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Transmission ideas to get engine speed down


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I read with interest the posting below about swapping in a overdrive transmission. While driving home with our newly purchased '70 avanti yesterday, I was bothered by the engine speed. 2500 rpm @ 55mph. (350 engine automatic trans, new 205/70 tires). I'd sure like to get those rpms down before taking the car on long trips.

I've read that many like the 200R GM transmission. Which model car contains the best version for our cars (in other words, where's the best place to go looking for one)? Will it have a mechanical speedo drive to work with our speedometers?

thanks,

Mike S

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RQB3263...My 81 with a 305 runs 1750 at 70 mph....i installed a 700r4 w a lock-up converter about a year ago....this process was detailed here in the forum somewhere....and obviously works well for me..I also have 205 tires.....BUT.... my rear end ratio is 2.78 as per the original tag on the rear coverplate....this makes as much difference as transmission..it sounds like in your case you may need both...any good trans shop can build you a 700 or every hot rod mag offers complete kits guaranteed...but chk the rear gear ratio first ....good luck....RQB3263

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What are you willing to spend? Going to a rebuilt tranny with all the other changes necessary could go $3000 or so. For that money either the 200 or 700 are in play. 700 is longer and has a lower first gear as it was used to get heavy cars/trucks rolling. 200 was for smaller cars and is somewhat shorter than the 700 and a higher first gear. Avanti came with both so the choice is yours. My 83 has a built 200 but it had a 700 from the factory.

If you want to keep costs down, it would be a lot easier to find 700 in decent shape in a wrecking yard. The 700 also called a 4L60 later but about 92 they changed to 4L60E which had shifting controlled by the ECM. You can use any 700 except the E for your use. The later electric speedo can be converted to mechanical with OEM parts for about $100 or so. You also need to redo the tranny mount, shorten the drive shaft, add a TV cable to control shifting and add a way to lockup the converter if you don't use a special converter. You will also need to add cooling for the tranny if you car doesn't have it.

Shifter is different as is the quadrant. It's a nice upgrade but don't go in with your eyes closed. If you can't do it yourself which will keep costs down, either find a local mechanic familiar with chevy tranny exchange or go to Bowtietransmissions for a kit to add an overdrive tranny to something like a Camaro or Monte Carlo.

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I agree with wildfeir that the rear end ratio should be determined before you do anything else.....Many Avanti owners didn't like the 'high' rear ratio from the factory and had 'lower' (higher numerically) gears installed.

Good for off the line but lousy on the highway!

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Ya, I plan to check the ratio in the axle after work tonight (after mowing). Art couldn't remember but thought it was in the 3:55 range.

I do all my own work. I have my own machine shop & metal fab tools, so no worries regarding experience or effort on doing the work. I also am experienced in working on automatic transmissions, so not too worried about that either.....I'm just not experienced with the newer versions of trannys & need to catch up. If I know which vehicles the 200R's were installed in, I could start searching for one & that way I can get all the "extra bits" (brackets, cables, clips, etc) along with the tranny when we pull it from the vehicle.

thanks for the help,

Mike S

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RQB3263...A non "E" 700 is the way to go...plentiful and strong....Ive used them in 3 hot rods ive built recently ..(in the last 15 yrs)..I have one i adapted to a 461 ci V-12 flat head and its working perfect...BTW...I had to lengthen my drive shaft about an inch..(complete retube w new universals)...My complete swat was about $2000 w trans cooler...there may be a little metal tag on rear gear cover plate with factory ratio stamped on it .KEEP UP THE GOOD WORK

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RQB3263...Wildfelr@copper.net...I can text to your smart phone pics of fabed trans mount mod req for 700r4... easily....if you want them (2) let me know 386-466-6434C....BILL

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I would be interested in seeing your pics, but we're still in the "dumb phone" phase of our lives. If you can email them, my address is miso7@wabash.net.

BTW, where do you guys mount tranny coolers? I would think (hot) air management is an important consideration with these cars.

thanks,

Mike S

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I would be interested in seeing your pics, but we're still in the "dumb phone" phase of our lives. If you can email them, my address is miso7@wabash.net.

BTW, where do you guys mount tranny coolers? I would think (hot) air management is an important consideration with these cars.

thanks,

Mike S

Scrolling down this post a few comments will give you the complete list of 200 installs.

http://67-72chevytrucks.com/vboard/showthread.php?t=426846

Don't throw out the 700.4l60's as Bill suggested. There are a lot more of them, they came in more cars and trucks and in much newer models. As I said, I have a 2004R in my 83 built to stage II specs with a 4:10 rearend and it's fine. But remember the 700 was the standard install for large cars and 1/2 ton trucks with rear gears up to at least 3:73. My 54K has a 700 with a 3:42 posi that was standard issue in the 9C1 police special Caprices of the early/mid 90's.

It's irrelevant to me what you install but I want you to be aware of the options available to you. Being you have the ability to install them I saw a great piece of advice in the SDC forum on finding a tranny. One member said he cruised the Pick n pulls until he saw a clean tranny in an old car which indicated it was probably a newer rebuild or install. A good used tranny should keep your install costs under $1000 and well worth the investment. Even if you pull a complete install from a car, Google TV cable adjustment to be sure it's correct. A bad adjustment will burn one up muy Pronto.

You can do the lock up by supplying a switched 12V source to the converter and energizing the lock up on Highway cruises. You'll remember to turn it off as you slow down to exit the expressway. I did that on my 200.

In the 700, OEM parts will let you go to a mechanical speedo drive for about $100 or less. I'm not sure that's an option in the 200. Google will be your friend there.

I added a Derale tranny cooler in front of the radiator, it's probably 9 X 12" or so.

Lastly, if you need a few shots of my install, the Avanti is currently on the hoist.

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RQB3263...Sounds like someone misread or misinterpreted my post.....or maybe i wasnt clear enough..The mid80s 700 is what you need to install.......there is no rocket science to the TV cable hookup ...there is plenty info on web....however if you get it wrong (almost impossible) you will burn up #3 bands very quickly...but its not a big deal to get it right....and after you burn one up like me you wont do it wrong again...Crate trans kits will have directions supplied....Ive used the aluminum tubular trans coolers in 3 cars w good success...they come in various different lengths.and impart no heat into your radiator...cheap and easy...

The trans mount used the original rubber mount (buy a new one) and the original frame crossmember removed and cut down and bolted to the !/4 inch plate i sent in pics that is then bolted to the x-member....easy deal no welding....WRG RQB3263

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RQB3263 BILL wildfelr@copper.net........is someone will send me there email address i will fwd the 4 pics of the trans mount and cooler installation that you can upload to forum....if it will help......thats above my pay grade....BILL

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thanks for all the advice. I'll start snooping around to see what's out there in my area. A guy at work races a buick grand national & keeps up with where all the rear wheel drive stuff hides these days. I like the idea of making the fewest "changes" from stock as possible. That's why the 200 sounded better, but being a typical caso, what ever bargain I come across will influence the direction..... I've got a spare drive shaft, so I'll be able to keep the original in it's original form.

Mike Sal

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thanks for all the advice. I'll start snooping around to see what's out there in my area. A guy at work races a buick grand national & keeps up with where all the rear wheel drive stuff hides these days. I like the idea of making the fewest "changes" from stock as possible. That's why the 200 sounded better, but being a typical caso, what ever bargain I come across will influence the direction..... I've got a spare drive shaft, so I'll be able to keep the original in it's original form.

Mike Sal

If he has a 200 from those, great tranny. Continue to be aware that both 200 and 700 were offered in the later 80-83 Avanti's so both should fit without any unreversible changes. You will need a shifter change or mod, tranny frame mount change and driveshaft (which you have discussed) with either. The tranny frame mount is about as easy a fab as you'll find in an Avanti. Also be sure the BOP engine mount configuration on the 200 also has the SBC setup to bolt it to the SBC block.

Note the rear mounting points and total installed length on each trans. I keep sounding like I'm humping the 700 which I'm not but the choice is more complicated than most posters seem to appreciate.

BTW, wildfelr does have a nice setup in his Avanti. Rode in it and it performs well.

tranny_dimensions.jpg

Good luck, you'll appreciate the change. Bob

Edited by Avanti83
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All great info. Talked briefly this morning with my racer co-worker & he's sure he has some spare 200 4R's in his pile of spare cores. He's going to look thru them this weekend for me.

thanks,

Mike S

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I wonder what the weight delta is between the 200 4R and the original stock unit. Unloading that spare transmission last weekend reminded me how heavy those BW units are....

Mike S

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The B-W PowerShift has a cast iron case while the 200- and 700-R4 have aluminum cases. There is a big difference in weight. While you're doing the conversion, you might consider getting an aluminum driveshaft. That will further reduce vehicle weight and reduce rotating mass resulting in better performance.

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Yes, I'm very familiar with the BW tranny & how heavy it is. I can still remember horsing one up into a '64 ford without the aid of a jack.....yes, young & dumb at the time.....now just dumb....

Looking around on the web, it appears the BW tranny is about 228 lbs & the 200 4r is around 150 lbs. The springs will have to love that!!!

Mike S

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