BUILD THREAD Motor Swap, Transmission and Torque Converter Swap, and Rear End Upgrade...

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Tynan918

Royal Smart Person
Aug 2, 2021
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What's up guys? It's been a long time and a long way since I posted in this forum...

I played a lot and have fixed a lot with this car and motor since I've been here last.

I'm beginning to generate some decent income and I would like to replace my motor, torque converter, transmission, and upgrade my rear end or replace it.

I've learned that my 305 is a 1981 LG4 with L69 (H.O.) heads. I replaced the camshaft in February with a Comp Cams 260H camshaft and lifter kit, 212 int./212 exh. @.050" lift. Still the same Edelbrock Performer EPS Intake Manifold. Replaced the 750cfm Edelbrock carb for a 600cfm 4160 Vacuum Secondary Holly/Quikfuel. Timed at 12° initial, 34° total.

Transmission is a BOP THM350-C with a stock 1397 stall 30 spline lock up converter.

Rear end is a 7.5/7.625 10 bolt with a 2.41 gear ratio, non posi peg leg.

Right now, my top speed is 104 @ 3300 RPM...I'm being told the 2.41 rear gears are too much/too tall for my 305 to go any faster or higher in RPM.

I have a vacuum secondary opening issue with my carburetor. The housing whistles because I lost a check ball to the vacuum secondary housing...not sure if that would disable the vacuum secondaries or not, but it wasn't whistling until I removed the housing to install a new diaphragm and quick change kit, not aware of the check ball. I'm also told with my 305 and my max RPM only being 3300, it may not produce enough vacuum to open up the secondaries.

Transmission I don't know much about other than it's a BOP THM350-C. Torque converter is a 1397 stall lock up converter. 3spd and a small converter also not matching up to the too much/too tall rear gears.

I want to swap it all out and upgrade it all.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
1,136
249
63
In general, I want this street strip ready, but as fuel mileage friendly as possible for cruising and highway driving...the most I commute is 150 miles total as far as distance to and from.

I plan on rebuilding the new motor, and transmission and rear end if need be.

As far as the motor I want to keep things carbureted and mechanical as possible, no computers or sensors or extra wiring like an LS swap. I also prefer something I can install a roller cam into...moving away from flat tappet.

As far as the transmission I want a 700R4 with a higher stall range converter and I'm not sure of the difference between lock up and non lock up to know which one I want to roll with.

As far as the rear end, I'm advised 3.55 or 3.73 limited slip posi... I definitely want to burnout, donuts, and drift and slide around.
 

Tynan918

Royal Smart Person
Aug 2, 2021
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So how is this all calculated/formulated ?

Do I start with the rear end, then transmission, then torque converter, and then engine ?

...Or is it the opposite direction starting with the engine ?
 

Rt Jam

G-Body Guru
Mar 30, 2020
623
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Ontario Canada
In general, I want this street strip ready, but as fuel mileage friendly as possible for cruising and highway driving...the most I commute is 150 miles total as far as distance to and from.

You will need an overdrive and lower rear gears to do both.
How much power you plan on making will determine the rear. I would not trust a 7.5 after 400hp or 11 seconds or so. Not the best gauges for differential abuse but it's some guidance.

700, 200 or 4L60 transmission. The rear could be an 8.5 but they are getting hard to find.

If you do the engine first, the trans will probably not survive.
 
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Built6spdMCSS

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Jun 15, 2012
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Oh boy... I'm just here...


Anticipation Popcorn GIF
 
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Tynan918

Royal Smart Person
Aug 2, 2021
1,136
249
63
You will need an overdrive and lower rear gears to do both.
How much power you plan on making will determine the rear. I would not trust a 7.5 after 400hp or 11 seconds or so. Not the best gauges for differential abuse but it's some guidance.
Gotcha.

So somewhere in between 350 and a 400 Gen 1 SBC, but can I convert them to roller cam ?

5.3 or 5.7 Vortec if Vortec ?
700, 200 or 4L60 transmission
Which is better for street strip, 200 or 700 ?

Will the 4L60 require any electric wiring ? How hard would it be to fit the 4L60 into the G-Body ?
If you do the engine first, the trans will probably not survive.
Ok transmission before engine...got it. But which comes first between transmission and rear end ?

If 8.5 is recommended I'll look for one, what vehicles can I pull one from if I decide to pull one from a salvage yard and would it be a direct fit ?

What are the pros and cons between 3.55 and 3.73 gear ratio ?
 

Built6spdMCSS

Geezer
Jun 15, 2012
5,839
9,778
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Florida Beach
Lol at the 8.5 from a Gbody.. you got like 10 years worth of reading to catch up on of how to find one of them now.

Same as your other posts, guys here will take their wasted time to give you advice that you won't listen to, you'll do the literal opposite and run your sh*t into the ground.

So why are you here?
 
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UC645

Royal Smart Person
Apr 20, 2020
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Kittanning, Pa
Gotcha.

So somewhere in between 350 and a 400 Gen 1 SBC, but can I convert them to roller cam ?

5.3 or 5.7 Vortec if Vortec ?

Which is better for street strip, 200 or 700 ?

Will the 4L60 require any electric wiring ? How hard would it be to fit the 4L60 into the G-Body ?

Ok transmission before engine...got it. But which comes first between transmission and rear end ?

If 8.5 is recommended I'll look for one, what vehicles can I pull one from if I decide to pull one from a salvage yard and would it be a direct fit ?

What are the pros and cons between 3.55 and 3.73 gear ratio ?
Tie-bar lifters exist for the conversions. They’re not cheap, but the lower end of those run the risk of being trash in today’s economy. Haven’t heard anything bad about Howard’s yet.
Best bet would be to get a 86’-up 350, ditch the heads if they’re swirl ports, have a shop magnaflux them if they’re Vortecs. Keep an eye around swap meets, but don’t count on getting lucky there. 5.3’s are LS based, the Vortec SBCs were only 305s and 350s.

200’s have a lower numerical gear ratio for 1st which lends itself better for drag strip use, but both the 700 and 200 require some upgrades in hard parts to hold torque. 200’s are more of a fine art, and 700’s tend to be a minefield in the aftermarket.
Couple tips: clutches and a shift kit don’t make a transmission capable of holding 700hp, and stay far away from Monster Transmission. If you go 200, stick to the known turbo Buick builders.
4L60E is a waste, requires wiring. The 4L60 (no E) is just a 700R4 with a different designation.

If I say this once, I’ll say it a thousand times: for the price of a G-Body 8.5, find a Fox 8.8, rebuild it, get a swap kit, get 5 lug axles, stick to drums and be done.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
1,136
249
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Lol at the 8.5 from a Gbody.. you got like 10 years worth of reading to catch up on of how to find one of them now.

Same as your other posts, guys here will take their wasted time to give you advice that you won't listen to, you'll do the literal opposite and run your sh*t into the ground.

So why are you here?
Have had it up and running the last two years because of advice from 1,000's of others in other forums and other online resources...

I have came a long way and have learned alot, even from bad apples, like you, which ironically I only get here.
Screenshot_20230925_233125.jpg
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Last thing I posted here I believe was late 2021-2022 about a camshaft replacement but left it unfinished...so I'll catch you up on everything I've worked on after...

Also, this Monte isn't my first old school chevy, or Gbody for that matter...
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Well I got that camshaft and those lifters swapped with a Comp Cams 260H 212 int./212 exh. camshaft and lifter kit.
Screenshot_20230925_235050.jpg
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Went ahead and raised the motor up enough to pull the oil pan, inspect the crankshaft, and replace the gasket while I was at it.
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Managed to do away with the push button theory and actually fix my actuator rod in my steering column...was a complete tear down and rebuild. Now I start my car with my key..have been awhile now.
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Managed to get a balancer bolt in my crankshaft snout...
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Deleted my AC/Heater box and replaced the hole with a block off plate...
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Replaced the driver door hinges, handles, and the hood with a cowl hood, and hood hinges all at once...
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Replaced my broken shifter cable and swapped my factory floor shifter with a B&M Star Shifter.
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Tynan918

Royal Smart Person
Aug 2, 2021
1,136
249
63
Have had it up and running the last two years because of advice from 1,000's of others in other forums and other online resources...

I have came a long way and have learned alot, even from bad apples, like you, which ironically I only get here. View attachment 228679 View attachment 228680

Last thing I posted here I believe was late 2021-2022 about a camshaft replacement but left it unfinished...so I'll catch you up on everything I've worked on after...

Also, this Monte isn't my first old school chevy, or Gbody for that matter... View attachment 228667 View attachment 228668 View attachment 228669 View attachment 228670 View attachment 228671 View attachment 228672

Well I got that camshaft and those lifters swapped with a Comp Cams 260H 212 int./212 exh. camshaft and lifter kit. View attachment 228673 View attachment 228674

Went ahead and raised the motor up enough to pull the oil pan, inspect the crankshaft, and replace the gasket while I was at it. View attachment 228675 View attachment 228676 View attachment 228677

Managed to do away with the push button theory and actually fix my actuator rod in my steering column...was a complete tear down and rebuild. Now I start my car with my key..have been awhile now. View attachment 228681

Managed to get a balancer bolt in my crankshaft snout... View attachment 228678

Deleted my AC/Heater box and replaced the hole with a block off plate...
View attachment 228682 View attachment 228683

Replaced the driver door hinges, handles, and the hood with a cowl hood, and hood hinges all at once... View attachment 228684 View attachment 228685 View attachment 228686 View attachment 228687 View attachment 228688

Replaced my broken shifter cable and swapped my factory floor shifter with a B&M Star Shifter. View attachment 228689 View attachment 228690
Replaced my drivers side upper control arm because of bad bushings, and also the top and bottom upper ball joints, and both sway bar links...
Screenshot_20230925_233036.jpg
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Ripped the interior out to the floor plan for sound system wiring, and swapped the bucket seats for a bench seat...
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I replaced my flexplate...
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Installed a digital gauge kit..
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Fabricated the rear deck to fit 6x9 speakers instead of factory 4x10s without adapters.
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Sealed up my exhaust leaks at the Y pipe...
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Replaced the cluster gauge circuit board...
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And hours of timing, valve adjustments, Holley carburetor tuning and maintenance, compression testing, vacuum watching, recurving the distributor...anything else I might have missed.

I've been doing it all successfully...with good apple and sound advice.
 
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