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

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.

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.

Re: Enginge/Trans opinions
 

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?

Re: Enginge/Trans opinions
 

350 with factory 4 speed manual trans here. I can hold 75 all day long on the freeway :)

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

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.

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.

Re: Enginge/Trans opinions
 

So you feel the sm465 is decent tranny for weekend back road cruising?

Re: Enginge/Trans opinions
 

Did you drive it with the 4 speed? Why did you take it out?

Re: Enginge/Trans opinions
 

Thanks for the advice.

Re: Enginge/Trans opinions
 

I am leaning toward the sm465. There are a lot of them around and they are fairly easy to rebuild.

Re: Enginge/Trans opinions
 

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!

Re: Enginge/Trans opinions
 

Thanks for the reply.

Re: Enginge/Trans opinions
 

My pleasure; hope it is helpful!

Re: Enginge/Trans opinions
 

I have an sm465 I’d 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.

Re: Enginge/Trans opinions
 

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.

Re: Enginge/Trans opinions
 

I wish we were closer. I have a SM465/NP205 that came with the Blazer when I bought it.

My 72 Blazer has the same set up.

I have always been an automatic guy with the old trucks. I switched my 69 to a 350/205 from a 3spd/Rockwell T-221.

I enjoy the 4 speed I have now but would prefer the automatic. My son, and all my friends say the 4 speed is the way to go.

It is a 'to each his own' type thing. It is a personal preference and personal use debate.

Best of luck.

If you happen to be in NC and happen to have it in the back of the truck, drop me a line.

Best of luck.

Scott

Re: Enginge/Trans opinions
 

Everyone will have their own opinion on what drivetrain combo is best. Here is what I run and why:

SM465/NP205/Gear Vendors OD setup behind a fuel injected 400 SBC - I tow heavy trailers and do a lot of travel in very remote areas so the SM465 is bombproof and will get you home every time. Yes it shifts like a dump truck. So it is definitely an acquired taste. The granny low is great for slow 4x4 ascents and for getting you moving from a stop with a heavy trailer. The NP205 is a bombproof cast iron gear driven case. Nuff said. The Gear Vendors gives me overdrive and allows me to split every forward gear. This allows me to cruise at 80mph and keep my engine in its rpm sweet spot while towing up mountain passes. I went with an EFI 400 SBC and not an LS because I can work on a SBC and know them inside out. I can't say that about an LS.

I should note that I run 4.10 gears with a 35 inch tire. This combo works perfectly with the overdrive, and allows me to run 4th gear non-OD on the highway when traffic speeds are lower. I personally think that 4.56 gears will be a tad too deep to get the full advantage of an overdrive if you want to cruise 75-80 mph with low rpms.

Re: Enginge/Trans opinions
 

I'm on 33's with 4.11's with the 355/465 and it is a tad much on the highway but I do not put that many highway miles on it anyway.

I live relatively close to the lake so towing is for short distances. And the low gear is one that will pull hell up off its hinges.

Like it has been said, it is all dependent upon personal preference and what the truck/blazer will be used for.

I prefer the automatic but that is just me. I have friends that think I am crazy for even thinking of the swap.

Scott

Re: Enginge/Trans opinions
 

So you think the rpm is too much? if my chart is right you should be running 2700 rpm @65 mph. Is that about right?

Re: Enginge/Trans opinions
 

For me, it sounds like a lot.

It has rained here all week and have yet to put the top back on mine.

It is suppose to be clear on Monday.

I have never really noticed the actual RPM's on the highway. It sounds and feels like I'm turning a little hard.

With the 33's and 4.11's I can pull off in 2nd gear as easy as most trucks can pull off in their first gear, that part makes it feel a little tall.

Scott

Re: Enginge/Trans opinions
 

I should add that "highway cruising speed" is definitely different depending which state you are in. When I lived in Maryland, the speed limit was 55 mph and the brave would cruise at 65 mph. I live in southern California now and the speed limit is 65 mph. Normal cruising speed is 75+ mph. But there are always people passing you doing 80+ mph!

Re: Enginge/Trans opinions
 

Thank for your input. At one point I had decided to go with a 700r4. I figured the 4:56 would give me the range to go either 35 or 37” tires and keep rpm around 2500 at 65. I don’t have a problem with changing them again to a 4:10 if that will work better with the sm465. I just can’t get the idea of a 4 speed out of my mind. I want a Blazer that looks and feels like an “old” truck. I mostly drive around on the gravel country roads and rarely go over 55 mph. LSs are great I have one in my daily driver, but I want to open the hood and have something that is “somewhat” era correct. Engines are not my strong point , but I have some experience with a basic small block.

Re: Enginge/Trans opinions
 

I agree that an LS engine would be awesome, but there just is something to say about and old rig with an old engine :)