With the overwhelming selection of potent small block crate engines, and factory motors from fourth gen F-bodies to choose from today, the age old big block swap isn't as popular as it once was, but it's still a foolproof way to add brute torque and smooth running power to your third gen F-body!

Overall, the swap isn't really that difficult, but there are some things to be aware of. The common big block engines of the late 60s, 70s and early 80s all physically bolt up to the same bellhousings and motor mounts as a small block, so on the surface, it's something of a "bolt-in" swap.

Below is a list of factory GM part numbers and a description of the part(s) referenced. I don't know if all of these items are still available over the counter at your local Chevy dealer, but back several years ago when I worked at a local dealership they were.

PART # PART DESCRIPTION
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14039437 Frame mount (two required)
334970 Engine Mount Bracket (LH)
14039436 Engine Mount Bracket (RH)
14089455 Spacer Plate (LH)
14089456 Spacer Plate (RH)
14023147 Big Block front pulley (two groove)
14023148 Big Block front pulley (three groove for AC)
3985999 Chevelle oil pan (BB)

The spacer plates allow the engine to sit up enough for chassis clearance, and the frame mounts are standard V8 F-body parts. Obviously, the pulleys are listed as either a two groove for cars without air conditioning or three groove for applications where keeping or adding air conditioning is desired.

TRANSMISSIONS...

Transmissions are an important consideration in any big block (or hot small block) third gen F-body program. I personally prefer the time-proven TH-350 for this swap, and it's what I'm using in mine. The TH-350 is cheap, common, rugged enough to handle a stock or mild big block in a car this light, and easily fits into a third gen F-body with the aid of an aftermarket changeover kit.

The TH-400 can also be used, but it's increased size makes the fit in the stock transmission tunnel VERY tight, and unless you're running a seriously potent big block, it's really overkill for this application.

Myself, I don't like the later overdrive automatic transmissions, but if you really felt brave, you COULD run one behind a big block...for a little while, anyway!

I've heard of big block swaps backed by four speed manual transmissions, and even a couple five speed ones, but I've never seen one in person, and don't know how well the cars and the transmissions handle it! For my car, the TH-350 is more than enough behind a smog motor 454!

To install a TH-350 transmission, you'll need one of two aftermarket changeover kits that I know of. B&M makes one, as does Hurst. The B&M kit is a little cheaper, but the Hurst kit is a little more complete. Either one will do the basic job for you, which is to adapt the torque arm to your TH-350 tranny, but I bought the Hurst kit for my swap.

Both kits are available mail order through Jegs, and the part numbers with current prices as per the latest catalog are listed below:

PART # DESCRIPTION JEGS PRICE
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30299 B&M TH350 Changeover kit $79.99
550-0001 Hurst TH350 Changeover kit $95.99
550-0002 Hurst TH400 Changeover kit $135.99

The above part numbers are the manufacturer's part numbers for the kits. If ordering from Jegs, you would need to include the manufacturer's prefix code to the part number, which would mean that the B&M kit would be ordered as part number 130-30299, and the Hurst kits would be ordered as 530-550-0001 or 530-550-0002. The Hurst TH-400 kit includes a new crossmember, so that's why it costs a bit more.

If using the stock rear axle and a short tailshaft TH-350, I'm told that you can retain the stock driveshaft, but I haven't gotten far enough along to confirm that for certain yet. It looks like it should work, and I'll let you know when I can say for sure. If not, having a new custom driveshaft made is no big deal, and probably a good idea anyway.

(At the very least, you should take your stock drivesahft in to have it checked for straightness, balanced and new u-joints. It's better to be safe and do this before you bolt the shaft in...because the big block will put some serious hurt on a weak or wounded driveshaft in a big hurry!)

The Hurst changeover kit for the TH-350 includes a shift cable to adapt the TH-350 to your stock floor shift automatic shifter, but in my case, I'm using an aftermarket shifter (Hurst V-Matic), so that's a moot point. Still, for a low dollar, stock appearing installation, it's nice that the Hurst kit includes a new cable for those wanting to use the original shifter.

Torque converter choice is largely up to you, your vehicle combination, and how you plan to use it. Several companies make aftermarket converters if you desire something more than a stock stall speed. I've always ran TCI converters and had good luck with them, so I bought a TCI "Sizzler" for this car. It's one step over a stock torque converter, increasing stall speed by 400 to 500rpm behind a big block, but it's stronger than a stock converter too. For a stock or very mild engine (mine is a smog motor 454 with a very mild cam) with stock gears out back, it's a great converter for a daily driver. Moving up the rung, you could go with a TCI Saturday Night Special, a TCI Breakaway or a TCI Streetfighter converter if you plan to run taller rear gears and more radical cam profile.

MAKING IT FIT!!!

The big block is going to fit REAL tight into your third gen F-body engine compartment, but it does slide in there! Some issues to be aware of are oil pan clearance, and brake booster clearance. Some oil pans may not fit the front crossmember as well as others. I've seen aftermarket pans on big block third gens, but I don't know what brand these guys used, or what part number. The old Chevelle big block pan just clears with the mentioned spacer plates in the first parts list above, though...so I can tell you that the pan listed will work...but there's no room to spare!

Short valve covers will make your life much easier if your car is equipped with power brakes! I bought stock style short chrome covers and when doing the initial test-fit, there was adequate clearance for the brake booster. It may be a trick to remove the valve cover once the engien is in place for the final time and bolted down, but we'll wait and see on that. From what others have told me, it's tight, but you can do it.

Firewall clearance is really tight for distributor fit, too. I would have run a standard, large diameter HEI distributor, but it didn't look like it would fit without some heavy handed hammer work. Instead, I opted to go with a stock Delco single point distributor. It fits okay, but I dented the firewall/upper cowl area for a little extra room to get the cap on and off for changing points down the line. For the low rpm levels my car will see, a stock single point distributor is fine. I just made sure to buy the proper resistor for the coil, which will be wired in when I do the car's electrical system (a whole project in itself!).

EXHAUSTING WORK!!!

I thought I'd be able to get away with using a set of "block hugger" style headers on this car, and they MIGHT work on the passenger's side, but the steering clearance on the driver's side has me thinking twice! Hooker still sells a set of Super Comp headers for this swap (part number 2226), but I was going to wait until I've exhausted (ha ha!) all other options before ordering a set of those. A friend has a set of block huggers I can borrow for a test fit, and if they look like they might work with no or slight modifications, then I'll buy a set myself and see if I can make them fit. I would really like the added ground clearance that a shorter header like this would provide over a full chassis header, but you gotta go with whatever works, so I'll bite the bullet and buy the Hookers if I have to!

Whatever headers I end up using, I plan to have a full set of duals installed by a local shop that's done me proud in the past. Other big block F-bodies I've seen have run duals dumped at the rear axle with Flowmasters or turbo mufflers bouncing off the pavement, but I was wanting to run a cross-flow muffler in the stock location for as much ground clearance and noise reduction as possible. Hey...it's a Berlinetta...ya GOTTA play that "sleeper angle" for all it's worth, right?

I'll have more info on this swap for you down the road, but for now I just thought I'd post a few thoughts, notes, observations and part numbers to help out anyone else planning to carry on the tradition of the legendary big block Camaro!

As I get further, discover new parts and pitfalls, I'll add to this post and try to save you some headaches in the process!!!

 

nice write up man.....thanks

 

good info! (speaking from experince)

 

Thanks bro.. I am currently installing a 454 in my 84 camaro. I built the motor myself its out of an old truck that got junked. When i took the motor apart i saw that the cylinders still had hone marks in them and no lip on the wall. So i left the bottom end alone aside from a hv oil pump and new gaskets. THe top half i got a little crazy, i ground the valves ported and pollished the heads installed a .540" lift @ 286 intake .540 @ 296 exhaust cam Performer RPM intake holley 750 carb and using the stock HEI distributor. I don't know what im goign to do for the headers but that will come. I am currently rebuilding the TH700R4 so it might beable to handle that motor. I also had to get a hood scoop to clear the motor. I have not tried to fit the engine in the car yet but i ahve taken some measurements and i think the 7 qt oil pan will clear. If not ill just beat the **** out of it hahah. I think ill need to do some triming on my firewall for the distributor. Im glad im not the only one doing this kind of swap. Thanks for the info again.
Hutch

 

On mine I used a factory early Chevelle style oil pan,didn't have to modify it any.I had an MSD Pro Billet,but I'm pretty confident that an HEI would fit without any modification.

 

The distributor will clear just fine, had to remove wiper motor to get motor in but could be put back on afterwords, that was the ONLY clearrance issue i had...

 

What ate the frame mounts for and how big are the spacers I am looking at putting in a 396 in my 86 iroc