retarding the cam
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From: Escondido, CA
retarding the cam
I have been fooling around with desktop dyno waiting for my new isky cam to come in. Well I found that retarding the cam -4.0 degrees ups the rpm range for the HP and increases it 11 @ 6000 and 17 @ 6500. However overall TQ decreases just a tad but the power producing range rpm increases as well. So I can have over 500 HP and TQ for a longer rpm band by retarding the cam 4 degrees. Now my question, what else will I lose that I am not thinking about? Increased power is great but I don't want to look at it one sided.
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From: Escondido, CA
I am using the generic canted/oval pocket ported large valve profile. I haven't seen a set of flow #'s for the D3VE with 2.19 intake and 1.76 exhaust valves with port work done to them. Not to mention that every set of heads is different with flow profiles. The isky cam is a 280 mega with .565 lift on both intake and exhaust with a LCA of 108. I have looked for specific intake and exhaust opening point on isky's website but they don't have that info posted. So I am using the high performance profile with seat to seat measurements.
All of this is generic and totally based off a computer program. I know there are a lot of other variables to take into consideration with actual power results. Hence why I wasn't claiming I have a huge power motor just noting some of the differences and what other things need to be accounted for with the valve opening and closing times changing. Will the carb vacuum signal be more pronouced or reduced? Things like that.
All of this is generic and totally based off a computer program. I know there are a lot of other variables to take into consideration with actual power results. Hence why I wasn't claiming I have a huge power motor just noting some of the differences and what other things need to be accounted for with the valve opening and closing times changing. Will the carb vacuum signal be more pronouced or reduced? Things like that.
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I am using the generic canted/oval pocket ported large valve profile. I haven't seen a set of flow #'s for the D3VE with 2.19 intake and 1.76 exhaust valves with port work done to them. Not to mention that every set of heads is different with flow profiles.
By the way, here's a link to the cam card for the 280 Mega. I don't know why Isky made it so dang hard to find.
http://www.iskycams.com/timingchart....g_chart_id=644
Is your engine shop hogging out the exhaust ports? The 280M is a single-pattern design. Your D3's would benefit greatly from a dual pattern design with a little more exhaust duration unless they have been really massaged on the exhaust side.
Also, I know why your DD sims are screwy. DD wants to see more exhaust flow on the heads to support the cam. When you put in the 4deg retard did you notice the off-idle and midrange power curves got strange - kinda notchy and rough? My advice is don't try to max out the HP number at the expense of the rest of the powerband. Yes, you may end up with over 500 hp but you've lost some of the beautiful response and driveability your combo is capable of. Dial in 5 deg of advance and watch what happens. You lose a little upper-end HP, but the midranges bulk up nicely.
Just my .02, but I'd consider a different cam. The Mega 280 will make okay power, just understand that there are better options given your choice of heads. Single-pattern cams are old tech when it comes to 385-series engines. They are not the best for making streetable power. I think you could do better with a dual-pattern grind.
Brad
Last edited by Brad Johnson; Oct 16, 2006 at 03:48 PM.
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From: Escondido, CA
I was running a dual pattern Comp 4x4 Extreme cam until it ate itself. The specs on it were .554 with a 270 duration intake and .574 with a 278 duration exhaust. I do admit the TQ was better but the curves are almost identical with the isky. When I first built the engine I worked the exhaust ports over pretty good and had the head guy check them out. I liked the power of the old cam but I wanted to experiment a little and see what an isky can do.
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From: Escondido, CA
Ok you convinced me to stay with the dual pattern cam after farting around with DD. I ordered a Comp 34-247-4 to replace the Isky 280 mega. I am very glad summit doesn't raise a stink changing orders. So I will see the cam by Friday I believe vise the end of the months since the Isky's are back ordered.
