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Old 12-14-2010, 09:58 AM   #1
GoldOlds
 
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Default advancing cam question

I've heard that advancing a cam 4 during installation can allow the engine to run on a lower octane of fuel (depending on the application, I suppose). Would doing this have any negative effect on performance?
TIA,

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1969 Cutlass Supreme: original 350 sbo (stock?), TH350 w/ shift kit, 2.25" dual exhaust w/ Flowmasters, 120gph Carter fuel pump, Edelbrock double-roller timing chain, 12 bolt Chebby rear w/ 3.73 gears, 255/60/15 rear tires, HEI @ 15 initial and 38 advanced w/ Moroso recurve kit (light/medium springs), Accel cap and rotor, Taylor 8mm wires

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Old 12-14-2010, 11:44 AM   #3
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Default Re: advancing cam question

Quote:
Originally Posted by captjim View Post
That sounds backwards to me.
To me as well.

I have never heard that advancing the cam allows using a lower octane fuel. What is your source for this information?
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Old 12-14-2010, 01:39 PM   #4
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Default Re: advancing cam question

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Originally Posted by captjim View Post
That sounds backwards to me. Generally speaking, advancing the cam INCREASES cylinder pressure. Of course, it depends on the cam and Cr. What are you working on?
Hmmm, chances are good that I DO have it backwards. The cam in question is a Voodoo 60801 that I'm leaning towards for my 350 (still got some measuring to do, but it should be around 9.2:1 or so - still also considering the 60802).
Thanks!

- GoldOlds
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2.0 litres is great . . . for a Coke bottle.

1969 Cutlass Supreme: original 350 sbo (stock?), TH350 w/ shift kit, 2.25" dual exhaust w/ Flowmasters, 120gph Carter fuel pump, Edelbrock double-roller timing chain, 12 bolt Chebby rear w/ 3.73 gears, 255/60/15 rear tires, HEI @ 15 initial and 38 advanced w/ Moroso recurve kit (light/medium springs), Accel cap and rotor, Taylor 8mm wires

PBs: ET - 15.259 sec., trap speed - 88.39 mph
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Old 12-14-2010, 03:52 PM   #5
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Default Re: advancing cam question

I'll get some conflict on this I'm sure but neither one of those cams are right for your application imo.
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Old 12-14-2010, 04:49 PM   #6
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Default Re: advancing cam question

60801: .485/.499 lift, 213/219 @ .050, 112 LSA

Sounds about right for use in a 9.2:1 compression ratio 350 to me.

60802: .499/.510 lift, 219/227 @ .050, 112 LSA

Maybe slightly big for 9.2:1 compression ratio without also having a higher stall converter, but as the car already has headers and 3.73 gears it may be OK.


Quote:
Originally Posted by Cutlassefi View Post
I'll get some conflict on this I'm sure but neither one of those cams are right for your application imo.
Why don't you think either one is right for the application? Just wondering.
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Last edited by 71CutlassConvertible : 12-14-2010 at 04:51 PM.
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Old 12-14-2010, 05:02 PM   #7
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Default Re: advancing cam question

Quote:
Originally Posted by 71CutlassConvertible View Post
60801: .485/.499 lift, 213/219 @ .050, 112 LSA

Sounds about right for use in a 9.2:1 compression ratio 350 to me.

60802: .499/.510 lift, 219/227 @ .050, 112 LSA

Maybe slightly big for 9.2:1 compression ratio without also having a higher stall converter, but as the car already has headers and 3.73 gears it may be OK.




Why don't you think either one is right for the application? Just wondering.
Simple, because although he has enough compression he's running stock heads, we all they know don't flow real well. All those fast ramp cams aren't designed for that. They'll tell you they are if you call and ask them but they're really designed for better flowing heads and/or something with less compression. I don't like the VooDoos especially because they don't address the fact that you'll make more torque if you couple a fast intake lobe with a slower exhaust lobe, it's a fact. I like Lunati and I like some of Comps stuff too but they aren't right for a stock headed 60's V8.
The generic stuff isn't any better, the same pattern exists, the exhaust lobe is the intake on the next size up and so on, i.e. 270/280-204/214, 280/290-214/224 etc. The don't address what's known to make torque, plus they're slow and normally on a wide lobe sep, a compromise.

Besides the Ersons I sell there are few others that I believe address the application in the right way, the others just don't have the off the seat time needed on older stock heads.

Jmo.
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Old 12-14-2010, 08:58 PM   #8
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Default Re: advancing cam question

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Originally Posted by Cutlassefi View Post
I don't like the VooDoos especially because they don't address the fact that you'll make more torque if you couple a fast intake lobe with a slower exhaust lobe, it's a fact.
So what you are saying is that with the fast opening rate of the exhaust lobe, the blow down (i think thats the term I am looking for) period takes place at too quick of a rate, thereby losing some exertion on the piston during the power stroke?
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Old 12-15-2010, 08:27 AM   #9
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Default Re: advancing cam question

I would have to agree with Mark. The 60801 cam advanced 4 degrees opens the exhaust valve 67 degrees BBDC which is to early. The problem I see is the wide lobe separation. If you had a tighter LSA it would open later.

Also as he said, the heads flow like doo doo, on the exhaust side especially.This is why the factory cams have up to 14 degrees more duration on the exhaust side.

The VooDoo cam will work but not as good as something else.
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Old 12-15-2010, 09:57 AM   #10
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Default Re: advancing cam question

Quote:
Originally Posted by 80Rocket View Post
So what you are saying is that with the fast opening rate of the exhaust lobe, the blow down (i think thats the term I am looking for) period takes place at too quick of a rate, thereby losing some exertion on the piston during the power stroke?
Yes holding the pressure in longer will enhance torque. Conversly you will get to a point where you'll need to get rid of it either more quickly or earlier depending on the application.
But for most street driven, moderate rpm vehicles a slower exhaust lobe will do the trick.
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Old 12-15-2010, 04:02 PM   #12
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Default Re: advancing cam question

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Originally Posted by Cutlassefi View Post
a slower exhaust lobe will do the trick.
Keep in mind that the fast ramp rate is on the opening side of the lobe and the closing side has a much slower ramp rate - I got this directly from Harold Brookshire when I was discussing cams for my engine with him several years ago. He told me it would be extremely difficult to measure the actual valve closing point when degreeing the cam due to the slow ramp rate.
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Old 12-15-2010, 04:47 PM   #13
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Default Re: advancing cam question

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Originally Posted by 71CutlassConvertible View Post
Keep in mind that the fast ramp rate is on the opening side of the lobe and the closing side has a much slower ramp rate - I got this directly from Harold Brookshire when I was discussing cams for my engine with him several years ago. He told me it would be extremely difficult to measure the actual valve closing point when degreeing the cam due to the slow ramp rate.
That's only true on an asymmetrical lobe. A symmetrical lobe will have the same rates on both open and closing. As far as measuring, yes it is difficult to some degree but remember that's why they have numbers for .006 or .050 of tappet lift for reference points.
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Old 12-16-2010, 05:00 AM   #14
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Default Re: advancing cam question

Culassefi:

So what is a good cam for his application?
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Old 12-16-2010, 06:19 AM   #16
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Default Re: advancing cam question

That's true Jim they are asymmetrical. As far as what's the best cam for this application? He could do a custom VooDoo, using the current intake lobe matched to a slower exhaust, that's my contention. Plus with a 3.73 gear the bigger exhaust lobe might extend his rpm range a bit.
But with decent compression, which he has, and crappy heads, especially on the exhaust side, which he has, I think he would benefit from an intake a bit slower as well. But at the very least do as I mentioned. Lunati's lobe library is pretty extensive. I've done a couple of custom Lunati's, I like some of their stuff, just not the way they do the VooDoo's for lousy heads.
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Old 12-16-2010, 06:59 AM   #17
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Default Re: advancing cam question

Cool! Thanks for the tips.
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Old 12-16-2010, 02:54 PM   #18
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Default Re: advancing cam question

Thanks for the replies, everyone... lots of interesting and important things to consider. I don't have headers on the car YET, but they (Hooker Comps) WILL be added before any cam swap is done. Not sure exactly what to do about heads yet; gotta get back into the world of the employed before taking on that one. In a perfect world, I'd be able to find a set of heads that have already been reworked (porting, adjustable valvetrain, maybe bigger valves), but that'll also have to wait until I find a new job.

- GoldOlds
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2.0 litres is great . . . for a Coke bottle.

1969 Cutlass Supreme: original 350 sbo (stock?), TH350 w/ shift kit, 2.25" dual exhaust w/ Flowmasters, 120gph Carter fuel pump, Edelbrock double-roller timing chain, 12 bolt Chebby rear w/ 3.73 gears, 255/60/15 rear tires, HEI @ 15 initial and 38 advanced w/ Moroso recurve kit (light/medium springs), Accel cap and rotor, Taylor 8mm wires

PBs: ET - 15.259 sec., trap speed - 88.39 mph
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Old 12-16-2010, 04:53 PM   #19
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Default Re: advancing cam question

What about the new Lunati High Efficiency series has 207 duration intake and exhaust lobe with .461 lift on both. Would that cam work better over the smallest Voodoo on a low compression stock head Olds v8?
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Old 12-16-2010, 07:30 PM   #20
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Default Re: advancing cam question

Quote:
Originally Posted by olds307 and 403 View Post
What about the new Lunati High Efficiency series has 207 duration intake and exhaust lobe with .461 lift on both. Would that cam work better over the smallest Voodoo on a low compression stock head Olds v8?
Not necessarily. With low compression that heightens the need for a fast intake lobe. I do something small but on a tight lobe sep like a 208/214 on a 108. Remember Olds exhaust flow is not good, you need help there unless you have headers vs. a restrictive intake.
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