06-10-2016, 08:06 AM | #1 |
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I6 250 swap for 454
1971 GMC C10 2wd with 250 inline.
I am swapping the I6 for a 454. Do they use the same motor mounts, or do I have to buy mounts for the 454? Once I get the I6 out, I want to be prepared and stick the 454 back in without having to run around and find motor mounts if I need different ones. |
06-10-2016, 08:15 AM | #2 |
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Re: I6 250 swap for 454
I think you need new frame brackets also.
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06-10-2016, 08:23 AM | #3 |
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Re: I6 250 swap for 454
Frame brackets, yep, da, thanks, I didn't even think of that... so I need the frame brackets and motor mounts too maybe?
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06-10-2016, 09:01 AM | #4 |
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Re: I6 250 swap for 454
I've never messed with big blocks, but Rock Auto lists different part number for the 1971 250 and 402 motor mounts.
The I6 and V-8 frame brackets are different. We put a small block on I6 brackets once. It fit but it stuffed the distributor against the firewall. So I imagine the BB brackets will move the engine forward. Point being - if you get BB brackets, you may have to slide your transmission cross member forward too. I'm not an expert on this. I know there's a difference between small-block and I6 brackets, but I don't know if there's a difference between SB and BB brackets. Someone here who knows will be along shortly with all the correct info...
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67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce |
06-10-2016, 11:41 AM | #5 |
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Re: I6 250 swap for 454 Mount question
Oh man!... surely the tranny won't have to be moved too?
I'm hoping maybe just some new perches is all I need... Motor mounts will be the same, and the new perches will situate the BB to the tranny and firewall as it should be? I'm staying optimistic I'd say there has to be not less than 100 people on here who have made this swap... maybe they'll chime in. |
06-10-2016, 11:48 AM | #6 | |
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Re: I6 250 swap for 454 Mount question
Quote:
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1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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06-10-2016, 03:04 PM | #7 |
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Re: I6 250 swap for 454
Yeah, I've been gearing-up toward this project for several years now while still driving the truck regularly. I've added BB coil springs and shocks when I rebuilt the front end and added a large aluminum radiator, wired it for HEI, I have all the pulleys and brackets etc., I pulled the tranny (PG) and had it redone about a year ago. I even have the exhaust ready, only using one side right now. I just have to modify it to fit perfect once the BB is in. Everything that I have done to this truck so far I have done it thinking "Big Block" because I knew where I was eventually headed.
But now I'm actually there, so I'd like to be prepared for the mounting situation before I pull the engine out. |
06-10-2016, 03:32 PM | #8 |
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Re: I6 250 swap for 454
That Powerglide is not a great choice to have behind that 454.
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06-10-2016, 03:32 PM | #9 |
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Re: I6 250 swap for 454
I done this with my 71 283.
If you want it done right, everything has to be moved into the forward position for the frame mounts. Since you are using an PG, moving the trans will be easy (unless you don't have tools to break any rivets) The BB motor perches are different than the small block ones, if I remember correctly, SB may work. The center hole is bigger for BB. Someone else will chime in that has some. You will need to extend the driveshaft. A few smaller details to ad, but I just got back from flying half way around the globe. Shoot me a PM if you have questions. Thanks, Smitty
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71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 69 C30 Former Motor Home, Flat Bed time 70 G20 Red-E-Kamp Conversion "I'm your Boogy Van" |
06-10-2016, 04:24 PM | #10 |
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Re: I6 250 swap for 454
big block moumt dip for thr exhaust manifolds
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06-10-2016, 04:27 PM | #11 |
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Re: I6 250 swap for 454
side view for ya
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I was hooked on these trucks since 1982 when I drove my budys fathers 1968 Custum GMC 396 automatic dana 60 rear with a power lock diff what a ride more fun then we will we can ever tell!! |
06-10-2016, 06:55 PM | #12 |
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Re: I6 250 swap for 454
Willy thanks for pics. Now, remove those from your truck and send them to me. When you get them ready pm me for my address
I just got home where I could actually look at it, and the motor mounts on the I6 look totally different too, so I'm now convinced that I need perches AND motor mounts for sure. Using a tape measure and eyeballing it, the I6 and the BB both measure 16" from center of the mount to the back of the block. I have a good 2" between the I6 and the firewall. It "appears" that it would fit. Will the BB perches move the block forward? Therefore moving everything forward? Is that why I'm going to have to move my tranny forward too? |
06-10-2016, 08:43 PM | #13 |
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Re: I6 250 swap for 454
Look at the frame holes, the front two are for V8's and the back are for I6 (2wd). You can try to use the 6 holes for the 8. I never did a BB, but I did have to use it initially for my 283 and it worked, but the valve covers, HEI were too close to the firewall for me. Didn't look right for a 2wd in my opinion. 4wd's are a different animal and use the back holes for 8's and use a different crossmember.
Tall valve covers will have issues in the 6 spot, large HEI cap, hits the wall, it did for the SB.... Yes, the perches move it forward just like the SB ones do. Smitty
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71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 69 C30 Former Motor Home, Flat Bed time 70 G20 Red-E-Kamp Conversion "I'm your Boogy Van" |
06-10-2016, 11:25 PM | #14 |
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Re: I6 250 swap for 454
You have to use the BB towers but you can use SB mounts with a large washer on the bolt because the BB towers have a larger hole in them. The dive shaft will need shortened and balanced. Mine was shortened to 59.5 inches and I used the front two holes in the frame to mount the towers. I have a SWB truck. If yours is LWB you will just have to measure to see what driveshaft length you will need. I used a square body 3-row radiator and the lower neck is a little low, as it is straight and the radiators for 67-72 have a curved lower neck. I cut a piece of the old radiator hose and put it between the new hose and the frame where it kicks up to keep from wearing a hole in the new hose. Mine is short water pump. You will need a big block shroud also. I did have to move the transmission crossmember to the rear holes. The block lengths are the same from the rear face to the motor mount holes, but the shape of the mounts made it necessary to move the trans crossmember. I have a TH400, I don't know If you would need to move it with the PG. If I think of anything else I will let you know.
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70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear Last edited by 70STOVEBOLT; 04-05-2020 at 03:38 PM. |
06-13-2016, 08:03 AM | #15 |
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Re: I6 250 swap for 454
OK, "if I want it done right" (and I want it done right) the motor goes forward. I see in Willy's picture, he's in the front holes.
So I'm thinking the procedure goes like this: 1.) Remove I6. 2.) Grind/drill/beat/kick/cuss the rivets out of cross-member/frame, slide tranny forward and stick some bolts in it where the rivets were? 3.) Remove old towers, replace with BB towers & BB mounts 4.) Drop in BB - bolt it down and bolt up converter and tranny. 5.) Find a longer drive shaft and stick it in there. 6.) Then I'll worrying about fans/water pumps/hoses/linkages/headers and all that crap. That's my current plan anyway. Am I getting it right? I haven't looked under there at my cross-member yet. Does the frame have extra holes already in it for the cross-member to move forward? |
06-13-2016, 08:15 AM | #16 |
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Re: I6 250 swap for 454
Yes, your game plan sounds correct. There should be an extra set of holes to bolt the crossmember to. My 70 had them anyway, I would think if the holes for the engine are there, the holes for the crossmember are there.
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70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear |
06-13-2016, 06:08 PM | #17 |
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Re: I6 250 swap for 454
Thanks to all of you for the info ....only I'll be going I250 to 383...700R4...Or LS5.3...in my '71...Hair good luck with your build...
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06-14-2016, 02:58 AM | #18 |
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Re: I6 250 swap for 454
I did this swap in my 69 gmc original I 6 to a 454. I have the original Th350 though so I did not have to relocate Trans cross member because I used the correct BBC engine stands and mounts for this year. I believe the newer clamp she'll mounts were forward more so I opted for the old style which are very pricy. Then when dropping engine all you need to do is check clearances for distributor . You will then want to change Everything in the engine bay to BBC a good catalog is LMC you can use as reference it will make your swap a breeze but if you want it period correct prepare to drop some coin. Have fun it will be worth it
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06-14-2016, 08:53 AM | #19 |
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Re: I6 250 swap for 454
I also used the 68-71 towers but I still had to move the trans back to the rear set of holes and have the driveshaft shortened. I have no clearance issues with valve covers or HEI distributor cap and the firewall.
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70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear |
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