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#1 |
Registered User
Join Date: Jul 2009
Location: Chatsworth Ga
Posts: 400
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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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#2 |
Registered User
Join Date: Jul 2001
Location: North Delta, British Columbia
Posts: 1,344
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Re: Big Block Conversion in '72 Blazer ?'s
big block motor mounts...
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1992 Gmc 2wd 1972 Chevy Blazer 2wd |
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#3 |
Registered User
Join Date: Nov 2012
Location: Freeland, Michigan
Posts: 1,385
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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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#4 |
Senior Member
![]() Join Date: May 2006
Location: Philadelphia, Pa. 19454
Posts: 9,529
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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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Semper Fi...Uncle Sam, you da man All parts offered to help are free, unless otherwise noted Dont try this stuff in my build thread, unless you have 55 years of mechanical OTJ training SAFETY FIRST AS usual, off topic They say your mind goes second, can't remember the first Jim |
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#5 |
Registered User
Join Date: Nov 2012
Location: Freeland, Michigan
Posts: 1,385
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Re: Big Block Conversion in '72 Blazer ?'s
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#6 |
Registered User
Join Date: Jul 2009
Location: Chatsworth Ga
Posts: 400
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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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#7 |
Registered User
Join Date: Sep 2009
Location: Otisville, Mi.
Posts: 53
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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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#8 |
Registered User
Join Date: Jan 2012
Location: Seguin Texas
Posts: 160
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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.
Evan Q. |
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#9 |
2WD Jimmy
![]() Join Date: Mar 2005
Location: Davis County, Utah
Posts: 2,564
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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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#10 |
Registered User
Join Date: Sep 2009
Location: Otisville, Mi.
Posts: 53
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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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#11 |
Registered User
Join Date: Nov 2012
Location: Freeland, Michigan
Posts: 1,385
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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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#12 |
Registered User
Join Date: Jan 2012
Location: Seguin Texas
Posts: 160
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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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#13 |
KEEP ON TRUCKIN'
![]() Join Date: Jun 2005
Location: Sterling, Va.
Posts: 5,731
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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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JIM '97 GMC Sierra K1500 '95 Chevy Silverado C1500 '71 Cheyenne Z71 / LT1 & 4-Speed SWB K/10 ![]() http://www.youtube.com/watch?v=4l689JKXPnA http://67-72chevytrucks.com/vboard/payments.php "LIVIN' FREE FOREVER" ![]() |
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#14 |
Registered User
Join Date: Oct 2011
Location: St Petersburg, Florida
Posts: 154
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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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#15 |
Senior Member
![]() Join Date: Aug 2007
Location: Morgan County Utah
Posts: 694
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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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#16 |
Registered User
![]() Join Date: Apr 2010
Location: West Chester Pa
Posts: 965
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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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!972 K5 Blazer,Highlander,A/C a twin to the one I Had 1972 K/5 Blazer ![]() 2003 Silverado Crew 2500HD (Daily driver) 1997 Ford focus (Beater) 2003 ford Taurus (student) 2014 Ford Fusion HYB (wife) 2003 Jetta ( Student) |
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#17 |
Registered User
Join Date: Feb 2000
Location: Modesto, CA
Posts: 1,842
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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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1972 K5 MPFI454/Sm465/Np205/D60/14FFd/Re-Centerd H1s w/Swamper Iroks ![]() |
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#18 |
Registered User
Join Date: Mar 2012
Location: Main Street, USA
Posts: 87
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Re: Big Block Conversion in '72 Blazer ?'s
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#19 |
Registered User
Join Date: Sep 2009
Location: Otisville, Mi.
Posts: 53
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Re: Big Block Conversion in '72 Blazer ?'s
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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#20 |
Registered User
![]() Join Date: Apr 2012
Location: Michigan
Posts: 389
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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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#21 |
Registered User
Join Date: Nov 2009
Location: Cranbrook, BC
Posts: 253
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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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#22 |
2WD Jimmy
![]() Join Date: Mar 2005
Location: Davis County, Utah
Posts: 2,564
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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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#23 |
Registered User
Join Date: Nov 2009
Location: Cranbrook, BC
Posts: 253
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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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#24 |
Registered User
Join Date: Feb 2013
Location: Fort Worth, TX
Posts: 29
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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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#25 |
Registered User
Join Date: Nov 2009
Location: Cranbrook, BC
Posts: 253
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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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