sweetC5

Anyone run a cam with about -1 overlap? Can you post a vid if you do. I was wondering how the idle sounds. My exhaust is 2" tube headers and 1 chambers with a H pipe so my exhaust is pretty loud and should help make any cam sound good. Just want to get an idea thanks.

00pooterSS

iTrader: (40)

Curiousity is killing me here, why would you ever want a cam with no overlap? I assume you are asking about negative 1 degree overlap correct?

If so then it will sound just as mild or more mild that the stock cam, the chopping sound from a big cam is from overlap, overlap is also a big part of how cams increase horsepower. If you are boosting the motor then less overlap is needed since scavenging is not as crucial.

sweetC5

The cam is 217/228 112 , I am a bit confused on how to figure it out but from what I have seen that comes to -1.5 This is a new lunati grind for the ls3. Tech said it would have a bit of a coppy idle but nothing crazy.

217+228 /2 112x2 then you take 222.5-224 to get over lap? Or am I doing this wrong?

If you take a 224/224 on 112 you get 0 for over lap, that cam sounds pretty tuff, so I figure -1 with my exhaust should sound pretty good.

00pooterSS

iTrader: (40)

I would call and ask them about the overlap, I don't think that formula is necessarily accurate. I honestly can't say 100% because the actual way of measuring is knowing the valve opening and closing events in degree's. I think that the formula is more of a generic estimator, but i'm not 100%.

A little overlap is good for scavenging and helping fill the cylinder with more air by taking advantage of the velocity of airflow. With the right amount you can achieve over 100% VE, that is basically having a little bit of boost! Also more overlap gives a choppier idle. Without the exact specs on your cam I can't say how much overlap it does or does not have..

That is my understanding after the research I have done. I will look around a little and see if I come up with anything more helpful.

sweetC5

Thanks man, I figure that was a generic way of figuring it out. Cams can be the same at 05 but different advertised duration so. This cam is made for ls3 heads and lunati has done me good in the past, I just dont want a stock sounding car after I put a cam in it even though they told me it wont.

00pooterSS

iTrader: (40)

Found a neat video. But it doesn't help with the calculation.

Thought you might find it interesting to watch.

http://www.youtube.com/watch?v=Pa3mKXN-tIY

00pooterSS

iTrader: (40)

Well it may be near 0* overlap. It really is a pretty small cam. If you want it to chop hard, and make more power I would go with more duration. You can go quite a bit bigger and still have great drive-ability.

sweetC5

That was pretty cool, so basicly seems every cam has to have some kind of overlap.

speedtigger

iTrader: (16)

I had the Comp XR275H12 (222/224 @.050"). It had -1 degree overlap. It idled smooth in my car. I have seen others claim that they had a chop in their idle with a 224, but not in my car.

sweetC5

The thing is were I want the power, I am doing a small cam because I drive it everday and the weight of this car with stock gears. If you look at the ls3 cam test the GM hot cam was a winner till about 5 grand, it was making killer power and torque right were I want it. The specs on that cam are VERY simular 218/228 on a 112 and that cam sounds tuff too. This lunati cam is basicly the same at 05 with 217/228 112 but with more lift so it should do even better and has faster lobes.

If you look at the bigger cams they dont start doing anything impressive till high rpms and that is not what I am looking for. A guy I know has a 231/239 in his camaro and it drives good but it feels like stock power untill you get up in the revs. I feel its miss matched for this car without a gear. I just wish I could figure out what it would sound like

00pooterSS

iTrader: (40)

Generally speaking you could say that. Cams get very very technical and complicated. But overlap is a good thing when it comes to making power. As long as it is not too little not too much.

sweetC5

You dont a video of it do you? What do you have for exhaust, I am thinking my 1 chamber flowmasters would help. Also what was your idle set at? Thanks

I have actually heard that cam in a few cars that sounded good on youtube, maybe its in the tune IDK
Another camaro guy I know has a decent size cam in his camaro but with quite exhaust, you cant even tell that much.

5 Liter Eater

iTrader: (5)

IMO That formula of averaging the duration and subtracting twice the LSA is a good one to get a SWAG for the overlap. It's not 100% accurate by any means but it gets you in the ballpark. Withoug knowing the ICL and LSA to determine the actual valve events its the only way.

If you're only concerned with sound I would not expect that cam to sound much different than stock. If you want it to sound nastier, lower the idle.

speedtigger

iTrader: (16)

My car has a carb, so being to creative on the idle tuning is not a possibility. My idle was set at 900 in park and 750 in gear.

sweetC5

My concern is really how the power comes in, thats why I am looking at these smaller cams. I just hate to cam a car and it sound like stock, this is my first cammed LS engine so I have some learing to do. My old school first gen engines were so easy, even little cams sound good in them. Lunati said I would definitly hear the cam in it, just nothing like a old big block he said. Right now my idle with the stock cam is very quite compared to what I am used to, do these smaller cams at lest make the car louder at idle?

speedtigger

iTrader: (16)

Oh, well that makes what you want much more clear to me. Let me tell you about my recent cam change then. I had the 222/224 on 112 LSA comp cam that idled smooth. I switched to a 226/234 on 110 LSA on 109 ICL. It now has a nice lope to it and actually 60 foots quicker than the old 222/224. I have a 2800 converter and my 60' times are 1.67.

Here is an idle clip:

http://www.youtube.com/watch?v=54cOWJ8UtB8

sweetC5

Ok, so maybe a 650 idle would have sounded better. How did the car pull? This cam says fair idle, lots of mid range torque and top end power from 1800-6400. That is pretty much just what I am looking for. No cam card though, the cam is brand new and they dont have it listed on there site with all the specs.

sweetC5

Thanks that sounds real good! That is actually a little more lop then I need, did the old cam not sound cammed at all? You dont have a vid of the old cam do you?

quik95lt1

iTrader: (7)

many ways to calculate it..........

take ur IVO and you're EVC numbers off your card and add them.....make sure they are the advertised numbers......this is you're actual overlap period im assuming and looking at the above post you calculated using your .050 duration numbers which is how you got -1......i can assure you that is not your ACTUAL overlap lol....even the most mild cams in stock pickup trucks have 10* or so of overlap......

another way to do it if you dont have that info is with your ADVERTISED (.004 lift) duration numbers.....formula as follows...i will use a 286/294 112LSA cam for example (with a somewhat mild lobe translates to a 224/236 @.050 ish cam)

1. Add your advertised intake and exhaust durations together....
286+294 = 580

2. Divide by 4
580/4= 145

3. Subtract your LSA

145-112= 33*

4. Multiply by 2.....

33*2= 66*

So from the .004 Intake Open point to the .004 Exhaust from closed point there is 66*.....which is 66* of time where there is in theory a non-sealed chamber due to both valves being slightly open.....

speedtigger

iTrader: (16)

The old cam idled dead smooth once the car warmed up.