Would IRTB bump my Miata from SS to Production GT

[MiltonP]

It looks like the best non-blown intake option for my car is an IRTB (4 throttle bodies w/trumpets) such as that available from fuji-racing.com not to mention that sweet look resembling side draft Webers.  I have been eyeing these as a potential next step following the addition of a megasquirt pnp ecu next year.

I don't anticipate any problems keeping the car on the street but so far none of the IRTB manifolds I have found are CARB certified and therefore are labeled for Racing Use Only.   I am guessing there are a few SS and RS entries out there running non-carb equipment but I would like to do the right thing if I make the change.  Am I correct in assuming the right class would be Production /GT ?  Thanks.

[LittleLiner]

I am not an official but I am a rule book geek.

As I read the Super Street rules I'd say your MX5 would still be able to run in SS.  It is still Tagged, Insured and has the full complement of street equipment (wipers, horn, etc, etc), right?  I'd bet that most of the cars that have been setup to run Maxton in SS or RS have any number of parts that aren't CARB certified and are labeled for racing only.  The Super Street rules specifically (reading the 2007 and not the 08 rules here) allow "Multiple Carburetion, Fuel Injection,  . . ." etc., etc.  So the IRTB setup should be OK . . .  BTW your car is also legal for the GT and MS classes. 

Maxton records you could chase are:
G/FMS  116.559
G/GMS  139.124
G/GT 139.925
G/FSS  126.424
G/GSS  129.247

See ya at the track in three weeks . . .

[panic]

Not your answer, but going to IR means really big TB.
If this is a 2.0, assuming a 6mm shaft and 8K RPM you need almost 51mm TB to have 1.5" Hg. pressure loss.
How big are the ports?

[MiltonP]

Fuji's IRTB Kits for the both the 1.6 and 1.8 litre engines use 2x2 45 mm throttle bodies.  I am running a 1.6 litre so expect 45 mm to be just fine when matched up with a megasquirt ecu.  Plenty of support out there for that combo.  Fuji also sells 47 and 50mm 2x2s seperately.  Fuji appears to be the most reputable IRTB kit but many folks have built their own manifolds and used both car motorcycle TBs.

[panic]

At 8K power peak, 4 × 45mm loses about 1.6" Hg, not bad. Going up to 50mm drops the loss to about 1".
Do you have cammed (progressive) linkage?

[MiltonP]

I haven't acquired any of the components yet.  I just completed the exhaust and have decided on the megasquirt ecu as the next step.  I will likely remove the afm following installing the ECU change and reevaluate the situation at that point before biting the bullet on the Fuji-Racing system. 

I am currently commuting with the miata in addition to LSR and previously touring road courses with it.  I have run on 10 circuits so far and plan to hit others down the road with this car at some point so I am taking my time and trying to make improvements that won't impede performance on the road courses.

I may replace my Jeep Cherokee next year and use its replacement for LSR as well.  I commute 420 miles a week though so I may want to replace it with something economical and lighetn the load on the miata which is averaging 33 mpg in track trim.

[panic]

Just a guess: Fuji may be much less work (adapt, fabricate), but using ITB from a late ZX14, Hayabusa etc. has to save $$$. I don't know the sizes though, and the injectors may not be easy to find in all sizes (thread, length, electrical coupler).

[Sumner]

..............decided on the megasquirt ecu as the next step....................

Let me know how you like it.  I plan to put EFI on my pickup next winter using it and would also like to change the jeep over to it and if all goes well run it on the lakester,

Sum

[wolcottjl]

Just a guess: Fuji may be much less work (adapt, fabricate), but using ITB from a late ZX14, Hayabusa etc. has to save $$$. I don't know the sizes though, and the injectors may not be easy to find in all sizes (thread, length, electrical coupler).

For anyone contemplating using bike throttle bodies for another application - Here is a link to a list with pictures and specs of quite a few bike throttle bodies.

http://forums.vwvortex.com/zerothread?id=2838896

The notoriously cheap VW crowd has converted quite a few bike throttle bodies for use on water cooled VW motors.