1965 350HP Piston Configuration?

[Bill M.]

Re: 1965 350HP Piston Configuration?

Because of different stroke lengths, 302 and 350 pistons have different compression heights to achieve nominal .025" deck clearance and different dome heights to achieve the target CR. I don't remember the data for all, but the 327 forged piston dome is 0.125" and the compression height is 1.675", which is easy to measure within a few thou with a caliper; 350 compression height is 1.560, and 302s should be 1.825".
Duke

I calculate the 302 at 1.800?

[Joe C.]

Go Figure?

I calculate the 302 at 1.800?

C.H._302 = .5 (delta stroke 350 v 327) + 1.675
C.H._302 = .5 (2.48 - 2.25) + 1.675

[John H.]

Re: 1965 350HP Piston Configuration?

302 Compression Height:

Nominal deck height = 9.025"

Less 1/2 of 3" stroke = 1.5"

Less Rod length = 5.7"

Compression Height = 1.825"

[Bill M.]

Re: 1965 350HP Piston Configuration?

Thanks, John

Based on that I get:

1.700 for the 327 (9.025-5.7-3.25/2)

1.585 for the 350 (9.025-5.7-3.48/2)

Bill

[Joe C.]

Re: Go Figure?

C.H._302 = .5 (delta stroke 350 v 327) + 1.675
C.H._302 = .5 (2.48 - 2.25) + 1.675

Above, I arrived at the C.H. of the 302 by starting with the KNOWN 1.675" of the 327, but I plugged in the wrong numbers.
Here is a corrected version:

C.H._302 = .5 (delta stroke 302 v 327) + 1.675
C.H._302 = .5 ( 2.25 - 2.00) + 1.675
C.H._302 = .5 (.25) + 1.675
C.H._302 = .125 + 1.675 = 1.800

The correct way to visualize C.H. is:
nominal # deck height - rod length - (stroke/2) - nominal # crown-to-deck clearance

#: varies as much as .020 or more. In addition, deck height is often different front-to-back, and bank-to-bank.

In the case of the 302:

CH = 9.025 - 5.700 - 3/2 - .025
CH = 9.025 - 7.200 - .025 = 1.80

[Michael H.]

Re: Go Figure?

Above, I arrived at the C.H. of the 302 by starting with the KNOWN 1.675" of the 327, but I plugged in the wrong numbers.
Here is a corrected version:

C.H._302 = .5 (delta stroke 302 v 327) + 1.675
C.H._302 = .5 ( 2.25 - 2.00) + 1.675
C.H._302 = .5 (.25) + 1.675
C.H._302 = .125 + 1.675 = 1.800

The correct way to visualize C.H. is:
nominal # deck height - rod length - (stroke/2) - nominal # crown-to-deck clearance

#: varies as much as .020 or more. In addition, deck height is often different front-to-back, and bank-to-bank.

In the case of the 302:

CH = 9.025 - 5.700 - 3/2 - .025
CH = 9.025 - 7.200 - .025 = 1.80

Wouldn't the dimension for the stroke radius, rod length and pin C/L to piston top flat be just that and not include the dimension that the piston head/flat was down in the hole?

The .025" deck height shouldn't be a factor.

[Joe C.]

Re: 1965 350HP Piston Configuration?

Thanks, John

Based on that I get:

1.700 for the 327 (9.025-5.7-3.25/2)

1.585 for the 350 (9.025-5.7-3.48/2)

Bill

Bill:

327ch = 9.025 - 5.7 - (3.25/2) - .025 = 1.675
350ch = 9.025 - 5.7 - (3.48/2) - .025 = 1.560

[Joe C.]

Re: Go Figure?

Wouldn't the dimension for the stroke radius, rod length and pin C/L to piston top flat be just that and not include the dimension that the piston head/flat was down in the hole?

The .025" deck height shouldn't be a factor.

You mean to say : "crown to deck height", don't you?

It's a matter of semantics....what you call "compression height", "pin height", "compression distance".

The thread started out by discussing piston configuration, with a 5.7" rod, and installed in a (assumed) unmodified SBC with standard deck height of 9.025 (nominal), and the critical diff between 302/327/350 pistons is "pin height", "compression height", "compression distance" or, whatever you choose to call it. Crown config, and all of the other differences pointed out above, in addition to C.H. is only fluff. A piston is interchangeable as long as the C.H, bore size and ring depths/widths are compatible. Crown config can always be adapted if need be.

Look here for some clarification:

http://www.srp.com/cat/auto/chevy_sb/302-327_dome.shtml

http://www.srp.com/cat/auto/chevy_sb/350_flat.shtml

[Bill M.]

Re: 1965 350HP Piston Configuration?

I measured one OE fuelie 283 piston and got 1.8265 (calipers) (edit: measured the dome at 0.185)

I measured my aftermarket 12.5:1 302 pistons and got 1.794. I'm guessing these pistons are designed to be used with a decked block.

[Joe C.]

Re: 1965 350HP Piston Configuration?

I measured one OE fuelie 283 piston and got 1.8265 (calipers) (edit: measured the dome at 0.185)

I measured my aftermarket 12.5:1 302 pistons and got 1.794. I'm guessing these pistons are designed to be used with a decked block.

Bill,

If you were able to measure an actual 1.794, then that is close enough to 1.800 "for government work". Factory pistons, and many of the cheaper aftermarket ones are not very accurate. They can vary by more than .005. If they are FM pistons, then the accuracy would fall within that margin. Furthermore, if you look at the area inboard of the machined annulus around the outer edge of the piston (where crown measurement should be taken), you'll find rough casting which is a few thousandths higher than the machined area. In my case, I machined that area level with the machined annulus, so as to produce a more accurate and consistent quench area of .030".

Truly blueprinted engines using accurately machined race pistons are trial fitted first, matching pistons to rods, which will minimize variation. Only after this critical fitting is accomplished, that a top notch machinist will take his final deck cut, to arrive at his DESIGN deck height. In some cases, if the piston and rod combinations are accurate enough, the block is (properly) decked to 9.000, and a composition head gasket of .028-.038 (depending on piston material/bore clearance, bore size, max RPM, and rod strain) is fitted. The point is to minimize chamber volume, and from this starting point, arrive at any combination of piston dome (plus or minus), crown-to-deck height (plus or minus), ring land volume, head gasket thickness, and head gasket bore to actual bore volume, to achieve design SCR, while keeping quench within a reasonable range. Some lunatics have successfully gone as low as .022" on a SBC. I like it at .030.

[Bill M.]

Re: 1965 350HP Piston Configuration?

Bill,

If you were able to measure an actual 1.794, then that is close enough to 1.800 "for government work". Factory pistons, and many of the cheaper aftermarket ones are not very accurate. They can vary by more than .005. If they are FM pistons, then the accuracy would fall within that margin. Furthermore, if you look at the area inboard of the machined annulus around the outer edge of the piston (where crown measurement should be taken), you'll find rough casting which is a few thousandths higher than the machined area. In my case, I machined that area level with the machined annulus, so as to produce a more accurate and consistent quench area of .030".

Truly blueprinted engines using accurately machined race pistons are trial fitted first, matching pistons to rods, which will minimize variation. Only after this critical fitting is accomplished, that a top notch machinist will take his final deck cut, to arrive at his DESIGN deck height. In some cases, if the piston and rod combinations are accurate enough, the block is (properly) decked to 9.000, and a composition head gasket of .028-.038 (depending on piston material/bore clearance, bore size, max RPM, and rod strain) is fitted. The point is to minimize chamber volume, and from this starting point, arrive at any combination of piston dome (plus or minus), crown-to-deck height (plus or minus), ring land volume, head gasket thickness, and head gasket bore to actual bore volume, to achieve design SCR, while keeping quench within a reasonable range. Some lunatics have successfully gone as low as .022" on a SBC. I like it at .030.

Joe:

I remeasured and got 1.801 (makes more sense) for these TRW pistons.
These came from a street/strip 302 that a friend sold me cheap about 25 years ago. He let his car sit in an unheated garage with only water in the block and broke out the whole side of the block. I stripped the guts and scrapped the block. The rotating assembly was blueprinted and balanced. In addition to the pistons, it has full-floating pins, ARP(?) connecting rod bolts with the divots for measuring stretch. I stuck the rods in a vat of oil 25 years ago, and haven't looked at them since, so I don't know what I've got for sure. I covered the crank in grease, and it's still covered. It had a 30/30 cam and lifters too. The friend replaced the 302 with a 400 block, 350 crank set-up. He has it installed in a '60 Falcon with a Muncie and Dana 60.

Thanks for the education. I'm years away from building the 302 guts into one of my 519 blocks, but it could happen...

Bill

[Clem Z.]

Re: 1965 350HP Piston Configuration?

Joe:

I remeasured and got 1.801 (makes more sense) for these TRW pistons.
These came from a street/strip 302 that a friend sold me cheap about 25 years ago. He let his car sit in an unheated garage with only water in the block and broke out the whole side of the block. I stripped the guts and scrapped the block. The rotating assembly was blueprinted and balanced. In addition to the pistons, it has full-floating pins, ARP(?) connecting rod bolts with the divots for measuring stretch. I stuck the rods in a vat of oil 25 years ago, and haven't looked at them since, so I don't know what I've got for sure. I covered the crank in grease, and it's still covered. It had a 30/30 cam and lifters too. The friend replaced the 302 with a 400 block, 350 crank set-up. He has it installed in a '60 Falcon with a Muncie and Dana 60.

Thanks for the education. I'm years away from building the 302 guts into one of my 519 blocks, but it could happen...

Bill

make sure you radius all those sharp edges on those pistons before you use them.

[Joe C.]

Re: 1965 350HP Piston Configuration?

Joe:

I remeasured and got 1.801 (makes more sense) for these TRW pistons.
These came from a street/strip 302 that a friend sold me cheap about 25 years ago. He let his car sit in an unheated garage with only water in the block and broke out the whole side of the block. I stripped the guts and scrapped the block. The rotating assembly was blueprinted and balanced. In addition to the pistons, it has full-floating pins, ARP(?) connecting rod bolts with the divots for measuring stretch. I stuck the rods in a vat of oil 25 years ago, and haven't looked at them since, so I don't know what I've got for sure. I covered the crank in grease, and it's still covered. It had a 30/30 cam and lifters too. The friend replaced the 302 with a 400 block, 350 crank set-up. He has it installed in a '60 Falcon with a Muncie and Dana 60.

Thanks for the education. I'm years away from building the 302 guts into one of my 519 blocks, but it could happen...

Bill

Rare for anybody to build a tricked-out/blueprinted short throw SBC anymore. Just try and find top quality SHELF STOCK pistons for a 302 or a 327. Same goes for 283 parts. I came close to having SRP make a set for me, using 1/16, 1/16, 3/16 rings. The bang for the buck was not there, so I decided to blueprint my TRW pistons instead, since they are almost new, with virtually no scuffing. They still use the old fashioned 5/32, 5/32, 7/16 rings, and are heavy as door stops, but the main reason I liked them, is that they are forged out of TRW's version (proprietary) of 4032 rather than 2618. I can run tighter skirt clearances with the 4032 pistons, and I wanted that, so as to avoid excess piston slap on a cold engine.

Alas, Horatio, most people like to build large throw SBC's (truck motors), like 383's, 400's and 406's.

[Bill M.]

Re: 1965 350HP Piston Configuration?

make sure you radius all those sharp edges on those pistons before you use them.

Will do. Thanks.

Rare for anybody to build a tricked-out/blueprinted short throw SBC anymore. Just try and find top quality SHELF STOCK pistons for a 302 or a 327. Same goes for 283 parts. I came close to having SRP make a set for me, using 1/16, 1/16, 3/16 rings. The bang for the buck was not there, so I decided to blueprint my TRW pistons instead, since they are almost new, with virtually no scuffing. They still use the old fashioned 5/32, 5/32, 7/16 rings, and are heavy as door stops, but the main reason I liked them, is that they are forged out of TRW's version (proprietary) of 4032 rather than 2618. I can run tighter skirt clearances with the 4032 pistons, and I wanted that, so as to avoid excess piston slap on a cold engine.

Alas, Horatio, most people like to build large throw SBC's (truck motors), like 383's, 400's and 406's.

My brother built a 302 for his '67 and loved it. I would like to try a high-rpm 302 replacement for my L78 while it's being refreshed. Never know, I might not want to go back to the BB!

[Clem Z.]

Re: 1965 350HP Piston Configuration?

Joe:

I remeasured and got 1.801 (makes more sense) for these TRW pistons.
These came from a street/strip 302 that a friend sold me cheap about 25 years ago. He let his car sit in an unheated garage with only water in the block and broke out the whole side of the block. I stripped the guts and scrapped the block. The rotating assembly was blueprinted and balanced. In addition to the pistons, it has full-floating pins, ARP(?) connecting rod bolts with the divots for measuring stretch. I stuck the rods in a vat of oil 25 years ago, and haven't looked at them since, so I don't know what I've got for sure. I covered the crank in grease, and it's still covered. It had a 30/30 cam and lifters too. The friend replaced the 302 with a 400 block, 350 crank set-up. He has it installed in a '60 Falcon with a Muncie and Dana 60.

Thanks for the education. I'm years away from building the 302 guts into one of my 519 blocks, but it could happen...

Bill

F/M list 302 compression distance as 1.805"