4.2L @ 3500 rpms possible?????

Plink · 09-14-2002, 03:57 PM

YEP! Did it today on my way to Lowes! I got kinda scared but it accelerated very smoothly. Sweet huh!

johny1i · 09-14-2002, 05:37 PM

Dude, there is no way I would spin mine up that high as old as it is

. It sounds like a piston is about to come through the hood at 3000! I am glad to hear that it can be done, though

.

Plink · 09-14-2002, 09:16 PM

I'm not sure who had the Jeep before me and what they did to it but the engine is really tight. I'm really not sure how many miles it has on it but I was really crap'n my pants when I looked down and saw the tach!

4wheeler4CJ · 09-16-2002, 09:41 AM

They can be pushed even higher. They just sound loud. It's a lot of mass with that huge crank, LOL

Plink · 09-16-2002, 11:07 AM

I've got an 87 XJ w/ a 4.0L. I think I've got a lifter knock'n. It knocks when it's cold then goes away once the engine warms up. Do you think I should drop 20W50 in it hoping that it will eliminate the knock??

johny1i · 09-16-2002, 11:50 AM

i've been running 20-50 in mine since about 70,000 miles to keep the valves from rattling when i first crank it (mine had an odd problem with that) and i like to think that it helps the tapping lifter problem, also, because my #5 cylinder is prone to do that. It's very intermittent, but it always stops when the engine warms, like you said. I have found that consistent city driving (like days and days of it) where i never really push the engine over 2000 rpm makes it worse. I now try to push it on up to about 2200-2300 rpm when i shift once it is warmed up and it helps keep that lifter freed up for the next time I start it. Just my experience--

Dan Morera · 09-16-2002, 03:57 PM

I think that it also helps if you have the Peugot, when I shift gears at 2200RPMs is smother that at 1900RPMs.

What gear were you running at 3500RPMs???

Plink · 09-16-2002, 07:42 PM

I hit it in 1st, 2nd, and 3rd. I pretty sure I have 4:10 in the rear. That would help alot. What is really wild is that I'm runn'n on 32's!

UglySkunk · 09-16-2002, 08:23 PM

you guys need to live a little more, I have a 91 YJ with the 4.0 and I regually see 3500 and 4000 rpms

Alheim · 09-16-2002, 11:06 PM

Quote:

Originally posted by UglySkunk
you guys need to live a little more, I have a 91 YJ with the 4.0 and I regually see 3500 and 4000 rpms

Me too, and more . . .

BigDaddESean · 09-16-2002, 11:37 PM

hey to u guys who are running 20-50 oil..... I started using it in mine and it did help. but one night at work right b4 a long trip I needed an oil change and didn't have extra money for 20-50 so I used the 10-30 we had at work. later that weekend on interstate 380 the motor blew. so if u use it, don't go back. just my expaerience, later

94gclimited · 09-21-2002, 05:45 PM

I spun my 5.2 to 5300 which is where the rev limiter is. It felt fine up there although with the truck cam I don't recommend doing it on a regular basis.

Just curious but what rpm does the 4.2 peak at? I would think they'd be fine at least up to 4200 or so as far as the bottom end goes. Any Chevy smog motor of the late 70's big or small block will spin to 5k fairly easily.
Jason

Gator · 09-22-2002, 09:03 PM

My old 2.5L in my 95 Yj " Gator " factory would spin 5200 Rpms in 1st ,2nd. After i rebuilt the engine, the 2.5L would spin constant 7000 Rpms< trust me on this when i say I TEST my engines!>
I've got a 78 Chevy with a inline 250 6 cyl, factory it would spin barely 3600 Rpms, after i rebuilt the engine, well that jumped through the roof to 6500 Rpms, this engine saw A BUNCH of 75 Mph 2nd gear runs < Muncie 3 spd with 3.08 gears> < have seen one 250 6cyl, at the drag strip turn 11000 Rpms>
My 94 Gmc Dually < tow truck> with 7.4L < 454> sees regular 5500 Rpms,

a 4.2 can easily do 5000, 4.0 can go as high as 5000.

I'm a firm believer in DRIVING a vehicle, dont half A$$ shift the gears in lower Rpms, Lower Rpms causes problems as do Higher Rpms, Lower Rpms causes fouled plugs, alot of Carbon build up in the head area & valves
this is me tho, when my 4 banger was running, i had several people look at me going through something & duck & Cringe looking at me like i was crazy, holding 2nd gear in 4 low with 4.88's & 36" Sx Swampers, at 7,000 Rpms was NOTHING

I dont lug the engine but i wont redline when shifting either, but i do pick a higher Rpms to shift in... you'd be amazed on how much smoother the vehicle may run

I'm a bit of a speed freak, if ya couldnt tell.... i think the Hp Gods grabbed me when i was born & said screw everything else

I think this is why i'm putting a 400 Hp 350 Chevy in my Yj, but then again i could be wrong... who knows LOL

KG4PAM · 09-23-2002, 09:05 AM

i know for a fact that a 4.0 will go to 5000rpm. my xj routinely sees 4k, but i have hit 5k several times. it makes the sweetest sound! a nifty trick to pull is when you get stuck behind bicycle riders, you can floor it and the rpms will climb VERY steadily and the cyclists will hightail it out of the middle of the road... one reason that i let it get so high is the thing has an automatic(not my choice

) and i dont wait for it to shift.

iroc22 · 10-16-2002, 10:52 PM

Quote:

Originally posted by 94gclimited
I spun my 5.2 to 5300 which is where the rev limiter is. It felt fine up there although with the truck cam I don't recommend doing it on a regular basis.

I've bumped mine off of the rev limiter many times. The 5.2 is an excellent engine. It's a far cry however from the 6500 I was seeing in my hopped up 305 in my Camaro!