bainer1290

Building a 72 Cutlass S, want it to be a fun street car, it won't see much time on the strip. Had cutlassefi do up my cam and he said to aim for a 2,500 stall. Looking for recommendations for a brand or model that won't blow my budget.

Car specs
-Olds 455 with a TH400
-KB 277 30 over pistons (comp around 10:1)
-Cam 232/240 @ .050 on a 110, with .568 lift on both
-Comp Roller Rockers, Springs, Pushrods, etc...
-stock rods & crank align honed/balanced
-Large Valve 2.07/1.71 G heads light porting job (crossover filled and dividers done)
-Edelbrock Performer 2151 intake / Quadrajet jetted to match engine
-Hooker Comp non-tuned Headers 3902 / Pypes 3 inch dual exhaust / X pipe
-HEI Distributor
-TH400 trans, red alto perf rebuild with Transgo 400-Stage 2
-Rear end is a 3.70 posi

droldsmorland

Go to Jegs and look at the converter application chart there. It has all the cam, rear gear matching info etc...Search my name as well as I just answered this same Q last week. TCI, Coan, Hughes etc...all high quality converters. Use the TCI clear synthetic fluid.

bainer1290

Thanks Dr Olds

Was looking at Hughes at Summit, they have 2 options GM25BPO vs GM25BPOHD looks like one has a HD Sprag, not sure what that means?

Also should I be looking for a 12, 11 or 10 inch stall, I know smaller usually relates to s higher stall but the internals also do that.

I want to find one that will be able to allow me to cruise nicely but if I do decide to put my foot in it I can also have some fun.

JCMC64

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droldsmorland

I think you would be happy with the TCI Breakaway. With your engine, rear end combo. Stock size no need to go to a 10". I would go with either that or the Staurday Night special (or slimilar from Hughes). HD parts in a converter are a must. Sounds like Hughes has that covered. A converter is somewhat of a personal choice how much slip is enough for you. The Saturday Night Sp is one step above stock the Breakaway is the next step. I have the Breakaway in a .030 over, 11:1, G400, TCI Street n Strip semi-manual valve body TH400, W30ish spec 400HP (396 on the dyno), 308 rear. I like its all around manors. Flashes nice when needed yet not too much slip for cruzing. I would like another gear to bring down the Rs at highway speeds. Thinking Gear Vendor overdrive soon

Stevec

Bainer I have a tci breakaway with less than 200 miles on it in the box. Ill give you a great deal on it.

bainer1290

Thank you again for your feedback Dr Olds

MDchanic

It seems to me that most of your question is one of nomenclature, not of what parts to get.

Before buying custom parts, it is always wise to learn how those parts work and what their constituent parts are called.

Here are two articles about torque converters, one in Diesel Power magazine, and one from Wikipedia.

A sprag clutch is a one-way overrun clutch that uses tiny sprags to grip a (usually knurled) surface, like this:



Here is a video describing the operation of a sprag clutch:


To answer your question:

Whether to buy a light-duty or heavy duty sprag model depends on your power level and the price difference between the two models.

Stall speed is related to converter diameter, in that a larger converter will stall at a higher speed, all other things being equal, but you are primarily interested in stall speed. Get the converter with the stall specification recommended for your cam.

Larger diameter converters will generally handle more power, all else being equal, so, unless you have a good reason not to, get the largest converter that will fit your application.

- Eric

bainer1290

Thanks for that info Eric, good stuff helps me understand the inner workings of the stall.

So I think its down to the TCI Breakaway vs the Hughes.

Breakaway 240900
-The first step into serious high performance, the Breakaway is a great torque converter for moderately modified street machines and weekend racers also used as daily drivers. It provides approximately 2400 to 2600 RPM flash stall without negatively affecting part-throttle driving. Designed for efficiency at highway cruising speeds and to launch hard at wide-open throttle.
-10 inch
-Furnace-brazed fins
-Needle bearings
-Hardened, pre-ground pump hub
-Computer Balanced
-Installed Hardware Included

Hughes GM25BPOHD
-The "Street" converter was design for the driver who is looking for that competitive advantage. By raising the stall RPM you can eliminate that slow, sluggish start. Recommended for stock to slightly modified engines to achieve performance, along with a smooth idle when the car is in gear.
-12 inch
-2,500 stall
-HD Sprag
-Steel Turbine Spline
-Spot Brazed Fins
-7/16" Mounting

So the TCI is a 10 inch and sounds like it can be driven nicely at part throttle. The Hughes is 12 inch with no mention of part throttle driving. The Hughes does have the HD sprag but the TCI doesn't mention the sprag? Both are around $320 new so tough call as I like features of both of them...

Leaning towards the TCI Breakaway anyone have more feedback on them?

droldsmorland

Thought the Breakaway was a 12 incher? Furnace braze is better IMO. Again it’s a personal choice both are quality units. I have not personally used Hughes. Bud has one in a 70 Z28 Camaro, Strip/barely street car, drag radials, high 10s with a 502 TH400 w/a break. Hasn’t broke it yet flashes the hell out of it. 5 seasons no sign of ballooning etc...Personal choice. The main reason I went with TCI was to match the tranny. Mines been going for 14 years without incident.
Be sure you getting the right application with the correct feet to mate with the Olds flywheel. Inspect and or replace your flywheel. Look at the vibe damper too. TCI has a killer vibe damper.

bainer1290

Just talked to TCI they recommend 240901 which is similar to 240900 except it has an anti-ballooning plate.


TCI® Breakaway Torque Converter
The first step into serioushigh performance, the Breakaway is a great torque converter for moderatelymodified street machines and weekend racers that are also used as dailydrivers. It provides approximately 2400 to 2600 RPM flash stall withoutnegatively affecting part throttle driving. Designed for effeciency at highwaycruising speeds and to launch hard at wide-open-throttle, the Breakaway is afantastic all-around torque converter featuring furnace-brazed fins, needlebearings, a hardened, pre-ground pump hub and computer balancing.
Applications:
Fits1965-91 GM TH350/400 with Dual Bolt Pattern

Features& Benefits:
■ Needle bearings
■ Hardened pre-ground pump hub
■ Computer balanced
■ Higher rpm launches & increased torquemultiplication for lower e.t's
■ Furnace-brazed fins
■ Fully streetable (no modificationsrequired)
■ 2400-2600 Stall (depending on vehicleweight and engine torque & horsepower)
■ With heavy-duty front anti-ballooning platefor nitrous applications

Fun71

I have the Hughes GM25BPO in my car and I have no complaints. The slippage at cruise is around 200 RPM or so, even when I had a 2.56 rear and was well below the stall RPM during steady cruising on 45 MPH roads (turning ~1800 RPM).

bainer1290

Thats good feedback on the Hughes also, miking my decision tough! haha

oldcutlass

I have the Breakaway with the anti ballooning plates in my car. I have 3:08 gears and it works well.

anthonyP

I noticed you had 3.08 gears in your Cutlass and are still thinking of an overdrive. I am planning on installing 3.08 gears in my '71 442 to keep the RPM's down, with possibly 15" tires. Should I be looking at 2.73 gears instead, as I'm trying to stick with a TH400?


Also, do you possibly know the factory stall speed for a '71 442, and the torque converter diameter size?

Fun71

Any idea what RPM you would like for a given MPH? That will tell you what gear and tire combo to shoot for.

I have 3.23 gears and 245-60-15 tires and the engine turns around 2900 RPM at 65 MPH, which is fine with me. Some folks are freaked out with the engine turning that RPM, though. Too used to modern cars that are set up for economical highway driving I guess. If you go with 15" wheels you could lower the RPM a bit with taller rear tires such as 275-60s. Check out some of the online calculators to see what RPM different gear and tire size combinations give.

MDchanic

Or too concerned about the car performing well.

In your case, with the modifications you've done, your final drive ratio seems about right, but note the torque curves for cars with a factory setup:




You can see that torque begins to roll off between 3,200 and 4,000 RPM, depending on the motor, so running around three grand on the highway might be detrimental to drivability.

- Eric

bainer1290

Anyone heard of Freak Show Performance, lots of good feedback from them on other forums for building custom converters. Prices seem close to that of an off the shelf TCI or Hughes stall except they will build to your specs.

matt69olds

A good quality converter wont feel mushy at low throttle, but will flash the engine into its happy place when standing on the loud pedal. Coan, ATI, Hughes, all make excellent converters. Call them, be prepared to spend some time detailing exactly whats in the engine, and have one custom built.

bainer1290

Talked to Hughes they recommended the GM25BPO-400BP,

Here's a comparison from them of the GM25BPO models they offer:

• GM25(BPO), 3 x 10.75" bolt pattern, 12" model, M10 x 1.5mm metric bolt threads, $229.00 cost
• GM25(BPO)-400BP, 3 x 11.50" bolt pattern, 12" model, M10 x 1.5mm metric bolt threads, $254.40 cost
• GM25(BPO)-HD, 3 x 10.75" bolt pattern, 12" model, M10 x 1.5mm metric bolt threads, heavy duty upgrade includes additional spot brazing of impeller and turbine fins, heat treated turbine spline, and heat treated sprag race, $299.75 cost

The HD ones is a bit stronger build but smaller bolt pattern... I this I will go with the one they recommend the GM25BPO-400BP.

bainer1290

I actually ended up going with a converter from Freakshow Performance out of Texas. I called and talked to Mike he custom builds each converter. He builds them in a 9.5 inch case that has the dual bolt pattern on it. Sounds like he knows his stuff and the feedback from him on other forums is very positive. Will post some pics when I get it in the next few weeks.