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Owners of Accufab throttle bodies, please make sure that when you install the throttle cable to the Accufab throttle body that you place a throttle stop underneath the accelerator pedal at the point of WOT to prevent the throttle cable to put any strain on the throttle shaft.

The accelerator pedal should hit the stop at the same time than WOT, if you do not do this adjustment you will put too much strain on the throttle body shaft at WOT which in turn will cause the throttle shaft to break at the point where one of the two screws goes threw it. This will cause the screw to fall in the engine and possibly cause major damage.

This was disclosed to me today (02/07/05) by John, from Accufab.

Moderators please make this a sticky.
 

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Hi Chris,
John had his wife push the accelerator pedal to the floor while he examined the cable on the Accufab throttle body. There was still some slack in the throttle cable with the pedal on the floor, so the cause of the failure is not what Accufab is claiming. Torque Freaks had the exact same failure mode on the Accufab throttle body on a DSM race car of theirs, and they too, had slack in the accelerator cable at full pedal travel. John Reed told me that several MKIVTT Supras have also had this exact same failure mode with the Accufab. I think Accufab is trying to evade responsibility.

Here are pictures of John Santesson's head and pistons after the screw from the Accufab went through the engine :(
Head:




Pistons:



Note the screw, embedded in the head, near the one o'clock position on the valve:(top center of the picture)




Best regards,

Ken
 

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Run AccuFab at your own risk on higher boost cars. I have seen way to many(adjusted correctly) do this on cars running higher boost, and have stopped using them. We are trying a new option out, and will see how it works. A high profile team has also made the switch on their ProRWD car, for the same reason. No failures since switching from the AccuFab.

This is a heartbreaking thing to have happen. John is an awesome guy, and was getting close to being able to enjoy that new engine. This is an expensive road I hope no one else has to go down.


John Reed
TorqueFreaks Inc.
 
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All i can say is i wish accufab nothing but the worst of luck in their business pratices

This motor was sooo sick, i raced a built to the nuts rx7 for like 3 miles over and over again and i was only at 14psi and i smoked him, (except one time i missed a gear) this was they greatest street mr2 ever, i doubt chirsk can replicate that work of art.......

this sucks nuts, well i guess i better pay john the 500 i owe him right away.....ugg

depressing
 

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The objective conclusion we should all draw from this as a progressive community would be for those of us with ANY of the aftermarket throttle bodies to have a good look at them to make sure the plate screws are mechanically locked in place; this might involve removing the throttle bodies for inspection, but that's easier than the alternative...

Thank you for bringing this potential problem to light for all of us - the information is definitely appreciated!!!
 

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The first problem isn't the screw coming loose, it is the throttle shaft breaking in half! They usually break right where the screw is, and then it has nothing left holding it in. Our DSM usually goes WOT at this point, and you will find the throttle linkage and half the shaft laying at the bottom of the firewall. :eek: And of course the rest goes through the engine.

I would have warned John earlier, given my personal experience (and that of many others), but his boost is a lot lower than the other cars I have had this problem with.

We have switched to a throttle body from Wilson Manifolds. I have no testing yet on this throttle body, and therefore am not to the point of personally recommending them. But the ProRWD team I referenced earlier has not has issues since switching.


John Reed
TorqueFreaks Inc.
 

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Actually the the shaft broke at one of the screws and that screw went through the motor. Still not sure why this happened. I was just about done with all my upgrades so now I'm going down rebuild road again. Hopefully the head is not junk but I will leave that up the ChrisK to determine. I will not be using an Accufab on the next motor. Torquefreaks has switched to Wilson throttle bodies but they don't make one to fit Chris's intake manifold. I will look at BBK and Ford motorsport for the next one. For those that are interested I was on the dyno at the time of the failure and made 320 rwhp on pump gas at 12 psi. We did a few more pulls before we knew what happened and still made around 300 rwhp with 50 psi. in cylinder one. Car wouldn't idle, thought it was ignition related but found the shaft of the throttle body broke in two.

Just so everyone knows my opinion I don't buy what Accufab claims. There was plenty of slack in the cable and there is a stop on the throttle body to keep from binding the plate. All was adjusted like the stock throttle body. John
 

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Let's do a quick calculation of the forces that are acting on the shaft. That is a roughly 3" diameter throttle plate so the area on it is 7 square inches. John has run at least 22psi of boost on it. If you caculate the instantaneous load on the shaft from slamming the TB shut on 22psi, you need to consider both the 22psi on the turbo side of the plate plus over 20 inches of Hg of instantaneous vacuum that is going to build on the inside of the plate. That means you have around 1.5 bar pushing in and 0.7 bar pulling in for a total of 2.2 bar or around 32 psi. 32 psi on 7 square inches is 224 pounds of force on that shaft. This is probably worst case although if the blow off valve is a bit slow you might get close.

Only Accufab knows what the shaft is made out of and how much material is left when it is drilled for the screws. I wonder what kind of repeated stress testing has been done on this throttle?
 

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Ouch,

I didn't know John had such a setback. I was still on the lookout for those new dynoplots. I was impressed with the numbers and results thus far, as well. Keep the faith John...hang in there.

Kevin
 

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:scared: :scared:

I just bought an accufab TB during the GB and it has not been installed yet.

Is this on all accufab TB's? There is a stop that hits the housing of the TB at WOT...how can additional strain be put on the shaft since it can't rotate past the stop?
 

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Not sure about stress testing but their website does say that this throttle body is used for supercharging applications. Just makes me wonder what I should do on the next throttle body so it doesn't happen again. I too do not understand how you can overstress the shaft with your right foot. That stop looks plenty meaty to me. Maybe the shaft material is just too soft. John
 

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Crap...I have a 70mm Accufab as well. Now I dont know what to do. I purchased this per ChrisK's recommendations to go with his intake manifold that I also have. Dont know if I should use it or not???
 

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hello guys.
i hang out in the honda world alot an the race shops i hang out with all preffer the bbk tbs an i have not heard of 1 break.. i will find out once my set up is done with the 75mm tb from bbk...
henri
 

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Ouch. I had the same thing happen in December 1984 on my new 4age powered Corolla GTS. The throttle stop was not adjusted correctly from the factory and on a high speed run at WOT the Toyota butterfly retaining screw broke. The butterfly went all cockeyed and refused to close. luckily the stock fuel cut kept the engine from detonating. though the little screw that busted did a major rework of the number 3 piston top and head. Luckily back then the Toyota warrenty would not cover the fix as I had some HKS parts on the car :(
Just shows how important throttlestops are, not only for modified engines.
 

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I was originally gonna go with a a bbk throttle body, but i believe chrisk reccomended i go with the accufab. Now im starting to get paranoid.
 
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