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Old 12-01-2021, 11:15 PM   #1
memo43
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What do you recommend

So I am at wrk contemplating what to do.

I daily drive an 85 K20 350 600cfm Holley carb
rusty long tube headers and exhaust held with bailing wire
Th400 that's starting to slip.
Gears are 4:10 tires are 265/75/16
My daily commute is 53 miles each way, all highway miles
I know I have to replace the trans since lately I need to give it a bit more gas in the mornings just to get it to engage gears Reverse or Drive.

I have an L31 sbc with roughly 15k miles on it, that I will eventually replace my stock 350 that will get Max EFI kit from summit.
If not the L31 engine what SBC would you do.
not really keen on doing the whole LS swap since that's roughly 3-5g for a high mileage engine.
Ant insight would be appreciated

Memo
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Old 12-01-2021, 11:20 PM   #2
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Re: Whats do you recommend

Buy a Corolla.

https://reno.craigslist.org/ctd/d/sa...413792215.html
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Old 12-01-2021, 11:20 PM   #3
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Re: Whats do you recommend

I put an L31 in my 72 Blazer and I'm really happy with it.
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Old 12-01-2021, 11:25 PM   #4
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Re: Whats do you recommend

Warrens69GMC I have no interest in ever driving a newer car, although heated seats are nice. Please don't think I'm being rude, I'm trying to get close to 15mpg, similar to newer 1500/2500 trucks
My last one a 2015 GMC 1500 (bought new) spent more time at the dealership than my garage. Besides I love driving my old square body
Truckster I've read your post on your build, that what got me to pull the trigger on the engine.
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Old 12-02-2021, 10:18 AM   #5
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Re: Whats do you recommend

With all due respect....you will never get 15mpg with a 4.10 gear unless you go to an OD transmission..... or change to a taller gear..
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Old 12-02-2021, 01:03 PM   #6
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Re: Whats do you recommend

Get a OF trans, and stay with AT tires.

I personally would go 4L80e, but next choice would be a 4L60e. Myself I prefer the electronic controls over the TH700r4 mechanical TV cable.

Yes I would use a L31 as power steering is easier to keep with it, but a 5.7 LT1 is not a bad option either. Bolts right in, but accessories are a touch annoying. Compared to early styles for ease of modification.

Get a wide band O2, and a vacuum guage in the cab. This way you can maximize tuning, and thus mpg.

As for the max efi. I would look at Holleys terminator or equivalent for trans control too
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Old 12-02-2021, 10:17 PM   #7
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Re: Whats do you recommend

Quote:
Originally Posted by A1971Blazer View Post
With all due respect....you will never get 15mpg with a 4.10 gear unless you go to an OD transmission..... or change to a taller gear..
Agreed, I eventually want to go to 3:73 gears, but that wont happen until I get a full float axle, that way I can do rear disc swap as well
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Old 12-02-2021, 10:20 PM   #8
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Re: Whats do you recommend

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Originally Posted by Ziegelsteinfaust View Post
Get a OF trans, and stay with AT tires.

I personally would go 4L80e, but next choice would be a 4L60e. Myself I prefer the electronic controls over the TH700r4 mechanical TV cable.

Yes I would use a L31 as power steering is easier to keep with it, but a 5.7 LT1 is not a bad option either. Bolts right in, but accessories are a touch annoying. Compared to early styles for ease of modification.

Get a wide band O2, and a vacuum guage in the cab. This way you can maximize tuning, and thus mpg.

As for the max efi. I would look at Holleys terminator or equivalent for trans control too

A what trans "OF"?
As for tires I'm running Dick Cepek tires, their AT versions
was not aware that either holley terminator could also control trans signal, might look into that. Every one I called has a ridiculous wait time for a rebuild trans, avg 5-9 weeks
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Old 12-03-2021, 06:17 PM   #9
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Re: Whats do you recommend

F all this 4L talk, get a nicely built 200-4R since your swapping trans anyways. Better gear spread.
L31 is your best best for ease of install and price. I had a L31 in my 79 c10, all stock besides the RPM intake manifold, edelbrock 600cfm, and some ram horn manifolds. I'd get 15mpg with 3.07 gears.
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Old 12-03-2021, 06:35 PM   #10
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Re: Whats do you recommend

IMHO....

Grab a reco 350, preferably a Vortec style.

Have the TH400 built correctly, 4L80e are great transmissions but the a 4L80e would run you more than the new engine and built TH400 combined.


Grab a new set of long tube headers and have an exhaust shop do the pipes and mufflers....why? Do you really want to lay on the cold ground and try and build an exhaust system?

IMHO, you dont need to get into the swap out and go electronic scenario...

Seems most of your problem is a tired trans and old exhaust.
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Old 12-03-2021, 11:39 PM   #11
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Re: Whats do you recommend

Keep the 4:10 gears and get a Gearvendors overdrive for the 208 transfer case.
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Old 12-04-2021, 10:16 PM   #12
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Re: Whats do you recommend

I use to get 14 mpg in my Jimmy on road trips. The secret with no overdrive is a manual trans. I'd keep the motor, swap in a manual trans and try a 255 85 16 tire. That should get you close.
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Old 12-05-2021, 11:07 AM   #13
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Re: Whats do you recommend

I'm with Warren. Buy a Corolla. I used to work with a guy who had a long commute and he drove some little GM product like a Geo or something. I'm not sure if I remember the name correctly.
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Old 12-05-2021, 04:45 PM   #14
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Re: Whats do you recommend

Get a 2nd older vehicle and build it optimized for highway mileage. Then you can rebuild your K20 as an honest off road 4wd.

A quick search found this around here: https://oklahomacity.craigslist.org/...406247938.html

Might be similar in your area.
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Old 12-07-2021, 04:31 PM   #15
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Re: Whats do you recommend

Quote:
Originally Posted by Mike C View Post
I use to get 14 mpg in my Jimmy on road trips. The secret with no overdrive is a manual trans. I'd keep the motor, swap in a manual trans and try a 255 85 16 tire. That should get you close.
Weird, my 78 got 10mpg with the SM465. I swapped in an M20 and still, 10mpg
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Old 12-08-2021, 09:25 PM   #16
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Re: Whats do you recommend

Thanks all for the response's
I will be doing the basic reman trans swap for now. I never would have imagined that
there would be a nation wide shortages on th400's. Something like a 4 week wait time.
The worse is maybe by March, first toilet paper and now transmissions.
I guess while I drop my trans I will address the exhaust issue, and prep the L31 for going in.
This turned out to a might as well project.
Maybe I will do the blazer tank an get rid of the dual saddle tanks, sending unit on the driver side tank is bad. Good time as any to prep for going fuel injected I guess
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Old 12-08-2021, 09:29 PM   #17
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Re: Whats do you recommend

An M20 in a truck?
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Old 12-08-2021, 09:52 PM   #18
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Re: Whats do you recommend

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Am M20 in a truck?
A who?
sorry at work and my Google Foo is not strong
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Old 12-08-2021, 10:23 PM   #19
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Re: Whats do you recommend

A M20 Is a Muncie wide ratio 4 speed. Going off memory was the weakest of the M line we know.
M20 is the wide ratio
M21 is still wide, but not as much.
M22 aka the rock crusher was close ratio. Which needed deep deep gearing to work.

The M20 is not weak in the sense of a Saginaw 4 speed, but relatively to its brethern. It is good to 400hp depending on abuse factor, and whom you ask. I would rather have one the a OG T10.
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Old 12-08-2021, 11:26 PM   #20
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Re: Whats do you recommend

Quote:
Originally Posted by Ziegelsteinfaust View Post
A M20 Is a Muncie wide ratio 4 speed. Going off memory was the weakest of the M line we know.
M20 is the wide ratio
M21 is still wide, but not as much.
M22 aka the rock crusher was close ratio. Which needed deep deep gearing to work.

The M20 is not weak in the sense of a Saginaw 4 speed, but relatively to its brethern. It is good to 400hp depending on abuse factor, and whom you ask. I would rather have one the a OG T10.
Thanks for clarifying,
For now I'm sticking to keeping close to factory equipment without going to crazy.
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Old 12-09-2021, 01:11 PM   #21
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Re: Whats do you recommend

Quote:
Originally Posted by memo43 View Post
Thanks all for the response's
I will be doing the basic reman trans swap for now. I never would have imagined that
there would be a nation wide shortages on th400's. Something like a 4 week wait time.
The worse is maybe by March, first toilet paper and now transmissions.
I guess while I drop my trans I will address the exhaust issue, and prep the L31 for going in.
This turned out to a might as well project.
Maybe I will do the blazer tank an get rid of the dual saddle tanks, sending unit on the driver side tank is bad. Good time as any to prep for going fuel injected I guess
A stock L31 engine block isn't machined to support the use of a mechanical fuel pump, and the stock cam doesn't have a lobe for the fuel pump push rod. This means you'll need to add an electric fuel pump, which you would be doing anyway if you're switching to fuel injection.
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Old 12-09-2021, 02:36 PM   #22
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Re: Whats do you recommend

Quote:
Originally Posted by vince1 View Post
I'm with Warren. Buy a Corolla. I used to work with a guy who had a long commute and he drove some little GM product like a Geo or something. I'm not sure if I remember the name correctly.
Geo Prizm AKA Toyota Corolla. Both made on the same line

Ours got 38mpg at 65mph (1.8)

My brothers got 41mpg at 65mph (1.6)
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Old 12-09-2021, 03:22 PM   #23
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Re: Whats do you recommend

My daily bomb around town is a Subaru Wagon--28mpg. Gas prices in Calif is killing me at almost 5.00 per
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Old 12-09-2021, 07:16 PM   #24
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Re: Whats do you recommend

Quote:
Originally Posted by Ziegelsteinfaust View Post
A M20 Is a Muncie wide ratio 4 speed. Going off memory was the weakest of the M line we know.
M20 is the wide ratio
M21 is still wide, but not as much.
M22 aka the rock crusher was close ratio. Which needed deep deep gearing to work.

The M20 is not weak in the sense of a Saginaw 4 speed, but relatively to its brethern. It is good to 400hp depending on abuse factor, and whom you ask. I would rather have one the a OG T10.
Plus, it would take a lot of effort to make it work, for no good reason in the first place. IIRC, it can/has been done? The shifter being quite an obstacle.
Even at the widest available ratio spread, it's still not truck friendly and a truck is just to heavy to drive like that....and forget towing.
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As for reading directions...
The directions are nothing but another man's opinion.
Learn from the mistakes of others, you won't live long enough to make them all yourself...

Bad planning on your part does not necessarily constitute an instant emergency on my part....

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Old 12-09-2021, 08:11 PM   #25
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Re: Whats do you recommend

Quote:
Originally Posted by Ziegelsteinfaust View Post
A M20 Is a Muncie wide ratio 4 speed. Going off memory was the weakest of the M line we know.
M20 is the wide ratio
M21 is still wide, but not as much.
M22 aka the rock crusher was close ratio. Which needed deep deep gearing to work.
M21 is close ratio like the M22. M22 was stronger version. M21 is slightly stronger then an M20 but nothing worth mentioning. And yes, I put one in a truck.
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