Bigblock engine guys: Ring gap recommendations?
Thread Starter
Tech Contributor
Joined: Jun 2004
Posts: 20,953
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Bigblock engine guys: Ring gap recommendations?
Hey engine guys,
I'm currently building another (track toy) 427 for my '69. Right now I'm just measuring (and eventually setting up) the ring end-gaps. I've seen several different recommendations for end gap size (depending on what sourcebook I look at), so I'm just curious what gaps you guys have been having success with. This is a normally aspirated engine, and is going to be for street and road course usage.
thanks,
Mike
I'm currently building another (track toy) 427 for my '69. Right now I'm just measuring (and eventually setting up) the ring end-gaps. I've seen several different recommendations for end gap size (depending on what sourcebook I look at), so I'm just curious what gaps you guys have been having success with. This is a normally aspirated engine, and is going to be for street and road course usage.
thanks,
Mike
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
i was just machine file fitting rings in a Cosworth DFV motor last night. The rule is the hotter the motor the bigger the gap. But it is always a formula.
My 427 block uses total seal gapless top ring.
http://www.totalseal.com/TechPage.as...plessPistRings
My 427 block uses total seal gapless top ring.
http://www.totalseal.com/TechPage.as...plessPistRings
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
IME the rings should have come with the manufacturer's recommended specs, which I'd use by default, but if not I'd think you'd probably be good to go with bore x .0040 -.0045" for top, and bore x ~.0030" for 2nd. Moly, right?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Also recommend supplier specs
In recent years, most have changed their protocol to include a 2'nd gap LARGER than Top gap ... helps prevent top ring flutter & blowby
for ten years now, speed pro shows following for a 4" bore
Moderate performance
top = .016-.018 .004/bore inch
2'nd= .020-.022 .005/bore inch
drag/oval
top = .018-.020 .0045/bore inch
2nd = .022-.024 .0055/bore inch
*note ... the total seal specs in George's post above are for sets with "gapless" top ring ... the speed pro specs are for conventional rings ... Again, refer to specs from Your rings' maker.
In recent years, most have changed their protocol to include a 2'nd gap LARGER than Top gap ... helps prevent top ring flutter & blowby
for ten years now, speed pro shows following for a 4" bore
Moderate performance
top = .016-.018 .004/bore inch
2'nd= .020-.022 .005/bore inch
drag/oval
top = .018-.020 .0045/bore inch
2nd = .022-.024 .0055/bore inch
*note ... the total seal specs in George's post above are for sets with "gapless" top ring ... the speed pro specs are for conventional rings ... Again, refer to specs from Your rings' maker.
Last edited by jackson; Apr 21, 2010 at 10:03 PM.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
jackson, you're right about the larger 2nd gaps coming into favor by many, and I accept the thinking behind it. Don't know why I quoted an old formula for that. Please, excuse my brain fart... :o
