Cam timing and reversion solutions
Moderator: Team
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Cam timing and reversion solutions
On my 377 , its time to inspect and freshen. This engine may even grow to a 406.
So I pull off the Victor Ram and notice the worst reversion I've ever seen in my engines. I don't know exactly when or why it started but I've had this engine apart recently ( heads off ) and the ports were nothing like what I see today. Reversion , soot , oil all the way up the ports.
The only change was going to larger carbs ( 750s as opposed to 660s ). The carbs are calibrated by Patrick James , based on his experience with similar combos. Also of note...........those carbs are worth approx 2 MPH over my 660s. Remarkably the car still ran well enough ( 5.90s-6.00s ) at 3000lb.
If the engine was already experiencing SOME reversion , could larger carbs decrease port air speed enough to "aggravate " it.
The current cam is a 109 LCA installed on a 107 ICL.( Bullet ). Based on internet research the cam timing is the most likely culprit. I have another option of using my ( Cam Motion )112 LCA installed about 110.
My guess is the Cam Motion cam will reduce or eliminate the reversion...........
BTW 23 degree std port heads. 14-1.
So I pull off the Victor Ram and notice the worst reversion I've ever seen in my engines. I don't know exactly when or why it started but I've had this engine apart recently ( heads off ) and the ports were nothing like what I see today. Reversion , soot , oil all the way up the ports.
The only change was going to larger carbs ( 750s as opposed to 660s ). The carbs are calibrated by Patrick James , based on his experience with similar combos. Also of note...........those carbs are worth approx 2 MPH over my 660s. Remarkably the car still ran well enough ( 5.90s-6.00s ) at 3000lb.
If the engine was already experiencing SOME reversion , could larger carbs decrease port air speed enough to "aggravate " it.
The current cam is a 109 LCA installed on a 107 ICL.( Bullet ). Based on internet research the cam timing is the most likely culprit. I have another option of using my ( Cam Motion )112 LCA installed about 110.
My guess is the Cam Motion cam will reduce or eliminate the reversion...........
BTW 23 degree std port heads. 14-1.
modified wanna be
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Re: Cam timing and reversion solutions
I guess I'm the only one with reversion issues?
modified wanna be
-
- Pro
- Posts: 223
- Joined: Fri Nov 22, 2013 2:44 pm
- Location: Wright City, Missouri
Re: Cam timing and reversion solutions
Have you checked the timing chain for 'slack'? Possibly the retarded intake valve closing could allow an increase in the amount of intake reversion. Check that chain.
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Re: Cam timing and reversion solutions
Based on what I'm seeing / reading...............advance cam and spread lobe centers.CharlieB53 wrote: ↑Sat Nov 18, 2017 10:01 pm Have you checked the timing chain for 'slack'? Possibly the retarded intake valve closing could allow an increase in the amount of intake reversion. Check that chain.
modified wanna be
Re: Cam timing and reversion solutions
Reversion happens only at part throttle, and nothing can prevent it when using long duration cams. You probably have very rich part-throttle AFR which soot everything inside engine.
Re: Cam timing and reversion solutions
That's definitely not true, it's a necessary evil on a high performance engine, just need to keep it in check. The narrower the power band the easier it is
Re: Cam timing and reversion solutions
You're right, but reversion from late intake close won't make intake dirty. It's exhaust reversion which makes intake black and it is inevitable at part throttle and if part throttle afr is very rich intake will be very black.
-
- Guru
- Posts: 2858
- Joined: Thu Jan 06, 2011 8:57 am
- Location:
Re: Cam timing and reversion solutions
I would say that the real question is weather or not it hurts anything...
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Re: Cam timing and reversion solutions
I've wondered the same thing................but evidence from Kaase's video illustrates how counter productive reversion is and how blow back into the intake can be very severe. So any effort to reduce that has to be beneficial?DaveMcLain wrote: ↑Sun Nov 19, 2017 7:54 amI would say that the real question is weather or not it hurts anything...
Frankly I'm surprised this topic hasn't drawn more interest.
My guess is still cam timing has to be changed , at least on this engine , with these heads , with this induction . Others , apparently have different results.
modified wanna be
Re: Cam timing and reversion solutions
Have you tried shear plates?
Channel About My diy Projects & Reviews https://www.youtube.com/c/BOOTdiy
I know as much as I can learn and try to keep an open mind to anything!
If I didn't overthink stuff I wouldn't be on speedtalk!
I know as much as I can learn and try to keep an open mind to anything!
If I didn't overthink stuff I wouldn't be on speedtalk!
-
- Guru
- Posts: 1508
- Joined: Sun Apr 03, 2016 1:17 am
- Location:
Re: Cam timing and reversion solutions
How long are the primary tubes on the headers? My guess is they are 36 inches or longer. That's probably 6-8 inches too long.joespanova wrote: ↑Sun Nov 19, 2017 2:53 pmI've wondered the same thing................but evidence from Kaase's video illustrates how counter productive reversion is and how blow back into the intake can be very severe. So any effort to reduce that has to be beneficial?DaveMcLain wrote: ↑Sun Nov 19, 2017 7:54 amI would say that the real question is weather or not it hurts anything...
Frankly I'm surprised this topic hasn't drawn more interest.
My guess is still cam timing has to be changed , at least on this engine , with these heads , with this induction . Others , apparently have different results.
Re: Cam timing and reversion solutions
Not that I have any advice to offer, just trying to learn: what’s on the exhaust side as far as the headers etc. go?
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU
https://www.instagram.com/ptuomov/
Put Search Keywords Here
https://www.instagram.com/ptuomov/
Put Search Keywords Here
-
- Guru
- Posts: 2858
- Joined: Thu Jan 06, 2011 8:57 am
- Location:
Re: Cam timing and reversion solutions
If the engine had only seen wide open throttle running or mostly anyway I wonder if you would have seen any signs of reversion at all? I just wonder if it really is happening all that much when the manifold vacuum is close to zero.
The reason I'm wondering is that I never see much evidence of this on my two barrel circle track engines yet they have more than five inches of depression in the intake at wide open. That's still less than most engines even with a large cam would have with the throttle closed.
The reason I'm wondering is that I never see much evidence of this on my two barrel circle track engines yet they have more than five inches of depression in the intake at wide open. That's still less than most engines even with a large cam would have with the throttle closed.
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Re: Cam timing and reversion solutions
The headers ARE 1.875 Hookers.......as far as the primaries , they are indicated in the catalog as 30-38 inch primaries.............and since I am not using any of the extensions I have to guess , right now , they are close to 30 inches long.
modified wanna be
-
- Expert
- Posts: 876
- Joined: Sat Dec 01, 2007 5:15 pm
- Location: McDonough Ga.
Re: Cam timing and reversion solutions
I'm trying to visualize what you are saying here.................if the manifold vacuum is close to zero explain the connection?DaveMcLain wrote: ↑Sun Nov 19, 2017 3:16 pm If the engine had only seen wide open throttle running or mostly anyway I wonder if you would have seen any signs of reversion at all? I just wonder if it really is happening all that much when the manifold vacuum is close to zero.
The reason I'm wondering is that I never see much evidence of this on my two barrel circle track engines yet they have more than five inches of depression in the intake at wide open. That's still less than most engines even with a large cam would have with the throttle closed.
modified wanna be