Calling all cam gurus - I have questions

[garmo]

I am trying to decide what cams I want to run in a 3.0l rebuild that I will embark upon some time soon I hope.

Referring to the chart in the 3rd post of the following link:

help with cam profiles


which shows several cam profiles, I entered these into an Excel worksheet so that I could do some analysis. I took the Exhaust lift and divided it by the intake lift to get a % and did the same thing of the exhaust duration just so I could see the differences between cams. Maybe this is a waste of time, but I was curious. What jumps out at me is that the S cams have the lowest percentages of both of these measures than any of the other cams. Is this significant? The S cams also have the shortest exhaust lift and next to shortest intake lift as well. Yet it seems to be one of the more popular profiles - why?

I know all the factors of each camshaft are important and provide certain characteristics of engine performance. I have heard a great many good things about the S cams, but wonder, given what I have seen in my analysis, what is the best way to choose a cam?

In my younger days (small block chevy hotrods) intake lift seemed to be the first and only thing anyone talked about when talking about cams. I have seen some current cam makers say that overlap is the best way to determine a profile.

Does anyone know of a chart that shows the performance specs of a given cam profile? My engine will be used mostly on the street for some rather spirited driving with maybe a few auto cross events here and there and a DE once in a while. A nice set of Webers will sit on top and I will be deciding on p/c too.

The more I try to learn about cams, the harder it becomes to make a decision - I think because I have not learned enough yet or I am analyzing unimportant information. Given the carbs, is cam choice the next logical step?

If so - do you start with one characteristic of a profile and then move on to a second and a third?

It seems like there would be some sort of combined measure of the characteristics that would "grade" a profile and produce the kind of information I am looking for. Does that exist?

[larrym]

S cams will move you up the rpm curve & you won't be happy at street & AX speeds

discussed at length all over these forums - try searching the engine rebuilding forum

read everything on RennsportSystems site, search for user "camgrinder" 's posts & DRC cams site

i currently run a 8.5CR motor with webers & solex cams, (which, like S cams, were a "hot ticket opinion ") 10 yrs a go when i put 'em in - turns out the opinionators were wrong - they were inapproriate - don't "come on" until 2800 -

- then call John at DRC & he'll walk ya thru the best choices - he just did that for me last Friday

he knows "what works with which" - something you don't get from all the web-opinionators

solution - a regrind for better street perfortmnace - only $345

.

[RWebb]

what induction system will be used?

[garmo]

Larrym - thanks for your input. I do know that cam choice to a large degree is subjective. I have a friend who ran a 2.4 with S cams and did not feel low end performance suffered and really loved the high rpm dynamics. I have searched a lot and have not found the answers to the questions about the relationship of exhaust stats to intake stats. As much as I want to decide on the right cams for me, I am trying to understand the subtleties of cam lobe specs and the relation between intake and exhaust that I have not yet been able to find.

RWebb- I am going to start with IDA40 Webers.

[Reiver]

Where do you spend most of your driving time...what rpm range. It is not nec how much HP/T but where it makes that HP/T.
Many fixate on overall HP numbers and are not happy streeting the car because the figures are for WOT or nearly that.
Be conservative unless it is for the track.
You want low end grunt with a nice top end...not the other way round. BTW, not only will 99% of folks be happier with a less radical cam but your valve train will be too.

[RWebb]

ok, you are not limited by CIS then

you might look thru Wayne's engine book for many examples of proven combos that work well - that will relieve you from studying the subtleties of cam lobe specs and the relation between intake and exhaust - not to mention that newer designs can alter ramp angles...

3.2L heads breathe real well right out of the box - 3L heads not as good w/o some massage

"it has all been done before
and it will all be done again"

[jpnovak]

Comparing lift or duration ratios will not give you much useful information.

I suggest you start reading here.

Camshaft Selection -- First Draft

A few pointers about picking camshafts.

1. What is your desired rpm range? street (low rpm), mix (mid rpm), or track (high)
2. rpm range is dictated by exhaust duration
3. match lift to the head flow. There are numbers on the board for stock heads.
4. cam overlap helps determine how "peaky" the behaviour is. Narrow lobe centers have more Kick at a given rpm, wide lobe centers have a more broad torque curve
5. Careful picking a cam by lift - you have to make sure it clears your pistons. Stock CIS pistons from a 3.0 do not allow for much lift (limited by the exhaust side
6. With carbs you will want a 98 -102 lobe center to maximize their function.


Happy reading.