small block truck to BB converion ?

[miket]

Does the tranny hump in the cab need to be replaced when converting from a small block 350/350 to a 700R4/502?

[drlow]

your gonna need the "big hump" pan because of motor placement. 700r4 isnt any bigger per say but the motor is & needs to be back further.

[1970 CST Short Wide]

There are LOTS of trucks out there with BB and small hump cab. Mines soon to be

[hobby67stepside]

I'm going to run a big block with a Muncie 4-sp in a low hump cab and I've got plenty of room between tranny and cab. I made my own rear tranny mount but its about the same height-wise as the stock configuration would be.

[mikep]

I think you really only need the hi hump with a big block and factory 4 speed. I know my 4 speed came all the way to the top of the hi hump. It wouldnt have fit with the low hump .

[miket]

Thanks MikeP...I was going to PM you tonight to see what your opinion was.

I am feeling much better...I thought I was going to be forced to abandon my 700R4/502 effort and head to a small block....which I wouldn't be satisfied with.

[mikep]

OK I know I am going to get jumped on for this. 700R4' are weak transmissions that cannot handle large amounts of torque for very long . The 700 R4 can be built to handle a lot of torque but the modifications necessary to build it to handle over 500 ft lbs are EXPENSIVE !!! If you never hook up thats one thing but if you dont intend on building the chassis to hook up then whats the point in having the 502? Not only that but since theres plenty of low end torque with the 502 why not just go with a TH400 and a fairly hi geared rear end like a 3.08 . That way your'e not dumping $2000 or more into a transmission that is of questionable strength and with the hi rear end gearing you are having the same net fuel consumption effect. And lastly...why are you worrying about your gas mileage and getting a 502? They are two fundamentally opposite concepts.

[Longhorn Man]

I have to agree with Mike on the 700R4 opinion.
As for the floor pan, try it. If it don't fit, then hack the low hump out, get a high hump out of another truck, and bolt it in. Real easy mod.
As for will it fit...I have my caddy 425/TH350 in the one ton and had no problems...but that is a caddy and not chevy though. But I think it'll fit.

[miket]

Mikep,

Noone's gonna jump on you and you have valid points...and I may change my mind but I am assuming by your post that you are interested in knowing why the combo. First off, gas mileage isn't an issue... have two other vehicles I can drive for mileage.

I want an overdrive transmission due to highway driving which I due some of. Yes I could change the rear end, but (and I may do it anyhow) until I get a 700R4/4L60 installed I won't know. I believe there to be several benefits to this tranny...one is the 4th gear and the other being the lockup converter. This will help mileage. This will also allow me to have the other gearing to pull my 66 Chevelle if needed.

The case for T400/350 vs a 700R4 are subjective. I did some searching on this forum and found enough pros and cons to force myself to talk to a few tranny shops. They confirmed exactly what you said. To build a 700R4/4L60 combo to withstand enough torque will cost some money. I happened to have one in my 01 Burb with a 496 (455lb/ft torque with 7000lb's). I averaged 13 mpg towing my Chevelle back from Great Falls MT cruising at 75mph with a 4.10 rear.

I am not going to race the truck (that's what the Chevelle is for) but it sure would be fun to haze those 275/60's and give the import guys something to think about!

Great argument Mike...I will have to think about it.

[Longhorn Man]

Here is another solution that is the best of both worlds.... http://www.gearvendors.com/commercial.html

[crazy longhorn]

On the small hump, if you run into a problem my guess would be the lip where the floor welds together. You can cut the lip off, & butt weld the floor back together in the area across the hump. As far as the trans.......if you are going to spend the cash for a built 700 r4, you could build a 400t, & hang a Gear vendors on the back. Then you could run what you want for rear gear.... the setup would be d@mn tough too! crazyL

[spinning wheels]

when I spoke to the owner of Bowtie overdrive, he informed me that he hauls a 15,000lb. trailer to shows and swapmeets. This is with their beefed up 700r tranny. That tranny sells for under 2 grand installed at their shop. Second item, the Gear Vendors. Gear Vendors also sell a standard and a heavy duty commercial. A good friend of mine that used to own a trans shop in Flagstaff, AZ. tells me they (Gear Vendors) aren't all that strong. They have a tendency of burning up the clutches. He prefers the 700r. He runs a '72 Nova with a 700r. He drives it to Phoenix, changes the rear tires and rims, to sticky DOT tires. Runs it in the 13's. Then changes back to his street tires and drives home. This is with a small block. The 700r also has that nice stump pulling first gear
When my brother tows his camaro to Vegas, with his BB dually, he gets worse gas milage than his race buddies with overdrive trannys. Plus, they put less strain on their trucks. Oh yeah, back to the little hump part. I thought the 700r tranny is almost the same size as the turbo 350.
Miket are you going with a new 502 or are you building up a 454? Just wondering cause I was thinking of building my 454 into a 496, but now I thinking 500 cu. in. plus

[mikep]

If you can fund a shop offering a fully warrantied 700R4 for at least 2 years behind a 502 then go for it. Otherwise with the low end torque of the 502 you have no need for the gear multiplication in the lower gears and it will in fact hurt your performance. Remember...with a big enough motor you dont even need a transmission. IMHO your better off with hiway gears and a beefy TH 475 behind that big rat.

[crazy longhorn]

A nice big rat will happily pull a lot taller gear than a smallblock. I like a mid 3s gear for the "best of both worlds" with a BB. The 400 turbo is my choice of trans behind a BB(475 would be better!) My longhorn ran a 3.40 gear with a 461" olds, & cruised 72 mph @ 3000 rpms......you didnt dance on the throttle till it was running about 40mph, unless you like a smoke show. A kick into pass gear @ 65 mph, would lite up the tires.......& the shift to high would lite them again! (Thats 500 ft lbs tork at its best) I am running a sb now, still have the 400T, but with 4.10 gears. The truck needs another gear out on the open road, but I dont see a 700r4 .......for the money, I feel that the Gear Vendors is a better deal. I dont know how that vendors will hold up under towing, but there are a couple guys Drag racing Olds, with the Vendor behind the 400t & report no problems with the unit! For more info on racing the vendors unit, try this link..... http://www.realoldspower.com/ ask these guys, they laugh at the GM factory overdrives behind a BB.........crazyL

[jays68yak]

IMO I would put in a high hump just cuz you can get to the cooler lines on the tranny and tighten them easier. Not to mention you could almost unbolt the tranny from the top and drop it from there too. When I put my 700r4 in my suburban it was by far the easiest swap cuz of the hump being able to unbolt and moved out of the way. Then again if you dont need to why change it.

If you do want to change for what ever reason I have one for sale.

[miket]

Well,

Guys I am leaning towards the T400...for budget reasons...I tallied up my project list last night and found it to be...ummm...shall we say...high. I expected it, but there are other things I need for the truck....so I am leaning towards saving on the tranny to spend somewhere else.

Spinningwheels: I am going to buy the GM Crate ZZ502...it's complete from pan to carb and includes everything I need. I liked it because it would be dependable, strong and hopefully easy to graft in. I also did some comparing to World Products (Merlin) crate motors (www.theengineshop.com) and found some other motors I am still very interested in, but can't afford...like a 500HP 427 small block and a 540...I really like the Merlin block but have a feeling I would be getting farther into the finicky racing engine side of things and thats not what I want for the truck...I already have to spend $6.00 a gallon for 114 for my Chevelle everytime I take it out.


I guess I will proceed assuming the small hump will work....I will keep you posted.

[mikep]

BTW MikeT ....There is a US gear bolt on dual range underdrive unit for a TH400 in the buy and sell paper . Its located in Tacoma and it comes with electric shifter etc. $500 . Thats a steal. That way you could run a tall rear end gear for mileage and still have low strting gears.

[Longhorn Man]

At work we deal woth a heavy duty tranny shop and they are a dealer for the gear vendors OD/Ud. I asked them a butt load of questions and they said they have NEVER had anyone come back with troubles. Motor homes are there biggest market out of that shop.
[quote]He runs a '72 Nova with a 700r. He drives it to Phoenix, changes the rear tires and rims, to sticky DOT tires. Runs it in the 13's.[/img]
In all reality...13's aren't al that hard to do..esp in a light weight like a Nova.
Put it a heavy truck and parts break easier.
plus 13's isn't all that hard to do...a cam, carb, intake, exhaust and good tires can get you there....I've seen just a little more get a long bed with an open diff and one slick dip into the 12's. (no joke)

The 700r also has that nice stump pulling first gear

Problem with that low first gear is the huge gap from first to second gear. It bogs most engines...even if undetectable...it does. Imagine riding your old 10 speed and missing a gear (you KNOW you tried shifting like a car at least once) If you went from first to third, your accelaration rate dropped becouse you went below your legs ideal RPM (which is about 90 RPM for most riders in good shape) The 700 does the same exact thing to your motor.
Besides, like mentioned...a big block don't need grars like that.

[miket]

Well,

I am moving ahead with a T400 and changing the rear gear to 2.73. I need to put a posi unit in it anyway...this will leave me enough money for now to get my accessory mounts/pulley's and new cooling system.

Thanks for the input.