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Old 02-10-2013, 08:57 AM   #1
chastain90
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Big Block Conversion in '72 Blazer ?'s

What are most people having to do to put a big block in a blazer? I have found a 402 and would like to put it in it if nothing extreme has to be done. Thanks for any help.
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Old 02-10-2013, 05:13 PM   #2
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Re: Big Block Conversion in '72 Blazer ?'s

big block motor mounts...
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Old 02-10-2013, 05:41 PM   #3
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Re: Big Block Conversion in '72 Blazer ?'s

I'm interested in this as well. I plan on doing the same thing to my 1972 jimmy. I have big block mounts from a 1972 burb. I wondering if either of the drive shafts will have to be altered??
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Old 02-10-2013, 06:03 PM   #4
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Re: Big Block Conversion in '72 Blazer ?'s

From what ive seen, youre going to have to massage the firewall where the valve covers hit
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Old 02-10-2013, 06:12 PM   #5
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Re: Big Block Conversion in '72 Blazer ?'s

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From what ive seen, youre going to have to massage the firewall where the valve covers hit
How much massaging??? Will a HEI distributor clear??
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Old 02-10-2013, 06:15 PM   #6
chastain90
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Re: Big Block Conversion in '72 Blazer ?'s

well I heard the motor mounts will fit a small block and big block but just clearence issues. You would have to run a distributor with an external coil and move the mounts up a couple inches is what I have heard.
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Old 02-11-2013, 10:31 PM   #7
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Re: Big Block Conversion in '72 Blazer ?'s

About this much cutting. 72 GMC Jimmy 454 big block, pro comp aluminum heads (taller than cast) and tall valve covers for roller rockers and hei distributor. We were unaware of big block motor mounts when we did this. I'm putting a 454 in my 68 p/u with cast heads and shorter valvecovers but i dont know yet if it will fit much better.
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Old 02-11-2013, 11:26 PM   #8
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Re: Big Block Conversion in '72 Blazer ?'s

Use of large valve covers definately requires some serious firewall massaging. I also did relief cuts and welded in new sections. Fits perfect now. I used the DI4Yx crossmember and the HEI fits very well.
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Old 02-12-2013, 09:09 AM   #9
Tom Vogel
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Re: Big Block Conversion in '72 Blazer ?'s

Hmmm... No massaging neccessary on my 2wd. I used the stock 72 BB motormounts, and trimmed and welded a small bit on the driver side valve cover. Thats it.
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Old 02-12-2013, 01:34 PM   #10
68 GMC step long
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Re: Big Block Conversion in '72 Blazer ?'s

Has anyone used small block mounts on a 2wd and not had to cut the fire wall? Is there a company that sells big block crossmembers or a conversion kit?
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Old 02-12-2013, 06:20 PM   #11
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Re: Big Block Conversion in '72 Blazer ?'s

68 GMC Step long and Fw190d9.... I'm assuming you guys kept the transfer case mounting position in the original position and modified the firewall according for clearance??
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Old 02-12-2013, 06:22 PM   #12
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Re: Big Block Conversion in '72 Blazer ?'s

I switched to an Atlas 4 speed Tcase which necessitated moving the crossmember back about 1". The DIy4x engine mount will allow you to move the engine forward or back slightly, about 3" total.
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Old 02-12-2013, 06:25 PM   #13
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Re: Big Block Conversion in '72 Blazer ?'s

My '71 K10 shortbed had a 396 in it when I bought it. The only thing that had been done to the firewall was a little massaging with a big hammer to clear the distributor.
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Old 02-13-2013, 03:19 PM   #14
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Re: Big Block Conversion in '72 Blazer ?'s

I think all chevy motor mounts are the same for 6 cylinders, small and big v-8's. Now the frame brackets on the other hand are all different. if you go from a small block to a big block then you need to change out the motor frame bracket. The tranny and transfer case stay in the same position.
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Old 02-13-2013, 05:37 PM   #15
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Re: Big Block Conversion in '72 Blazer ?'s

If you rig is a 4X4. In short 3 things that needed to be delt with. 1. is the massaging talked about. you can see in the first picture what was done on the left side of fire wall above trans and for valve cover and in center for HEI (not real pretty but functional). 2. was modification of motor cross member in second and third picture a donor cross member was used to lengthen. 3. notch right side top of frame rail for exhaust manifold in the fourth picture. the motor mounts are SB mounts in the stock location and TH350 trans and transfer case in stock location.
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Old 02-13-2013, 06:44 PM   #16
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Re: Big Block Conversion in '72 Blazer ?'s

very good question Iam thinking of doing the same . All i thought was needed was to move the motor crossmember forward and use short fan/water pump/fan shourd? Gm wouldnt alter every cab to suporrt small/block VS Big /block
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Old 02-14-2013, 10:11 AM   #17
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Re: Big Block Conversion in '72 Blazer ?'s

There are older threads here you can search for as all the different ways to do it and the different experiances people had.
I did the swap:




got a 74 454 from a 2x4 truck
got a SBC engine crossmember (3piece) from a 73+ 4x4 truck
bought ORD SBC engine mounts
bought 4core Rad and longer mounts
bought new clutch pp assy & flywheel for my SM465 & 454
converted to Hydro Clutch so I didn't have to worry about the Thorley Tri-Y heders I wanted to run
beat the drivers side firewall with a 4lb sledge..not real bad, just a bit of a dent for the valve cover.
shoehorned the 454 in there and been rockin eversence
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Old 02-14-2013, 01:44 PM   #18
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Re: Big Block Conversion in '72 Blazer ?'s

Quote:
Originally Posted by Tom Vogel View Post
Hmmm... No massaging neccessary on my 2wd. I used the stock 72 BB motormounts, and trimmed and welded a small bit on the driver side valve cover. Thats it.
Thats one sweet looking engine bay! Whats the tube coming off the carb/EFI some kind of cold air intake?
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Old 02-15-2013, 01:17 PM   #19
68 GMC step long
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Re: Big Block Conversion in '72 Blazer ?'s

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68 GMC Step long and Fw190d9.... I'm assuming you guys kept the transfer case mounting position in the original position and modified the firewall according for clearance??
The big block came out of a 78 c30 p/u. We used the origional 350 trans and np205 t-case and didn't have to move any cross members. The only cutting that was done was on the firewall and not even 1/2" worth of trimming on the frame for header clearance.
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Old 11-09-2013, 10:18 AM   #20
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Re: Big Block Conversion in '72 Blazer ?'s

So, my truck has had a big block 454 installed, my issue now is that the headers are leaking, turns out someone put sq port headers on oval port heads hense the leak. the headers that are currently on it are the 69110 headman headers. i want to replace the headers but the other issue is that the exhaust pipe coming out of the num 2 cyl hits the frame. I believe the engine towers are the orig sbc towers and the firewall has been beat back in some spots to make clearance. my question is has anyone just put a bbc in on the stock 350 towers and mounts if so what headers did you use? Any help would be great.
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Old 11-14-2013, 11:38 PM   #21
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Re: Big Block Conversion in '72 Blazer ?'s

I am having the same dilemma. My 2wd Blazer has a tired 350, but I have a line on a lightly modded 402, donated from a friend from his 82 Chevy, (came out of his Camaro). Would love to put it in, but am concerned it will be more work than it's worth. I have read a ton of threads, but they seem to be all over the place. Some firewalls modded, some not. Wouldn't the trans move? or does the block sit further forward? Sounds like some guys drop them right in. If I could use the engine, mounts, headers and rad from his truck, and bolt them in, I would be all over it. Not too keen on banging up the firewall. And if the trans moves, would have to ship my drive shaft out of town to get it shortened. No one locally does it. Again, a pain. But a BB would be cool.
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Old 11-15-2013, 08:17 AM   #22
Tom Vogel
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Re: Big Block Conversion in '72 Blazer ?'s

Get the 72 BB mounts (I think there is a set for sale on the forum). You Wont have to mod your firewall because you have a 2wd. You will have to move your trans mount, but that only requires drilling holes. Shortening your driveshaft is no big deal, just measure and ship it off. Youll get it back in a week or two.
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Old 11-15-2013, 10:20 AM   #23
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Re: Big Block Conversion in '72 Blazer ?'s

Only a week or two. True. Guess I shouldn't be impatient at this point. Had it for 13 months so far, and still haven't got to enjoy it. Parked for the winter now. So it could be a spring project. Still waiting on e-brake parts so I can get the provincial inspection done.
Wonder if I should change the trans at the same time.... It never ends does it.
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Old 11-22-2013, 01:21 PM   #24
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Re: Big Block Conversion in '72 Blazer ?'s

I did this with a '72 2wd without any firewall modifications and am running an HEI distributor. What I don't have is a mechanical fan on the front of the water pump. The engine, towers and mounts are from a '73. When I did the swap I kept the same transmission and just located the '73 towers so that the transmission would stay where it was (truck had a 327 when I bought it). It does sit a little higher than the small block did and there was no room for any kind of fan on the water pump. I am running a dual electric fan set-up which works great. No firewall modifications and no driveshaft changes since the tranny stayed where it was.
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Old 11-23-2013, 01:14 PM   #25
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Re: Big Block Conversion in '72 Blazer ?'s

I was wondering about the rad as well. Had heard it could be a tight fit. I think electrics would work great. Hoping to grab all the parts I can off the donor truck. Would the rad from the 82 fit in the 72? You guys have me sold. Get the inspection done, then park it again for the transplant. Can't wait!
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