Camshafts for DCOE cams

So here is what I found on the inglese website.

http://www.compperformancegroupstor...N&Product_Code=12-490-8&Category_Code=ChevCam

Looking at the cams for their weber getups they have HUGE lobe seperations.

So I was thinking. Instead of replacing my cylinderheads I can use the HUGE lobe seperations to reduce the dynamic compression of the motor, and I can hopefully cope with the fact that I would 11.5:1 compression.

So here is what I am thinking. 288/288 and a 116 LSA and 4 degrees of advance? Put that on top of my 396 with flat tops and I would have 11.5:1 compression.

If I am going to keep my heads, I will probably take them down to the local circle track shop for new seats, and guides, maybe bigger valves.

The dynamic compression ratio would in theory be 8.3:1, but I am not entirely bought into the concept as other than a rough order magnitude thing.

Yes, big seperation to minimize overlap. Otherwise you will get serious reversion and without a plenum to act as a buffer it will spit fuel out the carbs. All IR systems have that issue.

Instead of staring blind on the separation angle, compare the actual overlap, and not just the degrees but the actual lobe overlap area. That's what's real important, especially if you want to compare apples to apples.

272/276 and 115lsa is about 44 degrees of overlap.

Well I guess I could ask someone, at a cam company. Probably easier.

The big block cams all have the same 115 LSA and durations in the 280s.

There is another approach to this, with roller cams that is. Regarding overlap and spitback what counts is total overlap, so not just overlap at the .05 figure. To reduce this you could use a more radical cam that opens a lot faster, some cam with around 30° major intensity. That way you can keep your total duration at .05 which makes the same power but reduce your total duration...

Exactly, that's why I advised him not to go blind on the lobe seperation, it's just an indicator but not a measure of true overlap. That's where the lobe profile comes in.

Remember that these cams are not always available off the shelf. It may require a custom cam and the associated investment. At least that is what I did.
Don't ask me for the results as i still have to install the new cam etc.

I will probably give cammotion and compcams a call when i get teh money for a new cam. Custom cams arent that much more expensive than an off the shelf cam.

You could start from a given cam and calculate the 30-32° mayor intensity from there. If you have the knowledge to do so any way. That's the way I did it and using DCR in the calculation.

Probably the companies have no way in determining what exactly a dcoe needs. Not that I exactly know what it needs. There will always be some trial and error and trade off's. If you know your rpm-band try to find out what you need in terms of open duration and then try to make the overlap not to big. I suggest you keep lca's in between 112-115°

What is the 30-32 mayor intensity?

difference in degrees between the seat figure and the .05" figure. But be cautious with different kind of cams (hydraulic, flat tappet, roller) since they employ different seat numbers and you cannot compare them outright. Anyway a major intensity of 30-32° is considered by far to radical for a flat tappet and certainly for a hydraulic flat tappet. Don't know about a hydraulic roller. Do a search on the net for this. I also suggest you read a good book on camshafts like the one from D. Vizard.

Mr. Vizzard has a book on cams?

Camshaft and Valvetrains by D. Vizard.

Powerpro series from Motorbooks International.

ISBN 0-87938-595-2

I found it very good and it explained everything in detail. After that you should be able to decide the basic numbers for a custom cam and from that your cam company can grind a lobe with their expertise.

Mr. Vizard has some very strong opinions about camshafts that arent really appreciated by everybody, based upon the articles I have read.

I am really thinking I need something at least 230 at .05 on the intake.

I agree, but at least he gives a good reasoning in detail behind everything and that is not what most do. But you can always go you own directions or crossreference certain things with what other say and form your own opinions.

I have allways stayed away from cam designs, and just go with the KISS principal....lemme know operating rpm, torque, and total lift....

all the rest is a black art.....highest comp ratio I ever had is this L98 at 10.5 to one.....well maybe back WHEN, but I don't remember the numbers all that well....iron headed Pontiacs and all....probably only 10-1....

:gurney::banghead::clobbered:

True Gene, but sometimes, you build and engine that you tuned and changed so much that it doesn't resemble the original or its intended use anymore and that you need to change the cam. Otherwise you would end up with a combo that would not be working well. Camshaft manufacturers only offer cams for a type of engine they know have got a big power potential. ITB engines are not one of these. I had a second problem and that was that my basic engine design was in between a full out circle track and high performance street engine. I could not start using a full out race cam without getting into problems. Figuring out my own cam was the only option.

It looks like black art, but once you know what all these numbers are meaning and how they interact, you can basically give the cam company a very good idea about what you need. The will design the lobe based on that and what they consider to be working in practice.

Could be that I've gotten it all wrong. Time will tell. I've got my street roller as a backup if it does.

In any case I am going to just call cammotion.