point. It's easier to change than an IM, or doing cams/headporting which are the real choke points and so people do the easy way out and focus on it for the wrong reasons - affordability and expedience.
Excellent piece of information. Thanks for the thorough reply. As for "posting" in the performance forum, I just ran a search about TB's and found that thread. It was useful, but I still had a question about FI setups. I think starting a new thread asking that question would have yielded "please search" as responses.

Hey, I'm just utilizing the tool you guys promote most. =)

Thanks again

-Johnson
 
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