Overdrive options?
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Senior User
Joined: Dec 2007
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Overdrive options?
Hi,
I'm wondering a bit.
I'm busy with my 400 in my lincoln, on wich i plan to do a lot of highway miles.
Now, if i rebuild it with a huge amount of torque, ain't it a good idea to change the final gears?
Now, i'm running approx. 2100Rpm highway drive at 60 miles.
If i change that to, lets say, 1700Rpm at 70 miles, would that be an huge MPG increase? Or would it just use more fuel at the 1700RPM's?
Anyone giving some (expirienced?) info always appreciated, as it helps me to decide on how to build my 400..
thanks.
I'm wondering a bit.
I'm busy with my 400 in my lincoln, on wich i plan to do a lot of highway miles.
Now, if i rebuild it with a huge amount of torque, ain't it a good idea to change the final gears?
Now, i'm running approx. 2100Rpm highway drive at 60 miles.
If i change that to, lets say, 1700Rpm at 70 miles, would that be an huge MPG increase? Or would it just use more fuel at the 1700RPM's?
Anyone giving some (expirienced?) info always appreciated, as it helps me to decide on how to build my 400..
thanks.
Posting Guru
Joined: Jul 2007
Posts: 1,355
Likes: 1
hmmm you must be refering to rear gears on your differencial,
Im not that knolegdable in this area, but in what i understand, if you change to that kind of gears you will suffer alot in performance, i mean if you diff is stock the you must have something around 2.50 gears (crap), To change to 1700 rpm at 70 miles you will need higher gears, something like 2.25.
People around here even with huge torque engines prefer lower gears and change their originas with 3.50s or even higher making their engine rev faster giving them better acceleration.....
I have 3.00 gears and im planning to go 3.50 or 3.75 in my car with my 400...
anyone correct me if im wrong, thats what ive understanted so farr.
my opinion..
Im not that knolegdable in this area, but in what i understand, if you change to that kind of gears you will suffer alot in performance, i mean if you diff is stock the you must have something around 2.50 gears (crap), To change to 1700 rpm at 70 miles you will need higher gears, something like 2.25.
People around here even with huge torque engines prefer lower gears and change their originas with 3.50s or even higher making their engine rev faster giving them better acceleration.....
I have 3.00 gears and im planning to go 3.50 or 3.75 in my car with my 400...
anyone correct me if im wrong, thats what ive understanted so farr.
my opinion..
Thread Starter
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Senior User
Joined: Dec 2007
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ok, no problem, but can it get the same or rather better economy then when revving higher?
i mean: it seems to me, that the engine consumes more fuel at, lets say, 3000Rpm as it does with 2100Rpm...
If not, i'd change gears indeed to the opposite in order to be (a lot!) quicker!)
i mean: it seems to me, that the engine consumes more fuel at, lets say, 3000Rpm as it does with 2100Rpm...
If not, i'd change gears indeed to the opposite in order to be (a lot!) quicker!)
Posting Guru
Joined: Jul 2007
Posts: 1,355
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Actually your are right about fuel consuption, you will loose a bit of your milliage running lower gears but those stock gears are really not worth having with a mild performance 400, and besides the lose in gas/milliage aint that significant....
Junior User
Joined: Jul 2007
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When you select a cam you need to identify the range (RPM) the cam is designed for. Then match your torque converter to that range. Then match your gear set & tire size. If your motor is built to be in the power band at 1700 rpm then it might not have very good power at higher RPM for passing or accelleration.
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Senior User
Joined: Dec 2007
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well, everything i did on the engine started with enhancing the gas/milage in the first place, so i really have to keep that in mind. Prices are going up and up of the gas, and they reach a price that it ain't funny enymore to drive such a boat as a daily...
So, in order to be able to keep it, i have to increase overall performance, accompanying with the MPG figure...
So, it IS important, actually...
So, in order to be able to keep it, i have to increase overall performance, accompanying with the MPG figure...
So, it IS important, actually...
Laughing Gas
Joined: Jul 2002
Posts: 843
Likes: 1
From: USA
I'll get to work on the header measurements for you Stef. With the long wheel base of the Lincoln you might consider something like the Gearvendor overdrive unit. (Gearvendors.com) That way you could enjoy the bottom end torque of your motor and still get the low final drive ratio you're looking for milage.
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Thread Starter
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Senior User
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i know them, but they are about $3k or so..?
i could do a full rebuild for it.
They definately are very nice though.
A nice used one to reduce $$ would be great, but i think quite hard to find...
thanks.
i could do a full rebuild for it
.They definately are very nice though.
A nice used one to reduce $$ would be great, but i think quite hard to find...
thanks.
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Tuned
Joined: Jul 2003
Posts: 455
Likes: 3
From: Berkeley
if you're already running 2.1k at 60mph, you don't want an overdrive. you might want an UNDERDRIVE to raise that final drive ratio for better off-the-line performance, or replace your differential with a higher drive (eg: 3.50 or 3.73 or 4.10) AND THEN add an overdrive to get you back down to 3.00 or 2.75 for economical (relatively speaking) cruising. That's all big $$, and might get you better acceleration, but will be unlikely to get you better economy.
In a truck, that came with 3.73 or 4.10 stock final drive, an overdrive could help. My van, for example turns ~3000 rpm @ 68mph with 3.73 and stock tires (~29"). An overdrive could bring that cruise RPM down to 2200-2400 rpm, which MIGHT result in better cruise economy. Then again, it might not make much difference, as these motors tend to have pretty flat torque curve in that range. I'm tempted to do it anyways, just to lower cabin noise on the freeway, and i have a NOS American Overdrive unit sitting in the garage...
In a truck, that came with 3.73 or 4.10 stock final drive, an overdrive could help. My van, for example turns ~3000 rpm @ 68mph with 3.73 and stock tires (~29"). An overdrive could bring that cruise RPM down to 2200-2400 rpm, which MIGHT result in better cruise economy. Then again, it might not make much difference, as these motors tend to have pretty flat torque curve in that range. I'm tempted to do it anyways, just to lower cabin noise on the freeway, and i have a NOS American Overdrive unit sitting in the garage...
Cargo Master
Joined: Apr 2001
Posts: 2,364
Likes: 3
From: Eustis FL
All it takes is a matched ring and pinion set... But setting it up can be tricky with the right crush to get a good wear pattern between gears. Might want to leave that to the pros. Auburn gear has sets available, though they are pricey. Best bet is to find a junkyard set of gears. Might get lucky and find an axle housing that is the same dimensions and perch location with the gears you want so you can bolt it in and go, but for that car, you might be scrounging...