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Cam degreeing
https://slantsix.org/forum/viewtopic.php?t=33866		 Page 1 of 1
Author:  oklahoma joe [ Thu Feb 19, 2009 6:32 pm ]
Post subject:  Cam degreeing
Hi,

I have a cam that I had ground by a local cam grinder. After installing it I get the following opening and closing points at .020 and .050 at the push rod. Don't really know which numbers to use (.020 or .050) so I put them both down.
I have never done this before but would like you folks to look at it and see if I'm close or not and also give some input on what the cam is going to be like with these numbers (if they sound about right). I told him I was going to be using an auto tranny and wanted a street mannered cam with a little more lift. He said he new just what I needed. The engine is a 198 slant with mild porting, stock valve, and 8.7 static compression.

So here it goes.

Intake lift at valve = .391
Exhast lift at valve = .400

numbers a .020 lift

Intake opens at 10 degrees before TDC
Intake closes at 41 degrees after BDC
Intake Duration 231 degrees



Exhast opens at 124 degrees after TDC
Exhast closes at 20 degrees after TDC
Exhast Duration 256 degrees
overlap of 30 degree

Numbers at .050

Intake opens at 0 degrees TDC
Intake closes at 26 degrees After BDC
Intake Duration 206 degrees

Exhast opens at 138 degrees after TDC
Exhast closes at 10 degrees after TDC
Exhast duration 232

Overlap of 20 degrees


Thanks Joe
Author:  emsvitil [ Thu Feb 19, 2009 6:46 pm ]
Post subject: 
At 020

Lobe Seperation 106.8
Intake Centerline 105.5

At 050

Lobe Seperation 104.5
Intake Centerline 103.0


Also exhaust opening figures are usually given as Before Bottom Dead Center BBDC or 56 and 42 in your case


I also think the exhaust duration is too much...........
Author:  oklahoma joe [ Thu Feb 19, 2009 7:13 pm ]
Post subject: 
Quote:
At 020

Lobe Seperation 106.8
Intake Centerline 105.5

At 050

Lobe Seperation 104.5
Intake Centerline 103.0


Also exhaust opening figures are usually given as Before Bottom Dead Center BBDC or 56 and 42 in your case




I also think the exhaust duration is too much...........
ok you lost me should the center lines change at the diffrent lifts or is that my error in measurement and just in general the exhast is to long of a duration?
Author:  Dart270 [ Fri Feb 20, 2009 8:05 am ]
Post subject: 
Centerline and LSA must be an error in either or both of the two measurements.

Lou
Author:  Doc [ Fri Feb 20, 2009 9:58 am ]
Post subject: 
Another cam grinder that knows "exactly what to do..." for a V-8 :roll:

Degreeing events aside, it looks like you are on the right track with using a dual pattern cam but the SL6 likes more intake duration and less exhaust valve open time, basically a Reverse Dual Pattern grind. (RDP)

What are the recommended lash settings?

If I was set on using this cam, I would advance it 4 to 6 degrees to get the intake events to happen a little sooner and just put-up with the early exhaust "blow-down" by running the exhaust lash as loose as possible.
DD
Author:  emsvitil [ Fri Feb 20, 2009 3:42 pm ]
Post subject: 
Quote:
Centerline and LSA must be an error in either or both of the two measurements.

Lou
If the opening and closing ramps aren't symetrical, you can get different seperation and centerlines depending on the measured lifts...........
Author:  oklahoma joe [ Fri Feb 20, 2009 5:09 pm ]
Post subject: 
So assuming I measured correctly. Would it be better to go with a stock cam that I have laying around or this one with the overlap centered on TDC? I want low end and midrange power. What is the down side to exhaust blow bye, with the late closing exhast valve? I have the engine out right know and would like to change it now if need before it goes in the the car later this year.

Is there a relation to power and the amount of time the power stoke has before the exhast valve starts to open? I was reading brents cam card for eillen and noticed it has about the same overlap as mine but my cam closes the intake sooner and opens the exhaust a little later. It seems that my cam would build more dynamic compression and then have a longer power stroke which may make for a better low end cam in comparision. I believe brents cam is made for high end preformance so I may be comparing apples and oranges.

thanks joe
Author:  Dart270 [ Sun Feb 22, 2009 6:54 am ]
Post subject: 
Good point, Ed, but most are pretty symmetric of the ones I've measured.

Joe, this is a huge can of worms. What are your goals for the car in terms of performance, usage, parts available, fuel type (or comp ratio) and budget?

Thanks,

Lou
Author:  oklahoma joe [ Sun Feb 22, 2009 2:49 pm ]
Post subject: 
Quote:
Good point, Ed, but most are pretty symmetric of the ones I've measured.

Joe, this is a huge can of worms. What are your goals for the car in terms of performance, usage, parts available, fuel type (or comp ratio) and budget?

Thanks,

Lou
I want the car to be as peppy as possible for daily driving (under 4500 to 5000 rpm). It has a automatic transmission and will be running power brakes. So I need a some what steady idle and enough vacuum for the brakes. This all started when I bought a remanufactured cam and it was way under factory lift specifications. So I wanted to get at least factory specs to keep as much proformance as possible. I am on a budget so any of the high dollar cams are out of the question for me. the engine has been completly rebuilt and has a compreesion ratio or 8.5 to 8.9 static and is a 198 not the typical 225 variety. It has a supper six conversion with a v8 double barrel carter on it and a stock exhast manifold.

The cam grinder charged me $30 to grind it so no big loss if I have to take it out. Any input is appreciated. I guess I'm trying to buy caviar with at the price of frog eggs.

Joe
Author:  Dart270 [ Sun Feb 22, 2009 3:23 pm ]
Post subject: 
Well, your grinder has the right LSA for that motor (106). Just ask him for something with 218 deg on the intake @0.050" lift and 212 deg on the exhaust with about 0.440" lift on both. Can't beat $30 if he can do that for you. You might have to start with another stock cam for the regrind?

Lou
Author:  oklahoma joe [ Sun Feb 22, 2009 5:14 pm ]
Post subject: 
thanks I will try that I have a stock cam shaft laying around so I will take it in to him.

Thanks joe
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