Guanaco.13 Posted March 8, 2012 Share Posted March 8, 2012 I have a 1989 4.0l 2wd and it is slow as dog $#!& the speedometer only goes up to 85 mph. so what is the big difference in that motor or new 4.0l's how come they top out higher. what can i do to go faster, i mean come on I like to cruise on the highway at 80 mph. that is a big motor to be so slow. :fs1: Link to comment Share on other sites More sharing options...
Pete M Posted March 8, 2012 Share Posted March 8, 2012 did this slowness come on quickly or slowly? also, what size are those tires? Link to comment Share on other sites More sharing options...
Guanaco.13 Posted March 8, 2012 Author Share Posted March 8, 2012 did this slowness come on quickly or slowly? also, what size are those tires? I mean it hasnt got slower or nothing I just don't feel comfortable driving a truck thats speedometer only goes to 85 and 80mph, and i want to know what is the difference in the newer 4.0l's and mine and how to get mine to the new 4.0l top speed. Link to comment Share on other sites More sharing options...
Guanaco.13 Posted March 8, 2012 Author Share Posted March 8, 2012 and i am scared to buy the new rims and 32x11.5 r15 and then the truck be even slower Link to comment Share on other sites More sharing options...
lexluthier72 Posted March 8, 2012 Share Posted March 8, 2012 pretty sure an MJ was not designed to go 80mph down the freeway. Just because the speedo says it will does not mean its a good idea. Are there no speed limits where you are? Link to comment Share on other sites More sharing options...
Guanaco.13 Posted March 8, 2012 Author Share Posted March 8, 2012 pretty sure an MJ was not designed to go 80mph down the freeway. Just because the speedo says it will does not mean its a good idea. Are there no speed limits where you are? The speed limit here is 70 on the freeway but i tend to have a heavy foot and drive 75-80 but in my mj I just stay at 70-75 75 at the most. and I know the mj is not designed to going 80 down the freeway but if the xj's speedo say 140 you would assume that it could easily go 100 no problem and so it would be safe to cruise at 80. I am just wonder what would make my truck capable of those speeds. Link to comment Share on other sites More sharing options...
lexluthier72 Posted March 8, 2012 Share Posted March 8, 2012 :thumbsup: Link to comment Share on other sites More sharing options...
Pete M Posted March 8, 2012 Share Posted March 8, 2012 have you changed the speedo gear to account for the bigger tires? Link to comment Share on other sites More sharing options...
mnkyboy Posted March 8, 2012 Share Posted March 8, 2012 The numbers on the speedometer have nothing to do with how fast a vehicle can go. most vehicles from the 1980s speedos only go to around 85 it doesn't mean that's as fast as they can go and having one that reads higher doesn't mean its faster. Top speed between a Renix 4.0l truck and a 4.0l HO truck is about the same. And FWIW a 2.5l MJ will go over 85mph. Link to comment Share on other sites More sharing options...
Guanaco.13 Posted March 8, 2012 Author Share Posted March 8, 2012 The numbers on the speedometer have nothing to do with how fast a vehicle can go.most vehicles from the 1980s speedos only go to around 85 it doesn't mean that's as fast as they can go and having one that reads higher doesn't mean its faster. Top speed between a Renix 4.0l truck and a 4.0l HO truck is about the same. And FWIW a 2.5l MJ will go over 85mph. :agree: Yeah i got you the only difference I have found is 4.0 Litre 173 hp (129 kW) @ 4500 rpm 220 lb·ft (300 N·m) @ 2500 rpm 1987 177 hp (132 kW) @ 4500 rpm 224 lb·ft (304 N·m) @ 2500 rpm 1988−1990 190 hp (142 kW) @ 4750 rpm 225 lb·ft (305 N·m) @ 2400 rpm 1991−1996 Link to comment Share on other sites More sharing options...
AMCJeepMJ Posted March 8, 2012 Share Posted March 8, 2012 ...I just don't feel comfortable driving a truck thats speedometer only goes to 85 and 80mph... Better stay away from 1989 Corvettes too, then. Note the 85 mph speedo. /sorry about the image size. Link to comment Share on other sites More sharing options...
Automan2164 Posted March 8, 2012 Share Posted March 8, 2012 Shoot... My ZJ can go 120. Rob Link to comment Share on other sites More sharing options...
Pete M Posted March 8, 2012 Share Posted March 8, 2012 you wish! ha! :D but seriously, bigger tires will both make the truck feel sluggish and make the speedo read lower than you're actually going. :thumbsup: Link to comment Share on other sites More sharing options...
mvusse Posted March 8, 2012 Share Posted March 8, 2012 Don't know what the actual top speed is, as I never hit it, but when my truck was still stock I've had it close to 100 (as recorded by my GPS) passing two cars and a semi truck in a single move. 100 is way faster than a pickup truck needs to be able to go. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 8, 2012 Share Posted March 8, 2012 you wish! ha! :D but seriously, bigger tires will both make the truck feel sluggish and make the speedo read lower than you're actually going. :thumbsup: Absolutely. Check your speedo with a GPS. Probably a good idea to keep from getting tickets, too, since you're more than likely going faster than indicated due to the tire size. Link to comment Share on other sites More sharing options...
SW86 Posted March 8, 2012 Share Posted March 8, 2012 Shoot... My ZJ can go 120. Rob haha! ive had my buddies grand over 120 to where the speedo was almost touching the orange line where odometer is. funny as hell. it was shaking so violently and he was freaking out telling me, "don't you think we should slow down?".. and it was HIS zj! :rotf: Link to comment Share on other sites More sharing options...
Guanaco.13 Posted March 8, 2012 Author Share Posted March 8, 2012 you wish! ha! :D but seriously, bigger tires will both make the truck feel sluggish and make the speedo read lower than you're actually going. :thumbsup: Absolutely. Check your speedo with a GPS. Probably a good idea to keep from getting tickets, too, since you're more than likely going faster than indicated due to the tire size. you wish! ha! :D but seriously, bigger tires will both make the truck feel sluggish and make the speedo read lower than you're actually going. :thumbsup: I have lifted it 4.5 but haven't put bigger tire on it yet and if i was to put the 32x11.5 r15's all i need to do is change the speedo gear and bigger gears in the rear to make it now drink fuel right ???? Link to comment Share on other sites More sharing options...
mnkyboy Posted March 8, 2012 Share Posted March 8, 2012 Pretty much you regear it and if the speedo is still off then you swap the speedo gear. For now your truck should drive ok with 32s and stock gears,just GPS your speed so you know how far the speedos off then just adj for it. My truck at 60 is doing a little over 70 so I just keep that in mind when I'm driving. Up till recently my 2.5l MJ was getting daily driven on the freeway with a 6.5" lift 33x12.5 tires and 3.55 gears Link to comment Share on other sites More sharing options...
ParadiseMJ Posted March 8, 2012 Share Posted March 8, 2012 :eek: "don't you think YOU should slow down?".. :nuts:So, you think your 20+ YEAR OLD Jeep should go faster :no: I sure hope you are drinking heavily when you're driving. Link to comment Share on other sites More sharing options...
SW86 Posted March 8, 2012 Share Posted March 8, 2012 waoh, i never said anything about going fast in my jeep. i don't, period. i do 65 on the interstate, IF i even get on there. that was a 96 zj iirc with a 4.0. i was amazed it went that fast! i was just commenting on Robs post :thumbsup: Link to comment Share on other sites More sharing options...
ParadiseMJ Posted March 8, 2012 Share Posted March 8, 2012 waoh, i never said anything about going fast in my jeep. i don't, period. i do 65 on the interstate, IF i even get on there. that was a 96 zj iirc with a 4.0. i was amazed it went that fast! i was just commenting on Robs post :thumbsup: No, sorry, I just used the quote for the OP. Around here the CHP would be on you like flies on s@%t for going 85 (especially in a Jeep), boom, arrested, not just a ticket. 65-70 OK - 85 is ridiculous. Link to comment Share on other sites More sharing options...
MancheKid86 Posted March 8, 2012 Share Posted March 8, 2012 Thread hijack I got my 2.5L 155 km/hr, That's just under 100 mph :) :shake: Link to comment Share on other sites More sharing options...
88pioneer Posted March 8, 2012 Share Posted March 8, 2012 pretty sure an MJ was not designed to go 80mph down the freeway. Just because the speedo says it will does not mean its a good idea. Are there no speed limits where you are? The speed limit here is 70 on the freeway but i tend to have a heavy foot and drive 75-80 but in my mj I just stay at 70-75 75 at the most. and I know the mj is not designed to going 80 down the freeway but if the xj's speedo say 140 you would assume that it could easily go 100 no problem and so it would be safe to cruise at 80. I am just wonder what would make my truck capable of those speeds. I've never seen a normal XJ with a speedo at 140, plus they were limited to around 97 or so. These things aren't speed demons Link to comment Share on other sites More sharing options...
carnuck Posted March 10, 2012 Share Posted March 10, 2012 My speedo goes to 180 KMPH. Got one for my Jtruck too, but I figured out it has to turn 4600 RPM to go 180 MPH with 38" tires, 4.10 gears and .7 AW4 O/D in high range. Don't think my stroker has quite enough power with only 300 HP at 3800 RPM Link to comment Share on other sites More sharing options...
Blue88Comanche Posted March 11, 2012 Share Posted March 11, 2012 Shoot... My ZJ can go 120. Rob haha! ive had my buddies grand over 120 to where the speedo was almost touching the orange line where odometer is. funny as hell. it was shaking so violently and he was freaking out telling me, "don't you think we should slow down?".. and it was HIS zj! :rotf: my Boss's Hummer H2 well we where not really going that fast.. his cluster is broke... my 4.7L 05 WK speedometer tops out at 140 MPH i think. however the GPS, and radar gun.., top out much higher. Link to comment Share on other sites More sharing options...
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