torque converter lm7 swap 4l60e 84 Monte

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doood

Amateur Mechanic
Sep 24, 2020
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I got back the rebuilt 4l60e yesterday with a 4843TWBX GoPNH (precision of New Hampshire) refurbished torque converter, which was original equipment with the 5.7litre 2004 GTO. GTO weighs 500lb more than my 1984 Monte (3700lb vs. 3200lb) and has 50 more horses (350 vs. 300). The powerband of the LM7 shows like 340ft-lb torque at 2500RPM. I'm having a hard time determining what will be the approximate stall speed with stock 300hp LM7. The engine/trans came from 2003-2004 RWD Silverado. Do I have a good torque converter? My friend told me it is probably 1700 RPM stall speed - I contacted the manufacturer and asked. I see people on gbody forum using 1900-2500 stall speed torque converter. Trans not installed yet, so I can change the converter if convinced.

I'm going to put a 3.73 posi in the 7.5" rear - found a kit with rave reviews here: https://www.quickperformance.com/GM-75-7625-10-Bolt-Posi-Gears-Bearing-Kit_p_20409.html
 
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doood

Amateur Mechanic
Sep 24, 2020
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Unless you're drag racing, the stall speed won't really matter, and I certainly wouldn't drag race that trans/rear combo.
Building a driver for sure. I figure the rear will hold up; keeping the 7.5" 10-bolt stock rear seems to be my cheapest option at this point.
 

64nailhead

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Dec 1, 2014
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If you have a stock cam and want to cruise, then a stock stall of most anything below 2200 is what you're after. A cam swap is what makes a low stall converter SUUUUCK.

For a 3.73 gear you need a 27" tire at a minimum. If you're still on the stockish height of 25-26", then a 3.23 gear will work and a 3.42 gear for a little more rpm.

Is your motor stock and what is your rear tire size? Better recommendations will follow.
 
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doood

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Sep 24, 2020
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If you have a stock cam and want to cruise, then a stock stall of most anything below 2200 is what you're after. A cam swap is what makes a low stall converter SUUUUCK.

For a 3.73 gear you need a 27" tire at a minimum. If you're still on the stockish height of 25-26", then a 3.23 gear will work and a 3.42 gear for a little more rpm.

Is your motor stock and what is your rear tire size? Better recommendations will follow.
Ok. Car has 26" OD 235/45ZR-17 on 8" width TorqueThrust2 - new - keeping them. The motor is stock LM7 5.3L. The rear gear is currently the 2.41 original equipment that was paired with the V6 and THM250 3 speed. So you think 2500 RPM at 70 mph is too high and I need to go with 3.42?

car still has the v6, 3-speed, and 2.41 gears. I just got the trans rebuilt and gathering parts.
 

64nailhead

Goat Herder
Dec 1, 2014
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A stock motor will cruise happily at 1700-1800. You mention 70 mph, if that’s a speed that you intend to drive it a lot, then I would aim at 2000-2300 rpm window.

With a 26” inch tall tire I would definitely pick between a 3.23 or 3.42. The stock cam is super friendly at low rpm’s. The nice thing about the taller (numerically lower) gear is that it will easily downshift from OD to 3rd when you want to accelerate and not be screaming and also getting great fuel economy when it’s cruising.
 
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ssn696

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The 4L60 has the steep 3.06 first gear. You might also consider a 3.08 rear ratio. I’m not sure you can find new 2-series limited slip carriers anymore, so that may be the deciding factor.
 
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doood

Amateur Mechanic
Sep 24, 2020
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A stock motor will cruise happily at 1700-1800. You mention 70 mph, if that’s a speed that you intend to drive it a lot, then I would aim at 2000-2300 rpm window.

With a 26” inch tall tire I would definitely pick between a 3.23 or 3.42. The stock cam is super friendly at low rpm’s. The nice thing about the taller (numerically lower) gear is that it will easily downshift from OD to 3rd when you want to accelerate and not be screaming and also getting great fuel economy when it’s cruising.
Ok. I thought the 3.73 was safe because that's what came on the SS starting in '85 when they went to the 2004R overdrive, but actually doing the gearing math shows that the 3.42 with the 4L60E is closer to the overall SS gearing. Yeah it's safe to say that this car is going to do more highway driving then burnouts. Back to the first part of the original question, do you believe this GTO torque converter with a slightly higher stall speed is good? It's not a particularly expensive part and the shop said they will exchange it if I want another - it's not installed on the trans yet. The trans is going to sit in my basement until the spring.
 

ssn696

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It’s a locking converter, yes? If so, the stall RPM should not have a major impact the cruising RPM.
 
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doood

Amateur Mechanic
Sep 24, 2020
549
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The 4L60 has the steep 3.06 first gear. You might also consider a 3.08 rear ratio. I’m not sure you can find new 2-series limited slip carriers anymore, so that may be the deciding factor.
Do you see that link up above where I posted 7.5" 10-bolt posi upgrade? Mechanic down the street says he'll put that $600 kit to replace my 2.41 for $600 labor. I'm not qualified to do it myself.
 
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