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ITBs = Overkill?

Old 02-13-06, 09:12 PM
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ITBs = Overkill?

I recently got ANOTHER RX7 ('83 GSL with GSL-SE drivetrain) and I'm most likely going to sell both of my other RX-7s (both turbocharged) and try to make one great, almost fully restored, all-around daily driver/canyon carver/autocross/track machine. The engine will be stripped down with no accessories but the alternator and water pump, lightweight tubular true dual exhaust, the car already weighs 2300lbs. wet but further weight reduction will be simple (still has sound deadening, A/C, air pump, heavy exhaust, stock glass).

Anyways, enough of that crap. I have a question about Individual Throttle Bodies . I've been searching through some previous threads on the forums, and everyone says that ITBs are overkill for anything but insanely modified (high overlap - bridgeport/j-port/peripheral port) racing-only rotary engines.

That doesn't make sense to me really, because people slap on twin Weber 48mmIDA carbs on to their stock 13B engines and they seem to work great. All I'm looking to do is use the Weber IDA sidedraft manifold and instead of twin 48mm carbs I'll be using twin 48mm throttle bodies. On top of that I'll have the engine pulled apart, rebuilt and streetported. With upgraded coils, new distributor and a standalone fuel computer I'd hope to make over 200rwhp N/A. How could individual throttle bodies be considered "overkill" for a street driven car? Would they kill part-throttle driving because they don't use the three-plate system of the stock throttle body?
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Old 02-13-06, 09:31 PM
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Individual throttle bodies sound cool as hell, and nothing that sounds cool is a waste!

Apparently they're good for an increase in performance (more flow?), and they give better throttle response...plus less restriction than using a manifold.

The late-generation Toyota 4AGE used four ITB's as well, so I'd say it's not nessicarily a bad thing for street cars, either.

I'd say go for it, if that's what you want.
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Old 02-13-06, 09:47 PM
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Originally Posted by Valkyrie
Individual throttle bodies sound cool as hell, and nothing that sounds cool is a waste!

Apparently they're good for an increase in performance (more flow?), and they give better throttle response...plus less restriction than using a manifold.

The late-generation Toyota 4AGE used four ITB's as well, so I'd say it's not nessicarily a bad thing for street cars, either.

I'd say go for it, if that's what you want.
Well, it's not just about the super-neat induction noise they make (although that's a plus). Mostly I want to save weight and clean up the engine bay. No offense, but the stock "RE-EGI" manifold setup is easily the least attractive manifold on any fuel injected 13B. Call me a ricer, but I want to clean up the engine bay, and considering all the bends in the stock intake setup, I'm not too sure if it could support 200hp...
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Old 02-13-06, 10:15 PM
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itb's cause the least amount of intake restriction, unlessyou want to step up to a slide tb.. but thats more of an On / Off switch than a throtal
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Old 02-13-06, 10:16 PM
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well, here's my contribution -

first of all, i can't speak for anyone else. all i can do is call things like i see them. i think there is a lot of sour grape syndrome going on with ITBs. i suspect that a lot of the people that say it's overkill would opt for them if given the opportunity. however, in the same breath, unless your passion is deep (feathering the line of foolishness) it is hard to justify the cost of an ITB setup on 20-something year old otherwise stock car. they are expensive to setup right and if you can't tune it yourself, then it'll cost you get someone else to do it. for those reasons, it really makes no sense for stockports, even though they would do wonders for everyday life driving the car.

if you have the money and time, then i'd say go for it. definitely port the engine! if you can, use some 12A side housings. however, the setup you described sounds more like the DCD-based system, not the IDA. the IDA is a down-draught. it's actually the one that i plan to go with. also, twin 48s sounds like you'll have some issues with low-RPM use. if you're hell-bent on a twin system i'd go with smaller throats. you could build a single DCO system with a 48 or 50 though.

hope this is useful to you.

Last edited by diabolical1; 02-13-06 at 10:19 PM.
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Old 02-13-06, 10:29 PM
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naw, try ITB's on a 12A. I've seen carbed 13B's. It gives more lowend power.
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Old 02-14-06, 01:35 AM
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Originally Posted by diabolical1
well, here's my contribution -

first of all, i can't speak for anyone else. all i can do is call things like i see them. i think there is a lot of sour grape syndrome going on with ITBs. i suspect that a lot of the people that say it's overkill would opt for them if given the opportunity. however, in the same breath, unless your passion is deep (feathering the line of foolishness) it is hard to justify the cost of an ITB setup on 20-something year old otherwise stock car. they are expensive to setup right and if you can't tune it yourself, then it'll cost you get someone else to do it. for those reasons, it really makes no sense for stockports, even though they would do wonders for everyday life driving the car.

if you have the money and time, then i'd say go for it. definitely port the engine! if you can, use some 12A side housings. however, the setup you described sounds more like the DCD-based system, not the IDA. the IDA is a down-draught. it's actually the one that i plan to go with. also, twin 48s sounds like you'll have some issues with low-RPM use. if you're hell-bent on a twin system i'd go with smaller throats. you could build a single DCO system with a 48 or 50 though.

hope this is useful to you.
Well, I'm talking about putting almost $10,000 into restoring and upgrading this car, so yes I will say that I have the monetary "passion" to put ITBs on a 20 year old car, haha.

I looked into the Mazdatrix website and you're right, the down-draft setup is the IDA style and the side draft is the DCOE, and the side draft system uses 45mm primary runners. Would that be more optimal for a lower-hp, more daily driven car? Do ITBs have advantages over the stock intake system for things like gas mileage if given a good tune on a standalone ECU?
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Old 02-14-06, 08:38 PM
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Hey Snub, I have thought about ITB's for quite a while now, and I have (what I think) is a pretty good/cheap way to get ITB's on your car. Just fab a DCOE style upper intake mani like this and buy a set of motorcycle TB's. 4 throats and the TBs range in size from 38mm to I think the biggest I have found are 48. You can purchase these for ~$100 on ebay.
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Old 02-14-06, 10:36 PM
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Originally Posted by j200pruf
Hey Snub, I have thought about ITB's for quite a while now, and I have (what I think) is a pretty good/cheap way to get ITB's on your car. Just fab a DCOE style upper intake mani like this and buy a set of motorcycle TB's. 4 throats and the TBs range in size from 38mm to I think the biggest I have found are 48. You can purchase these for ~$100 on ebay.
I've heard about doing this, but it also adds a bit more custom work to the project. Even though it's a little pricey ($380 for twin DCOE carb replacing TBs), going with companies like TWM Induction give you the convenience of adding things like throttle linkages, injector bosses, fuel rails, throttle position sensors, etc. You can basically make a "bolt-on" ITB kit, although it does cost more than the used motorcycle TB idea. I'll have to see how the budget is at that point.
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Old 02-15-06, 07:19 AM
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Snub - how many port engine are you going to use?
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Old 02-15-06, 08:34 AM
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ITB's

Guys, I am in the midst of building a full ITB setup for my secondary bridged 91 6 port. I am using Hayabusa Throttle Bodies (48mm) that I picked up for under $300 Canadian. I have had some assistance with developing the proper runner lengths from Bill Shurvington, to get some chamber charge filling.

Based on my studies and also in working on the intake packaging, I can tell you that it would be pretty hard to package on a street car. The runner length has to be a minimum of 13 inches long. A 13" long runner puts the charge pulse peak at over 8,000 rpm. To get a power peak somewhere within a normal rpm range, say 5,000 rpm, the runners need to be over 16" long. Go out to your car and see if you can fit that long of a runner under your hood, as well as some sort of filtering media. It gets in the way of a ton of stuff.

I don't have any street emissions stuff on my racecar. I am running a stand alone as well so I don't need the stock ecu hookups for ignition, emissions, etc... Just building the manifold alone has taken a lot of machining and welding skill.

It looks really cool, sounds great and more than likely will perform very well. I just don't know how you would package it under the hood of a street car. Stick to the new Upper Manifold piece shown earlier in the thread, buy a TWM (or similar) 50 mm dual throttle body and you end up with a ton of power with an easy bolt in situation.

Just some advice from someone who is in the midst of doing this.

Eric
Attached Thumbnails ITBs = Overkill?-b3_12.jpg  
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Old 02-15-06, 10:03 AM
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My heavily modded out 2nd gen NA DD makes 193.9 HP with the S5 manifolds. I haven't measured the runners but they look pretty long, probably well over 12 inches. What is the perfomance gain to go with ITBs? I would guess that the reason is overall throttle body flow.

Who makes that upper manifold? Do I need 4 TBs or just 2? Is there anyone near MD with experience in making a setup like this?
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Old 02-15-06, 10:18 AM
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I don't have any experience w/ ITB on 13B but by looking at a video (which shows BP NA FD w/ ITB by anniversary factory racing), it looks it works on street. Because the video shows only spirited driving senses it's hard to tell it has enough low end for daily use - it looks to me below 3K is not quite useful. Anyway, go for it! If I were you I would go that direction.
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Old 02-15-06, 10:51 AM
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Originally Posted by buzz2
My heavily modded out 2nd gen NA DD makes 193.9 HP with the S5 manifolds. I haven't measured the runners but they look pretty long, probably well over 12 inches. What is the perfomance gain to go with ITBs? I would guess that the reason is overall throttle body flow.

Who makes that upper manifold? Do I need 4 TBs or just 2? Is there anyone near MD with experience in making a setup like this?
http://www.mazdatrix.com/racing.htm

Depending onm the manifold, you will need two or four TB's, stand alone is required or going carb.
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Old 02-15-06, 12:24 PM
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23racer, good point about runner length. I'll be using the Mazdatrix side-draft upper manifold, and with no emissions and a fairly bare-bones block it shouldn't be a problem to have a longer intake runners.

How much power do you think I could make? I'll have a medium streetported 6-port GSL-SE engine, 9.4:1 compression, Haltech E6X standalone and twin 45mm TBs. Has anyone dynoed a similar setup? I can't realy find one searching.
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Old 02-17-06, 07:03 AM
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Is it possible to run with ITBs and still use as a DD?

If so, then I also want mine to idle at 1K rpm or less. Is this possible?

Finally, aside from the upper intake manifold what else do I need?
2 throttle bodies - 48mm or 50mm?
Stock injectors? (I have a Microtech LT10 for engine management)
Fuel rail
Air Horns
Fabbed up OMP rod
Fabbed up filter box
Fabbed up throttle cable
Fabbed up vacuum lines for oil injectors
Fabbed up intake runners

What else am I missing?
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Old 02-17-06, 08:38 AM
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Originally Posted by 23Racer

Based on my studies and also in working on the intake packaging, I can tell you that it would be pretty hard to package on a street car. The runner length has to be a minimum of 13 inches long. A 13" long runner puts the charge pulse peak at over 8,000 rpm. To get a power peak somewhere within a normal rpm range, say 5,000 rpm, the runners need to be over 16" long. Go out to your car and see if you can fit that long of a runner under your hood, as well as some sort of filtering media. It gets in the way of a ton of stuff.
Here's a 17" ITB 12A setup:
Attached Thumbnails ITBs = Overkill?-dscn3421.sized.jpg  
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Old 02-17-06, 11:07 AM
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Nice setup. I am not wrapping over the engine. I am going up at about a 45 degree angle from the intake ports. A 13 runner length (actually 12.895 inch) includes; port runner, flange, throttle bodies and velocity stack. Based on a 4 stroke formula, this gives me a power peak at about 8,000 rpm.

It should be packageable (is that a word?), but I may have to bump the hood a bit to get the filters underneath. Another interesting thing I read was that if you have a air cleaner wall in front of the openning that becomes the effective rversion point. This tends to artifically lengthen the runner in a lot of cases.
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Old 02-17-06, 11:40 AM
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not exactly related to what you guys are talking about, but would ITB's provide the same performance gain on a turbocharged engine? i just think the idea of ITB's is cool, and i'm always looking to modify some part of my car. i've got an FD by the way.
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Old 02-17-06, 11:46 AM
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Ahhh, I see. On the air cleaner thing, I have a "V" shaped piece of Al on the back plate with the point placed toward the stacks so as to deflect/reflect the pressure/suction waves so they don't interfere with the desired one generated from the end of the stacks. You're correct, this will confuse things if a flat plate is placed perpendicular to the stacks, reversing the sign of the wave. I plan on dynoing this 12A again in a couple of months and plan on doing a couple of pulls with and without the "V". Bill S., where are you?

-Mike
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Old 02-17-06, 12:25 PM
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Originally Posted by vspecpgt
not exactly related to what you guys are talking about, but would ITB's provide the same performance gain on a turbocharged engine? i just think the idea of ITB's is cool, and i'm always looking to modify some part of my car. i've got an FD by the way.
If you're running enough power for your stock intake runners/TB to be a restriction, then yes you could gain horsepower, but the primary advantage of ITBs is the weight advantage and also the increase in throttle response. If you're making big power and need more flow in the intake, try to find a Jay-Tech single throttle body setup, their intakes can make BIG power and simplify the intake setup quite a bit.

I don't know if I will do a downdraft or sidedraft setup. From what you've said, 23racer, a sidedraft setup would be a better call to keep intake runner length up and keep the power peak at a reasonable rpm.
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Old 02-19-06, 02:17 AM
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Originally Posted by snub disphenoid
I looked into the Mazdatrix website and you're right, the down-draft setup is the IDA style and the side draft is the DCOE, and the side draft system uses 45mm primary runners. Would that be more optimal for a lower-hp, more daily driven car? Do ITBs have advantages over the stock intake system for things like gas mileage if given a good tune on a standalone ECU?
keep in mind that i DO NOT have any hard data to back this up, but my feeling is that you may improve gas mileage with your proposed setup simply because you're shifting your engine management from 1980s into modern times. that's one of the advantages to stand-alone engine management. the extra breathing is gravy!

there is a user on this board (and on nopistons), Kahren, he put a stand-alone and custom intake manifold (while retaining the stock throttle body) on a Gen II 13B-E and made significant power on stock ports. i'm throwing that in just show the potential when you consider breathing improvements plus porting.

personally, i prefer the IDA-based setup for an N/A engine and as i said, that's what i'm going to go with for myself, but if you decide on a DCO-based system you'll be fine, too. i drove on a Dell'Orto DHLA system for years so i can attest to it's streetability, adding EFI to that setup would only make it that much better. a single 48 or 50 should be good with a decent streetport.
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Old 02-20-06, 03:19 PM
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Check out the 2nd Gen section Time slips and Dyno. There are a few N/A 13B using factory intakes that approach 200HP at the rear tires. Seems its all in the tuning and ofcourse a good engine.
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Old 02-23-06, 10:04 PM
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On piston engines, IRTB's benefit from having an airbox to draw their charge from, or some form of ram-air induction. This seems strange, to have the sweet-looking tb's covered up by a big plastic or sheetmetal box. Obviously this is mandatory on FI applications, but NA applications seem to benefit highly from a properly sized airbox. Just look at sportbikes; they've had IRTB's or independent carbs for years and they still use the airboxes.
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