How much power will a stock PG and 12 bolt handle? - Impala Tech
Transmission & Driveline Transmissions & Differentials

 
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post #1 of 11 (permalink) Old 09-29-2009, 10:13 PM Thread Starter
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How much power will a stock PG and 12 bolt handle?

Alright, so I just joined the forums and my first question is how much power can I get through a stock driveline without breaking something?

The car in question is a 66 Biscayne, 283 original, 350 swap when I bought it, and eventual big block.

I am looking at a 12 bolt from a 66 Impala to swap out with the current 10 bolt and I was wondering how much power it will handle in a street application?

Also, is there going to be any difference in the internals of my powerglide versus the internals of a powerglide that originally went behind a 396? If so, about how much power would each be able to handle?
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post #2 of 11 (permalink) Old 09-30-2009, 07:07 AM
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A PowerGlide will hold 2,700 horse power. Of course there isn't a GM part used (not even the oil pan) but it looks and acts just like a PowerGlide. If you replace enough parts inside the case and replace the case with an Auto Bell and a Super Case assembly (the bell housing has to be explosion proof to meet NHRA-SFI specifications so they use a titanium alloy to cast it) then yes it will hold that level of power. As to a stone stock PowerGlide your pushing your luck at 325 horsepower as the TH400 was invented in 1965 to bolt behind a BBC motor with more power than a 325 horse 396.

The 12 bolt rear end will hold at most 1200 horse and this assumes all aftermarket parts (nothing that was made by GM they just look like them and act like them and bolt in place of one.). Once again with an axle upgrade and fresh bearings I think you can safely hold 750 horsepower with a stock casting after you weld the axle tubes solid to the center section.

I raced a number of cars at about that level of power for over twenty years and only broke three. I now use Dana 60's (the 12 bolts big brother as the Spicer 12 bolt was made by Spicer which is also called Dana and is comparable to what Dana calls a Dana 44) for my high powered cars because everyone is making more power now.

Think of Dana and Spicer just as Chrysler thought of Dodge and Plymouth back then. Two semi-independent companies competing for sales owned by the same parent company but uncontrolled in what they call their products and how they marketed them.


Big Dave
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post #3 of 11 (permalink) Old 09-30-2009, 08:44 AM Thread Starter
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Right, I know the powerglide and the 12 bolt are used by a lot of drag racers but that they only resemble their stock counterparts in outward appearance only. I also know that the PG can be made to handle just about anything and that the 12 bolt is strong, but not as strong as the Ford 9"...

My real question is what can I safely put through a stock PG and 12 bolt. I'm not a drag racer, just a 24 year old guy trying to build his first 'hot rod'. By hot rod I mean I just want a streetable car that has some bite to it. I am thinking in the area of 500-600 hp/ torque...enough to be faster than most other cars running around but still be relatively streetable.

To better explain my situation I plan to pull the current 350 in the next few months and upgrade the engine and drivetrain as necessary within my budget...

The first option I looked at was to do a budget 383 build to make about 400-450 hp/ torque. I have read several articles on this topic and you can build said engine for about $2,000. The second option was to find a decent 396 or 454, slap on a few minor upgrades to hopefully get about the same power range with the same price tag.

Given factory engine specs, I had figured that for both those scenarios the stock 12 bolt would be sufficient, but the PG would not be. With the price tag of those two builds I could still afford to upgrade the transmission and even if the stock PG would handle the power I had planned on doing some upgrades anyway to improve shifting.

The other option I considered is to sell one of my project cars and parts in order to buy a complete big block crate engine that makes about 550-600 hp/ torque... But I was wondering if the stock 12 bolt would handle that much power because I can't afford to upgrade both the transmission and the rear end after buying the crate engine.

Long story short...will the stock 12 bolt handle 600 hp and how much do you need to upgrade the PG to handle the same level?
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post #4 of 11 (permalink) Old 09-30-2009, 02:32 PM
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!2 bolt wlll hold any warmed over big block (and in stock form it is half again stronger than a FORD nine inch rear end). You are confusing those Strange, and Moser, or Currie rear ends for a Ford product which they are not. A stock 8.5" ten bolt is on par with a Ford nine inch as found in a salvage yard in terms of torque capacity.

The strength of the rear goes down as the gear ratios goes up since it is ultimately torque that breaks a rear end, not horsepower. So as you add torque multiplication by installing a deeper gear, the axles have to grow in spline count to keep them from breaking if you ever find traction. On the street, with street tires and gearing, you will not break a 12 bolt with even the strongest BBC that Chevy ever produced (460 horse 454 only put out 490 ft/lbs of torque).

The PowerGlide won't last behind a BBC or even a hot small block Chevy without a full rebuild and a lot of aftermarket parts thrown at it (hardened input shafts, steel drums, sprags and output shaft for starters). The factory only used a TH400 behind a big block.

Everybody loved the idea of a third gear so much GM reworked the TH400 by making a 4/5 scale model of it and called it a TH350, and then promptly stopped producing the powerslide as demand for it fell off with the new TH350 in the mix. Once again do not let those race cars running Glides influence your decision there as they don't use a 'glide at all but a B&M, or TCI or J&W or some other aftermarket hand made with all aftermarket parts tranny. It is a PowerGlide in name only.

Big Dave
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post #5 of 11 (permalink) Old 09-30-2009, 05:00 PM
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As far as gear sets go for the 12 bolt it's been my experience (and the guys at my drive line shop) that OEM GM gears are the best as far as durability and strength.
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post #6 of 11 (permalink) Old 09-30-2009, 06:22 PM Thread Starter
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Thanks for the info guys. Glad to hear that a stock 12 bolt will work for me.

As for the Powerglide, the main thing I was thinking was simplicity (no mods to the shifter linkage or cutting holes in the floor) and less power loss through the drivetrain. Correct me if I'm wrong but a built PG would have lower losses that a built TH400 because of the lower rotating mass right?

Of course I also just kinda want to have a PG since most of the other Chevy guys I know don't like the PG and swapped it for a TH350 for better cruising and I just want to be different and stick with a PG...even though it would end up being a TCI 'Powerglide' and not the GM PG.

Any recommendations on the best converter size for my car? Again, not drag racing so I don't need to launch the car or anything, just want good from-stop acceleration. So in my case I would want a converter with a lower stall right? How do you determine what the best size is for a given car?
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post #7 of 11 (permalink) Old 09-30-2009, 09:44 PM
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Higher stall speed converter has a bigger number which is to say it is built looser or more prone to slip. You have to have a stall speed that is below your cruise RPM as you don't want a slipping transmission going down the road. think of a converter as slipping a clutch, the higher you rev the motor before the clutch fully engages (in torque converter terms we say it flashes or "locks-up" which is another misnomer). You don't want to drive with a slipping clutch because it will burn up. Same with a high stall speed converter it converts all that power that isn't being use to drive the car (the slipping percentage) into heat.

A store bought PowerGlide will work behind a BBC if it is built to handle the torque; but I wouldn't necessarily buy an off the shelf tranny from TCI or any other national builder (such as B&M). Reason there are a lot of local shops were you can talk to the tech who will build your tranny for you customized to work with your motor and they can build it to hold the same power for less money than the national tranny can for a generic one (and it saves on shipping). I have J&W down the street from where I live so they build my converters (I build my own transmissions and motors).

Go to your local race track and ask around who built theirs. Word of mouth is great advertising and it doesn't get added to the tranny you buy's bottom line the way a national company does with their advertising budget. This is especially true with torque converters. Get one built for the gear that will be in your car and to the car’s weight; tuned for your cruise RPM so that the PowerGlide will be happiest behind your motor. Even though you can buy an off the shelf 3200 RPM stall converter; it will only stall at 3,200 RPM behind a 350 with a TH350 and with only one cam grind and only one size of carb and with only one set of heads, etc. If you change anything from the motor that they tested it on it will not stall where you think it will. Besides the car’s weight is the single biggest factor in when a converter stalls with a given amount of torque.

I would rather wear someone else’s under-ware than use some one else’s torque converter. It is the most unique part in your car and should be tailored to fit your car.

Big Dave
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post #8 of 11 (permalink) Old 10-02-2009, 03:46 AM
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Quote:
Originally Posted by Big Dave View Post
!
The PowerGlide won't last behind a BBC or even a hot small block Chevy without a full rebuild and a lot of aftermarket parts thrown at it (hardened input shafts, steel drums, sprags and output shaft for starters). The factory only used a TH400 behind a big block.
Big Dave
I'm far from trying to correct anyone, but just as a point of info, Chevy used the PG behind the 427 in the corvette.
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post #9 of 11 (permalink) Old 10-02-2009, 08:36 AM Thread Starter
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Wow, I had no idea that a torque converter was such a custom fit part. I thought rpms were the only thing that mattered to it. Thanks for all the info, it certainly puts the selection of my transmission & converter combo in a new light.

We do have a good set of shops in the area and a lot of local racers who could point me in the right direction. Given what you told me I will definately be going the route of having a local builder custom build me a transmission & converter since I think both of those tasks are a little out of my league given my experience level.

As far as the powerglide behind the 427...that brings me back to my earlier question in that isn't the powerglide that went behind a 396 or 427 different than the powerglide that went behind my 283? I have heard before that they are and surely GM wouldn't put a transmission that can handle 400 hp behind a motor that only makes 200 right?
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post #10 of 11 (permalink) Old 10-02-2009, 04:32 PM
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Quote:
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As far as the powerglide behind the 427...that brings me back to my earlier question in that isn't the powerglide that went behind a 396 or 427 different than the powerglide that went behind my 283? I have heard before that they are and surely GM wouldn't put a transmission that can handle 400 hp behind a motor that only makes 200 right?
Not having built a PG I would have to believe that internally a PG from a small block and big block may have some differences, but nothing out of the exotic or unusual. TH350's, 700R4's/4L60E's have been used across a wide range of vehicles and power ranges(I-6, V-6, V8). Most of the internal beefing up is limited to extra clutches!! The geartrain that is used in V8 700r4s are the same as the ones used in a 4.3L V6. The 2.8L version has the same geartrain but uses less clutches. Meaning the transmission is acutally overbuilt for the smaller engines and yet can still hold up to the V8. It's one of the reasons I look for 4.3L 700R4's when building, due to the V8 bell housing and the fact that the 4.3 doesn't have the power to do damage to the trans.

As you said, you were going to use this car to cruise and have a little added punch. If you were going to race it then I would say there are better choices, but for cruising, the PG is an amazing little trans. I've been driving my brother's 69' Impala PG 327 4dr sedan around and find it quite a blast!
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post #11 of 11 (permalink) Old 10-02-2009, 05:40 PM
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GM made three PowerGlides; two have aluminum cases and one has a ventilated air cooled cast iron case. There was a six cylinder version in aluminum and a V-8 version. The 1966-67 427 C2 corvette was a flyweight car weighing only 3340 pounds even with a BBC installed. The 427 and 396 were not high torque motors being an over square high reving motor along the line of a high reving small block like the 302 or 327. So a low torque lightweight car could benefit from a PowerGlide especially when equipped with a 4.10 or 4.56 street gear or a 5.13 to 5.38 for racing.

Behind a stroked 454 in a heavy car I couldn't recommend one, especially with a low three series gear.

Big Dave
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