SBC swap. A little confused.

Hopefully this thread won't be like every other SBC swap thread out there. As in, I won't hear anything about how great the 4-oh is. Or something about how I should go search because 'there's lots of info'.


It seems to be oft-stated that you must lift a XJ at least 3" for the UCAs to clear the oil pan on a SBC. However, I've seen two examples of 2wd trucks that aren't lifted. In fact, one of them was dropped. So, did they defy the space-time continuum to make this happen?

AA seems confident that if you use their motor mounts, it will not clear. Although, in the fine print they say you actually have approximatly 2.5" of clearance between the UCAs and the motor mounts, not the oil pan. Which would make sense since the UCAs have mad horizontal seperation and should be outboard of the oil pan. But will they be? Another question would be hood clearance since they list it as being 'minimal' for a TBI application. TBIs are rather tall, so I'd be tempted to say they sit the motor lower than should be necessary. Although, that is perhaps partly to do with why they off-set it too, to avoid disty clearance issues.

It seems rather confusing to me. However, I know neither of the trucks I saw used the AA mounts. In fact, one used drop mounts for a circle track car. Now that makes you think.




FWIW, I think I'd use a LT1 if I go this route. No disty clearance issue, and the intake is foreward, giving some more clearance for the hood. Not to mention they're pretty cheap now and come with aluminum heads. They have ignition problems, but I know the fix on that.

DirtyMJ said:

Hopefully this thread won't be like every other SBC swap thread out there. As in, I won't hear anything about how great the 4-oh is. Or something about how I should go search because 'there's lots of info'.


It seems to be oft-stated that you must lift a XJ at least 3" for the UCAs to clear the oil pan on a SBC. However, I've seen two examples of 2wd trucks that aren't lifted. In fact, one of them was dropped. So, did they defy the space-time continuum to make this happen?

AA seems confident that if you use their motor mounts, it will not clear. Although, in the fine print they say you actually have approximatly 2.5" of clearance between the UCAs and the motor mounts, not the oil pan. Which would make sense since the UCAs have mad horizontal seperation and should be outboard of the oil pan. But will they be? Another question would be hood clearance since they list it as being 'minimal' for a TBI application. TBIs are rather tall, so I'd be tempted to say they sit the motor lower than should be necessary. Although, that is perhaps partly to do with why they off-set it too, to avoid disty clearance issues.

It seems rather confusing to me. However, I know neither of the trucks I saw used the AA mounts. In fact, one used drop mounts for a circle track car. Now that makes you think.




FWIW, I think I'd use a LT1 if I go this route. No disty clearance issue, and the intake is foreward, giving some more clearance for the hood. Not to mention they're pretty cheap now and come with aluminum heads. They have ignition problems, but I know the fix on that.

Click to expand...

I'll be honest about one thing - I'd vastly prefer having an inline six over a V8 in a small truck. You get more useful torque at a lower crankshaft speed...

Having said that, I'd like to hear about your experiences with the swap, as you go about it. I've not done one myself, but I would be interested in hearing about it (some people are better served with the V8.)

Also, you may want to check out this Yahoo! group - http://autos.groups.yahoo.com/group/v8cherokeexjowners/?yguid=157814082 They seem like they'd be the people to ask about a V8 swap (just because I'm not keen on the idea for a DD doesn't mean there aren't people who are, and it's usually just a matter of finding them...)

I'm not bent on doing this swap yet, it just might be the best way to get the power numbers I want.

I hate the yahoo groups format, but if they're the people that know I'll put up with it.

The truck is really ment to be more of a balls to the walls experience, 4.56 gears and 27" tall tires should allow for a V8 to be a little more usable when it comes to the torque band. Not to mention that if I use a LT1 they have a lower torque peak than most.

5.2poweredxj said:

What are they saying won't clear? The 5.2 I got fits nice but the oil pan could be an issue if I didn't have stiff springs. I would say if your tring to fit header then you could have an issue. I got the stock manifolds on mine the exhaust goes right beside the uca.

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Header clearance may be at issue, but "shorty" or "block-hugger" headers tend to be easier to find for SBChevvy than SBMopar anyhow. How much work did you do to clear your 318 into the engine bay?

5-90 said:

I'll be honest about one thing - I'd vastly prefer having an inline six over a V8 in a small truck. You get more useful torque at a lower crankshaft speed...

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You really think so? Explain how the cylinder arrangement makes a difference in torque output, please. Yes, I know semi trucks are big inline motors.. and?
Displacement makes low end torque, not I or V or boxer or whatever.

I think it would have to do (if analysed) with the elimination or inherent balancing-out of harmonic vibrations in the bottom end, caused by firing impulses.

The inline six has long been praised as a "smooth-running" engine from that viewpoint - I think it's only really outdone by horizontally-opposed engines (a la Volkswagen & Porsche) or opposed piston engines (not in common use.)

V-block engines tend to suffer from crankshaft harmonics, which become worse when the included angle between the banks isn't at what is considered "optimum" (90* for V8 engines, generally, although 45* can also be acceptable, 60* or 120* for V6 engines, 30* or 60* for V12, 36* or 72* for V10, ...) That was similar to the "odd-fire/even-fire" problem that GM ran into with the 3.8L early on - they had to split the crankpins to create the even-fire V6-90* engine to get it to run smoothly.

Yes, displacement and breathing efficiency have a good deal to do with power output curves - but the effects of harmonics and such cannot be neglected, either.

What 5-90 said is exactly true. it has alot to due with the harmonics. i-6's, and v-12's (and any multipul there-of) are naturally harmonicly balanced. basicly meaning that it isnt fighting its opposing firings. yes, displacement does have a lot to do with it, but, that's why they use i-6's in semis. if v-8's or anything else for that matter worked better, they'd probably use that.
Yes, i do personally know a person that put a 350 stroked to 383 into his xj. (so much power it's actually twisting the unibody) he loves it. BUT he likes to race with it more than off road. it all depends on what you like to do i guess......

just because i can a mack truck has been known to run a v8:laugh3:

5-90 said:

I think it would have to do (if analysed) with the elimination or inherent balancing-out of harmonic vibrations in the bottom end, caused by firing impulses.

The inline six has long been praised as a "smooth-running" engine from that viewpoint - I think it's only really outdone by horizontally-opposed engines (a la Volkswagen & Porsche) or opposed piston engines (not in common use.)

V-block engines tend to suffer from crankshaft harmonics, which become worse when the included angle between the banks isn't at what is considered "optimum" (90* for V8 engines, generally, although 45* can also be acceptable, 60* or 120* for V6 engines, 30* or 60* for V12, 36* or 72* for V10, ...) That was similar to the "odd-fire/even-fire" problem that GM ran into with the 3.8L early on - they had to split the crankpins to create the even-fire V6-90* engine to get it to run smoothly.

Yes, displacement and breathing efficiency have a good deal to do with power output curves - but the effects of harmonics and such cannot be neglected, either.

Click to expand...

There you go again...
8 cyliner v-block engines don't tend to suffer from crankshaft harmonics. You are confusing this with discussions of 6 cylinder (and less) designs.
I'd like to see you come up with a power output formula that includes "the effects of harmonics and such".

Didn't seem to have to do anything it really tight to the hood but I got he stock magnum intake which is pretty tall. I got all under the stock hood.

http://www.cardomain.com/ride/2523955/1

I would think the crank in a V8 has to go through a lot more pressure and stress being how the pistons are coming to it from 2 different directions, thats a lot of downward force from 2 sides. A I6 only comes from one direction which I would think is a lot less stress.

Back to the OP's original questione:nono:
The rear of SBC in my '88 has the crank center line just about where the 4.0 was--both vertically and horizontally--meaning it's off-set to the passenger-side, just like the 4.0; however, the engine sets more level than the 4.0, implying it's lower in the front than the 4.0 was. Using Advanced Adapter's (AA) motor mounts, which, by the way, had to be significantly modified to clear the stock ('94) Chevy exhaust manifolds, results in lowering the engine somewhat; if you use center dump, or early car manifolds, they should clear the AA mounts.
The throttle body on mine sets taller than a stock TBI because I've installed the Edelbrock MPFI conversion. This required a new, flat cover for the air cleaner housing in order to clear the hood. Also note that the hood slopes to the front, resulting in less clearance between the engine, not more. But, I've seen pictures of a TPI installed, without hood mods, so the LT1 should fit, as well.
The UCA's could be a problem clearing the engine mounts/exhaust manifolds if you do not do a lift, as can there also be steering linkage to oil pan issues.
And, with regard to exhaust manifolds, late model truck manifolds --~1987 to '95 (maybe latter??) cannot be installed without significant cutting of the frame (something that California made me do to be SMOG legal:soapbox: .

Here's a shot of what happens with inadequate bump stops, when running high steering.
I'm at 6.5 inches of lift. But note the AA motor mount position (upper left) and the UCA position (the tall, square-looking appenditure on top of the axle, which is really the track bar mount, but the track bar height equals the UCA height):

If anybody cares, the yahoo group appears defunct.

xjbubba:
I'll be leaving the steering as the stock stuff, or at least the stock y-link design and the physical dimensions of it will be reasonably the same. I don't plan to have a lot of up travel in the suspension. Or really travel at all for that matter.

However, it has been suggested to me that I re-design the front 4-link/panhard bar setup on the jeeps to better suit my needs. However, I'm not entirely convinced I should bother. But I'd be more than willing to change the suspension if that would allow for me to get away with everything being a little lower.

IIRC, the LT1 intakes are really quite low in the valley. Hence I think it would clear better even if it is a front intake. The hood dropps maybe 3-4" across its whole length, and I'd think a TPI setup would be at least 4" higher than the LT1 intake. Although, I should check.

It's unfortunate I do not currently have a truck to take measurements off, other than my trail MJ. Nor a LT1 or other SBC at my disposal.


Does anybody have good pics of chevy's swapped in? I'll take anything I can get.

MaXJohnson said:

There you go again...
8 cyliner v-block engines don't tend to suffer from crankshaft harmonics. You are confusing this with discussions of 6 cylinder (and less) designs.
I'd like to see you come up with a power output formula that includes "the effects of harmonics and such".

Click to expand...

I haven't. Have you?

I was just guessing - that's why I started it with "I think." If I'm wrong, I'm perfectly willing to be educated - but just telling me I'm wrong doesn't teach me anything different.

For instance, I've been inclined to think that crankshaft harmonics (due to firing intervals) would be a small issue (at least!) here - but if it's not, can you point to a sound reason why not, so I can correct my thinking?

Since I have a second opinion that agrees with me (cody) and one that dissents (you,) I'm really interested. I know my understanding of all of this is still imperfect (and probably will be for some time - which is why so many of my statements and answers are qualified with phrases like "I think," "As I understand it," and the like...) so I would really rather learn - but I also want to be able to verify information for myself - a sort of "jumping-off point" for your answer, if you will. I'm one of those odd people who also like to see raw data that go into a position or an opinion...

So please do! Educate me...

DirtyMJ said:

However, it has been suggested to me that I re-design the front 4-link/panhard bar setup on the jeeps to better suit my needs. However, I'm not entirely convinced I should bother. But I'd be more than willing to change the suspension if that would allow for me to get away with everything being a little lower.

IIRC, the LT1 intakes are really quite low in the valley. Hence I think it would clear better even if it is a front intake. The hood dropps maybe 3-4" across its whole length, and I'd think a TPI setup would be at least 4" higher than the LT1 intake. Although, I should check.

It's unfortunate I do not currently have a truck to take measurements off, other than my trail MJ. Nor a LT1 or other SBC at my disposal.


Does anybody have good pics of chevy's swapped in? I'll take anything I can get.

Click to expand...

I figure you should be able to make the LT1 fit quite nicely. The LT1 tunnel ram is among the lowest profile setups for the traditional SBC. If you do some LT1 googling you should be able to find a dimensioned front view of the LT1 that shows the numbers. I remember seeing one around when I was considering it for a non-Jeep build.

The TPI setup is considerably taller.

I'm not following what difference the suspension type makes. The arms are well out to the sides. With a rear dump exhaust manifold they should clear the factory stuff easily (research this further - my guess). Center dump, "Rams horn" manifolds may work too.

FWIW, if you haven't spent any money on this project sourcing drivetrain bits yet I'd suggest not doing the LT1. Go LS6 (basically "truck" version of the LT1 with an iron block). More modern/efficient and it is the future of SBC. If you are planning on keeping the factory style EFI the complexity level is about the same. Also, price compared to LT1 should be very close. Depending on where you are or whom you know which one is cheaper will be a wash.

You mentioned the DIS issues. LS6 is DIS as well - and more modern implementation that doesn't have the LT1's DIS issues. If you were planning on spending money to solve the DIS LT1 issue you might as well go with the LS6 upfront and have it solved already since at that point the money difference will definitely be a wash.

Maybe I missed it... Did you plan to lift the Jeep? Slam it? How many inches? Regardless, proper bump stopping and careful attention to what goes where will make the difference. You might want to mock something up in the engine bay before buying any mounts. If you don't weld, mocking stuff up in cardboard and then tack weld in steel to take to a pro welder will save gallons of green and get you what you want in the end. Even going to your local hot rod shop and getting ~$20 generic SBC mounts could help you visualize things in the engine bay, they may even be good enough to cut to shape and get to the other stuff in the project.

$0.02, HTH, etc.

5-90 said:

I haven't. Have you?

I was just guessing - that's why I started it with "I think." If I'm wrong, I'm perfectly willing to be educated - but just telling me I'm wrong doesn't teach me anything different.

For instance, I've been inclined to think that crankshaft harmonics (due to firing intervals) would be a small issue (at least!) here - but if it's not, can you point to a sound reason why not, so I can correct my thinking?

Since I have a second opinion that agrees with me (cody) and one that dissents (you,) I'm really interested. I know my understanding of all of this is still imperfect (and probably will be for some time - which is why so many of my statements and answers are qualified with phrases like "I think," "As I understand it," and the like...) so I would really rather learn - but I also want to be able to verify information for myself - a sort of "jumping-off point" for your answer, if you will. I'm one of those odd people who also like to see raw data that go into a position or an opinion...

So please do! Educate me...

Click to expand...

A lot of V-8's have issues with harmonics at certain RPM's, however there are simply too many factors that have an effect on harmonics to draw a conclusion that "all V-8's have this problem". Usually, it not a "problem", -particularly on the SBC. GM certainly seems to have done their homework on the SBC/BBC platforms. Harmonic issues with these engines are very very rare. When you look at how some of these engines are built and run, -it a wonder that they stay together as long as they do.

Without a doubt, the SBC is probably the most popular engine to be hot-rodded. I have seen many "would be" hotrodders do budget "sloppy" builds on these things and run the ever-living snot out of 'em, -and they always hold together and run just fine.

Without a doubt though, the inline sixes are smooth running, have decent power potential, and will last a long time (usually outliving a V-8).

The fact is though, if you gotta have cheap, easy to build muscle, -the SBC is without a doubt the BEST platform out there, -end of discussion. Will it last as long as the inline? -That'll probably depend on how it is run. I have seen SBC's that had over 400k on them. One was in a worktruck, -it had heads on it at 220k, -but other than that, -nothing, -not even a timing chain. If ya run the V-8 like you stole it, -then all bets are off!

My .02

Rich.

The discussion of harmonics and such doesn't really matter. The OP wants to put in a V8. End of story.

The Jeep 4.0 gets decent (note I didn't say great) low end torque for its displacement and is reliable. It does this in spite of having the cam in the block, being a push rod tractor grade engine, with a non-crossflow head (some of where the torque comes from actually).

If it wasn't for the amazing things you can do with modern electronics this engine would have been put out to pasture back in the early 90s. To say that this tractor engine is smooth is incorrect. Go drive a BMW or any other modern implementation of a I6 is you want to feel what a smooth I6 feels like.

Comparing the Jeep I6 to even a Gen I SBC for smoothness is just silly. Go drive them back to back. Want to compare displacement to displacement? Go drive the Jeep engine and then compare to a 4.0 liter Toyota 1UZ V8. No comparison.

You can throw lots of money at a Jeep I6 to make it make V8 type performance numbers. Some people like that. Some don't. That's life.

I figure a supercharged and stroked Jeep I6 would be awesome but would I build one? Not likely when there are more modern engines with similar power at the wrecker with the same install complexity.

When the time comes I'll get a reman 4.0 for my Jeep. If I wanted to do a swap a LS6 or 1UZ would be what I'd been looking at.

$0.02

Some pictures, of I consider a successful 5.7 implant:

ratman572 said:

A lot of V-8's have issues with harmonics at certain RPM's, however there are simply too many factors that have an effect on harmonics to draw a conclusion that "all V-8's have this problem". Usually, it not a "problem", -particularly on the SBC. GM certainly seems to have done their homework on the SBC/BBC platforms. Harmonic issues with these engines are very very rare. When you look at how some of these engines are built and run, -it a wonder that they stay together as long as they do.

Without a doubt, the SBC is probably the most popular engine to be hot-rodded. I have seen many "would be" hotrodders do budget "sloppy" builds on these things and run the ever-living snot out of 'em, -and they always hold together and run just fine.

Without a doubt though, the inline sixes are smooth running, have decent power potential, and will last a long time (usually outliving a V-8).

The fact is though, if you gotta have cheap, easy to build muscle, -the SBC is without a doubt the BEST platform out there, -end of discussion. Will it last as long as the inline? -That'll probably depend on how it is run. I have seen SBC's that had over 400k on them. One was in a worktruck, -it had heads on it at 220k, -but other than that, -nothing, -not even a timing chain. If ya run the V-8 like you stole it, -then all bets are off!

My .02

Rich.

Click to expand...

I never said that the SBChevvy was a "bad" engine - I've built dozens of them myself, and usually performance buildups.

I did log my opinion that the inline six was probably a better compromise of power and efficiency for the platform - but that wasn't meant to dissuade the OP from the project. It's just my opinion. One engine isn't "better" than the other - it all depends on how you intend to use them (for the way I use my XJ - primarily work truck - the AMC242 serves me quite well.)

If you want to race the thing, you will probably enjoy the V8. If you want to tow heavy loads, you're going to need to reinforce the rear of the unibody - at least - as well as the engine (and the engine will probably want some small mods to improve low-end torque as well.)

The idea behind bringing harmonics into the discussion wasn't to say that one engine was "better" - merely, to present a theory (probably erroneous, but I'm still waiting...) as to why the inline could make more power at lower RPM. Yes, V8-level power can be had from an inline - for the most part, what you get is power output curves similar to what you get from a V8, just shifted to a lower crankshaft speed. The fact of equivalent power at lower crankshaft speeds allows for lower cruising speeds, which saves some fuel. Also, it allows you to "get off the line" easier with a load, since you make torque rather more quickly (generally speaking. I know, you can build a V8 to give you stump-pulling torque at low crankshaft speeds, as I've done it myself. It's still more the exception than the rule - check most torque curves on production V8s, and you'll usually see peak torque up around 4000-4400RPM or so, still.)