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tndonor
01-16-2008, 09:45 PM
Upon urging (which I agree) I think a few things need to be brought to light.

This being an FSJ forum, engine conversions would be listed to FSJs primarily (yes we have side non Jeep stuff laying around). I list this because I disagree with the representation that the 4B will get 35+ mpg in "almost anything".

Its great people have them for sale. I wish there were more of them to be more common. What gets me is what I feel a misrepresentation to those who do not know a great deal about them.

It will never get 35+mpg in a FSJ due to weight and wind resistance. I detuned mine with an OD transmission and road tires and almost got 27 once. Putting my mud tires back on I got 22.75 on a highway only tank. I have talked with 2 other FSJ conversions and none got 30.

I know personally about 15 conversions with 4B motors, and none get 30+

It is a great motor with great fuel economy and power. However, I feel it necessary to point out it wont get the high numbers some claim.

Dont take my word for it. There is a whole forum dedicated to it

www.4btswaps.com Talk to some people who have done it.

Mikel
01-17-2008, 06:28 AM
My J300 is somewhat similar to your J10. 4BT, NV4500, NP200 and D60/70 with 3.08's. With the taller gearing, smaller tires and stock height, I hope to get into the upper 20's. We'll see this spring...

Lindel
01-17-2008, 06:40 AM
I don't recall anyone claiming or expecting to get 30 mpg or more from a 4BT, 20's yes, but not 30 or more.

I don't have a dog in this hunt, so to speak, but I am interested enough to watch the diesel threads.

FSJeeper
01-17-2008, 07:48 AM
I don't recall anyone claiming or expecting to get 30 mpg or more from a 4BT, 20's yes, but not 30 or more.

I don't have a dog in this hunt, so to speak, but I am interested enough to watch the diesel threads.

Lindel, a guy posted an ad for a 4BT "kit" saying you could get into the 30's with this engine in a FSJ, that what these 2 threads are referring to.

I have done a ton of research in this matter. I know a guy with a 4BT swap, he is getting mid 20's. High 20's seem reasonable to attain but at speeds above 65mph our poor aerodynamics are going to hurt potential fuel economy. Big tires and lifts will only hurt fuel economy also which is the direction most go. Here is a nice example of a K-5 4BT swap that claims 28 mpg. While I find that hard to believe, the guy seems credible.

http://coloradok5.com/forums/showthread.php?t=220510&page=3

I was serious about a 4bt swap but with them averaging MPG in the mid 20's, I could put a 6BT in and have better power, a little less MPG, and A LOT less vibration and noise. A 6BT in my case was a lot cheaper to buy than a 4BT and my engine is virtually new, 60,000 original miles. I am also going to be towing and the 4BT would not be up for that so the 6BT was the logical choice.

I have owned 3 Dodge Cummins trucks. I bought a 91 about 6 months ago and still have not had to put fuel in it nor has the gauge gone down but I only use it on weekends and not very much. The 2001 I had averaged 20mpg on a 2300 mile trip to ouray for the first FSJ invasion. My 2004.5 used to get very poor mileage and now at 100K miles, it is averaging 17mpg. This was some city driving and 70+ mph Highway cruising. Some people calculate their mileage at 55mph which I have never done. They don't bother to tell you that when they tell you what their mileage is.

The 1st Gen (89-93) Cummins 6BT engines offer the best fuel economy potential and the current Dodge cummins offer the poorest from what I am hearing from new owners. The second Gen Cummins seem to get great fuel economy and are also the easiest to build big HP in. I think the maximum I could hope for in my Wag/6BT setup will be 25mpg and I am reasonably sure I can get 20-22 mpg.

All that said, I think if you got one of the balanced 4BT's and did a lot of sound proofing, the 4BT is one hell of a swap. Plus you don't have to swap to one ton axles or do a lot of frame beefing. Looks to be a fairly straight forward swap and I do believe high 20's and possibly 30 mpgs if you ran normal tires and no lift and kept the aerodynamics clean.

I can't wait for Mikel's results on his project.

The PIG Smith
01-17-2008, 08:29 AM
My brother has a 1997 Ford F-150 that is powered by a Cummins 4BT.

In the past, he told me that because of the 3:55 read end ratio, his 4BT operates outside of its power sweetspot.
He would like to increase the ratio to 3:27 to lower his 4BT operating RPM's at highway speeds.
On the interstate, I recall him telling my he gets around 20 or in the low 20's.

Today, when I emailed him if he thought his truck could obtain 30MPG, this is what emailed back to me:


I have personally seen around 27 to 32 MPG if I drive around 50-55MPH.
I had to drive for miles in some low-speed construction zones and when I had to fuel up next it was pretty high mileage. I will say that the 4BT is more sensitive to fuel variance then any other engine that I have personally ever driven. It would be very easy to get a 4BT that is turned up and in a heavy vehicle with a low-end granny rear-end and not have any better mileage then a gasser. If a person went through all of the variables and worked on it then I believe that a fuel-efficient larger vehicle is possible.
So, if a 2WD, Ford F-150 can get 30ish MPG, then maybe it is possible to get high 20's or over 30MPG in a Full Size Jeep.

Allow me qualify a few things.
1. My brother's intent was to have a full size truck and get high economy on Diesel fuel and then later on BioDiesel.

2. If a 4BT powered FSJ were to get 30MPG, it would only do so after the owner/builder purposely and by design built it to get good economy.
Which means no rock crawling lifts and tires, huge heavy axles, monster bumpers with winches, etc...

smearig
01-17-2008, 08:40 AM
This is a great thread. I'm very interested in doing a diesel swap but I would like to distinguish between the interweb legends and the truth before I get started. Granted, any of these diesels will be better than the 10 mpg that I'm getting right now.

joe
01-17-2008, 09:03 AM
Wasn't McInfantry getting 23 or so in his 4BT M715? I don't know at what speed that was though or if he'd swapped out the seriously low stock gears.

FSJeeper
01-17-2008, 09:04 AM
This is a great thread. I'm very interested in doing a diesel swap but I would like to distinguish between the interweb legends and the truth before I get started. Granted, any of these diesels will be better than the 10 mpg that I'm getting right now.

Don't overlook the GM 6.2/6.5 diesels. Easy swap and easy 20+ MPG. Parts are cheap and plentiful. They are not in the same league as a Cummins for reliability, but they are a very good diesel engine. I almost put a GM diesel in your FSJ when I owned it.

There is a guy I sold a GM turbo diesel engine to putting it in a J-20 in Austin right now. He works for Glenn at Krawtex.

tndonor
01-17-2008, 09:38 AM
[quote=Lindel]I don't recall anyone claiming or expecting to get 30 mpg or more from a 4BT, 20's yes, but not 30 or more.

Yeah, the "kit" for sale. I think that is desecption in every sense of the word. Stating it will get 35-40 in ALMOST ANYTHING. Thats why I started this. Although I started this the wrong way and in the wrong section.

But the FACT is that people who HAVE installed them into whatever vehicles DO NOT get 35-40. If they did, the majority of conversions would report these numbers and they dont. 20 something is par. I have found two that reported 30-33. (both vehicles are 1/4 ton chassis, tall gears, road tires, and to get said mileage didnt turn anything above 1800 rpm to get it (per them).

If someone can weasel out 35 in a wrangler, that is the execption not the rule and shouldnt advertise accordingly.

smearig
01-17-2008, 10:05 AM
Don't overlook the GM 6.2/6.5 diesels. Easy swap and easy 20+ MPG. Parts are cheap and plentiful. They are not in the same league as a Cummins for reliability, but they are a very good diesel engine. I almost put a GM diesel in your FSJ when I owned it.

There is a guy I sold a GM turbo diesel engine to putting it in a J-20 in Austin right now. He works for Glenn at Krawtex.

I never hear many good reports about those engines, but the cost is certainly low.

FSJeeper
01-17-2008, 10:15 AM
I never hear many good reports about those engines, but the cost is certainly low.

There is a LOT of mis-information about them. Go to the 6.2 6.5 diesel page if you are interested in them. They have everything you would ever need to know about them.

Lindel
01-17-2008, 02:27 PM
I haven't owned any of the 6.2/6.5 engines, but I've driven tons of trucks that have them (Texas Air National Guard had loads of them when I was in). They moved some impressive loads (in excess of 10,000 lbs) and got 15mpg in the process. We did have one Blazer (the real deal, not the little one) that would move fairly quickly and would regularly see mid to hi 20's.

Never suffered a breakdown with one, and we weren't gentle with them.

smearig
01-17-2008, 03:10 PM
I haven't owned any of the 6.2/6.5 engines, but I've driven tons of trucks that have them (Texas Air National Guard had loads of them when I was in). They moved some impressive loads (in excess of 10,000 lbs) and got 15mpg in the process. We did have one Blazer (the real deal, not the little one) that would move fairly quickly and would regularly see mid to hi 20's.

Never suffered a breakdown with one, and we weren't gentle with them.

Good to hear. That would also open up a range of nice overdrive manual transmissions as well.

Lindel
01-17-2008, 04:17 PM
Since I was in a hurry I didn't have a chance to mention that these were normally aspirated and the trannys were standard TH400's, nothing special.

I'm not sure what transfer cases were in them, probably 205's or 208's.


The pick-ups, when empty, could scoot too.

DieselSJ
01-18-2008, 02:06 PM
Don't overlook the GM 6.2/6.5 diesels. Easy swap and easy 20+ MPG. Parts are cheap and plentiful. They are not in the same league as a Cummins for reliability, but they are a very good diesel engine. I almost put a GM diesel in your FSJ when I owned it.

There is a guy I sold a GM turbo diesel engine to putting it in a J-20 in Austin right now. He works for Glenn at Krawtex.

I'm getting a consistent 21mpg in daily commuting (lots of side streets), and 24mpg on the freeway (75mph). I really like the performance.

jaber
01-19-2008, 09:27 AM
THANK YOU for this thread.........

I have a j-20 I would like to do a deisel swap on for a work truck/ tow rig and am watching these threads closely. My swap will depend on the engine I come across first and what oppions there are for it.

There are a crap-load of power Strokes in this area and wonder why no one talks about these. My boss has an overdrive 5 speed auto behind his. The 7.3 in the one I get to drive seems to do Very well with a load behind it and my foot :thumbsup:.

Mikel
01-19-2008, 09:50 AM
THANK YOU for this thread.........

I have a j-20 I would like to do a deisel swap on for a work truck/ tow rig and am watching these threads closely. My swap will depend on the engine I come across first and what oppions there are for it.

There are a crap-load of power Strokes in this area and wonder why no one talks about these. My boss has an overdrive 5 speed auto behind his. The 7.3 in the one I get to drive seems to do Very well with a load behind it and my foot :thumbsup:.

From what I hear, the 7.3 is a pretty decent motor. Certainly a lot more durable than the 6.0... :rolleyes:

Lindel
01-19-2008, 11:21 AM
Not at all positive about this, but I think the 7.3 might be a tough shoehorn because of it's physical size (width).

tndonor
01-19-2008, 06:19 PM
The 7.3 is a mess of wiring and computers.

tndonor
01-20-2008, 07:48 AM
For what its worth.......

When my conversion was first completed, I was getting 22.75 on highway consistantly. 22 max PSI

Now I have put stage II injectors in, turned the pump up, moved the fuel plate forward for more timing. I get 18-19........ and play with mustangs in fourth gear:D 33 max PSI. I have a new turbo to throw on and on shooting for40s PSI wise. I have a more aggressive fuel plate to put in as well as a bigger intake. We'll see what happens

It will flat out MOVE

FSJeeper
01-20-2008, 01:29 PM
For what its worth.......

When my conversion was first completed, I was getting 22.75 on highway consistantly. 22 max PSI

Now I have put stage II injectors in, turned the pump up, moved the fuel plate forward for more timing. I get 18-19........ and play with mustangs in fourth gear:D 33 max PSI. I have a new turbo to throw on and on shooting for40s PSI wise. I have a more aggressive fuel plate to put in as well as a bigger intake. We'll see what happens

It will flat out MOVE

Tndonor, I enoyed reading about your project both here and at the 4BT site. Are you going to dyno this thing one day?

I think for the average FSJeeper on a budget, the GM diesel offers the most in terms of fuel economy than most other engines. They were ground up designed specifically for fuel economy and automotive applications. The Blazers of the time were rated at 29mpg in the Naturally Asperated 6.2.

The swap could actually be cheaper than a gas engine swap if you shopped around for a good donor truck. 80's era Chevy diesel trucks go for cheap these days. The guys buying CUCV's usually give them away when they part them out and the CUCV has the desirable J series block.

Another common diesel I think could make an excellent FSJ swap choice for is the Mercedes 5 cylinder diesel. They are making adapters for these engines to common US made common transmissions. They are very reliable, common, and can be upgraded to impressive levels of power. I used to drive a mercedes coupe with this engine and a standard transmission and routinely got 33 mpg with it on flat Texas highways. I think you could get close to 30 mpg with one of these engines in a FSJ.

tndonor
01-20-2008, 09:58 PM
If I can find a dyno, Ill get on it as I am real curious.

The truck had a 6.2 when I purchased it. Yes it can be a cheap swap. I bought it with the intentions of swapping out the 6.2. But I drove it for about a year before it threw a rod through the oil pan and cracked the block....... on its way to the Cummins conversion.

You cant get the power and reliability I wanted out of the 6.2 so for me it was not a good choice. Some people have them and like them and good for them. They are happy and have something not everyone else has.