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lobe separation
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mrhuntdwn
New User
| Posts: 44
| Joined: 06/08
Posted: 08/26/08 06:29 PM
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is a cam with a wider lobe separation perform well in a daily driven street/strip motor? i found a camshaft on comp's catalog 12-240-4 xm270 .480 .489 226/236 @.050 16-5800 lsa 112. i like the specs and i wanted to stick in a stock bore 350 with trw forged slugs. i plan on using nitrous as an power adder no more than 150 hp shot. get this their xtreme energy xe268 cam specs are merely identical. will it be better to with that stick. i heard that the wider the lobe separation the lesser the cylinder pressure but i listened to the xm278 12-244-4 on their cam sounds page i hear no loss in pressure there REALLY. it sounds mean and nasty. how vital is cylinder pressure to a performance engine? i need either cam to give power down low and throughout its power range. thanks any knowledge will greatly appreciated
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GibTG
Moderator
| Posts: 1904
| Joined: 10/03
Posted: 08/27/08 10:00 AM
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It's well known that nitrous favors wide lobe separation angles.
Cylinder pressure is really an ambiguous term when talking about lobe separation angle. "Cylinder pressure" will vary in certain rpm ranges in different ways with the variances in camshaft overlap, and it's also dependent on other factors such as compression and induction/exhausting port areas.
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mpayne
Administrator
| Posts: 595
| Joined: 10/07
Posted: 08/28/08 02:11 PM
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Also check out our tech articles we have a Comp Cams story you might be interested in.
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mrhuntdwn
New User
| Posts: 44
| Joined: 06/08
Posted: 08/28/08 05:02 PM
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so with the motor having a 9.5 cr will the cylinder pressure will be greater or lesser in certain rpm ranges? drivability wise whats the difference between a cam with a 110 lsa compared to a cam with a 112 lsa?
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mrhuntdwn
New User
| Posts: 44
| Joined: 06/08
Posted: 08/28/08 05:03 PM
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which one lol?
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GibTG
Moderator
| Posts: 1904
| Joined: 10/03
Posted: 08/28/08 08:27 PM
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I'm not going to address your first question...
A 2° spread in lobe separation angle means a reduction in overlap by 4°. This means an increase in manifold vacuum of about 1-2", slightly more extreme bottom end, and probably a more noticeable difference in power with the throttle not fully open.
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mrhuntdwn
New User
| Posts: 44
| Joined: 06/08
Posted: 09/03/08 03:49 PM
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so the wider the lobe angle the more power a engine has down low in the rpm range? now what happens at full throttle. lately i been reading up on build ups using wider lsa cams. but the thing is the build ups are on the track oriented side instead of being a performance street build.
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GibTG
Moderator
| Posts: 1904
| Joined: 10/03
Posted: 09/03/08 03:58 PM
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I would imagine less overlap (wide lobe separation) would favor power production with the throttle blades closed.
If the exhaust system is properly sized, not capped (restricted), and creating a significant vacuum in the chamber around top dead center a narrow lobe separation can show big power gains in terms of WOT runs (definitely a racing scenario).
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Posted: 09/04/08 07:13 AM
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Will you be spending more time with the car wide open? Drag racing etc, or driving on the street with the occasional trip to the track? If living on the street go with the wider lobe separation, if building more for the track go with the narrower lobe separation.
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