tristan21

ok so I'm tryin to figure out why cummins wouldnt want to have a cam with the same profile as the helix 2 or similar if the truck spools faster and I thought I read somewhere that it also got a little better mpg?

May seem like a goofy ? But when you think about it if it idles the same and runs better why not? Also I'm curiouse if you California people still have to smog test and if that could be a reason?

carl48

i am trying to verify this now, cummins tech with rocky mountain cummins had showed me where in 04.5 they started overlapping the intake and exhaust valve timing i am not very good at explaining things but another member explained it this way , to meet the new regs cummins is using in cylinder egr , i type with one finger and i would be here all day trying to explain what he said in six words this is why i like this site

GaveUpOnTV

A lotta stuff Cummins does (3rd injection event, of course the cat, the little turbine in turbo, and the cam too) is for emissions. I've always heard that a bigger set of injectors will give you better mileage and run smoother too, but I guess smog considerations trump mileage gains.
We don't have emissions test for diesel's here yet (at least where I'm at in middle of state in California) I heard in the next couple of years, though.

Don M

The exhaust valve is held closed too long in the 04.5 and up engine for the best HP production. The post injection event ( third and final ) is later in the cycle than many Diesel engines with Common Rail. Both of these are done to oxidize more soot before opening the exhaust valve. In order to add some heat to oxidize the remaining soot left over after the main ( second ) injection event, the post ( event ) is used along with a late opening of the exhaust valve. Timing when the valve begins to open along with when the post event starts and stops is what Cummins is calling "in-cylinder egr"

Since temperatures are lower when the piston is lower in the bore, the formation of NOX after the 3rd event is not a concern with stock tuning/fueling. EGR is a soot lowering idea first.

So, it was easy to see that opening the exhaust valve earlier was the first thing to do. This does a couple of things: lowers the pumping loss that a late exhaust valve has as baggage so improved efficiency results. And second, it uses some of the 3rd injection events energy that would be used to oxidize soot in the cylinder to help spool the turbo faster. Like popping open a bottle cap, opening the exhaust valve while the pressure is still high raises the pressure difference on the inlet of the turbine, so the turbo zings up faster.

airforceivan

Is there a downside to using a helix cam. What about long term wise.

XLR8R

Great post, Don!


Yes - government studies have shown that it's impossible to wipe the Helix-induced smile off of your face...

tristan21

Alot of the stuff Don says goes over my head sometimes but I figure its like advertising, if I see it enough times hopefully I'll get it. The amount of knowledge you have on these thing amazes me.

You got any in depth knowledge of head porting. There is a thread at comp d that is gettin pretty heated. It has some of the same ol players you seem to like to set straight. Fun to watch like the spring and cam conversations over there.

jmccart

That i a cool little read, thanx. Does an after-market cam still make spool up faster?

Thanx.

Kman9090

yes spool up is faster with a cam.

GaveUpOnTV

I heard torque peak is quite a bit lower too, and at least the PDR cam is supposed to get 2 MPG better than stock.
Not a cheap upgrade (maybe if you do yourself, but it's a lotta work) though.

Kman9090

I can get consistantly 22mpg out of my setup with a light foot. Cam will help some with mileage but I like it because the spool up with this 66 is almost instant. Also keeps the egts way cool. Can't even hit 1300.

53 willys

have you put your truck on the rollers?...I was wondering what kinda numbers your set up is getting you?

tristan21

I would guess just short of 6's only till he can get a cp3 on that beast.

matego

So Tristan, are you getting a Helix cam? I was wondering if there was any improvement to be found with stock injectors? Would there be any benefit to advancing or retarding the stock cam? Since the exhaust is closed too long I was thinking that advancing the cam would open the exhaust valves a little sooner and may help, but what does that do to the intake timing?

abc4yew

I was told that the longer you keep the exhaust in the head the more torque the engine will make at the expense of HP. My H2 kept things cool and spooling of my twins was fast. I don't think a cam is needed unless you are running bigger injectors and a modded CP3. It does make the engine run more efficient.....it is an expensive mod that is more a supporting mod than a power adder mod. KS