700R4 vs. 350 Transmission

Hi, all. It's been a while since I've checked in, pretty much right after G-Man left us. My van hasn't moved or been cranked during that time.

I'd lost hope a bit in the van project after many unexpected surprises and problems from the get go, but I've saved some money, sold some things, and I've found someone who is hungry to work. He has a background in motor rebuilding (worked in machine shop and was professionally schooled) and he also does any metal fabrication work needed. I will likely have him do the paint work as well if I like what I see at his shop (he doesn't have a pro-booth but has a fairly sterlized/ventilated environment.

He is also young and not established like bigger shops with bigger overhead and higher costs. The work he would be doing would be more work than I could ever afford other than over a period of years. He views this as an opportunity and that appeals to me.

I've decided to stop chasing problems, leaks, etc and get the motor and tranny rebuilt. He doesn't do trannys but will be rebuilding my 350 motor both cosmetically and internally.

I am curious if going with a 700R4 is worthwhile if I have a 10 bolt rear end. Since I'm rebuilding or purchasing a rebuilt tranny anyhow, should I go with 700R4? He will build me a new driveshaft for a very reasonable price. I realize that you get an overdrive gear and better gas mileage on the hwy, but he wasn't positive I would see a huge difference since I had a 10 bolt rear end.

Glad to be back because this is going to happen. I plan on having the van towed to him right after Christmas to begin work on the motor removal and overhaul.

A 700R4       is an excellent choice for an AOD Trans, what is your rear tire size and any idea what rear gears you have? While cutting/ balancing the drive shaft, go ahead and install new u joints. With a 700R4    your mpg will also increase due to rpms dropping from +/- 3000-3200 w TH350 @ 65-70mph to +/- 1970- 2150 rpms @ 65-70mph    (tuna can factor/ sheet metal rattles will decrease proportionately   ) Good luck with the build. JM2C....

Like Space trucking said. The 10 bolt part means little , it's all about your rear gear ratio and what RPM your engine likes. If similar to Steve's van specs the results would be pretty close to the same. On the highway it would definitely be happier.

Digz wrote:Like Space trucking said. The 10 bolt part means little , it's all about your rear gear ratio and what RPM your engine likes. If similar to Steve's van specs the results would be pretty close to the same. On the highway it would definitely be happier.

Thanks, guys. 10 bolt part is probably my misunderstanding of gear ratio thing. I have never been able to wrap my head around it.

STruckin, I have standard tire size, whatever that is (not home to look.) They are 70's era Vette wheels. They aren't staggered but I might like to go that route eventually.

I need to find out what I have, but it sounds like 700r4 is the way to go. I know DTVMan is an advocate as well, and I always respect his advice. Any idea of what is a reasonable price to pay for a rebuilt 700r4? I think I've seen $700 locally?

I don't think I'm going to hop up the motor much, if at all, in terms of cams, so it should be a straight ahead motor and tranny. Probably add headers. I eventually would like to add fuel injection and make this as easy to drive and start as possible

How does one determine rear end ratio? Also interested in ANY suggestion as to what else should be done when this is all out.

Don't know if you have ever opened up the rear axle to drop the gear oil? but if not it would be something good to do and then see what the ratio is for certain. You can jack it up and get close with a driveshaft:tire revolution count. The 10 and 12 bolt is just the difference in the size of the carrier in the center section. The 12 bolts are just beefier and usually contain the 3.73 or 4.11 ratios. If it is original to the van the typical 10 bolt ratio is 3.36 which would gain the most in an RPM drop at higher speeds. An O.D. trans with the 12 bolt ratios makes them tolerable on the highway and a blast at takeoffs. Can't help you with trans cost. One of my best buds owns a trans shop so... . The original speedo cable may have to be routed a little different to gain some length also. Don't know if you will have to do anything with the shifter as you have an automatic already? Already having an auto in it should make things bit easier to swap over I'd hope.

the first thing I would do is find out your gear ratio. you do not want one too low, or youre not going to gain mpg's, because the engine wont be running in a comfortable rpm range. search for gas mileage on here and see what others are getting with their od trannys. a lot of them have gear ratios in the high 2's and low 3's seem to be really suffering with a 700r. one guy has a 256 rear with a 700r, and gets 10-12. no real point in adding it, unless he plans on a gear swap. I though about it for mine, but I have a 230 six and 3 speed, and I get 18-20 mpg's with a 12 bolt and a 373 gear. I have found that i'm already at the top of the spectrum. just lucky I guess. but I suffer in power and find my van to be happiest around 65mph.
I hope this helps a little.

There IS a point at which, the combination of a freeway rear end ratio, overdrive ratio and fourth gear lockup can be too much to pull in the absence of enough horsepower..... As an example.... my 4500# Olds wagon (91 Custom Cruiser) came stock with a tbi305 (chevy), a 700r4, and 3.23posi..... When the trans was rebuilt, the shop converted the lockup wiring to a single wire, eliminating the lockup ground wire connection to the ECM, which would cut the lockup off in "heavy load" situations......
There are a lot of sustained grades here with a 35mph limit and this car will shift all the way to fourth gear, tripping the sensor that puts it in lockup. The car would start lugging!
I have since wired in a toggle switch and only use overdrive lockup on the highway.

I'd say that in one of these vans (especially the 90's) that a 700r4 is likely to help fuel mileage with almost any of the engines, if replacing a t-350. The efficiency of a stick shift might be hard to beat with a 700r4, especially with a six, which actually likes a little more rpm. Your ears will like the lower RPM exhaust note too!
It is my plan to use a tbi305/700r4/323posi out of my "donor car" wagon....In my 69LWB project.....I believe the van is lighter than the wagon if not quite as aerodynamic.....The posi rear end housings from the 91-96 wagons are only 1 inch longer (d-2-d) than the ten bolt in the van......The wagon (also a 91 OCC) is a rare, future collectible, but I'm not getting any serious offers that surpass the drivetrain value, sooo.......

^^^what he said^^^X2.... you need to know rear end gears (including tire/ wheel change = effective gear ratio) and sweet spot of engine (hp/ torque)

Play with this...

http://www.coastdriveline.com/htmlfolder/calculator2.html

Here you go:

210 gear ratio which presumably came in the van with the V-6.

225/50/16 tires. I am likely to stay with the same size or maybe stagger with slightly beefier back tires.

My guy feels this will be a dog off the line if I just add a 700r4.

He suggests going with 3:73, adding a modest cam.  He feels this will give me best of both worlds:  Low end torque and better MPG and better cruising on hwy.

If I go this route, what is the most affordable part/place to get the new ratio gear?

He estimates $250 in labor.

He mentioned Richmond Gear and Eton, but thought they might be more race oriented and expensive.

Thanks for the help!

Are you sure about the 2.10 rear gears, and also where did the V6 come from??? 64's only came 3.36, 3.73 and 4.10's as you only had a choice of a 153ci 4 banger or 194ci 6 banger

Richmond Gear - and along that Yukon Gear - are RPO manufacturers. Between them you can get more or less any ratio for any diff carrier, so he was essentially saying that you could up to a 3.73 ratio.
Summit Racing has a wide selection, an RPO set runs 200-300... Then of course you need shims, pinion bearing, and a few other things that elude me ATM.

Eaton makes Limited Slip units and lockers, which replaces your open differential. It helps with traction. Eg, if your right tire is stuck, and your left tire is in the air, you won't be going nowhere.
If you plan on doing some mild dirt/off road driving, or have to deal with lots of snow, I would definitely consider it.

Like Space T. said, I'm curious about that 2.10 ratio as well. If the rear is really that low, your guy is right, it will be sluggish off the line. Shift points would also be weird as you're spreading out the space between your ratios (read gears).
You're dude's right though, that 3.73 ratio is a good bet for your current tire. 4.11 would give you better accel, however you'd lose a bit of highway flying. At the end of the day, a 700 w/ 3.73 would be a great all around driver... At least I would think.

Space Truckin wrote:Are you sure about the 2.10 rear gears, and also where did the V6 come from??? 64's only came 3.36, 3.73 and 4.10's as you only had a choice of a 153ci 4 banger or 194ci 6 banger

Well, I figured that the 2.10 came in it, so that's what I get for figuring.  Perhaps he had a 350 laying around and that lower gear ratio worked better?  I dunno...and this gear ratio boggles my brain.

I texted my guy and he is going to pull the cover.  He said the number on the cover or wherever its located indicated 210.  Maybe the cover was changed out unless there is a compelling reason to have gone with a lower ratio.  

And, if the cover says 210, it must have come off of something other than an early van?

I can't tell you if it's currently slow off the line as it has never run very well.

End of day, I am looking for a great cruiser around town and on the hwy but that I can also jump of the line with some authority.  Gas mileage improvement is always welcome.  I could see it suck down on the hwy.  I'd also like to make an occassional trip to the car show in Charlotte 3.5 hours away without having my brain droned to death at higher rpms.

I have no plans to make this 400 h.p., no snow to deal with, and this won't be off roading.

We will occassionally have a little weight in the back, mostly folding tables and a load full of packed plastic bins.

Only hills here are a good climb over our cable stayed bridge and a pair of fixed interstate bridges.

Xelmon wrote:Richmond Gear - and along that Yukon Gear - are RPO manufacturers. Between them you can get more or less any ratio for any diff carrier, so he was essentially saying that you could up to a 3.73 ratio.
Summit Racing has a wide selection, an RPO set runs 200-300... Then of course you need shims, pinion bearing, and a few other things that elude me ATM.

Eaton makes Limited Slip units and lockers, which replaces your open differential. It helps with traction. Eg, if your right tire is stuck, and your left tire is in the air, you won't be going nowhere.
If you plan on doing some mild dirt/off road driving, or have to deal with lots of snow, I would definitely consider it.

Like Space T. said, I'm curious about that 2.10 ratio as well. If the rear is really that low, your guy is right, it will be sluggish off the line. Shift points would also be weird as you're spreading out the space between your ratios (read gears).
You're dude's right though, that 3.73 ratio is a good bet for your current tire. 4.11 would give you better accel, however you'd lose a bit of highway flying. At the end of the day, a 700 w/ 3.73 would be a great all around driver... At least I would think.

Good info and interesting thought because it always seemed to shift out of first gear way too quickly. I had the governor replaced and it still seemed to shift too fast. As soon as I got some momentum going, it would shift. Don't know if that is related. Will have a definite answer on ratio in the a.m.

Lazarusvan wrote:Good info and interesting thought because it always seemed to shift out of first gear way too quickly.  I had the governor replaced and it still seemed to shift too fast.  As soon as I got some momentum going, it would shift.

That is the nature of the beast, the 700 is known to have a very very low 1st gear. The 200R4 I sport is not much better, although it is used when I'm crawling along about 5mph or so.

Lazarusvan wrote:I dunno...and this gear ratio boggles my brain.

This is actually fairly easy... Wall of text incoming!

In essence you have two reduction and a wild card in your average car, including our vans.
First reduction is your transmission, second is your RPO, and the wild card is your tires.

Let's look at the wild card, tires, takes the least effort to change. Compare 25" or 30" diameter tires. The 25" will have better acceleration/power, while the 30" tire will have better top speed/economy as the bigger tire rotates fewer times to cover the same distance.

Then there is the RPO. RPO's generally run from about 2.xx to 4.xx with heavy truck cases reaching 5.xx. This is the reduction between the transmission and your wheels. Higher reduction will net you better acceleration/power, however your top speed/economy will decrease... See a pattern yet?

Finally you can have the planetary gear sets changed out in your transmission... Yeah, let's not go there, it gets really expensive in a hurry.

Armed with that basic knowledge, I used this site to do my math:
http://www.apexgarage.com/tech/gear_ratios.shtml

You can look up your tire diameter online or just do a rough measure. By random guess, let's say it's 25".

For RPM put in 2300. From what I've seen on random forum posts, oil pressure fully develops in SBC's around 2000-2400 RPM, favoring the higher number. I have seen 3000 RPM mentioned, and others replying that that's a bit much.

You tranmissions ratios are:
1 - 3.06:1
2 - 1.63:1
3 - 1.00:1
4 - 0.70:1

And Final Drive Ratio = RPO, so toss in the recommended 3.73.

Then poof, in theory you should be cruising at 66 MPH @ 2300 RPM.

In my 2nd gens I've had a 3.36 w/ Powerglide and a 3.08 w/ 200R4.
The 3.36 + Powerglide definitely didn't fly off the line, and more or less topped out at 60MPH. Also unless you had a running start, it went up hills at about 40MPH.
The 3.08 + 200 on the other hand had a bit more pep, and climbs hills better. It is still far cry from decent acceleration, and the RPO is honestly too low for and OD transmission.

So in my case, I got another axle with an RPO 4.11, and going from a 25.5" tire to a 27.7"
This should raise my shift points as my van has a tendency to putt around in 4th at 40MPH - not good - and it will hopefully get me some tangible increase in acceleration.

... Ok, so it takes a bit to understand. Hopefully this helps.


TL;DR:  (Too long, didn't read)
If you want to stick with your tires, go with an RPO 3.73, maybe 3.80
Any lower will be a bit of a lugger, slower off the line, and any higher is starting to reach droning/high RPM territory.

Xelmon, thanks for the info.  That did help a good bit.  Getting clearer for me.

Digz wrote:Don't know if you will have to do anything with the shifter as you have an automatic already? Already having an auto in it should make things bit easier to swap over I'd hope.

Thanks, Digz.  Yes, auto with a Quick Silver shifter.

Confirmed that I have a 3:36.   The assistant was looking at a serial number on the plate or something and brought back the wrong info.  The boss actually pulled the plate and counted teeth.

Consensus seems to be bump up to 3:73 (or higher) for nice overdrive ratio with a 700r4 but that a 4:xx, while giving more low end torque, would not be a happy place to drive out on the open road for a 2-3 hour trips.

My guy indicates that using the current 3:36 would not achieve much more with a 700r4 than I currently have with my 350/350 setup, even with overdrive, and that the overdrive rpm's would stay about the same IF I didn't change out the current RP0.

Hoping this scenario gives me nice launch/low end torque and great hwy. cruising RPM's.

My guy also discussed the idea of using a shift kit if necessary to change the shift points.

Does this sound correct?

Thats not completly correct.

The final out put of the TH350 or most all other TX is 1/1
the final output of the 700R4 is .70/1  

That is a 30% difference. in engine RPM example if your on the highway with the TH350 and your engine is doing 3000rpm. That would be 2000RPM with the 700r4 (all else staying the same)

However the truth is it would actually be worse by  about 5% more becaude nonlocking TCs cannot "lock up" to 100% drive Which is the whole point of a "lock up TC".
At the very best case senario, if the nonlock torque converter was brand new in perfect condition it could only ever get to about 95% of stall.

If your van is a 90" you should seriosly consider a 200R4 because the 700R4 in a 90" van makes for too short of a custom made drive shaft and you will forever have rear end driveline vibrations.

the difference between a 336 and a 376   is even less of a difference then the Th350 to a 700r4 and the cost involved is about as much. You can make that same difference up wwith just changing tire size.  

Have I got something wrong? I thought you are interested in better fuel economy. I ask this because the proposed gear change to a 376 is going the opposite way.

If you just chage to either a 200r4 or a 700r4 you are automaticaly going to get better off the line torque and better highway economy and performance. (providing you tune the transmision correctly)


M1D

m1dadio wrote:Thats not completly correct.

The final out put of the TH350 or most all other TX is 1/1
the final output of the 700R4 is .70/1  

That is a 30% difference. in engine RPM example if your on the highway with the TH350 and your engine is doing 3000rpm. That would be 2000RPM with the 700r4 (all else staying the same)

However the truth is it would actually be worse by  about 5% more becaude nonlocking TCs  cannot "lock up" to 100% drive Which is the whole point of a "lock up TC".
At the very best case senario, if the nonlock  torque converter was brand new in perfect condition it could only ever get to about 95% of stall.

If your van is a 90" you should seriosly consider a 200R4 because the 700R4 in a 90" van makes for too short of a custom made drive shaft and you will forever have rear end driveline vibrations.

the difference between a 336 and a 376   is even less of a difference then the Th350 to a 700r4 and the cost involved is about as much. You can make that same difference up wwith just changing tire size.  

Have I got something wrong? I thought you are interested in better fuel economy. I ask this because the proposed gear change to a 376 is going the opposite way.

If you just chage to either a 200r4 or a 700r4 you are automaticaly going to get better off the line torque and better highway economy and performance. (providing you tune the transmision correctly)


M1D

Hi, Michael. Thanks for the help.

It's becoming clearer for me, but I don't fully understand lock up in relation to TQ's.

Gas mileage, quite frankly, is not the biggest factor for me, but it is important. The shift to 3:76 was to improve low speed torque, if I understand correctly.

I definitely want better gas mileage, but I really want it to get down the hwy without rattling my brain to death and being louder than it has to be. I will be installing a custom insulation kit that I have in hand, and anything additional to help in that regard is ideal.

Steve mentioned the "tuna can effect" at higher RPM's and I understand that 100%. Smoothing things out would be great. My 350 is loud and high revving on the hwy unless it was worse than usual because of the poor running condition.

But, yes, I want good gas mileage, DEFINITELY want some pop off the line. Gas is so much cheaper now, but we all know it's not going to to stay this cheap long term.

Ultimately, I want to eliminate the rattle can hwy speed issue as much as possible, be able to drive up to 3.5 hours on a trip, hear my radio when going down the road and still have a fun to drive vehicle that takes advantage of a V-8 engine.

If someone wants to give me a little something off the line, I want to be able to return the favor...  

The 200 tranny sounds interesting since it mates right up and since you say it is less likely to rattle.

He estimated around $300 or so to make the drive shaft fit the 700r4, so if the 200 bolts right up and give me the same benefits, I like the idea.  That would free up some money for him to install your brakes that I've had for two years now..

At the end of the day, I'm looking for the best combination that gives me fun off of the line and enjoyable, cruising hwy speeds.

Lee

Unless you are doing hole shots and slow races you shouldn't need the 3.73s or the 4.11s. I run 4.11s with a 700 and it doesn't sound like that's what you are looking for. The OD trannys have a lower first gear ratio that will give you plenty of take off with that 3.36 RA. IF I was building a Xway runner I'd keep that ratio.
Something I do not understand is the prices for shortening the drive shaft 2" for a 700. I have heard that number before and just can't figure out why something that takes less than an hour to do is so costly. If you had to buy new yokes and such maybe more but you should be able to reuse those as an automatic is already in place.

Digz wrote:Unless you are doing hole shots and slow races you shouldn't need the 3.73s or the 4.11s. I run 4.11s with a 700 and it doesn't sound like that's what you are looking for. The OD trannys have a lower first gear ratio that will give you plenty of take off with that 3.36 RA. IF I was building a Xway runner I'd keep that ratio.
Something I do not understand is the prices for shortening the drive shaft 2" for a 700. I have heard that number before and just can't figure out why something that takes less than an hour to do is so costly. If you had to buy new yokes and such maybe more but you should be able to reuse those as an automatic is already in place.

Thanks, Digz.

You are correct i.e. price. My guy said the same thing regarding driveshaft. He mentioned checking the yolks and seeing whether or not they were useable. That might be an "all in" number with his labor. I am pretty sure that is the case because I think he would have the tranny guys do the shortening.

If I can get the same benefits from the 200 without much work, that might be my ticket.

And, you seem to concur with M1D that keeping the current gear is acceptable. Is a 3:36 considered a low 3's ratio or mid ratio? (Referencing a prior post regarding poor gas mileage using a low 3's RPO with a 700r4.)

Considering tires, let's presume that I MIGHT go larger diameter if it makes sense in that all 4 need replacement soon due to age.


As far as hole shots are concerned, not likely on a regular basis. If I'm first in line at the stop light, I'd like to make my presence known from time to time and be able to accelerate when merging onto the interstate.

A free way runner sounds like the right terminology. Sporty around town but smooth on the open road.

A 4:11 ratio would not be a great one for highway due to higher overdrive revs/poor gas mileage? Essentially, where I live, I have to drive 25-35 minutes to be anywhere. One route takes me over two fairly steep bridge climbs followed by 55-70 mph speed limits. The other could take me over a very steep bridge or keep me more at around town speeds.

I want to be able to make a trip 3-4 hours away once or twice a year for the Charlotte car show. Not sure I would ever drive much further than that and certainly not on a regular basis.

What M1 and Digz, Xelmon have all said is correct. Also you need to decide on what rims/ tires you are going to run cause any swap in the future will not only change speedometer reading but also effective gear ratio

Unless you are hell bent on stop light to stop light, I would stay with the 3.36's for torque/ mpg (3.73's/ 4.11's towing or street racing). As far as 700 R4 vs 200 4R it is a matter of preference, with either swap I would put new u joints and build new or balance existing drive shaft (yokes too, buy once/ cry once). JM2C

I checked your first post and I thought you already had a 700, apparently not the case. As the guys mentioned and something I can confirm, going with a 200R4 is definitely the painless solution.
Power rating wise the 200 is the "lesser" compared to the 700, and from what I've read it'll handle in the ranges of stock I6, a Vortec V6, and 2 BBL 350. If you don't hop it up too much and drive usually lightly, you could also probably rock a 4 BBL 350.

Either transmission would need a bracket welded up for it. Difference is, the 200 is dimensionally the closest to the Powerglide and I believe the TH350. So if you already have one, you don't need to modify it at all.

+1 for Space T., as you're always on the highway it seems like you won't need that much of a pep off the line, so that 3.73 may not be your cup of tea. The lower 1st out of either the 200 or 700 will give you a bit of extra pep for rolling off, so it won't be that boggy.

Ya know how I mentioned that the 3.08 + 200R is a "bit of a slow one off the line"? Whelp, what it does pretty well is highway cruising as it does humm along around 65 wonderfully. I'm just a city slicker, as such I'm going into the experimenting phase of seeing if a different ratio fits my driving style better.

Speaking of style, if you change your tire to something that is roughly the same size, say, going to a 215/55R15 or something, you probably won't notice the difference.
Now if you decide to toss on say, a 235/75R15, you'll definitely feel that.

Xelmon wrote:I checked your first post and I thought you already had a 700, apparently not the case. As the guys mentioned and something I can confirm, going with a 200R4 is definitely the painless solution.
Power rating wise the 200 is the "lesser" compared to the 700, and from what I've read it'll handle in the ranges of stock I6, a Vortec V6, and 2 BBL 350. If you don't hop it up too much and drive usually lightly, you could also probably rock a 4 BBL 350.

Either transmission would need a bracket welded up for it. Difference is, the 200 is dimensionally the closest to the Powerglide and I believe the TH350. So if you already have one, you don't need to modify it at all.

+1 for Space T., as you're always on the highway it seems like you won't need that much of a pep off the line, so that 3.73 may not be your cup of tea. The lower 1st out of either the 200 or 700 will give you a bit of extra pep for rolling off, so it won't be that boggy.

Ya know how I mentioned that the 3.08 + 200R is a "bit of a slow one off the line"? Whelp, what it does pretty well is highway cruising as it does humm along around 65 wonderfully. I'm just a city slicker, as such I'm going into the experimenting phase of seeing if a different ratio fits my driving style better.

Speaking of style, if you change your tire to something that is roughly the same size, say, going to a 215/55R15 or something, you probably won't notice the difference.
Now if you decide to toss on say, a 235/75R15, you'll definitely feel that.

Great info from everyone.  

4 barrel Edelbrock carb, fyi. Stock or modest cam is planned.

Can't say I'm always on the hwy.  It will be a combo of things, mainly never more than 30-40 minutes away.  Chance are, if I'm driving around for fun and not using the van in a working fashion, it will be around town.  And, around town here is a few stoplights unless you hit the interstate.  I'm thinking 200R.  Now I need to really figure out this tire thing.  Not sure what you mean by "feel that" with larger tires, but that would be the presumtion.  I have 70's Vette wheels now that I like if they were in good shape, but not sure how large a tire can go on them.  Another place I get lost...

Lazarusvan wrote:Great info from everyone.  

4 barrel Edelbrock carb, fyi.  Stock or modest cam is planned.

If you don't floor it all the time and tend to roll off easy, you'll probably get away with it. When I have a bit more time I'll be reading up on what has to be changed and hard is it to change to be able to mildly up the power.

Lazarusvan wrote:I have 70's Vette wheels now that I like if they were in good shape, but not sure how large a tire can go on them.  Another place I get lost...

Honestly, you can go as big as you want, if they make the tire for the rim... As long as it fits in the wheel well at full lock. =)

Stay with the 336, do the trans first, if youdon't like the rear gear later you can change tire size and/or rear gear.

The differences between the 200r4 and the 700r4 are debatable you can get good ones or crap ones in both. The differences genneral equate to the differences of the TH350 vs the TH400
The basic 700R4 apparently handles more torque than the basic 200R4 which is usefull when your towing a 2000lb trailer up a 13% grade for 2 miles. (do you need that?)

I have a 700R4 in my 90" with a 342 gear. I think it would be better with a 336 based on the fact that the 1st gear is plenty low amd I would get lower engine speed and better fuel economy with the lower gear. Most of these 4 speed lock up trans came in vehicles with factory 308 range of rear gear.

I am going with a 200R4 "Z" code trans from a 1988 Montecarlo SS which had a 342 gear and the HO SBC into my 68 90". I think it will be a much stronger trans than the stock 700R4 I have in my 65.

With the 200R4 I will use the stovk drive shaft with the 200R4 yoke and new ujoints. U joints come in all sizes and you just pick the right one to addapt any yoke to drive shaft. (special yokes and shit are not requried. If you go to a 700R4 I think there is a 2nd gen drive shaft that can be used if you have a 108" van. But if you have to make a drive shaft you get a good junk yard shaft with the same ujoint ends (because larger DIA tube is better) have it cut down and ballanced and use what ever new U joints make it fit. Mine cost less than 200 CND which would be about $150USD.

The torque converter lock up is a very important function to make the R4 transmisions work correctly and achive the best they can be. Just as is the TV cable set up to the carb. Either one set up wrong can make the trans performance be poor or less than optimum and/or can cause transmision failure in a short period of driving. The physical geometry of the TV cable connection and the Lock up wiring both inside and outside the trans is not rocket science but it does have to be built up correctly. This is the area where most people end up very happy or totally disatisfied with thier transmision change.

The lock up TC is for improved fuel economy in cruise. By nature of the beast no TC can achive 100% transmision of engine speed or torque to the transmision because the fluid drive conection between input and output will allways have some loss. This loss can be anywhere from 5% or more depending on the condition of the TC . The older they get the less eficient they become. The Lock up feature is to overcome this inefeciency and cause 100% transmision of power by physically locking the imput and the output of the TC together. Again this is only done at cruise speeds, not when accelerating or decelerating. There are other factors within the transmision that are tacken into account when lock up is needed or not needed. Again if the TV cable and TC wiring are not set up righ you can ruine a good transmision or have one that works like crap.

If you are going to do disc brakes than don't buy different wheels until the time you are doing disc brakes because you need to end up with wheels that fit the disc brakes and your 70,s corvette wheels allready do fit disc brakes.

I recomend you change the transmision first and get it opperation correctly before doing any other changes. Too many changes at one time will lead to many hard to diognose and resolve issuse.


m1d