interested in what 110+4 actually means probably 4 degrees advance on the valve timing. They don't list a cam card on their site. Too secret The less duration E ? did you tell him that you had a long tube header dual exhaust?

 

Or its designed for headers and free flowing, no cats, dual exhaust, instead of restricted systems.

 

The answer is obvious you have a problem with not enough air on the intake side at 7000ft , not getting the exhaust out regardless of your exhaust system exactly why I mentioned a single pattern cam the exhaust is not your problem. I really like the cam he suggested , smart move contacting him. It does not take a genius to figure out you need help getting air in not exhaust problems. What good does it do to have a good exhaust system if you can't get any friggen air in your cylinder exactly why it has more intake duration and lift there. The man is not stupid.

 

Maybe I'm not as good at this as you are.
But the way I understand it the exhaust assists getting the fresh charge into the cylinder during during the exhaust's exit. So the speed and duration of the exit of the exhaust and overall depression created by it's exit is of importance.
It could be that too much exhaust duration or lift or both over scavenges the cylinder Right?. That would make the exhaust your problem then.
No reason to optimize the intake side if your just gonna shove too much of it out the exhaust pipe.

I say let's just see what answers we get. None of us are cam experts that I know of.

 

Here is his reply:

"At your 7,000' elevation, the air density is about 79% of what it is at sea level. This means your cylinder will only have 79% as much mass to evacuate during the exhaust stroke. Less mass, requires less time to evacuate. That's why the exhaust duration is shorter then the intake. With that shorter duration on the exhaust, the velocity of the mass in the exhaust port will be increased, closer to what you would normally see at sea level. This increase in exhaust velocity will pull harder on the intake port, during overlap, increasing the flow in the intake port, and increasing the mass in the cylinder."

 

Are you glad now you contacted him and not the idiot's answering a phone line at a big company. If you don't know gold blood at comp can talk to him on the phone you are screwed may as well pick your own cam. He is doing more time to get in air in your intake and further using the exhaust for help on the intake air problem you have. No one can fix that problem but he can do as much as a bad situation allows.

 

Definitely. I'm very appreciative of the recommendation. Its nice to know that I'm not crazy. Kind of know the idea of why I would want a special cam, vs being told by somebody who knows something I should use a special cam.

 

no problem just passing on what anyone that visits speed talk regularly know. You want a good quality cam made by him and his knowledge or chris straub.

 

Make sure your lifters rotate, without that just a matter of a few miles before a lobe is gone no matter how well you break it in. Folks put in a flat tappet do nothing to check the lifter bores all it takes one bad one in 16.

 

Great information!! Thanks for posting that.
I can only assume that the valve events on the intake and the exhaust are markedly different to accommodate the altitude as well.

 

Thanks, I'll pay special attention to that.

 

Anybody got a guess as to what he meant here? I think he meant to say "less lift". I could see how that may create a nozzle effect with less lift, but less duration, I don't see how that would increase the velocity.
There is a piece of the puzzle missing here, must be the timing of the opening of the exhaust valve? Open it a little earlier so pressure is higher?
OP are you getting a cam card with this cam?

 

Yes,timing. That exh will find its way out..unless one has a crappy exh or puny port I dont see the need for a bunch of exh lift or duration never made sense to me. Im no expert though!

I do prefer single pattern cams and a real good flowing exh port.Id imagine the less time and distance one has to hang the valve open there could be a small gain just from that. Spring isnt being compressed as much???

 

Typical Chevy heads do have crappy flowing exhaust ports, that's why usually the duration and /or lift are increased, to accommodate that. Except heads like AFR.
But if the intake flow/volume is compromised then the exhaust doesn't have to flow as well due to the loss of intake flow. That is if the ratio of intake to exhaust flow is changed for the worse. The ratio on the head hasn't been changed in this case but the intake flow is compromised to some degree due to lack of air density. So I guess it does take less time to evacuate the exhaust due to lack of volume or "mass" as Mike says. This should allow for the exhaust valve to open sooner (if we assume that the increased velocity is due to lower lift and opening exhaust valve at a higher exhaust pressure) and close sooner (lower duration).... I think.
If you can close the exhaust sooner you can open the intake sooner, giving the intake more time to fill the cylinder. I could be completely off base here, I'd like to see the cam card to confirm or deny.

I can also see an argument for opening the exhaust valve later since there is less to evacuate and close it sooner for the same reason. However opening it later would not increase the velocity and in fact might decrease it, this the reason for less lift? To create that nozzle effect?

So far I like my single pattern cam as well. I'm pretty sure it's not optimized for my scenario, but it's pretty good.

 

so if I add all this up I think this is what may be able to be done.

You can open the exhaust valve slightly early to take advantage of high exhaust pressure to evacuate fast and create a nice big depression for the intake charge, but not so early as that you loose any significant pressure on the piston during it's down stroke. Then make it low duration so it can close earlier capturing more intake charge. The low lift vs higher lift, I'm not sure what to make of that, duration again? More lift takes more time, flat tappet has it's limits.
Now you open the intake valve earlier.
By opening it earlier you either have the option to have greater duration here and/or closing it earlier or both. Preventing less loss due to intake reversion and capturing more intake charge. It seems to me that less dense air is going to more easily revert back with the pistons rise.

These things should give you the most intake charge in the cylinder with the least loss either out the exhaust or back into the intake...if my logic is correct that is.