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Duration gap? 

 

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 Post subject: Duration gap?
Posted: Sat Apr 15, 2006 6:44 pm 
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When looking at the gap between the In & Ex duration @ 0.050 lift, is it always about 6 degrees maximum? What happens if its 8 or more?

 

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Posted: Sat Apr 15, 2006 8:40 pm 
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You loose torque.

 

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Posted: Sat Apr 15, 2006 10:15 pm 
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what exactly do you mean by the gap??

 

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Posted: Sat Apr 15, 2006 10:18 pm 
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By gap, I mean if the duration @ 0.050 is 214 / 220 like on the Crane 2031, it's got 6 degrees separation. What would happen if that gap is greater?

 

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Posted: Sun Apr 16, 2006 2:16 pm 
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the different duration for intake vs: exhaust biases the cam one way or the other. heads that flow realy well on the intake side and not so good one the exhaust side, can benifit from a cam with more exhuast duration.

works the other way too if the intake doesn't flow so well you bias the cam towards the intake.

 

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Posted: Mon Apr 17, 2006 12:52 am 
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blow down also helps with economy as it reduces pumping losses, so larger exhaust durations arnt normally a bad thing

 

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Posted: Mon Apr 17, 2006 1:06 am 
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Jaysen wrote:
blow down also helps with economy as it reduces pumping losses, so larger exhaust durations arnt normally a bad thing


helps keep the exhaust valve cooler in high strung supercharged engines too.

 

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Posted: Mon Apr 17, 2006 1:11 am 
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I still would like to know what happens if the duration gap is longer than 6 degrees? What is the overall effect?

 

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Posted: Tue Apr 18, 2006 12:35 am 
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Vic wrote:
I still would like to know what happens if the duration gap is longer than 6 degrees? What is the overall effect?

Whatcha got ur eye on Vic a new grind

 

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Posted: Tue Apr 18, 2006 6:36 pm 
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I have been fiddling...

 

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Posted: Tue Apr 18, 2006 10:14 pm 
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hmmm, with my last hi po clevo I had a couple of custom grinds, heres the first grinds specs, which produced 544hp @ 6700rpm
but I can't show the specs of the better one, they asked me to keep it a secret, but I can say that it made 581hp @ 6800rpm both at the flywheel of a***! and had another 15 or more degrees with lifts much bigger!

 

 

Attachments:
cam specs.pdf [260.08 KiB]
Downloaded 71 times

 

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Posted: Tue Apr 18, 2006 11:19 pm 
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That's a mighty amount of duration Kenny. I'd be guessing that you have an aftermarket computer that deals with that? What is the lift at the valves because I can't quite convert the lift at the cam to lift at the valves.

 

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Posted: Tue Apr 18, 2006 11:32 pm 
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Vic wrote:
That's a mighty amount of duration Kenny. I'd be guessing that you have an aftermarket computer that deals with that? What is the lift at the valves because I can't quite convert the lift at the cam to lift at the valves.

no computer, it was in a 416'' clevo stroker, but the lift is calculated by cam lift x rocker ratio , .333x1.8 =.5994'' then take away the tappet clearance .020'' , which is basicaly .580'' int and around .600'' exhaust
the BETTER cam has .690'' int with and .735exh, and yeah that is BIG, acctually too big (for the street)
but the old cam now runs in the ol' fella's GT, and has decent drivability from 2000rpm and has 380 hp at the treads, but even better it gets better economy than the XR8?!

 

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Posted: Tue Apr 18, 2006 11:44 pm 
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Lol.

I have tried doing some custom grind calculations and the figures I get are impressive but I have been advised that there is more to a driveable cam than just figures on paper. The OTS cams have at least had testing done to them and my custom grind won't have this to back me up. A shame really but if I had more money to play with then it would be worth it to find out but right now, the rebuild is very budget with proven parts and will be a known quantity.

 

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Posted: Tue Apr 18, 2006 11:55 pm 
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testing, too true note the cam grind #355 this is the 355th cam they have ground for dyno testing ,just for the 4V headed, tunnel rammed big cube clevo, they do a few different engines but have more experience with clevo's, when I asked them to grind one for the XR8 ,I was advised to get a big name stick cos they haven't done enough research with EFI windsors
atleast they were honnest!

 

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