cam install overlap ?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
sjre
Member
Member
Posts: 80
Joined: Sun Nov 23, 2014 9:38 am

cam install overlap ?

Post by sjre » Sun May 20, 2018 7:15 pm

Degreeing cam in a bbc mild solid roller intake opens at 19 btdc . Cam is 244 at 50 107 lsa.Usually use the open at 50 then check lift at overlap.Checking this with lifters on #1 cyl. usually ends up with the intake lifter higher by about .030 .On this one the exh is higher by about .060 WTH?.Double checked-verified tdc and open at 050 but this doesnt make sense.Please any suggestions.
Thanks Joe.

User avatar
John Wallace
Guru
Guru
Posts: 1356
Joined: Tue Jan 04, 2005 10:20 am
Location: was Central Illinois - Now in Sunny Florida!
Contact:

Re: cam install overlap ?

Post by John Wallace » Sun May 20, 2018 8:10 pm

Degreeing cam in a bbc mild solid roller intake opens at 19 btdc
That's open at .050"?

What does the exh open at?

What are the specs on the cam card?

:?:
John Wallace
Pontiac Power RULES !
www.wallaceracing.com

amc fan
Pro
Pro
Posts: 436
Joined: Wed Jul 11, 2012 7:03 am
Location: BETHLEHEM PENNA.

Re: cam install overlap ?

Post by amc fan » Sun May 20, 2018 8:15 pm

Most cams... not all are ground split overlap at tdc on exhaust stroke in that case .060 higher on exhaust would be retarded.We have seen an Olds cam and a SBC cam over the years... with exhaust lobes ground 20 degrees late! I do not know if it is an easy mistake that happens when they are being ground but they do run hot and start to get black death on the pistons.The Olds was a hydraulic flat tappet street cam, the SBC was a solid roller in a oval track stock car.

sjre
Member
Member
Posts: 80
Joined: Sun Nov 23, 2014 9:38 am

Re: cam install overlap ?

Post by sjre » Sun May 20, 2018 8:27 pm

Yes sorry at .050, exh opens at 56 bbdc at .050.

Geoff2
Expert
Expert
Posts: 899
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: cam install overlap ?

Post by Geoff2 » Mon May 21, 2018 6:36 am

Maybe the cam is a dual pattern, with extra exh duration....

paulzig
Pro
Pro
Posts: 446
Joined: Sun Aug 03, 2008 6:29 am
Location: Australia

Re: cam install overlap ?

Post by paulzig » Mon May 21, 2018 5:24 pm

Geoff2 wrote:
Mon May 21, 2018 6:36 am
Maybe the cam is a dual pattern, with extra exh duration....
Looks like its a 244/250@50thou 107LSA 103ICL 111ECL...

If its 19° for the Intake then its 4 degrees advanced.

F-BIRD'88
Guru
Guru
Posts: 6146
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: cam install overlap ?

Post by F-BIRD'88 » Mon May 21, 2018 10:02 pm

Why not check the .050" open and close events onstead of making this a guessing game.?

Post Reply