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Discussion Starter #1
Alright so I'm gonna start you guys with the basics of my car before hitting y'all with questions:

I have a 1970 Buick Skylark.

The Skylark is already swapped with a Chevy 350, meaning it already has the chevy bolt pattern at the transmission.

I am NOT going for a period correct motor, as buick engines are expensive, hard to find, and more.

ok so here's the story:

Recently I stumbled upon a used carbureted 454 that a guy pulled out of his engine bay for an LS Swap. Engines in good shape besides the usual high mileage, no cracks, no spun bearings etc, functions well (before it sat in his garage for a year or two). I plan to gut it and clean it up, most likely keeping the stock crank and pistons etc. The top half and exhaust I'm planning to do all aftermarket.

Here are the questions I have:

What difficulties can I expect to run into swapping from a Chevy 350 to a chevy 454?

Should I swap my current th350 for a th400 if I have the cash for it? (I plan to eventually swap anyway, I'm really just wondering if itll hold up to roughly 550 horsepower for a bit)

Will it bolt directly to the transmission?

Can I replace the block without pulling the transmission? If so, SHOULD I still pull the transmission?

Do you believe this is a project a person with intermediate experience can do? (I can tear apart the top end of my motor no problem but I've never installed pistons or anything)

If I do need to change the motor mounts, can you tell me which ones to buy?

And if you're REALLY feeling generous: Can you give me a step by step process of putting in the new block and what order I should do everything?

Any funny stories from your own swaps are also greatly appreciated! often the best lessons come from a great story.
 

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More for Less Racer
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Good news for you is other than putting another SBC back in place of the current engine, the swap to a BBC is about the easiest other engine swap you could do.
Skylark is GM A-body = Chevelle for parts look-up.

Since rear face of block, flexplate, trans bolt pattern, and motor mount locations are the same for SBC and BBC, that stuff is all easy. The BBC will sit right on the SBC mounts, and bolt right up to the transmission with no problems other than you need an external balance 454 flexplate with the correct bolt pattern to match the torque converter(GM has 2 possible, but you can get dual pattern flexplates).

You'll need a car/Chevelle oil pan. Truck, Corvette, and some full size car pans will not clear the crossmember and inner tie rod ends at full steering lock.

Current alternator will bolt right up but you need BBC brackets...same for power steering pump. Engine fan will be the same, fan shroud is BBC specific but available(BBC Chevelle).
1970 would have been long waterpump and related bracketry and pulleys. Radiator hoses may be able to be re-used, but plan to replace if needed. You want a big enough radiator, the current unit that cools a 350 may not be enough.
Distributors are the same, plug wires of course are different lengths and BBC usually needs 135° spark plug boots.

If the 350 has the 14" flexplate and staggered bolt pattern starter(or an aftermarket mini starter) then it can be used on the BBC also.
Flexplate is 454 specific though, can't use the 350 flexplate due to different balance issue.

Tall BBC valvecovers will have a clearance problem to a stock 12" power brake booster, the ways around this are a notched valvecover, a smaller diameter aftermarket brake booster, or booster elimination and convert to manual brakes.

Some of the tall Air Gap style single and dual plane intakes may not fit under a stock flat hood.

You'll need BBC Chevelle headers.

If the TH-350 trans is in good shape(as in been rebuilt at some point, not a 40 year old stocker), it will live for a while but needs a full rebuild with some aftermarket HD parts to really survive long...or you can just do a stock TH-400 rebuilt and not worry about it. The 4L80E overdrive is another possibility, but will need driveshaft shortening, an electronic shift controller if keeping it automatic shifts, or conversion to "brain dead" (no electronics) operated as a full manual valvebody.
TH-400 or 4L80 will both require driveshaft shortening and the TH-400 size slip yoke, and the trans crossmember slid back to the 400 location(Holes may or may not already be in the frame for this) or custom fit for the 4L80.

Whatever you end up with for driveshaft, either TH-350 length or shortened stock shaft make sure it has good u-joints in it. The BBC will punish them.

If you use the TH-350 trans, it can stay in place, just lay the headers in the engine bay and tie them in place near their final location, and set the engine down on the mounts while aligning with the trans and jockeying the headers around as needed to avoid crushing them.

From that point, just a matter of bolting all the external stuff back on to make it ready to run.

It really isn't any harder than pulling and replacing a small block, you're just changing a few specific pieces on the outside of the engine to fit the different engine - exhaust, engine accessory brackets and stuff up front, and the valvecover/brake booster issue.
 

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Welcome Julian and thanks for choosing Hotrodders as your go-to for information. Eric has begun well with your education, leaving room for others of us to chime in on different subjects.

Big block Chevies with stock pistons have a very low static compression ratio, (high 7 to 1 in most cases) which does not work well with a hot rod cam. Here is an article that I wrote several years ago that will give you an idea of what cam works with what static compression ratio. This article was written with a small block Chevy in mind, so add a little cam timing to the chart for big block Chevys.
https://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility

You may want to set the block up for aluminum heads if you will want to use them down the road. As an aside, aluminum heads do not want to play well with steel shim head gaskets. They like a composition-type gasket with a pre-flattened fire ring that will not have the tendency to imprint on the head surface.
From the factory, the block is cut at a block deck height (centerline of the main bearing bore to the top of the block where the heads bolt on) of ~9.800". The "stack" of parts that fits into the block measures ~9.780". That's half the crank stroke at 2.000", connecting rod center to center length of 6.135" and piston compression height (measurement from the centerline of the wrist pin to the crown of the piston) of 1.645", for a total stack height of ~9.780". When this stack is fitted into the block, the piston is down in the bore by 0.020" with the piston at top dead center. Factory head gasket (PN 12363414, compressed thickness 0.039", pre-flattened fire ring suitable for aluminum heads) can be used, but the combined thickness of the piston deck height (0.020") and the gasket thickness (0.039") will make a Squish/Quench clearance of 0.059".

It is desirable to have the piston come closer to the underside of the cylinder head at top dead center (Squish/Quench) to help prevent detonation on pump gas. As the piston approaches top dead center on the firing stroke, air/fuel mixture that is above the piston and being compressed is squeezed between the crown of the piston and the underside of the cylinder head. This action "jets" the mixture across the chamber, breaking up larger clumps of fuel in the mixture and making the mixture easier to light off and more detonation-resistant. The thinner this dimension is, within reason, the more detonation-resistant the motor is. "Within reason" means between 0.035" and 0.045".

In a previous paragraph, we left off with a Squish/Quench of 0.059", which will need to be thinner if we are to achieve any benefit from the "jetting" of the mixture across the chamber at top dead center. There are a couple of ways to do this:
1. Mill ~0.020" from the block decks to bring the piston deck height to zero, having only the thickness of the head gasket to describe the Squish/Quench.
2. Use pistons with a 0.010" taller compression height and cut the decks only 0.010", retaining more structural integrity in the block.
These taller pistons are manufactured by Wiseco and sold through Skip White Enterprises. Here is a +0.030" and a +0.060" piston with a 20cc dome, for instance, that results in static compression ratios shown in the chart.....
https://skipwhiteperformance.com/catalog/bbc-chevy-454-wiseco-forged-pistons-rings-4310-060-over-20cc-dome-kp432a6_92630/

The compression ratio chart included in the Skip White link will give you an idea of how the motor could end up, using either +0.030" pistons or +0.060" pistons. There are several different combustion chamber volumes shown also. That's one of the things you will need to do, measure the combustion chambers of the heads you will use. Here's a budget cc kit for 25 bucks.....
Steiger Performance - Universal Cylinder Head CC Kit
I usually use Isopropyl alcohol (rubbing alcohol) from the drug store and food coloring from the grocery store, but currently, with this Covid 19 scare, it may be hard to find Isopropyl. In that case, drop by the local liquor store and pick up a half pint of the cheapest Vodka they have. It'll work fine.

I'll stop here and let you get wrapped around what you have read so far and ask any questions you may have. Then we'll move on to other areas of the motor and or the swap in general, although as I said above, Eric has covered that pretty well.

Please remember that everything in the motor depends on something else in the motor. No single part stands alone. For instance, you have no idea what cam to use until you know the static compression ratio and you can't figure that until you know the volume of the combustion chambers in the heads that you will use.

Oh, one other thing before I forget it......Nothing electrical in the car works right until you have everything grounded properly. It's easy to miss re-connecting ground straps when you are doing an engine swap, so here's what I do. I toddle on down to the local auto parts house and get two braided ground straps. I connect one end of strap 1 to somewhere on the motor, usually down by the starter and run the other end of that wire to a hole that I drill in the frame rail, after making sure that I will not be drilling through a brake line or some other equally necessary part of the car. Attach the ground strap with a self-tapping screw. At the same location, attach one end of ground strap 2. The other end of ground strap 2 will attach at a hole drilled in the body somewhere above the well where the passenger places his/her feet. Now, you will have the motor grounded to the frame and the body, the frame grounded to the body and the motor, and the body grounded to the motor and the frame. All lights should burn brightly and all electrical accessories should work faultlessly......:thumbup:
 

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Looks like Ericnova and Tech have you well covered, I'm not adding a thing. Work safe, this should be a very satisfying project. Keep us in the loop.

Bogie
 

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Discussion Starter #5
Good news for you is other than putting another SBC back in place of the current engine, the swap to a BBC is about the easiest other engine swap you could do.
Skylark is GM A-body = Chevelle for parts look-up.

Since rear face of block, flexplate, trans bolt pattern, and motor mount locations are the same for SBC and BBC, that stuff is all easy. The BBC will sit right on the SBC mounts, and bolt right up to the transmission with no problems other than you need an external balance 454 flexplate with the correct bolt pattern to match the torque converter(GM has 2 possible, but you can get dual pattern flexplates).

You'll need a car/Chevelle oil pan. Truck, Corvette, and some full size car pans will not clear the crossmember and inner tie rod ends at full steering lock.

Current alternator will bolt right up but you need BBC brackets...same for power steering pump. Engine fan will be the same, fan shroud is BBC specific but available(BBC Chevelle).
1970 would have been long waterpump and related bracketry and pulleys. Radiator hoses may be able to be re-used, but plan to replace if needed. You want a big enough radiator, the current unit that cools a 350 may not be enough.
Distributors are the same, plug wires of course are different lengths and BBC usually needs 135° spark plug boots.

If the 350 has the 14" flexplate and staggered bolt pattern starter(or an aftermarket mini starter) then it can be used on the BBC also.
Flexplate is 454 specific though, can't use the 350 flexplate due to different balance issue.

Tall BBC valvecovers will have a clearance problem to a stock 12" power brake booster, the ways around this are a notched valvecover, a smaller diameter aftermarket brake booster, or booster elimination and convert to manual brakes.

Some of the tall Air Gap style single and dual plane intakes may not fit under a stock flat hood.

You'll need BBC Chevelle headers.

If the TH-350 trans is in good shape(as in been rebuilt at some point, not a 40 year old stocker), it will live for a while but needs a full rebuild with some aftermarket HD parts to really survive long...or you can just do a stock TH-400 rebuilt and not worry about it. The 4L80E overdrive is another possibility, but will need driveshaft shortening, an electronic shift controller if keeping it automatic shifts, or conversion to "brain dead" (no electronics) operated as a full manual valvebody.
TH-400 or 4L80 will both require driveshaft shortening and the TH-400 size slip yoke, and the trans crossmember slid back to the 400 location(Holes may or may not already be in the frame for this) or custom fit for the 4L80.

Whatever you end up with for driveshaft, either TH-350 length or shortened stock shaft make sure it has good u-joints in it. The BBC will punish them.

If you use the TH-350 trans, it can stay in place, just lay the headers in the engine bay and tie them in place near their final location, and set the engine down on the mounts while aligning with the trans and jockeying the headers around as needed to avoid crushing them.

From that point, just a matter of bolting all the external stuff back on to make it ready to run.

It really isn't any harder than pulling and replacing a small block, you're just changing a few specific pieces on the outside of the engine to fit the different engine - exhaust, engine accessory brackets and stuff up front, and the valvecover/brake booster issue.
THANK YOU SO MUCH! You took all the guess work out for me:D
 

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True Hotrodder
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The only thing I can think of would be the front motor mounts and to be honest I am not sure if there is a difference or not and whether the difference if there is one is in the frame mount or the engine mount. I looked at a couple of places and the same parts were listed for both, then one place had it just listed for the rat motor. You might also have to upgrade your radiator. The TH350 will give up if you hammer it, drive it normal like and you can take your time putting a TH400 together. You didn't say what you had for a convertor but that too should be okay.


Have fun!:D
 

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As far as pulling/installing the engine separately, or pulling/installing the engine/trans together:


i've always preferred pulling the engine separately. There are special wrenches and "wobble joints" to make disconnecting the trans bellhousing bolts easy. i will try to provide a link when there is time.


It's a personal preference though. Some like pulling the engine and trans together.
 

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Now as far as giving you a step-by-step for installation, i'm actually into that kind of thing but i don't have a lot of time these days----working alot---which is bad and good at the same time, but that's another topic for another thread......




If you can find the book, "How to rebuild your small block chevy" by David Vizard, he gives you a pretty good step-by-step with pics.
 

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Cars, Trucks, Boats, Motorcycl
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Recently I stumbled upon a used carbureted 454 that a guy pulled out of his engine bay for an LS Swap. Engines in good shape besides the usual high mileage, no cracks, no spun bearings etc, functions well (before it sat in his garage for a year or two). I plan to gut it and clean it up, most likely keeping the stock crank and pistons etc. The top half and exhaust I'm planning to do all aftermarket.
Hello,
Where are you located? Our info off to right ====>
Some of our 150,000+ members may be near you...

Did you ever turbocharge the SBC?

Any more info on the engine? Car or truck? Year? All iron? Aluminum intake or heads? Numbers on it?

Going aluminum heads, intake, and water pump can help get the weight down to close of that of a SBC... keep the stock suspension springs usable...
.
 

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...ericnova just reminded us why gm was so popular with gearheads. :thumbup:
That and the little SBC mouse motor made more power than it looked like it should be capable of... GM was also popular with ALL car buyers, having 52% of the market in the 1950's - 1970's... all the other automakers together sharing the remaining 48% of the market... Until the Govt told them they had to downsize... become less popular... or be broken up as a "monopoly"... like they did to AT&T, broke it into 8 pieces... now GM is smaller than Toyota...
.
 

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Use cheater valve covers, they are roughly 3/4" taller, and have the notch for the booster. I use them on mine and they clear roller rockers just fine.

New motor mounts and frame stands are around $100-$150, I used stock ones with the locking tab.

You'll need a drop base air cleaner with flat lid unless you have a cowl hood. The mr gasket base and lid are what I have and clear. This is with an air gap intake.

If you decide to buy aftermarket heads, be aware most of them have raised exhaust ports, that pushes headers farther outward, but you're car has around 1" more room at the steering shaft than the 64-67 A bodies. If not, check eBay for 1-7/8" headers, they'll be plenty for that engine.

I have a 64 skylark, these are things I went through putting a 496 in it.

The th350 will live unless you have sticky tires and a lead foot, just drive normal with the occasional loud pedal childishness and you'll be fine. External trans cooler would help out greatly as well.
 
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