Cam question

[ekaphoto]

I did a search but never found exactly what I was looking for. I have a 71 240 with a 280 engine. I want to put in a cam. My qusetion is how far can I go (stage I, II, III etc) before it affects drivability on the street or gas mileage. I want to maintain street ability, reliability, and not hurt gas mileage to any extent. The motor has 150-160K miles but is in good shape. I also want to do the occasional autocross event. At this time I am leaning twords the stage II can but want to learn more before buying a one.

[Zs-ondabrain]

STage 2. It's a 470/280 grind and is perfect for streetability and autocrossing. I get great fuel milage and awesome top end (3000 to 6000 is the best range)

Dave.

[jmortensen]

I ran the equivalent of a Stage IV, with stock compression, SU's and 2.5" exhaust. It ran fine on the street, made much more top end power than the smaller cam I had before (which was probably about a Stage I) and mileage was fine; mid 20s on the highway with 5 speed and 3.70s. I bought the cam from a friend who warned me that it was much too big for my motor and that it was going to really suck off the line, be hard to drive in traffic, etc. I'm glad I took a chance because he was flat wrong. That bigger cam made a whole lot more power than the smaller one once you got up in the revs, say above 3000 or 3500, and below that there wasn't too much to distinguish them, aside from a more lopey idle with the bigger cam.

The thing you need to look out for is that when you get above about .480 or .490 lift you run into coil bind on the stock springs and the retainers hit the valve stem seals. Dealing with these issues is well worth the effort.

[ozconnection]

I saw this question in Hybridz but I thought I might add my bit here too.

Be wary of the statement..."Lopey idle".:paranoid: That to me suggests low speed engine inefficiency due to camshaft overlap and intake mixture contamination from residual exhaust gasses. Usually it means a faster idle speed and richer idle mixtures just to keep the thing running. At high idle speeds with weak distributor springs or one removed to alter the distributor advance curve, the advance is kicking in, creating a hunting idle behaviour that is a PITA to sort through.

At the point in the rpm range where maximum engine torque exists, maximum fuel efficiency is very close as well. Having said this, a camshaft like the one suggested to you moves the torque band up the rpm scale so you're left with less low speed torque. You can't have everything!!! Take from here and give to there is what will most commonly happen with those camshafts.

The biggest problem I see with bigger cams is the amount of overlap that gets included along with big valve lift figures and durations. I asked this question in Hybridz a few days ago and asked what would a dedicated performance TURBO grind be like to drive?

From my own investigating, it has merit. Healthy valve lift...yes. Acceptable intake and exhaust durations...yes. Minimal valve overlap....YES. Loss of low speed torque...Not as much as a similar cam used for normally aspirated use. More power..I can't see why not, but probably not as much as the N/A cam of approximately the same size...but who cares? Keep the bottom end smooth and responsive with more kick up top...I'm convinced I'm going to have to try this one for myself.

I'll test my car again soon on the dyno for a new baseline. Then I will go and change over to a Schneider turbo cam I already have and re-dyno the thing. (I already have some dyno graphs posted here and you can see how much torque a stock cam can muster). If all goes to plan, then there should be an increase in the top end without loosing too much down low.

Any thoughts???

Cheers.

[jmortensen]

Be wary of the statement..."Lopey idle".:paranoid: That to me suggests low speed engine inefficiency due to camshaft overlap and intake mixture contamination from residual exhaust gasses. Usually it means a faster idle speed and richer idle mixtures just to keep the thing running. At high idle speeds with weak distributor springs or one removed to alter the distributor advance curve, the advance is kicking in, creating a hunting idle behaviour that is a PITA to sort through.

The fact that the large cam makes low speed running less efficient is what makes high speed running more efficient. The ideas of "contamination" or the other common complaint of "bleeding compression" gives a negative connotation to something that is really a positive when taken as a whole. With my cam, which again was very similar to the Stage IV, I had my idle set at 950, never had a hunting idle issue and the only side effect of the lope was that people would often ask if I had a V8 in my Z.

At the point in the rpm range where maximum engine torque exists, maximum fuel efficiency is very close as well. Having said this, a camshaft like the one suggested to you moves the torque band up the rpm scale so you're left with less low speed torque. You can't have everything!!! Take from here and give to there is what will most commonly happen with those camshafts.

What is the point of adding the cam? For me, the point was to make MORE POWER. When the camshaft was added, the car went faster at autox and at the big track. It was not hard to drive on the street even with a light flywheel and it was not sluggish off the line. What the cam allowed the car to do was HIT the rev limiter instead of TOUCHING the rev limiter. When I later added triples I was able to SLAM the rev limiter instead of HITTING it.

The biggest problem I see with bigger cams is the amount of overlap that gets included along with big valve lift figures and durations. I asked this question in Hybridz a few days ago and asked what would a dedicated performance TURBO grind be like to drive?

From my own investigating, it has merit. Healthy valve lift...yes. Acceptable intake and exhaust durations...yes. Minimal valve overlap....YES. Loss of low speed torque...Not as much as a similar cam used for normally aspirated use. More power..I can't see why not, but probably not as much as the N/A cam of approximately the same size...but who cares? Keep the bottom end smooth and responsive with more kick up top...I'm convinced I'm going to have to try this one for myself.

The first cam that I installed had high lift and low duration (sorry, don't remember specs). It idled nicely and got better mileage than the stock cam with a very modest increase in mid range power. If that's what you're looking for then go for it. Where my cam fell short was in the upper rpm range. In order to make the high end power you need to bleed compression and contaminate the low speed charge to make power, which again, is NOT a bad thing.

I'll test my car again soon on the dyno for a new baseline. Then I will go and change over to a Schneider turbo cam I already have and re-dyno the thing. (I already have some dyno graphs posted here and you can see how much torque a stock cam can muster). If all goes to plan, then there should be an increase in the top end without loosing too much down low.

When it performs under expectations, get a bigger NA cam and dyno that one too and let us know... ;-)

[ozconnection]

I personally have nothing against using a big cam in an engine if that is what is required for the situation. Race, rally, drag etc. You're obviously happy with your choice of cam and thats fine.

In this situation, ekaphoto wanted suggestions about a combination that would work well on the street, suggesting that low speed driving was a priority and fuel efficiency was important. Suggesting a stage 4 cam to someone who is asking for our opinions is a little ambitious IMO.

I think we'll never agree on this since our ideas on what is appropriate are so fundamentally different. What we have provided for this guy are some ideas on what he can go out and try on his ride and perhaps which direction to take. Good luck ekaphoto, let us know how you get on with your project.

Jon, I have posted dyno graphs on this web site for you all to see. Read what I have written about them and you might begin to understand the reasons why I have what I have under my hood. It's the most appropriate combination for MY situation.

Cheers.

[ekaphoto]

Thanks for the input everyone. Ill let everyone know the results of my handy work when finished.

[wishihadaz]

I want to maintain street ability, reliability, and not hurt gas mileage to any extent.

We all know that performance comes at a price.

To make significant gains at no sacrifice in gas mileage is a contradiction.

I personally tend to lean toward Jon's opinion and from my own experience.

You did say you wanted to auto-x, right?

Ask yourself, do I just want to auto-x or do I want to enjoy it?

Maybe that means different things for different people.

As for a stage IV cam's streetability, I can vouch for that too.

My former set-up was a 300/.500" with no other internal mods to the 2.4L other than competition valve springs. I did use Weber DCOE40's, 6-into-1 header and MSA's twice pipes. The performance gains far outweighed the sacrifice in gas mileage and it was "streetable".

My current set-up is an Isky L-490 (290/.490") in a 2.8L. I'll detail the extras in another upcoming post.

You really don't notice gas mileage under normal driving conditions anyway, it's only when you put your foot down.

Don't forget the cam is going to be the same price so don't disappoint yourself by being too conservative.

[ozconnection]

I decided to attach a dyno sheet of a run I made several years ago, comparing the stock cam I had in the engine with a modified, aftermarket grind from Ivan Tighe 462C spec.

No other changes were made other than to instal the camshaft correctly. A/F ratio's were tested and deemed to be acceptable and a solid basis for comparison.

Yes, the rpm ceiling was higher, up to 7200rpm, but what about the rest of the power and torque bands?

I may have been 'put off' by this venture but I have the dyno sheet to prove the worth of 'changing the camshaft'. Would you recommend a bigger cam to someone if you had results that looked like this???

http://tighecams.com.au/profiles3/nissanlseries.htm

[jmortensen]

I don't honestly know how to read that dyno printout. It doesn't look like the ones with SAE hp and torque that I'm used to seeing. I'll tell you this though; for my money, I want the peak hp to come about 1000 rpm before the redline of the engine. Getting a camshaft that peaks at 7000 rpm with a 7000 rpm redline doesn't do you very much good, nor does using one that peaks at 5000 rpm. And for my own project I've repeatedly made the error of going too small, while "experts" told me that I was going to regret buying something so big.