Re: camshaft lobe sep
[Re: mopar dave]
#2702503
10/01/19 08:25 AM
10/01/19 08:25 AM
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Joined: Jan 2003
Posts: 13,496 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,496
Marion, South Carolina [><]
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My take on it...a mild street motor that you're more concerned w/ street manners than speed...use a wide LSA. Big cubes, big heads, and/or high rpm narrow powerband...use a wide LSA. Smaller engines that turn a lot of RPM use wide LSA too. This is NA of course. Power adders change things. I'm no expert, but I've tried a few things over the years. Best thing I've done was talk to Dwayne Porter and learn from him.
A moderately headed 511" engine like the OP has is not one I'd consider a wide LSA for. Put some B1/MC heads on it, a tunnel ram, and a BIG cam to spin some RPM and it'd likely want something wider. My 572 w/ heads flowing 430 cfm hemi heads only has a 112 LSA in it. My 446" w/ 340 cfm Indys uses a 108 LSA.
After trying that wide LSA cam in my 440 years ago and being disappointed w/ it, I talked to several other cam manufacturers for a recommendation. EVERY SINGLE ONE OF THEM recommended a 108 LSA cam for that combo.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 4 speed, Dana 60 '71 Demon 340, no drivetrain, on blocks behind the barn '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: camshaft lobe sep
[Re: an8sec70cuda]
#2702532
10/01/19 09:36 AM
10/01/19 09:36 AM
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Joined: Jan 2003
Posts: 14,539 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,539
So. Burlington, Vt.
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I’d love to see a dyno test, for any make of motor, that saw any kind of real power gain, where the only change was the exhaust rocker ratio....... in a combo where the exhaust port wasn’t just horrible(relative to the intake port), or way too good for the application......... and the cam wasn’t just flat out wrong for the combo.
In other words....... nothing appears out of place or way off for the combo...... you do nothing but swap the ex rocker ratio...... and see a worthwhile improvement.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: camshaft lobe sep
[Re: fast68plymouth]
#2702538
10/01/19 10:04 AM
10/01/19 10:04 AM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
master
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master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
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So, this may seem like apples and oranges here, but my experience with dynoing dohc engines, where changing lsa is easily done on back to back pulls, shows that THE most important cam timing event is intake centerline. It doesn’t matter whether it is NA or boosted/ nitrous. LSA on these engines seem to have minor effects when in normal ranges when NA. Much more pronounced on nitrous, a bit less so on boosted(turbo) never tried a supercharged example.
"use it 'till it breaks, replace as needed"
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Re: camshaft lobe sep
[Re: 340Cuda]
#2702604
10/01/19 12:46 PM
10/01/19 12:46 PM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
master
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master
Joined: Sep 2014
Posts: 4,457
Washington
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I have a 348" small block built for NHRA SS/BS. It has 15:1 compression and is restricted to a 750 CFM carb. I have been messing with this engine for a long time.
A well respected cam guy at Comp recommended a more modern cam for it, it was ground at 115 LSA and was to be installed at 113.
On the dyno the engine made a little more power than the old cam, both were over 700 peak HP. However the guys at the shop that dynoed it thought the lobe center was wide for that engine.
The guy I had been working with at Comp left and I was assigned another. The new guy kinda wondered about it also and reground my old cam at no charge. The regrind had a LSA of 110 and was installed at 109.
On the dyno with the reground cam the engine made about the same peak HP but made more power and torque at all RPM levels below peak.
Your mileage my vary... This is exactly what I've found over the years. It's funny how the words always mouthed are "I don't care about peak HP I want bottom end" and "peak HP means nothing...its area under the curve that matters". And yet, if the customer thinks the LSA is too "narrow" he will squeal his brains out and the cam gets changed out for a wider LSA, which means the timing had to change to do that. Doesn't matter that the area under the curve took a beating. Doesn't matter that the car would be quicker in the gear change because the CORRECT LSA made the middle of the HP curve fatter. Doesn't matter. The customer is only right all the time when it comes to underwear and bras. J. C. Penney made a statement and the morons have run with it.
Last edited by madscientist; 10/01/19 12:47 PM.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: camshaft lobe sep
[Re: Cab_Burge]
#2702732
10/01/19 07:51 PM
10/01/19 07:51 PM
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Joined: Jan 2003
Posts: 10,088 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
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Posts: 10,088
Frostbitefalls MN (Rocky&Bullw...
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Comparing different LSAs between split duration and single duration cams doesn't Work well. The extra duration on the exhaust side increases overlap, effectively making it a narrower LSA cam for three out of four events.
8.582, 160.18 mph best, 2905 lbs 549, indy 572-13, alky
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Re: camshaft lobe sep
[Re: 340Cuda]
#2702734
10/01/19 07:59 PM
10/01/19 07:59 PM
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Joined: Feb 2005
Posts: 4,333 Prospect, PA
BSB67
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master
Joined: Feb 2005
Posts: 4,333
Prospect, PA
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On the dyno with the reground cam the engine made about the same peak HP but made more power and torque at all RPM levels below peak.
Your mileage my vary...
How did the HP look after peak? Curve after matters as well. I think as a general rule, if you compare hp only up to peak hp, the narrower lsa, and move advanced ICL will be the winner. But I don't think best ets come from shifting at peak, at least for me.
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Re: camshaft lobe sep
[Re: fast68plymouth]
#2702768
10/01/19 09:15 PM
10/01/19 09:15 PM
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Joined: Jan 2003
Posts: 4,395 The Pale Blue Dot
Skeptic
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master
Joined: Jan 2003
Posts: 4,395
The Pale Blue Dot
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I’d love to see a dyno test, for any make of motor, that saw any kind of real power gain, where the only change was the exhaust rocker ratio....... in a combo where the exhaust port wasn’t just horrible(relative to the intake port), or way too good for the application......... and the cam wasn’t just flat out wrong for the combo.
In other words....... nothing appears out of place or way off for the combo...... you do nothing but swap the ex rocker ratio...... and see a worthwhile improvement. I thought Hod Rod did something like that. I don't recall the results. Off to the Googles!
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Re: camshaft lobe sep
[Re: mopar dave]
#2702901
10/02/19 09:12 AM
10/02/19 09:12 AM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Here's the gist of Vizard's article, since I don't see it online and am not sure I still have the magazine after The Great Car Magazine Purge of 2014 (or somewhere around then): 1. Intake more sensitive to lift, given sufficient duration, and generally "more lift is better" 2. Exhaust more sensitive to duration, and it's possible to have too much lift and/or rate of lift that causes losses in power 3. If you start with an "optimized" set of valve timing events and lifts, then start increasing rocker ratios (or go to significantly more aggressive lobes, I suppose), then your effective overlap triangle increases and it can require spreading the LSA to compensate 4. Too little overlap is worse than too much from a power perspective (doesn't take into account issues w/ excessive overlap w/ closed exhaust systems, though) 5. If you have to spread the LSA to get the desired driveability, what you probably need is a shorter duration cam on a tighter LSA to achieve the same overlap triangle and restore the lost torque from delaying the intake closing event
Please note that I'm not saying this is "The Truth", only that it's what DV discussed in that particular article. He also tends to be so focused on SBC and BBC that IMO he states things that don't necessarily apply verbatim to other brands/architectures of engines.
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