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

ALBATROSS · 08-07-2004, 11:46 PM

Hi All, I know this is been discussed about a million times but I dont see a search on this site. What is involved to put a big block in a 71 4x4. I know obviously motor mounts. A friend of mine swears that should be it. But I remember reading on here that it's not. I thinking of building either a 468 or a 496 not sure yet.But i want it injected, I've got a 383 right know but I NEED MORE POWER! Any help would be greatly appreaciated.

**Yukon Jack** · 08-09-2004, 10:19 AM

I read up on this subject prior to putting a 454 in my 69 K20. Generally I read you could use your original crossmember/towers and motor mounts and you would have to bash in the firewall a bit. Also read some said a minor body lift would give you adequate clearance. Others said all you have to do is move the engine forward a bit. Using a newer engine crossmember is supposed to make life easier if you are going with headers.

I went with doing a body lift and at least for me a 2" body lift did not give adequate clearance at the firewall using the stock crossmember/towers. I had to go with a bigger body lift and still had to modify the firewall considerably.

I will move my engine forward in the future and I think that is the best option. I think moving the engine forward 1 1/2 to 2" forward should be sufficient.

I have seen pics of trucks where the owner states it is in the small block position with minor firewall massaging, but for the life of me I can't see how that is possible after seeing the amount of firewall interference I had.

ALBATROSS · 08-09-2004, 04:23 PM

Thanks Yukon, I also have a 2" body lift, but I will probably go with moving everything 2" forward. I also have a 14bolt and eight lug 44 so it might be best to do them at the same time since I will have to have a driveshaft built anyway.Damn the front shaft will probably need worked too. I 've got a 6" lift and the angle is already questionable. I can see the $$ adding up real quickly on this one.

ryanroo · 08-10-2004, 12:34 PM

i had a 454 in my 72 to check for clearance probs and i really didn'thave any, the Pass side head was clase to the firewal, but i tapped it in a little with a hammer to fix that. the only problem i could see was my headers interfering with the clutch linkage. i have no body lift and rotten body bushings.
Ryan

smokekiki · 08-11-2004, 09:46 AM

My 71 4x4 suburban has a 402 in it.The valve covers where very close,but cleared.I hammered and smoothed the firewall just a little for clearence.You can't even see it.

Destructo · 08-11-2004, 09:57 AM

So what was the difference between a factory big block truck? Maybe if yall knew that then you could determine the best way to make it fit. Was the factory big block further forward?

smokekiki · 08-11-2004, 10:16 AM

They never made a pre73 big block 4x4.You have to decide to massage the fire wall,or move the engine ,trans transfer forward,or move the engine forward and install an od trans.

08-07-2004, 11:46 PM	#1
ALBATROSS Registered User Join Date: Feb 2004 Location: Redway,Ca Posts: 30	Big block ? Hi All, I know this is been discussed about a million times but I dont see a search on this site. What is involved to put a big block in a 71 4x4. I know obviously motor mounts. A friend of mine swears that should be it. But I remember reading on here that it's not. I thinking of building either a 468 or a 496 not sure yet.But i want it injected, I've got a 383 right know but I NEED MORE POWER! Any help would be greatly appreaciated.

08-09-2004, 10:19 AM	#2
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,686	I read up on this subject prior to putting a 454 in my 69 K20. Generally I read you could use your original crossmember/towers and motor mounts and you would have to bash in the firewall a bit. Also read some said a minor body lift would give you adequate clearance. Others said all you have to do is move the engine forward a bit. Using a newer engine crossmember is supposed to make life easier if you are going with headers. I went with doing a body lift and at least for me a 2" body lift did not give adequate clearance at the firewall using the stock crossmember/towers. I had to go with a bigger body lift and still had to modify the firewall considerably. I will move my engine forward in the future and I think that is the best option. I think moving the engine forward 1 1/2 to 2" forward should be sufficient. I have seen pics of trucks where the owner states it is in the small block position with minor firewall massaging, but for the life of me I can't see how that is possible after seeing the amount of firewall interference I had. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

08-10-2004, 12:34 PM	#4
ryanroo Senior Member Join Date: Apr 2004 Location: sw colorado Posts: 2,720	i had a 454 in my 72 to check for clearance probs and i really didn'thave any, the Pass side head was clase to the firewal, but i tapped it in a little with a hammer to fix that. the only problem i could see was my headers interfering with the clutch linkage. i have no body lift and rotten body bushings. Ryan __________________ 72 K20 12v build 72 K20 "parts truck" A place for your diesel swap questions

08-11-2004, 09:46 AM	#5
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	My 71 4x4 suburban has a 402 in it.The valve covers where very close,but cleared.I hammered and smoothed the firewall just a little for clearence.You can't even see it. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

08-11-2004, 09:57 AM	#6
Destructo Registered User Join Date: Sep 2003 Location: Lewisville, NC Posts: 1,836	So what was the difference between a factory big block truck? Maybe if yall knew that then you could determine the best way to make it fit. Was the factory big block further forward? __________________ 1985 Scottsdale Shortbed 4x4 Stout 350 with some "upgrades"-700r4-33x12.5" Mud Tires, Warn 8274-50 winch. 2005 Chevrolet Colorado Regular Cab 2wd 4-banger, 5 speed, Street Pack with 3.73 axle.

08-09-2004, 04:23 PM	#3
ALBATROSS Registered User Join Date: Feb 2004 Location: Redway,Ca Posts: 30	Thanks Yukon, I also have a 2" body lift, but I will probably go with moving everything 2" forward. I also have a 14bolt and eight lug 44 so it might be best to do them at the same time since I will have to have a driveshaft built anyway.Damn the front shaft will probably need worked too. I 've got a 6" lift and the angle is already questionable. I can see the $$ adding up real quickly on this one.

08-11-2004, 10:16 AM	#7
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,473	They never made a pre73 big block 4x4.You have to decide to massage the fire wall,or move the engine ,trans transfer forward,or move the engine forward and install an od trans. __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires



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