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Cam phasing vs. intake reversion

Posted By: BradH

Cam phasing vs. intake reversion - 10/09/10 05:10 PM

If you wanted to reduce the likelihood of intake reversion w/ a particular camshaft, would you want to advance it to close the exhaust sooner OR retard it to delay the point where the intake opens?
Posted By: maximum entropy

Re: Cam phasing vs. intake reversion - 10/09/10 05:14 PM

i would get the appropriate cam. if you advance the cam, you'll have pulse reversion, and if you retard it, you'd get pulse and exhaust. i think. or is it the other way around?
Posted By: Brian Hafliger

Re: Cam phasing vs. intake reversion - 10/09/10 06:34 PM

Quote:

If you wanted to reduce the likelihood of intake reversion w/ a particular camshaft, would you want to advance it to close the exhaust sooner OR retard it to delay the point where the intake opens?



reducing overlap is usually going to help so advancing or retarding will only show you "trends".
Closing the exhaust sooner is more likely to help reversion problems but without changing overlap it's not going to make much of a difference.
This is for WOT tuning only.
Posted By: mac56

Re: Cam phasing vs. intake reversion - 10/09/10 07:20 PM

Good to see a post from you Brian. I haven't noticed you posting much lately. I always like to hear your opinions.
Mark
Posted By: Twin Turbo Mower

Re: Cam phasing vs. intake reversion - 10/09/10 07:32 PM

you could try a anti reversion plate.
Posted By: Brian Hafliger

Re: Cam phasing vs. intake reversion - 10/09/10 07:39 PM

Quote:

Good to see a post from you Brian. I haven't noticed you posting much lately. I always like to hear your opinions.
Mark



Nice to be posting again...been soooo busy!!
Thank you!!!!!
Posted By: HEMIFRED

Re: Cam phasing vs. intake reversion - 10/09/10 08:13 PM

Quote:

If you wanted to reduce the likelihood of intake reversion w/ a particular camshaft, would you want to advance it to close the exhaust sooner OR retard it to delay the point where the intake opens?



where is the occurring and why assuming a likelihood ?
Posted By: BradH

Re: Cam phasing vs. intake reversion - 10/09/10 08:47 PM

Quote:

where is the occurring and why assuming a likelihood ?


When Dwayne P. freshened up the heads, he mentioned seeing more indications of reversion in the intake ports than expected. The cam's worked well on the dyno and the track, but might have a bit more overlap than "ideal" for a full exhaust system and street-driven car. No plans at this point to change the cam (again), so I was curious if the phasing might have any impact on it.
Posted By: Brian Hafliger

Re: Cam phasing vs. intake reversion - 10/09/10 08:57 PM

Quote:

Quote:

where is the occurring and why assuming a likelihood ?


When Dwayne P. freshened up the heads, he mentioned seeing more indications of reversion in the intake ports than expected. The cam's worked well on the dyno and the track, but might have a bit more overlap than "ideal" for a full exhaust system and street-driven car. No plans at this point to change the cam (again), so I was curious if the phasing might have any impact on it.



What are the engine/cam/exhaust specs?
Posted By: dannysbee

Re: Cam phasing vs. intake reversion - 10/09/10 09:34 PM

Did the reversion occur at cruising speeds or wide open throttle or both? Without knowing that, it would be hard to know if it was hurting your performance.
Posted By: BradH

Re: Cam phasing vs. intake reversion - 10/09/10 10:20 PM

Quote:

Did the reversion occur at cruising speeds or wide open throttle or both? Without knowing that, it would be hard to know if it was hurting your performance.


How would somebody be able to tell under what conditions it was happening?
Posted By: BradH

Re: Cam phasing vs. intake reversion - 10/09/10 10:24 PM

Quote:

What are the engine/cam/exhaust specs?


RB 452 w/ ported Stage VI heads, 10.8 CR, Comp XX 266 @ .050", .600", 1.5 rockers, 108 LSA (104 ICL measured at .050"), Victor 4150 intake w/ BG 4150 carb w/ 1.42" venturi x 1.75" throttle, 2" TTI headers & 3" x-pipe exhaust system.
Posted By: 602heavy

Re: Cam phasing vs. intake reversion - 10/09/10 11:24 PM

I think seat to seat duration has a direct effect regard reversion , closing intake valve too late can cause a positive pressure differential between cylinder & back of intake valve.....had reversion problems with a 440 , advanced ICL from 108* to 104* & reversion cleaned up , i believe the earlier closing int valve helped regards reversion..........same applied with the 605" , tightened intake lash .006" tighter from cam card & noticed soot around intake runners & underside of carb , loosened lash & reversion cleaned up.
Posted By: 602heavy

Re: Cam phasing vs. intake reversion - 10/09/10 11:26 PM

Quote:

posted twice

Posted By: dannysbee

Re: Cam phasing vs. intake reversion - 10/10/10 12:11 AM

Brad I was just making a point. But you could clean every thing up, take it out and cruise it a bit then pull the intake.
Posted By: HEMIFRED

Re: Cam phasing vs. intake reversion - 10/10/10 01:25 AM

Quote:

Quote:

Did the reversion occur at cruising speeds or wide open throttle or both? Without knowing that, it would be hard to know if it was hurting your performance.


How would somebody be able to tell under what conditions it was happening?



I understand that reversion occurs big time upon deceleration and it might show to be misleading but has no effect on much else
Posted By: moper

Re: Cam phasing vs. intake reversion - 10/10/10 01:39 AM

I think the reversion may be occuring at lower rpms and less than WOT. Kind of what I think Fred's talking about.
Posted By: HEMIFRED

Re: Cam phasing vs. intake reversion - 10/10/10 01:56 AM

Posted By: Brian Hafliger

Re: Cam phasing vs. intake reversion - 10/10/10 02:20 AM

Quote:

Quote:

What are the engine/cam/exhaust specs?


RB 452 w/ ported Stage VI heads, 10.8 CR, Comp XX 266 @ .050", .600", 1.5 rockers, 108 LSA (104 ICL measured at .050"), Victor 4150 intake w/ BG 4150 carb w/ 1.42" venturi x 1.75" throttle, 2" TTI headers & 3" x-pipe exhaust system.



If it was driven on the street even a short time you'll see exhaust in the intake tract.
Sometimes all the way up to the carb! No way to get rid of it carbed.
I will say that with full exhaust system, I will run as much as 12° split between intake and exhaust lobes.
Brian
Posted By: HEMIFRED

Re: Cam phasing vs. intake reversion - 10/10/10 02:25 AM

now here's a chart to follow use only the red path unless it's past 5pm and you are using 89 pmup.
otherwise the black and race gas

Attached picture 6241808-ctrp_1008_01+intake_reversion+.jpg
Posted By: BradH

Re: Cam phasing vs. intake reversion - 10/10/10 04:58 AM

Quote:

now here's a chart to follow use only the red path unless it's past 5pm and you are using 89 pmup.
otherwise the black and race gas


Looks like my daughter got hold of that one w/ a box of Crayons.

I should have mentioned that the reversion I'm talking about is the dilution of the intake charge during overlap when the burnt exhaust gets pushed back up the intake tract after the intake opens, not the effect of the intake valve being left open too long.

As Brian H. mentioned, being a street-driven car there may be no way to really eliminate the issue which (I'm assuming) is happening during low(er) RPM part-throttle operation. The deposits weren't showing up as far back as the intake manifold, but were concentrated above the valve and into the bowl entrance.

Perhaps I should pour a can of BG 44K in the 'Pig once in a while...
Posted By: Mike Swann

Re: Cam phasing vs. intake reversion - 10/10/10 09:51 AM

Quote:

now here's a chart to follow use only the red path unless it's past 5pm and you are using 89 pmup.
otherwise the black and race gas



Fred, It looks to you were using 100 proof when you made that graph, lol.
Posted By: 451Mopar

Re: Cam phasing vs. intake reversion - 10/10/10 09:59 AM

wider LSA to reduce overlap.
Posted By: HEMIFRED

Re: Cam phasing vs. intake reversion - 10/10/10 10:27 AM

Quote:

Quote:

now here's a chart to follow use only the red path unless it's past 5pm and you are using 89 pmup.
otherwise the black and race gas



Fred, It looks to you were using 100 proof when you made that graph, lol.



it looks much clearer when you include the use of the yellow lines suggested by the beer stops along the way
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