350, 700R4 install fimally !

[Cliff]

hello everyone. I just thought I'd post because I am finally putting a 350 back into my truck. It has had a 305 in it since I bought it 2 years ago. The 350 is out of a 1989 caprice unmarked cop car, allong with the traney. I have the 350 o na stand in the driveway while i replace gaskets and such. I swiched the manifold, and also bought a new carb for the beast. I just wanted to know of any things to watch out for from those of you who have done the 700R4 install in our trucks. installed the complete lock up kit from bowtie overdrives so I should be set there. I know i'll need to have the driveshaft shortened. Thanks a lot fellas. Cliff

[ckhd]

My biggest problem from the start is that my engine didn't have enough oomph to drive my heavy Suburban at 1800 rpms. It was OK if the road was flat or downhill, but even the slightest climb would mean a downshift to drive... If you've been to Eastern AZ, then you know it's not like the Phoenix area... there are mountains! In fact, I live a 8000'! There isn't a flat road within 100 miles of here, so it would downshift a lot.

I put a stronger engine in and it does better... funny thing is that before the 700r4, I got 11mpg. After the 700r4, I got... 11mpg. Still trying to figure out why.

[Cliff]

thanks for the response. I'm hoping that the motor should be pleanty powerful enough. it's just a 1/2 ton truck and from the factory it would have had a 350. I've been running it with a 305 and a 350 traney and am getting 10 mpg on the highway. I guess i'll just have to try and see. I'm about ready to pull the motor out of my truck. Any tips for that ? I'd much rather pull the traney at the same time but I didn't know if this would cause problems or not. Thanks again Cliff

[SCOTI]

Ckhd, what gears were you running? Seems to me your milage should show improvements as long as the engine wasn't bogging down.

At what RPM's does/did your engine spin in drive @ 35-40mph? You should have similar RPM's in O.D. Anything below & the engine is bogging. Also, the convertor shouldn't have a higher stall speed than that cruise RPM either.

[ckhd]

I have 3.73 gears. Don't know what the rpms were, but given that the OD is 30% lower, I'll bet that they are now 30% lower at 35-40mph. I do know that I used to cruise 65-70 in the 3000 range, and now cruse that at the 1800-2000 range (I attribute the rest of the rpms to tq slip).

I actually initially got 7mpg after the tranny swap, but rebuilt the carb to get to 11. I haven't done a mileage test since I put the beefier engine in. One of these days, I'll have enough money to fill the 40 gallon tank, cruise it to work a few days, then put another 40 gallons in again and see what the mileage is with the different engine...

As far as the power goes, it takes about 43% more power to do the same job with a 30% overdrive (the same way 1st gear multiplies power, od divides power). Pushing 6000 pounds of Suburban isn't too bad for an underpowered 350 at 3000rpm, but pushing the same at 1800 and requiring 43% more power was probably bogging the engine down.

[SCOTI]

I checked this out tonight in the T/A (Ls1, auto/stock convertor, 3.23's) coming home from the flics. On the highway @ 70mph in O.D., RPM's were just under 2200. On the side streets @ 40mph in drive/3rd, RPM's were 2000.

I agree w/your torque division theory. It sounds like your app was below the engines ideal torque peak w/the gearing, tire diameter, & weight @ that time.

Instead of filling up a 40 gal tank & emptying to refill.... fill it once & record the milage, then when you run out some gas just top it off & record the miles vs the amount of gas it took to refill. Do that a couple of times for your avg. Man.... I'd hate to have to pay to fill up a 40 gal tank.

[Phillip Johnson]

I would like to do a 700r4 in my 71. Gas here is going up again!

[Huck]

Some comparisons---I believe GORDO with a 350, 700r4 and 373 gears in his short bed 1/2 ton 2x4, gets about 20 mpg on the east coast. I get 20mpg easy with my 350, 5speed, 308, 1/2 ton long bed. We both utilize HEI, headers and newer carbs. But at altitude, the gas mileage would be severely affected. I'm in ky and my truck only gropes for power pulling a trailer up hill and with the tall gears, it's understandable. Ideally I feel that 342 gears or 354 gears would be best for performance and mpg. At 70mph, I'm doing about 2200 rpm and at 80 am doing about 2500 rpm.
My pure stock 71 truck with 350/350, gets 13mpg and is running 3,000 rpm at 70 mph.