1965 350HP Piston Configuration?

[John N.]

My machinist is building a motor for a client and wants to know what is the proper configuration of a 1965 327 350 HP piston. The picture below is of a GM NOS piston (usage unknown). It has a .125 dome. Is the dome height correct? Is the eyebrow configuration correct?

Thanks

[Joe L.]

Re: 1965 350HP Piston Configuration?

My machinist is building a motor for a client and wants to know what is the proper configuration of a 1965 327 350 HP piston. The picture below is of a GM NOS piston (usage unknown). It has a .125 dome. Is the dome height correct? Is the eyebrow configuration correct?

Thanks

John-----


I can't say, for sure, that this is the correct piston for the application. However, the dome height and dome/relief configuration appear to be correct for the application. Are there forging numbers on the underside?

[John N.]

Re: 1965 350HP Piston Configuration?

John-----


I can't say, for sure, that this is the correct piston for the application. However, the dome height and dome/relief configuration appear to be correct for the application. Are there forging numbers on the underside?

Joe
Thanks:
3866954
GM

[Joe L.]

Re: 1965 350HP Piston Configuration?

Joe
Thanks:
3866954
GM

John----


From what I can tell, GM #3866954 was one of the forging numbers used for 1965-67 SHP 327 pistons used for L-79, L-76, and L-84.

[John N.]

Re: 1965 350HP Piston Configuration?

Joe-Thanks

[Joe L.]

Re: 1965 350HP Piston Configuration?

Joe-Thanks

John-----


Since I'm not 100% sure of my information, as a final check before I installed these pistons I would compare the position of the piston pin to another known 327 piston. They should be the same regardless of what the configuration of the known 327 piston is. I'm 99.9% sure they will be, but it's worth the little bit of effort to confirm it.

[Joe C.]

Re: 1965 350HP Piston Configuration?

My machinist is building a motor for a client and wants to know what is the proper configuration of a 1965 327 350 HP piston. The picture below is of a GM NOS piston (usage unknown). It has a .125 dome. Is the dome height correct? Is the eyebrow configuration correct?

Thanks

It looks exactly like the Federal Mogul replacement piston, which for all intents and purposes is identical to the original GM forging. If it has a 4.00" diameter, then it's a standard bore piston from a 302/327/350. Dome height is .125".

One sure fire way to determine which of those engines it came from, is to measure the compression height. Assuming that the engine was originally built with 5.7" rods (which all three of those were), the compression height for a motor of 3.25" stroke and 9.025 (nominal) deck height will be 1.675". This is the dimension measured from the centerline of the wrist pin boss, to the machined annulus around the outside edge of your piston.

[Michael H.]

Re: 1965 350HP Piston Configuration?

It looks exactly like the Federal Mogul replacement piston, which for all intents and purposes is identical to the original GM forging. If it has a 4.00" diameter, then it's a standard bore piston from a 302/327/350. Dome height is .125".

Joe,

It couldn't have been a GM piston for a 302. The dome configuration for 302 was much different. I believe the LT1 dome is also the same as 302, but shorter.
If I remember correctly, only 283 and 327 pistons used the dome configuration pictured in a post above.
Z28/LT1 used the configuration below.

[Duke W.]

Re: 1965 350HP Piston Configuration?

Joe,

It couldn't have been a GM piston for a 302. The dome configuration for 302 was much different. I believe the LT1 dome is also the same as 302, but shorter.
If I remember correctly, only 283 and 327 pistons used the dome configuration pictured in a post above.
Z28/LT1 used the configuration below.

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". 327 piston oil return configuration is also different - a slot behind the oil ring rather than holes for the LT-1 piston and (I think) the 302 piston.

Push the pin out so you can measure the distance from the bottom of the pin to the crown (the machined ring around the outer circumference of the piston), then subtract half the pin diameter.

Duke

[John H.]

Re: 1965 350HP Piston Configuration?

The 302 piston also had grooves in the pin bore for Spirolox retainers - the pins full-floated in the rods.

[Duke W.]

Re: 1965 350HP Piston Configuration?

That piston looks like it's seen some detonation.

Duke

[Michael H.]

Re: 1965 350HP Piston Configuration?

The 302 piston also had grooves in the pin bore for Spirolox retainers - the pins full-floated in the rods.

I don't remember if the 67 and 68 Z28 pistons had the groove? Wasn't there a new part number for 69 with full floating pins??

[John H.]

Re: 1965 350HP Piston Configuration?

That piston looks like it's seen some detonation.

Duke

Yes, it has - that's why it's now a paperweight; it came out of a '69 Z/28 that had a rough life.

[John H.]

Re: 1965 350HP Piston Configuration?

I don't remember if the 67 and 68 Z28 pistons had the groove? Wasn't there a new part number for 69 with full floating pins??

Yup - '67-'68 Z/28's had pressed pins, 69's had floaters.

[Michael H.]

Re: 1965 350HP Piston Configuration?

Yup - '67-'68 Z/28's had pressed pins, 69's had floaters.

I vaguely remember a new 68 Z28 short block I had that had grooves for the wrist pin locks even though the pins were pressed. I suppose the groove was added some time during the 68 run in preparation for the soon to be released full floating pin design for 69.