Splitting hairs on cam advance?

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BradH
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Splitting hairs on cam advance?

Post by BradH » Wed Oct 11, 2017 9:40 am

Old combination was 10.8 CR and 108 LSA cam installed + 4.

New combination has 11.5 CR, better flowing heads, and new 108 LSA cam with same effective seat duration, .020 & .050 specs, but more lift to suit flow of new heads better.

Degreed new cam in at 106 ICL, 2 degrees less advanced than old combination. Rule of thumb is typically to go with 4 degrees advance, but I'm looking at the CR increase as offsetting any torque loss from less 2 degrees less advance and helping the engine at higher RPM.

Does this make sense to anyone else? And am I getting a bit OCD about 2 freaking degrees on the ICL?

Back to work...

mag2555
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Re: Splitting hairs on cam advance?

Post by mag2555 » Wed Oct 11, 2017 9:44 am

It's been said many times , by many top tuners that in dyno or better yet track testing you need to make these Cam advance or retard changes in no more then 2 degree steps when you get get down to the fine tooth comb phase!

DaveMcLain
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Re: Splitting hairs on cam advance?

Post by DaveMcLain » Wed Oct 11, 2017 9:59 am

Check the centerline on a few cylinders around the engine and see how it looks see if most of them are at 106, ahead of 106 or behind 106.

I don't see 4 degrees advanced as any sort of magic number and it might be better at 106. You won't know until you try.

PRH
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Re: Splitting hairs on cam advance?

Post by PRH » Wed Oct 11, 2017 10:55 am

Here's my take on it, in a typical bracket type build......

As long as the camshaft has enough duration to keep up with the heads, cubes, induction, exhaust....... Then it's the combination of those components that will determine where the peaks occur.
Sure, you can broaden the curve some by playing with the cam, but the intake manifold, heads, headers are going to "tune" to a certain rpm depending on the size of the motor they're bolted to.
I can't think of any time I've moved the cam and "traded" power at one end of the power curve, and moved it to the other end.

My experience has been that there will be a sweet spot where the cam just works best.

Most of the time I've seen someone retard a cam on the dyno(from a normal installed position to another normal installed position), it usually plays out where you lost on the bottom end, and it never caught back up again.

This is the situation I see many times when changing cams or moving cams....... Start low(power wise), end low.

I'm referring to the normal "bread and butter" type builds.

Obviously, YMMV
Somewhat handy with a die grinder.

BradH
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Re: Splitting hairs on cam advance?

Post by BradH » Thu Oct 12, 2017 9:18 am

PRH wrote:
Wed Oct 11, 2017 10:55 am
Here's my take on it, in a typical bracket type build.....
...
I'm referring to the normal "bread and butter" type builds.
From what you know about this build, does it fall within these guidelines? :lol:

PRH
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Re: Splitting hairs on cam advance?

Post by PRH » Thu Oct 12, 2017 10:43 am

IMO, it does indeed.

The types of builds where I can see the trend I was referring to not playing out the way I described would be like a Super Stock or Comp type build, where they seem to have power curves that, in my mind at least, seem to "defy the odds".
Somewhat handy with a die grinder.

kimosabi
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Re: Splitting hairs on cam advance?

Post by kimosabi » Fri Oct 13, 2017 4:31 am

Depending on what fuel you're gonna run ofcourse, if you're thinking about running the same fuel as before you might as well retard the cam 2 degrees.

F-BIRD'88
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Re: Splitting hairs on cam advance?

Post by F-BIRD'88 » Fri Oct 13, 2017 5:07 am

Are you tuning or de-tuning it?

digger
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Re: Splitting hairs on cam advance?

Post by digger » Fri Oct 13, 2017 5:24 am

Just ask the engine what it wants

Geoff2
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Re: Splitting hairs on cam advance?

Post by Geoff2 » Fri Oct 13, 2017 5:44 am

Only way to find the optimum cam adv/ret is to experiment. I think it was Crane cams that advised making a minimum 4* change, & then fine tuning from there. Also what needs to be borne in mind is: what is more important, low speed tq or higher rpm hp because adv/ret cams typically shifts the power curve slightly.

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Re: Splitting hairs on cam advance?

Post by kimosabi » Fri Oct 13, 2017 5:47 am

What also comes into play is the CID. A bigger engine might not care too much. Depending on cam ofcourse.

BradH
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Re: Splitting hairs on cam advance?

Post by BradH » Fri Oct 13, 2017 6:59 am

452 c.i.
4500 stall (flash)
6500(+?) shift RPM
7200 max RPM
266 at .050"
93 E10 + a blend of race fuel to push the octane up 3-4 points
3800 #s with driver street/strip pig

Decided to reset it to +4 (104 ICL) last night as the baseline for upcoming dyno session... will see how it works.

GARY C
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Re: Splitting hairs on cam advance?

Post by GARY C » Sat Oct 14, 2017 1:22 am

BradH wrote:
Fri Oct 13, 2017 6:59 am
452 c.i.
4500 stall (flash)
6500(+?) shift RPM
7200 max RPM
266 at .050"
93 E10 + a blend of race fuel to push the octane up 3-4 points
3800 #s with driver street/strip pig

Decided to reset it to +4 (104 ICL) last night as the baseline for upcoming dyno session... will see how it works.
Testing it on the dyno will be the best way to know, each engine is different but you will probably see little to no power gain just a movement in where it happens.

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