SM 420 ? transfer case ? ls1 ?

[67GMC3/4]

I am trying to get a plan of attack together for my 67 GMC 3/4 4x4, it seems to have a 327 small block, sm420 4 speed, dana 60 rear, dana 44 front but any idea on what the transfer case would be ? so I have a few ?s about these two,
currently the truck has 32 inch tires and everything else appears stock but at 50 - 55 mph it seems to be maxing out at speed, any ideas what the stock gear ratio options were ? I am planning on swapping to a c5 corvette ls1, dana 60 front, and 37 inch tires, would a freshened up and cryo treated sm420 take the abuse of an ls1 ? or a supercharged ls1 ? also any suggestions on what transfer case combination and gear ratios to run if I plan on mudding and trail driving the truck with trips to the sand dunes as well ? want something that will allow me to go down the highway at a decent rpm level and still pull me out of trouble. I was also considering swapping to a jeep 5 speed trans and transfer case any suggestions appreciated, thanks



thanks guys.

[andrewmp6]

If it was me i would look in to what sticks gm used on the 99 up trucks that will bolt on a ls.Or figure out how to use a nv4500 on a ls.The t cases i don't know a lot but most run a 205 or 203.

[MalibuSSwagon]

Might just be a gearing thing, what kind of condition does the 327 look to be in?

[duallyjams]

The stock transfer would be a rockwell t221. I would guess that you have 4:56 gears in the rears. To do a nv4500 conversion you are looking at 2 to 3 grand.

[RatRod68]

Originally Posted by andrewmp6

If it was me i would look in to what sticks gm used on the 99 up trucks that will bolt on a ls.Or figure out how to use a nv4500 on a ls.The t cases i don't know a lot but most run a 205 or 203.

^^ Do this. Run a 205 if you want to stick to the passenger side pumpkin, if you want to go drivers side, go with a NV241 (I think its NV. It's either NV241 or NP241. Transfer case found in 88-98 trucks)

I was told that the only difference between the 4500 and a gen 3 manual is the flywheel has 1 extra bolt hole that you wont need to use. I believe they make conversion flywheels for the manuals along with the autos. When we do the gen3 swap on the K10, I will most likely get an adapter for a 4L60E to bolt to my 205, and call it a day.

[67GMC3/4]

very nice I was thinking the same thing with the rear axle but im currently in school and graduate in a few months and instead of buying a new car or truck I am going to drop some cash into my 67, so I am doing the dirt work now so I can make a list of everything that I need before I get there, the nv4500 i can pick up for 800-1000, the ls1 1000-2000 just depends if they got one if not they are still around the same price. 1000 to adapt both together, and 500- 800 for another tc. sound about right ? 500-1200 on a locked dana 60 front, overall i was thinking of going with 4:10 gears, anyone have experience with them on the highway ?

[Redcap]

Originally Posted by 67GMC3/4

very nice I was thinking the same thing with the rear axle but im currently in school and graduate in a few months and instead of buying a new car or truck I am going to drop some cash into my 67, so I am doing the dirt work now so I can make a list of everything that I need before I get there, the nv4500 i can pick up for 800-1000, the ls1 1000-2000 just depends if they got one if not they are still around the same price. 1000 to adapt both together, and 500- 800 for another tc. sound about right ? 500-1200 on a locked dana 60 front, overall i was thinking of going with 4:10 gears, anyone have experience with them on the highway ?

The gears you will want will depend on tire size.

[67GMC3/4]

i was thinking 37s

[RatRod68]

1st- Im not trying to tell you how to build anything, just putting my opinion out there

ok, now that is out of the way, lets get to work.

The LS1 is great, especially if you are wanting to go fast. If you are wanting a gen 3 motor in your old pickup, go with the 6.0 or 5.3. They are loads cheaper, and are stronger. They are an Iron block, so they are much heavier, but have better low end torque. You can even bore a 5.3 out to a 5.7 and probably still be cheaper than buying an LS1.

4.10's are pretty high for 37's IMO. I have 35's on my Ranger and am running 4.56's. A buddy of mine is running 40's with a LQ4(6.0)/4500/241 setup with 5.13's. I have 4.10's in my 71 with 35's. When i put the LQ4 in my Ranger, I will be going to 4.88's

I am putting the 4.8 and 4l60e in my 71. They are cheap and easy to come by. Still pushing around 300 HP, and with a couple mods and a tune, you're easily over 300. And your still getting rather good mileage.

If you are going to be wheeling the old truck, I'd go up to a 60. If its just going to be driven and maybe some light playing in the mud, i'd stick with the 44. 60's are the hot ticket item right now, so they are going for 700-1200 for old worn out complete setups.

[67GMC3/4]

josh, thanks man its completely fine, thats why I started this post so that I can figure out what the best for the truck will be, itll eventually be a daily driver, I thought about the 6.0 and got some ?S for it, will the nv4500 bolt up to that one with out an adapter ? and the reason why i was thinking the ls1 is because of the speed and the block and heads being aluminum, i wanted something light that will put out the power so that my front end is not so front heavy, also because the dunes is where one of the main spots that I will be enjoying this truck will be. but the 6.0 wouldn't be as bad because I am thinking of turbos in the future and the iron block would have an advantage there. what would you recommend for gears than ? I do want a 5 speed since the truck is originally a 4 speed truck and would like to have something that looks some what stock from the outside and modern on the inside.

[RatRod68]

since you asked, i would go turbo 5.3 They are the best motors to turbo because of their relatively low compression compared to the 6.0 and LS1. Not saying you couldn't turbo a 6.0, just wont be able to run as much boost on the stock motor.

As i said, the LS1 is an awesome engine. I have one in my 68. But i also paid 5 grand for the motor, tranny, and ecu shipped to my door. That setup with a 5.3 or 6.0 would be less than half that.

That is the main reason i am not going that route. You can run LS1 heads, LS6 intake, Z06 cam, CAI, headers, and a tune, and be at almost 400 hp in a 5.3. That is plenty to scoot your truck through the dunes.

I am not 100% positive if you will need an adapter. I know the bell housing will bolt up, but you may have to buy a conversion flywheel like you do if you want to run a TH350/400/700R4 on the gen 3's.

The guy who is doing the swap says you just have to use the flywheel off the gen2 engine, but i will ask him tonight one more time to be sure that is all you need to do.

If you do go with a driver side pumpkin, (Ford, Dodge, Jeep axle) than you can just take the trans and t/c out of an 88-98 2500/3500 truck.

If you stick with the passenger drop, you will most likely need an adapter to mate the 4500 to the 205.

As far as gearing goes.... If you are going 4500/241/37's and are planning on doing some wheeling, I'd recommend 4.56's. it will still have a relatively low cruising RPM, but will be able to have the torque on demand like you want in a 4x4.

If you are going 35's and keeping it a street queen/DD, then 4.10's would be plenty

[67GMC3/4]

sweet man thanks for your help, I was just thinking ls1 because i can get one for 1400 with low miles and ecu and harness, what harness did you use for your swap ? ill look more into the 5.3 than and see what I can do going that route, you think the sm420 and transfer case can handle the power from a 5.3 ? cause if so ill just rebuild them parts and send the gears off to cryo treat for more strength, witch will allow me to do more with the truck faster and get it on the road faster.

[67GMC3/4]

http://www.advanceadapters.com/products/pn-712500m/

so im taking the motor and sm420 would mate than ? just run this clutch and flywheel ? cant be that easy

[RatRod68]

oh hell yea. The SM420 could easily handle the power, but you are going to get **** for gas mileage. The t-case behind the 420 is a 205, and that t case can take a beating, it's just high geared. They make a gear set to lower the gearing for the 205 though, but again, that is something you wouldn't need unless you were out rock crawling this thing. (Please do not destroy your truck by turning it into a rock crawler)

As far as harness, I went aftermarket. I called up Howell, had them reprogram the ECU to the truck, erase all the emission codes, and squeeze every ounce of power they could out of it. Their harness is AMAZING. A retard could install it. Everything is labeled, its super clean, and completely customizable. Only down fall is that you pay for what you get.... My setup cost a whopping 1600 bucks...

[RatRod68]

AS far as the 5 speed goes, here is the email he sent me....

I went and bought the flywheel spacer and longer bolts that everyone says you need, but turns out I didn't need them? It bolts right up and the input shaft on the tranny hangs into the crank just fine. Just need to drill the lower two bellhousing boss's out to run bolts into the oil pan (it's threaded for them) and that's it! I bought a flywheel for a 4.8L/6.0L for $80, and bolted it right up.

[67GMC3/4]

I believe mine is a rockwell t221, I was searching everywhere last night and everywhere i looked they said that my trany is a 2wd truck trans, and the transfer case is divorced mounted. I found a rebuild kit for that one also, every time I took it out it seemed to handle itself pretty good,

[RatRod68]

never heard of it, so i wouldn't be able to help when it comes to that t/c

[67GMC3/4]

Ya i think ill look more into a 5.3 than and spend some cash on hopping it up and than swap a custom wiring harness and keep the rest of the truck, I graduate in two months and am planning on just working and saving up cash to buy parts over the summer and enjoy the truck how it is, than I am planning on going off to boot camp in september and when i graduate from that step is when I want to tear into the truck.

[RatRod68]

boot camp for.....?

[67GMC3/4]

its between coast guard and the navy, still talking to both recruiters trying to narrow it down,