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Bored Throttle Body

greenday9d1

NAXJA Forum User
Location
CA Bay Area
I'm thinking about getting a 62mm bored TB for my '92 XJ 4.0, and my friend also wants one for his '99 XJ 4.0. I was reading the fine print and unlike most of the other modifications I see, this one says it makes no guarantee on whether or not it is smog legal. Could this have enough effect to make my car not pass smog in CA?
 
It will only make your engine more efficient. Also a 62mm throttle body is a major waste of money unless it's going on a stroker. You can bore your own throttle body to 60mm extremely easily, almost free. If you can't do the work yourself you could have a machine shop do it for probably under $20. You will never notice the 2mm difference.
 
juicexj24 said:
If you do it yourself, XJ-Armor has the larger plates for the 58mm, 60mm and 62mm. www.xj-armor.com
Juice
Why would you need a 60 mm plate when stock already has that?

BTW, I have a write up on boring your own if you want to do it and agree that a 62 mm is only needed when your have done a lot of internal engine work.
 
As a CA licensed smog tech, I would fail a Jeep with a RE style bright red throttle body. Entirely due to the fact that they don't have approval as an authorized replacement part. They will not affect the vehicle emissions, but nevertheless t-bodies, just like some intake manifolds, that aren't CA approved aren't legal to be run on pollution controlled vehicles. If you wanted to slip one by the smog tech, bore out a stock t-body and they will never know. No smog tech will be able to tell if the throttle bore has been enlarged just by looking at it. I wouldn't even bother checking for it.

Bryan
 
I posted the plates sizes for those that have non-ho tbs as well as those with HO Tb's. Just helping out the masses. Juice
 
scottsxj said:
yeah thatd be cool if you could post the link to your write up. Im interested in doing this myself. Thanks

Nicks already done it as that is my write up. :roll:
 
What kind of performance benefits can I expect out of boring my TB? Do spacers do any good?
 
I fell for the hype and used a spacer on a different xj and found no benefit. People with carburetors get the most benefit from these if I remember correctly as it allows the fuel to atomize better or something like that. We have fuel injectors so I don't see how it would help.
 
Probably the most noticeable difference with any throttle body modification is in throttle response, becomes snappier. Phenolic spacers on a carb act as a heat insulator between the manifold and actually do make a difference. I build a 1" phenolic spacer on my XJ and there is no noticeable difference whatsoever (non-HO motor).
 
I've experienced both the 60mm and 62mm bored TB's and there's no noticeable difference between the two performance-wise. Going from stock tapered 60mm->56mm to a full 60mm TB improves throttle response and there's a small torque gain. Definitely worth doing.
When I decided I wanted more HP, I bought a TB from a junkyard, had it bored to 62mm at a local engine shop, and made my own 62mm throttle plate to match. It worked great but there was no SOTP difference. At the time my engine was internally stock but since then, I've ported the head so the bigger TB may be producing more benefit here. One thing's for sure, when the engine hits 3500rpm it's like the blue touch paper's just been lit, and it's still pulling hard when it hits the rev-limiter.
_______________________________________________________________
- 1992 4.0 XJ Laredo UpCountry with modifications - 173k miles - AX15, NP231, D35c, D30
Estimated 240hp@5250rpm/280lbft@3500-4000rpm, 1/[email protected], race weight 3465lb
- Future mods -
4.6L stroker (under construction)
- Websites -
Jeep 4.0 performance, 4.6L stroker build-up
- Tech Webpages -
CTS resistor trick, Dual electric fans, IAT sensor relocation, Intake manifold heatshield, MAP adjuster, Oil temp. gauge install
- Info Pages -
Automotive formulae, Jeep 4.0 cam specs, Jeep engine dyno graphs
 
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