Gear Vendors vs 4L60E

I did write 500 + less RPM than the 3,000 he said he is cruising at now. I agree you don't need to be in the max torque RPM range when cruising as long as the engine is still in its power curve. When cruising the car may only need to produce less than 100 HP that even includes running accessories to keep it moving down a flat road.

A 401 NH should be able to make enough power in the lower RPM range now that I know where the peak is probably can handle 1800 RPM to cruise at 70. With peak torque around 2800 the engine is probably making enough power right off of idle for driving in O/D at lower speeds as well.

To bad you can't(or if you could the cost would be prohibitive) bolt a gear vendors unit behind a gear vendors unit to overdrive the overdrive! Then you could run a 5 something rear gear and have a final drive in the 2s! LOL

Or get an overdrive trans and the gear vendors unit and run both!

Man I really need to get my '64 Skylark out of storage, together and start driving it so I know how that 401 wants to run!(the old time and money scenario!)


Derek

 

I totally agree with yah. I was just looking at what i thought the best set up is for the money. The trannies you listed are all over $2k if not close to $3k requiring mods he may not even be capable of doing. I myself can do just about anything to a car but am limited by time and like to keep my car on a cheap budget so i am opting to rebuild my 400 tranny fairly aggressive and then start looking for another GV unit. The used units are out there to be had if one is patient. Like i mentioned i missed one that was on a TH400 in a 2X4 truck. I know of another fella around my area who found one off a Dodge tranny with no wiring for $750. All he did was buy the correct adapter and wired it to a toggle switch and loves it. All in what the OP can afford, his abilities and budget.

 

i was going to mention a used unit can be found pretty cheap. i see some on ebay alot. i saw one from a C30 truck for about a grand a while back. the adapter is so high is the big issue with other trans. you guys with built sp400 gv is the way to go. now if your going have to rebuild the 400 anyhow then step up od gm trans is a better idea i would think.

 

I realize my comments are late in the game on this thread. Seems like you have your heart set on a GV. Go for it.
Keep your project fun and happy.
If you are only seeing 10 mpg's now, dropping the rpms a bit isn't going to magically make it that much better.
There's a much bigger return considering aerodynamics and tuning. One of these is more adjustable than the other
Your best time spent right now is in your distributor, if not already tweaked.
Please realize you can only do so much with a truck.
I would recommend a rear gear change over anything else.

Good guess on using a full throttle dyno run torque curve to ascertain best rpms to cruise at, but no.
The full throttle loading is at a higher rpm than your target cruise speeds.
Too bad there isn't an easy way to hold a standard for part throttle torque curves, that would tell you way more.

So far there are fantastic responses regarding fitment, cost, mechanical feasibility, even the concept of calculating what the real savings are over long periods of time.
It is an excellent assumption to believe that 500 rpms lower might improve things (thanks Derek).
It is also a good idea to copy someone else's combination and adapt it to your project best you can.
Nailheads do better than others at low rpms because of things like mixture motion and port velocity. It's why the ignition advance curve is different.

An easy strategy for mileage with large cubic inch engines regarding OD and low rpms is to road test with a vacuum gauge.
You will find after doing this for hundreds of thousands of miles that the lowest rpms you can cruise at (and maintain mileage) is a few hundred above where the cam wakes up.
[Assuming there's enough torque at light throttle to maintain speed without undue throttling, otherwise you will have to use slightly higher rpms or more cubic inches]
You also will notice the vacuum gauge jump way up when it does.
What you are looking for is the lowest rpms you can see the highest vacuum at.
This might be a lower rpm than your torque converter. It may be 3000 rpms if you have enough cam.
If you have a well tuned combo, you might see respectable mileage maintained through higher rpms (as a result of faster road speeds) as you are spending less time operating the engine (@60 hp or whatever).
As long as you have enough torque at minimal throttle, real low rpms will work [This comment is more directed at the idea of using double OD's or really low gears]

It is a waste of $$ to have your carbs tuned professionally before having your ignition curve tuned.
You can guess aggressively and make minor adjustments, this will allow your carbs to be tuned in close enough, if that fits your timeline.
The only way you are really going to hone in is with plenty of road testing, using the same vacuum gauge as you track mileage and carefully watch for part throttle detonation.

Maybe work on tuning your combo and tracking mileage if possible while you consider the options presented in this thread and keep your eyes peeled for used GV's, etc.
Even though I'm steering you away from your assumptions, I hope this helps