Stock vs. bolt-on dyno numbers?

[Pro Stock John]

I have a 95 Country auto.

What does it dyno stock? I'm guessing it would run mid 16's in the 1/4? (Dr. Dyno???)

How about with a big KN filter, Rusty's tube (got one used), and a hi flow aftermarket muffler?

[BBeach]

There's lots of variables, tire width, tire height, traction, using 2wd vs 4wd, elevation, added weight, wear on engine, atmospheric conditions etc. A bone stock 4wd cherokee with driver say 70 degrees should be running mid 16's assuming theres no wheelspin in 2wd. Ive yet to go back to the dragstrip (its all in good fun) to see what I can do. Maybe in May or whenever they open.

[j99xj]

My last 1/4 mile was an 18.55 @ 75 mph.

But my engine was near stock back then and I was racing at 5000 feet.

[Pro Stock John]

Yeah you can add a tenth in ET for every 700 ft above sea level.

[Dr. Dyno]

I have a 95 Country auto.

What does it dyno stock? I'm guessing it would run mid 16's in the 1/4? (Dr. Dyno???)

How about with a big KN filter, Rusty's tube (got one used), and a hi flow aftermarket muffler?

Most 4.0 XJ automatics will dyno 150-155rwhp and 190-195rwtq with stock tires and gears. Yes, mid-16's is about right for a stocker.

[Pro Stock John]

Cool. Do you think air filters and mufflers really add to the XJ or just a very small gain?

[BBeach]

Cool. Do you think air filters and mufflers really add to the XJ or just a very small gain?I'd say an intake and catback would give you the chance for high 15's, maybe a few more mods like bored TB and a higher flowing cat as well as keeping it in good shape with a nice tune up.

[Dr. Dyno]

Cool. Do you think air filters and mufflers really add to the XJ or just a very small gain?

By themselves they don't do much. The airbox and the front part of the exhaust (manifold, downpipe, cat) of the 4.0 XJ are the biggest restrictions, so you need to address those to make any meaningful HP gains. That means a cold air intake with a Powerstack cone filter, header, mandrel-bent 2.5" downpipe, and a 2.5" high-flow cat. Then you can add a 62mm bored TB and spacer to improve throttle response and low rev torque.
With all the external bolt-ons, you could shave nearly a full second off the 1/4 mile ET and get down in the mid 15's.

[Pro Stock John]

Thanks for the reply, what do you think about using a Rusty's transition tube with 6x9 cone filter vs. FIPK kit?

Do you guys ever mess with increasing the timing and running higher octane gas? With my old 5.0 stangs we would that and run 93 octane.

So what does a stocker run at sea level, like ~16.5@80mph? I think the Jeep has good response off the line but it feels flat in higher rpms.

[Michaelarchangelo]

You really can't adjust the timing on the jeep.

[j99xj]

Yeah you can add a tenth in ET for every 700 ft above sea level.

By that rule I should have run low 17s.

I don't understand why I was running so slow at mid 18s.

[badron]

Reread BBeach's post.

[Pro Stock John]

Could be a few reasons why you did not run faster, I only run my best times if I go a lot.

[Flash]

Could be a few reasons why you did not run faster, I only run my best times if I go a lot.

Yup, there is a knack to pulling off your best E.T. and every vehicle is different.


Flash.

[JJacobs]

Worn out Renix motors make about 110 rwhp, SAE corrected.

[j99xj]

Hey JJacobs, whats your 0-60 time in Fort Follins? I'm in Fort Collins right now and can only manage about 11 seconds.

[JJacobs]

Jeez, I don't know- the XJ I'm driving now probably belts out about 85 to the tire. Compression's in the 80 psi range..
I have some MJ times but that's not 4.0 related.