Re: camshaft lobe sep
[Re: fast68plymouth]
#2702948
10/02/19 10:21 AM
10/02/19 10:21 AM
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Joined: Oct 2007
Posts: 4,205 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,205
New York
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Exhaust far more sensitive to opening point than to lift. Once the valve cracks open, there is easily 70 psi escaping. Compare this to perhaps 1 psi at the intake seat...
Comparing LSA between cams is meaningless unless that's the only change.
Boffin Emeritus
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Re: camshaft lobe sep
[Re: Skeptic]
#2702950
10/02/19 10:23 AM
10/02/19 10:23 AM
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Joined: Jan 2003
Posts: 4,394 The Pale Blue Dot
Skeptic
master
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master
Joined: Jan 2003
Posts: 4,394
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! Here it is No surprises here SBC with a small HR cam.
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Re: camshaft lobe sep
[Re: als499]
#2702958
10/02/19 10:35 AM
10/02/19 10:35 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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I was under the impression that bigger motors like a wider lobe seperation . So a 600" motor may respond better to a 114-116, a 500" may run better with a 110-112, a 400" motor may like a 106-108' , etc.... Like about 90% of the questions asked here, the only valid answer without knowing more of the details is: "It depends..."
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Re: camshaft lobe sep
[Re: BradH]
#2702973
10/02/19 11:06 AM
10/02/19 11:06 AM
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Joined: Jan 2003
Posts: 19,304 Las Vegas
Al_Alguire
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 19,304
Las Vegas
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I have played rocker ratio roulette before myself. On my current predator deal in fact. I have even played with lash as well. Usually if you find something with ratio or lash for a given cam all you are learning is that you likely didn't get the correct cam the first time.
FWIW my current predator had a few cams and different ratios in it. The current one picked up 25 peak HP and 22 average from opening up the intake lash .010 and closing the exhaust .015, so what's that tell you? It made the best average and peak and is still in the engine but when we freshen it will likely have a new cam in it once again. And let me tell you those 60MM stocks dont come cheaply but I am trying to dqueeze all I can from this limited bore engine, while still maintain some semblance of reliability, so far so good on both fronts.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: camshaft lobe sep
[Re: Skeptic]
#2702974
10/02/19 11:07 AM
10/02/19 11:07 AM
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Joined: Jan 2003
Posts: 14,479 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,479
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. I thought Hod Rod did something like that. I don't recall the results. Off to the Googles! Here it is No surprises here SBC with a small HR cam. Actually, that’s a camshaft LSA test in the link, not an exhaust rocker ratio test.
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: BSB67]
#2702990
10/02/19 11:35 AM
10/02/19 11:35 AM
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Joined: Apr 2003
Posts: 3,496 Tulsa, Oklahoma
340Cuda
master
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master
Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
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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. I would have to dig out the dyno sheets but my recollection is that the power was flat after peak. However we did not run it very far past peek. On the track both cams quit pulling at peak.
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Re: camshaft lobe sep
[Re: 340Cuda]
#2703049
10/02/19 01:49 PM
10/02/19 01:49 PM
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Joined: Jan 2003
Posts: 14,479 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,479
So. Burlington, Vt.
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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. I would have to dig out the dyno sheets but my recollection is that the power was flat after peak. However we did not run it very far past peek. On the track both cams quit pulling at peak. Sounds like you dyno and track tested both cams. 115lsa in at 113 vs 110lsa in at 109. Which went quicker, and just how much difference in ET between the two?
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]
#2703360
10/03/19 10:56 AM
10/03/19 10:56 AM
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Joined: Apr 2003
Posts: 3,496 Tulsa, Oklahoma
340Cuda
master
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master
Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
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Sounds like you dyno and track tested both cams. 115lsa in at 113 vs 110lsa in at 109.
Which went quicker, and just how much difference in ET between the two?
Unfortunately I don't have a definitive answer on track times. The new cam seemed to have more horsepower, enough to introduce some chassis problems. All the car wanted to do was turn right at the start. I found some things wrong with the chassis but that did not solve the problem. Turns out it was a bad slick. I got new tires and it went straight. However tighter LSA means less valve to piston clearance. I knew that and checked it. It was tight but not as tight as some folks said they got away with on this thing called the Internet. Turns out the exhaust valves were touching the entire time I ran this cam. At 6,450 RPM in low gear a head came off an exhaust valve and destroyed the block. I am in therapy, the head is being repaired and a replacement R3 block I had is in Maryland being machined. Maybe I can give you a better answer next spring.
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Re: camshaft lobe sep
[Re: 340Cuda]
#2703372
10/03/19 11:39 AM
10/03/19 11:39 AM
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Joined: Jan 2003
Posts: 14,479 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,479
So. Burlington, Vt.
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The new cam seemed to have more horsepower, enough to introduce some chassis problems. The “new cam” being the 110lsa?
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]
#2703740
10/04/19 10:03 AM
10/04/19 10:03 AM
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Joined: Apr 2003
Posts: 3,496 Tulsa, Oklahoma
340Cuda
master
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master
Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
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The new cam seemed to have more horsepower, enough to introduce some chassis problems. The “new cam” being the 110lsa? Yes sir...
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