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Old 08-20-2007, 05:43 PM   #1
Mark Smith
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Engine Swap - 1971 4WD - Small block to Big block

HELP HELP - I have a 1971 GMC 4WD I would like to install a 502CID Big Block Chevrolet in. Does anyone have or know of a kit that includes the engine mounts that are affixed to the frame rails that includes a cross member as well?

I am concerned about where to bolt up engine towers in relation to the distance from the fire wall and also how it will effect all other placement of drivetrain components.

I have the 502CID and also a beefed up 700R4 and NP205 transfer case.

At this juncture I am contemplating the purchase of a small block engine mount and cross member kit from DIY4X4. Since it is the only kit I've found I was thinking I might modify the cross member to try and make it work for a big block. Spacing is still an unknown from the firewall however.

I realize this will most likely effect the positioning of the transmission cross member as well, which leads me to ask, is there a cross member kit available for it also??

I look forward to you help. If you should prefer to call, my cell phone is 414-378-9234 or my email is mksmith@trinitypetroleum.com

Last edited by Mark Smith; 08-20-2007 at 05:51 PM. Reason: Mistake
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Old 08-20-2007, 06:45 PM   #2
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Re: Engine Swap - 1971 4WD - Small block to Big block

I haven't dealt with any of the automatic transmissions so I don't know how long your 700R4 is compared to an TH350 or TH400. Assuming it is longer I would sure think moving the motor forward would be the way to go. Someone who has moved their motor forward will chime in on how much forward you would need to move it to be sure to have no firewall issues.

Would really enjoy seeing some pics of this project. Blown 502 ci just peaks my interest big time!!!
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Old 08-20-2007, 07:08 PM   #3
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Re: Engine Swap - 1971 4WD - Small block to Big block

It will be a while before pictures to my standard and worthy of on-lookers are available.

For now, all of the body and interior work has been completed. The truck is canary yellow with a gray tweed interior and oak floor in the bed with stainless trim. I am pleased with the body and interior progress.

I have rewired all of the truck with the Painless wiring kit.

The cab is set up for air conditioning also.

The engine compartment is canary yellow as well. The truck has a 6" suspension lift. I did not go nuts on lift because I want more of a proportionate look over all.

I have a canary yellow blown gas 1969 Camaro as well. I plan to pull the drag car on a gloss black open car trailer with the blown gas 1971 4WD Pick up. The combination should be a nice eye catcher.

Thanks for your support.
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Old 08-20-2007, 10:08 PM   #4
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Re: Engine Swap - 1971 4WD - Small block to Big block

sounds awsome.. it don`t have to be done to share pics!! lol
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Old 08-20-2007, 10:38 PM   #5
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Re: Engine Swap - 1971 4WD - Small block to Big block

I used cross-member and motor mounts out of an '80 3/4 ton. I have about 3 inches clearance from my dist to the firewall, and about 1 inch on the valve covers. I did have to open the hole forward a bit for my sm465 though. From what I've read on this site....I would just bolt it in the stock location and beat the firewall where necessary. This will save you all the other mods, including drivelines!!! It sounds like you could do it in a way that looks good....artistic hammer work!!!
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Old 08-21-2007, 11:03 AM   #6
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Re: Engine Swap - 1971 4WD - Small block to Big block

That will be a sight to see when you get the truck done and hook it to that trailer.

I have to agree with jamie72 - we love seeing progress pics around here. The finished product is nice to see but I really enjoy seeing the work people put into their trucks.

What kind of times do you get out of your blown Camaro?
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Old 08-22-2007, 06:07 PM   #7
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Re: Engine Swap - 1971 4WD - Small block to Big block

Hello again,

The blown Camaro is not all that fast. I see consistant 1/4 mile et's in the 10.10 to 10.20 range.

With a little suspension work I think it would see 9's but I never wanted to narrow and tub the car. So, all things considered I put up with 10's and don't plan on doing anything more to the car for now.

I used to run top alcohol IHRA in the dragster category with a 280" Hal Canode chassis. Aries 8 Liter Hemi with 1471 supercharger. That car was 6 seconds in the 1/4 so modifying a Camaro to hilt doesn't particularly interest me all that much.

Any how, we'll see about getting the gang a few photos one of these days. In the mean time, I certainly appreciate your input.

Thanks,

Mark
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Old 08-23-2007, 05:52 AM   #8
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Re: Engine Swap - 1971 4WD - Small block to Big block

you could use this one it is from ORD and made for a big block $189 . I hope your going to spend some cash on that 700 a 502 will eat that trans up.
http://www.offroaddesign.com/catalog...rossmember.htm
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Old 08-23-2007, 06:17 AM   #9
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Re: Engine Swap - 1971 4WD - Small block to Big block

For got speed way is an option as well and they are the cheapest but theres are all universal so some cutting and welding required.
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Old 08-23-2007, 07:42 AM   #10
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Re: Engine Swap - 1971 4WD - Small block to Big block

the diy4x engine crossmember set is nice...
super strong and very nice work,using one to put ls1
in 1970 k5.only custom mounting to get 1" forward and 3" down.
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Old 08-23-2007, 11:16 PM   #11
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Re: Engine Swap - 1971 4WD - Small block to Big block

Yes thanks, I am aware of this cross member but it is really designed for the 73 and newer stuff. My truck is a 1971. I'm actually thinking of using both this for a cross member and frame stiffiner in conjunction with the DIY 4X4 small block kit. We'll see, I'm still getting feed back from everyone. Not sure who you mean my Speed Way. Thanks again
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Old 08-23-2007, 11:18 PM   #12
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Re: Engine Swap - 1971 4WD - Small block to Big block

I'm assuming you mean 1" from the fire wall right? What are you referring to when you say 3" down?
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Old 08-23-2007, 11:49 PM   #13
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Re: Engine Swap - 1971 4WD - Small block to Big block

Speed way is a race parts place kinda like jegs but with a lot more custom parts and parts with there name so you can get a better deal . There mainly known for hot rod parts if you dont have a catalog from them I would get one there great for off the wall stuff . here is a link to there universal cross meber
http://www.speedwaymotors.com/p/3273...0MOTOR%20MOUNT
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Old 08-24-2007, 07:52 AM   #14
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Re: Engine Swap - 1971 4WD - Small block to Big block

the diy kit is for 1st gens:
http://www.diy4x.com/engine.htm

it is very nice...
yes i mean 1" forward....gave me a little extra firewall room,plus an extra 1" on rear driveshaft length.
by 3" down, i mean i made a 3" channel to box in the frame at the engine crossmember.which lets the engine crossmember still bolt in,just 3" lower.
that will help keep center of gravity lower and help with frt and rear driveline angles((my k5 will have aprox 20" of lift!))
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Old 08-24-2007, 01:40 PM   #15
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Re: Engine Swap - 1971 4WD - Small block to Big block

Quote:
Originally Posted by Mark Smith View Post
HELP HELP - I have a 1971 GMC 4WD I would like to install a 502CID Big Block Chevrolet in. Does anyone have or know of a kit that includes the engine mounts that are affixed to the frame rails that includes a cross member as well?

I am concerned about where to bolt up engine towers in relation to the distance from the fire wall and also how it will effect all other placement of drivetrain components.

I have the 502CID and also a beefed up 700R4 and NP205 transfer case.

At this juncture I am contemplating the purchase of a small block engine mount and cross member kit from DIY4X4. Since it is the only kit I've found I was thinking I might modify the cross member to try and make it work for a big block. Spacing is still an unknown from the firewall however.

I realize this will most likely effect the positioning of the transmission cross member as well, which leads me to ask, is there a cross member kit available for it also??

I look forward to you help. If you should prefer to call, my cell phone is 414-378-9234 or my email is mksmith@trinitypetroleum.com
The big block should bolt to the same crossmember and mounts as the small block. You don't need a different one. To use it in the stock location you have to use short valve covers and bump the fire wall out a little on the passenger side. If you have the short output shaft for the 700r4 from advanced adapters you only need the stock th350 adapter to hook it to the 205 and it moves the 205 back 2 inches. You can use the stock crossmember for the 205 and move it back. To clear the firewall with the engine you should be able to move the stock crossmember forward a inch then you only need to move the transfercase crossmember back one inch or engine forward 2" and tranfer in stock location. You just have to watch oil pan to diff clearance.
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Old 09-01-2007, 06:23 AM   #16
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Re: Engine Swap - 1971 4WD - Small block to Big block

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that will help keep center of gravity lower and help with frt and rear driveline angles

The Rocks alone are gonna do all that.
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Old 09-16-2007, 09:57 PM   #17
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Re: Engine Swap - 1971 4WD - Small block to Big block

My guess is that if you have painted your engine compartment you are not going to want to do any firewall bashing. I am getting ready to start a similar build next week. Its a 1970 K10 swb fleet. I am using a 454/TH400/NP205. I will be moving the entire setup forward to allow a plenty of room so I dont have to use a prybar to change the distributor cap. I am a fabricator by trade so I will be fabricating my own mounts and crossmember. I will be doing it all with the body off of the frame with a lot of reference measurements so it should be a piece of cake. Good Luck
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Old 09-27-2007, 02:04 AM   #18
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Re: Engine Swap - 1971 4WD - Small block to Big block

Put a big block in my 68 and used all the 68 parts. Just moved all crossmembers forward 1 and a half inches. I did have to use stock valve covers and put a small quarter inch by two inch long notch in the frame for the driver side headers (hookers). There were a few things moved for my 4 speed but your not using that. I even used the small block motor mounts.
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Old 02-08-2008, 03:13 PM   #19
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Re: Engine Swap - 1971 4WD - Small block to Big block

I'm putting in an LS2 into a 72 4x4 and I just got the diy4x4 crossmember and some S&P engine mount relocators. When I went to bolt everything together I found that the mounts on the LS engine are about an inch farther apart than an old style small block. Did you run into the same problem?

I can fab up some new motor mounts but I was a little dissappointed that the engine mount relocators didn't put the engine mounts in a factory position. BTW, I tried out the diy4x4 crossmember on a big block I had around and it did not clear the oil pan. However it was not a stock oil pan.

Quote:
Originally Posted by tallhoedude View Post
the diy4x engine crossmember set is nice...
super strong and very nice work,using one to put ls1
in 1970 k5.only custom mounting to get 1" forward and 3" down.
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Old 02-09-2008, 09:59 AM   #20
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Re: Engine Swap - 1971 4WD - Small block to Big block

I'm gonna do this again here shortly......My question is if I ran tall valve covers, with engine in stock location, how much firewall will need to be removed? And, is there anything back there I should be worried about moving first before I go to cutting?

Thanks,

A..........
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Old 02-09-2008, 04:22 PM   #21
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Re: Engine Swap - 1971 4WD - Small block to Big block

I had tall valve moon style valve covers on my 454 and no issues with the firewall. I did not do the swap so I'm not sure where the stock location is but the engine stands were in the forward holes. There was about 1/4 inch clearance from the back corners of the valve covers.

Quote:
Originally Posted by DieselEater View Post
I'm gonna do this again here shortly......My question is if I ran tall valve covers, with engine in stock location, how much firewall will need to be removed? And, is there anything back there I should be worried about moving first before I go to cutting?

Thanks,

A..........
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Old 02-09-2008, 08:44 PM   #22
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Re: Engine Swap - 1971 4WD - Small block to Big block

While the DIY4X4 crossmember is a quallity peice, I dont believe it will work in your case. I'm using one and oil pan clearance is very tight with my stock small block oil pan.
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Old 02-10-2008, 12:32 AM   #23
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Re: Engine Swap - 1971 4WD - Small block to Big block

If your truck came with a T350/205 combo from the factory switching to a big block and using a 700R4 is one of the easiest ways to go!
The 700R4 is just over 2 inches longer than a T350. Leave the trans crossmember and transfer case in the stock location which means no mods to drive lines, shifter etc, doing so puts the big block far enough forward for valve cover to firewall clearance. Then you could use just move the stock small block engine cradle forward to fit and drill 8 holes, but if you are concerned with strength then maybe opt for the 73 and up 4X4 front crossmember that uses the "clam shell" style mounts which are known to be stronger than the 71's, If I remember correctly you will have to mod the crossmember a bit and will have to drill all the holes in your frame to mount it.

Good luck with your swap.. PICTURES PLEASE!!!
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Old 02-15-2008, 03:52 AM   #24
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Re: Engine Swap - 1971 4WD - Small block to Big block

Quote:
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If your truck came with a T350/205 combo from the factory switching to a big block and using a 700R4 is one of the easiest ways to go!
The 700R4 is just over 2 inches longer than a T350. Leave the trans crossmember and transfer case in the stock location which means no mods to drive lines, shifter etc, doing so puts the big block far enough forward for valve cover to firewall clearance. Then you could use just move the stock small block engine cradle forward to fit and drill 8 holes...
Yep, that is what I did, very simple.
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Old 09-29-2008, 04:15 PM   #25
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Re: Engine Swap - 1971 4WD - Small block to Big block

i spoke to the guy at diy4x today and he said that his cross member should work with a big block. He did say that stock oil pans should clear better than aftermarket because they are more rounded in front so i looked at mine and i believe he is right i should know more soon.
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