IgorT.455/406

Hey guys,

I did some reading, and lots of ppl. talk about drilling an idle hole for a 58mm TB that does not have it (most aftermarket). I understand this needs to be done?

How will the 58mm TB effect the daily characteristics of my car that has most of the boltons, but otherwise stock heads/cam (for now)?

Can I get away with running a 58mm TB now or do I have to stock with stock or 52mm?

I plan on heads/cam 355 in the near future.

Would a 58mm TB work with my Nitrous Works 75-175 wet plate kit?

Thanks guys.

SS RRR

I just read somewhere that the BBK's needed to be drilled out. Don't know how much truth there is to that. A 58mm will be fine for even a bolt-on car. The TB does not have enough influence to change the behavior of the breathing characteristics w/in the plenum. As long as you go with a TB that contains about the same outer dimensions as stock you can use a plate system no problem. The only trouble you'd have is if you went w/ an Accel billet piece which is longer than stock.

Injuneer

An oversize TB can reportedly cause issues with shifting if you run an A4.

What's the height of the opening in your nitrous plate? Is it at least 58mm tall?

I think the throttle body idle hole issue is getting blown out of proportion. I've run the Holley and the BBK 58mm TB's with no idle problems. Never had to drill a hole and never even looked to see if the TB had a hole directly through to the plenum.

96capricemgr

Fred the car will idle without the hole but try it and I bet the idle gets better. We are not recommending some freak modification it is replication of a factory function. Many people think they are fine without till they try it.

Injuneer

I don't have to make it "idle better" because its always been perfect.... 800rpm on a moderate solid roller cam.... smooth as silk.

96capricemgr

All goes well I will be at Englishtown next month for a b-body raceday. If you are interested you could try mine.
Even with the old ZZ3 cam(mild) setup the idle improved when I drilled it.

91RSLT1

Which brand of 58mm tb?

neversummer

The BBK's have some funky chunk cut out on the inside of the TB - the side the faces the plenum. Maybe that is their alternative for a hole?

96capricemgr

I have a Edelbrock/BBK, the IAC circuit on it is sealed to the manifolds IAC circuit so it is not a metter of a difference there, I believe it is the AS&M that does not seal the circuit.

526 SS 96

Cars that have working IAC's and are tuned properly do not need any changes. The "drill mod" is popular because most people like to cut corners, or just don't know any better.

96capricemgr

Like I said we are reproducing a factory feature. I would argue that those of you who neglect it are the ones cutting corners. I have GMs engineering department on my side what evidence do you have????

How is it cutting corners to make sure the TPS is zero and getting IAC counts proper not terribly unlike what you do opening the blades and slotting the TPS we just choose to use the IAC circuit GM though was necessary to cast into the intake as fully as they intended it rather than treating the thing like a carburator and opening the blades.

Injuneer

But we ARE getting the correct TPS voltage, correct IAC counts, smooth idle and no split BLM's.... without drilling any holes. I've done it with two different 58mm TB's on my car - Holley and BBK. I've done swaps for people and never had a problem.

96capricemgr

You are wallowing out TPS mounting holes and tweaking it to get the TPS volage right correct??? How is that better than reproducing a factory hole? Or how is it easier or anything?

Injuneer

You just don't get it.... not everyone has a problem with the 58mm TB's and it not rational for you to intimate that anyone who doesn't have a problem is just too stupid to realize they do have a problem. Seems like you have no tolerance to anyone who does not totally, 100% agree with you.

Definitely my last post to this thread, since its pointless.

Injuneer

Oooops.... and just to clarify... YES my TPS sensor has been slotted. It was slotted by the guys that assembled my engine. They couldn't get the TPS voltage below 1.0V, even with slotting the sensor. After I looked at it for a while, I realized that when the removed my NOS electronic WOT switch from the TPS harness, they inadvertantly switched the blue and the gray wires on the harness connector. I rewired it correctly, and the TPS voltage is completely normal, WITHOUT relying on the slots.

Many people slot the holes because they BELIEVE that they have to set it at exactly 0.50V, which is not necessary at all.