well now i'm still confused..I asked for a reverse pattern cam, and they send me the wrong grind..?? see what you make of this:
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| Author: | twister6 [ Fri Jul 08, 2011 5:03 pm ] |
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well the reason for that is you have the 280/270 and i have the 270/280 reverse pattern cam..Hmmm makes sense now.. |
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| Author: | ceej [ Fri Jul 08, 2011 5:32 pm ] |
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270/280 is not a reverse pattern. 280/270 is. CJ |
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| Author: | twister6 [ Fri Jul 08, 2011 9:36 pm ] |
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well now i'm still confused..I asked for a reverse pattern cam, and they send me the wrong grind..?? see what you make of this:
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| Author: | twister6 [ Sat Jul 09, 2011 2:11 pm ] |
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Ok . I hooked the vac gauge up and took it for a run. At 60 mph i'm sucking 13Hg's, when i floor it, it bogs to 1Hg and bounces up and levels off to about 3-4 and holds, and slowly climbs as i pick up speed. If I floor it at a stand still it goes to 3 and slowly climbs as I pick up speed without a bog from the stand still. At idle in park at 700rpm's its sucking 10Hg's, in gear at about 500rpm's we at 7Hg. This is with the 8.5 pv. |
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| Author: | wjajr [ Sat Jul 09, 2011 5:19 pm ] |
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Brian, Power valve selection won’t affect vacuum readings. Vacuum is determined by valve event timing. If there is no over lap of intake & exhaust opening & closing vacuum will be high throughout full rpm range. If there is considerable over lap of these events, in other words intake is still open when exhaust valve opens causing a bleed off, vacuum will be low at low rpm, and increase as rpm increases due to the way the flow of gasses entering and exiting the combustion chamber behave. I have a big old lumpy cam with a lot of over lap that makes 3 to 6 Hg of fluttering vacuum at 600 rpm, and 15 Hg at 3500 rpm. But, at 5500 rpm the engine develops 18 Hg of vacuum, and when the throttle is closed at high rpm, the vacuum jumps to the mid twenties. As a result of the crappy vacuum signal at low rpm the carburetor has a hard time metering fuel under 1000 rpm. Thus idle is what you get, as it is almost untunable due to the ever changing air fuel mixture at 600 rpm. Quote: . At idle in park at 700rpm's its sucking 10Hg's, in gear at about 500rpm's we at 7Hg. This is with the 8.5 pv.
With a vacuum reading of 7 at in gear idle, you need a 3.5 power valve. With the 8.5, the power valve is dumping extra fuel at idle causing a rich condition. This will lead to excessive fuel consumption. Recall every time the vacuum drops below the rating on the power valve it opens to enrich the air fuel mixture. Check the Holley tech tutorial on power valve selection from my previous post. How many turns are your idle mixture screws out from being seated? And, did you use a vacuum meter to tune the idle mixture and rpm? Do you get run on or back spin after shutting down the engine? For about ten bucks you should buy a copy of a book: Holley Carburetor Handbook 4150 & 4160 selection, tuning & repair by; Mike Urich. I found this book to be very helpful to understanding these carburetors. Bill |
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| Author: | ceej [ Sat Jul 09, 2011 6:54 pm ] |
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With those numbers, your cam is backward for a six. You want the exhaust event to be the short one. Give them a call and tell them the profiles are backward. Not sure what to make of the intake centerline. What's the LSA? Seems like you have to lead cam grinders around by the hand to get a six cylinder cam done right these days. Probably sounds pretty gnarley though!  2¢ CJ |
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| Author: | Doc [ Mon Jul 11, 2011 9:17 am ] |
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Quote: ...Seems like you have to lead cam grinders around by the hand to get a six cylinder cam done right these days...
This has always been the case... A SL6 cam is way different then the "90 degree firing"engine that makes-up most of the cam grinder's business.We are working with an engine that fires every 120 degrees, is intake airflow limited and way over-square... there are not many engines out there like that. Some cam grinders just can't bring themselves to do the "weird" SL6 cam design(s) I ask them to grind... they say "OK" and then just do the grind "their way"... like a V 8 would like it.    Your conventional Dual Pattern grind is a good example of that... that is the cam design most V 8s respond well to! (exhaust flow limited engines) DD |
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| Author: | twister6 [ Wed Jul 13, 2011 7:47 am ] |
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Hey Doc,, So what do I tell Erson I need..Is is going to be a mirror image of what I have on all aspects of the one they sent me. I must say the engine came alive with this cam, I can only image what it will do if I had the correct cam. If you have a cam card with this same cam let me know what yours has, so I can compare, post it if you have one. Thanks |
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