Help to identify a 63-67 300 vs350 HP 327

[Mark Evans]

I want to purchase a 350 hp 327 for my 1967 Corvette convertible. How can you identify the difference between a 300 horsepower block and heads verses the 350 HP. The casting numbers are the same. Is there any other identifying attributes with out disassembling the short block?

[Bill Stephenson]

Re: Help to identify a 63-67 300 vs350 HP 327

------The balancer is different if its still on the crank.........Bill S

[Bill Stephenson]

Re: Help to identify a 63-67 300 vs350 HP 327

------The balancer is different if its still on the crank.........Bill S

[Joe L.]

Re: Help to identify a 63-67 300 vs350 HP 327

Mark and Bill-----

The balancer is one quick way to tell, presuming that it hasn't been changed. The 300 hp uses a balancer which is 6-1/8" OD and 3/4" thick. The L-79 350 hp uses a balancer which is 8" OD and about 1-11/16" thick. Also, check the timing pointer. The originals were spot-welded to the cover and different placements were used for the 2 size balancers. The timing tab should be spot welded on and very close to the balancer.

Also, the 300 hp uses a cast iron intake manifold whereas the L-79 uses aluminum. Of course, this is easily changed. And, just keep in mind, that anything can be changed.

[Joe L.]

Re: Help to identify a 63-67 300 vs350 HP 327

Mark and Bill-----

The balancer is one quick way to tell, presuming that it hasn't been changed. The 300 hp uses a balancer which is 6-1/8" OD and 3/4" thick. The L-79 350 hp uses a balancer which is 8" OD and about 1-11/16" thick. Also, check the timing pointer. The originals were spot-welded to the cover and different placements were used for the 2 size balancers. The timing tab should be spot welded on and very close to the balancer.

Also, the 300 hp uses a cast iron intake manifold whereas the L-79 uses aluminum. Of course, this is easily changed. And, just keep in mind, that anything can be changed.

[Joe L.]

Addendum

Also, and it's so obvious that it didn't come to mind immediately, you can check the engine stamp pad for the suffix code.

HE, HH, HO, and HR= 300 hp

HD, HP, HT, and KH= 350 hp

[Joe L.]

Addendum

Also, and it's so obvious that it didn't come to mind immediately, you can check the engine stamp pad for the suffix code.

HE, HH, HO, and HR= 300 hp

HD, HP, HT, and KH= 350 hp

[Zachary K.]

Re: Help to identify a 63-67 300 vs350 HP 327

You can also look at the engine pad. Right hand side(passenger side)of block just below the head. If the block hasn't been decked (or restamped, and no one ever does this) you will see the vin number of the car it originally came out of and the following two letter codes.
For 1966 or 1967, if it's a 300 hp block you will see: HE, HH, HO or HR. If it's a 350 hp block you will see HT, HD, HP or KH.
For 1965, there are quite a few hp combinations. If it's a 250 hp block you will see: HE, HI, HO or HQ. A 300 hp block HF, HJ, HP or HR. HO,or HQ. A 350 hp block HT, HU, HV or HW. A 365 hp block HH, HK, HL or HM. A 375 hp block HG or HN.
For 1964, there are also a few combinations: A 250 hp RC, RP, SC or SK. A 300 hp block RD, RQ, SD or SL. A 350 hp block wasn't available. A 365 hp block RE, RR, RT or RU. A 375 hp block RF or RX.
For 1963, there was a 250 hp block with codes RC or SC. A 300 hp block with RD or SD. A 340 hp block with RE. And a 360 hp block with RF.
Hope this helps.

[Zachary K.]

Re: Help to identify a 63-67 300 vs350 HP 327

You can also look at the engine pad. Right hand side(passenger side)of block just below the head. If the block hasn't been decked (or restamped, and no one ever does this) you will see the vin number of the car it originally came out of and the following two letter codes.
For 1966 or 1967, if it's a 300 hp block you will see: HE, HH, HO or HR. If it's a 350 hp block you will see HT, HD, HP or KH.
For 1965, there are quite a few hp combinations. If it's a 250 hp block you will see: HE, HI, HO or HQ. A 300 hp block HF, HJ, HP or HR. HO,or HQ. A 350 hp block HT, HU, HV or HW. A 365 hp block HH, HK, HL or HM. A 375 hp block HG or HN.
For 1964, there are also a few combinations: A 250 hp RC, RP, SC or SK. A 300 hp block RD, RQ, SD or SL. A 350 hp block wasn't available. A 365 hp block RE, RR, RT or RU. A 375 hp block RF or RX.
For 1963, there was a 250 hp block with codes RC or SC. A 300 hp block with RD or SD. A 340 hp block with RE. And a 360 hp block with RF.
Hope this helps.

[Brandon K.]

Re: Help to identify a 63-67 300 vs350 HP 327

The blocks are the same casting. Pistons and camshafts were different. The heads were the same, except that the 350 horse uses larger valves (the difference in size is so small you can hardly even tell by looking.)

[Brandon K.]

Re: Help to identify a 63-67 300 vs350 HP 327

The blocks are the same casting. Pistons and camshafts were different. The heads were the same, except that the 350 horse uses larger valves (the difference in size is so small you can hardly even tell by looking.)

[Duke W.]

Re: Help to identify a 63-67 300 vs350 HP 327

'65 L-79s also have the "big" oil pan with the deep portion extending about 3/4s the distance of the engine length versus about half for the standard pan, but '66 and later L-79s have the small pan to allow room for the power steering piston.

Duke

[Duke W.]

Re: Help to identify a 63-67 300 vs350 HP 327

'65 L-79s also have the "big" oil pan with the deep portion extending about 3/4s the distance of the engine length versus about half for the standard pan, but '66 and later L-79s have the small pan to allow room for the power steering piston.

Duke

[Page C.]

Re: Help to identify a 63-67 300 vs350 HP 327

Hi Mark,
The front of the crankshaft should be drilled and tapped for a bolt to hold the 8" balancer to the crank. The crank pulley and water pump pulley should be the 3/8 wide groove type. The water pump should have a bypass fitting to connect to the alum. intake
Hope this helps,
Page Campbell

[Page C.]

Re: Help to identify a 63-67 300 vs350 HP 327

Hi Mark,
The front of the crankshaft should be drilled and tapped for a bolt to hold the 8" balancer to the crank. The crank pulley and water pump pulley should be the 3/8 wide groove type. The water pump should have a bypass fitting to connect to the alum. intake
Hope this helps,
Page Campbell