The Stovebolt Site Forums The Parking Lot Big Bolts Needing opinions

69, C60, 427, 5 speed, 2 speed rear end, 24k. Currently has a 6:50/8:87 gear and tops out at 59 going down hill. I plan to haul around 15k ish pounds at the absolute max and the truck is just over 8k empty. I would like the top speed to be at least 70 though I will cruise at 65 most of the time. This engine is like a diesel, happy as can be down low making its torque but not not so happy over 3k rpm. Currently empty I take off in 2H.

My options are 5:29s, 4:88s or 4:56. Here is a link to all the options spelt out in the correct pattern, shifted at 3200 rpm with cruise speeds at the bottom for 65 and 70 mph and rpm at those speeds, I would like to use the high gears as an over drive if it's possible and only use them while empty or cruising on the flats https://imgur.com/gallery/SYYS0se

Honest opinions or first hand knowledge is what I'm looking for. What low gears are you running and your set up? How do you like it? I know it wasn't designed to do 100 mph and I don't plan to but want to make it more drivable then a max speed of 59 and get "run over" on the highway.

I have thought about this same issue with my 69 T50, 20K, and not really decided to do anything as for me it really is not worth the trouble. I don't drive it enough to get too excited.

However, your deal sounds different so you gotta do what you gotta to do.

Your numbers show that you if you start out now in 2H, your shift point is 16 mph. If you go all the way to 4.56 and start in 1H you are below your current 2H start ratio, shifting at 12 mph so the 4.56 should pull a normal start better, just one more shift to hit the top gear. And you still have one choice below that for hard starts (which is ~30% higher than your current low-low, you lose one ratio on the bottom). If that doesn't worry you, then the low end looks OK to me.

The splits on the gears will be wider so the engine will need to make that up with a wider power band than you need now. The top shift split with the 4.56 is 12 mph, with 6.50 it is only 8 1/2 mph, I don't know what that translates into rpm difference. (I would drive the truck at a steady speed and shift from 4H to 5H, noting the rpms in the two gears, then compare that to the power curve for your engine. Comparing the rpm difference to the difference of the current and proposed rear end ratios. That should tell you if you have enough power to pull that wider split.) If your power band is wide enough, you could use any of the ratios and be fine.

If you go as far as 4.56, the engine will be in the power mode more, running richer, and fuel mileage might actually decrease. If you retune the carb, you might get that back.

If you run the truck for long periods in a lower gear, the trans will run hotter, same for the diff. Will that be a problem? I have no clue but I would want to cruise in HH if I was on a cross country trip. 4.56 might be too high for that.

Your clutch mileage will vary.

I would not go with the 4.56.
You didn't say what size tire your running?

I would think probably 9.00-20 and with 4.56 ratio the motor is not
Going to like it when loaded or empty on a hill.

I would try the 4.88 ,or most likely the 5.29
Tire diameter play's a big part if final ratio.

My MT80 (C80) with 427,5 &3, 3rd being OD pulls good until I come to a hill.
Even empty at 18,000 I have to shift back to direct to pull it.
That's with 7.17 ratio and 10.00-20 tires

My .02

Tom

The truck will mostly be used to drive within 3-4 hours of home loaded with the occasional daily driving it because I can. Shifting empty currently 4H-5H the power band I don't feel is broad enough but doable and that's empty. I'm not too worried about mpg, it's an old 2 and a half ton truck with a big block so it's only going to be so good anyways but I won't complain about an improvement. I do have an HEI distributor, fresh tune up, timing adjusted, block hugger headers and will be building an exhaust for it soon, the original was rusted out. I will also be ditching the governed Holley before too long also. That's about all I plan to do for adding power to it. I had to pull the trans a couple weeks ago and replaced the ring gear. While I was there I had the flywheel resurfaced and clutch rebuilt, it has a dual disc clutch from the factory.

Currently it does have 4 out of 6 9.00-20 but I will be going with a set of low pros on 22.5 295/75R22.5 are what I have in mind or roughly 40" and that is what all my ratios are figured at in the link. My trans 5H is my 1:1 and I was hoping to do the gear swap once and be done while using 5H as a sort of OD for those long halls but I also don't want to take away from my mid range where I'll be most of the time. I don't want it screaming at 72 mph at 3200 either because it doesn't like it.

What is easily available, that might be your determine factor. With a big load one could always cruise at 65 in direct(is your 5 speed OD?) or so but 70 with no load, figure out those rear ratios if they are available.

I don't know if Temperance is a state of mind or a location, state would help, mountains or not?

Ed

I can get any of the 3 ratios I mentioned. 5H is my 1:1 ratio so no OD. I have a 17221 (10 spline axles) rear end with air brakes and a spicer 5756-B transmission. Temperance, Michigan (I fixed it). Mostly flat lands within a few hours every direction of me with the exception of some long hills here and there but by no means mountains. The ratios are already figured in 5H in the second picture at the bottom of each of the 4 pieces of paper per gear set one is at 65mph the other is at 70 mph.

Just out of curiosity, what axle do you have? A T170? That"s what I have in my truck. I've searched high and low for a different ring/pinion that would work and I always get the "good luck finding that" response. I have an NV4500 sitting around that I keep kicking the idea around of putting that in instead and leaving the 6.50 rear.

I got a 4.33 two speed to replace the 6.5 with my OD 5 speed with a 503 in my '54 GMC, works well. Gentleman in Duluth had gears.

Ed

I would say figure what torque peak RPM is and figure that at 65, with whatever that ratio would be.

Ed

The very limited info I can find on a 427TD says torque peak is 405tq@2600 rpm and 260hp@4000 rpm but I don't know how that can be since I'm governed at 3200.

With 4:56 gears and cruising at 65 I would be at 2298 and at 70 I would be at 2682 rpm. Now I have no problems not using the final gear unless I'm on the flats driving. My worry is my spacing between gears is too much for the 427 though it's a torque monster for what it is and it struggling to get to speeds. The difference between my next option 4:88 is minimal. The 5:29s I've pretty much talked myself out of because of the top speed of 72.

Pvmt-Pndr, do you think the engine is running ok?, I drove a lot of 366 and 427's in city beer delivery, our single axle tractor/ trailer combo's were 32000 -48000 lb. plates and had no problem with that weight and getting it rolling, even on the big road we could go 65 - 70mph. This was back in the 1970's and 80's so they were all Holley 4bbl. carbs. it wasn't until the late 80's that we changed over to diesel. I have no clue what the axle ratio was but tranny's were 5spd with 2 spd rears.

I'm not 100% convinced it's in top notch shape currently. I only have 1 four hour ride in it to get it home. Once the weather warmed up I pulled the trans, rebuilt the clutch, reaurfaced the flywheel, replaced the starter ring gear and have driven it a total of about 2 miles since all of the work has been done. I found there was never a new wire run to the hei distributor, so I ran one, it was getting 9V and now 12 volts. I set the timing, replaced the springs and weights in the distributor, pulled the useless exhaust off, exhaust manifolds were upgraded to a set of block huggers headers, new plugs and wires gapped to .045. All that was done at the same time and I've driven it roughly 2 miles since I did all of that. I've yet to replace the exhaust past the headers. All of those things made it a completely different truck to drive. Just the other day I was under the hood and noticed that I have a bad gasket on the carb allowing gas to spray just a little onto the intake manifold. Hence the reason for getting a different non governed 650 carb. I can pull the carb off of my wife's truck just to see what kind of difference it would make. Her truck has a 366TD in it but it's an apples to oranges comparison and I honestly don't know what size carb she has on hers. All I know for sure is it's an edelbrock for now. I could just rebuild mine but what's the fun in that.

I plan to do a leak down test on it when I have time to just to see what kind of shape it's in. It pulls it's own weight quite well in the lower rpms, the higher rpms it does it too but not nearly as happily as riding the torque of the engine down low. Since this is my first medium duty I don't know exactly what to expect with it loaded down with the weight I plan on hauling or how much I'll be able to tell the load is back there. What I've read a lot of is that they usually don't change a lot between empty or loaded as far as getting up to speed.

Currently it also needs tires and it's still on the stock 20" rims with tires that make me cringe and wonder how I made the 4 hour ride home so the last thing I want to do is load it up and take it for a spin. 22.5" rims and tires are in the works. Since they're easy to come by I figured I'd look for personal experience and opinions on how it should react to that kind of weight with a different gear set.

I guess put as simply as possible could someone tell me if the 427 prefers to be wound out to 3200 or should it prefer what I have said being down low in the rpms? If it prefers to be wound out to get up to and maintain speed I'll go with the 5:29s. If down low then I'll get the 4:56/4:88 and call it good.

Thanks for all the input fellas

Well back in my beer delivery days we would pretty much run the higher gears up to the governor, if your thinking about 900R - 22.5 tires then I would go with the 5:29 axle, I wish I could tell you what axles we had. As a comparison, in the OTR trucks we ran back and forth to Columbus in, we had anywhere from 307hp to 350 hp, 9, 10, and 13 speed trannies. We were maxed out at 80,000 lbs on the haul north, 3.90:1 twin screws, but of course with diesel that made their torque at 1700 - 1900 RPM, with the governor at about 2100. The 350 Cummins with a 9 speed hardly new it had a load.

The earliest year 427 I've got HP/torque info on is 1974. That year it was rated at 230 HP @ 4000 RPM, and 360 Ft/Lbs of torque @ 2000. They started dropping the numbers in 75, and by 81, some of them were down to 195 HP and 340 ft/lbs.

I'd suggest using the 4.88 gears and shifting at 3500-3800 RPM, wherever the shift puts you at or neat the torque peak in the next higher gear. Obviously, you'll need to do some tinkering with the governor to get it to wind up that much.
Jerry

I've been leaning toward the 4:88s and back to the 5:29s. I'm torn on them. The 5:29 is the gear set for a good price. The 4:88 is the whole 3rd member for a lot more. I haven't been able to find a definite answer on what the power is in this truck but I know it has a ton of torque compared to its up.

Thank you guys for all the info. Tires I'm planning on 295/75R22.5 low profile or a very similar size. Since I have an HEI distributor and plan to swap the carb shifting her that high shouldn't be a problem. It's going to take some driving around empty to figure out what makes her happy. I have a handful of things to do to her before I put a plate on it and drive it down the road though.

As dumb as I may sound I've been on YouTube a lot looking at videos of guys driving down the road in these old trucks, looking at their engines/trans/rear ends and I'm fairly confident with the opinions I've gathered that I should be best off with the 4:88s as a happy medium. I plan to have this truck for a very long time so if I happen to over gear it I'll just have to add more power to it. Weather it be an engine swap or something else creative. I've come across an 8.1L vortec complete with harness, all sensors and an automatic transmission for $1800 (I wouldn't use the trans).

Buckshot... that sounds like it was a good time cruising all over the place! I can't wait until mine is all set and ready to go! I'll probably get me a new saddle tank this week if I get time so I can go further then 50 miles on a tank.

I think I saw a Craigslist add for some tanks in Belleville.

The hotrodders like the tall deck 366's and 427's as base blocks for some incredibly high RPM engines, but they're going for an entirely different set of parameters than trucking. The basic blocks, crankshafts, and heads will handle much higher RPM and horsepower than a big rig will ever see, so you've got lots of room to play in where performance is concerned. The dirt track where I raced in California back in the late 1970's had a 375 cubic inch size limit on engines, so one guy built up a 366 truck engine with a slight overbore to hit the max displacement right on the nose. When he could get the tires hooked up coming out of the turns, he was hard to beat. That engine was a torque monster!
Jerry

I found a great deal on a saddle tank right down the road from me, $40 with brackets and everything else.

I haven't heard of anyone building a 366 until now. The 427 on the other hand can be made into a beast but I have no interest in building my motor at all. Cost wise it makes more sense to do a motor swap. I've priced out a stroker kit and a rough price on the tip end, it makes no sense for what I intend to use the truck for.