TB porting half shaft

**redbird555** · 04-17-2010, 10:03 AM

Hi guys I ported my throttle body a while back and all seemed to be good. So yesterday I got bored and decided to man up and try the half shaft mod.... Everything went fine but the blade was sticking a little bit when I put it back in, my friends had this happen and just raised the idle screw a bit. I did the same to mine and it doesnt seem to idle any higher than before, although when I was driving it yesterday all of a sudden the idle jumped up 200 rpms and it began to shift odd. I readjusted everything and put it back, so far so good but the issue wasnt consistent so idk if its taken care of. My question was could this be because the idle screw was raised? It'd seem to me if it was the case it'd be idling high all the time not just on occasion I was thinking maybe I cause a possible vacuum leak some where?
Dan

**Cutlass** · 04-17-2010, 10:27 AM

I had to recenter my TB blade to keep it from sticking. To do so, remove the TB from the car, back the idle screw out, and loosen the 2 screws that hold the blade to the shaft. Open and close the tb several times and that should recenter the blade. tighten the 2 screws that hold the blade to the shaft and adjust the idle screw back to where you think it should be. Make further adjustment to the idle screw when the TB is back on the car.

**redbird555** · 04-17-2010, 10:56 AM

Thats exactly what I did lol and it was still sticking a little bit so I adjusted the idle screw until it stopped when it was back on the car I was just wondering if making the adjustments will piss off any of the sensors on the car?

**Cutlass** · 04-17-2010, 05:59 PM

yes it can. for the computer to think its at idle the TP sensor needs to read less than .7 volts (or something like that, exact voltage unknown)

**redbird555** · 04-18-2010, 05:14 AM

Ok thanks cutlass I looked it up and its around .6 volts is what it should be so ill make sure its in the ball park. Does it have to be exactly .6? I imagine theres some variation between cars..

**redbird555** · 04-18-2010, 05:20 AM

mine is sitting at about .65-.7v anyone see a big iissue with just a tenth of a volt

**Cutlass** · 04-18-2010, 07:47 AM

I looked in the GM service manual and it says less then .67 TPS voltage at idle. So yeah you need to back that down. I think the generally accepted range at idle is .4 to .6 volts

**redbird555** · 04-19-2010, 09:15 AM

Ok cutlass thanks I got it down to about .62 so its fine now. However its still weird sometimes after the car gets hot the idle will bump up 100 rpms almost like the throttle body is sticking open a hair. At idle when this is happening it'll settle down to about 600rpms then ill blip the throttle and its sticks a tad but the idle will settle to 500 where it normally is. Im reasonably sure its the tb sticking but now I'm back at college and cant really do much about it for a couple weeks. It hasnt thrown any codes and seems to be running fine. Will there be any loss of power or driveability issues other than the high idle? It seemed to drive fine the 200 miles back to school

**Damian** · 04-22-2010, 10:42 AM

If you do the half shaft mod, you need to get some washers that seat against the head of the tapered TB blade bolts. This will help center the blade and prevent sticking. If you'll notice on the half shaft, the holes were tapered. This was directly intended for keeping the blade centered.

I quit removing the half shafts a while back when porting stock TB's. Too many sticking issues and removing it doesn't do any good HP wise.

**JRENIGAR** · 04-22-2010, 02:11 PM

^^^ good to know. I was going to do this soon. How about using pan head screws that fill the shaft hole snug even if drilling to the next size is needed and re tapping the blade to the new size screws???

**Damian** · 04-22-2010, 07:02 PM

Originally Posted by JRENIGAR

^^^ good to know. I was going to do this soon. How about using pan head screws that fill the shaft hole snug even if drilling to the next size is needed and re tapping the blade to the new size screws???

You could give that a shot, but it'd suck if it didn't work. I just leave the half shaft alone nowadays. Too much headache over weighs the benefits (or lack thereof).

The biggest focus on porting a TB is removing as much material as possible in front of the blade without punching through, and blending all the "bumps" and "stops" in the casting flaws. Then of course the "bump stop" or WOT mod is a good idea also. I've actually seen a 6rwhp increase on the dyno doing the bump stop on an automatic, because it was only getting 89% WOT from the factory.

Also, don't get too caught up with the polishing. Mirror finishes can actually HURT flow. I usually finish off the porting with a 120grit sanding drum, which gives the TB a nice smooth finish but there's still cuts in the metal to prevent air turbulence.

**redbird555** · 04-25-2010, 10:51 AM

Thanks Damian I see what your saying I think because if I center mine it open and close with no sticking but as soon as I tighten the bolts down it sticks. So if use small washers between the blade and the screws it will help? What size and thickness?