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 :)

Re: Enginge/Trans opinions
 

Very cool.

Re: Enginge/Trans opinions
 

My plan for my 70 has been: truck LS/nv4500 (100% has to be a manual) - seems to be the most cost effective way to get fuel injection & over drive. There are a lot of good opinions/options discussed here, definitely has me thinking...

Re: Enginge/Trans opinions
 

When you do your rpm calculations you need to consider that an automatic transmission may be turning a few more hundred rpms than a manual transmission at the same speed driven. Manual transmissions have a solid link to the engine's crankshaft so they turn at the exact same rate as the crank. Automatic transmissions are linked to the crankshaft via torque converter and friction belts that can allow for "slippage". I guess if you have an auto transmission with a positive lock up on the torque converter this slippage can be eliminated. But I thought I would just bring it up.

Re: Enginge/Trans opinions
 

Well , I found a sm465/np205 that was pulled out of a 69 chevy truck. It has all the clutch linkage and cross pivot pieces with it. Cleaning it up should give me something to do while I decide if i'm going to use it. I'm sure I can rebuild them both, I mean I have watched a couple Youtube videos. Ha.

Re: Enginge/Trans opinions
 

Are you going to use an Advance Adapter to hook up to a NP205?

Re: Enginge/Trans opinions
 

So what tire size and gear do you run? What RPM at 75MPH?

Re: Enginge/Trans opinions
 

Not 100% on tcase yet. I have a passenger drop np241 out of an 89 k5 that I might use. I will have to replace the input shaft and maybe some other parts? But I bought the 241 when I was a planning for an auto (boring!) it bolts right up to a 4l60e.

This thread came at a perfect time because I’m currently searching for a donor truck. 1999-2007 gm with 5 speed. Yesterday I was reading that the 241 will bolt right up to the nv3500. Just not sure the 4.8/nv3500 is a good fit for a k5 - I’ve posted this question a couple times & get mixed responses. So for now I’m still between 6.0/nv4500 & 4.8/nv3500 (since I want a complete donor truck and don’t want to piece everything together).

Re: Enginge/Trans opinions
 

May be a little bit late being you’ve bought stuff already, but if truely I decide yet let me list a few things for thought.
1: you said a cruising vehicle, as much as I like manuals they aren’t just cruising transmissions, put an auto in drive and cruise. Also if you’re married and your wife ever needs to drive it for any reason. Can she drive a manual?
2: SM465 ratio is so deep 1st is useless and no overdrive, unless you go with a highway rear gear to drop RPMs.
3: 700r4 & 4l60e both have the same ratio so sbc or LS you can compare trans the same way. 1st gear is a 3.06 ratio vs sm465 2nd 3.58, which you use as first. So not much different starting out except with an auto you can ease into motion with something heavy and not be hard on the clutch. Then again how heavy will you be pulling with a blazer.
* side not you already have a 27 spline np205 which matches a 700/4L60
4: NV4500 is somewhere around 5.4 1st if I remember correctly, similar to the sm464 but with overdrive.

Engine
1:Depending on where you live and emissions laws old school may be a little more of a pain to meet standards
2: If going old school and wanting to stay correct to the truck, can get pricey if you want all parts period correct. But ultimately the simplest
3:carb vs efi Offroad, normal Offroad no difference. Hard angles and steep grades aren’t affected with fuel injection
4: ls drivetrain is proven and in millions of vehicles since mid 1999 with hundreds of thousands of miles, and if staying with a stock setup you don’t have to worry about maintence anymore than the next guy driving his used Silverado.

Personally if it was me I’d get a used drivetrain from a trailblazer 4wd or Buick rainier awd and have the computer flashed just to delete downstream O2s and anti theft. Keep in mind unlike the trucks they don’t have a TAC module and makes gas pedal compatibility a lot easier. Also all 5.3 trailblazers, rainiers, envoys, and Saab 9-7x used an aluminum block and the 4l60e which you have a transfer case already for.

Now at last if you want a play toy that’s cheap and fun but not to concerned with comfort and cross country reliability/parts availability, extreme cold weather starts and go. Go old school carb with the manual.
By no means am I saying carbs don’t work reliably, just looking at overall conditions and parts availability.

Re: Enginge/Trans opinions
 

Looks like you got the short throw shifter option there!

Re: Enginge/Trans opinions
 

I don't think the guy would have cut it off if he knew it would be worth $100 some day.

Re: Enginge/Trans opinions
 

Thank you for all the info/advice. I still haven't decided yet. I just bought the sm465 because it was a good deal. I can always resell it. I have the short output shaft kit for the 700r4, I should probably just go that route. It just seems like a lot of hassle and extra $ to use an nv4500 with the np205.

Re: Enginge/Trans opinions
 

It is funny how in that huge hunk of metal the 'short stick' jumped right out at me too.

The hit wrench is sometimes quicker.

S