Topic: RPM's in 4th gear

[MakoML]

I have my 97' TJ on 33's and 4.10's.  I am noticing that no matter how far I mash the skinny peddle down, on the hiway I cannot get it above 3200 RPM down hill.  I just replaced the plugs with OEM RC12LYC and it made zilch difference. 

With the tires and gearing, what should I be able to rev to in 4th if all else is functioning well?

[Torch_Ind]

when your taking off can you rev through the gears? past that rpm? or is it only in 4th and 5th?  with 4:10's and 33's depending on what speed your at it may just be topping out

[MakoML]

I can shift at 4500rpm  into 4th at 60mph or so, but there is little to no acceleration in 4th and none in 5th.  It seems 3200 is tops RPM in 4th, and maybe 70 mph with the wind, 60 mph into the wind.

I had 31's on it before and don't recall it being that RPM restricted.  There is zero top end power in this engine right now.   Around town its fine, gas mileage is horrid of course though.

I would drop back to 31's before I messed with the gearing.  Eventually there will be a V8 with auto in it and 4.10's will be fine.

I am wondering if this could be due to catalytic converter starting to plug up, or something like that.

 

[sharpxmen]

could be the cat or lack of fuel. 65mph in average (which would mean no wind) is a bit low, you should be able to do at least 75 if you have no mods on the motor (in 4th, forget 5th with you gears and tires).

[MakoML]

I think I am going to start whacking on the cat to see if it is plugged and if so order the Magnaflo 23227 for it.  I have owned it for less than a year and don't know what has been done maintenance wise other than what I have done myself.

[Bounty Hunter]

If the cat is plugged, performance will get worse as the engine and cat warm up.  The catalyst contaminants will expand and block airflow as they heat up.

I'd look elsewhere, losing that much top end doesn't sound uncommon with 33"s and 4.10 gears.

[Torch_Ind]

check the cat

but thats why I asked if it was all gears or not because if it 's the cat it should do it almost all the time!!  especially when you start getting in to the high rev's

and going 60-70 with 4.10's isn't that bad.

how wide of 33 did you get?

[MakoML]

They are 285/75/16 on moabs,  about 33x11x16 or so.

[sharpxmen]

i had 33x12.5 with 4.10 and had no problem doing 75 in 4th but had a 4.0 t.b and high flow filter - engine was in good shape though.

EDIT: just occurred to me - are you talking about what the speedo is showing? did you replace the speedo gear or account for the larger tires? if not then keep in mind you're about 16% faster than what the speedo is telling you, same for the distance (to calculate mpg) so if you think you're at 65 in fact you're going 75.

[Torch_Ind]

EDIT: just occurred to me - are you talking about what the speedo is showing? did you replace the speedo gear or account for the larger tires? if not then keep in mind you're about 16% faster than what the speedo is telling you, same for the distance (to calculate mpg) so if you think you're at 65 in fact you're going 75.

+1

[MakoML]

No guys,  my speedo is 9mph off at 6o mph.  If I went what the speedo said, it would be top speeds of about 60mph and 63mph on a good day no wind top speed skinny pedal mashed RPM's 3200................

[Torch_Ind]

humm.

your stock eng no mods?  cause I can get more out of mine but I have a quite a bit of bolt on adders on my 2.5L

you could just be out of power my friend. also how tired is the eng?

but I would check for restricted exhaust or plugged air filter.

[sharpxmen]

sounds like out of fuel, plugged exhaust and such - no wind i was getting it to 80mph (if not 85), pedal to the floor and would take a bit of time but would get there - but that was only once i got he high flow filter and larger t/b, stock filter and t/b sucked with 33s and 4.10 gears

[b.hog]

replace the speedo gear with the correct one ,it will help ,did on mine anyway.

[jfrabat]

replace the speedo gear with the correct one ,it will help ,did on mine anyway.

Not to mention it is cheap ($20?) and fast (5 minutes) to do