Gen 1 Small Block Swap?

[OldFarmTruck22]

I have an old Chevy 350 and a 700r4 K case transmission in the shed. Been thinking about doing a swap.
Trying to get better gas mileage and better gas mileage. lol I'd run Vortec heads and a carburetor on the freshened up 350. Probably put a new cam and lifters in it to the max that the vortec heads will handle.

I'm wondering if a company makes the motor mounts I would need to do this? I'm sure somebody has them by now.

And as far as 'accessories' for changing over from the AMC 360 to a Chevy small block, is there gonna be a lot of trouble there?

Thanks for your help.
OldFarmTruck22

[akguy09]

There are some universal 350 mounts that you could weld in, Speedway motors makes them. Advance Adapters I believe has some too. Accessories are probably the easy part since AMC had so many GM parts. My alternator is from a Chevy. Power steering is the GM style as well.

I think the hard part will be Transfercase, unless you already have one with the correct drop that mates to to transmission, then its just a matter of modifying the crossmember. Easily done with some cutting and welding.

[sierrablue]

Pretty sure BJ's has them, too. Accessories shouldn't be a big deal; if they're not the same, they're easy enough to swap while everything's out.

Are you still gonna be using the Qtrac? If you're going for mileage, the full time 4wd is going to put that all out the window. If you have a 700r4 behind the 360, with a part time case, I wouldn't expect a carbureted 350 to magically get better mileage. It's about the same size and will be fighting about the same drag; the only way it would really be better would be if it had some monster low end torque, which with the big cam and Vortec heads, is pretty much out the window.

Max mileage (with easy, bolt-in Jeep stuff) would be a 4.0L (built up if you want) with a 5-speed or a 4-speed auto out of an XJ or ZJ, a part time case, and locking hubs (some claim these don't help any, but they gain me about .5 mpg, which over the course of a year equates to over 40 gallons aka 2 tanks aka $150).

[OldFarmTruck22]

I think advance makes an adapter for the 700r4 to the Quadratrack, right?

[sierrablue]

They do, but it has front driveshaft interference problems. Don't you already have a 700r4 in it? Or did you take it out?

The Qtrac is going to kill mileage anyway though. Having to spin a chain, an extra diff, two extra axle shafts, an extra driveshaft, and 5 extra joints ALL the time is gonna suck more gas.

With that combo I'd look at swapping the 700r4 in behind the AMC, and then putting an np 208 or np 241 in behind it. Or a Dana 300 if you have the $ for that. And locking hubs if you can. But the first gen SBC is just as hard to find parts for at a parts store as the AMC is anymore (aka if you break something, they're not going to have it on hand whichever way you go)...I know 'cause the HEI and plug wires and points and everything are more or less the same between the Buick and the SBC, and they don't usually have that stuff in stock anymore.

[OldFarmTruck22]

I wonder if that 241 can handle the right side offset rear axle I have?

[sierrablue]

Based on what I've read, it can, but it has lots of vibrations. If you put in a third u joint (can't think of the name of that rn )(double cardigan joint?) like the front has, it'll work ok. Not ideal but it'll work.

I guess you could get the 700r4 to Dana 20/Dana 18 adapter and run a Dana 18, which has the offset, but that's going to be kind of loud and unpleasant due to straight cut gears. You're probably looking at either a double cardigan or a centered rear axle, no matter what route you go.

[OldFarmTruck22]

I think I'll get more opinions on this.

Not replacing any axles.

[OldFarmTruck22]

Pretty sure BJ's has them, too. Accessories shouldn't be a big deal; if they're not the same, they're easy enough to swap while everything's out.

Are you still gonna be using the Qtrac? If you're going for mileage, the full time 4wd is going to put that all out the window. If you have a 700r4 behind the 360, with a part time case, I wouldn't expect a carbureted 350 to magically get better mileage. It's about the same size and will be fighting about the same drag; the only way it would really be better would be if it had some monster low end torque, which with the big cam and Vortec heads, is pretty much out the window.

Max mileage (with easy, bolt-in Jeep stuff) would be a 4.0L (built up if you want) with a 5-speed or a 4-speed auto out of an XJ or ZJ, a part time case, and locking hubs (some claim these don't help any, but they gain me about .5 mpg, which over the course of a year equates to over 40 gallons aka 2 tanks aka $150).

My GM HT383 has the vortec heads, factory roller cam and 465 ft.lbs. of torque from the factory on the dyno. I put 1.6 roller rockers on it. So, you're wrong on that.

[akguy09]

Based on what I've read, it can, but it has lots of vibrations. If you put in a third u joint (can't think of the name of that rn )(double cardigan joint?) like the front has, it'll work ok. Not ideal but it'll work.

I guess you could get the 700r4 to Dana 20/Dana 18 adapter and run a Dana 18, which has the offset, but that's going to be kind of loud and unpleasant due to straight cut gears. You're probably looking at either a double cardigan or a centered rear axle, no matter what route you go.

Why would it be "loud and unpleasant" its not locked in 4 wheel drive all the time?

And its a Double Cardan joint Cardigan is the sweater Mr Rogers wore

[OldFarmTruck22]

Based on what I've read, it can, but it has lots of vibrations. If you put in a third u joint (can't think of the name of that rn )(double cardigan joint?) like the front has, it'll work ok. Not ideal but it'll work.

I guess you could get the 700r4 to Dana 20/Dana 18 adapter and run a Dana 18, which has the offset, but that's going to be kind of loud and unpleasant due to straight cut gears. You're probably looking at either a double cardigan or a centered rear axle, no matter what route you go.

Why would it be "loud and unpleasant" its not locked in 4 wheel drive all the time?

And its a Double Cardan joint Cardigan is the sweater Mr Rogers wore

I tend to agree with you akguy09.
Another important detail that I need THOSE THAT HAVE installed a 241 behind a 700r4, nobody else ... is:
Will it hit the corner of the factory gas tank on the drivers side???
Can't have guess work on this, need to hear from those that have installed a 700r4 and a NP241 and KEPT the factory fuel tank.
Really appreciate feedback from those guys.
Thanks.

[sierrablue]

Pretty sure BJ's has them, too. Accessories shouldn't be a big deal; if they're not the same, they're easy enough to swap while everything's out.

Are you still gonna be using the Qtrac? If you're going for mileage, the full time 4wd is going to put that all out the window. If you have a 700r4 behind the 360, with a part time case, I wouldn't expect a carbureted 350 to magically get better mileage. It's about the same size and will be fighting about the same drag; the only way it would really be better would be if it had some monster low end torque, which with the big cam and Vortec heads, is pretty much out the window.

Max mileage (with easy, bolt-in Jeep stuff) would be a 4.0L (built up if you want) with a 5-speed or a 4-speed auto out of an XJ or ZJ, a part time case, and locking hubs (some claim these don't help any, but they gain me about .5 mpg, which over the course of a year equates to over 40 gallons aka 2 tanks aka $150).

My GM HT383 has the vortec heads, factory roller cam and 465 ft.lbs. of torque from the factory on the dyno. I put 1.6 roller rockers on it. So, you're wrong on that.

Oooo, a big number. The Vortec heads make more ultimate torque, but WHERE do they make that torque? Based on the graphs I'm seeing, that's not until ~4k rpms. They sit at ok torque and at about 3500 it starts a gentle climb to its peak around 4k. Are you really going to be driving at 4k rpms all day long? If so, your mileage is OUT THE WINDOW. I don't doubt they make big power, but they don't make big low end power.

There's a reason that you don't really see SBC swaps in these Jeeps; just the tranny+tcase. You don't really gain anything with the SBC--it's the same or worse in every aspect except parts availability, and most parts for them aim to improve hp, not torque (and certainly not low-end). Unless you plan on launching it and want to be able to do 60-90 faster than anybody else, that's not going to be a huge help in an FSJ.

You don't have to have guess work on that measurement, you know. Measure the housing of your 700r4, and look up/ask about the length of a 241. Factor in an extra inch or two for the clock ring you have to run, and 2-3" for the AMC to SBC bellhousing adapter. Then measure from the back of the block straight back, and see where that lands in proportion to the gas tank. I doubt you'll have problems but I don't have those mods done, so I can't swear to it.

[sierrablue]

Based on what I've read, it can, but it has lots of vibrations. If you put in a third u joint (can't think of the name of that rn )(double cardigan joint?) like the front has, it'll work ok. Not ideal but it'll work.

I guess you could get the 700r4 to Dana 20/Dana 18 adapter and run a Dana 18, which has the offset, but that's going to be kind of loud and unpleasant due to straight cut gears. You're probably looking at either a double cardigan or a centered rear axle, no matter what route you go.

Why would it be "loud and unpleasant" its not locked in 4 wheel drive all the time?

And its a Double Cardan joint Cardigan is the sweater Mr Rogers wore

It would be loud and unpleasant because straight cut gears are noisy and not as smooth to run. This is the big advantage of the Dana 20 over the 18, according to the threads on IFSJA. Well, that and the centered rear axle.

This $^##[!_€*~!' phone! That's what I typed the first time, and it said it was wrong! *%%#]€'dh autocorrect.

[thej10guy]

Coming from someone that has done an ls swap, I would recommend it. I understand that you have the sbc and 700r4, but in the long run, you would save yourself a lot of time and probably even a little bit of money (if you can find a fairly cheap ls drivetrain. My dad gets them for $600 with engine tranny t case from our local salvage yard). By the time you do the cam and heads and everything you would have a good chunk of change in it and still have a sbc. Pushing impressive numbers, but an ls can push those numbers easily and cheaper. Besides motor mounts and tranny cross member, there is very little fabbing/welding required, and a sbc would be the same amount in that respect. Overall, I would say ls would be the way to go. It’s reliable, easier to find parts for than a sbc, better on gas, and less work to make it happen.


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[akguy09]

Based on what I've read, it can, but it has lots of vibrations. If you put in a third u joint (can't think of the name of that rn )(double cardigan joint?) like the front has, it'll work ok. Not ideal but it'll work.

I guess you could get the 700r4 to Dana 20/Dana 18 adapter and run a Dana 18, which has the offset, but that's going to be kind of loud and unpleasant due to straight cut gears. You're probably looking at either a double cardigan or a centered rear axle, no matter what route you go.

Why would it be "loud and unpleasant" its not locked in 4 wheel drive all the time?

And its a Double Cardan joint Cardigan is the sweater Mr Rogers wore

It would be loud and unpleasant because straight cut gears are noisy and not as smooth to run. This is the big advantage of the Dana 20 over the 18, according to the threads on IFSJA. Well, that and the centered rear axle.

This $^##[!_€*~!' phone! That's what I typed the first time, and it said it was wrong! *%%#]€'dh autocorrect.

But the Transfer case gears are not making whole lotta noise until the transfer case is locked in 4x4...at that point it seems irrelevant

[sierrablue]

Here.

https://forums.ifsja.org/forum/tire-kic ... p?t=184342

Honestly the D20 and the front axle make enough noise with the hubs locked, let alone in 4wd (and low is super loud), I don't think the 18 would be pleasant, if the 20 is known as the "quiet" one.

[akguy09]

I don't need to read that, I have had 2 jeeps with Dana 20's so I have first Hand experience with them... they aren't loud and who drives around with the hubs locked except maybe when it snowing. Still not a loud T-case now a 205 makes a little noise.

[tgreese]

Jeep advertising when they introduced the Dana 20 called it the "silent" transfer case. If it's noisy, even in 4WD high, there is something worn out. The Dana 18 makes more noise than the 20, and it gets really LOUD when the intermediate shaft bearings are worn (a common problem, and another reason they went to the 20).

Kinda suspect you'd need a lot of miles (or water or neglect) before a 20 needed rebuilding. Possible I suppose. The intermediate shaft is not driven when in 2WD, and suffers little wear normally.

The 20 should not be much different in noise when in 4WD high and 2WD high. Run with the hubs in if you want; IME it does not affect noise at all, and wear/mileage probably won't be detectably different.

Low range will whine. These gears are straight cut, and noisy. Same kind of whine you hear in reverse gear of a manual transmission.

Chain driven transfer cases are very quiet.

[OldFarmTruck22]

Pretty sure BJ's has them, too. Accessories shouldn't be a big deal; if they're not the same, they're easy enough to swap while everything's out.

Are you still gonna be using the Qtrac? If you're going for mileage, the full time 4wd is going to put that all out the window. If you have a 700r4 behind the 360, with a part time case, I wouldn't expect a carbureted 350 to magically get better mileage. It's about the same size and will be fighting about the same drag; the only way it would really be better would be if it had some monster low end torque, which with the big cam and Vortec heads, is pretty much out the window.

Max mileage (with easy, bolt-in Jeep stuff) would be a 4.0L (built up if you want) with a 5-speed or a 4-speed auto out of an XJ or ZJ, a part time case, and locking hubs (some claim these don't help any, but they gain me about .5 mpg, which over the course of a year equates to over 40 gallons aka 2 tanks aka $150).

My GM HT383 has the vortec heads, factory roller cam and 465 ft.lbs. of torque from the factory on the dyno. I put 1.6 roller rockers on it. So, you're wrong on that.

Oooo, a big number. The Vortec heads make more ultimate torque, but WHERE do they make that torque? Based on the graphs I'm seeing, that's not until ~4k rpms. They sit at ok torque and at about 3500 it starts a gentle climb to its peak around 4k. Are you really going to be driving at 4k rpms all day long? If so, your mileage is OUT THE WINDOW. I don't doubt they make big power, but they don't make big low end power.

There's a reason that you don't really see SBC swaps in these Jeeps; just the tranny+tcase. You don't really gain anything with the SBC--it's the same or worse in every aspect except parts availability, and most parts for them aim to improve hp, not torque (and certainly not low-end). Unless you plan on launching it and want to be able to do 60-90 faster than anybody else, that's not going to be a huge help in an FSJ.

You don't have to have guess work on that measurement, you know. Measure the housing of your 700r4, and look up/ask about the length of a 241. Factor in an extra inch or two for the clock ring you have to run, and 2-3" for the AMC to SBC bellhousing adapter. Then measure from the back of the block straight back, and see where that lands in proportion to the gas tank. I doubt you'll have problems but I don't have those mods done, so I can't swear to it.

I want to respond to a few people who gave input on this.
First sierrablue:
In my most courteous way of saying it ... you are wrong again Sir. The GM HT383 has been developed and proven to be a low RPM torquer. Unlike you, I own one and have had it dyno'd to prove the GM specs. With my addition of 1.6 rockers, it makes 420 ft. lbs at 2500 rpm all day long. At 3800 rpm 450 ft.lbs. I'm very happy with that. The engine was designed as a TRUCK engine, low rpm torque. So, once again, you are wrong. You say "Ooh Big Numbers!" but I think you are just being fececious. I don't need "Big Numbers" to be happy. I'm not going to entertain your ASSUMPTIVE comments anymore like "unless you plan on launching at 4500 rpm ..." etc., that's just nonsense talk.
Next, I did say in my original post that I'm keeping my axles and I have an engine and 700r4 transmission already. Nothing is LESS expensive that already having the engine and transmission sitting in the garage. That takes care of those that want to suggest an LS swap. Ain't gonna do it.
Next akguy09:
I like your style! You and me know that reading something in an internet blog is NOT the same as owning the item. These cowboys that quote shi they read somewhere to US that own it and know it inside and out ... laughable huh? Thanks for your input akguy09, I appreciate your experience.

So trying to get back to my original post and the nature of this thing, like to hear from members that have put an NP 241 behind a 700r4 in a fullsize jeep and all your input and feedback. The engine dont matter.
Thanks!

[thej10guy]

I’m guessing you will not listen to this information because it’s not exactly what your requirements are, but I doubt there are many people active on hear that can answer your question. I have a 4l60 with a 241c in my truck which is the same length as a 700r4/241c combo would be. With my factory tank and centered rear axle I had plenty of clearance between the tank and driveshaft, and there was quite a bit of room between the tank and transfercase lengthwise as well. I don’t know about your offset rear axle question although I am pretty sure other people have run the 241c with the offset rear axle. As far as passenger side drop, it will clear everything (oil pan, etc). I have a passenger side drop 241c t case behind a 700r4 and 350tbi in a k5 blazer, so no matter what vehicle you put it in, it should clear just fine.


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