Help me Figure out Compression Ratio please!

Reply Subscribe

Thread Tools

Search this Thread

Sep 29, 2016 | 05:39 PM

yoshgixxer

Thread Starter

On The Tree

iTrader: (74)

Joined: Mar 2010

Posts: 197

Likes: 0

From: York PA

Help me Figure out Compression Ratio please!

Trying to figure the CR on his 427 motor I was looking at

70cc chambers
OEM GM 6.2L gaskets
4.1" stroke
6.2" Rod
4.070 bore 5cc pistons

Thanks!!

Sep 29, 2016 | 06:02 PM

1FastBrick

TECH Senior Member

iTrader: (16)

Joined: Apr 2007

Posts: 9,723

Likes: 629

From: JunkYard

Quote:

Originally Posted by yoshgixxer

Trying to figure the CR on his 427 motor I was looking at

70cc chambers
OEM GM 6.2L gaskets
4.1" stroke
6.2" Rod
4.070 bore 5cc pistons

Thanks!!

Is this a dish piston?

Is the piston above or below the deck?

Sep 29, 2016 | 06:07 PM

yoshgixxer

Thread Starter

On The Tree

iTrader: (74)

Joined: Mar 2010

Posts: 197

Likes: 0

From: York PA

The build sheet dosnt say if the Pistons is above or below the deck so that's tricky to answere. Build sheet also says "weisco custom Pistons NO NOS 5cc " there's no "-" before the 5 so I'm assuming a domed Piston?

Sep 29, 2016 | 06:07 PM

thompson

Banned

iTrader: (4)

Joined: Jan 2010

Posts: 914

Likes: 17

Quote:

Originally Posted by yoshgixxer

Trying to figure the CR on his 427 motor I was looking at

70cc chambers
OEM GM 6.2L gaskets
4.1" stroke
6.2" Rod
4.070 bore 5cc pistons

Thanks!!

If you are using a Flat top w/ -5cc valve reliefs you are looking at about 11.1:1 CR ,

If you are using a +5cc you are looking at about 12.5:1 CR

I hope this has helped you out..

Thanks,
Dustin
Thompson Motorsports
972-853-2450

Sep 29, 2016 | 06:21 PM

yoshgixxer

Thread Starter

On The Tree

iTrader: (74)

Joined: Mar 2010

Posts: 197

Likes: 0

From: York PA

Yes that helps a lot. The motor made 558hp/513tq so it's most likely 11.1 I'd guess. Is like to be closer to 12.1 and get some more NA power out of it with a 150-200 shot ontop. I guess I could Mill the heads down to 60cc or so to get it up some. Cam in it is a 254/262 on a 112+3 so it seems like it would be a decent cam on spray though a can change isn't a big deal

Sep 30, 2016 | 03:43 AM

KCS

Moderator

iTrader: (20)

Joined: Mar 2005

Posts: 8,859

Likes: 323

From: Conroe, TX

Quote:

Originally Posted by yoshgixxer

You probably don't want to spray this engine. You did say the piston spec sheet said "NO NOS" right?

Sep 30, 2016 | 07:16 AM

yoshgixxer

Thread Starter

On The Tree

iTrader: (74)

Joined: Mar 2010

Posts: 197

Likes: 0

From: York PA

Yea that's what I'm trying to figure out what that means. I'll call weisco today. Other then ring gaps im unsure what NO NOS would mean on a forged piston? I was thinking maybe means no Gas port.
I'll have to call weisco today and see if hey got some insight on that lol