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Old 02-18-2005, 06:55 AM
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Single Pattern VS Dual Pattern

Just have one small question. If you have a head with about a 75% intake to exhaust flow ratio, which cam type would produce better overall power and torque? Im wanting to run an XE dual pattern, which is a much newer and more aggressive design than the single pattern magnum cams, but, will i over scavenge with the more exhaust duration and lift? Im wanting to run the XE284 with 240/246 at .050 and 507/510 lift. if i go single, i would run the Magnum 292 but i would really like to use a newer more aggressive design. thanks for all your opinions.

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Old 02-18-2005, 07:23 AM
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Will He? I have heard some AFRs flow enough on the Exhaust side that problems arise, but that is internet hearsay
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Old 02-18-2005, 09:43 AM
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75% is OK flow ratio but you would still want a dual pattern cam. What head is it?
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Old 02-18-2005, 09:48 AM
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You want to run a single pattern or a dual pattern with no more then around 3 degree split.

Chris
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Old 02-18-2005, 05:50 PM
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I have some AFR 180cc heads on the way. I talked to a Comp cams technician and he still recommended the dual pattern over their single pattern cams even with a 80% e/i ratio. I ordered the heads last november, i was told that they were to ship out last friday, and then, turned out that during their inspection, one of the castings had a bad spot in it, so they hard to start fresh with new castings. so it will be about another month, Good to know they wont send me a defective product, but man im tired of waiting, so now, since they had to restart the process, im trying to upgrade to the comp package, we will see how that goes. Anyway, thanks for any more suggestions.
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Old 02-18-2005, 05:54 PM
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Patterns

Dual pattern cams are more efficient but Single pattern cams give better top end torque and HP.
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Old 02-18-2005, 06:02 PM
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In your case I think the XE284 will make more power than the Magnum 292H. The RPM band will be roughly the same except the XE cam will do better down low and make power to right about the same max RPM.

Generally speaking, dual pattern cams will have a little wider power band then the single pattern while the single pattern cam in some cases can make a hair more midrange power. Dual pattern cams do not over-scavenge or cause any problems with good flowing exhaust ports -- 75% E/I ratio is good for a basic dual pattern SBC cam with 4-6* spread.
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Old 02-18-2005, 06:15 PM
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There is no way to tell without trying both. It is just like rocker arms. You have to see wether 1.6s or 1.5s or both work the best.
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Old 02-18-2005, 07:33 PM
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Split pattern cams are designed for stock type heads that don't flow well on the exhaust side. They are made to crutch the poor exhaust design and back pressure. DO what Chris advises, you have a head you won't have to crutch unless you design the exhaust pipes very poorly.


lluciano77.

I've never witnessed a combo that ran better than a shorter cam and increased ratio. I'ts easier on the valves, springs, and less pushrod deflection. Not to mention you get less moving weight in the valvetrain. Increasing from 1.5 to 1.7 or even 1.8 with less cam will provide more usable on good heads. We do this with our unlimited engines. 358 to 406's with brodix heads and 15 or better compression. Our cam is only .550 lift but with 1.8 jesel rockers we get .660 without the lifter and pushrod movement.
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Old 02-18-2005, 07:36 PM
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More lift does increase throttle response and power.

Sometimes you will not see any gain by going to a higher ratio rocker.
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Old 02-18-2005, 11:41 PM
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On a AFR 195 headed 383, 10:1 compression motor with a 212/218 @ .050 and .487/.485 Comp hydraulic cam spun 356 to the wheels, which is exceptional for a NA 383 driven on the street any day of the week. contrary to all the mag garbage out there very seldom do you see a N/A streetable 383 spin the rollers over 300 HP or an engine dyno over 450 HP. The same motor on Engine Analyzer Pro shows 467hp on the sim. This motor has never been on an engine dyno to verify the flywheel numbers. The 195's are really pretty close to the 195 across the flow curve so the point being. absent not knowing your displacement and such, be careful with duration. Also a hyd roller, given the right application, is hard to beat. Low duration for great cruising, tons of midrange and power up to 6000. This motor also works very well on a 150 shot.

240 is a lot of duration so you'll be spinning the crap out of this to make some power. I simed that cam with the above 383 and compared the two power curves. The 284 is way down on torque below 5000, an average of 40 ft/lbs below 4000 where the cam starts coming into it's range. At 5000 it's a wash and the cam peaks at 6000 with 498, for a peak gain of 31 HP. So out of a powerband from say 2500 to 6000 the small cam wins from 2500 to 5000. And that's with the bigger heads. The smaller 180 heads would not show as big a gain on the top as the 195's do, so this is really generous. Ona 350 it would be even more peaky on top and soggy on the bottom.

One other thing I know about running AFR heads over the pst 10 or so years is they do like lift. Why buy a head that flows to .550 and beyond without falling off and only lift the valve to .500. That 383 would have done even better with a custom grind on the lift. You need to talk with AFR though if you choose to lob the valve some more to make sure the install the correct springs, at the proper installed height and rate, especially if you go roller. Comp, Crane, Elgin, Howard, Herbert can all work with you on grinding almost whatever your heart desires. So don't think you have to settle for a cat grind. by the way, the 292 is a horrible old grind when compared to newer stuff out there.
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Old 02-19-2005, 08:12 AM
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Heres some other specs that i had planned on running. IN a 383, i had also planned on running 1.6 rockers to give more lift under the curve. I had planned on running a 3000 rpm stall as well. On that sim you did, what kind of torque did the motor produce at 3500 rpm with the XE 284? I would like to actually have the torque and horsepower about equal. In all honesty i would like to have a little less duration, like a 236 at .050, but they dont make an XE with that, sooo, i may talk to my engine builder and see what we can come up with, and also, im trying to get my heads upgraded to the competition package, the 180cc comp heads flow more than the 195 street heads, but we will just have to see. THanks for the help.
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Old 02-19-2005, 08:23 AM
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Would it be possible to get a custom grind with a 236/240 at .50 with the same lobe design and about the same lift? I guess i would just have to talk to comp about that..
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Old 02-19-2005, 01:51 PM
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question

I'm just a beginner compared to most of you characters on this board, but Let me see if I understand: If I put larger ratio roller rockers on my 427 bb I'll get a higher valve lift and a bit more duration and it's easier on valvetrain components than a bigger cam? Do you have to change the valve guides or pushrods because of the change in geometry? What's the downside to doing this other than more money.
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Old 02-19-2005, 02:15 PM
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No, you will not gain any more duration with a higher ratio. The cam will act like it has 2 to 4 degrees more, but it will not actually gain duration.
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