DCR Investigation?
Thread Starter
Pro
Joined: Jun 2005
Posts: 725
Likes: 1
From: FL.
DCR Investigation?
Would anyone know whether or not, duration would increase, with an increase in Rocker Arm Ratio from 1.5 to 1.6?
The HR Cam with 1.5 rockers has advertised duration int.269 exh.276,
Duration @.050 int.218 exh.224. The lift is int.495 exh.503
I built the combo with 1.6 ratio Rockers So, the Lift increased to int.528
exh.536.
LSA=112*
SCR is 10.0 to one.
Im very interested in whether or Not I may have squeeked a Little helpful Duration increase with the rocker ratio increase, Especially with the Intake Valve, Because The DCR "may" be getting into the dangerzone for Detonation with My engine. It would make a difference if the @.050 Duration int.of was really up to 219* or even 220* from the Grinds advertised 218* Number Dropping the DCR into a sweeter area.
The engine is timed @ 36*. has Vacuum at 12" 800rpm's , Idles smooth , Never Runs over 180* temp , No matter what conditions and Pulls very hard 1500 to 5500 rpms.
I use 92oct. Fuel and Have Aluminum Heads.
Your thoughts?
Thanks in advance..
The HR Cam with 1.5 rockers has advertised duration int.269 exh.276,
Duration @.050 int.218 exh.224. The lift is int.495 exh.503
I built the combo with 1.6 ratio Rockers So, the Lift increased to int.528
exh.536.
LSA=112*
SCR is 10.0 to one.
Im very interested in whether or Not I may have squeeked a Little helpful Duration increase with the rocker ratio increase, Especially with the Intake Valve, Because The DCR "may" be getting into the dangerzone for Detonation with My engine. It would make a difference if the @.050 Duration int.of was really up to 219* or even 220* from the Grinds advertised 218* Number Dropping the DCR into a sweeter area.
The engine is timed @ 36*. has Vacuum at 12" 800rpm's , Idles smooth , Never Runs over 180* temp , No matter what conditions and Pulls very hard 1500 to 5500 rpms.
I use 92oct. Fuel and Have Aluminum Heads.
Your thoughts?
Thanks in advance..
Last edited by 69vettester; Oct 30, 2007 at 10:42 AM.
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
As i remember this correctly, it should give an increase of 4° of advertised duration.
Wether or not it will prevent detonation can not be estimated correctly. You need to know how many degrees abdc your intake valve is closing and you need to calculate the total swept volume above the piston at that point. Based on that you can calculate the DCR. The ideal would be around 8-8.5/1.
I used to have a spreadsheet that would allow to calculate this, but i don't seem to find it anymore.
Based on what i can see on your engine i don't think you will be in the danger zone.
Wether or not it will prevent detonation can not be estimated correctly. You need to know how many degrees abdc your intake valve is closing and you need to calculate the total swept volume above the piston at that point. Based on that you can calculate the DCR. The ideal would be around 8-8.5/1.
I used to have a spreadsheet that would allow to calculate this, but i don't seem to find it anymore.
Based on what i can see on your engine i don't think you will be in the danger zone.
Thread Starter
Pro
Joined: Jun 2005
Posts: 725
Likes: 1
From: FL.
As i remember this correctly, it should give an increase of 4° of advertised duration.
Wether or not it will prevent detonation can not be estimated correctly. You need to know how many degrees abdc your intake valve is closing and you need to calculate the total swept volume above the piston at that point. Based on that you can calculate the DCR. The ideal would be around 8-8.5/1.
I used to have a spreadsheet that would allow to calculate this, but i don't seem to find it anymore.
Based on what i can see on your engine i don't think you will be in the danger zone.
Wether or not it will prevent detonation can not be estimated correctly. You need to know how many degrees abdc your intake valve is closing and you need to calculate the total swept volume above the piston at that point. Based on that you can calculate the DCR. The ideal would be around 8-8.5/1.
I used to have a spreadsheet that would allow to calculate this, but i don't seem to find it anymore.
Based on what i can see on your engine i don't think you will be in the danger zone.
I just Got some spreadsheet numbers indicating DCR to be 8.2 to 1 for my engine..Not sure how dead on that measurement is but Im getting more comfortable hearing it. I was starting to Plan for a Quick Cam swap Over this. Now Im Lapsing back onto My old plan of next spring, Maybe Putting a New cam with a bit more Duration on the intake..and try for as little lift increase as I can find. I like the reassurance Im getting from the memnbers..Thanks
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
DCR is usualy figured on seat-to-seat intake valve closing point. The seat-to-seat valve duration is not changed when you swap rocker arm ratios. Zero is zero no matter how fast you lift the valve after the follower gets off the base circle.
The advertised duration @ .050" will be changed by a degree or two with high ratio rockers but that does not enter the equation for DCR.
-Mark.
The advertised duration @ .050" will be changed by a degree or two with high ratio rockers but that does not enter the equation for DCR.
-Mark.
Thread Starter
Pro
Joined: Jun 2005
Posts: 725
Likes: 1
From: FL.
OK, Thats clear. I knew the Duration was set in stone when ground into the cam Lobe, But wasnt sure if DCR would be affected by any Virtual (lack of better term) increase in Duration by the rocker ratio. your reply is what I was looking for..Thanks
Last edited by 69vettester; Oct 30, 2007 at 02:46 PM.
