Guest DaneL24 Posted April 12, 2003 Share Posted April 12, 2003 I was wondering how a reground cam with the stock duration but extra lift would affect the performance of a motor, specifically if this would negatively affect the idle quality and low RPM power of a motor. As far as I know, a big cam hurts low RPM power because the extra duration reduces the effective compression ratio and the extra valve overlap biases it towards higher RPMs. How does valve lift factor into this though? Do higher displacement cams have more lift just to equalize the slope of the cam lobe with the extra duration, or is there another reason? I know that while a high lift cam may have the same advertised duration as a stock cam, it will have a little more duration after .050" of lift because of the increased slope on the cam lobe. That shouldn't be enough extra duration to affect idle quality though right? The air velocity through the ports wouldn't be affected either (except at the valves at peak lift), so it shouldn't affect turbulence and mixing too much. The extra lift and slope of the lobes will also put more stress on the valve springs, but that isn't an issue concerning low end power. So how does it affect performance at low RPMs. I figure it would improve flow a little bit throughout the powerband, just not as much high RPM flow as a traditional performance cam with extra duration. If it does work the way I think it does, I figure a high lift cam would be a nice addition to a turbo motor. So what do all you think engine tech gurus think? Quote Link to comment Share on other sites More sharing options...
Mudge Posted April 12, 2003 Share Posted April 12, 2003 It will have more bleed off, yes, and you'd still be mostly stuck with power loss/death at higher RPMs, and it would be harder on valve springs. But supposedly aggressive cams like this are good torquers for down low. New springs, rockers and etc just for a little torque? I'd go for some HP, even if its only a modest cam. JMO though Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted April 12, 2003 Share Posted April 12, 2003 If you bumped up your compression a little by say milling your head, you could run a longer duration cam without much if any loss in power. I would not go thru the trouble of replacing a cam with one with stock duration. Topend Performance has an ITS cam that has a little more duration then stock. It is a cheater cam. If you want a good mild cam, why not get the comp cams 260 for the Z car engine. It is not very large at all. Quote Link to comment Share on other sites More sharing options...
Mudge Posted April 12, 2003 Share Posted April 12, 2003 I'm no expert, but I have looked at cam stuff and I agree. Stock cams are weenie cams, you can upgrade without major loss of torque, and you will gain some top end RPM and power. If you stick with something around a 220 duration @ .050" on the intake side I think you will be happy. From there you might want to ask opinions on single, vs split pattern cams, I'm not sure how these cars react to that since that is somewhat dependant on desire and headflow etc Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted April 13, 2003 Share Posted April 13, 2003 I've been trying to do research on cams grinds for turbo motors but haven't found very much useful information. All the info I find is about N/A cam grinds, but the logic between a turbo and N/A cam is very different. Like valve overlap for example...its needed on a high performance N/A motor for cylinder scavenging, but on a turbo motor the pressurized intake air scavenges the cylinders without much overlap. Too much overlap can result in fuel in the exhaust manifold that will combust and possibly damage the turbo. Also with exhaust duration, the hotter the exhaust gases are, the more responsive the turbo will be, too much heat can damage the turbo though. So I had the idea of adding exhaust duration to a cam BBDC to increase temp for a faster spool, as well as more duration at high RPM. I'm not sure about it though. Duration isn't necessarily as good for a turbo motor as an N/A motor, so I thought it would be a good idea to increase the lift and simply let the air flow in and out with less restriction, without having to worry about the odd effects of extra duration on the turbo motor. The small amount of info I find on turbo performance cams seems to hint at extra lift without extra duration anyways. Do you see what I'm getting at? Quote Link to comment Share on other sites More sharing options...
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