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ISX

Valve Lash

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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 :doh: Thankfully valves tend to loosen over time rather than tighten.

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With all your experimenting I am really surprised you have not taken the extra 5 seconds during a valve adjust ment to run down the adjustment screw and see actually how far you need to go before piston the valve contact happens.:ahhh:

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I think I did but didn't make note of it for some reason. I'll do it tomorrow! Good thing I got exact TDC etched into the damper. I also want to figure out how much longer it is open per 0.001" lash difference per crank degrees. I think the minimum was 6 intake 15 exhaust with a max of 15 intake 30 exhaust. I'll have to dig around for that spec. I'm wondering now if there is a certain combination that yields the best results. Like is having the intake open too long eating into the compression? Is having the exhaust open too soon eating too much of the power stroke? I'll dig up that other thread where I measured everything so I can pick up where I left off. I'm pretty sure the only reason we use 10/20 is because it is midrange to the specs. In school we were told to do that as well, if it is 10-20 then you set it at 15.. But I think this isn't efficient but want to figure out the issues (other than hitting the piston) that go along with running it tighter. Am I losing power?.. I want to exhaust all questions until we know everything about this topic, same with all the other topics in this section. This particular topic might take a bit of excel work to figure some things. I'll dial indicate the hell out of it tomorrow.

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Posted Image

Now take notice to the note at the bottom... :shrug:

Ah there we go. I'll prove the disclaimer wrong tomorrow as well :evilgrin:

--- Update to the previous post...

I don't know what to say now.

What I found as per W&F's request was astonishing.

Going by my original chart I made in another post, it shows that at TDC, the only pistons actually at TDC are 1 and 6, as long as those 2 pistons are good to go, all the rest are as well since they are all set up exactly the same. So in the chart we can see that 1 and 6 both open the intake and exhaust valves during opposite TDC cycles so only #1 or #6 has valves open. This is the only time the valves are getting close to the piston as they are both open, the other TDC phase involves having both valves completely shut, so there is no contact issue there.

Posted Image

The setup I did was setting the valves to the appropriate valve lash (I-10, E-20) and put a dial indicator right on top of the valve spring retainer cap thing, so I would get absolute vertical movement, not the arced movement the rocker makes. After setting the valve lash to stock 10/20 settings, I barred the engine over to absolute TDC, with both valves open on the valve overlap phase. I then zeroed out the dial indicator so I could get a measurement of how much farther I had to go before the valve hit the piston.

Here is what is mind boggling. Tightening the lash screw starting from the original 10/20 settings, I could go another 0.070" on each valve. That means the intake could be tightened completely up, and then go another 0.060". The exhaust could be completely tightened up and could go another 0.050". I barred the engine 1/4" to either side of TDC and checked the piston contact and it was always an even bigger gap meaning my TDC mark is right on the money.

So what gives! Am I missing something or what? This would mean you have absolutely no worries at all about piston contact. I am going to measure #2 to make sure my #1 piston just isn't melted down to nothing or something.

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Ok... But lets toss in another angle of valve float. There is a certain amount of time that the spring takes to return the valve to closed position. I know this is a big factor on high performance engine and why they use heavier valve spring. I know the 24V cummins has 60# spring from the get go but I was hunting one time with ISX and found that they had 150# (plus) valve springs for the really crazy race nutz... So of course the valve float would occur early for stock springs vs a heavy valve spring. This is a gasser video but the same principals apply...

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I was never talking about valve float, though it is another aspect of all this. In any instance that only occurs above 3200 on my truck "supposedly". Tightening the valves is really for the low end, as boost is built incredibly quick. Usually these things seem like they won't build boost at all under 1500RPM, there just isn't enough flow allowed to go through the engine with stock valve lash to get the turbo to do anything. You can dump all the fuel you want to it but it really doesn't help matters. I decided to go for a week making videos as I drive to and from work showing every aspect that I can that shows the difference in valve lash. Right now I got it on the minimum 6/15 so it will be there all week long. Next week I will set it on the maximum 15/30 and do the same thing. I will also try and keep a MPG report of it, being as consistent as possible. The drive will always be the same so that won't be a problem and I will keep the speeds the same. I will hook up the trailer and take it up some hills at low RPM speeds in 5th, where it really makes a huge difference.

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ISX, very cool idea. :thumb1:This is interesting to see the results. Another idea I had while sitting here was that there may be a 3rd and 4th option. 6/15; 15/30You could set lash at opposite ends... So 15int/15exh & 6int/30exh. My best guess is that this would shift your best power around a little... But since you are experimenting, it might be interesting to try.

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Here is what is mind boggling. Tightening the lash screw starting from the original 10/20 settings, I could go another 0.070" on each valve. That means the intake could be tightened completely up, and then go another 0.060". The exhaust could be completely tightened up and could go another 0.050". I barred the engine 1/4" to either side of TDC and checked the piston contact and it was always an even bigger gap meaning my TDC mark is right on the money.

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ISX, very cool idea. :thumb1:

This is interesting to see the results. Another idea I had while sitting here was that there may be a 3rd and 4th option.

6/15; 15/30

You could set lash at opposite ends... So 15int/15exh & 6int/30exh.

My best guess is that this would shift your best power around a little... But since you are experimenting, it might be interesting to try.

I thought about doing that as well. It would hopefully make each valves effect stand out. If I made the intake 15 and left the exhaust 15, would it choke the whole engine and the tight exhaust valves would have no benefit? It's interesting and I will try each combination out to see what happens.

--- Update to the previous post...

:) I knew it would blow your mind thats why I wanted you to see for yourself. I didn't want to post it as some would have "Lashed" me "Pun intended",:lol: for saying it was that much.:moon:

When you said it, it seemed like you meant I was an idiot for tightening it when the chance of it hitting was that great :lol: It really is incredible. I am wondering if the only reason the valves don't sit at 0 lash is because there needs to be some oil between the rocker and valve to keep it nice for a million miles. Incredibly interesting :pant: But why the difference in lash settings? I don't see why they couldn't both be 10 or something now. I know the valves are different diameters so maybe that has something to do with it, something with harmonics of the flow or something :shrug:

--- Update to the previous post...

Another thing, I measured how far the valve opened but I was using calipers which you are not as accurate with those as a dial indicator. I need a longer indicator thing as the one I use is only 1/4" travel. Nevertheless, I was getting around 0.4" of travel out of both valves. I will get a longer indicator so I can accurately tell how much each 0.001" lash effects the actual travel.

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I thought about doing that as well. It would hopefully make each valves effect stand out. If I made the intake 15 and left the exhaust 15, would it choke the exhaust? It's interesting and I will try each combination out to see what happens.

--- Update to the previous post...

:) I knew it would blow your mind thats why I wanted you to see for yourself. I didn't want to post it as some would have "Lashed" me "Pun intended",:lol: for saying it was that much.:moon:

When you said it, it seemed like you meant I was an idiot for tightening it when the chance of it hitting was that great :lol: It really is incredible. I am wondering if the only reason the valves don't sit at 0 lash is because there needs to be some oil between the rocker and valve to keep it nice for a million miles. Incredibly interesting :pant:

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That's the thing. The valves don't just open when you hit *Exhaust stroke* or *Intake Stroke*, so you are right on the compression thing. I measured this as well back on the old thread. Compression seems to have a lot to do with efficiency, but look at these numbers, the intake valve is only open 10* into the compression stroke whereas the exhaust is opening 50* before the end of the power stroke, so when I tighten the exhaust it cuts into it even more. Problem is, is any of that last 50* usable power? Does the first 10* of compression matter? Maybe it needs that 10* to keep jamming in more air, scavenging I guess.

I'll do all I can to try and make each result stand out.

Here's that chart I was talking about where I measured valve duration. These are all in crankshaft degrees.

Posted Image

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I think you are right. The Compression ratio is a huge factor in efficiency. The tighter you cram the mixture before it auto ignites, the more pressure is has to expand and make power. Its like starting higher up on a hill when you are sledding down. The high compression ratios we have in our Diesels are what make them so efficient compared to spark ignited gas engines.

If we could get the weight down on a Cummins and run it in Nascar, we could make a lot more laps between fuel stops than Gas! I knew a guy who was a consulting engineer for the Penske Indy Car team and tried to get them to make a diesel car for years but never could get them to do it.

I don't have any of my thermodynamics stuff around right now, but I found a chart that illustrates CR vs thermodynamic efficiency.

Posted Image

The difficult thing for me in thinking about cams, and how they are designed, is thinking about it at the speeds the valve/piston see. Meaning, that things are happening so fast in that engine, that when the exhaust valve opens before the piston is even at BDC on the power stroke it takes a certain amount of time for the piston to "feel" that pressure wave from the valve being open. Ideally, we would open the valve so that the piston would "feel" the pressure drop right when it is at BDC.

Same for the intake, ideally, we would open it just in time to push (scavenge) the last of the previous charge out of the cylinder. And then, we would close it right when the valve "felt" the pressure change of the piston coming back up on the compression stroke.

I'm really looking forward to your results.

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I found some more out as to why things are what they are. Valves heat up during operation, due to this, they expand. The lash is there so when they expand, they have room for play. Exhaust valves run a lot hotter than the intake valves since all the exhaust gases are rushing past it, meaning it heats up more. That accounts for why the exhaust valve has a bigger gap for lash. If you did not account for this, the valves would expand and push against the rocker at all times, keeping the valve open. So that explains the 6/15 minimum specs. Nothing to do with piston clearance. I'm also wondering about engine speed. There was an F1 page I found that talked about how their valves actuated sooner as RPM went up because they needed more time to scavenge. I do not run past 2000RPM hardly ever so I think running the valves tight is letting the air in, then the piston is pushing part of it back out. Just like CSM said, you want the intake to close right when it senses backpressure from the piston traveling back up. I think my lash tests over the next couple weeks may prove this.

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this is intresting suff. beings i need to adjust my valves in the near future i will be watching closely. i can be used for a guinea pig if that would help, but my tanny must go on first. after that i will be happy to try or just use some of this information to my benefit. either way it sounds l like a win win situation.

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Alright I don't have the patience for this MPG testing :lol: I want to get some more seat of pants feel so each day I am going to set the valves to the max or min in all difference configurations like CSM listed. Right now the truck is at 6/15 and well I don't want to say what I think it is like until I change the valves to a different configuration so I have something to compare to. I'm driving 70 miles a day again so I have a good run each day to get the feel for each configuration. I'll keep updating this. To start I am going to set the intake at max lash (15) and leave the exhausts alone (which at 15 as well).

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Valves heat up during operation, due to this, they expand. The lash is there so when they expand, they have room for play. Exhaust valves run a lot hotter than the intake valves since all the exhaust gases are rushing past it, meaning it heats up more. That accounts for why the exhaust valve has a bigger gap for lash.

Ah, that makes total sense, I guess I won't go to .010/.010 like I was planning to then. (I lost a lot of exhaust lift with the 12v cam in my 24v)

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Ah, that makes total sense, I guess I won't go to .010/.010 like I was planning to then. (I lost a lot of exhaust lift with the 12v cam in my 24v)

I'm not sure how much the valves actually expand. You are supposed to set them when the engine coolant is under 100F. I set them yesterday when coolant was at 108F and checked the lash first to see and it was a very tight 0.005" on those intakes which I set to 0.006 the day before, so they must expand a pretty good amount. Now that I thought about it, I will try and check the lash right when I get home to see what it is while hot. Right now the valves are at 15 intake and 15 exhaust. So far I haven't noticed too much of a difference. It seems like I am giving it more fuel yet it is building less boost, guess it makes sense since it is making up the the air amount with more fuel, making it burn more inefficiently but providing the same power. I rarely saw it over 5psi today whereas I rarely saw it under 5psi with the intakes at 0.006. I am going to set the exhausts at 30 so all valves will be at max tolerance.

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This is becoming interesting. With the intake at 6 and exhaust at 30 I am noticing that boost is of course slower to build giving off black smoke for a lot longer period of time, but it seems to still build the same amount in the end. I thought of something that sort of ties with all of this but its too big of topic to just add to this thread.

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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.

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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.

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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.

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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

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