Bored Throttle Body ?s

[Karlm]

OK, I've been interested in getting a bored TB for a while now. Here is my question. I've seen them from anywhere from $130 or so, all the way up to $400. Now I just called a local machine shop after wincing at the price, and the local guy said he could bore my TB for between $15 and $25. Is there something I am missing here? Why are these so expensive? I know that the cost of the TB has to factor in, but most of the lower priced TBs also tack on a core charge. Is there something that my local guy doesn't know about that makes this special? It seems like a simple straight bore to me. Thanks for any help.

 

[HossHoffer]

Apples and Oranges

A true bored throttle body is bored all the way thru and requires a new butterfly valve to compensate for the larger bore. I would guess that for $15-$20 he is boring out the bottom of the throttle body to match the hole in the intake manifold. This is a common practice that you can do yourself and adds a little better throttle response because of better laminer airflow. I did mine with my drill press, tapered rotary files, sanding wheels and scotch brite. Here is one of many sites on the subject:
throttle body boring
Any questions just let us know.

 

[Karlm]

Yeah, he's talking about just boring out the stuff below the butterfly, but isn't that what most of the aftermarket ones do?

 

[DharmaDog]

Just got mine done today!

I took my TB and spacer to a local shop and had them bore them out to get rid of the tapering and make it the same diameter straight through. I noticed a definite improvement in throttle response and a bit more power as well. I was considering getting the one from Turbo City, but that would have been $200 plus the core fee of $200 plus shipping. And then you have to deal with the turnaround time. And that would not have taken care of my spacer either. If someone is willing to do yours for less than $25, I say do it. That is an even better deal than what I got and I thought I was saving money by doing it locally.

 

[Lucas]

Aftermarket TBs are bored to 62mm, even the $300+ rubicon express one (it sure is pretty though). Anything larger than that and you would have to bore your intake manifold. The top half of the TB is already 62, and then it narrows down to something like 58. Just get someoneone to bore that out or do it yourself.

 

[RyanT]

I echo the others... do it yourself. However, it is a True bored throttle body, and I know on the newer XJ's that removing the taper inside is as much as you can do without buying a different TB. I actually used a Dremel to do mine and I was very happy with the results, I used course sanding wheels and a carbide bit. DO NOT PAY MUCH MONEY TO GET THIS DONE. I wondered myself how the mod companies were making so much... and it is simply because some people don't want to mess with it, it's easy and well worth it.

 

[RyanT]

Yeah, he's talking about just boring out the stuff below the butterfly, but isn't that what most of the aftermarket ones do?

Yes that is exactly what the mod companies do... I've talked to others who paid for it. Use the link that is listed on this thread, Go-Jeep knows his stuff, and has a great how to section.
http://www.go.jeep-xj.info/

 

[KarmirXJ]

:anon: :arrowl: one of the suckers that did pay for it... man I wish I could of done this myself than rushing into it

 

[RyanT]

:anon: :arrowl: one of the suckers that did pay for it... man I wish I could of done this myself than rushing into it

It's ok man, we all make mistakes, as long as you aren't paying for things like brake jobs, or tune ups you're ok.

I saw in Off-Road Magazine tonight that Rubicon Express charges $300.00 for theirs..... WOW .... what a rip off ....

 

[Ted Z]

Ok i admit it... I have been charging about $80-90 to bore them straight thru (remove the step below throttle plate)

If i could find a source for throttle plates i'd make bigger ones...

 

[KarmirXJ]

I got mine from Jeepers&Creapers. they charge 235.00 and then return 125 for the core, you pay 110.00 thats the cheepest Ive seen on the web. Later I went to my good machinest and asked him how much he would charge to bore mine out just for reference. he told me 10.00 for it and he would even hot tank it if i wanted it for free... The rest of the day wasnt so great from then on.

 

[satan]

the boring is easy (and cheap) as many have discovered...

The "trick" part is the proper fabrication of a throttle plate (the shape is oviod and the thicknes is shaped to be parallel with the bore when closed) - production shops usually have a jig for suppoting the plates while cutting the basic shape and angles... it's kind of a PITA - (the HO TB closes at something like 5* and the Renix TB is closer to 12* when closed, so youve gotta project that shape onto a thin piece of stock and account for the angle as you work your way around)

It's not really that tough and you can fit an oval plate into a completely bored TB (ignoring the edge shaping) with a little DIY effort.

True, many of the "bored" TBs for the HOs only have their throat removed, but be sure that you're looking at the same thing - many have been completely re-bored.

The HOs to about '97 have a 60mm bore with a throat-taper of 55mm below the throttle plate. Look at the bore of what you're buying (e.g. Accurate Machine bores to 62mm or a bit more, something akin to a 40CFM flow gain over just de-throating - so they're working the entire bore and replacing/fitting a new throttle plate)

The Renix years are stock at 51mm (there's a little lip in the bore, but no throat-taper) and can easily be opened-up to 60mm or larger (with the proper fitting of a good throttle plate)

For a "DIY Throttle plate", I recommend working in brass (harder is better) of about 0.05" or so... you can trace your OEM plate as a guide and test-fit often - go at it slowly with a good file and you should be able to get a controllable idle.

 

[RyanT]

Look at the bore of what you're buying (e.g. Accurate Machine bores to 62mm or a bit more, something akin to a 40CFM flow gain over just de-throating - so they're working the entire bore and replacing/fitting a new throttle plate)

"Negative Ghost Rider that pattern is full"... hold on ... my 99 HO measures 62mm above the throttle plate and it tapers down (UNDER the plate) to about 50mm, I did a straight bore, removing the taper, and mine is 62mm all the way throughand I DID NOT replace the throttle plate. If I went any bigger than 62mm I would have to buy a bigger TB, because the top (above the Throttle plate) is 62mm with 2-3mm walls around it... NO room for boring anything out there. Also the where the TB connects to the Engine measures 62mm... so to go bigger than that you would have to buy a bigger TB so you can bore bigger all the way through (then and only then would you need a bigger throttle plate, and you would have to make the hole into the engine larger.

Check around, the TB you get mod companies are all 62mm straight bores, I have EXACTLY THE SAME THING as they are selling.

 

[satan]

Yep - wherever that switch was made (in '97 and post, I'd recon) the TBs were opened-up a bit more -- to 62mm...

... so it'd fit that your '99 (somewhat later than '97) would have the larger bore at the plate (above the throat-taper).

The folks with the HOs up to '97 or so aren't quite that lucky and have a smaller diameter at the plate (60mm) so for them to go 62MM they'd need to full-bore and fit a new plate...

 

[RyanT]

Got ya.

 

[Faux4X4]

I am happy with my 68MM throttle body, but as discussed before you need to bore out your intake manifold. I have seen the turbo city unit, and for the money they charge I would do it myself. The largest you can go withour modifying your intake is the rubicon express 62MM. Flometrics where I got my 68MM from also has a 66MM that only requires that you taper the intake.

 

[KarmirXJ]

So if the 97+ years have a 62mm plate... and the pre 97s have a 60 plate... would boring out a pre 97 and using a plate and shaft from a 97+ TB work???

 

[Gojeep]

Yep - wherever that switch was made (in '97 and post, I'd recon) the TBs were opened-up a bit more -- to 62mm...

... so it'd fit that your '99 (somewhat later than '97) would have the larger bore at the plate (above the throat-taper).

The folks with the HOs up to '97 or so aren't quite that lucky and have a smaller diameter at the plate (60mm) so for them to go 62MM they'd need to full-bore and fit a new plate...

Are you sure abut this as it is the first time I have ever heard of it?
Very interesting indeed if this is true
My 95 is 62 at the very top too but the throttle plate in only 60 mm. Are you sure this is not the same as what you are seeing?

 

[HillbillyLes]

If the post 97 (or 95 whichever the case may be) TB's are 62 mm internally and the pre are 60 or smaller, why not just replace the earlier one with a post 97 (95) 62 mm and just have the taper or step honed out rather than honing the entire early TB to 62 throughout and putting a throttle blade from a newer one...

I have a 94 HO but haven't measured mine... I did do a honed/bored TB (replaced the stock 55mm with bored 62 mm) on my 89 5.0 coupe with definite improvement...then again it was mostly mid and upper RPM and redline was 6800 as opposed to the much lower powerband and redline on the XJ.

Les

 

[j99xj]

I said in another post that I think the intended size for the 4.0 was 62mm because all the H.O. intakes are that size. The only reason they have the "lip" is to make the take off smoother.

I have a stock throttle body with the lip removed and it runs great. Takes a little while for the computer to adjust if you forget to disconnect the battery like I did but after about 20 mins it smooths out.