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  • 10/5/2011
After getting sick of people offering up cam suggestions without any facts to back then up I decided to do some fairly basic research for myself; both to help me pick out an appropriate camshaft for myself and part to help me help others. These are a few of the most popular cams for DSMs: FP1/Comp 101100 FP1X/Comp 1011FP FP2/FP101200 HKS 264 HKS 272 Web 546/547 Web 452/228 Web 463/228 Delta 272 The first graph I have shows a comparison of cam lift and duration of all of these cams at .050" on the same scale. One of the first things you can see right off of the bat is why the Web cams seem incredibly more "lopey" at idle than the others. Look at the vast difference in duration they put on the intake and exhaust! While they open the valves right between where an FP or HKS does, the 463/228 keep the intake open significantly longer (more air transferred in). What I focused on was really the HKS vs FP on this one, because we are always hearing how comparable they are and get HKS was always getting more attention than the significantly less expensive FPs. Why is this? The FPs open the valves a little MORE, providing greater volume airflow than the HKS...and usually more air means more performance, right? ...hmm The duration, especially, is much longer on the FPs on the HKS. So how is it exactly that the HKS gets such good numbers? Here we go, physics kiddies. On a 1g head, especially a ported 1g head, you have those giant ports bringing in high volumes of air, giving 1g heads that big power factor the big racers want. They are needing to spool those big turbos and bring in massive amounts of air. Great, for the big racers! What about the little guys? With the smaller turbos? Or especially the guys running a 2g cylinder head? I have a 1g, yes, but I am running a 2g head for a very specific reason. You'd think on the second generation Mitsubishi wouldn't intentionally downgrade their designs, so why did they put such a smaller port size on the 2gs? The 2gs are all about the VELOCITY of the air. The runners on the intake manifold are proof of this themselves. They are beautifully designed to maintain a high level of velocity. Small about of air, but it is moving much more rapidly. So thinking about it this way, HKS cams are opening a moderate amount but are opening and closing the valves very quickly. So, my question remains in which is technically better for a 1g head and which for a 2g head. The route I've gone down so far (hence my choice of mixing a 264/272 HKS cam in my setup), is that the valves opening and closing more quickly while opening a little is the best use of the high velocity air. Since they aren't opening as far hopefully the velocity isn't disturbed. But, maybe, rapid opening and closing does disrupt the flow. If I had a 1g head, I would be looking to grab the FP's because they are moving that greater volume of air, which is definitely needed.Deep breath, you aren't shutting me up yet. The next thing I wanted to look at was WHEN these cams were opening and closing the valves. Again, we're finding that HKS is going to be the tricky cam on this. Starting ~0 deg.: FP2 Open intake...Close intake...Open exhaust...close exhaust...lather, rinse, repeat With all but HKS one set of valves is getting closed briefly before the next set is opened. It is almost, if not is exactly, simultaneous. HKS has an overlap of the valves being open. This reaffirms my thoughts on HKS being the correct choice for a high velocity design. Starting ~0 deg.: HKS 264 Open Intake...Open Exhaust...Close Intake...Close Exhaust...lather, rinse, repeat.Please feel free to point me in the right direction if I'm missing something here. If there is anything that you'd like to see let me know and I'll do my best to figure out what I can and offer my suggestion for your setup. Thanks for reading!
  • 10/6/2011
Hot damn nice work. Love seeing your train of thought. I do know that D-Sport had an excellent write-up in their #105 issue (August 2011) on the camshaft/valvetrain. Helped me get a good grasp on exactly what you're talking about here regarding lift/duration and valve timing (in regards to opening/closing early/late). Really makes me with that I had even SOME options on my B5254T3. I know that somebody is making them overseas, but I believe they're damn near impossible to get in the States.
  • 10/15/2011
Wow, I wasnt even aware that there were posts outside the general discussion area! I apologize for missing this! I have limited knowledge on which cam is better (lift vs duration), but I have taken a few fluids classes which helps a lot with the concept. I actually think that opening the cam more provides more flow because the cam isn't there obstructing the flow. At first glance this seems like a simplistic thought, but lets dig in a little deeper. How do you maintain the highest overall velocity? Keep the flow laminar, as soon as the flow becomes turbulent you have the air working against itself. Turbulent liquids have a much high LOCAL velocity because air is travelling every which way, but when you zoom out and look at the big picture the overall flow of the system is slowed. When you introduce a disturbance like a cam you are introducing turbulence, no way of getting around that. Now lets take your idea of a smaller lift creates more velocity. The cross sectional area that the air has to travel is smaller, so yes the velocity HAS to be higher in order to fill the cylinder, but there is a huge disturbance creating a lot of turbulance. The local velocity will be extremely high, but the overall flow will be slowed. Now, on a higher lift cam there is less of an obstruction, but the cross sectional area is much larger. Because the air can maintain more of a laminar flow combined with the larger area available the local velocity will be much lower. However when you zoom out and see the entire system, the overall velocity would be much higher. In theory this is 100% accurate, but in the real world when you have a flow range from 800rpm to 8500rpm I think these differences even out. One is more ideal at lower flows, and the other is more ideal at higher flows. I think what you were alluding to with the valve overlap is the big reason for better flow/more velocity. On the FPs the cycles don't overlap so when the exhaust valves are open the only way that the exhaust gas comes out is by the cylinder pushing the air out, and some scavenging due to port velocities. So when both valves close the pressure inside the cylinder may be slightly below atmosphere, it certainly isnt a full vacuum, meaning that there are still dirty exhaust gasses stuck in the compression chamber to be mixed with the fresh intake charge. This is where the HKS overlapping cams shine. As the exhaust valve is beginning to close the intake valve is opened allowing pressurized air into the cylinder which swirls around in the cylinder and helps push more of the exhaust gasses out. Not only that, but when both valves are open the "volume" that the intake air sees is much higher so the velocity at the intake valves will be much higher, which will in the end add more pounds of air into the cylinder at the same intake manifold pressure. Sure, some intake air is lost out of the exhaust side, but it is more than evened out with a cleaner compression cycle and higher intake velocities. :end of my fluid dynamics theory: Now like I said, I do not have any real world experience with different cams, but from reading things and just letting the concept sink into my head, that is what I see. I myself was planning on the 264/272 cam combination. It seems like the best combo for the street... Unless you like a super lumpy idle!
  • 10/15/2011
You're absolutely right, and my curiosity is stemming from why people are seeing better numbers going with the low duration, low lift 264 on small builds. I am hoping to take my setup, with the unported 2g head and matched unported intake manifold with the 264/272 get some numbers, then change nothing and slap another 272 in there and see what happens.
  • 10/15/2011
Originally posted by MoparDSM
You're absolutely right, and my curiosity is stemming from why people are seeing better numbers going with the low duration, low lift 264 on small builds. I am hoping to take my setup, with the unported 2g head and matched unported intake manifold with the 264/272 get some numbers, then change nothing and slap another 272 in there and see what happens.
By better numbers are you meaning peak horsepower, or larger area under the curve? I think that the low lift, low duration cams give a wider operating range, where the higher cams are only efficient at a smaller specific rpm. Orrrrr I could have this logic completely backwards. Itd be pretty cool if it were possible to see the pressure and flow differences of an individual runner throughout the RPM range.
  • 10/15/2011
http://amsperformance.com/camtest.phpI didn't say that correctly. One isn't necessarily better than the other. Sure, one may be better than the other in the sense of matching a setup. Really they are just different. I am not built for top end...at all... Sticking with the 264 I keep my low end torque and therefore acceleration. If I went with straight 272s it would hurt my low end torque, which I can afford with the setup, and it would give me more top end. It would compensate a bit more. Just depends on what you intend to do with them. I'm just very interested to see what the torque numbers come out to be changing that one cam on my personal setup. The link above is a great test of a similar setup.
  • 10/15/2011
Hmmm, good to know. It looks like the differences between the 264s and 272s is pretty minimal, especially when compared to stock cams. Sounds like I just need to upgrade the cams regardless!
  • 1/31/2012
Damn!!! This is a nice little thread! Cant believe i did not see this months before when I joined....
If you talk the talk, you better crankwalk the walk.
  • 2/1/2012
Lol, yeah this area of the forums are a bit hidden. Maybe there is a better way to display new posts in these sections?
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