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What is the difference between gen 1 and gen 2 350s? I have a 350 roller block purchased new off summit. I assumed it’s a gen 1 but have been told it’s a gen 2 because it has roller block provisions. So can someone tell me the difference between the two so i don’t order the wrong parts for it while I’m building it.
 

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As far as I know, Gen 2 is considered the reverse cooled LT1 stuff. Lower end and cams are interchangeable, but block deck and heads are different due to reverse cooling water routing.

What is the block casting number you have?.

Gen 1 started to convert to roller cams in 1986 and are still considered Gen 1, the Gen 1 designation didn't change just because they added the provisions for factory roller cams .
Gen II is LT1 '92-97 Reverse cooled, and they still continued to make Gen I at the same time they were making the Gen II.
The last Gen 1 was the 2001 Vortec engines.

Gen III is the LS engines.
 

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In addition to roller cam provisions, within the Gen I engines you also have the earlier 2 piece rear main seal and the later 1 piece rear main seal, and you need to know which one you have when you buy your flex plate and other parts. There were also variations in heads, including the later TBI heads and Vortec heads that require a different intake manifold.

Parts are readily available for all the variations of blocks and heads. You just need to know which one you have, and that information should be included in the specs provided with your engine.

Bruce
 

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Gen 2 was reverse cooled and ran a distributor off the front of the cam called an opti spark. The motors that you would know by the brand names LT1 and LT4 most commonly. There were some iron head big car versions too, but I can't remember what Chevy called those. It's been a looooooooooong time since I worked on one I can't remember if the block had a hole for a distributor in the traditional location or not. It probably did as GM is cheap.
 

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Gen 2 was reverse cooled and ran a distributor off the front of the cam called an opti spark. The motors that you would know by the brand names LT1 and LT4 most commonly. There were some iron head big car versions too, but I can't remember what Chevy called those. It's been a looooooooooong time since I worked on one I can't remember if the block had a hole for a distributor in the traditional location or not. It probably did as GM is cheap.
X2.

Yes there is a way to drive a conventional distributor and GM sells a carb intake for these with a hole for a conventional distributor.

Gen I engines are all conventional cooling of block first with return through the heads to intake manifold based coolant return. Basically 1955 through 1986 use a two piece rear seal and flat tappet cam. In 86 and 87 changes began to appear with a one piece rear seal, roller cam provisions, elimination of the machanical fuel pump provision, a change to powder forged rods, a shorter projection of the lower cylinder bore into the crankcase, hypereutectic cast pistons, and moly rings, among many other changes to heads such as self-aligning rockers and induction becoming either port or throttle body injection. Through 95 these blocks could be roller cammed usually for passenger vehicles or flat tappet cammed usually for trucks. The truck blocks can have the provisions anywhere from the unfinished casting through partial to complete machining of them.

Gen I continues into 1996 as the L30 and L31 Vortec for trucks I think these are known as Gen I revision E. All have roller cam's with central port sequential injection, these continued into 2002 production on some lines.

Gen II were available from 1992 through 97. These use a unique block and heads for head first cooling, a very complex water pump and thermostat system, special front mounted optical distributor, and intake with port injection. However, much of the internals like crank, rods, pistons, camshaft, lifters, pushrods, rockers, and valves are either totally or with slight modification compatible with earlier and contemporary Gen I engines. The LT4HOT cam being a popular choice in 87 up Gen I engines provisioned for roller cam's.

There's more but I don't want to write a book.

Bogie
 

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As far as I know, Gen 2 is considered the reverse cooled LT1 stuff. Lower end and cams are interchangeable, but block deck and heads are different due to reverse cooling water routing.

What is the block casting number you have?.

Gen 1 started to convert to roller cams in 1986 and are still considered Gen 1, the Gen 1 designation didn't change just because they added the provisions for factory roller cams .
Gen II is LT1 '92-97 Reverse cooled, and they still continued to make Gen I at the same time they were making the Gen II.
The last Gen 1 was the 2001 Vortec engines.

Gen III is the LS engines.
so idk if this cam I have is for a gen 1 of gen 2 tbi 350 sbc it’s a flat tappet cam would it still work on my tbi even if it’s ment for a gen one?
 

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Yes the flat tapped cam will work in any Gen I block. Somewhere I remember something about GM using a small letter designation for various improvements which actually are quite a few it looks something like this.

- The original had no oil filter, mount provisions were on the front facing the radiator, cam had a transfer groove in the bearing for moving oil.

The oil transfer grooves were removed from the cam’s bearing journals to be machined into the block behind the cam bearing shell.

- Then came the mods to put an oil filter on the block, the original was a can with a replaceable element, a few years later that changed to a spin on.

- Then the mounts were moved to the forward side of the block.

- Heads were modified to allow accessory brackets and accessory to be secured to the front of the heads. This, also, drove the long version of the coolant pump.

- The intake and block was modified to remove the oil fill passage and the road tube cast provisions as PCV cam. This also made changes to the valve covers.

- Thin wall casting gets introduced in the early 1970’s.

- The two piece rear seal was changed to a one piece and the accessory drive converted to serpentine belts which includes a modification to the coolant pump for counter clockwise rotation.

- The fuel pump mount area remained but for engines expected to get fuel injection it wasn’t completed, there are exceptions to this. At first only blocks going to passenger cars getting roller cams were cast and finished with the needed provisions. A separation was made for heads going to Tuned Port Injection (TPI) or Throttle Body Injection (TBI) the latter getting Swirl Ports the former did not. Eventually all blocks got roller provisions as castings but blocks headed for trucks were left somewhere between as cast to fully machined. Inside this time frame rods were changed from mild steel forgings to powder metal forging. Pistons became hypereutectic castings, and the spigot length of the cylinder wall extension was shortened as the tighter fit hyper pistons didn’t need as much wall support through the BDC event.

- The 1996 introduces a completely different top end from the heads up and many changes made to support the OBD 2 electronics plus a modified coolant pump to change the bypass locations to fit to and around the new fuel injection, these being the L30, 305 and L31, 350 Vortecs.

These just touching on some of the mods made to the Gen I engines over their life time, there are many smaller tweaks as well not just on the engine but to its manufacturing and casting processes. To emphasize all the above are considered Gen I engines.

Gen I roller blocks can use the earlier Gen I flat tapped cam by simply using the flat tapped cam timing set. Flat tapped blocks can use what is called a retro-fit roller cam with a thrust bumper, you can actually do this to a roller block as well. The factory roller prepped blocks use what is called the OEM roller cam, it uses a bolt on thrust plate and the can has a reduced diameter extended nose to accommodate that which retro-fit cams do NOT have. The bolt circle between flat tapped and retro-roller cams is different from OEM roller cams so the timing sets do not interchange

Gen II introduces the 1990’s LT1 and LT4 engines ( note the original LT-1 of the late 1960’s early 1970’s has a dash between the letters and the number of the designation where the 1990’s version does not.

* Enter the LT1 and LT4; these are designated as Gen II engines. The basic block and head castings are unique and do not interchange even though bolt patterns for the man caps and the heads to block are the same.

- The cooling system is reversed where the pump feeds the block but that is now a passage that immediately reroutes the coolant into the heads first. Coolant then flows down into the block from the heads and returns through new passages in the front of the block to a completely different front assembly that includes a cam driven coolant pump and an optical distributor. None of this interchanges with the Gen I engine.

- What can be interchanged with the Gen I engines is the crankshaft rotating assembly including rods and pistons. The roller cam will interchange with the Gen I roller block castings if they are finished out by the factory or the motor builder. The lifters interchange as do push rods and rockers for use on Gen I heads that use self-guiding rockers, design change that came around 1987 I forgot to include in the above list of Gen I changes. Valves and springs will interchange but the LT4 uses a 2 inch intake where the LT1 retains the familiar 1.94.

Yes the flat tapped cam will work in any Gen I block. Somewhere I remember something about GM using a small letter designation for various improvements which actually are quite a few it looks something like this.

- The original had no oil filter, mount provisions were on the front facing the radiator, cam had a transfer groove in the bearing for moving oil.

The oil transfer grooves were removed from the cam’s bearing journals to be machined into the block behind the cam bearing shell.

- Then came the mods to put an oil filter on the block, the original was a can with a replaceable element, a few years later that changed to a spin on.

- Then the mounts were moved to the forward side of the block.

- Heads were modified to allow accessory brackets and accessory to be secured to the front of the heads. This, also, drove the long version of the coolant pump.

- The intake and block was modified to remove the oil fill passage and the road tube cast provisions as PCV cam. This also made changes to the valve covers.

- Thin wall casting gets introduced in the early 1970’s.

- The two piece rear seal was changed to a one piece and the accessory drive converted to serpentine belts which includes a modification to the coolant pump for counter clockwise rotation.

- The fuel pump mount area remained but for engines expected to get fuel injection it wasn’t completed, there are exceptions to this. At first only blocks going to passenger cars getting roller cams were cast and finished with the needed provisions. A separation was made for heads going to Tuned Port Injection (TPI) or Throttle Body Injection (TBI) the latter getting Swirl Ports the former did not. Eventually all blocks got roller provisions as castings but blocks headed for trucks were left somewhere between as cast to fully machined. Inside this time frame rods were changed from mild steel forgings to powder metal forging. Pistons became hypereutectic castings, and the spigot length of the cylinder wall extension was shortened as the tighter fit hyper pistons didn’t need as much wall support through the BDC event.

- The 1996 introduces a completely different top end from the heads up and many changes made to support the OBD 2 electronics plus a modified coolant pump to change the bypass locations to fit to and around the new fuel injection, these being the L30, 305 and L31, 350 Vortecs.

These just touching on some of the mods made to the Gen I engines over their life time, there are many smaller tweaks as well not just on the engine but to its manufacturing and casting processes. To emphasize all the above are considered Gen I engines.

Gen I roller blocks can use the earlier Gen I flat tapped cam by simply using the flat tapped cam timing set. Flat tapped blocks can use what is called a retro-fit roller cam with a thrust bumper, you can actually do this to a roller block as well. The factory roller prepped blocks use what is called the OEM roller cam, it uses a bolt on thrust plate and the can has a reduced diameter extended nose to accommodate that which retro-fit cams do NOT have. The bolt circle between flat tapped and retro-roller cams is different from OEM roller cams so the timing sets do not interchange

Gen II introduces the 1990’s LT1 and LT4 engines ( note the original LT-1 of the late 1960’s early 1970’s has a dash between the letters and the number of the designation where the 1990’s version does not.

* Enter the LT1 and LT4; these are designated as Gen II engines a well as a miserable cast iron headed 265 inch version call the L99. The basic block and head castings are unique and do not interchange even though bolt patterns for the man caps and the heads to block are the same.

- The cooling system is reversed where the pump feeds the block but that is now a passage that immediately reroutes the coolant into the heads first. Coolant then flows down into the block from the heads and returns through new passages in the front of the block to a completely different front assembly that includes a cam driven optical distributor under the coolant pump driven with a gear an short jack shaft off the timing set. None of this interchanges with the Gen I engine. The idea was that putting the recently cooled coolant into the head first would allow higher compression ratios than the head in a conventional engine receives coolant previously heated in the block. This is an old idea that rears its head down through industrial age time always with less than conceived results. An example Pontiac tried this on their OHV, V8’s. It lasted from 1955 to 1959 where the inservice failure rate drive a more conventional design, Chevy got about the same life out of theirs from 92 to 96.

- What can be interchanged with the Gen I engines is the crankshaft rotating assembly including rods and pistons. The roller cam will interchange with the Gen I roller block castings if they are finished out by the factory or the motor builder. The lifters interchange as do push rods and rockers for use on Gen I heads that use self-guiding rockers, design change that came around 1987 I forgot to include in the above list of Gen I changes. Valves and springs will interchange but the LT4 uses a 2 inch intake where the LT1 retains the familiar 1.94 inch intake.

OK this is at detail complicated, the simple answer is the Gen II engines consist only of the LT1 and LT4, 350 cast iron block with aluminum heads and the all cast iron L99, 265 made from or rather made from 1992 through 1996, some sources suggest 1997 was the last year. These were replaced by the clean sheet of paper, newly designed Gen III, LS1 which shares nothing with the Gen I or Gen II engines.
Yes the flat tapped cam will work in any Gen I block. Somewhere I remember something about GM using a small letter designation for various improvements which actually are quite a few it looks something like this.

- The original had no oil filter, mount provisions were on the front facing the radiator, cam had a transfer groove in the bearing for moving oil.

The oil transfer grooves were removed from the cam’s bearing journals to be machined into the block behind the cam bearing shell.

- Then came the mods to put an oil filter on the block, the original was a can with a replaceable element, a few years later that changed to a spin on.

- Then the mounts were moved to the forward side of the block.

- Heads were modified to allow accessory brackets and accessory to be secured to the front of the heads. This, also, drove the long version of the coolant pump.

- The intake and block was modified to remove the oil fill passage and the road tube cast provisions as PCV cam. This also made changes to the valve covers.

- Thin wall casting gets introduced in the early 1970’s.

- The two piece rear seal was changed to a one piece and the accessory drive converted to serpentine belts which includes a modification to the coolant pump for counter clockwise rotation.

- The fuel pump mount area remained but for engines expected to get fuel injection it wasn’t completed, there are exceptions to this. At first only blocks going to passenger cars getting roller cams were cast and finished with the needed provisions. A separation was made for heads going to Tuned Port Injection (TPI) or Throttle Body Injection (TBI) the latter getting Swirl Ports the former did not. Eventually all blocks got roller provisions as castings but blocks headed for trucks were left somewhere between as cast to fully machined. Inside this time frame rods were changed from mild steel forgings to powder metal forging. Pistons became hypereutectic castings, and the spigot length of the cylinder wall extension was shortened as the tighter fit hyper pistons didn’t need as much wall support through the BDC event.

- The 1996 introduces a completely different top end from the heads up and many changes made to support the OBD 2 electronics plus a modified coolant pump to change the bypass locations to fit to and around the new fuel injection, these being the L30, 305 and L31, 350 Vortecs.

These just touching on some of the mods made to the Gen I engines over their life time, there are many smaller tweaks as well not just on the engine but to its manufacturing and casting processes. To emphasize all the above are considered Gen I engines.

Gen I roller blocks can use the earlier Gen I flat tapped cam by simply using the flat tapped cam timing set. Flat tapped blocks can use what is called a retro-fit roller cam with a thrust bumper, you can actually do this to a roller block as well. The factory roller prepped blocks use what is called the OEM roller cam, it uses a bolt on thrust plate and the can has a reduced diameter extended nose to accommodate that which retro-fit cams do NOT have. The bolt circle between flat tapped and retro-roller cams is different from OEM roller cams so the timing sets do not interchange

Gen II introduces the 1990’s LT1 and LT4 engines ( note the original LT-1 of the late 1960’s early 1970’s has a dash between the letters and the number of the designation where the 1990’s version does not.

* Enter the LT1 and LT4; these are designated as Gen II engines a well as a miserable cast iron headed 265 inch version call the L99. The basic block and head castings are unique and do not interchange even though bolt patterns for the man caps and the heads to block are the same.

- The cooling system is reversed where the pump feeds the block but that is now a passage that immediately reroutes the coolant into the heads first. Coolant then flows down into the block from the heads and returns through new passages in the front of the block to a completely different front assembly that includes a cam driven optical distributor under the coolant pump driven with a gear an short jack shaft off the timing set. None of this interchanges with the Gen I engine. The idea was that putting the recently cooled coolant into the head first would allow higher compression ratios than the head in a conventional engine receives coolant previously heated in the block. This is an old idea that rears its head down through industrial age time always with less than conceived results. An example Pontiac tried this on their OHV, V8’s. It lasted from 1955 to 1959 where the inservice failure rate drive a more conventional design, Chevy got about the same life out of theirs from 92 to 96.

- What can be interchanged with the Gen I engines is the crankshaft rotating assembly including rods and pistons. The roller cam will interchange with the Gen I roller block castings if they are finished out by the factory or the motor builder. The lifters interchange as do push rods and rockers for use on Gen I heads that use self-guiding rockers, design change that came around 1987 I forgot to include in the above list of Gen I changes. Valves and springs will interchange but the LT4 uses a 2 inch intake where the LT1 retains the familiar 1.94 inch intake.

OK this is at detail complicated, the simple answer is the Gen II engines consist only of the LT1 and LT4, 350 cast iron block with aluminum heads and the all cast iron L99, 265 made from 1992 through 1996, some sources suggest 1997 was the last year. These were replaced by the clean sheet of paper, newly designed Gen III, LS1 which shares nothing with the Gen I or Gen II engines.

Bogie
 

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OK this is at detail complicated, the simple answer is the Gen II engines consist only of the LT1 and LT4, 350 cast iron block with aluminum heads and the all cast iron L99, 265 made from 1992 through 1996, some sources suggest 1997 was the last year. These were replaced by the clean sheet of paper, newly designed Gen III, LS1 which shares nothing with the Gen I or Gen II engines.

The detail, you might want to clean your glasses and get some coffee.


Yes the flat tapped cam will work in any Gen I block. Somewhere I remember something about GM using a small letter designation for various improvements which actually are quite a few it looks something like this.

- The original had no oil filter, mount provisions were on the front facing the radiator, cam had a transfer groove in the bearing for moving oil.

The oil transfer grooves were removed from the cam’s bearing journals to be machined into the block behind the cam bearing shell.

- Then came the mods to put an oil filter on the block, the original was a can with a replaceable element, a few years later that changed to a spin on.

- Then the mounts were moved to the forward side of the block.

- Heads were modified to allow accessory brackets and accessory to be secured to the front of the heads. This, also, drove the long version of the coolant pump.

- The intake and block was modified to remove the oil fill passage and the road tube cast provisions as PCV cam. This also made changes to the valve covers.

- Thin wall casting gets introduced in the early 1970’s.

- The two piece rear seal was changed to a one piece and the accessory drive converted to serpentine belts which includes a modification to the coolant pump for counter clockwise rotation.

- The fuel pump mount area remained but for engines expected to get fuel injection it wasn’t completed, there are exceptions to this. At first only blocks going to passenger cars getting roller cams were cast and finished with the needed provisions. A separation was made for heads going to Tuned Port Injection (TPI) or Throttle Body Injection (TBI) the latter getting Swirl Ports the former did not. Eventually all blocks got roller provisions as castings but blocks headed for trucks were left somewhere between as cast to fully machined. Inside this time frame rods were changed from mild steel forgings to powder metal forging. Pistons became hypereutectic castings, and the spigot length of the cylinder wall extension was shortened as the tighter fit hyper pistons didn’t need as much wall support through the BDC event.

- The 1996 introduces a completely different top end from the heads up and many changes made to support the OBD 2 electronics plus a modified coolant pump to change the bypass locations to fit to and around the new fuel injection, these being the L30, 305 and L31, 350 Vortecs.

These just touching on some of the mods made to the Gen I engines over their life time, there are many smaller tweaks as well not just on the engine but to its manufacturing and casting processes. To emphasize all the above are considered Gen I engines.

Gen I roller blocks can use the earlier Gen I flat tapped cam by simply using the flat tapped cam timing set. Flat tapped blocks can use what is called a retro-fit roller cam with a thrust bumper, you can actually do this to a roller block as well. The factory roller prepped blocks use what is called the OEM roller cam, it uses a bolt on thrust plate and the can has a reduced diameter extended nose to accommodate that which retro-fit cams do NOT have. The bolt circle between flat tapped and retro-roller cams is different from OEM roller cams so the timing sets do not interchange

Gen II introduces the 1990’s LT1 and LT4 engines ( note the original LT-1 of the late 1960’s early 1970’s has a dash between the letters and the number of the designation where the 1990’s version does not.

* Enter the LT1 and LT4; these are designated as Gen II engines. The basic block and head castings are unique and do not interchange even though bolt patterns for the man caps and the heads to block and the exhaust manifold/headers are the same.

- The cooling system is reversed where the pump feeds the block but that is now a passage that immediately reroutes the coolant into the heads first. Coolant then flows down into the block from the heads and returns through new passages in the front of the block to a completely different front assembly that includes a cam driven coolant pump and an optical distributor. None of this interchanges with the Gen I engine.

- What can be interchanged with the Gen I engines is the crankshaft rotating assembly including rods and pistons. The roller cam will interchange with the Gen I roller block castings if they are finished out by the factory or the motor builder. The lifters interchange as do push rods and rockers for use on Gen I heads that use self-guiding rockers, design change that came around 1987 I forgot to include in the above list of Gen I changes. Valves and springs will interchange but the LT4 uses a 2 inch intake where the LT1 retains the familiar 1.94.
 
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