Planning Ahead - Engine Swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Thundarr · 02-22-2018, 08:15 PM

My 71 Sierra Grande has a late 80's GM Goodwrench 350 SBC with 3 speed auto. I have no idea what the actual miles are on the drivetrain. It runs well as I have updated everything short of an actual rebuild but lacks any real cajones.

If and when this motor or tranny dies, I want to be ready with it's more reliable and powerful replacement. That could be tomorrow, but I think I have some time. Can you offer up some experienced suggestions on what I should start to assemble.

I'd like to have somewhere in the upper 300 range horsepower and torque. I don't need to melt any tires, but i'd like some power when I need to haul or pass someone in traffic.

LS conversion or something more easily swapped with the parts I've already upgraded?
Which transmission?

garyd1961 · 02-22-2018, 09:57 PM

GM L31-R crate motor with a TCI Street fighter th350 trans is what I'm running. The only problem I had was the pan gasket on the trans leaking which seems to be a common thing. I got it fixed with a new gasket but if it ever leaks again I think I will install a better oil pan.

**HO455** · 02-22-2018, 10:09 PM

What kind of budget are you living with? What updates have you done to your current engine? Have you done a compression test on the current engine?
Just like real estate people have a saying so do we " Pictures pictures pictures "

truckster · 02-22-2018, 11:32 PM

Another vote for the L31 Vortec. It's a great, reliable motor. Put in an HT 383 cam and you'll be running around 330 HP and close to 400 ft/lb torque with rams horns manifolds and a Quadrajet.

Thundarr · 02-23-2018, 12:31 AM

Quote:

Originally Posted by HO455

What kind of budget are you living with? What updates have you done to your current engine? Have you done a compression test on the current engine?
Just like real estate people have a saying so do we " Pictures pictures pictures "

I'll get some pictures tomorrow. It's definitely no dog, but it drives like a 70-80s SBC. Here is the low down.

I've owned it for 5 years. Valve clearance and cylinder compression was checked when I purchased and everything was good there.

This is what I've done to the drivetrain:
Exhaust Headers, Carb clean out, Corrected timing, Replaced intake gasket, New plugs/wires, New Alternator, Electric Fans, Replaced all vacuum lines, All New fuel lines with under bed tank relocate, New fuel pump, Transmission rebuilt, Rearend rebuilt. Probably more, but I think I've run out of tricks to squeeze more out of it.

I love this truck and will keep it forever, God willing, so the budget limit is fluid as I assemble the upgrade. But at the same time, I want to be rational with it. I'm thinking 5-7k.

Thundarr · 02-23-2018, 12:42 AM

Quote:

Originally Posted by garyd1961

GM L31-R crate motor with a TCI Street fighter th350 trans is what I'm running. The only problem I had was the pan gasket on the trans leaking which seems to be a common thing. I got it fixed with a new gasket but if it ever leaks again I think I will install a better oil pan.

Quote:

Originally Posted by truckster

Another vote for the L31 Vortec. It's a great, reliable motor. Put in an HT 383 cam and you'll be running around 330 HP and close to 400 ft/lb torque with rams horns manifolds and a Quadrajet.

Nice to see two of the same.
Can I use the same headers and what about the vacuum operated ac/heater valves and brake booster?
What transmission do you have? I'm sure that getting rid of the 3 speed will help alot.

Thundarr · 02-24-2018, 05:04 PM

Engine Bay

mikecaddy500 · 02-24-2018, 05:15 PM

Add a bigger cam and a pair of vortec heads and intake

truckster · 02-24-2018, 07:56 PM

Quote:

Originally Posted by Thundarr

Nice to see two of the same.
Can I use the same headers and what about the vacuum operated ac/heater valves and brake booster?
What transmission do you have? I'm sure that getting rid of the 3 speed will help alot.

You can use the same headers and you'll have plenty of vacuum. I'm running a TH350 and NP205 transfer case.

You will need a different intake manifold, as the bolt pattern is different. You'll probably need an electric fuel pump too. Most of the Vortec blocks aren't drilled for a mechanical pump.

Brofle1402 · 02-24-2018, 10:51 PM

Buy a set of good heads AFR or Trick Flow, 480 to 490 lift cam and a injection unit

1972RedNeck · 02-24-2018, 11:03 PM

Big block will get you there...

02-22-2018, 08:15 PM	#1
Thundarr Registered User Join Date: May 2013 Location: Coppell, Texas Posts: 176	Planning Ahead - Engine Swap My 71 Sierra Grande has a late 80's GM Goodwrench 350 SBC with 3 speed auto. I have no idea what the actual miles are on the drivetrain. It runs well as I have updated everything short of an actual rebuild but lacks any real cajones. If and when this motor or tranny dies, I want to be ready with it's more reliable and powerful replacement. That could be tomorrow, but I think I have some time. Can you offer up some experienced suggestions on what I should start to assemble. I'd like to have somewhere in the upper 300 range horsepower and torque. I don't need to melt any tires, but i'd like some power when I need to haul or pass someone in traffic. LS conversion or something more easily swapped with the parts I've already upgraded? Which transmission? __________________ 1971 GMC C15 Sierra Grande SWB 1972 Chevy C10 Custom Deluxe LWB 2018 GMC Yukon Denali Last edited by Thundarr; 02-22-2018 at 08:35 PM. Reason: -- Added new tranny

02-22-2018, 09:57 PM	#2
garyd1961 Registered User Join Date: May 2016 Location: Henderson NC Posts: 975	Re: Planning Ahead - Engine Swap GM L31-R crate motor with a TCI Street fighter th350 trans is what I'm running. The only problem I had was the pan gasket on the trans leaking which seems to be a common thing. I got it fixed with a new gasket but if it ever leaks again I think I will install a better oil pan.

02-22-2018, 10:09 PM	#3
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,393	Re: Planning Ahead - Engine Swap What kind of budget are you living with? What updates have you done to your current engine? Have you done a compression test on the current engine? Just like real estate people have a saying so do we " Pictures pictures pictures " __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

02-22-2018, 11:32 PM	#4
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 7,981	Re: Planning Ahead - Engine Swap Another vote for the L31 Vortec. It's a great, reliable motor. Put in an HT 383 cam and you'll be running around 330 HP and close to 400 ft/lb torque with rams horns manifolds and a Quadrajet. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-24-2018, 05:04 PM	#7
Thundarr Registered User Join Date: May 2013 Location: Coppell, Texas Posts: 176	Re: Planning Ahead - Engine Swap Engine Bay __________________ 1971 GMC C15 Sierra Grande SWB 1972 Chevy C10 Custom Deluxe LWB 2018 GMC Yukon Denali

02-24-2018, 05:15 PM	#8
mikecaddy500 Registered User Join Date: Jan 2015 Location: howard city mi Posts: 83	Re: Planning Ahead - Engine Swap Add a bigger cam and a pair of vortec heads and intake

02-24-2018, 10:51 PM	#10
Brofle1402 Registered User Join Date: Feb 2018 Location: Birchwood Tn Posts: 13	Re: Planning Ahead - Engine Swap Buy a set of good heads AFR or Trick Flow, 480 to 490 lift cam and a injection unit



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