Is it worth going to an individual throttle body set up on the n/a. I have a 89 motor. Just thinking about going to individual throttle bodys but not sure if its worth it and what ones I should get.

 

Short answer: Yes.

Long answer: Yeeeeeeeees.

 

You should be able to do it relatively cheap on an NA RX-7.

Get a Holley style intake manifold from Summit, etc.

Get non injector Holley style 4 barrel throttle body.

Get a top hat or air cleaner assembly- check for hood clearance.

Run 720cc or 1000cc injectors only in the primary position (good for 200+RWHP)

Megasquirt or some other aftermarket ecu.

Could get it done for under $2,000 with all new parts I think.

 

worth it?

very much so. it's the modern-day carb upgrade.

 

i don't think i have to say much more! ITB's all the way with Star Mazda one piece intake manifold

 

where did you get that intake manifold from? its sweet

 

Well that answers my question. I will be going with the ITBs. How much power would I be looking at with a good streetport job.

 

$100 eBay manifold, 750cfm Holley that I had lying around, blower hat and a 4" cone air filter, TPS from a 4.6 Ford (goes in the correct direction) mated to the throttle shaft by cutting two slots in the end, two GSL-SE injectors = 230 crank HP. I'm kinda injector limited but not really, the torque curve never really falls off but I don't feel comfortable revving past where I rev it so I'm calling it good enough. Maybe it would make the power lower down if I had a more free-flowing exhaust, but that would make the car less enjoyable to drive.

Way way way way way under $2000.

The sound it makes when you whack the throttle open below the powerband is worth the price of admission

 

Can you post a pic of what it looks like

 

Here is my setup and it works okay. Sorry for the cell phone picks. Got to replace my Blackberry, LOL.

Eric

 

motorcycle throttle bodies?

 

The manifold is four holes with no plenum, so it's technically ITB.

 

^ your intake is doing nothing but suck hot air from your engine. You would pick up much more power if you extended it down in front of a headlight away from the heat.

 

I keep hearing that, but...

Intake temps are within 20 degrees of ambient, better with the fans on full blast. There's not much air temp increase across the radiator - high air volume per heat removed from the coolant - and the fans will pull the radiator down below t-stat temp anyway. There is no kill like overkill.

Long ducting = bad because the more connections there are, the more possibility of an unfiltered air leak. Unfiltered air leaks result in rapid and severe compression loss followed by scrapping of everything in the engine but the eccentric shaft. I pay very close attention to air leaks. I smoke-tested the whole intake tract, there are a surprising number of places where a Holley gets unfiltered air. Also, that carb hat is siliconed down, as is the hold-down bolt. As is the carb itself. As is the intake gasket. No leaks means the engine lasts a long time instead of 400 miles. (There's no kill like what now? )

The area in front of the headlight is the WORST place to get air from. Full of dust and such thrown by the tire. See issue #2. The air comes from the cleanest part of the engine bay.

Getting air from in front of the radiator might be a good idea, but the coolant reservoir and coils are on the driver's side of the engine bay and thus no room for ducting. The passenger side can't work because the carb hat would be right up against the strut tower.

I've played with the idea of boxing that part of the engine off and feeding it air from a hood scoop, BUT... then the alternator might be starved for air. It's an S5 unit and I'm technically using more current than it can provide at any RPM when I have the fans on. Alternator life is not so good for me as it is. Plus, see #1 - the gains are minimal for the effort.

 

Anyone ever try this set up?
KIT: Mazda 13B on Atkins Intake Manifold

 

Peejay, your two injectors are in the original primary injector locations correct?

 

Star mazda makes them. they are in california.

 

How much did the manifold set you back?

 

you know i have been on the fence about this setup for a while now.

my main debate is "do i spend the money for a "ok" turbo build with a 2k budget or just build a quality itb bridge setup......................."

the main push to stay NA is the easy access in the engine bay, way less heat soak, and ability to really thrash on the engine day and night.

plus high diff ratio would make this car a BLAST to drive

 

Can I eliminate most of the vacuum line crap by going this route. And 23racer what tbs did you use?

 

I throttle bodies are from a Suzuki Hayabusa 1300 cc motor. They are 50 mm per throat necking down to 44 mm. I am using a Megasquirt and the TPS is the one that came on the end of the bodies, the factory Suzuki one.

The car makes great torque, as it will easily spin tires in first and second gear. Pulls hard from 3500 rpm to over 9,000 rpm if I want to and the throttle response is unreal. The only issues were the lack of strong vacuum signal which forced a conversion to Alpha N tuning and the fact that I had to build a manifold myself. Also, there are no setup tips or maps that you can build off of, so you need to tune from scratch.

And yes, the sound under full throttle without the trumpet socks, is amazing.

Eric

 

Ok thanks. I'm just trying to see where I should start. And what did you do about the 2nd dairy injectors?

 

Eric, I've got a set of throttle bodies in front of me from a Honda 600 f4i, the flange, and a megasquirt I built downstairs - I'm working on a stock port 12A, so I don't think I need to be quite so ambitious with flow. At 38mm, it's still more area than the ports. I'm hoping you'll share a little as far as setup tips.

I've always been curious, what's your runner length and exhaust setup?

 

The runner length is 16" from the mounting flange at the keg to the end of the trumpet, but you also have to take into consideration the id of the piping. I am using 2 different pipe ID's for the secondaries and the primaries that were determined to be a hair bigger than the ports in the irons.

The exhaust is a ported Racing Beat Racing header going in to 2 pipes at 2" ID all the way back to the rear subframe where they join together through a Burns venturied collector to a single 3" pipe that takes 2 90 degree bends and goes through a single 16" Borla Race Muffler and then out using a bell shaped exit pipe.

The car seems to be working great and is very flexible and has pulled over 185 rwhp before. Now that I have it working far better (to be confirmed this weekend at TMP) I am going to get it tuned on the dyno to max out the power and see if we can't break 200 rwhp. I am a 1/2 bridge 4 port.

Thats it.

Eric

 

i want to say they are $350 polished. its a 6 port so if you are not using a 6 port you will have to port it.