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Old 01-16-2020, 01:36 PM   #1
chc1955
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Conflicted

Hello all,
I am very conflicted. I have a 1972 C 30 single wheel rear end that I have been driving daily for over a year. It has a 292 with a sm465 without Ac or power steering. I am not sure on the rear end. Mileage is not that great, I figure maybe 8-9 mpg. I recently bought a 2002 Chevy Silverado 3500 for a very good price from a friend of mine. It has an 8.1 496 with an Allison 5 speed. My intent was to swap the motor and trans and possibly the rear end with bendix system. I salivated when he told me the price and jumped on it. In the middle of all of that, I ran into a 292 with a sm465 and had the elusive power steering brackets. I drive about 15 miles a day but occasionally like to get on the freeway and step on it. Now, I don't know which way to turn... What do you guys think???
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Old 01-16-2020, 02:02 PM   #2
weim55
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Re: Conflicted

The swap to the 496 Allison is a massive labor and expense drop. You would never get your money back with any additional mileage(OK, maybe a couple decades of driving and you might get it back). The truck would be many times more enjoyable to drive with the modern drivetrain but again, is it really worth it.? In my opinion, no. Likely your rear gear is a 4.57 or 5.13. Id swap the rear gear to a 3.54 or 4.10 ( cheap and easy ) and do a razor sharp tune on that stock 292. I bet money those two things would get you to 12 mpg which is a pretty good mpg jump percentage wise, enough to make a difference. And you still have your nice simple, stock and reliable C 30........

Steve weim55 Colorado
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Old 01-16-2020, 02:03 PM   #3
kwmech
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Re: Conflicted

Personally I'd keep the 292 and put the power steering on it. Then I'd add an overdrive
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Old 01-16-2020, 02:13 PM   #4
truckster
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Re: Conflicted

Maybe drive the Silverado for a while before you make the decision...
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Old 01-16-2020, 02:21 PM   #5
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Re: Conflicted

The choice would boil down in a simple way to me.

Power and Complexity with Money

Simplicity, and now you have parts. Undoubtedly more parts will be needed in the future. Sourcing can be a little problematic at times.
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Old 01-16-2020, 02:23 PM   #6
Grumpy old man
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Re: Conflicted

The only problem is the engine on the back of your flatbed is a 250 not a 292 , Those power steering brackets are still in high demand but won't fit your 292 in the truck .
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Old 01-16-2020, 02:43 PM   #7
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Re: Conflicted

Transplanting the late model drivetrain is a large project that experienced shops take several months to complete, with people working 40 hour weeks on it. Are you and your family in a position to commit that amount of time to complete such a project? I only ask this as there is a continuous stream of unfinished projects for sale, and I know most of their owners have felt a fair amount of heartache and grief.
Myself I would rather spend that time driving my truck, especially a looker like yours.
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Old 01-16-2020, 09:28 PM   #8
BigBird05
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Re: Conflicted

Grumpy, how can you tell that, that is a 250 in the picture? What are the differences externally between a 250 and a 292?
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Old 01-16-2020, 09:45 PM   #9
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Re: Conflicted

The fuel pump is on the wrong side of the engine mount
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Old 01-16-2020, 09:56 PM   #10
Grumpy old man
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Re: Conflicted

250 has smaller lifter panels on passenger side like this picture below of a 250 also looking from the pass side you have front to back

250 - oil filter - fuel pump - engine mount

292 - oil filter - engine mount - fuel pump

292 has larger side panels 5.5" tall
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Old 01-17-2020, 12:42 AM   #11
GASoline71
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Re: Conflicted

I doubt that 8.1 and Allison will get 12 mpg. I know 2 cats that have 8.1's in their late model rigs and barely get 10 mpg on a good day, downhill with a tailwind.

Gary
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Old 01-17-2020, 01:56 AM   #12
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Re: Conflicted

the 8.1s were paired with Allison 5-speeds and 3.73 gearing, as opposed to 4.10 in the 6.0 trucks. The best mpg I've seen in my 01 8.1 is 13 - that was on a long highway drive with the cruise control on for hours at a time. In general day to day use (which is still mostly country road driving), I average around 10-11 mpg, just like Gary said. It's not likely your truck has rear gears as highway friendly as 3.73s (relatively speaking...) - I agree with Steve, the best you could hope for is a 4.10 in that thing, but it's not very likely, so your mpg would be notably worse than what is seen in the GMT800 series with the 8.1 drivetrain, generally speaking. At the very least, before you go down this road, you need to determine what your current rear end ratio is (unless you do swap the rear from the 02). If your 02 is a decent, driveable truck, I sure wouldn't yank the drivetrain out - the early GMT 800s with the 496 are desirable trucks - if you don't care for it, sell it for a profit and buy an overdrive unit for your 72. It is a large undertaking and not an easy swap.
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Old 01-17-2020, 01:47 PM   #13
chc1955
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Re: Conflicted

Grumpy I appreciate your knowledge. I'm gonna have to get rid of that engine now. Lol, it happens. I will drive the 2002 for the spring and make a decision at the end of it. The power it has is when I drive it is what really gets me going. I know it wouldn't be an easy swap. Gonna have to work some ot and side jobs to get it done if I don't sell it to pump up the 292. I am dying to find out the rear end ratio. I will in the next few weeks when i redo that axle seal that is leaking a bit.The 2002 has a 4.10 posi with disk brakes. Which would make stopping pretty cool. I guess its nice to have the problems I have. This board is really Great!!! The knowledge i have gotten in the last few years is amazing. Thanks everyone for your thoughts and opinions!!! I appreciate your help!!!
Cesar
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