Small Block to Big Block Conversion - Chevelle Tech
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Old Feb 24th, 10, 9:12 PM   #1 (permalink)
 
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Small Block to Big Block Conversion

I just bought a 454 bb to put into my 72 Camino (Cami as i call her). It originally came with the 327 so other than changing the motor mounting brackets (because they are the same as the 6 cylinder) what else do I need to change?

What about the suspension? Are the stock springs strong enough?

And last but not least, I have a custom radiator that has the same dimensions as the stock one, do I need to upgrade to a bigger one, or will that radiator be enough to keep the engine cool?

Thanks everyone in advance,
Jody
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Old Feb 24th, 10, 9:13 PM   #2 (permalink)
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Re: Small Block to Big Block Conversion

You'll want heavier springs in the front to compensate for the extra weight of the big block.
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Old Feb 24th, 10, 11:32 PM   #3 (permalink)
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Re: Small Block to Big Block Conversion

if its a small block shroud, you can trim it to fit. bbc ps, alt, crank pulley is different, headers of course, use the 454 flex plate, and fuel pump. Give your radiator a try it may work it may not. my chevelle has a 3 core and has no temp issues, my 71 has the same 3 core and runs at 210 in the tucson summer. But, i have the ac condensor on the 71. jim
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Old Feb 24th, 10, 11:40 PM   #4 (permalink)
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Re: Small Block to Big Block Conversion

By 1972 the 327 was a pleasant memory. What is the V.I.N.? It will reveal what engine came in your Cami from the factory.
I'm also swapping a BBC in place of a SBC, so I've been following the various threads on the topic on T/C. A search on the key words will reveal a bunch of info.
I bought a new aluminum 3 core radiator from an eBay seller - $170 delivered to my door! No worries about a +40 y.o. radiator anymore.
If you like the lowered look, SBC springs will still support the front. Might want to move up to SBC w/ A/C to get a little more lift.
Engine mounts are easily available online. Make sure you have enough fuel supply to feed the beast.
What trans?

Dan
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Old Feb 25th, 10, 12:02 AM   #5 (permalink)
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Re: Small Block to Big Block Conversion

I'm using a stock-style 3 row with a clutch fan, and have no cooling problems. It's the same one that was spec'd for a 327/clutch in the rad shop's reference materials.

My rat is sitting on SBC frame stands. The Milodon 7-quart kickout style pan is a little close to the crossmember, but does not hit it.

Putting a rat where a mouse lived may not drop the ride height at rest much, but when you cross an intersection dip or go over a speed bump you will probably wish you had stiffer springs (at the least). The SB springs just can't do well with the dynamic (in motion) loads put upon the front end, even though they appear to hold up the car well in the driveway.

In my '66, a BBC with long water pump and clutch fan and 3-core radiator puts the fan very close to the radiator itself. There is hardly room to pull a fan belt between the fins and the fan.
On the other hand, I have absolutely zero cooling problems, and do not need a shroud.
I built one from .050" aluminum, but it acts more as a finger guard, since the proximity of the fan to the rad promotes great flow.
If I had chosen a short water pump setup, this might all have turned out differently.

Also, my engine compartment is vented very well, so even in traffic on a 100-degree day, there is no overheating from soak or trapped heat.

Headers on the '66 are a tight fit for 2" under chassis style. A couple of spots rubbed the frame, and a driver side primary tube just kisses the steering shaft unless you ding it a little bit.
These would be Hooker #2455 or 2217s. Hope I got those numbers correct !!
I yanked the same headers that were in my BBC 2nd gen Camaro, and they fit right into the Chevelle setup. I think this is the same deal for the '68-'72s.
These headers hang down with a fair amount of room between them and the underside of the floor. There is plenty of ground clearance to be gained here for a lowered car. At least a full inch, which makes a big difference when you are just skiffing speed bumps and lousy driveways (like the one they have at Classic Industries).

A tall intake (such as an air-gap or Victor) + a tall air filter definitely will not fit under the flat hood of my '66.

I'm running pass-side alternator, and the p/s is from an '80 Camaro. The mount is standard GM, although I customized it at the side of the road a few months back (@@!!@@) when I had no choice. Those pictures are still on the site here, likely, since I didn't cancel them.

With the Milodon pan, I cannot pull the engine+trans together. I have to yank the trans, McLeod scattershield, clutch, and flywheel, then helicopter the engine straight up. This is due to the little clearance left between pan and crossmember.

On that issue, I noted a while back in Hot Rod Magazine which ran a multiple crate-motor test using (I think) a '69 Chevelle, that they had whacked the stock crossmember for a welded tubular one, and gained a great deal of room.
I really would like to see and hear more about that. I'd do it if I could be assured of equal or better strength.

I had to use a 7" dual-diaphragm brake booster due to lack of clearance between the larger diameter ones and my fabbed valve covers (large, to clear rollers and a girdle). The normal stock Chev v/c height should allow at least an 8" booster, or better a 9" one. That is what I had at first when I had just stuffed in the rat with a stock bellhousing and Super T-10.

I plan to raise my engine up by about 3/8ths of an inch using motor mount spacers. I will make them from aluminum plate.
The reason for this is two-fold:
1. Increase clearance between the crossmember and the large Milodon pan.
2. Gain some extra ground clearance for the Hooker 2"x 3.5" headers.

Of course, raising the engine will require also raising the trans, and re-adusting the pinion angle of the rear end. I could leave the trans where it is and just increase the angle of the engine, but that would just put more stress on the u-joint, in my reasoning. I could be wrong, though.

Raising the rat motor is not normally a good idea, due to c/g considerations. However in my case most of the engine is aluminum, the battery is gone, the hood is race-weight 'glass, and other weight-saving measures have been taken. I don't foresee any increase in tendency to roll, since it is not an iron engine.

I recommend increasing the front sway bar to at least 1-1/8th dia. Many people run 1-1/4, or even 1-3/8ths. For sure, though, the rat in its all-steel form is a formidable heavy-weight to stuff into such an engine-forward design as the A-body is.
I highly recommend budgeting time and funds to develop the front suspension with the new balance. It is well worth it !!

These are just quick thoughts, based upon what I actually did. I hope some of it helps !

Eric
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Old Feb 25th, 10, 11:47 AM   #6 (permalink)
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Re: Small Block to Big Block Conversion

All I did on my 72' was nothing. Bolted right in, was a SBC originally. It had no shroud though.
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Old Feb 25th, 10, 12:44 PM   #7 (permalink)
 
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Re: Small Block to Big Block Conversion

Wow! I didn't expect this much help. Thanks so much.

I noticed a typo in my original post. I have a 307 car not a 327.

As for my transmission, as of now, I'm running a THM350 and according to how we feel when we put the motor in, we may put our stock 700R in. But, next winter, we plan to put either a TKO 500/600 or a T-56 transmission in it.

Now I just hope that we get it done before Chevelleabration.
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Last edited by jglenn6; Feb 25th, 10 at 12:45 PM. Reason: typo
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Old Feb 25th, 10, 1:22 PM   #8 (permalink)
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Re: Small Block to Big Block Conversion

I am planning the same swap on my '72, a 402 for my 350. An article I found claimed that the accelerator cable and bracket needed to be changed as well. Anyone confirm this or will the stock SBC setup work?
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Old Feb 28th, 10, 10:57 AM   #9 (permalink)
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Re: Small Block to Big Block Conversion

I'm finishing up a 350 to 402 (72) conversion on an original 72 - 402 sprint. The accelerator cable from the SBC fits, but the bracket does not. I bought an aftermarket one - the type that connects to the carb studs and includes the return springs. I still have the H/D radiator, but the SBC shroud does not fit. I've ordered a new one.
Car does sit lower, as I have SBC front springs. The driver-side header sits lower than I'd like.
The power steering and alternator brackets are different, as is the pressure line for the power steering. I haven't installed A/C though it is an A/C car.
The biggest frustration for my swap was my failure to realize that the oil pressure sender on the BBC is in different location (side of engine vs. back of intake on SB). The motor was already in car when I realized this, and I could not remove any of the plugs without stripping them (probably could have gotten one out if the motor was still on a stand). I ended up installing and customizing an oil filter sandwhich adaptor (usually used for an oil cooler) to which I connected the pressure gauge.
The dizzy is the same (had an HEI), though the spark plug wires, though they fit, will be replaced. they're the 90 degree boots - will probably go with 135 degree boots after I fire her up).
Will probably fire it up this afternoon for the first time since the rebuild. Got the zddp additive in with the valvoline racing oil (10-30) for the break in.

good luck to you.
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Old Feb 28th, 10, 2:05 PM   #10 (permalink)
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Re: Small Block to Big Block Conversion

if your careful, you dont even have to remove the hood to make the swap.
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Old Feb 28th, 10, 3:00 PM   #11 (permalink)
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Re: Small Block to Big Block Conversion

http://www.chevelles.com/techref/ftecref10.html read this
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Old Feb 28th, 10, 4:20 PM   #12 (permalink)
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Re: Small Block to Big Block Conversion

If you have a flat hood be aware that the air cleaner is mighty close. You could install it with out the water pump and accessories, put just the air cleaner base on with no carb stud and shut the hood. From the front slide under the car and measure the distance from the base to the hood. My clearance was so close that I had to use a regular 1/4" nut to hold the lid on. Be careful with the height of the intake and carb spacer. Also using a drop base air cleaner should be considered. Moroso springs for a small block will make your car sit almost lever with the big block.
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Old Mar 1st, 10, 11:48 AM   #13 (permalink)
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Re: Small Block to Big Block Conversion

Quote:
Originally Posted by jglenn6 View Post
Wow! I didn't expect this much help. Thanks so much.

I noticed a typo in my original post. I have a 307 car not a 327.
You'll probably need to either use 307 motor mounts or change the stands on the frame as the 307 was the one odd duck as I recall. Can anyone confirm?
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Old Mar 1st, 10, 10:19 PM   #14 (permalink)
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Re: Small Block to Big Block Conversion

As long as you use 307 motor mounts with the 307 stands, the big block will fit just fine. Done it myself on a 72 and a 71 Camaro. Fan shrouds even lined up the fan.
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Old Dec 1st, 11, 12:26 AM   #15 (permalink)
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Re: Small Block to Big Block Conversion

Quote:
Originally Posted by bln View Post
THIS is why "search" is a good tool.

Still don't know what to use though; solid, rubber, polly, mix, etc. However, I DID learn something from this thread and that link.
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