1965 409 conversion

[65SS409]

Hi everyone:

I have just finished a conversion on my '65 Impala Convertable from as 283 Powerglide to a 409 four speed....quite a project, but I'm really happy with the results and we have just put the car back on the road. My question is: what rear end ration did Chevy typically run with the 409/four speed combination? I am running about 3400 rpm at 70 mph, which is much lower than I need. Can anyone help me out.

Also, I am looking for a flywheel inspection plate for the '621 bell housing I used for the project.

Thanks from a new member.

Roy

 

[64ss409]

My 340hp/4speed came from the factory with 3.36. It currently has 4.11. A little slow on the highway, but much more fun.
Ron

 

[Bungy]

Roy, what size rear tire are you running and what RPM do you want to turn at 70? 3400 seems kinda high to me. JMO

 

[Rockfish39]

Hi everyone:

I have just finished a conversion on my '65 Impala Convertable from as 283 Powerglide to a 409 four speed....quite a project, but I'm really happy with the results and we have just put the car back on the road. My question is: what rear end ration did Chevy typically run with the 409/four speed combination? I am running about 3400 rpm at 70 mph, which is much lower than I need. Can anyone help me out.

Also, I am looking for a flywheel inspection plate for the '621 bell housing I used for the project.

Thanks from a new member.

Roy

Typical rear was 3.31:1

 

[65SS409]

409 conversion

Thanks for the replys, guys. I'm trying to keep the rpm down a little with the price of gas where it is, and I have other cars to do a little "light to light" racing, so I'm not worried about that part....so 3:36 may be close to what I'm looking for.

I'm running 215/70R-14's on the rear now. I would like to sit around 70 at 3000rpm, as the 409 is plenty torquie, as you know....maybe even a little lower rpm wouldn't hurt...I'm not sure....any ideas?

And hi to Coffee Creek....Cut Bank here. We'll see you at the May 8th cruise in Great Falls maybe...

Roy

 

[Fran Preve]

Unless you need to keep the stock hub caps switch to a 225x15, that will get you close to 3000. 3400 at 70mph with small 14" tires (relatively) doesn't sound like a stock 3.08 axle (for a 283 powerglide) car.

 

[MK IISS]

If I remember correctly the rear end assembly was all new for the '65 Chevy. I think there was a 3.31 ratio in a heavy duty rear end that was used in 409s. In any case 3.08 was the normal ratio for small blocks with the powerglide with a couple exceptions. Convertibles and station wagons, if they had certain equipment had the 3.36 or 3.31 ratio to compensate for the extra weight. In other words since you have a convertible you may have a 3.36 factory installed rear end. Also if I remember correctly there was also both three and four link rear suspensions depending on the body weight and and engine size.

 

[SSpev]

you got a 10 bolt or a 12 bolt? (first year for both in a big car) 3.36 is a 10 bolt ratio 3.31 is a 12. All the 12 bolts I have seen have 4 control arms. The 10s have 3. Most likely you have a 10 (283 w/glide) But with the rag top it coud go either way. Could even option up to the 12. My rag is a 327 250hp with a 3.31 12 bolt with 4 arms. A hard top rear I have is the same. 6 cyl Biscayne 10 bolt 3.36 with 3 arms.

 

[Fran Preve]

SSpev has it, 1965 was the first year for the non-hogs head rear. Pluses: MANY complete rear ends to pick from, the same size (full size) until 72 (?and later?). 12 bolts common and cheap (as opposed to Chevelles/Camaros). MK II is right, about gear ratios being different between "hogs head" and the later style. Don't know about convertible standard ratios, wagons were higher (numerical). Minus is it's a little more expensive to change gears. In my opinion a 12 bolt 3.31 would be almost perfect for a street car, one that's taken out on the highway regularly. If you have to change gears because it's a 3.08 (or you have to find a 12 bolt and it's 3.08) then I'd go with a 3.55.

I believe a full size had a 60" track, 64 to 67 Chevelles are 56", 68 to 72 Chevelles are 58". I put a 64-67 12 bolt under my wifes 1984 Monte Carlo, and I know a 68-72 would bolt in too, except it's 2"'s too wide. Now, can you put a 56 or 58" Chevelle rear end under a 65 up full size?. Neat way to mount a narrowed rear end under it for wider tires. I'd have to see a full size rear next to a Chevelle to know.

 

[63z11]

65-70 rear diffs

The 65-70 10 and 12 bolt rear ends are unique to the big car. The upper arms mount to the axle tube and go straight to the frame. Unlike the angled uppers used on the A-body style housing. Also the coil spring on the full size mounts to the lower control arm not the housing like the A-body. Eric

 

[Bungy]

Roy, After a little math I came up with the following. Your car has 3.73 gears now. To get 70mph@3000 you would need 3.29 gears. (or a 3.31) If you did as Fran suggested and went with 225/70-15 rear tires and your current 3.73s you would get 65mph@3000 and 74mph@3400

 

[65Impala409]

Hi,

Just wanted to let you know that my 65 Impala 409 car is a factory original with the 3.31 posi rear, I believe the code is DH.... Good luck on your car
Ned
65Impala409

 

[Fran Preve]

63z: Thanks, I din't know about full size to A conversions. But should have figured out there would be some things major. 3:31's and 225x15's seem like a good compromise (if you don't need stock hubcaps).

Also thanks for the MPH vs RPM numbers, good to know. That said, 3000 at 65 is about MY personal upper limit, geez I don't like buzzing it up much more on a regular basis. THAT said, a lot of my driving is on 65-70 mph roads, I'm leaving on a run to Florida Friday, all at 70-75, and I'm spoiled by running cars with A/OD for so long. The Xtreme has 3.42's and runs 2100 at 70!.

 

[65SS409]

65 conversion

Thanks to everyone for the information on rear end ratios for the '65. I think I have it figured out....the 3000rpm at 65 sounds best, so I'll work in that direction.

I'll be watching the site to see if I can help in return.

Roy

 

[CarlK60]

I would just like to add to what SSpev was saying, the 10 bolts had 3 control arms unless they came in a Caprice. Caprices had 4 control arms regardless of 10 or 12 bolts or engine size.