I have searched the forum and google and havent really gotten a good answer so I thought I would just ask.

Are there any issues using the M21 currently in my car with a big block? Any clearance issues with the dreaded z bar? Any issues with the transmission cross member? I know the clutch and flywheel have to be changed obviously, but will the actual transmission be able to handle the torque?

I may as well ask this as well... Is it even worth the time to do this conversion, or would a built small block be better? I found a good running 454 for about what a good 4 bolt block normally sells for, just have to pull it.

We really need to get a sticky on the small block to big block conversion as many people as there are that ask questions.. links to all the accessory kits and other bits of knowledge all together in one place would be awesome.

 

I just put an all iron 427 in front of my Super T10 in my 75 and finally got it on the road, everything just bolted up for the most part, no clearance issues. The motor is a relatively mild solid lifter cam, with 60s square port close chamber heads. I'm using a centerforce II clutch setup on a GM 15lb nodular iron flywheel. I just started to put miles on it so we shall see. It's a street car though.. I'm not planning on putting sticky tires on it and take it to the strip, so I'm expecting it to hold up.

I used a march serpentine kit to keep my A/C and power steering. There are other options.. The kit is not cheap after you add the custom lines / reservoir / reverse rotation water pump / Sandin A/C compressor. But no belt jumping issues / squealing (at least up to 5500 so far) etc.. and it does not tie in to the intake or exhaust manifolds at all. But if all you have to run is the alt / Wp then you have many more options..

As for cost, depending on what you do for front springs /sway bar/ accessory drive / exhaust, it may be considerably more then building up a small block with similar power and less weight.... so it's up to your taste. I just wanted a quick revving BBC 427.. no other logical reason

 

im not sure about your year but on the mid years the z bar is different from the sb to bb.....is it worth the time to do the conversion????.....hell yes!!.....your m21 will be fine

 

M21 will bolt right in, but you will need all the BB brackets SB will not work.
I installed the BB pick a vender and order all the brackets you will need.
crossmember and clutch will fit either application, SB or BB.
enhance the Z bar and clutch with Rod ends.
I have been a SB guy for 30 years because they are plentiful with parts avaliable anywhere,
But there is no better than a BB Corvette ! I recently chnaged mine over to 454 also.
69VETTE

 

Awesome, thats what I wanted to hear. I have a 74 and was just wondering how much of a straight fit it was. I have already swapped to a larger front sway bar and stiffer springs for autocross, and I am considering eliminating my power steering and going manual, so would only have the alt and wp to run.

I may have some more questions later. Its a running 454 out of an early 70's pickup. Truck is wrecked in the rear, motor starts and runs great. I figured if I didnt need too much extra, and didnt have to do any real fab work to get it to fit, a couple hundred dollar bbc would be a fun project.

 

make sure that is not a tall HD truck BB, it won't fit under the hood of a corvette.
standard passenger BB is what you want.
also you will need a double pulley for the power steering pump if you go that way.
69VETT

 

Just as an FYI - my 427 block is a 74 454, 4 bolt block. It's been a while, but I believe Mortec listed it as a truck block. When I bought it, it already had the 427 rotating assembly in it..(de-stroked 454 ;-) I just changed out the 11.25 to 1 TRWs for lower domes and had the rod ends cut after having some ARP wavelocs put on them and the whole shebang balanced.

I thought only the 427/366 truck block was a tall deck. Did they make a tall deck 454 in the 70s?

 

The vette-specific pulleys, brackets, and water pump are not cheap. Also there are no BB brackets that fit your R4 a/c compressor (76L-82)-if that is a concern. Early 70's truck stock 454s are not exactly power-houses. The truck intake manifold probably will not fit under a stock hood. You will have to have Vette-specific exhaust manifolds or headers. Not to mention you will probably have to have a new radiator and a 454-specific flywheel. If you want a BB, that is one thing. But if you are doing this thinking you can do it for a couple hundred, I think you may want to re-evaluate.

 

I think the reason there's no sticky for this swap is that it's really a fairly straight fowrard project. An AIM and well illustrated catalog (such as Paragon's) will help. Do resist Bubba'ing it up and use the correct BB bits...

 

I have been planning on side pipes for a while, so getting the bb hookers instead of sb wouldn't be a biggie. Only using the PS and ALT right now, and may drop ps, so no worries about the AC. I have an L-88 hood on it so It should fit fine with that.


Im still just kicking it around, but for a fully running good condition BB, its very enticing. lol

 

Its all doable I did the same swap in a 70 Camaro and Never regretted it. I used standard GM brackets and the engine was a bolt in with headers. I have also helped friends do this to vettes. It is not cheap unless you have some doner for the accessory mounting.

I may be wrong, However i think that "Z" bare should work as the BBC and SBC are the same dimentions at the bellhousing mount area and the same bell housing works. The BB should have the boss for mounting the "Z" bar. BBC sit a little higher than SBC and the dimentions from the bellhousing to the motor mounts is the same.

The block between the left and right motor mount cross section is the same. The BBC is about 1.5 inches longer and approx 100 lbs heavyer depending on cast iron or aluminum heads.

Show photos when your done...

 

Sorry.. forgot to mention.. I reused the zbar / ball stud / bell housing from my L-48 on the BB, no issue.

 

The larger 3" 75-79 half shafts would be a good addition.

 

I'm just finishing a SB to BB swap in my 71, so fire away with any specific questions you have. I think personally the biggest thing I ran into was assuming I would just use many of the original parts, but ended up having to buy many new ones. This was not because they won't work with a BB, but more so because they are 38 yrs old and just needed to be replaced "while I was at it." Examples are having the tranny worked on, replacing nuts and bolts, replacing the radiator housing, new radiator, most hoses, new starter, etc. It honestly is a straight forward swap, but all the "little" things add up.

 

I didn't think about the fan shroud. Does it need to be replaced or will the existing work with either engine?

 

There are different BB and SB fan shrouds. I'm not sure if you can make the SB work...I put in a Dewitts radiator with spals, so I don't have the mech fan anymore and thus, no shroud.

 

ttt

 

did mine a few years back. Took me 2.5 years to rebuild the engine. You can check out my trials & tribulations at my sites below. The site is no longer supported and I can't edit it any more so some of the links won't work.

good luck finding a triple groove WP pulley $$$$

 

There were no 454 tall decks.

I swapped a 502 into mr '69 a couple years ago. Really the only parts I changed was the exhaust, alternator brackets and pulleys. I reused the radiator and shroud, fan, hoses, clutch, springs, everything.

 

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