• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Throttle Body Boring Questions

98XJSport

98XJSport

Destiny is the rising sun
Location
Western Maine
OK so im planning to bore my tb over to 62 mm on my 98 4.0, just curious if i can bore straight through the top after taking it apart or do i need to avoid changing the area close to the butterfly? A straight bore through would obviously be easier, if it can be done that way of course...any insight? Thanks
 
If you're going to do it yourself just go to 60mm. If you go to 62mm you will have to replace the butterfly with a larger one.

Check out the go-jeep website.
 
Basically what im wondering is if the area around the butterfly needs to remain at 58mm or whatever it is now, and leaving a ridge for it to seat in and then bore 60mm to that ridge? Or can i just bore straight through so its 60mm at all points in the tb?
 
i always thought myself that 98s came with 60mm throttle bodies, ...anyway, those who did that on 98s and similar engines, did you notice any difference? how much? worth it? or what?
 
I you look at my write up you will see the the bore on all HO's acutally start at 62 mm taper straight away to 60 mm until past the butterfly and then neck down to 58 mm. So unless changing the butterfly as well you can the bore out from 58 to 62 mm if you taper it back to the 60 mm just below the butterfly.

www.go.jeep-xj.info
 
ok so if i went with no taper i can bore 60mm to match the butterfly, or i can taper it from 60mm at the butterfly instead of the stock 58 up to 62mm at the exit. What is the diameter of the hole in the intake manifold, 62mm I assume? Anyways, exactly what i needed to know, thanks everyone.
 
Here's what I did with mine. I bored the taper below the butterfly to 60mm, manufactured a 62mm by 1.25" thick spacer and installed a K&N Cone intake. Acceleration seemed to improve (sounds ballsy). I have a 2700 lb. camper, highway manners improved with that, and my around town mileage jumped about 3 mpg. I do have a little whistle that is noticable at only a certain throttle position. Since I did all of the boring and manufacturing myself, limiting the cost of the whole mod to the K&N filter and tube ($36 off Ebay) and a $20 block of T6 aluminum, it was worth it. On the other hand, if you had to purchase everything at retail price, you may not feel you are getting the most bang for your buck.
 
XJ-HEAT said:
...Acceleration seemed to improve ...
... my around town mileage jumped about 3 mpg.
Click to expand...

:dripping sarcasm: WOW! More power and 15% to 20% increase in gas mileage over stock. All for only $56.00. How did the Jeep engineers miss this. :/dripping sarcasm:
 
maybe I'm being dumb here, but does it make sense to bore without replacing the butterfly? You still have a bottleneck there if you dont replace the butterfly and just bore the top and bottom out. Isnt the whole point to make the whole pipe larger so it can suck in more air?
 
dakotus said:
maybe I'm being dumb here, but does it make sense to bore without replacing the butterfly? You still have a bottleneck there if you dont replace the butterfly and just bore the top and bottom out. Isnt the whole point to make the whole pipe larger so it can suck in more air?
Click to expand...

No one is boring above it at all? The boring below the butterfly removes the restriction from the 60 mm butterfly down to the 58 mm that is there stock.
 
98XJSport said:
ok so if i went with no taper i can bore 60mm to match the butterfly, or i can taper it from 60mm at the butterfly instead of the stock 58 up to 62mm at the exit. What is the diameter of the hole in the intake manifold, 62mm I assume? Anyways, exactly what i needed to know, thanks everyone.
Click to expand...

The intake manifold plenum inlet is indeed 62mm in diameter. You can either:

1. Remove the 55mm taper below the stock throttle butterfly and increase the bore there to 60mm, keeping the stock butterfly or,

2. Remove the stock butterfly, bore the whole length of the TB to 62mm, and install a 2mm oversize butterfly.
 
my 3cents worth! i basicaly followed go-jeep and did the bore out at work. i think that if you look closely it seems that the bore "neck down" isn't quite round.what i looks like is that the jeep engineers made the tb so at very small openings the butterfly exposes roughly 2/3 of the bore. this made for a less abrupt power surge at small openings. i say this because what i noticed most is a very large power surge off the bottom when in 4low 1st. i also have a flow master when i first did the bore.oddly enough, a spacer plate smoothed that out a bit.though now i run a 2000 intake manifold,hi flow cat and a banks header. the bore out makes it a bit tricky at first if you start bouncing a bit as it is pretty abrupt. my opinion anyway based on my rig,results may vary! like was mentioned above, since i did it myself i though it was a decent mod for the buck.
 
So where do you get the 62mm butterfly valve from? Anybody have a link?
 
It seems it would be OK to use a drill-press to do it yourself, but what can you use that is 62mm in diameter to open it up? What is it called and where would you get one?
 
xj92 said:
So where do you get the 62mm butterfly valve from? Anybody have a link?
Click to expand...

You cant buy one. Very had to make too as it is not round due to the fact it sits at 8* of tilt. Someone on here once made one but took a lot of time and effort to get it to seal just right and if I remember they never got the idle right afterwards. You really do not need a 62 mm T/B and those who have tried it didn't like it as it slowed responce. The only time you should use one is if you have a stroker and or done some major head work. No bolt on things will ever require you to need a bigger than 60 mm bore.
 
I my own 62mm diameter throttle butterfly made from 1mm thick stainless steel plate. Any engineering shop can cut & drill a plate for you. All I had to do thereafter was to file down the edges to make it fit precisely in the TB bore (I had that bored to 62mm) at an 8* angle when closed.
I found the difference between a 60mm and 62mm TB on a modified 4.0 to be very small. Not really worth it unless you're either going to increase the rev limit of the 4.0 or use it on a stroker.
 
You must log in or register to reply here.

Similar threads

S
Anyone running a BBK throttle body?
Replies
5
Views
1K
75SV1
7
M
New to my XJ & wrenching - How to choose parts and what to prioritize?!
2
Replies
28
Views
4K
flyin_ryan
F
B
Jeeper needs Help !!
2
Replies
22
Views
3K
denverd1
denverd1
D
89 cherokee stock timing issues...
Replies
3
Views
1K
DarkoShadow
D
Devilfrog
Throttle Body size Question
Replies
0
Views
745
Devilfrog
Devilfrog
Back
Top