Prather Throttle Body for 1.6 Miata/TPS

L

little bill

Well-known member
I know that Jesse will be busy this weekend so I thought I would try and find the answer here.

I have a Prather modded throttle body that I need to install on my car. While installing, I discovered that my current TPS wont work with the new TB. My current TPS has a D shaped female receiver for the throttle shaft, the Prather throttle shaft is flat, requiring a slot shaped female receiver. So the question is what are others running for TPS with the Prather throttle body? Any help would be greatly appreciated. :whisper:
 
you must use a 99 tps. i am currently building a 1.6,have had a lot of help from jesse. jess h.
 
To the OP: yes, you need a 99 TPS sensor. Your pre '94 is just an on/off switch. Your FI ECU will want to know the throttle position - or some like the TEC can run with just MAP sensor.

Hammill":efij6uot said:
So what exactly is being modified? :ask:
Click to expand...

If you know much about racing a miata, you know the little pressed-in screws on the throttle shaft back out and get gobbled up by the engine - or worse case, throttle shafts break.

The rule allows a different throttle shaft (see the GCR) and Jesse offers a pretty cool reman'd part.

Fuel Injection: All inducted air must pass through the
throttle body and be subject to control by the throttle
butterfly. The stock throttle body casting/housing must
be retained. The inside dimensions of the throttle body
casting/housing and all dimensions of the throttle butterfly
must remain stock. The throttle butterfly shaft must not
be relocated. The outside diameter of the portion of the
throttle butterfly shaft located in the throttle body bore
must be no smaller than stock. The contour of the inter-
face between the throttle butterfly shaft and the butterfly
must remain stock. The throttle butterfly and any throttle
butterfly to shaft screws/bolts can be attached to the
throttle butterfly shaft by any means including welding
or brazing. Holes or slots can be created in the throttle
butterfly for purposes of idle adjustment only.
Click to expand...

Sorry - look for smoking guns elsewhere.
 
No smoking guns! Just curious what others are doing. Not suggesting someone is cheating! Simple question
 
Sorry - no coffee this morning, and I got almost smashed into on the way to work, by none other than our CFO. Luckily I bitched him out in traffic before I recognized him.
 
I was also worried about engine eating the screws. I red loctite them when I cleaned, but I am sure if I had better parts to go to I would have done the same.

Is this something that my buddy building a ita miata should be concerned about?
 
From what I understand, the throttle body screws are a known fail on the miata engine once they start getting spun higher than the factory set 7200 rpm. According to Jesse, harmonics are the culprit and cause the head of the screw to break off, what follows is the nickle tour of the combustion chamber and exhaust system. The Prather modded TB seemed like cheap insurance to me, I really don't want to risk loosing an engine when there is a relatively inexpensive fix available. No screws, no screw heads to break off.....seems like a no brainer.
 
little bill":29lkqn0j said:
No screws, no screw heads to break off.....seems like a no brainer.
Click to expand...

Spec Miata's couldn't legally turn above 7,200 rpm, correct. :wink: :wink: :wink:

This post is in no way dissing Jesse. I have viewed E & F production screwless shafts broke at the end of the EDM'ed buterfly shaft slot. Maybe there's something these folks didn't know. Part of the game as I've heard is to leave/have the aluminum intake manifold support bracket from the block to the intake manifold in place & to have the steel bracket between the number 1 runner & the lower attachment bolts for the throttle body in place.

I have viewed a welded shaft/butterfly that (with screws) failed.

One guy fashioned a screen & inserted it after the throttle body shaft eariler in the game.

Another guy isolated the throttle body from the intake manifold.

Along with the harmonics it doesn't help with the weight sticking at the end throttle body shaft.
 
That is actually some great info on the intake manifold bracket. I was curious about that on my Honda motor. Seems to me that it would be wise for me to have that bracket installed. I figured I should put it on but had never thought about what effects not having it may cause on the throttle body.

Thanks for all the info guys
 
For what it's worth, I've lost throttle screws with the intake brace in place, and with it gone. Doesn't seem to matter. The harmonic is crazy -even with a well balanced motor, you can barely hold your hand on the valve cover at 8K on a dyno. Were there any other small stressed parts, I bet we'd be hearing about those breaking as well.

Best practice is to just get the throttle cable "tight enough" to get the throttle body wide open. Stress on that cable at full throttle is definitely bad.

I do know there is an "alternate" throttle body off of (I think) a Ford Escort, that had some weights attached to the front side to dampen the harmonics. You'd need to decide if using it would be legal - I do not believe it is...but there may be some relief for those prone to comb through the GCR. YMMV.
 
I think the throttle breaking issue is less about Harmonic vibrations of the rotating mass of the engine and it's accessories. I believe it is more the acoustic energy and harmonics in the intake tract that are breaking shafts etc.
 
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