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Discussion Starter #1,162
Char: 4.10's with 36" dia tires.

Randy
 

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Randy, according to that your engine should be turning 2297 RPM @ 60 MPH. 55 MPH would be 2106 RPM. Sounds like your OD must be engaged. 65 MPH would be 2488 RPM and 70 MPH would be 2680 RPM. Most any of those speeds without the OD would result in poor fuel economy and quite a drop in torque. A bone stock 4bt 105 HP hits full torque of 265 lb ft right near 1800 RPM and by time you hit 2500 RPM you'd be down around 225 lb ft. Cummins cam design makes the torque down low but doesn't hold it for any significant engine speed. HP goes up but torque drops like a rock after you pass 2000 RPM.
 

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Discussion Starter #1,164 (Edited)
Speedo Calibration.

So last night I downloaded a Free Speedo App for my I phone and went out to calibrate my Speedometer.

I had already made one correction to the number of Impulses/Mile from 16,500 to 15,500 which was purely a guess.

However while driving down the street first at 20 mph it agreed with the GPS exactly and then at 30 also then 40 also, above 40 the Speedo starts to oscillate about +/-5 mph but the basic readings are still right in agreement with the GPS. So I'm calling the calibration good. Possibly looking at sending the Speedo back for them to see if they can get it to not float around.

Above 55 it is all over the place. And at 65 the car is getting pretty scary due to the big tires not being perfectly balanced. 60 mph is decent but you can tell the tires are right on the verge of going stupid. Going on the freeway is no problem as long as it is smooth, but driving that fast on a road with many curves gets scary real fast. Anything below 55 is nice. Keep in mind this Jeep is wide open with no doors or anything to cut down on the effects of the wind, which is definitely a factor no matter how fast you are going. The car gets blown around pretty good by wind gusts. I have my Black Hat cinched down to where I look like a "Conehead," just to keep it on,,, and I still have to drive with my hand on top just to keep it on when it's really windy.

I now know why there aren't any 37 x 12.50 x 15" tires available any more. The 37 x 12.50 x 15 MTR's weigh right at 125 lbs each mounted. (Un-Sprung Weight) So there's a lot of rubber flying around.

The Smallest Rims out there now are 17's. This cuts down on the overall mass of the tire considerably and thus makes them easier to balance up more accurately which allows higher freeway speeds.

Maybe someday I'll get a set of 17's or 18's or 19's for this Jeep.. Then I can relegate these tires and wheels to Off Road only which is what they were meant for in the first place. I think it will settle down a little more when I add the extra weight of the Bumpers and Top to the Jeep, but how much remains to be seen.

On another note I found that at 55 mph the engine is running at between 1700 and 1900 rpms. depending on if you are going up hill or down hill. The Torque Converter is a factor here.

EGT Gauge quit completely last night, so I have to deal with it now too. Still making some headway.

Will be in the high 80's here tonight so I will be cruising the area after dark. Best time to have an open Jeep.

Randy
 

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...
However while driving down the street first at 20 mph it agreed with the GPS exactly and then at 30 also then 40 also, above 40 the Speedo starts to oscillate about +/-5 mph but the basic readings are still right in agreement with the GPS. So I'm calling the calibration good. Possibly looking at sending the Speedo back for them to see if they can get it to not float around.

Above 55 it is all over the place...
. If you are good to 40 MPH - I am suspecting the signal source. Before pulling the speedo and boxing it up, some (poorly organized) thoughts.


I'm not up to reading back 1,163 posts... Refresh me on the signal source for the electronic speedo. I've run several electronic speedos (mostly VDO) and one digital speedo.

Over the years, :

I've used drive shaft magnets (analog signal tapped off of a Rostra cruise control). Including my current 1962 Volvo with a Jegs digital dash - This digital speedo is unstable below 20 MPH - but, it was unstable with the junk JEGS GPS module that I removed. The drive shaft magnets worked fine with the VDO electronic speedos.

Analog signal generator (2 wire) that screws into the speedometer output on a manual transmission (VDO brand, GM thread, used on a couple of IH trucks)

Digital signal generator (3 wire) that plugs into my Ford manual transmission. Believed to be the original 1986 part. It is a little flaky on cold mornings, not bad enough to get my butt on a creeper... I run the Rostra cruise control on this digital signal.

Look for a connector that is not fully seated (the vibrations of higher speeds causing the connection to wiggle). If your sender is on a bracket (maybe a little more bracket bracing (watching this build - I suspect all your brackets are "TRAIL-RATED")).

An extra ground wire ("just because...").

Analog signals are susceptible to picking up noise from surrounding wires and electrical machinery. I've used shielded wire and also twisted the 2 wire pair to minimize picking up electrical interferance.
 

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Good info Russ. I guess I'm old school, but I like a mechanical speedometer. I was wondering if Randy's transmission may have a mechanical output or one on the transfer case. Most all the speedometers you see these days are electronic of some sort though. Some of them read off a GPS signal which might be good.
 

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Discussion Starter #1,167 (Edited)
I am using a pulse counter mounted on the body and driven by the Speedo on the transfer case. It is the one furthest to the left, the black one is for the Cruise Control. See Pics.

It is probably the gauge as it is an older model and they had problems with them, Same with the tach it was older and the mfg was making changes and not telling anyone about them which resulted in a "Course Correction" and now everybody knows what everyone else is doing.

The Speedo is accurate, it just bounces around above 40 mph. The EGT is dead also so it has to go back too.. We'll figure it out.

My next task is to get the O/D shifting. Then we'll know for sure what the RPM's VS Speed are in both gears. My original Calcs had the 1700-1900 at 60 not 50

Overdrive on this is 3.28:1 in total gearing. 4.10 is Direct.

Randy
 

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Yes, Randy, you have an 80% OD so your 60 MPH engine speed should be 1838 RPM which is an ideal number for these engines. Some companies do have a bad habit of making changes to products and forgetting to tell the customers about it. Just going to take a little time to work out the bugs.
 

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Discussion Starter #1,169 (Edited)
First Fuel Mileage Numbers.

OK so now that the Speedo is calibrated fairly close and the Tach works was able to come up with a early Fuel Mileage Number and it was 116.6 miles using 6.46 Gallons. or 17.5 MPG! I figure this is going to improve dramatically with the OD working. It has always been the goal to get 25 MPG which now appears to be doable.

This was all relatively low speed driving around town and short trips to Ventura and back. Looking forward to getting the OD working after I fix a few leaks here and there.

I have one really annoying one on the Speedo Drive on the Transfer Case. It is about 1 drop every 15 minutes while driving. It doesn't leak while sitting still, just when moving, and it makes a complete mess of the entire rear of the under carriage.

I also have a Coolant Leak at the over flow bottle which I just found today.

More to come.

Randy
 

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Discussion Starter #1,170 (Edited)
So after chasing the Speedo Leak and talking O-rings with AA, I put the thing together and glued it shut with Blue Permatex and let it set for a day. Great news,,, It still Leaked!

I was pissed. I stewed on it for a few days and was ready to yank the whole thing back apart and got under the car and removed the bolt that holds the Yoke that keeps the Speedo Drive Housing in place in the Tailshaft Housing.

The bolt was completely wet with oil. So rather than go deeper, I put a bunch of thread sealant on the bolt and reinstalled it.. Went back the next day and drove around for an hour,,, and SOB no leak!! The oil was seeping out thru the threads of the bolt! Who'da thunk? One more thing fixed.

Now I can finish cleaning the rear half of the undercarriage.

I lowered my Idle today down to 800 rpms and 750 rpms in gear, a little low in gear and vibration is noticeable. Might raise it back up a bit to like 850rpms. It had creeped up to 1000 and that was just too fast.

Also took 1/2 turn out of the Drag Link Heim Joint, so now the Steering Wheel is centered when driving on a strait road.

These are all small tweaks, but they all go together to refine the way the car drives, which is not too bad and getting better everyday.

I really need a Diesel Governor for a TH400 as it will refine the shift points to a lower speed that I can't get to as it sits with the Gas Governor. Anyone got one?

Engine is running great and I can get 60 MPH at 2000 rpms on the Freeway. bounce No OD yet,coming soon.

Randy
 

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I now know why there aren't any 37 x 12.50 x 15" tires available any more. The 37 x 12.50 x 15 MTR's weigh right at 125 lbs each mounted. (Un-Sprung Weight) So there's a lot of rubber flying around.

The Smallest Rims out there now are 17's. This cuts down on the overall mass of the tire considerably and thus makes them easier to balance up more accurately which allows higher freeway speeds.

Maybe someday I'll get a set of 17's or 18's or 19's for this Jeep.. Then I can relegate these tires and wheels to Off Road only which is what they were meant for in the first place. I think it will settle down a little more when I add the extra weight of the Bumpers and Top to the Jeep, but how much remains to be seen.
Might be a controversial opinion, but I think with OD that big I'd go straight to 20". 17" would be the pick up to around 33".
Reasons being, the bro-dozer crowd means there is excellent rubber choice in 20" and with 37" OD you've still got huge amounts of sidewall for rim protection. Same sidewall height as a 33" on 16" rim.

As you've found, big tyres have a low frequency bounce that's hard to control. Not to mention steering. Upping the rim size will fix both those.
 

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Discussion Starter #1,172
Yeah the different Tires and Wheels are a ways off. not looking forward to a $4000 bill for those.

the Rim size kind of depends on the actual tires I can get. I would be looking at 19's or 20's fo sho.

Good to hear from you, hows life in Kiwi Land?
 

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Haven't been doing much work on the car lately just driving it. It is settling in nicely and is getting more enjoyable to drive every day. The car has about 700 miles on it so far. Last fuel mileage was 17.5 mpg again.

it cruises willingly at 60-65 showing 2100 rpms and that is without the O/D operating yet. Looking at confronting that issue this weekend.

I have no Oil leaks, no Water leaks, and no new problems to fix, so it's time to go forward. :D

Randy
 

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Discussion Starter #1,174
Well been gone for a while, and the whole place has changed? Seems like some of my last posts got omitted, like the one where I told everybody that I got the OD working but the thing was already in OD so the last numbers posted are what I've got to live with until I can afford the change in gearing.

As it sits the engine is running [email protected] rpms at @65 MPH and about 2200 at 70 mph. I just came back from a refuel trip to Ventura. This tank was 342.8 miles on 18.246 gallons. Which works out to 18.78 MPG ! Which is up 1 full mpg from the last tank.

Pretty sure that if I ran <60 it would get 21 just like the truck does. I'm not going to see my proposed 25+mpg with 4:10's.

This last month I put @350 miles on it mostly around town and some short Freeway runs back and forth to Ventura. Learning how to drive the car better with every time out of the garage.I am finding the engine likes to be pushed harder and pushed up on the boost IE: more throttle off the line, and the trans acts better when pushed harder as well.

The entire drive train is working perfectly, no leaks or problems, and the car rides nice and I'm sure it will be nicer when the top and bumpers are finally on it.

It's 90 F here today, but supposed to be raining by mid week, so I'm running out of top off driving weather. Will probably be installing the top and doors soon.

I just turned 70 last Friday,,, Time marches on.

Randy
 

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Sounding good. Yeah, if you could get your operating RPM into the 1700-1800 range your fuel mileage should improve quite a bit. Once you pass the 2000 mark, both the torque and fuel mileage start to drop a lot. Automatics never get quite as good as manuals. Just the nature of the beast.
 

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Yeah, you can really tell when the slippage in the Torque Convertor is happening. Any time there's a load on the car like going up a hill or bucking a strong wind the speed falls off and the revs increase as the TC goes into Torque Multiplication. The boost also comes on. I have one hill I go up frequently and I can get 11 psi of boost on that one but can't get above 55 MPH. Not quite full throttle but close.

Going towards Ventura on the Ojai Freeway I am going directly into the Prevailing Wind, and in the afternoon it is pretty strong. I am carrying 5-7 psi of boost at 60-65 mph. As soon as I turn onto the 101 going South going across the wind,,, the boost falls off to nothing.

I've got right at 1000 miles on it now. Lots of complements everytime out of the garage. Quite the Chick Magnet!

Randy
 

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Discussion Starter #1,178
126541
126542
126543


OK,,,today I got the top down and sitting on the body. It fits OK?
It is definitely going to be a project, but I see a path so it shouldn't be too bad.

Biggest issue is the interface between the front of the top and the windshield frame. There is about a 1" square hole on either side which would effectively fill the cab up with water in a matter of seconds driving into a storm. I have to come up with a way to fill that gap on both sides that will become part of the top.

I will fit the Rear Window/Tailgate tomorrow and see if it is where it should be,,, if so then I'm on to bolting the whole shebang down to the body. Need 4 Over Center Clamps to clamp the front to the windshield frame but I only have two. I think they came from Lowe's or Home Depot?

Then it's on to the doors and they are definitely going to be a project.
 

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Coming right along there. Looks nice with the top on it. 1" holes up front in a rain storm would definitely be no fun. Would need some drains in the floor to let the water out. LOL.
 
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