Need help with my 1990YJ intake system

S

Shane

New member
1064976

ok i've got a 1990jeep wrangler, with a 4" lift; currently on 32x11.5's. its got the 4.2L carburated I6. I'm looking to buy the Holly intake manifold from JC Whitney, and the offenhauser 4barrel carb to go along with it. Currently i ahve little/no use out of Fifth gear, and the jeep is just generally underpowered for having such a beefy engine. Any comments, or previous experiences with these parts? Or better yet, are there better/cheaper parts out there that i just dont know about? Thanks a billion!![addsig]
 

1064977

I am not a mechanic or any thing but if you have a Inline 6 and are under powered you may need to change the gearing in the front and rear ends. Ring and pinion magic but I do not know what gearing you are running that will be the 1st step. Tug[addsig]
 
1064981

I am not as knowledgable about my jeep as the rest of you are. Its a stock 1990 YJ, so whatever gearing comes on the inline 6 is what i have. i do fine around and up hills, just a big problem from 55-70, i think i've hit 85once =P

also wanted to add, as far as modifications go-once i do some engine work (mainly intake/exhause revamp) what else should I look for, as far as non expensive mods for a jeep that is wheeled like 30%of the time, this is my daily driver =)

edited by: Shane, Apr 21, 2003 - 04:51 AM[addsig]
 
1064992

well, start with the usual, shane. Get a K&N Air filter. Either the cone or just replacement kit. Then start looking at your exhaust system. A hi-flow cat and muffler combo will increase power. But Tug is right. You've probably only got 3.07 gears in your differentials, and you need to go up to 4.11s. This is a ratio, you'll learn more as you hear about it. From there you should be good until your engine blows.... then just swap in a 350 small block.

c[addsig]
 

1065000

Over carburating a motor, will cause it to run bad at lower RPM´s. You say you have a problem now, running in fifth gear. Chances are, with the bigger carb, youd hurt your performance under 2000RPM. Right where you need it for, fourth and fifith gears.
I know a Dodge isn´t a Jeep, but the priciples are the same. My mud truck with 33´s and 4:11 gears, auto trans. Ran just fine with a small four barrel (vacumn secondaries), with the 36´s It ran much better with the two barrel.
As a rule of thumb, every couple of tire sizes, is like adding another gear on the high end. In effect 5th gear becomes 6th and first becomes somewhere between 1st and 2nd. A bigger carb. often makes the problem worse, by moving where the motor grunts best, to a higher RPM range.
A larger carb will often rev a little faster after a certain point, about 1600 RPM´s, but a smaller carb. often has more grunt at lower RPM´s below 2200 or so.[addsig]
 
1065014

Don't mess with the trouble of changing the intake manifold and adding a carb that's too big. If you want to replace the troublesome Carter BBD carb, get a bolt-on Weber replacement 2-barrel with the progessive secondary. I've seen them for about $375. Best carb you can get for the 4.2L engine.

Regearing your stock 3.07 axle gears would be the best way to improve performance. I'd look for a set of stock axles from a 2.5L 5spd YJ as they are 4.10 gears and a direct bolt-in. This would be cheaper and easier than swapping the ring & pinion in each axle.[addsig]
 
1065015

I have a 1990 YJ. I put on a 4" lift and 33x12.5 and the same time on put the MPFI on. I could not use 5th gear very well on the freeways. I think gearing the diffs to 4:11 will be a lot better than anything you can do to that engine. After I changed my stock 3:07 to 4:11 I noticed a very huge increase in power. [addsig]
 

1065065

Thanks so much!! I'll get on that right away. Got her stuck for the first time today, i found about 3acres, that is mainly flat, with a bunch of little 'jump' hills, lots of fun around 20-30mph. Landed in a mud pit, i managed to flag some guy down in an F250 turbo deisel; popped me outta that hole in no time at all. Thanks again for your input, i plan to post a few more questions soon![addsig]
 
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