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Old 02-11-2019, 02:35 AM   #1
Keith6987
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Engine/Trans opinions

I am getting down to decision time. My 69 Blazer did not come with an engine. I will probably go with a moderately built up 350. I have a TH350 that came with it and a 10 spline and 27 spline NP205. I believe it was a 4 speed originally. I have the clutch pedal bracket.. I have the gears changed out to 4:56 and I will run 35" tires. I kind of like the idea of going back to a manual trans, but I can live with an auto.
So... this Blazer will be an on road weekend cruiser and will probably never see the interstate. I would like to avoid a bunch of expensive adapters in order to use a five speed. (unless someone knows a combo that will work)

What are the opinions on these options.

SM465 using the 10 spline (is this trans worth the effort)

convert to a 5 speed (NV 3500-4500)

TH350 with 27 spline

700R4 with 27 spline

Or should I think about a complete modern LS and trans.


Thanks, Keith

Last edited by Keith6987; 02-11-2019 at 01:14 PM. Reason: Typo
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Old 02-11-2019, 01:21 PM   #2
SeventyOne
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Re: Enginge/Trans opinions

There's going to be a lot of opinion thrown around but really this comes down to your preferences and tolerances.

If you enjoy shifting and all that go with a manual. I have a '64 F100 that has a 3 speed in it that i originally thought about changing to a automatic for ease of drivability but...i think ive changed my mind and really enjoy banging through the gears. It makes me think more, and be more in tune with the truck - and traffic for that matter - which is sort of the whole point of driving an old rig. At least to me.

My Blazer has a 383 and 700r4 (37" tires and 4.56 gears). Now, I haven't driven it yet since I'm still putting it back together but I personally wanted an overdrive trans so my RPMs are lower at highway speed.

Now that said if you think you'll never see the highway, will you need an OD or even a 5 speed trans?

You need to really think about how the truck will be used and if you DO end up on the highway what are your tolerances for higher RPMs? Using a calculator and putting in your specs with a non-OD trans put you at 2850 at 65 mph. For comparison my K5 would run at 1900rpm at 65mph.

Figure out how you want it to drive then select the best combo for it.

My 2 cents.

Last edited by SeventyOne; 02-11-2019 at 01:36 PM.
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Old 02-11-2019, 06:12 PM   #3
Keith6987
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Re: Enginge/Trans opinions

Thanks for your input. The old trucks I’ve driven over the years have all been manual. My Jeep is a manual. There is just an old school feel to driving a stick once in a while. I like to downshift and let it cackle. I was 90% sure I was going with the 700R4 just because it would line up with the NP205 with the least trouble. From what I can tell the only manual that will pop right in is the SM 465.
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Old 02-11-2019, 08:24 PM   #4
SeventyOne
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Re: Enginge/Trans opinions

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Originally Posted by Keith6987 View Post
Thanks for your input. The old trucks Ive driven over the years have all been manual. My Jeep is a manual. There is just an old school feel to driving a stick once in a while. I like to downshift and let it cackle. I was 90% sure I was going with the 700R4 just because it would line up with the NP205 with the least trouble. From what I can tell the only manual that will pop right in is the SM 465.
The 700r4 needs either a new output shaft or an adapter to mate to the NP205.

If you get the new output shaft it bolts up just like your TH350 would. The other thing when you put in a 700r4 the trans is 1-7/8" longer than a TH350 so you need to either move the engine forward (my choice) or the tcase back.

I'd imagine the SM465 would bolt right in assuming you have the right crossmembers and such. The SM465 came in these as a stock option right?
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Old 02-11-2019, 08:47 PM   #5
simicrintz
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Re: Enginge/Trans opinions

350 with factory 4 speed manual trans here. I can hold 75 all day long on the freeway
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Old 02-12-2019, 12:39 AM   #6
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Re: Enginge/Trans opinions

I did the LS/4l60e swap. But....

Because its not a daily driver I've come to realize the LS and Overdrive tranny aren't really necessary. What do I care what mileage I get? Even with the LS and overdrive tranny I still only get about 12mpg....top off, 4" lift, 35" tires and 4.11 gearing (4.56 would probably be better.) What's the overdrive doing for me? Not much I figure.

Don't get me wrong. It's a cool thing to have and show people the swap. But it's not a must.

A really clean engine compartment with a carbed 350 or 454 would be just as cool!

If I were to do it again.... probably a 454 (or 383 for easy tranny mating.)

Keep the th350 or get a 700r and buy a cheap ($50) adapter to mate it to the np205. I like cruising and saving the work from shifting.

Wil
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Old 02-12-2019, 09:12 AM   #7
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Re: Enginge/Trans opinions

I would go the SM465 route. They are relatively inexpensive, common and robust. The granny gear gives you plenty of grunt down low to get moving if you pull a boat or something and lets you move slowly off road. It will keep the rpm down 10% or so compared to the TH350 as well.
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Old 02-17-2019, 09:20 PM   #8
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Re: Enginge/Trans opinions

I just sold a sm465 for 300 for everything so they are out there for cheap. I went with an ls3 and 4l80 so I can’t say I was staying with the cheap route for my build. The 4l80 bolted up to the 205 case with an adapter and 32 spline input. I’m going a little crazy for a driver.
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Old 02-17-2019, 10:44 PM   #9
Keith6987
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Re: Enginge/Trans opinions

Quote:
Originally Posted by simicrintz View Post
350 with factory 4 speed manual trans here. I can hold 75 all day long on the freeway
So you feel the sm465 is decent tranny for weekend back road cruising?
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Old 02-17-2019, 10:46 PM   #10
Keith6987
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Re: Enginge/Trans opinions

Quote:
Originally Posted by Blazerowner View Post
I just sold a sm465 for 300 for everything so they are out there for cheap. I went with an ls3 and 4l80 so I can’t say I was staying with the cheap route for my build. The 4l80 bolted up to the 205 case with an adapter and 32 spline input. I’m going a little crazy for a driver.
Did you drive it with the 4 speed? Why did you take it out?

Last edited by Keith6987; 02-17-2019 at 10:47 PM. Reason: typo
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Old 02-17-2019, 10:53 PM   #11
Keith6987
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Re: Enginge/Trans opinions

Quote:
Originally Posted by OldCreek View Post
I did the LS/4l60e swap. But....

Because its not a daily driver I've come to realize the LS and Overdrive tranny aren't really necessary. What do I care what mileage I get? Even with the LS and overdrive tranny I still only get about 12mpg....top off, 4" lift, 35" tires and 4.11 gearing (4.56 would probably be better.) What's the overdrive doing for me? Not much I figure.

Don't get me wrong. It's a cool thing to have and show people the swap. But it's not a must.

A really clean engine compartment with a carbed 350 or 454 would be just as cool!

If I were to do it again.... probably a 454 (or 383 for easy tranny mating.)

Keep the th350 or get a 700r and buy a cheap ($50) adapter to mate it to the np205. I like cruising and saving the work from shifting.

Wil
Thanks for the advice.
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Old 02-17-2019, 10:57 PM   #12
Keith6987
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Re: Enginge/Trans opinions

Quote:
Originally Posted by SeventyOne View Post
The 700r4 needs either a new output shaft or an adapter to mate to the NP205.

If you get the new output shaft it bolts up just like your TH350 would. The other thing when you put in a 700r4 the trans is 1-7/8" longer than a TH350 so you need to either move the engine forward (my choice) or the tcase back.

I'd imagine the SM465 would bolt right in assuming you have the right crossmembers and such. The SM465 came in these as a stock option right?
I am leaning toward the sm465. There are a lot of them around and they are fairly easy to rebuild.
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Old 02-17-2019, 11:41 PM   #13
simicrintz
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Re: Enginge/Trans opinions

Quote:
Originally Posted by Keith6987 View Post
So you feel the sm465 is decent tranny for weekend back road cruising?
I drove mine from Phoenix to San Diego when I picked it up. Hadn't driven a stick in probably 30 years and it did great. Since then we've taken it to the beach, the mountains, around town and up to get pumpkins on Halloween. I never use first (unless I'm just messing around) but feel like it is a great all around tranny!
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Old 02-17-2019, 11:46 PM   #14
Keith6987
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Thumbs up Re: Enginge/Trans opinions

Quote:
Originally Posted by simicrintz View Post
I drove mine from Phoenix to San Diego when I picked it up. Hadn't driven a stick in probably 30 years and it did great. Since then we've taken it to the beach, the mountains, around town and up to get pumpkins on Halloween. I never use first (unless I'm just messing around) but feel like it is a great all around tranny!
Thanks for the reply.
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Old 02-18-2019, 01:52 AM   #15
simicrintz
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Re: Enginge/Trans opinions

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Originally Posted by Keith6987 View Post
Thanks for the reply.
My pleasure; hope it is helpful!
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Old 02-18-2019, 10:10 PM   #16
ScottyTightdog
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Re: Enginge/Trans opinions

I have an sm465 Id love to trade you for that 27 spline np205. It will include the adapter and everything to bolt right up to the 10 spline you have. Let me know.
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Old Yesterday, 12:07 AM   #17
Keith6987
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Re: Enginge/Trans opinions

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Originally Posted by ScottyTightdog View Post
I have an sm465 Id love to trade you for that 27 spline np205. It will include the adapter and everything to bolt right up to the 10 spline you have. Let me know.
I will keep that in mind. I'm going to figure all of the gear ratios again before I rule out the 700r4. I have found several NP205s around here through FB marketplace.
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