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: 10,804	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,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 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 Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,798	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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