Big Block conversion
Thread Starter
Racer
Joined: Jan 2010
Posts: 367
Likes: 1
From: Christchurch Canterbury
Big Block conversion
Here's a summary of issues I found on re installing a big block in my 69.
Although I believe the car was origionally a 427, 435 hp car, previous owner had installed a SBC.
Bell housing will accept either blocks, as will clutch linkage and pivots.
I uprated my pressure plate and disc to handle power increase.
There are 2 flywheel options, 153 tooth ring gear and 168 tooth. there are 2 options with input shafts also, fine spline 26, and course spline, so there will be 2 size and slpine options with clutches.
I bought STD interlocking engine mounts from a local speed shop.
Exhaust will need to be re jigged, I installed sidepipe headers, or you will need BB headers. Some aftermarket heads use raised exhaust ports, this will probably cause issues with most headers, as they are a tight fit!
Distributor will work, you may need to re curve advance to suit .
Brackets were an issue, seems big block corvette brackets and pulleys are unique to corvette, so I purchased brackets and pulleys from a corvette vendor. ( not so cheap)
You may need to make a spacer to mount the rear mount on the alt bracket unless you are using factory exhast manifolds, as it locates on the last manifold mount bolt
At some point my power steering pump had been exchanged for a reco pump, seems early big block pumps had tapered shafts, and big block P/S pulleys are made to suit tapered pulleys, so i needed adapt a double row P/S pulley to work with a straight shaft pump, I machined a small spacer to align.
My engine had a weiand short water pump, I was having trouble aligning pulleys. I managed to pull, with a 3 legged puller the flange to suit pulley alignment.
So I ended with a double row crank pulley, double row water pump, and double row power steering pulley, I had to buy the correct alternator pulley to suit factory pulleys, its spaced forward.
My car had the BB rad support and 27 inch rad already in the car.
I used SB rad shroud I had, I did need to modify it to fit, this involved trimming the front lip and lower right corner for clearance to install.
I replaced both rad hoses with correct fitment hoses.
I reused the small block clutch mechanical fan, seems to be working fine, runs 210 deg.
I used a mechanical fuel pump, but needed to use corvette specific pump, or at least a rotatable inlet/ outlet unit , otherwise the inlet may foul on the chassis.
Manifold selection seems limited, I found a GM LS6 manifold, measured up ok with a dropped based filter, with my combo this manifold is not ideal but fits under stock big block hood.
I found with the manifold been so low, I had to modify holley carb throttle linkage so to foul on the manifold. ( hack saw remedied this)
Also I had to purchase suitable holley throttle bracket with return spring attachment.
I managed to find rocker covers to clear roller rocker and still be able to use Vac canister for wiper door. My car has manual brakes so rocker clearance was no issue on the drivers side. Covers are about 3 inches tall.
You will probably need to up rate front springs, I went from all iron SB with iron heads and water pump, I though alloy headed BB would be ok, but its way soft in the front!
Hope this helps someone, feel free to add aditional thoughts, and or critique as needed
Although I believe the car was origionally a 427, 435 hp car, previous owner had installed a SBC.
Bell housing will accept either blocks, as will clutch linkage and pivots.
I uprated my pressure plate and disc to handle power increase.
There are 2 flywheel options, 153 tooth ring gear and 168 tooth. there are 2 options with input shafts also, fine spline 26, and course spline, so there will be 2 size and slpine options with clutches.
I bought STD interlocking engine mounts from a local speed shop.
Exhaust will need to be re jigged, I installed sidepipe headers, or you will need BB headers. Some aftermarket heads use raised exhaust ports, this will probably cause issues with most headers, as they are a tight fit!
Distributor will work, you may need to re curve advance to suit .
Brackets were an issue, seems big block corvette brackets and pulleys are unique to corvette, so I purchased brackets and pulleys from a corvette vendor. ( not so cheap)
You may need to make a spacer to mount the rear mount on the alt bracket unless you are using factory exhast manifolds, as it locates on the last manifold mount bolt
At some point my power steering pump had been exchanged for a reco pump, seems early big block pumps had tapered shafts, and big block P/S pulleys are made to suit tapered pulleys, so i needed adapt a double row P/S pulley to work with a straight shaft pump, I machined a small spacer to align.
My engine had a weiand short water pump, I was having trouble aligning pulleys. I managed to pull, with a 3 legged puller the flange to suit pulley alignment.
So I ended with a double row crank pulley, double row water pump, and double row power steering pulley, I had to buy the correct alternator pulley to suit factory pulleys, its spaced forward.
My car had the BB rad support and 27 inch rad already in the car.
I used SB rad shroud I had, I did need to modify it to fit, this involved trimming the front lip and lower right corner for clearance to install.
I replaced both rad hoses with correct fitment hoses.
I reused the small block clutch mechanical fan, seems to be working fine, runs 210 deg.
I used a mechanical fuel pump, but needed to use corvette specific pump, or at least a rotatable inlet/ outlet unit , otherwise the inlet may foul on the chassis.
Manifold selection seems limited, I found a GM LS6 manifold, measured up ok with a dropped based filter, with my combo this manifold is not ideal but fits under stock big block hood.
I found with the manifold been so low, I had to modify holley carb throttle linkage so to foul on the manifold. ( hack saw remedied this)
Also I had to purchase suitable holley throttle bracket with return spring attachment.
I managed to find rocker covers to clear roller rocker and still be able to use Vac canister for wiper door. My car has manual brakes so rocker clearance was no issue on the drivers side. Covers are about 3 inches tall.
You will probably need to up rate front springs, I went from all iron SB with iron heads and water pump, I though alloy headed BB would be ok, but its way soft in the front!
Hope this helps someone, feel free to add aditional thoughts, and or critique as needed
Last edited by richiev88; Mar 28, 2012 at 10:31 PM. Reason: spelling, adding info
Drifting
Joined: Jan 2011
Posts: 1,853
Likes: 81
From: Hamilton Virginia
Great information. 
Thank you.
I am also in the middle of a BB swap. Got the motor bolted in, but had to pull to change the flexplate, didnt line up with the torque converter, had to order a dual pattern. Anyone else doing the swap measure your flex plate before you install
Thank you.
I am also in the middle of a BB swap. Got the motor bolted in, but had to pull to change the flexplate, didnt line up with the torque converter, had to order a dual pattern. Anyone else doing the swap measure your flex plate before you install
Drifting
Joined: Jul 2009
Posts: 1,532
Likes: 14
From: Dallas-Fort Worth TX
Good info and accurate. I guess I did not realize I went thru most of the same issues you did. I just took it slow, one step at a time, asking lots of questions and looking at lots of pictures.
The alt bracket mount spacer was a PIA. I worked on this one for a while because of the raised ex ports on the heads, I had to elongate the bracket hole and put steel spacers to turn it into a strange looking header bolt.
I had all the original BB pulleys. I was going to just use long bolts and spacers to push the alternator out, but instead I bought the alternator extended pulley to line up with the double ps pulley.
Did not have to worry about the fan since I went with a Dewitts/fan set up. VC are just under 3 inches, but enough to clear roller rockers. They look original but are 3/4 inch taller than OEM.
Had a heck of time finding the perfect geometry for the fuel pump inlet/outlets in order to get the fuel lines to fit.
I put in 550 springs before the swap.
The alt bracket mount spacer was a PIA. I worked on this one for a while because of the raised ex ports on the heads, I had to elongate the bracket hole and put steel spacers to turn it into a strange looking header bolt.
I had all the original BB pulleys. I was going to just use long bolts and spacers to push the alternator out, but instead I bought the alternator extended pulley to line up with the double ps pulley.
Did not have to worry about the fan since I went with a Dewitts/fan set up. VC are just under 3 inches, but enough to clear roller rockers. They look original but are 3/4 inch taller than OEM.
Had a heck of time finding the perfect geometry for the fuel pump inlet/outlets in order to get the fuel lines to fit.
I put in 550 springs before the swap.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
Likes: 281
From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Good info and accurate. I guess I did not realize I went thru most of the same issues you did. I just took it slow, one step at a time, asking lots of questions and looking at lots of pictures.
The alt bracket mount spacer was a PIA. I worked on this one for a while because of the raised ex ports on the heads, I had to elongate the bracket hole and put steel spacers to turn it into a strange looking header bolt.
I had all the original BB pulleys. I was going to just use long bolts and spacers to push the alternator out, but instead I bought the alternator extended pulley to line up with the double ps pulley.
Did not have to worry about the fan since I went with a Dewitts/fan set up. VC are just under 3 inches, but enough to clear roller rockers. They look original but are 3/4 inch taller than OEM.
Had a heck of time finding the perfect geometry for the fuel pump inlet/outlets in order to get the fuel lines to fit.
I put in 550 springs before the swap.
The alt bracket mount spacer was a PIA. I worked on this one for a while because of the raised ex ports on the heads, I had to elongate the bracket hole and put steel spacers to turn it into a strange looking header bolt.
I had all the original BB pulleys. I was going to just use long bolts and spacers to push the alternator out, but instead I bought the alternator extended pulley to line up with the double ps pulley.
Did not have to worry about the fan since I went with a Dewitts/fan set up. VC are just under 3 inches, but enough to clear roller rockers. They look original but are 3/4 inch taller than OEM.
Had a heck of time finding the perfect geometry for the fuel pump inlet/outlets in order to get the fuel lines to fit.
I put in 550 springs before the swap.
What valve covers did you run? I am slowing piecing together parts for my swap.
Drifting
Joined: Jul 2009
Posts: 1,532
Likes: 14
From: Dallas-Fort Worth TX
Read the description. They are towards the bottom of the page.
http://www.cfrperformance.com/Chevy_...overs_s/43.htm
part # HZ-9504-T
BTW I have p239 .40.. nice tool.
Thread Starter
Racer
Joined: Jan 2010
Posts: 367
Likes: 1
From: Christchurch Canterbury
Manifold height
Here's a summary of issues I found on re installing a big block in my 69.
Although I believe the car was origionally a 427, 435 hp car, previous owner had installed a SBC.
Bell housing will accept either blocks, as will clutch linkage and pivots.
I uprated my pressure plate and disc to handle power increase.
There are 2 flywheel options, 153 tooth ring gear and 168 tooth. there are 2 options with input shafts also, fine spline 26, and course spline, so there will be 2 size and slpine options with clutches.
I bought STD interlocking engine mounts from a local speed shop.
Exhaust will need to be re jigged, I installed sidepipe headers, or you will need BB headers. Some aftermarket heads use raised exhaust ports, this will probably cause issues with most headers, as they are a tight fit!
Distributor will work, you may need to re curve advance to suit .
Brackets were an issue, seems big block corvette brackets and pulleys are unique to corvette, so I purchased brackets and pulleys from a corvette vendor. ( not so cheap)
You may need to make a spacer to mount the rear mount on the alt bracket unless you are using factory exhast manifolds, as it locates on the last manifold mount bolt
At some point my power steering pump had been exchanged for a reco pump, seems early big block pumps had tapered shafts, and big block P/S pulleys are made to suit tapered pulleys, so i needed adapt a double row P/S pulley to work with a straight shaft pump, I machined a small spacer to align.
My engine had a weiand short water pump, I was having trouble aligning pulleys. I managed to pull, with a 3 legged puller the flange to suit pulley alignment.
So I ended with a double row crank pulley, double row water pump, and double row power steering pulley, I had to buy the correct alternator pulley to suit factory pulleys, its spaced forward.
My car had the BB rad support and 27 inch rad already in the car.
I used SB rad shroud I had, I did need to modify it to fit, this involved trimming the front lip and lower right corner for clearance to install.
I replaced both rad hoses with correct fitment hoses.
I reused the small block clutch mechanical fan, seems to be working fine, runs 210 deg.
I used a mechanical fuel pump, but needed to use corvette specific pump, or at least a rotatable inlet/ outlet unit , otherwise the inlet may foul on the chassis.
Manifold selection seems limited, I found a GM LS6 manifold, measured up ok with a dropped based filter, with my combo this manifold is not ideal but fits under stock big block hood.
I found with the manifold been so low, I had to modify holley carb throttle linkage so to foul on the manifold. ( hack saw remedied this)
Also I had to purchase suitable holley throttle bracket with return spring attachment.
I managed to find rocker covers to clear roller rocker and still be able to use Vac canister for wiper door. My car has manual brakes so rocker clearance was no issue on the drivers side. Covers are about 3 inches tall.
You will probably need to up rate front springs, I went from all iron SB with iron heads and water pump, I though alloy headed BB would be ok, but its way soft in the front!
Hope this helps someone, feel free to add aditional thoughts, and or critique as needed
Although I believe the car was origionally a 427, 435 hp car, previous owner had installed a SBC.
Bell housing will accept either blocks, as will clutch linkage and pivots.
I uprated my pressure plate and disc to handle power increase.
There are 2 flywheel options, 153 tooth ring gear and 168 tooth. there are 2 options with input shafts also, fine spline 26, and course spline, so there will be 2 size and slpine options with clutches.
I bought STD interlocking engine mounts from a local speed shop.
Exhaust will need to be re jigged, I installed sidepipe headers, or you will need BB headers. Some aftermarket heads use raised exhaust ports, this will probably cause issues with most headers, as they are a tight fit!
Distributor will work, you may need to re curve advance to suit .
Brackets were an issue, seems big block corvette brackets and pulleys are unique to corvette, so I purchased brackets and pulleys from a corvette vendor. ( not so cheap)
You may need to make a spacer to mount the rear mount on the alt bracket unless you are using factory exhast manifolds, as it locates on the last manifold mount bolt
At some point my power steering pump had been exchanged for a reco pump, seems early big block pumps had tapered shafts, and big block P/S pulleys are made to suit tapered pulleys, so i needed adapt a double row P/S pulley to work with a straight shaft pump, I machined a small spacer to align.
My engine had a weiand short water pump, I was having trouble aligning pulleys. I managed to pull, with a 3 legged puller the flange to suit pulley alignment.
So I ended with a double row crank pulley, double row water pump, and double row power steering pulley, I had to buy the correct alternator pulley to suit factory pulleys, its spaced forward.
My car had the BB rad support and 27 inch rad already in the car.
I used SB rad shroud I had, I did need to modify it to fit, this involved trimming the front lip and lower right corner for clearance to install.
I replaced both rad hoses with correct fitment hoses.
I reused the small block clutch mechanical fan, seems to be working fine, runs 210 deg.
I used a mechanical fuel pump, but needed to use corvette specific pump, or at least a rotatable inlet/ outlet unit , otherwise the inlet may foul on the chassis.
Manifold selection seems limited, I found a GM LS6 manifold, measured up ok with a dropped based filter, with my combo this manifold is not ideal but fits under stock big block hood.
I found with the manifold been so low, I had to modify holley carb throttle linkage so to foul on the manifold. ( hack saw remedied this)
Also I had to purchase suitable holley throttle bracket with return spring attachment.
I managed to find rocker covers to clear roller rocker and still be able to use Vac canister for wiper door. My car has manual brakes so rocker clearance was no issue on the drivers side. Covers are about 3 inches tall.
You will probably need to up rate front springs, I went from all iron SB with iron heads and water pump, I though alloy headed BB would be ok, but its way soft in the front!
Hope this helps someone, feel free to add aditional thoughts, and or critique as needed
