Which OD automatic is least trouble to install?
Thread Starter
Staging Lane
Joined: Jan 2011
Posts: 90
Likes: 0
From: Illinois
Which OD automatic is least trouble to install? Installing a stock LM7 5.3 into a 1970 Chevelle 307 inch SBC, TH350 and 2.73 rear gears.
I never figured out what overdrive transmission would be best, so I stopped working on it.
I would like overdrive, I need help. I want to get the car on the road this Summer. I want good gas mileage. Rear gear change is not in the budget. I spend little time on the Interstate.
The only reasons for keeping the TH350 is: (1) to limit the scope of the project and (2) use my original speedometer without any changes.
With the TH350, 26 inch tall 225/70-14 tires and the 2.73 gear I calculate 2293rpm at 65mph. Is that BAD for my engine?
Seems 2000rpm will get best gas mileage with carbureted engines, "lowest possible" rpm is best for EFI engines. Is 1500 or 1600rpm a little TOO low considering the weight and aerodynamics of a 1970 Chevelle?
The .7 overdrive of a 700R4 and 4L60 with my tires and gears indicate 1605rpm at 65mph.
The .67 overdrive of a 200-4R with my tires and gears drops engine to 1536rpm at 65mph.
The 200-4R is easiest to install, it is the same length as the TH350, others are longer.
Question 1: Which overdrive transmission is least complicated install: 200-4R, 700R4 or 4L60?
Question 2: From what vehicles (car or truck) and what Years transmissions is best for a totally street use car? Earlier transmissions do not have Pulse width modulation.
Question 3: Which is better to use the 4l60e with a cable speedo: (1) the cable-x box or (2) the swap kit that Street&Performance sells which allows use of a 700r4 cable driven tailshaft on a 4l60e?
Question 4: Would a camshaft change solve this gas mileage quest, and keep the TH350?
Thank you for your help on this, Summer is here early...:-)
I never figured out what overdrive transmission would be best, so I stopped working on it.
I would like overdrive, I need help. I want to get the car on the road this Summer. I want good gas mileage. Rear gear change is not in the budget. I spend little time on the Interstate.
The only reasons for keeping the TH350 is: (1) to limit the scope of the project and (2) use my original speedometer without any changes.
With the TH350, 26 inch tall 225/70-14 tires and the 2.73 gear I calculate 2293rpm at 65mph. Is that BAD for my engine?
Seems 2000rpm will get best gas mileage with carbureted engines, "lowest possible" rpm is best for EFI engines. Is 1500 or 1600rpm a little TOO low considering the weight and aerodynamics of a 1970 Chevelle?
The .7 overdrive of a 700R4 and 4L60 with my tires and gears indicate 1605rpm at 65mph.
The .67 overdrive of a 200-4R with my tires and gears drops engine to 1536rpm at 65mph.
The 200-4R is easiest to install, it is the same length as the TH350, others are longer.
Question 1: Which overdrive transmission is least complicated install: 200-4R, 700R4 or 4L60?
Question 2: From what vehicles (car or truck) and what Years transmissions is best for a totally street use car? Earlier transmissions do not have Pulse width modulation.
Question 3: Which is better to use the 4l60e with a cable speedo: (1) the cable-x box or (2) the swap kit that Street&Performance sells which allows use of a 700r4 cable driven tailshaft on a 4l60e?
Question 4: Would a camshaft change solve this gas mileage quest, and keep the TH350?
Thank you for your help on this, Summer is here early...:-)
TECH Fanatic
Joined: Oct 2011
Posts: 1,356
Likes: 2
From: Felton Pa
I had a 700r4 with a manual valve body so I didn't need to hook up the TV cable. Works great and loved the way it drove and at 80mph I was truning 2600rmp. Same as my LT1 Camaro. It has gear driven speedo and Hydraulic overdrive. I ran a toggle to the lockup converter. The only problem was it wasn't reliable behind a 454. About every six months I had to pull it out and fix it. I put 4.8 in it broke on the first test drive so I fixed it and it lasted a week. Not the old 350 is back in. Looking for a 4l80e and will put the wires back in my harness and send the stock speedo out to have it converted to electronic.
Thread Starter
Staging Lane
Joined: Jan 2011
Posts: 90
Likes: 0
From: Illinois
I am encouraged to restart the project.
An overdrive trans is still in the future if I can not find some magic camshaft for gas mileage at 2300 RPM.
1.) Do I have to change rear axle ratio to have a overdrive work well?
Rear gear change is not in the budget this year.
2.) Which transmission is the easiest install in a 1970 Chevelle behind a LM7?
a.) 200-4R
b.) 700R4
c.) 4L60
An overdrive trans is still in the future if I can not find some magic camshaft for gas mileage at 2300 RPM.
1.) Do I have to change rear axle ratio to have a overdrive work well?
Rear gear change is not in the budget this year.
2.) Which transmission is the easiest install in a 1970 Chevelle behind a LM7?
a.) 200-4R
b.) 700R4
c.) 4L60
It looks like cost and mpg is a major concern. That was true in my swap too (72 442, 5.3, 2.73 rear). I went with a 4 speed, because it came with the car, and I enjoy driving a stick.
With a 2.73 rear, you could get by without an OD trans. Just for comparison my old camaro had 2.73 rear and a 700R4. Driving with OD on saved about 10% in gas on the highway. The chevelle is bigger and less aerodynamic, so an OD trans might feel a little anemic with that rear.
If you go with a trans other than the 4L60 that comes with the LM7 makes it difficult to upgrade to the electronic trans later.
My suggestion would be get the LM7 with 4L60e and drop that in. See how it fits your driving. If you're not happy with it, keep your eyes open for a different complete rear end on craigslist. I see them fairly often pretty cheap.
As for gauges, just upgrade to new electric, it's the easiest solution. Or possibly swap faces on an electric guage that has the same sweep (I did this on a corvette tach)
With a 2.73 rear, you could get by without an OD trans. Just for comparison my old camaro had 2.73 rear and a 700R4. Driving with OD on saved about 10% in gas on the highway. The chevelle is bigger and less aerodynamic, so an OD trans might feel a little anemic with that rear.
If you go with a trans other than the 4L60 that comes with the LM7 makes it difficult to upgrade to the electronic trans later.
My suggestion would be get the LM7 with 4L60e and drop that in. See how it fits your driving. If you're not happy with it, keep your eyes open for a different complete rear end on craigslist. I see them fairly often pretty cheap.
As for gauges, just upgrade to new electric, it's the easiest solution. Or possibly swap faces on an electric guage that has the same sweep (I did this on a corvette tach)
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The desire for OD is understandable and I switched out my 350 for it as well, but at some point you have to consider that in this case you're throwing dollars away to save dimes. If you are not changing gears then there is no reason to go OD, and if you have no budget for gears then it might be worth consdering that for a 200 (and maybe 700 as well) to work you have to get it rebuilt with better internals, get the flexplate and tv cable stuff or the manual valve body, the shiftworks kit and maybe a new driveshaft, and all of those things cost money. If you are spending little time on the interstate this entire endeavor would basically be for nothing, and if you go into OD with those gears at non-interstate speeds the car will be a dog. I had 2.73s for a while and it sucked ********.
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The biggest gain is going to be the better 1st gear that comes in the od trans. W the 273 the car will lug at cruising speed. Even my new silverado doesn't do all that great with the 308 rear you can feel it struggle in od at 55.
I had a truck with a 700 swap and the tv cable was easy to setup and I'm doing the 700 in my coupe. We have a 72 w a crate 350 and the 700 and it's nice on the highway with 308 rear.
I had a truck with a 700 swap and the tv cable was easy to setup and I'm doing the 700 in my coupe. We have a 72 w a crate 350 and the 700 and it's nice on the highway with 308 rear.
TECH Fanatic
Joined: May 2010
Posts: 1,081
Likes: 8
From: Atlanta, Ga
Ditto on the deeper first gear. The big question to ask yourself is where you live with the car. Is it in town driving 90% of the time or on the open road 90% of the time. In my opinion building for the majority of driving makes more sense. I also agree that you can find non posi complete rear ends readily for short money.
As I say, this is just my opinion, and they are cheap and plentiful.
As I say, this is just my opinion, and they are cheap and plentiful.
