1970 Blue Trans Am
New member
1970 WS 400 Ram Air 3/4 434 Build
Am having a rebuild of my 1970 Trans Am's original WS/9799915 400 block, dated January 6, 1970. (Ram Air III code up front, with the Ram Air IV modified casting number, of which a few were built.) Factory equipped lucerne blue with deluxe blue interior, with M-21 close ratio Muncie and 3.73:1 ratio Chevrolet 12 bolt, produced in February 1970 in Lordstown, Ohio. I purchased the car in December 1979 from self identified 3rd owner who had found in Waco, Texas, and son afterwards had the engine rebuilt with stock specs, and a 0.30 overbore in 1977. At the time I purchased it, the car had a decal "City Motors, Fairborn, Ohio".
I drove it from 1980 to November 1982 when I spun a rod bearing and subsequently took the engine and car apart.
Started a resto-modification during the mid 1980s, with the idea of stock appearance with subtle and internal improvements.
R&R the sub-frame-suspension with better bushings, and big car spindles with ILE discs, and the 12 bolt, upgraded with c clip eliminator kit and 1979-1981 rear discs, with the main parts powder-coated, and replacing all brake and fuel lines with SSB stainless replacement parts.
Being aware of vin numbers but not of date codes, I sold the #12 cylinder heads to a friend of a friend who installed them on his 1977 or 1978 TA, and purchased a set of #614 service replacement heads, as part of a plan including two main parts: (1) upgrade to Ram Air IV, and (2) provide a greater punch with a longer stroke crankshaft, most economically then provided by a 3.25 main journal factory crankshaft re-machined to fit the 3" journals fof the 400. But not with a 4.21 stroke of a 455 but rather the 4" stroke of a 428, thus providing in the range of 433-435 cubic inches, to give some extra torque while retaining a greater degree of rev ability.
Stored indoors from late 1980s until Spring 2002 as I got distracted by a 1972 455HO GTO, and subsequently stored outdoors covered in plywood and plastic until February 2017, where the powder coat failed and needs redoing, though the SSB parts appear to not have aged a day. (Am seeking a shop to restore body before taking to a friend's "Firebird Farm" for assembly).
Engine parts stored indoors continuously, with the WS block which was stored continuously indoors, and is now in machine shop where it checked out ok for an overbore to 0.40. As we now have a multitude of aftermarket internal engine parts, rebuilding with stronger parts is considerably less money than during the 1900s. The best bang for the buck appears to be a SCAT 4" stroke forged standard weight crankshaft with BBC Callies rods, the latter being only about $250 costlier than Eagle or SCAT 4340s, but with apparently better strength qualities for greater sustained higher rpm operation.
I desire keeping this car with a manual transmission, but want greater flexibility, as the original M-21 close ratio with 3.73 differential gives nice torque multiplication (2.20 first gear), but alas 4000 rpm at 80 mph in top (4th) gear.
Ideally I want to switch to a 5 or 6 speed manual transmission. The most prevalent today appears to be the Tremacs, but I am more intrigued by the Richmond, for two main reasons: (1) its far wider selection of gearing options, and (2) what I read years ago when it was known as the Doug Nash, about the greater efficiency of placing the gear multiplication more within the transmission than in the differential, with steeper transmission gearing coupled with a 2 series rear rather than a high 4 series or 4 series differential coupled with an overdrive. But as I would like to reduce expenses where I already have something which could more easily be swapped later, I plan on switching to an M-20 wide ratio for now, (and with the rear having to come part to re-do the powder-coat) with the 3.73 gears replaced with either 3.31 or 3.07s. See and compare the following comparison between these transmissions:
M-21
2.20 1.64 1.24 1.0
with 3.73
8.206 6.1172 4.6252 3.73
M-20
2.52 1.88 1.46 1.00
with 3.31
8.34 6.22 4.8326 3.31
with 3.07
7.73 5.7716 4.48 3.07
Note, that the M-20/3.07 combo gives not all that much less overall multiplication than the M-21/3.73 combo, and that the M-20/3.31 combo gives a bit more. With regards to the greater torque of the longer stroke and more modern camshafts, never-mind that Pontiacs were generally more torquey than the Chevrolet engines that led the close ratio trend, this appears to give a great bang for the buck, especially with the 3.31.
Am having a rebuild of my 1970 Trans Am's original WS/9799915 400 block, dated January 6, 1970. (Ram Air III code up front, with the Ram Air IV modified casting number, of which a few were built.) Factory equipped lucerne blue with deluxe blue interior, with M-21 close ratio Muncie and 3.73:1 ratio Chevrolet 12 bolt, produced in February 1970 in Lordstown, Ohio. I purchased the car in December 1979 from self identified 3rd owner who had found in Waco, Texas, and son afterwards had the engine rebuilt with stock specs, and a 0.30 overbore in 1977. At the time I purchased it, the car had a decal "City Motors, Fairborn, Ohio".
I drove it from 1980 to November 1982 when I spun a rod bearing and subsequently took the engine and car apart.
Started a resto-modification during the mid 1980s, with the idea of stock appearance with subtle and internal improvements.
R&R the sub-frame-suspension with better bushings, and big car spindles with ILE discs, and the 12 bolt, upgraded with c clip eliminator kit and 1979-1981 rear discs, with the main parts powder-coated, and replacing all brake and fuel lines with SSB stainless replacement parts.
Being aware of vin numbers but not of date codes, I sold the #12 cylinder heads to a friend of a friend who installed them on his 1977 or 1978 TA, and purchased a set of #614 service replacement heads, as part of a plan including two main parts: (1) upgrade to Ram Air IV, and (2) provide a greater punch with a longer stroke crankshaft, most economically then provided by a 3.25 main journal factory crankshaft re-machined to fit the 3" journals fof the 400. But not with a 4.21 stroke of a 455 but rather the 4" stroke of a 428, thus providing in the range of 433-435 cubic inches, to give some extra torque while retaining a greater degree of rev ability.
Stored indoors from late 1980s until Spring 2002 as I got distracted by a 1972 455HO GTO, and subsequently stored outdoors covered in plywood and plastic until February 2017, where the powder coat failed and needs redoing, though the SSB parts appear to not have aged a day. (Am seeking a shop to restore body before taking to a friend's "Firebird Farm" for assembly).
Engine parts stored indoors continuously, with the WS block which was stored continuously indoors, and is now in machine shop where it checked out ok for an overbore to 0.40. As we now have a multitude of aftermarket internal engine parts, rebuilding with stronger parts is considerably less money than during the 1900s. The best bang for the buck appears to be a SCAT 4" stroke forged standard weight crankshaft with BBC Callies rods, the latter being only about $250 costlier than Eagle or SCAT 4340s, but with apparently better strength qualities for greater sustained higher rpm operation.
I desire keeping this car with a manual transmission, but want greater flexibility, as the original M-21 close ratio with 3.73 differential gives nice torque multiplication (2.20 first gear), but alas 4000 rpm at 80 mph in top (4th) gear.
Ideally I want to switch to a 5 or 6 speed manual transmission. The most prevalent today appears to be the Tremacs, but I am more intrigued by the Richmond, for two main reasons: (1) its far wider selection of gearing options, and (2) what I read years ago when it was known as the Doug Nash, about the greater efficiency of placing the gear multiplication more within the transmission than in the differential, with steeper transmission gearing coupled with a 2 series rear rather than a high 4 series or 4 series differential coupled with an overdrive. But as I would like to reduce expenses where I already have something which could more easily be swapped later, I plan on switching to an M-20 wide ratio for now, (and with the rear having to come part to re-do the powder-coat) with the 3.73 gears replaced with either 3.31 or 3.07s. See and compare the following comparison between these transmissions:
M-21
2.20 1.64 1.24 1.0
with 3.73
8.206 6.1172 4.6252 3.73
M-20
2.52 1.88 1.46 1.00
with 3.31
8.34 6.22 4.8326 3.31
with 3.07
7.73 5.7716 4.48 3.07
Note, that the M-20/3.07 combo gives not all that much less overall multiplication than the M-21/3.73 combo, and that the M-20/3.31 combo gives a bit more. With regards to the greater torque of the longer stroke and more modern camshafts, never-mind that Pontiacs were generally more torquey than the Chevrolet engines that led the close ratio trend, this appears to give a great bang for the buck, especially with the 3.31.