marky mark

On both. For instance, how will a particular motor run with a single pattern cam compared to a dual pattern cam, given roughly the same camshaft specs? Are the single pattern cams old school and the dual pattern cams newer technology?

thanks in advance!

Regards, Mark :flag :chevy


[Modified by marky mark, 4:38 AM 12/1/2001]

randy72

Here's my understanding. If I'm off base, somebody please correct me. A dual pattern cam will typically have more lift and/or duration on the exhaust side than on the intake side. This helps compensate for deficiencies elsewhere in your engine. ie, poor flowing heads or a restrictive exhaust.
I currently have a dual pattern in the 400 in my GTO. It seemed to wake it up from the single pattern that was in it, but it was also a hotter cam (more lift, slightly higher duration). I'm not sure if it was the hotter specs, the dual pattern or both that was responsible.

DeenHylton

Dual-patterns are newer tech...mainly used to overcome the smog-related exhaust systems and head designs of later model vehicles. I read a tech article put out by Isky cams a few years ago that stated an engine will actually make more power with a single pattern cam than a dual pattern cam on an all out, unrestricted (by exhaust) race engine. Deen

63Banshee

Randy is correct. Use single pattern cams on well balanced motors that breath well at both ends. Use dual pattern cams on motors that are restrictive on one side or the other (i.e. stock exhaust manifolds).

BTW, did you know that there are dual pattern cams ground with more lift and duration on the intake side?

ZD75blue

banshee will a dual patern cam with more lift on the intake make more torque than a standered?

Just thinking out loud

ZD

63Banshee

Whether or not you need more lift on the intake side and if it will increase torque is dependent on the entire motor combination. I haven’t actually targeted a motor combination that would benefit from more CAM duration or lift on the intake side, but I’ve seen positive results from people using higher ratio rockers on the intake valves. This is on Chevy motors only!

To answer your question, theoretically it would because of an increase of combustible gas in the chamber. It is safer to say that it would increase low end torque, but the torque curve could drop off dramatically at higher rpm if the exhaust side isn’t adequate.

I’m sure there are guys on the forum that have more Chevy motor experience then I and could offer some real life experience. If you want to talk in depth MOPAR or Pontiac let me know.

marky mark

Yes, that's what I was wondering too. On my 427 BB the intake is the low-rise aluminum that runs a quadrajet (oval port heads). Now, if I put headers on to help the exhaust side I'm still limited somewhat by the short/flat runners in the intake. If I don't wish to change the intake I was thinking a single pattern or even one like you described with more duration on the intake side might compensate for poor intake flow characteristics.

Next question. Is it true that you develop more cylinder pressure (and therefore more power) when you have a cam that closes the intake sooner? If true would this mean in the cams described above that the intake would be closing later thus reducing cylinder pressure (part of the fuel/air "charge" is pushed back into the intake manifold if valve closes later I believe)?

Oh these cam questions never stop!!!
Thanks again, Mark :flag :chevy

427Hotrod

This stuff gets wild and the technology continuously changes.

There are so many variables to cam design, and many of them compliment and/or counteract each other depending on what combination you use to design the cam.

You're right, closing the intake earlier will build cylinder pressure typically. Closing it later allows the reverse flow you described. It's all a fine balancing act to get the rpm range you want the cam to operform best in. That's why most "hot" cams lose low end performance. The cylinders are less full at low speed and make less power. Eventually as the rpm rises you reach a point where the cylinder begins to get filled properly and more power is made.

It's typically assumed that performance will increase as the intake side rate of acceleration increases. Meaning a very aggressive lobe on the intake side opening flank, then possibly a long duration lobe and then quick closing rate on the intake. This allows the valve to be open longer at higher lifts and then still get it closed early enough to trap it in there. The limit to all of this is primarily valvetrain harmonics and keeping things from getting out of control. Past that is the issues of piston/valve clearance that is affected by R/S ratios. This is essentially what the Comp cam Xtreme energy cams are doing as well as Engle has done it for years. The trick is making the lobe live.

The split duration ones that are longer on the ex. side are great for helping anything that is going to be run capped up, or has poor heads on the exhaust. Fords were always in this boat. The rate of acceleration on the Ex. lobes isn't as critical as the intake side due to the fact you have real pressure pushing it out. Often you will see a smaller lift , yet longer duration on the ex. side. This is a good indicator of a less aggressive lobe. Makes things live longer. The hardest thing on a cam is a short duration, high lift one that we all want. A nice long duration one is easier on the valvetrain.

You really have to look at lobe profiles to really compare them. two cams can have very similar overall specs (lift, .050 duration, LSA) yet actually be very different in performance.

Think of one cam that has 110 lobe centers on both intake and ex. It would have 110 Lobe Separation Angle also. Now compare it to another that has 110 LSA, but has an intake lobe ground with 106 centerline and the ex. with 114 centerline. They both are 110 LSA cams but will act a lot differently. The second cam has the intake closing much earlier than the second.

They could have identical duration numbers also. But what if one cam has a very aggressive lobe that opens the valve very quickly and closes it very late in the cycle, but also very quickly. Compare it to a cam that opens very slowly and closes very slowly. Though it's easier on the valvetrain, the valve will not be open as far at any given point and performance will suffer even though it has the same duration number.

See how crazy this gets?

Next you have to look at how many cams end up with more overlap (where both valves are open at the same time) as duration numbers increase. This is bound to happen if the opening rates don't change. Also bound to happen as Lobe centerlines move closer together unless rates change. If you look at some Pro Stock cams you'll see that they have unbelievable lifts and duration numbers, yet run very wide LSA. They idle like a pickup truck almost! They have so much duration that overlap is bound to happen and they can spread out the LSA to keep from overscavenging the cylinders at high rpm. If you have super tuned efficient exhaust (ain't happening on 99.9% of anything we drive) you run into the problem of the exhaust pulses actually sucking some of the fresh fuel charge out the exhaust at high rpm. I'm talking 2.0+ hp per cube type stuff. This is where the single pattern cams start shining again, maybe a little less power level , but still a real optimized setup.


Like I said, you gotta look at all of this stuff if you really want to pick the absolute perfect cam for your motor. Actual head airflow numbers get involved.

I know this is more info than you asked for, but it will make you ask a lot of questions about the cam you are looking at. The intake side of your motor is going to be a high velocity setup but airflow limited severely. A very quick opening/closing yet long (relativelY) duration cam might help. Could be interesting. Your heads are going to sign off in the .550-.625 range probably so there is no need to go much higher.


Jim

marky mark

Thanks Jim, great description of a complex subject (at least to me it is!). I gather from your info that a dual pattern with decent duration and lift is the way to go on a lightly modified or near stock street motor. An increase in the duration should, in theory, help with intake and exhaust limitations.Thanks for taking the time. Beautiful car by the way!!

Thanks, Mark :flag :chevy