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Old 11-20-2012, 07:40 PM   #1
boynton6spd
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68 Big Block Swap?

Just sold my 92 and bought a 68 Convertible!
I will be asking LOTS of questions to all the C3 experts on this forum...
I'm wanting to swap out the 300hp 350 for a 500hp big block.
The small block in there now has iron heads and intake, the big block I'm looking at has aluminum heads and intake...how much heavier will it be than the all iron 350?
What else will I need to swap out to get the big block in there?
Thanks in advance,
-Matt
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Old 11-20-2012, 08:24 PM   #2
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The weight will be about the same- trading all the iron for the aluminum pays off in this case.

Brackets and pulleys will be your biggest issue. Headers take care of the exhaust no problem. The radiator hoses are different size, so you might need to get that fixed or just go to a BB radiator.

Don't forget to stash some cash for driveline parts. The BB has enough more torque that if the tires stick something will break. And usually those "somethings" are not cheap.
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Horsepower is like potato chips. If you have 300, you want 500. If you have 500, you want 800. One is never enough.
Old 11-20-2012, 08:37 PM   #3
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Thanks Tim.
Great news...
The car has power steering now...should I switch to short water pump for more room for electric fans etc??
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Old 11-20-2012, 09:08 PM   #4
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Quote:
Originally Posted by TimAT View Post
The weight will be about the same- trading all the iron for the aluminum pays off in this case.
.
What's the weight differential for an L-82 w/aluminum water pump and aluminum top end kit vs oem, while we're on "C3 Weights & Measures" section of the Ought to be an Awesome Build thread!!!!
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Old 11-21-2012, 06:17 AM   #5
6880 Mike
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Quote:
Originally Posted by boynton6spd View Post
...What else will I need to swap out to get the big block in there?...
Purchase the 68 assembly instruction manual (AIM) and follow the assembly diagrams for the big block option. The AIM will list the parts you will need for the swap and the original GM part numbers for them.

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Old 11-21-2012, 06:17 AM   #6
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Quote:
Originally Posted by boynton6spd View Post
Just sold my 92 and bought a 68 Convertible!
I will be asking LOTS of questions to all the C3 experts on this forum...
I'm wanting to swap out the 300hp 350 for a 500hp big block.
The small block in there now has iron heads and intake, the big block I'm looking at has aluminum heads and intake...how much heavier will it be than the all iron 350?
What else will I need to swap out to get the big block in there?
Thanks in advance,
-Matt
Put in new rear axles or better yet Tom's upgraded axles. Look at Gary's upgraded diff or at least rebuild the diff. A Lakewood bellhousing is also a good idea for a manual car.

I put in an Autogear m22 too, and it's been good. Also look at upgraded front spings, I bought mine from VBP. The BB alternator bracket did't work for me, but a chrome one from a speed shop worked great (auto warehouse I think).

I tried a center force clutch but soon switched to a hd ram clutch.
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Old 11-21-2012, 08:01 AM   #7
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I got nothing here. Just want to say this will be a fun project to watch. Keep us updated, WITH PICS.
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Old 11-21-2012, 11:06 AM   #8
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Someone already mentioned that the front suspension springs are different. Larger sway bar(s), motor mounts?

You will likely want to go with the 11" clutch setup rather than the 10.5". Flywheel, starter, clutch, pressure plate and bell housing.

Radiator was bigger and the BB radiator support is different. The BB hood has more clearance that the small block hood.

What else..........tach red line will likely be different.

Additional heat in the passenger area, some form of heat deflecting or reduction might be considered.

All I can think of right now......... Keep us posted.
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