Need some professional advice on cams

[TomsSVX]

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

[oab_au]

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.

[oab_au]

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.

[SVXRide]

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

[TomsSVX]

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

[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.

[Trevor]

Originally Posted by TomsSVX

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

Tom, it is apparant that you know exactly where you are going and where you have come from.

Overlap is the important ingrediant. By grinding only the back of a cam, as an economically viable mod., lift is increased but the important factor is the associated extension of the opening time. Good to see that you have built up your cams with hard welding

There is no point in increasing the lift beyond a point whereby the open area of the valve exceeds the port area. A high lift increases mechanical stresses in a big way and involves further problems relative to valve bounce. Calculate the port area - OA area less the obstruction of the valve stem. The open valve effective area - The overall side surface area of a cylinder comprising diameter as above and hight as per valve lift.

You are not, on a basis of time and cost, able to experiment to the extent necessary to obtain an absolutely proven outcome, but with applied common sense you can be VERY close. Look up as many valve timing figures as you can, particularly performance related. In the back of your mind store all the characteristics and requirements of the cars involved. Compare, think, make a decission and when it gives results, as it will, rejoice with satisfaction, knowing you did it your way.

Believe me, alleged high tech. advice will not do more for you !

[Trevor]

Tom,

[For the first time in the years of using this service, (Special thanks to Chris and his helpers) contact has been delayed, but no moans from this part of downunder. As a result this post may be out in respect of time frame.]

This in effect a PPS to my previous post, so that you should also read it in conjunction. I appreciate that you started with this thread in the hope of obtaining positive confirmation that you had made a correct decision regarding your cam mods. and therefore make further comments, which I assure you, are the whole truth and NOT BS.

A few minutes ago I decided to have a look at the manufacturers figures in print. My immediate reaction was - increase the inlet opening and make inlet and exhaust near equal, which is the classic arrangement. My second thoughts back this up. For the fun of it I have not checked back in the thread, but I have a sneaking suspicion that you altered only the inlet cams and figure of eight was mentioned.

The resulting timing is still very mild, but the large valve area has the effect of increasing relative overlap as you will be aware. If we do both happen to think alike, two idiots must make a plus !

[SVXRide]

Trevor,
I've been talking with Tom and others on the Network about the cams in our engines, and it seems like we've arrived at the following:

1. The "welded&ground" intakes giving us 240 deg and 8mm lift do increase mid and upper rpm performance at the expense of a little low end (really not an issue with MT or 4.11/4.44 AT)

2. Looking for an "improved" profile for our exhaust cams has been a futile effort to date

3. Using our stock exhaust cam profile for "welded&ground" intakes is still open to discussion (i.e. additional 4 degress and I believe the ramps might be different than the profile Delta Cams is using for the 240 deg/8mm mod)

Thoughts?

-Bill

[Trevor]

Originally Posted by SVXRide

Trevor,
I've been talking with Tom and others on the Network about the cams in our engines, and it seems like we've arrived at the following:

1. The "welded&ground" intakes giving us 240 deg and 8mm lift do increase mid and upper rpm performance at the expense of a little low end (really not an issue with MT or 4.11/4.44 AT)

2. Looking for an "improved" profile for our exhaust cams has been a futile effort to date

3. Using our stock exhaust cam profile for "welded&ground" intakes is still open to discussion (i.e. additional 4 degress and I believe the ramps might be different than the profile Delta Cams is using for the 240 deg/8mm mod)

Thoughts?

-Bill

Bill, some more thoughts to add to my previous brain children. More importantly, simply to mix with yours and your associates ideas.

Please advise the BTDC and ABDC figures so that I know where the inlet opening period sits in relation to TDC and I will set loose another storm.

Cam grinders can or can not be a good source of knowlege. Some are simply expert machinists. Others take a keen interest and sift results after getting feedback from customers. But at the risk of labouring a point, beware of the BS artist!

Best of luck with the project, Trevor *<)

[TomsSVX]

Sorry I haven't really been around the past couple days, had many things taking up my time and mostly work. I have a full 14hr day ahead of me but I have this week off. Trevor, there is a ton more info on the cams we selected in a thread Chiketkd had started. It was a quick how-to for a mild N/A build. He has all the specs for the cams in there. If I can find my data sheet from my last set I will post it. Sorry for the delay, just super busy

Tom