|
|
Post by overland47 on Nov 12, 2008 20:06:15 GMT 11
Hey guys, writing from across the pond again to ask another silly question...
My Isuzu Pup conversion with a 4JB1-T is running great. Best money I ever spent, I am just loving this truck now. You guys are very lucky to have trucks like this available over there.
Only complaint is that 5th gear needs to be taller. Actually I could use some taller gears all the way through, but we are limited to only one choice for diffs (4.10), and I don't want taller tires.
I don't have a tach, but at 75 mph (120 kph) on flat ground it runs about 7-8 psi boost and 500* egt. I'm getting about 30 mpg (not sure what that is in kilometers) and the engine is hardly working at those speeds. I want to drop the rpm's some to get some more economy.
My question-
What is the make and model of the 5 speed manual transmission found behind the 4JB1? Anyone happen to know the gear ratios?
I'm thinking I can get a 5 speed from a gasser Rodeo or something sold over here and do some gear swapping in the transmission to get the results I'm after, but I need to do some research before I go taking my truck apart.
Thanks ;D
|
|
|
|
Post by James W on Nov 12, 2008 20:30:31 GMT 11
Hi, good to hear from you again.... the common Isuzu 5-sp manual gearbox for the 4JB1 is the MUA5... you might find it in some troopers? but to fit the C223 and different bell housings.... I have several spares if you get stuck. Most of 'our' diffs are 4.56... and some 4.3's.... so at least you have some advantage there. I could dig out some ratios for each gear for you to work out if it's better or worse... [Edit] My book says MUA... but I thought MUA5... for ratios, I pilfered off this site; fronteraowners.co.uk/info/gearbox.htm |
|
|
|
Post by geeves on Nov 12, 2008 21:23:37 GMT 11
Are you 2wd or 4wd? What size tyres are you running?
Looking at my bighorn book I get 3.767 2.314 1.404 1.0 0.809 and if you have 4wd the low ratio is 2.283.
Dropping revs does not automatically get more economy. Running the engine at its most efficiant revs does. This generally is close to the revs at which max torque is produced which is about 2500 for the 4jb1t. If your 30mpg is US gallons then thats around 8l/100km or 34 UK mpg which is a good figure for 75 mph or more typical mixed running
|
|
|
|
Post by overland47 on Nov 13, 2008 9:04:22 GMT 11
Thanks guys. Hey James, long time no hear. How's that green tractor of yours doing?
It's a 4x4 and I'm running 235/75/15's. I tried some 31's on there for a weeks, but I didn't like them. The driveability was better, and rpm's came down and economy went up a bit, but I just don't want that big of tire. It's more of a daily driver and I don't take it out in the woods much.
I need a tach before I do anything, it's just in the idea stage now and I'm exploring my options. It's like all the gears are between where they should be. 1st gear is too low for anything other than taking off. As soon as it's moving, I'm grabbing 2nd. 2nd is too high to take off in.
Only reason I'm looking into this is that when cruising down the highway the engine is hardly working at all but seems to be revving higher than it needs to be. It just FEELS like if I dropped the rpm's a bit it would be happier cruising long distances.
It's definately a high revving engine. It comes alive on the top end, which is different than I'm used to with other diesels.
What's the typical tire size you guys run?
Thanks again.
|
|
|
|
Post by geeves on Nov 13, 2008 10:30:48 GMT 11
This sit has some good size info although this particular tyre seems to be a little smaller than some others that are meant to be the same size www.maxxis.com/AutomobileLight-Truck/Light-Truck-SUV/MT-754-Buckshot-Mudder.aspxFrom this your tyre is 29 inches high The vat majority of the rest of us are running 31x10.5x15 which is 30.3 inches or bigger but we also have the 4.3 or 4.56 diffs. A good compromise would be the 30x9.5x15 or if you want to change your rims the 225x70x16 which is a tiny fraction narrower but still 0.6 inches higher. You could also look at the 235/85/16 which is the same width but close to other 32 inch tyres for hight. With the 4.1 diff this might drop the revs too much though. |
|
|
|
Post by James W on Nov 14, 2008 15:52:33 GMT 11
Hi, "overland47" no progress on the TD-9 for some time... been so busy, 70 hrs weeks, some things had to go. But will be back on that soon... found a dud piston, so is worth the strip down....
You say a high reving engine? How high? We are used to good boost and torque from say 2100 rpm, and maybe 1800-1900 if a 2-1/2" exhaust fitted... makes a nice difference.... Have you wound up the fuel flow at all?
|
|
