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boring throttle body

J

JWHIT67

NAXJA Forum User
Location
colorado
I have read about boosting horsepower by boring out the restrictor lip of the throttle body. There is a company that sells rebuilt throttle bodies (with the restrictor removed) and you send in your old throttle body for a refund (1/2 price.) This sounds relatively simple can't this be done yourself with a dremmel?
 
You can do it yourself. There is a company that sells bored TB's, but cant remember who it was off the top of my head. You will see little/feel little or no gain in power, unless you add other 'performance' mods along with the bored TB. Do a little searching in the Street and Performance section, you'll find some helpful info.
 
It truely depends on what you time is worth to you and what tools you have at your disposal. I bore mine and the local guys here at work after hours. Takes about 15 minutes on the lathe. I just knock down the lip for a straight 60mm bore. I have also done 62mm bores with a custom machined butterfly, to be honest, you can't tell the difference between the straight 60mm and the 62mm, have had both on my rig and the extra time was just not worth the power gain. Now if I had a fully custom 4.8+ liter stroker, then I would consider just moving straight to a Mustang 65mm throttle body and adapter plate.

You can use a drimel, just get a bunch of sanding drums and it takes a little time and don't go above the butterfly line, you'll never get it to idle.
 
It's simple. Remove throttle cables and un bolt throttle body. Use torks bits and remove the sensors. Remove the screws on the throttle plate and pull out the throttle shaft. Put a 2" drum sander in your drill or drill press and sand the bulg off being carfull not to sand down the part where the throttle plate closes. Clean up any sanding dust with soap and water or carb cleaner. This is very very easy and it would be hard to mess it up. It goes back together real easy and you will be done in an hour. Get a throttle body base gasket before you start incase yours gets messed up. Get a drum sander from a hardware store or harbor freight. You can also radius the very bottom a little to port match to the intake but just remember to stay away from the throttle bore that the throttle plate closes in. Simple as that and you will like the results at all throttle positions and loads. Remember to un hook your battery and turn the key on for 30 seconds to re-fresh your computer for the new mod.
 
Bump for a way old thread on diy tb boring:
I just finished mine and it's peppy for damn sure. The throttle is almost too light. It idles right about 1100 rpms, but when I put it in park, it goes to 2000. Does this sound like i didn't get the throttle position sensor seated quite right on the butterfly shaft?
 
DeftwillP said:
Bump for a way old thread on diy tb boring:
I just finished mine and it's peppy for damn sure. The throttle is almost too light. It idles right about 1100 rpms, but when I put it in park, it goes to 2000. Does this sound like i didn't get the throttle position sensor seated quite right on the butterfly shaft?
Click to expand...

Yea its pulling in air it shouldn't be pulling in. I suppose the tps could cause it to idle high like the renix which I've had experiance with the iac opening up cause of a faulty tps or bad ground. Or if u were stupid enough to bore around the butterfly, but I don't think anyone is.
Also I've got a renix TB (tiny 53mm doodoo hole) that I'm gonna bore to 60mm on my mini lathe as soon as I get around to it (already ported a 60mm on it). I've been wondering if it's gonna actually add power or just throttle response. Being so small it feels like thered be a restriction but I've heard it's all about the cam being the restriction point and then I've heard claims of 5hp off a ported 60mm. Same thing with TB spacers.
 
Well to clarify, when I fire it up it idles at 800. I figured out that the throttle shaft spring wasn't hooked into the throttle body. That seems to have cured and kind of super light throttle.

It still idles in Park at 2000 rpms. Again, it doesn't do that when you first start it up. That doesn't sound like a vacuum leak to me. Sounds like some kind of intermittent sensor issue.
 
DeftwillP said:
Respectfully disagree. Have you not seen the taper in the lower half of the tb?
Click to expand...


Yes, I've seen it and removed it on 2 occasions, back in 1988 and 1989. Performed the mod on two of my Comanche demos at the dealership. It helps a little. My point was that the butterfly becomes the biggest restriction after you remove the taper.

For that amount of work and minimal return, I'd sooner get a bored TB with a 60mm butterfly or larger, depending on application, directly from Leigh Machine for $90 . I've used 3 of his so far with excellent results.
 
ok so the link that was posted in the write up for an adapter plate to fit the h.o. t.b. on a renix is no longer in service. anybody know where to get on at?
 
As I mentioned in another thread, you can get a 60mm TB from www.strokedjeep.com that will bolt on to your Renix intake manifold. FWIW, the intake manifold is already 60mm, 2mm bigger than an HO TB. $90 for the TB and no expensive adapters for the TPS etc.
 
I bored mine out to 64.4mm only because I had access to a mill and the time to mess with it. The only difference I noticed was better throttle response. This would be a much better mod with some head work and a better header. I did have to match the opening in the manifold to the throttle body to take care of a stumble off idle and a gnarly whistle at part throttle. Matching the opening took care of both issues.
 
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