Big block engine swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Jack15T** · 04-22-2019, 07:05 PM

Hi folks, I bought a 1971 Chevy K20 Pickup about a year ago and it came with a 454. Whoever stuffed the 454 in it bolted it to the small block engine mounts and crossmember. This resulted in the 454 hitting the firewall and the exhaust headers hitting the frame rail. I bought a set of Big Block engine perches, but they won't fit the crossmember. Not even close. I can't be the first one to deal with a big block in a 71 K20 Pickup. I know they put a Big Block in the C10. I was wondering if the crossmember for a C10 would work in my K20 and if anybody had a source for them. No luck in the salvage yards so far. A new aftermarket one would be fine if an OEM one isn't available used or new. I pulled this 454 out to replace it with another 454 crate motor when I discovered the problem. Now I have a new 454HO from chevy and no way to mount it. Any help would be greatly appreciated. Thanks, Jack

**Captainfab** · 04-22-2019, 11:33 PM

GM never put a big block in the '67-'72 K series trucks. If you had a C20 instead of a K20 all you would need are a set of '68-'71 C series big block engine mounts and the brackets. The C series engine mount brackets are not going to work with the K series engine mount crossmember. A C series (2wheel drive) crossmember is not going to fit in your K series (4 wheel drive) frame without converting your truck to a 2 wheel drive. I believe guys that put big blocks in their K series trucks, move the engine mount crossmember forward 1-2" and drill new holes. Of course in doing this you will also have to move the transfer case mount forward, shorten your front driveshaft and lengthen the rear driveshaft, as well as all of the other things connected to the engine. You will also want to run the short water pump.

sweetk30 · 04-23-2019, 12:07 PM

give kert a call and ask if this will work for the big block swap .

http://diy4x.com/product.php?product...cat=252&page=1

Killer Bee · 04-23-2019, 12:34 PM

sorry to hear your troubles Jack.. I have encountered a few BBC hacked into 67-72 K models..

frame cuts, cut or missing cross members, "BBC installed, just needs front driveshaft, etc. etc."

K frames are narrower than the C frames I believe and the SBC sits a few inches further to the rear in a K than a C..

these differences require some thoughtful modifications to drop a BBC into a K functionally..

it's been done correctly, just need to find the pattern.. good luck!

cadillac_al · 04-23-2019, 03:41 PM

I wouldn't be surprised if Advance Adapters already makes a kit to do that.

**Jack15T** · 04-23-2019, 10:34 PM

Thanks for all the info guys, I appreciate it, Jack

USAF · 09-08-2022, 07:05 AM

I'm about to convert my 72 K20 to a big block. Did you ever determine what worked? Thanks.

04-22-2019, 07:05 PM	#1
Jack15T Active Member Join Date: Jun 2018 Location: Sandy, Utah Posts: 102	Big block engine swap Hi folks, I bought a 1971 Chevy K20 Pickup about a year ago and it came with a 454. Whoever stuffed the 454 in it bolted it to the small block engine mounts and crossmember. This resulted in the 454 hitting the firewall and the exhaust headers hitting the frame rail. I bought a set of Big Block engine perches, but they won't fit the crossmember. Not even close. I can't be the first one to deal with a big block in a 71 K20 Pickup. I know they put a Big Block in the C10. I was wondering if the crossmember for a C10 would work in my K20 and if anybody had a source for them. No luck in the salvage yards so far. A new aftermarket one would be fine if an OEM one isn't available used or new. I pulled this 454 out to replace it with another 454 crate motor when I discovered the problem. Now I have a new 454HO from chevy and no way to mount it. Any help would be greatly appreciated. Thanks, Jack

04-22-2019, 11:33 PM	#2
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,246	Re: Big block engine swap GM never put a big block in the '67-'72 K series trucks. If you had a C20 instead of a K20 all you would need are a set of '68-'71 C series big block engine mounts and the brackets. The C series engine mount brackets are not going to work with the K series engine mount crossmember. A C series (2wheel drive) crossmember is not going to fit in your K series (4 wheel drive) frame without converting your truck to a 2 wheel drive. I believe guys that put big blocks in their K series trucks, move the engine mount crossmember forward 1-2" and drill new holes. Of course in doing this you will also have to move the transfer case mount forward, shorten your front driveshaft and lengthen the rear driveshaft, as well as all of the other things connected to the engine. You will also want to run the short water pump. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE Last edited by Captainfab; 04-22-2019 at 11:43 PM.

04-23-2019, 12:07 PM	#3
sweetk30 Registered User Join Date: May 2012 Location: horseheads,ny rust belt Posts: 2,794	Re: Big block engine swap give kert a call and ask if this will work for the big block swap . http://diy4x.com/product.php?product...cat=252&page=1 __________________ 77-k30lb BIG truck build . 87-k30lb budget beater build . 85-k30lb the plow machine build . 85-c10sb summer fun toy . ----------------------------- HOLLEY SNIPER efi = worst case of p.i.t.a i ever had . EDELBROCK pro flo 4 = best deal going so far . love my setup works great.

04-23-2019, 12:34 PM	#4
Killer Bee Registered User Join Date: Jan 2016 Location: Barber City, CA Posts: 4,728	Re: Big block engine swap sorry to hear your troubles Jack.. I have encountered a few BBC hacked into 67-72 K models.. frame cuts, cut or missing cross members, "BBC installed, just needs front driveshaft, etc. etc." K frames are narrower than the C frames I believe and the SBC sits a few inches further to the rear in a K than a C.. these differences require some thoughtful modifications to drop a BBC into a K functionally.. it's been done correctly, just need to find the pattern.. good luck! __________________ *I started out with nothing - and I still have most of it*

04-23-2019, 03:41 PM	#5
cadillac_al Registered User Join Date: Oct 2013 Location: Maine Posts: 2,334	Re: Big block engine swap I wouldn't be surprised if Advance Adapters already makes a kit to do that. __________________ 76 Chevy K20 76 GMC K15 77 Chevy C10 77 Chevy K10

04-23-2019, 10:34 PM	#6
Jack15T Active Member Join Date: Jun 2018 Location: Sandy, Utah Posts: 102	Re: Big block engine swap Thanks for all the info guys, I appreciate it, Jack

09-08-2022, 07:05 AM	#7
USAF Registered User Join Date: Sep 2017 Location: Cayuga Wisconsin Posts: 34	Re: Big block engine swap I'm about to convert my 72 K20 to a big block. Did you ever determine what worked? Thanks. __________________ 1972 K20 2004 Chevy Aveo 2011 BMW X5 Diesel 2018 Chevy Silverado Diesel U.S. Air Force Retired - 1983-2017



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