I'm going to be using a blueprinted T5, and a casing stiffening system of my own design.
Lotsa Jeep guys down the T5, but yet they can handle decent power if built right.
And handle 500 FT. lbs. if ya dump $1,000+ into 'em.

They also need to be run with the right oil, which seems like a strangely uncommon occurrence in Jeep circles...

It was the easiest way to get overdrive without major mods. The strong, newer 5 spds. take LOTSA $$$ to use in a CJ5. There are 2 possible 1st gear ratios in a stock Jeep T5, and I'm uncertain of which one I have. Also, I didn't really want 90lbs of rotational mass when I'm going for economy, with a target of only @ 150-200 ft. lbs. Hence again, the T5.

PLUS, the Rare RODEO bellhousing I have that mates my 1.8L(Starter even correct!!) PERFECTLY to a T5(stock mid 80's Jeep 5 spd.) with VERY minor machining.

T5 seemed the logical choice...

 

Nope I'm not gonna down a T5, I've built a few for cars and I like them. The biggest thing I would say about one in a truck(2 or 4wd) is that the first gear isn't all that great and they don't take hits very well. But no aluminum case takes hits well. Get the steel input retainer and a third gear upgrade if you're rebuilding it. I wasn't sure if you were just going to run a complete Isuzu 5-speed and t-case or not. All the Jeep and truck T5's I've seen listed are 4.0:1 first gear, but there were probably some other option. The big thing I've read on Jeep T5's is that there are two fifth gear options, a .7* and a .8*. With 3.73 gear in your truck I hope you got the .8 OD. If you got the .7 you probably want to look at 4.10-4.56 gear. If you run too many RPM's you'll lose efficiency, but if you're too low you'll lose then too.

What's the engine's ideal cruse RPM @55MPH? Cause with a .86 OD, 3.73 gears, and 235's you're cruising at 2053RPMs. With the .76 OD you're looking at 1814RPMs. Just another bite in the butt to think about. I've seen lots of people drop in OD trannies looking for economy, or better mileage and then not get it cause they don't have enough gear.

I still think this will be a great build though.

 

I think it WAS 5th that was two diff possibilities! I've absorbed so much info, it's getting blurry. The whole trans thing really had me sweatin' for a good while. I thought I was going to end up hacking an isuzu trans. to make a custom bell housing.
I was DEFINITELY going to use a steel input retainer, and 3rd(I think, last gear, top row) is already munched, so I have to replace it(and matching lower gear to be safe) anyways. My guess is that someone was launching it hard. I bought it as ALL the Jeep T5's I have seen have been run hard behind a V8, and the input shaft was sloppy as all get out, and they STILL wanted $200-250 for 'em. I have @ $40 +$30 in gas in this one, and it was behind the original 6 cyl.
EXCELLENT sharing the knowledge/math, Bro!!! I was wondering what that all would equate to. I've done the prelim math on the S/C pulley size(the blower is almost as big as the engine displacement, but not the gear ratios yet. That is an excellent question. I haven't peeked inside the trans. for a while, so I'm unsure of tooth count. I HAVE been wondering if I could get any economy at all with the blower running full time. That would be MUCH easier than bypassing it(via A/C clutch, and intake blower bypass) at cruise. Thing about a blower is they make boost down low(just like a diesel), so If I could cruise with @ 2-3PSI and overcome parasitic loss... I dunno yet. It seems I'm the first to put THIS motor(done before with a later 223 Isuzu) in a Jeep, so lotsa sorting out. Which is weird, as it dang near bolts up to a factory Jeep T5. Must not be big enough motor for most Jeep guys, as you usually see 700+ lbs. antique diesels putting out @ same HP I'm shooting for. Whatev.
And I ain't rich by any means, so the R and D is a bit more challenging. And then, I'm not only putting a completely unique diesel conversion together, I am also putting a S/C on it, which is huge in comparison to the 1.8L.
We are truly our own worst enemy.
Guess I hope I have the .86 as well! But if I DO have the .76, it would be an excuse for steeper gears!
So, was the T5 simple to rebuild? I am VERY mechanically inclined (used to crew chief an F-15E, built NUMEROUS customs and hot rods), and can fab/design dang near anything. BUT, never rebuilt a manual trans before. Any advice? Parts suppliers? Anything you can share would be a huge help.

Glad you can appreciate my out there, self complicating insanity.

 

The T5's are pretty simple. All the ones I worded with were WC units out of Fox-body mustang GT's, but they're all basically the same inside. If it is usable I'd recommend the Ford Motorsports rebuild kit. Summitt had the best price on them last time I had to get one. And this book is really good, IMHO, and has almost all the case tag numbers for reference.

With you running the a SC with a clutch on it is kinda cool. Have you thought about a micro switch on the throttle bracket to cut the clutch in and out? You could adjust it so that it wasn't depressed until a certain amount of throttle was used. This was at idle and just off idle you'd have no boost, but at partial to full throttle you'd have boost. It would be nice if you had some sort of 5th gear switch too, then it could cut boost while cruising. This is basically how modern SC cars and trucks work, it's just done through the computer. You might find though that there's a pulley out there that'll give you 0-2psi at little to no throttle, but still let you top out at 10-12 psi under full load. I really don't have a clue on SC's, I'm more of a turbo guy. Which is kinda odd cause I really only like quick spool linear boost turbos. I hate turbo lag. I'm just goofy I guess.

 

I'll check those out. I'm not sure if the motorsports kit can be used with my T5. I would GUESS it could be, as I THINK all of the gear shafts and casings are the same.
But I know it would be in my best interest, as the FM kit has upgraded components than what came in the Jeep T5.

Actually, I was planning on using a simple toggle switch on the dash. I'll know when I need boost, so throwing a switch isn't a biggie. My biggest concern is that with a clutch/bypass system, I also have to figure out how to bypass the blower for N/A operation. So that means some sort of valve inside the intake, which would have to be airtight when closed so boost doesn't leak out. Maybe I could use a valve downstream of the blower, with a weak spring. I dunno. The factory Ford bypass is smaller than the main intake tube, so it would constrict N/A breathing on a diesel, I would think.

I know the rough math for pulley size is a @ .80 under driven(I think my nomenclature is right. Smaller pulley on the blower), so at the 4fb1 redline (5,000RPM) I'm turning the blower @ 6,000 RPM. Although I probably want full boost lower, say @ 3,500-4,000 engine RPM. Even though the redline is 5,000, I probably do want to keep it down to 4,000. But @ this drive, I'm not creating boost until 1,000-1,500.

Lots to think about, but I'm a few weeks away from the jeep running N/A. I'll have plenty of testing, benchmarking to do. THEN install blower, testing, benchmarking.
THEN think about bypass if I'm not happy with the MPG. I'm actually hoping I can live without the bypass, as it might get a bit complicated.

 

Hmmm.....a toggle switch in the dash to turn the blower on and off. Watch Mad Max much?

 

Got to wonder how much HP that s/c will take to spin.

 

With the old 6&8-71 roots blowers a "rule of thumb" calculation was that the SC would take 10% of the total engine HP @ wide open throttle. Now that's just the "seat of the pants" type guesstimation, so true numbers will vary. I can't find the actual formula to figure it out though. I'd guess it's probably in the 10-15HP range, kinda like the old Frigidaire and York AC compressors. Those things just sucked engine power.

 

The parasitic loss for a M90 turning @ 6,000PRM will be <20 HP. So if I'm putting out 150+ HP(which might be conservative), I feel it's acceptable, as I'll still be @ double factory rating of the 4FB1. And spinning the S/C so "slowly" will produces a VERY cool charge, esp. in comparison to a turbo. And I'll be using a charge cooler.

Considering my expenses will be $50 in TIG welding aluminum brackets, and buying a pulley or two. So what, $100 total?

Whereas a rough figure for turbo'ing (PROPERLY!!) would be @ $700-$1,000, and a LOT more fabbing...

And if I feel confident later to up the boost, I change a pulley. That's it.

 

I think it's a cool idea. SC's always cost to run, but the gains out weigh the costs.

Personally though I think I'd try to look into some type of throttle mounted clutch switch. But whatever floats your boat, it's your ride. Ideally the setup would also need to kick out while cruising. But that can start to get a bit tricky to wire out. Install a shift **** with a button and away you go.