i was still wondering how it compares to a basic turbo kit like the greddy, ive goten opinions but they were from people that are trying to push irtbs in the first place, especially from jimmy at fujiracing.

I've not driven an IRTB car yet, but I suspect it's a completely different animal than a stock Greddy kit car with 6 degrees of base timing BTDC.

im expecting the same thing but im trying to find out if its a good or bad thing... i like the sounds of a turbo and that kick in the pants that boost gives but supposadly a miata with irtbs can out accelerate 0-60 a turbo..
all i want to do is not be beaten so bad by a stock evo or sti or s2000 on the track... and when i go on rides not be left behind so bad when we get to the freeway or road

i rode in the fuji-racing IRTB miata the Gap last month. It's really impressive. basic NA chasis with a '99 motor and IRTBs. it launches hard like it was shot out of a cannon. throttle response is pretty insane too. i've thought about buying that kit, it's really very nice. james (the owner) had some great footage of himself driving his car in a prosolo. he admits to not being a great driver, but you can see the the nuts the car has out of the gate and digging out of corners.

good someone that has experianced both you have a turbo right?
well what do you think is quicker? he has quotes on his page from people that own both but seem open ended and only talk about throttle response like either they are ashamed to admit that N/a is faster than their 5k FM2 kit, or its not and they are just saying nice things...
im debating because turbo and the fuji kit are about the same price turbo i can upgrade, but with na i dont have the heating issues, required to run certain octane, lag, etc always worrying about lean problems or boost creep,

With regards to "which is faster," let me put this very succinctly: if you had an IRTB Miata that weighed ~2300lbs. and had the X,Y and Z for gears, suspension and tires and had a supercharger/turbocharged/JRSC/Greddy/BEGi/FM/BRP/whatever car that weighed the same and had the same gearing, suspension and tires components, and both cars made ~140rwhp, then they would be identical in acceleration, top speed, etc.

IRTBs do not magically turn a horsepower or a lb-ft. of torque into 1.2hp or 1.5lb-ft. of torque. A lb-ft. of torque is a lb-ft. of torque.

Now, any FMII kit worth its salt is making in the neighborhood of 205-230rwhp...vastly more than the 135-150rwhp you'll see out of Jimmy's IRTB kit. While it's true the FMII won't have the throttle response of the IRTBs, it'll certainly out accelerate it in any and every situation...no questions asked. Does that make the FMII kit "better?" Depends on your needs/desires.

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-Brian

Homebrew TD04-13C turbo w/ roughly equal-length tubular mani, 2.5" downpipe-back, BEGI AFPR, home-brew electronic boost-controller, 1.8L injectors, RX-7 AFM

brian is right to an extent. the IRTBs are a different feel. if you do a lot of close-quarter driving, like autocross or mountain roads, and you like instantaneous response, IRTBs are for you. if you like HARD accelleration all the way through your RPMs, forced induction should be your consideration.

with IRTBs, you're probably going to run premium fuel anyways. you will probably want a highly advanced timing setting for maximum effect. i suspect an untuned IRTB configuration will want to run a bit rich. peter brusa's rs aizawa IRTBs run VERY rich and there is a lot more to that story than i want to get into.

so, ok, the IRTBs are quicker out of the gate, but the top end really isn't there. idoes it offer better driveability? i can't comment on that.

i think you need to go find one and drive it. it's a matter of preference.

i have a good friend who is a design engineer. he made his own IRTBs and they were beautiful. he ditched it and went to a full-on fm2 (2.5 technically). he liked both systems, but enjoys the power from the FM2 more. as far as FM systems go, he has made adjustments to his that make his car brutally quick. i saw him take down an FD rx-7 (single turbo) on hoosiers bigger than my *** on a roadcourse. all he had was coilovers and falkens. better driver? marginally.

you need to find one, drive it, and start figuring out what sort of power delivery fits your needs/wants better.

i don't really understand irtb's for a car. Just seems too expensive without enough power. If my car had throttle the response of my cbr i'd be happy but if it still only had ~130hp and i was out thousands of dollars i'd feel like i made a poor purchase.

Okay, here we go again...this is exactly the argument that Jimmy and the IRTB fanboy parade kept trying to make: that IRTBs are going to be "quicker out of the gate," "faster off the line," etc.

I know you didn't intentionally step into the argument I'm trying to pick with you in my mind (), but please tell me how, between two well-launched cars, each with similar setups, each with ~140lb-ft. of torque and ~140rwhp, the IRTB would be any "quicker out of the gate."

There is something to be said for throttle response, but it cannot defy the laws of physics (love how often that phrase is used over at the "big M" forum).

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-Brian

Homebrew TD04-13C turbo w/ roughly equal-length tubular mani, 2.5" downpipe-back, BEGI AFPR, home-brew electronic boost-controller, 1.8L injectors, RX-7 AFM

i know what you're getting at, but if you look at the dyno graphs, you can see the difference.

The difference in what?

power delivery.

go drive one.

I think what kungfujesus is getting at is that granted while an IRTB and turbo miata may have the same peak torque values, the rpm or peak torque and more importantly, the area under the overall torque curve will really change the character of the power delivery.

Of course if the two cars launch from a dead stop with both cars setup exactly alike and the cars both at their rpm of peak torque, they should come off the line the same, but on a tight road course/auto-x a car with a torque curve with more of a sharp peak (like a turbo) vs. a flat line/broad peak (like a supercharger/IRTB) will definitely change the drivability and power delivery thru the corners where you will not always be at peak torque rpm, no?

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91 widebody brg - built 1.63L engine, worked head (MS solid lifters/shim under bucket/Supertech valvetrain/Integral cams), Flipside custom GT2871 turbo setup, Flipside custom IM w/65mm TB, 6-speed trans, 3.63 Rx7 diff, FM front sway, Tein Flex 9/7

Yes, but I'm not arguing there's a difference in power delivery; I've already said that in my first response.

But, well launched, the rear wheels don't care how the power is being delivered to the ground. Again, as far as acceleration, top-end and "quicker out of the gate" are concerned, 140lb-ft. is 140lb-ft.

Now, if you're referring to throttle crispness or quality of rev-matching, that's another story.

Gotcha. I haven't seen enough IRTB dyno plots to know, but maybe the torque drops off slower after the peak with IRTBs? But, I would guess not since the top end is where the IRTBs start to lose out. So I guess, you can't defy the laws of physics, unless you buy your gas from the same guy who sold jack his beanstalk beans...

i think if you had an ecu like the AEM where you use an "anti-lag" feature, you could launch like an IRTB car, but the turbo has to reach pressure to overcome the piping and the intake manifold. the IRTBs are grabbing as much air as they can swallor the instant the butterflies open.

Yeah, with anti-lag you can launch with a significant amount of boost. However, it has been my experience that it's somewhat difficult to control that boost (and therefore hp/torque) as you launch especially if you do not have enough tire to keep the car from loosing traction. I have never been in a car with IRTB's but I would think that throttle response and therefore launch control would be significantly easier for most drivers.

However, if you do have enough traction, look out. Launching at 10+ psi is sick. Assuming you don't break something, no IRTB car will keep up.

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The mystery behind ABSURDflow | Design Engineer at Jesel Valvetrain | '92 A-package @ 199k miles | 2.5 KL V6 turbo | 3.90 torsen from a '99 | AEM EMS | 3" stainless exhaust | Tein suspension | Kosei K1/BFG gForce Sports

I gaurantee that with either a) a turbocharger small enough that it has as flat a torque curve and roughly the same top-end as the IRTBs (GT2052 or TD09?) or b) a positive-displacement supercharger, you can achieve the same flat torque curve and throttle response (well, damn close to it) as the IRTB engine.

And again, if you have two cars that're the same weight, same torque, same horsepower, same gearing, same tires and good drivers, they're going to be within a few milliseconds of each other on any timed test.

never driven a miata with itb's but have drivena e46 m3 with itbs and its just insane how it sounds and just the overall "quikness" of the car.

I never driven a IRTB car but I talked to alot people that had IRTBs.

Its come to my understanding that a car with IRTB will not be any faster in the straight. As bripab007 keeps saying, in a straight line two cars with the same everything, one having IRTB and one not, but same HP. Both cars would be millseconds apart.

Now get turns in there and its a different ball game. IRTB are known for throttle response. In an eviorment were you are getting off the gas and on the gas alot, IRTB will pull ahead of turbo and supercharges even with more power. The reason is the throttle response, since the car and make the power to the ground quick it can shot out of the cornor faster which in the end.

Also the biggest advanage i have seen as for IRTB in racing is the abilitly to easily change where peak HP and Torque are and roughly their values.


Well that is what I have learned.