I was wondering what advantages and disadvantages of each are. I have been told that the dual patern cams have larger power ranges. I have also been told that they were more fuel effiecient. Some people have said that the dual paterns should be used unless you have really high quality heads. I was also told that dual patern should be used on mild street engines. I dont know if this was supposed to imply that higher performance engines benifit from single patern or what. I aslo heard that dual patern cams were better for torque. I ran a coupld of tests on desktop dyno. I have a pic attached that shows them. It does seem that the dual paterns power range lasts longer, but it doesnt seem like it has as much torque. They are both comp cams. One is the xe268 and the other is the magnum 270H. Everything else is set up identically.

Thanks for the help

Ben

 

Come on guys. Help me out.

Thanks

Ben

 

Well, I have to admit, I had the specs from comp cams on the 270H but did not have the valve opening and closing times for the xe268. They just sent them to me today and I changed the 268. Here is the new dyno. It brought the torque up some and still holds the power out a little longer. I am still looking for opinions though.

Thanks

Ben

 

Most cylinder heads don`t flow as well on the exhaust, so a dual
pattern cam will even things out a little.The better your exhaust
flows the less you need it.

 

the dual patterns are newer than the old single pattern. I have a single pattern and love it, but i have heard that the duals are better. if i were building another motor, i'd probably try a dual.

when serious racers pick a cam, they run the engine ona dyno, use a flow bench, and select a custom pattern that works best. i guess you would call that a dual pattern, but the ones that crane or whoever sells are not custom, they are designed to work in most engines.
the duals came about as engineers realized they could make more power, i.e. be more efficient by opening and closing the intake and exhaust valves at different times. i guess that means more power can be had with a dual, the hard part is picking one.

 

It depends on the engine. Most stock or mild engines benefit from a dual pattern cam.

 

Dual pattern cams help make up for heads with weak exhaust to intake ratio,the better the ratio the more a single pattern cam works. An example of a head that has a high exh to int ratio, is the vette alum. L98 . It has a ratio of 82%,Edelbrock rpm has a ratio of 69% although it it's intake flow more in stock form.

 

Thats how I thought it was, but I had heard different things from different people. So, stock style heads that are pocket ported and gasket matched should go with a dual patern then right.

Thanks for the help

Ben

 

Yes, virtually any stock heads will work better with more exhaust duration.

Think about flow: there are 2 ways to increase it; either open up the passages more, or hold the valve open longer. If you hold the intake open too long you get into emissions and low-RPM performance issues. But there's no such penalty for increasing exhaust duration. Even the factory has known this since the mid 60s, when they first came out with the POS .390"/.410 cam. The aftermarket mfrs have really taken advantage of it in recent years; nowadays almost all of the really strong running street cams are dual pattern.

 

Like everyone else said, it depends on the heads to some extent, if the exhaust side doesnt flow well, you want a dual pattern cam for sure.

You can adjust the scale on those graphs so it doesnt read to 11,000rpm

 

Thanks for the suggestion on the graphs. I hadnt really thought about changing it.

Ben

 

Hey Ben, when the weather warms a little more. Come on back over and take a ride, before you buy that cam.

 

Sounds like a plan. Is it snowing there now. We are currently being blessed with the white stuff. As of now I do think I am leaning toward the xe268. Is your motor the one that came in your car or is it a different one. Basically I was wondering if it is a roller cam or not. Thanks for the help.

Ben

 

NO, the block is a 74, and the heads are from a 87 cop car. My next engine will be a roller though. With a lot more poop.
Yea, it's snowing pretty good over here. Looks like the GTA will be parked a few days. Blazer needed a work out anyways.

 

So, was your car a 305 or 350 origionally. I look forward to riding in your car. Hopefully it warms up again soon, because I should have money for quite a bit of this stuff pretty soon.

Ben