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Author Topic:   Cam Lobe Seperation Angles
Kent
Dirt Maniac

Total posts: 102
posted January 23, 2005 10:02 PM  
I have a 355 SBC and have an Isky cam - Question - I have a cam with a 106 Degree lobe seperation angle and I am using this cam in a FactoryStock car at 3300#, Quadrajet carb, Ramshorn exhaust, 42" of 2.250 dia exhaust pipe - Does the 106 help or hurt compared to a 108. The car pulls up to about 6100 or so rpm and then thats it. I have a cloe adjustable timing set and wonder if it would be prudent to change it to the 108 setting. The year before I ran a Comp Cam with a 110 sep angle. trying to learn about all of this stuff and any help is greatly appreciated! Thanks, Kent

leapinlizard
Dirt Freak

Total posts: 402
posted January 24, 2005 08:08 AM  
You can advance or retard the cam but you can't change seperation angles. These are ground into the cam are not adjustable without changing cams. Seperation angles are measured in degree's and dictate overlap.

rico 08
Dirt Forum Champ
Total posts: 1139
posted January 24, 2005 02:46 PM  
The 110 lobe center cam(actually seperation angle)will pull better on top than the 108,uaually the higher the number the higher up in the rpm range the power is.I've got the opposite problem...my 112 lc cam doesn't pull off the corners well,but it's strong past 6000.

stockcar5
Dirt Forum Champ
Total posts: 578
posted January 24, 2005 03:25 PM  
in general the larger the lobe seperation the wider the powerband. the narrower the opposite. this is why alot of "street" cams use 112 and most circle and drag cams use 106 (some as low as 102).

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Kent
Dirt Maniac

Total posts: 102
posted January 25, 2005 02:37 AM  
LeapingLizard - Your RIGHT! I had a brain fart! So I guess I need to know if I would be better off going back to a 108 or 110 degree seperation angel instead of a 106. I have never watched the tach during a race while going thru a corner - Don't think I want too either! But as heavy as the car is, do you think I might need a wider powerband? I have an Isky cam that is supposed to kick in from 2800 rpm up to 6900 rpm. Also, why would someone want to change the timing gear from it's center 2 degrees either side if you already have it timed with #1 cylinder at tdc? Just trying to learn! Thanks, Kent
43 years old and I feel like I am still in grade school!

Speedracer92
Dirt Full Roller

Total posts: 70
posted January 25, 2005 06:47 AM  
Kent, if you are talking about the different keyways on the timing chain gear, changing the timing of the cam by either advancing it or retarding it is almost like advancing or retarding your ignition timing. Most racing cams already have about 4 degrees of advance in them when they are made so you can install it straight up anyway. If you want to be sure though, you can degree the cam. I think most racers want to advance the cam timing a few degrees, same sort of effect as advancing your timing. As far as your lobe seperation, if you have a 106 now and you want it to pull at higher rpms, you might want to try a 108 or even 110. I run a 106 now in a 3800 pound car that works perfect but i never turn over 6000. That is just my take on all of that but there are probably others on here who know more about it than I do!

[This message has been edited by Speedracer92 (edited January 25, 2005).]

Raz_900
Dirt Forum Champ
Total posts: 635
posted January 25, 2005 09:21 PM  
A 106 LSA (Lobe Seperation Angle) will have peak torque early and fall off faster at higher rpms. A 110 will build slower, have a lower peak torque but hold onto it longer.

A heavy car with too much duration will like the tighter LSA since it will bring torque on at lower rpm (coming off the turn). A light car, with alot of gear and ability to spin significantly over 6000, will like the 110 since the gear will keep the rpm's up off the corner and it can use the 6000 and up powerband more.

A dry slick track will also like the 110 or higher LSA. It will help to smooth the power off the turns and bring it on down the straight where the tires can use it.

A longer rod motor will typically like a wider LSA and less duration than a otherwise identical short rod motor.

Advancing the cam timing 4 degrees will lower the powerband 200-300 RPM. As retarding it will raise the powerband. If your cam has 4 degrees advance ground into it, you could set your timing chain to the retard setting and have a net of 'straight up'. That will add a little on the top end and soften it at lower RPM.

Takes a long time to figure which cam will actually work.

P.S. That 2.25" exhaust won't let it spin over 6000 with a jet engine twisting it over.

[This message has been edited by Raz_900 (edited January 25, 2005).]

Kent
Dirt Maniac

Total posts: 102
posted January 25, 2005 10:30 PM  
Thanks Guys - I appreciate your help in trying to teach me about LSA's. It makes sense a little better now. As far as the exhaust - Track rules and with rams horn exhaust it probably wouldn't help going with a larger dia. exhaust than what I have right now or does anyone think differently about that? thanks, Kent

hughes
Dirt Maniac

Total posts: 194
posted January 26, 2005 09:48 PM  
The smaller lobe center provides a scavaging effect. What that does is increase the air flow velocity through the motor due to both valves being open while the piston starts the compression stroke/ exhaust stroke. Catch 22 is that the air flows through the motor faster but you sacrifice some compression due to both vales being open at the same time. If your running a cast iron intake, a smaller lobe center may be beneficial since they don't flow as good as a aluminium intake. Do you have a good flowing racing head or a stock cast iron head that does not flow as good. Do you have a set of dart heads with 230 cc intake runners trying to run it on a 350 versus a 406, you may need to pick up the flow velocity. Does the track have long straights to wind the motor out (large lobe sep.)or do you need to establish your position quickly on a short track (shorter lobe sep). Theres a thousand "IF's". Who knows, truthfully you'll probably never be able to tell the difference when racing. If my motor quit turning rpm's at 6100 I would start with changing the valve springs. That can cause simular problems as well

[This message has been edited by hughes (edited January 27, 2005).]

6pack
Dirt Maniac

Total posts: 171
posted January 29, 2005 06:07 PM  
Hydraulic or solid lifter?

Kent
Dirt Maniac

Total posts: 102
posted January 31, 2005 02:39 AM  
I have an Isky hydraulic cam with fast bleed lifters and am running a stock intake with stock 882 heads with the 194 valve. I have a different intake for it - cast oem thats supposed to be good for up to 300 hp! kent

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