Supercharged 5.3 (GMT-900) - will stock(ish) torque converters live?
 

I finally pulled the trigger on a Magnusson supercharger for my '07 Silverado 1500 4x4 with the LMG. Also will be doing a Truck Norris cam, AFM delete with new lifters, with American Racing long tube catted headers (finished off with a full dyno tune, of course). I've already got a PerformaBuilt Heavy Hauler 4L60E with 5-pinion planets, beast sunshell, and Sonnax Smart Tech drum, along with all the associated mods in the Heavy Hauler line. I was told by the builder that the torque converter is the weak link in all this. It's an FTI converter (unknown p/n or model) - all I know is it's painted black and has a 2k RPM stall since I tow frequently.

All that said, I've seen posts on here of guys running boost through the stock torque converter, and I assume this FTI converter was built based on the stock unit (probably uses the stock lockup clutch inside). As you can probably tell, I'm dreading having to touch this transmission again - the install was a friggin NIGHTMARE straight from hell. If I can get away with leaving this converter in here, that would be fantastic ... but if there's any doubts as to it's longevity, I'll have to pull it. I've got $5k into this trans and can't afford to break it pumping metal through it.

What say you guys? Should I just put a converter in that's built for boost, or can I run this stockish FTI? The converter works FANTASTIC, so I'd hate to lose that. Made the stock truck feel like it gained 100 ft. lbs. off the line - dramatic difference. I bought the truck brand new, and it was always weak off the line. Not anymore. It will actually squeal the tires now if I stuff it.

Anyway ... anyone run boost through a stock converter, beating on it and towing for many tens of thousands of miles?

EDIT: Just as I posted this I received an email back from FTI on this converter. Unfortunately I'll be exceeding the limits of this converter. What do you guys recommend for a low-stall towing converter that can handle boost?

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I'd fill out the "Ask CDS" form on the Circle-D web page with all your trucks specs then either Brian or Chris will reply via e-mail. For a bulletproof street setup in your stall range I'd go with the 265mm triple disk. With the triple you can lockup the converter WOT with no clutch wear issues. They have a 4-5 week build time so get the ball rolling ASAP. The FTI converter will be ok while you wait but try to avoid WOT lockup on the stock type lockup clutch.

Be sure to change out the filter during the Performabuilt specified mileage. If you can achieve break-in on the FTI you'll save money on fluid & filter when you install the new converter if your in that window. Performabuilt tags the bottom of the filter during the build so they'll know if the filter has been serviced if warranty issues arise. Frank is a smart but sneaky guy lol

My Performabuilt "tagged" filter

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Thanks brother - appreciate the info. The supercharger is on a 14-16 week lead time right now, so it's going to be some time before this project gets rolling. Good thing, because I hadn't budgeted for a converter, and this is stretching me thin.

Ahh, I see you got the same one! Yeah, I noticed a tag on mine from a different guy when I changed the fluid last year. I did the install when my OE trans burned up 3 & 4 at 103k miles in November of '20. Had it built knowing I'd hot rod the truck at some point in it's life - didn't expect it to be this soon.

Hoping I never have to send this trans back. He was pretty confident that I'd never break it, but that's when it was stock. I'll be out of warranty by this fall. I'm dreading separating this trans from the engine again. It absolutely SUCKS on the 900 series trucks. Whoever thought it was a good idea to put a bolt right up at the very top of the bellhousing is an a-hole. The worst engineering I've ever seen. It's as if they did it on purpose to punish mechanics ...

Thanks again - I'm going to go to Circle-D's site right now. :cheers:

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The gmt900 are a piece of cake, I just R/R'd one last night. Takes 20 min to drop it out.
Try removing a 6sp manual in a coyote mustang if you want some fun :)
The converter will be ok for a little while if the tune is setup right and not locking the converter while in boost.
it took me 5 weeks exactly to get the last 3 converters from Circle D.

Nothing is easy in the Northeast, especially after 15 years of road salt. Took me 2 weeks to R&R the trans / transfer case .... WITH a LIFT.

Yeah, I HATE modern vehicles. Every year I hate them more! I'm in the wrong line of business, lol. Thanks for the info.

Filled out the form on Circle D's site - just waiting for a response.:cheers:

Just found the email - they got back to me this AM. I didn't see it buried in the 300 emails I get every couple hours.

Looks like they recommend the 01-13-06-1B Pro Series 265mm billet triple disc. Sounds like exactly what I need. That just SMOKED my budget. Wow, stuff ain't cheap today! I remember when sinking $300 into a vehicle would completely transform it. Now headers cost 6x that! I suppose this stuff ain't getting any cheaper, so might as well get it over with. This truck is going to be pretty sweet when it's done. Thanks for your help, fellas.

Any tips for GMT 900 owners?

I have the 265mm triple disc 1a, which is tighter than the 1b. CircleD recommended the 1b to me as well. Have you ever lived with a loose converter? If you drive this thing a lot, you might want to consider the tighter convertor.

i went 1a 2600 stall and had no regrets at all

I'm not sure I completely understand the terminology. Loose as in it will flash to its stall RPM easily, like at part throttle? I've owned a few hotrodded vehicles over the years, but never played with stall converters before. I don't fully understand what "tight" and "loose" are.

In their email they made it sound like it will be perfect for a daily driver, but still hold up to my abuse in MA traffic, towing heavier than I should be at higher than normal speeds, coupled with full throttle launches while loaded and still survive a long time.

At least there was no sales tax saving about $100. They offered me a $250 credit on my old 278mm Circle-D single disk... maybe they do the same for the FTI single?

How do you know you're getting the 1A or 1B converter? Just ordered the 258mm triple disk in the 3400 to 3600 stall range. No where on my receipt does it say 1A-1B. Maybe the lower stall range 3400 is the 1A and the higher 3600 is the 1B :confused: lol

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Loose as in you will have to rev the engine higher to get moving normally. My truck weighs 6k lbs on the dot and during a normal takeoff from a stop light, the engine revs to around 2400 rpm with the Cirlce D 265mm 1a. It was much lower with the stock convertor, like 1800 or 2k (don't remember exactly). Yes if you want a snails pace takeoff you won't need to go to 2400. If I didn't street drive my truck a lot, I would absolutely go higher stall (looser) for killer 4x4 takeoffs, but the higher revving for normal take off's really puts the mpg's in the crapper.

It really depends on what you are willing to live with. While I'm sure I could have better high throttle takeoffs with the 1b, normal driving is better with the 1a. The 1a for my heavy Crewcab 1500HD was looser than I was expecting. I believe it's just a stator change from 1a to 1b, so you could always send the convertor back to be reworked if you don't like the one you pick. So I went on the conservative side getting the 1a thinking I could send back for the 1b and stuck with the 1a.

Thanks, Red, for that info about turning in the old converter - I'll ask them about that whenever I scrape the cash together to order. Hopefully they'll take it.

Much appreciated, pknowles! I had it right, I just couldn't explain it. I remember discussing this with someone 30 years ago, but most of that info was all long since forgotten. That '78 Cutlass I had back then with a Crane 292H cam barely idled, yet had the stock converter! I used to get smoked by Ford Escorts at green lights for the first 100' because of that. It was embarrassing, lol. Didn't know how converters worked then. Once the tach hit 3k, HANG ON! She took off like a missile! :)

Red, I think that 1A / 1B thing could be a completely different build for our applications. I tow between 5,500 - 9k lbs. regularly with mine, so that could be why they suggested this custom build with a different part number. I think our clutches are probably the same, but everything else is different from there due to what we're doing with our trucks. My stall is going to be in the 2k- 2,200 RPM range not just for towing, but also because 4 months out of the year I have to drive in snow and ice. Flashing to peak torque doesn't work in snow, lol. You just spin endlessly and go nowhere.

That is a lot of stall for a blower , in my opinion. But it is all really personal preference.

Just an update ...

I talked with someone at Circle D about the "1A" vs "1B" subject. They stated that on the 265mm converters, the 1B is TIGHTER than the 1A.

On the 258mm converter, it is OPPOSITE. In that case, the 1A is TIGHTER than the 1B.

Hope this clears things up.

With the LS having such weak bottom end torque, I think with the blower it'll be just right. As it is in stock form, the truck hardly gets out of its own way until over 3k RPM, and really comes on nicely at 4k. Crazy high compared to what I grew up with.