Diablozx9

Anyone else use a similar combo (350/290 crate + 700R4 + 2400 Stall in 81 vette) ?
what do you think ?

A friend/mechanic is installing this in my Vette now. The only question remaining is,, I dont know the Diff ratio (my speedo reades 20 percent over - i think it was lowered).

I will add my opinion once done (probably very soon). My history over last couple years:
- Blown original motor (original ? Headers, Edlebrok intake, Holley carb)
- couldnt afford decent engine,, used junk-yard Orange block l48.
- in didnt run very well,,
- TH350c transmission slipping

Ran into small amount of money sooooo Crate it is.

Please dont tell me how much better another engine would be,, I just want to know if anyone else has this engine, especially if its with this transmission, and what they think.

cv67

Without knowing the rear gear those parts will play nice togehter you oughta be real happy. those motors last a long time

Youll know if you want to regear when its on the road.

7T1vette

If you want your speedo to read reasonably well, you will have to swap out the speedo DRIVE gear that is mounted onto the transmission output shaft (in the 700R4) before installing it. You will need to know the rear gear ratio and the rear tire size, then use one of the speedo gear calculator programs that you can easily find [and use] on the web to determine the correct combination of DRIVE and DRIVEN speedo gear for your vehicle. The DRIVEN gear is easily accessible from the outside of the trans; but the DRIVE gear is internal. And, for the large change in rear gear ratio made to your car, BOTH will have to be changed. Easy to do with the tranny out...difficult once it is installed.

Reaper19

If it is the stock rear end it would be 2.87 for a stock automatic and 2.72 if it was a 4 speed manual. I did not make as many changes to mine as yours but changed the 2.87 to 3.07 matched with the factory TH350C and it woke the car up. Since you are going with the 700R4 you probably want to do some ratio calculations, but take your tire size into consideration. You can google "axle ratio calculator" and pick one or several to try.

Diablozx9

i think it is a stock rear ratio (axle ratio calculator helped).
makes me wonder why speedo reads 20% high.

looks like 700r4's 1st gear will liven up the car, and 4th gear will be near useless ?

MSGT-R

Overdrive is never "useless" if you travel long distances on the interstate.

RIO68

OD is great but with a rear less than 3.08 and under 300 hp engine it might be short on response but great on fuel mileage.

CA-Legal-Vette

My current motor isn't all that much different than yours. I have a 200 4R transmission which is similar to the 700R4. I think you'll love the combo. It'll have some pep off the line with the lower first gear and will cruise very nicely at highway speed.

As for getting the speedo correct, you will need to know the rear end ratio and the color of the drive gear inside the transmission. Just look inside the hole when you remove the speedo cable and the bullet shaped fitting where it attaches. Much easier to do before it's installed. If you can't do it, not to worry, you just may have to do a little more trial and error. I like the calculator on the Bowtie Overdrives web site. You can buy the new driven gears from them as well.

Diablozx9

thanks all..
two week delay,, transmission crossmember ordered.

Dodosmike

I'm gathering parts for a 700r4 swap in my '78.

Mind sharing your parts list?

BTO crossmember I read about, is the way to go.

Wiring kit? Source?

Shiftworks dentent kit?


Tips or tricks?
Ive searched a lot but just cant come up with a "list" or the thread morphs into a 200 vs 700 discussion, and to be honest, I cant see any advantage of one over another, other than the cutting the driveshaft issue.

Diablozx9

i had to stop doing my own work on the car after an injurry sustained on military duty to my back. I have a mechanic friend (GM dealership) who is doing everything. Sorry but i wont be much help.

Jegs was my friend for engine and transmission, and cable bracket.
Crossmemeber from bowtie overdrives
My mechanic friend is having the driveshaft shortened
leaving shifter factory,, i know i cant choose 1st gear.
Mine is an 81, lockup should be on car - no kit required - dont care about lockup enough to invest anyways

200 vs 700r4 will start an emotional back and forth. In my opinion,,
200 advantage - same size as TH350 and has overdrive
700 advantage - much lower first gear, slightly lower 2nd, and overdrive

BTW, my mechanic friend who has done many conversions from 2 and 3 speed transmissions to 4 speeds, really pushed me towards the 700r4.

MSGT-R

I too am taking the leap; I traded my TH400 today for a 700R4 swap into my 71. I just need a cross member, I'll be sourcing Ecklers for the shifter quadrant.

Thank you Diablo.

spikebot 81

I have the 2004r with the stock 2:87 rear gear. The 7004r is a little lower in 1st than the 200. I still have plans for 3:55 rear gear. Right now at 70mph with lock up engaged in 4th gear engine rpm is 1700. Very happy with the overdrive swap. The set up, as is will fry the tires from a dead stop so no real rush to change the rear gear at this time.

Diablozx9

Crossmember finally arrived.
my car may be finished this weekend.
i will give update

MSGT-R

Thanks.

Would you mind taking a close pic of the tailshaft housing and how it fits to the new crossmember? I have concerns about what the TH400 looked like, and this new housing. The bolt holes are 90 degrees different (fore and aft) to accommodate the C4 connecting member (like a Miata).

fishslayer143

Swapping the old TH350 for a 700r4 will be a nice improvement... the original 2.87 rear gear might be a tad low but it will depend on the cam in your new motor... My 81 had the 2.87 gear... too small.. I went 3.36 after the 700r4 install, but wasn t enough with my 525HP.. pulled it and went to 3.73 and its perfect .. You will love the 700r4

Diablozx9

Thanks.
My mechanic friend has installed engine and transmission.
Had some delays do to other parts... He is concerned my dual exhaust is to close to transmission. he sent pic this morning, engine doesnt have intake/carb on.

Very excited... I intend to put 3.5 rear end in some day (next time i find money)

Diablozx9

Driveshaft shortened and balanced today. Less than $200 after taxes

Diablozx9

transmission cooler needs connection (cooler needed due to high stall converter), then mechanic break in of new engine (couple hours on engine without stress),, I will be driving by next week (just in time for winter storage)... but, enough time to give you an evaluation of crate engine and 700r4 switch

NewbVetteGuy

I hope it goes well. If you really have a 2.87 rear gear ratio you may find that the engine lugs at 60 mph in 4th with the TC locked up.

Having said that, I'm assuming that a 350 with only 290 hp has a pretty small cam, so the torque peak could be low enough that you'll still be ok.


Adam