What size should I have my new TB machined?

[fallacist]

I'm looking at swapping out my TB for one that is machined out a little larger. I know its common, and I was going to go through strokedjeep.com.

I did a search for throttle body, but I'm pretty horrible at using the naxja search feature. I found a bunch of other interesting stuff though..

I have an 01 btw;

Anyway, they'll machine it out to 62, 62.5, 63, and 64mm. I was thinking of going 63, since I could get a 63mm gasket to go with it. Why would I not want go with the 64mm option? If the whole point is to open it up, isn't that what I should do?

I ask because it seems like most people go with 62mm.

 

[cruiser54]

Go the biggest you can without needing to bore out your intake manifold. Jeff at www.strokedjeep.com can advise you. send him an email.

 

[VAhasnoWAVES]

is this going on a bone stock motor?

do you have other modifications?

i say forget it... but i dont dream of my 4.0 making gobs of power from bolt on mods.

 

[cruiser54]

I've gone from 52mm to 60mm on Renix Jeeps. The manifold is already bored to 60mm.
Better throttle response. Same fuel mileage.

IIRC, the HO is 58mm throttle body stock.

 

[old_man]

The only reason you get better throttle response is that it does the equivalent of opening the throttle quicker. Just push the pedal quicker and you get the same thing.

 

[offroadordnance]

If the TB is too large there will be more RPM variation at cruise (surge) if you have a twitchy foot as well

 

[fallacist]

is this going on a bone stock motor?

do you have other modifications?

i say forget it... but i dont dream of my 4.0 making gobs of power from bolt on mods.

2.5" exhaust exhaust, 784 injectors, poor mans CAI(cowl snorkel). This was probably going to be my final "performance" modification(other than gears). I'm looking to upgrade my battery wiring next if that counts though.

The only reason you get better throttle response is that it does the equivalent of opening the throttle quicker. Just push the pedal quicker and you get the same thing.

I hear that about this and the injectors. That the perceived hp/power increase is just throttle response. I also read that swapping out the TB is one of the most effective things you can do for more power(being all relative to the 4.0).

I'm not going for huge hp gains. If I wanted those, I'd get something with boost. What I want is a smooth running XJ, maybe some improved mpg(its a DD that does about 90% highway miles) with a bit of get up and go to make up for higher altitude. With 3 people, a dog and a trunk full of camping gear, she was taking her time getting up engineer pass this weekend at 12500'.

I know gears will be very effective at fixing that, but they're more expensive, and I really don't trust my capability to do them myself. So that's even more money. I'd be happy to do them myself if I had someone else to give me a hand who knows that they're doing, but I haven't noticed anyone on around my way.

By next summer, the goal is 4.56s and 33s. For now, just gonna try to build a good foundation to work from.

 

[offroadordnance]

Considering the air density at that altitude, opening up the TB probably wont have any affect on performance. That altitude is 5.5 PSI less than sea level

 

[Dr. Dyno]

Go the biggest you can without needing to bore out your intake manifold.

That's 62mm which is plenty big enough for a 4.0 and still big enough for a mild 4.6 stroker.

 

[Talyn]

Stock can be bored out to 63mm.

 

[O-Gauge Steamer]

Considering the air density at that altitude, opening up the TB probably wont have any affect on performance. That altitude is 5.5 PSI less than sea level

Nope. 3lbs of loss at best (worst?). I'm north of 6,000' and have a base MAP of 12.5psia instead of the sea level 14.64psia.

So, there you go, today's usless trivia about mean air density.

And I have been tracking my MAP for months as I continue to refine the tune on the supercharger installation.

But to the question, IMO, anything over 62mm will not gain much in therms of overall performance.

I ran a 65mm on the 4.7L 10 years ago, just for comparison.

 

[fallacist]

Sooooo for $90, is a 62mm TB worth it? Potential hp and mpg gains, smoother and more responsive throttle response?

I've heard good results from doing this, but some of you don't seem too sold on it...

 

[XJEEPER]

I bolted on a Fastman 62mm TB about 5 years ago when my Jeep (2000) was completely stock and noticed an improved off-idle throttle response, but I wouldn't expect any mileage improvement or significant performance gains on a stock engine.

 

[O-Gauge Steamer]

I bolted on a Fastman 62mm TB about 5 years ago when my Jeep (2000) was completely stock and noticed an improved off-idle throttle response, but I wouldn't expect any mileage improvement or significant performance gains on a stock engine.

Agreeed. By the very nature of performance mods, mileage is rarely, if ever, improved.

That being said, there are a couple of caveats. Properly geared, a Stroker or Forced Induction equipped XJ should do better in town as you stay a bit more out of the throttle.

I run P285/75R16s with 4.56:1 gears and a supercharger. On my "economy" tune, I get better than 17mpg in town. Flip the switch to the "performance" tune and the mileage drops like a rock...

There are hills here that I cruise up, in OD TC locked that, when it was still stock called for the TC to unlock and to down shift into 3rd.

 

[Johnnie Walker]

With my Renix, the strpokedjeep.com 60mm TB smoothed out my idle, throttle response is better, and did pick up a little MPG. Probably was the combo of 19lb injectors (which also smoothed out idle) even tho they were not done at the same time.

 

[DanMan2k06]

I bored mine out to 63mm when rebuilt the motor. Matched the intake hole as well. I had a friend CNC me a 63mm brass circle to use for the butterfly.

Compared to the other 2 jeeps in the family (96 sport, 98 police) it's extremely touchy. Anything over 1500rpm or so is fine but right off of idle it is very snappy. I like it, but it can be bothersome if you're in situation that requires precise throttle response, and accidentally hit a bump or something. Next thing you know the car is bucking back and forth because you can't keep your foot steady and keep bumping the throttle a little too hard. I've never encountered this in the other two jeeps.

No noticeable difference in gas mileage.

 

[O-Gauge Steamer]

Just an FYI, I ran a 65mm on the 4.7 Stroker back in '02. It was billed as a 68mm by Chryco and was used on the 4.7L V-8.

 

[DanMan2k06]

What kind of mods had to be made to mount up all the sensors? Did it line up to the stock 4 holes in the manifold? I'm assuming no.