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  #1  
Old 12-27-2005, 08:13 PM
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Need some professional advice on cams

I have been thinking about what we can do with our cams. This thread is for those of you who know more about the technical points about them.

As of now we are able to weld and grind our intake cams to 8mm of lift with 240 degrees of duration. Stockers are 7mm of lift with 236 degrees of duration. Now this gives us a nice noticable improvement in power without sacrificing any drivability on the street.

I, however am looking to do something a little more radical with my next set. Since Delta Cams has provided me with a good price on cams I don't want to go anywhere else, but they are limited to pre-set profiles. That being said, lets talk about what else we can do.

I did a little research and I found that the most vital parts of designing a camshaft is the overlap... Increase the overlap and you will increase your upper rpm power but lose down low and have a "rougher" idle. This is what I am looking to do but not so far that it cannot be driven normally. Now say we stick with the 240 degrees of duration, what if we were to offset the cam teeth a little? I mean each cam sprocket contains 50 teeth which means each tooth is worth 7.2 degrees.

Oh, almost forgot. The exhaust cam profile is 8mm of lift with 244 degrees of duration.

With this information, what configuration would be optimal for a person looking to increase their high end power on a stock block?

Thanks for your help and please limit comments an questions to ones that are well educated

Tom
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  #2  
Old 12-28-2005, 04:06 PM
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OK heres a start.

I'll start by saying that each cam does its own function. The lnlet has to provide enough lift and duration to suit the rpm that we want the engine to produce its miximum power at. The exhaust has to be able to release the gas pressure that is still in the cylinder, it enough time, so that there is no pumping of exhaust gas as the piston rises on the exhaust stroke.

The two cams are seperate, they don't have any relationship together, they are two separate functions, and have to be seen that way. Now I know that this is not what you read from the "tuners", as Tom has said they are tied up in 'valve overlap'. This is a result of the two cam settings, and have little effect on the way the cams are set.

If we look at what Tom has quoted," that we can just vary the overlap to do the job. If we incress the overlap with the standard cams, we would advanced the inlet lobe center, and retard the exhaust, which would have the torque appear lower in the rev range, not higher.

This is going to go against 'what they say' but this is the case. The change from two valve to four valves, has changed the way we do and think, about it. The four valve engine has superior breathing at high rpms. To give an example, a two valve engine, of 550cc cylinder size, would use a lift of 10 to 12mm, and a duration of 360* to have the torque at 7500. The same cylinder with four valves uses 9mm lift and 260* to produce more torque at the same rpm.

Harvey.
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  #3  
Old 12-28-2005, 05:47 PM
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A bit more.

On the example of the two/four valve engines.
The two valve that I gave has an inlet valve of 42mm and 12mm lift. Useing a valve throat dia of 40mm, the area of the valve circumference at full lift is = 1507 sqmm.
The eg33 has a 37mm valve, throat of say 35mm - 6mm for the valve stem = 934sqmm. At 8.5mm lift it has a circumference area of 934 sqmm X 2 valves = 1868sqmm.

This is why we don't need the big durations or lifts, that we did back then, to achive the breathing at high rpms.

Harvey.
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  #4  
Old 12-28-2005, 09:01 PM
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Harvey,
So, are you saying there is little to no benefit of increasing the exhaust cam duration by, say 5-6 degrees (keeping the lift stock)?
-Bill
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Old 12-28-2005, 11:14 PM
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Ok, thanks Harvey. I am beginning to understand a little better now. I am still confused as to what our best alternative would be, or have we already found it? This thread is here for the full purpose of trying to find our absolute best option. I am looking to make peak power around 6000-6500 rpm. I say this because my 6 speed is using the higher rpms. This is where I would need my power. autos would probobly be better making top power from 5500 to 6000 as it would be dead center of their drawn out shifts

Tom

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Old 12-29-2005, 03:56 AM
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Why we don't do the old things anymore.

I would like to continue to show why, the way we go after power has changed, with the introduction of four valve engines. It will explain why the things that we used, to modify a two valve, and what most hot-up books have taught us to do, no longer are the way.

When we worked a two valve, we used the biggest inlet valve that we could fit in the head. The biggest lift that the valve gear could operate, and the most duration that would allow the engine to start and idle. To assist cylinder filling we used the energy in the inertia of the inlet and exhaust gas. At the end of the inlet stroke, we relied on the inertia of the incoming gas to keep it flowing into the cylinder even though the piston is rising, forcing more gas into the cylinder. We used the inertia of the exhaust gas to create a vacuum in the cylinder, so the inlet gas would be sucked into the cylinder, when the inlet valve open, on valve overlap. To get the engine to operate at high rpms, long duration's were used, inlet valves opened at 60* before TDC, and the exhaust didn't close till after 50* after TDC, valve overlaps in the 100* to 140* were used. Even with all this, it was difficult to get the engine to produce power over 6000 rpm, and still have it with a useable low rpm torque.

The reason for this was in the type of energy we used to perform the cylinder filling. The gas inertia was too slow to allow the filling as the rpm increased. With the coming of the four valve, there was no need for the long duration's, and high valve lifts, as the four valves provided the breathing to run into the 6 to 7000 rpms, without the need for it. As we sort more HP at the higher rpms, we had to use a faster energy source to assist cylinder filling. Sonic pressure waves took the place of the gas inertia. We use a tuned length, resonate inlet tract, that develops negative pressures in the cylinder to draw more gas in.
Instead of a vacuum to start the inlet flowing at valve overlap. We use the sonic pressure waves developed in the exhaust pipe to develop a negative pressure in the cylinders combustion chamber, to deliver an intense start to the sonic pressure wave that will travel the tuned inlet tract, to produce the negative inlet pressures, that will fill the cylinder.

The change from inertia energy, to sonic pressure, has allowed us to rev the engine as hard as we like, as instead of the energy decreasing as the rpm rises, the sonic pressures become more intense as the speed rises. This changes the way we build exhaust systems, as they are the providers of cylinder filling. It is more important to create an intense start to the inlet pressure wave, than to use valve over lap to draw the air in.

This is why the modern four valve engine is so different to the older two valve, in its tuning, but that is progress, and we have got to move with it or fall behind.

Harvey.
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Old 12-29-2005, 06:13 AM
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Quote:
Originally Posted by oab_au
I would like to continue to show why, the way we go after power has changed, with the introduction of four valve engines. It will explain why the things that we used, to modify a two valve, and what most hot-up books have taught us to do, no longer are the way.

When we worked a two valve, we used the biggest inlet valve that we could fit in the head. The biggest lift that the valve gear could operate, and the most duration that would allow the engine to start and idle. To assist cylinder filling we used the energy in the inertia of the inlet and exhaust gas. At the end of the inlet stroke, we relied on the inertia of the incoming gas to keep it flowing into the cylinder even though the piston is rising, forcing more gas into the cylinder. We used the inertia of the exhaust gas to create a vacuum in the cylinder, so the inlet gas would be sucked into the cylinder, when the inlet valve open, on valve overlap. To get the engine to operate at high rpms, long duration's were used, inlet valves opened at 60* before TDC, and the exhaust didn't close till after 50* after TDC, valve overlaps in the 100* to 140* were used. Even with all this, it was difficult to get the engine to produce power over 6000 rpm, and still have it with a useable low rpm torque.

The reason for this was in the type of energy we used to perform the cylinder filling. The gas inertia was too slow to allow the filling as the rpm increased. With the coming of the four valve, there was no need for the long duration's, and high valve lifts, as the four valves provided the breathing to run into the 6 to 7000 rpms, without the need for it. As we sort more HP at the higher rpms, we had to use a faster energy source to assist cylinder filling. Sonic pressure waves took the place of the gas inertia. We use a tuned length, resonate inlet tract, that develops negative pressures in the cylinder to draw more gas in.
Instead of a vacuum to start the inlet flowing at valve overlap. We use the sonic pressure waves developed in the exhaust pipe to develop a negative pressure in the cylinders combustion chamber, to deliver an intense start to the sonic pressure wave that will travel the tuned inlet tract, to produce the negative inlet pressures, that will fill the cylinder.

The change from inertia energy, to sonic pressure, has allowed us to rev the engine as hard as we like, as instead of the energy decreasing as the rpm rises, the sonic pressures become more intense as the speed rises. This changes the way we build exhaust systems, as they are the providers of cylinder filling. It is more important to create an intense start to the inlet pressure wave, than to use valve over lap to draw the air in.

This is why the modern four valve engine is so different to the older two valve, in its tuning, but that is progress, and we have got to move with it or fall behind.

Harvey.
Harvey,
Great stuff! Like Tom stated, your discussion in this post is helping me "get my head" around the essentials associated with a DOHC, 4 valve engine! Thanks!
-Bill
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  #8  
Old 12-29-2005, 09:43 AM
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Thnx again Harvey, I grew up in a world of cammed out Chevy 350's and this discussion has helped me understand the differences between a pushrod 2valve and the OHC 4 valve.

Tom
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Old 01-04-2006, 08:17 PM
oab_au oab_au is offline
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Deciding what cam to use.

Deciding what cam to use, is really deciding what the engine needs, to do what we want it to. Of course every one says more power, so we need to find out why it won't do that now. To do that we have to look at the torque curve to see what is happening to the breathing. This shows that the torque,thus the breathing, is taking a nose dive after 4800 rpm. this can be caused by either the inlet area is restricting the air flow, or the inlet valve is not staying open long en ought to feed it as the rpm rises, or any number of things like a restricted exhaust or inlet,etc.

Seeing that it drops quickly after 4800, it won't be the duration, as it would slowly drop off as the rpm rise. So that suggests that the inlet is restricted. We know, thanks to Mychailo, that the pressure in the plenum is almost atmospheric, at full throttle, so it can't be any restriction in the air cleaner or throttle bodys. The inlet ports, can flow enough, thanks to VTSuby, so that leaves the valves themselves. At 37mm they are as big as any that I have seen, in a 4 valve, just leaves the lift.

This was my first assumption, as the designers wanted to keep the engine noninterference, they worked around a low lift. So we increased the lift by 1mm. This should have allowed the breathing to continue building torque as the rpm rises higher. Won't take the torque peak much higher, as the efficiency is very good as it is, but will allow that efficiency to continue higher up the rpm range. This will have the HP increase to a higher peak at a higher rpm.

At this point we do a dyno or a G-Tec run to see if the change we made, is doing what we wanted, (still waiting ) as there is no point in going to more duration, if it is not needed, as these things have side effects that we may be able to do with out, like the exhaust and inlet system resonate length.

The big change starts when we extend the duration. This will move the torque peak higher up the rpm range. This will, necessitate a change to the exhaust, to prevent interference between cylinders, and a change to the resonate length of the exhaust and inlet tract, to move the resonate peak up to where the cams have taken the torque peak.

There can be no doubt that this engine can produce high HP at higher rpms. It can go as high as the rods and pistons will allow it. I feel that it can run to around 7500/8000, with the necessary valve gear to match, but the whole set of things, cam, exhaust, inlet tract, valve gear, has to be done together, you can't just do the cams and expect the thing to work on its own, won't happen.

Just need to get some feed back to see the way ahead.

Harvey.
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Old 01-04-2006, 08:26 PM
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Well the feedback is going to have to wait. I need to do some stock runs, cammed runs and then see if we are making what we want. So that mean I have to order another set of cams for my silver car. In this case I am not going to want to spend another 300-600 dollars on research as I cannot afford to do so. I will try and get the info out there for you but I will more than likely stick with the same setup I had in the 5speed and leave it be. I do not have the money or the time to keeping changing my cams while shooting in the dark. Sorry... I know this is what we need to know to make it more efficient but I cannot do it on my own. Not to mention you will get more consistant #'s out of an auto rather than a 6mt anyway.

Tom
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Old 01-05-2006, 04:56 PM
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Quote:
Originally Posted by TomsSVX
Well the feedback is going to have to wait. I need to do some stock runs, cammed runs and then see if we are making what we want. So that mean I have to order another set of cams for my silver car. In this case I am not going to want to spend another 300-600 dollars on research as I cannot afford to do so. I will try and get the info out there for you but I will more than likely stick with the same setup I had in the 5speed and leave it be. I do not have the money or the time to keeping changing my cams while shooting in the dark. Sorry... I know this is what we need to know to make it more efficient but I cannot do it on my own. Not to mention you will get more consistant #'s out of an auto rather than a 6mt anyway.

Tom
Thats OK Tom, don't worry about it, You did well, you showed it does work in practice, on the strip.

Harvey.
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Old 05-03-2006, 09:41 PM
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The consensus is that the standard valve springs coil bind at about 9mm.

Can lifts of 10mm be obtained with a simple change in springs? Or are there inherent design problems necessitating an entire valve and spring change?

Has anybody measured the diameter of the hydraulic lash adjuster? This will also determine maximum cam lifts before the lobes try to rip off the lash adjusters.

Thanks,
Matt
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Old 05-03-2006, 10:04 PM
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Originally Posted by dynomatt
The consensus is that the standard valve springs coil bind at about 9mm.

Can lifts of 10mm be obtained with a simple change in springs? Or are there inherent design problems necessitating an entire valve and spring change?

Has anybody measured the diameter of the hydraulic lash adjuster? This will also determine maximum cam lifts before the lobes try to rip off the lash adjusters.

Thanks,
Matt
Oh Matt,I still owe you a PM, sorry about that. 10mm is just too much, and is not needed. The engine breathes really well with the 8mm we went to, lost a bit of the bottom end, more would lose more, with little to add to the top.

The cams used really need to be suited to the transmission used, the 3.5:1 auto is best with the 8mm lift and normal duration. If a 6 speed is used, and one is willing to use all the gears I would suggest 8.5mm inlet, 8 mm exhaust, with a duration of about 250/257*along with the necessary springs. Can still run hydraulic lifters, or go to solids.

If the lobes are built up, the lobe can still clear the side of the lifter well, some body checked, I think it was 9mm to touch.?

Harvey.
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Old 05-03-2006, 10:08 PM
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So Harvey, I will soon be in the market for a second set of cams. This time for the silver. You would suggest a 8.5mm lift on the intakes with 250* duration and exhaust with 8mm of lift with 257*? Just making sure this is what you are suggesting

Tom
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Old 05-03-2006, 11:12 PM
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I thought VTSuby's thread mentioned that he got peak flow of 255cfm (which is Australianised to about 150cfm) at about 10.5mm lift?

I'm talking in a competition sense, where, using the 6 speed, and revving the engine to around 7000-7500rpm, I would have thought this lift would have delivered the right power.

No arguments on the duration either (assume that's at .050"?) but the possibility exists to get more with more duration?

Or has all of my other learnings taught me wrong?

And I've read a bunch of the other threads now...but this isn't keeping the automatic, is going for bigger injectors and includes better air intake, exhausts and upping the compression oh and getting an aftermarket ECU.

Matt
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