One thing I have noticed a lot of difference in is valve lash. When you tighten the lash up (decrease the gap amount), you make the valve open sooner and close later. This allows for more air to get in and out. By tightening them up, the turbo lights sooner because more air is being shoved out at a lower RPM. This gives you a ton more efficiency down low from what I have noticed because boost helps burn fuel, when there isn't enough air, fuel is burned inefficiently. Inefficient burn can be compromised for less power by letting off and getting back into an efficient burn ratio, but this is inefficient in itself because you might be starting to go up a hill and you will either have to go up it slowly or maintain speed by giving it more fuel that will burn rich but get the turbo spooling eventually. Why should you ever have to wait for that turbo? Running the valves tight help out a lot, but there is more to it that I want to know. The exhaust valve is what drives the turbo sooner if you run it tighter, but what does the intake valve have to do with anything? Do they work hand in hand? As in to get more air out the exhaust valve do you need to run a tighter intake to get more air in? Is there any benefit to running it looser? One issue with running them tighter is you can only go so tight before the valve and the piston contact, which is not something that is very appealing Thankfully valves tend to loosen over time rather than tighten.

I'm working on it, keep your pants on. Have to research it more so I don't spew off a bunch of inaccurate crap, dealing with injector design and injection pump design...all the nitty gritty of it.

Sorry if I missed it, but go 180* out from where you measured and see when the contact!Valve contact doesn't occur on the compression to powerstoke (as valves are set) it happens on the exhaust to intake stroke. The reason you don't see much, if any, difference on valve lash on a stock or nearly stock motor is the design of the cam/tappet. The tappets are HUGE and give the valve a VERY steep opening rate, so .001 isn't going to manifest with any real measurable gain in flow.

Sorry if I missed it, but go 180* out from where you measured and see when the contact! Valve contact doesn't occur on the compression to powerstoke (as valves are set) it happens on the exhaust to intake stroke. The reason you don't see much, if any, difference on valve lash on a stock or nearly stock motor is the design of the cam/tappet. The tappets are HUGE and give the valve a VERY steep opening rate, so .001 isn't going to manifest with any real measurable gain in flow.

I think you are talking about when the valves hit the piston? I measured during the exhaust to intake stroke..valve overlap. I went both ways making sure I was at the right spot where the valves and piston were closest. I realize valve lash is next to nothing compared to the .400" lift (or around there) that I was seeing, but it does have an effect, I am just trying to make it obvious that it does. When you go from one drastic setting to the next, differences are seen very noticeably. Still testing though.

Gotcha... I didn't see where you said that and thought you were only checking it on the compression/power stroke. Stock lift on the intake side on your 97 is only .235. While you may notice differences in the bottom end the once spooled power is probably too close to tell a difference on. I am not saying that there is no difference, but you have to realize it's very small. These motors rely on boost not lift/duration for most of their air, at least where valve lash is an issue. The min setting is for preventing burnt valves and the max setting is where power starts to be really effected. You can look at this page and see where valve clearance becomes an issue. http://www.coltcams.com/html/Cummins_5_9_camshafts/index.cfm

Gotcha... I didn't see where you said that and thought you were only checking it on the compression/power stroke. Stock lift on the intake side on your 97 is only .235. While you may notice differences in the bottom end the once spooled power is probably too close to tell a difference on. I am not saying that there is no difference, but you have to realize it's very small. These motors rely on boost not lift/duration for most of their air, at least where valve lash is an issue. The min setting is for preventing burnt valves and the max setting is where power starts to be really effected. You can look at this page and see where valve clearance becomes an issue. http://www.coltcams.com/html/Cummins_5_9_camshafts/index.cfm

Yeah I am not really seeing too much of a difference on "once spooled" running. I drive really consistent but I need something like a generator with a set load to see if there is any difference while its running, it is just too tedious. That is cam lift which is different than valve lift. The cam goes up .235, but the rocker is not a perfect teter totter, it changes the lift by putting the fulcrum closer to the pushrod (look at my avatar). I measured the lift and although I didn't get a set value (calipers weren't as accurate as dial indicator), its within +-.010 of 400. It was the same lift for the intake and exhaust.

Ah yes, talking apples vs oranges!The exhaust rocker arms are longer than intake rocker arms so it stands to reason they will equal out even with the difference in cam lift.

Yeah I saw you posted that somewhere else, maybe earlier in this thread and I was wondering why I was seeing a lot more lift, it just hit me after seeing that site and looking at my avatar that the cam lift and valve lift had different relationships. I'd still like to measure it on the other side of the rocker and see lol.

I don't have a pic with the rockers on, but look how much further it looks from my pushrod to my exhaust bridge than on your motor. And how much closer my intake valve is!

Must explain the .299 exhaust compared to my .263. Hmmm, thats very interesting. Another thing if you look at post #12 of this thread you see my valve duration is much longer than what they post for my cam, I wonder why that is. I set them to the stock 10/20 values for my test. I definitely need to redo that and measure the other side of the rocker. I might have a stage 6 cam and not even know it

The CR cam is nothing special, short exhaust duration and advanced exhaust lobe make for a poor flowing exhaust!It's interesting what you measured thou!

It was 102 today down at the lake and with the valves still at 6 intake and 30 exhaust, it really showed it's effects. There are lots of hills down there and I usually never see smoke, or didnt with both valves set at the tightest tolerance. Well I just leasurely went up a hill as I always do, giving it a little more to get it up to speed, usually I have a lot more to go before it thinks about smoking. Well I looked back there and the whole road was blacked out. I notice these past couple weeks with it at 30 exhaust and being really hot out the thing has been a dog. It isn't like stock doggy, after all, I do have the AFC and fuel plate removed. But it just doesn't have the kick in the rear it usually does. In the winter with valves tightened all the way up, the thing rips. Right now with the heat and exhaust as loose as possible, the turbo doesn't stand a chance. I think it's a combination of the exhaust and the hot air since not as many molecules are getting into the engine since hot air is bigger. Mileage seems the same (if I leave A/C off) though. Overall I think the valves just change the spoolup. It barely spools up any more, with the exhaust tightened all the way it kicks the turbo to life as if I had an HY on it. Don't get me wrong, both settings get to the same PSI (I think), but the spooling is night and day.

I just wanted to tell everyone that i set mine at 7/17 and it really does drive different. Off the line is quicker. I use to have 10/20

I just wanted to tell everyone that i set mine at 7/17 and it really does drive different. Off the line is quicker. I use to have 10/20

Now you see what I mean. Imagine the valves on max lash 15/30 and you can think of what a piece of crap it is. I'm going to set it back to 6/15 when the thing cools off today.

I may do the same. I want to see if i can get more out of it.

I may do the same. I want to see if i can get more out of it.

If you ever pull a trailer, the effect is multiplied a number of times.. I was pulling steeep country backroad hills with our trailer at 1300RPM in 5th and it had no trouble giving me a ton of boost to let me get back up to speed after the hill/curve was over. I drive that route a lot and before I always had to downshift, it had no boost down there so if I left it in 5th, it would just blow smoke everywhere since the turbo wasn't doing anything.

Today I adjusted the valves on mine to 6/15. The difference is noticeable, the spool seems like it starts as soon as I touch the throttle. Thanks for all the research, and sharing it all!

Been doing any more playing with valves?

Funny how these old threads get dug up! I'm curious as well. I'm getting ready to adjust my valves (never been adjusted and I'm at 230k miles) Yikes! My two cents: First - when you were asking about the necessity for valve lash - On Volkswagen motors, the rockers are designed such that everytime the lifter comes down to contact the valve, it actually causes the valve to rotate ever so slightly so that the valve is contantly rotating during operation. This keeps it from wearing abnormally. Cummins valves may have a similar design. Second - when talking about intake valve vs boost, don't forget that all things equal, if you open the intake valve sooner in the intake stroke, your turbo boost (measured at intake) should be lower. Many people don't understand that boost pressure is truly a measure of restriction. If your turbo were allowed to flow from compressor directly to atmosphere, it would make 0 psi boost, regardless of how fast it spun or how big the compressor is. Confine that airflow and that's how boost pressure is made. If you were to set your intake where it opened sooner, it's going to allow more air into the cylinder, which means some of that air volume creating backpressure outside the cylinder is going to get consumed inside the cylinder. Cylinder pressure goes up, but boost pressure goes down.

I think it is the tighter exhaust valve specs that does it (the quicker spooling). When you allow the exhaust to open sooner it exhausts a higher pressure gas since the piston relieves pressure as it goes down.

My dad is bringing his 06 to town in a few weeks for some goody installs and I think we are going to adjust the vavles on both of our rigs. I plan to use 8/18 on mine, and since his in an 06 (10/26 stock) I am not sure what I am going to do, probably 8 on intake but ?? on exhaust.