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More cam questions
https://slantsix.org/forum/viewtopic.php?t=38439		 Page 1 of 2
Author:  HyperValiant [ Mon Dec 28, 2009 5:28 pm ]
Post subject:  More cam questions
I just receved my e470000 Erson cam and was wondering if anyone knows what the lobe separation angle is on this cam.
The intake centerline is listed as 108 but that is different from lSA isnt it?
Also , for those using this cam, what did you degree it too(108,106 etc)?

Any help you can give to help me understand these cam numbers is greatly appreciated.
Thank you.
HyperValiant
Author:  Joshie225 [ Mon Dec 28, 2009 6:53 pm ]
Post subject: 
If you post the valve timing events as listed on the cam card I can tell you the lobe centerline and the "straight-up" intake centerline or how far advanced the cam was ground.
Author:  HyperValiant [ Mon Dec 28, 2009 8:01 pm ]
Post subject: 
Thanks Josh,

intake opens:32 degrees exhaust closes:27 degrees
intake closes:68 degrees exhaust opens:63 degrees

59 degrees overlap

@.050 lift
intake opens:7 degrees exhaust closes:2 degrees
intake closes:43 degrees exhaust opens:38 degrees

Josh,would you please explain how you decipher these numbers to get lobe separation angle so I can add the formula to my ever growing Slant Six notebook.
Thanks
HyperValiant
Author:  Joshie225 [ Mon Dec 28, 2009 8:11 pm ]
Post subject: 
That's ground straight up on 108° lobe centers. I'd advance it 6-7° and run 102-101° intake centerline.

I plug the valve events into my Dyno Sim program and it spits out the LDA and intake centerline. You can plot out the valve events on a degree line and then count the degrees between events.
Author:  madmax/6 [ Mon Dec 28, 2009 9:03 pm ]
Post subject: 
I have that same cam in my car,I advanced mine 2 degrees.Whats the benifit of advanceing it more?Curious Mark
Author:  Terry Geer [ Mon Dec 28, 2009 9:09 pm ]
Post subject: 
Just for clarification- is this the RV15 reverse dual pattern that doc worked up with erson? (I did not go to the garage and pull the cam spec card.) I am curious what doc thinks about straight up or advanced. Advanced will help the bottom end, but may hurt at 4000 rpm. In a thread in may 09, doc stated the cam provided a good torque curve and revved to 5000. I assumed it was straight up, or that it was gound 4 degrees advanced.
Author:  Joshie225 [ Mon Dec 28, 2009 10:14 pm ]
Post subject: 
The cam in question is the Erson 280/270°, not the smaller 254/244 grind Doc designed.

The intake valve closing point affects how an engine runs more than any other valve timing event. By closing the intake valve earlier less mixture is pushed back out the closing intake valve by the rising piston. This increases the amount of mixture trapped in the cylinder and raises the dynamic compression ratio increasing torque. At higher engine speeds the greater inertia of the gas column keeps flowing into the cylinder even as the piston rises so a later intake valve closing can be used.

225s like narrow lobe separation and advanced cam timing. Retarding the cam (intake centerline is greater/later than the lobe displacement angle) almost always costs power as mixture is pushed back into the intake manifold on the compression stroke.

Dema Elgin writes: "The Intake Closed point – when the valve seals on the seat – is the most important valve-timing event. This event governs both the engine’s rpm range and its effective compression ratio. Closing the intake valve later optimizes intake flow for high rpm and allows inertia to pack in its last gasp of air. The drawback to that is back-flow at low rpm. But closing the valve earlier shuts down rpm. Pick your operating range. "

Read all about it here: http://www.elgincams.com/campaper.html
Author:  madmax/6 [ Mon Dec 28, 2009 10:53 pm ]
Post subject: 
Swell,,,,now I think I am a little re-tarded.Got me wondering if it would go quicker advanced a little.Guzzi Mark
Author:  MitchB [ Tue Dec 29, 2009 2:59 am ]
Post subject: 
Quote:
The intake valve closing point affects how an engine runs more than any other valve timing event. By closing the intake valve earlier less mixture is pushed back out the closing intake valve by the rising piston. This increases the amount of mixture trapped in the cylinder and raises the dynamic compression ratio increasing torque. At higher engine speeds the greater inertia of the gas column keeps flowing into the cylinder even as the piston rises so a later intake valve closing can be used.

225s like narrow lobe separation and advanced cam timing. Retarding the cam (intake centerline is greater/later than the lobe displacement angle) almost always costs power as mixture is pushed back into the intake manifold on the compression stroke
Well, everyone's got something to say about this. As rod ratio trends lower, the more you benefit by opening the intake earlier. The slant with it's long stroke and relatively low rod ratio is such an engine.

Mitch
Author:  Joshie225 [ Tue Dec 29, 2009 7:29 am ]
Post subject: 
Mitch,

I agree, but I wasn't going to bring that up or not yet at least. The rod ratio actually affects the relative piston position very little. For example, a 3.5" stroke engine going from a 6.2" to a 5.7" rod only moves the piston .023" farther down the bore at 90° ATDC. The affect on optimum valve timing is also small.

Some good reading on rod ratios: http://www.stahlheaders.com/Lit_Rod%20Length.htm

For those not good with geometry (myself included) there are calculators on line that will give you the piston's position relative to the crank position and acceleration graphs as well.
Author:  HyperValiant [ Tue Dec 29, 2009 7:42 pm ]
Post subject: 
Josh,
Thank you so much for this information.I have actually learned more about how engines operate on this board than anywhere else in my lifelong gearhead addiction.I have always known what a camshaft does but now I know what certain numbers mean and why they are important.

Thanks
HyperValiant
Author:  Joshie225 [ Tue Dec 29, 2009 8:37 pm ]
Post subject: 
People generally like to help and I'm glad to do it most days. :) In other words, you're welcome.

David Vizard also has a lot to say about valve timing and even how to choose optimum lobe centerlines. Of course you kinda need to know how much overlap you want before finding the optimum duration. Then we have intake to exhaust port flow ratio and on and on.

If you surf on over to my Photobucket album there are images of an excellent article by David Vizard on valve timing and camshafts. http://s20.photobucket.com/albums/b226/ ... e%20Stuff/
Author:  Dart270 [ Wed Dec 30, 2009 8:30 pm ]
Post subject: 
Hyper,

I assume you will run this in a 225? If so, then the starting point should probably be 102 deg centerline, but given Mark E's experience, maybe try 104. I designed this cam (picked lobes), and it seems several people have had good luck. Heck, I haven't even run mine yet.

Mark E, you have yours degreed at 106? You have a high stall conv and this centerline will push RPM range up, which is likely what you want. ALSO, with this "more intake duration" cam, we may want to try different centerlines than what works on an conventional even pattern cam (100-102). You may have stumbled onto a sweet spot. Mike and I spoke about cams over the weekend and were marvelling again at your car's power for what's in it.

Based on Vizard's stuff, I calculated 105 deg LSA was best, but 108 is not too different and will make it a bit more docile.

Lou
Author:  HyperValiant [ Wed Dec 30, 2009 9:44 pm ]
Post subject: 
Thanks for your input Lou,I was hoping that you would chime in.
Yes,this cam is for a 225that will eventually replace the 170 thats in the 60 Valiant.
Thanks
HyperValiant
Author:  Dart270 [ Thu Dec 31, 2009 6:43 am ]
Post subject: 
Thanks to Josh for the nice descriptions too.

Lou
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