bowtieboy

Hey guys still enjoying the wave! Had a few questions and you have always helped so here is another one.What do i have to change ;crossmember etc. in order to install a 700-R4 in my 77. I drove it to Atlanta a couple of weeks ago and it nearly killed me on gas! I don`t get to drop in on the forum much due to work,family etc. but i do enjoy talking to other members when posssible again Thanks.

wombvette

If the 77 is already an automatic, you will have it easy. You may have to make a mount for it, but not much problem. If is is a straight drive, there will be a few more considerations. You will have to supply a Joke and a cut down drive shaft.

Larry B.

If you reason for installing a 700R4 is for milage, you will gain a little but not as much as you may expect. The later model vettes do get very good gas milage but most of that is due to computerized managment of fuel, timing, and other parameters including head design. The TH 700R4 is not as trouble free as the old 400's and 350's. Running in OD at low speeds kills them ...FAST.

page62

I agree with Silvervetteman that low-speed OD driving will kill the tranny real quick. I lock out my 4th gear until I get on the freeway. When I get off, it's back down to 3rd. It's become second nature to me -- no big deal. Just do it!

I disagree with the part about not getting improved gas mileage. I've seen close to 40% improvement in gas mileage on the highway! Before, I couldn't even pass a gas station without having to fill up. Now, it's like driving a modern vehicle. And the screaming high rpms and engine heat are a thing of the past!

If you have a TH350, consider replacing it with a well-built 200-R4. It's lighter, uses the stock crossmember, and the driveshaft doesn't need cutting.

I have NO regrets about installing this tranny. My only regret is that I picked a bunch of turkeys to install it. Find a good tranny shop that charges a fair price. Shop around -- they're out there!


[Modified by page62, 5:55 PM 1/26/2003]

Metal Wulf

http://www.bowtieoverdrives.com/

Larry B.

I would think alot would have to do with the rear ratio that you start with. There is an RPM point at which milage will get real bad. I've seen conversions that helped very little. A lugged engine won't get good milage. Engines have a "sweet" spot where they are most efficient. I had a 92 with 3.07 rear that got the exact same milage in 3rd gear as in 4th (OD) at 70mph according to the onboard computer. I noticed only .5mpg gain at 78mph. High school physics... "x" amount of energy to the same amount of work. ;)

page62

Ahhhh...that has a lot to do with it! My '79 has a 3.55 rear end. At 70+ mph the engine turns 3200+ rpm with a non-OD tranny.

Most of the late-70's Vettes had higher-ratio rear gears to compensate for the lack of horsepower. Not to mention the 55 mph national speed limit. When I was a teenager back then, I remember driving from Ontario to Florida on I-75 -- at 59 mph!

UKPaul

The standard rear ratio on an '81 Auto is 2.87. I'll soon be fitting an O/D trans (200-4r) in the hope of getting better economy amounst other things. From previous experience in doing this type of mod, I didn't notice any change in fuel consumtion at the original cruise speed (as mentioned above). But what I did notice was that I had a higher cruise speed with good fuel economy at that speed. As my '81 was getting low 20's cruising at 65 -70mph, I'm hoping to get the same sort of figures, if not better, when cruising at 80 - 85mph. I'll let you know :)
Two strangers were seated next to each other on the plane when the
guy turned to the beautiful blond bimbo and made his move by saying, "Let's talk. I've heard that flights will go quicker if you strike up a conversation with your fellow passenger."
The blond, who had just opened her book, closed it slowly, and said
to the guy, "What would you like to discuss?"
"Oh, I don't know. How about nuclear power?"
"OK," said the blond. "That could be an Interesting topic. But let me
ask you a question first.
"A horse, a cow, and a deer all eat grass. The same stuff. Yet a deer
excretes little pellets, while a cow turns out a flat patty, and a
horse produces clumps of dried grass. Why do you suppose that is?"
"Oh brother," said the guy. "I have no idea."
"Well, then," said the blond, "How is it that you feel qualified to discuss nuclear power when you don't know poopie?"

Sorry, couldn't resist it :D
:cheers:

page62

:lolg: :lolg: :lolg: :lolg: :lolg: :lolg:

But seriously folks...

Paul, when you get that OD in there, the next thing you're going to want is a 3.55 rear end! With 3.55 gears, I don't even engage OD until about 65 mph. At 80+ mph, I'm just starting to see 2500 rpm...

Hey, I can spend OPM (other people's money) in a heartbeat!

UKPaul

Page,
The plan is, after fitting the OD trans, to fit AFR heads (not sure if 180 or 190 would be best). Then, having more power, I won't need to reduce the gear ratio, especially with the lower 1st ratio of the 200-4r. Does that sound sensible, or is there a serious flaw in my plan (plus I'll be spending even more of my money than you just have :lol: ). The heads will also raise the CR a bit, so hopefully it'll also change the exhaust note at idle from blop-blop-blop to more of a blat-blat-blat :D
:cheers:

page62

It's not necessarily a question of power. It's more about how well your engine runs below 2000 rpm. In my case, the L82 engine sacrifices a certain amount of low-end smoothness for high-rpm get-up-and-go! Also, I would speculate that carburetors are not as good as fuel injection at low rpm. After all, carbs simply dump fuel and air down a big hole. FI systems meter all that stuff precisely.

Modern engines (and engine management systems) mean that an engine can cruise more efficiently at low rpm. For example, I was riding shotgun in a C5 the other day, plodding along at 1100-1300 rpm. Put the foot down and the engine responds nicely without downshifting -- the result of a broad, flat power curve.

UKPaul

The cam I've fitted in the Vette gives a nice flat torque curve, without being too peaky. I chose it partly due to being computer friendly & partly due to the flat torque curve (I like engines with large, flat torque curves & aren't really worried about HP figures - that's just a side effect of the torque). It lost a bit low down, but fitting a Hypertech chip greatly improved the low end response. I'm fitting a 2200 stall & am hoping that more efficient heads & higher CR will give a bit more low down grunt. If not, then I'll be looking for new rear gears - which may not be fun as the '81 rear is probably hard to find here (most people think Dana is an old hippy singer!).
:cheers: