how much overlap to keep a semi-stealth idle?
how much overlap to keep a semi-stealth idle? Wondering if some of you experienced peeps could give me some input on overlap and idle quality. I'm doing cam research for a LS6 with shorty headers and a Z06 exhaust. Looking to tighten up the LSA several degrees to get a crisp and thick midrange, and add a little duration to get a few HP up top. Just not sure how far you can go on the overlap and still maintain a reasonably smooth idle and not take a hit on fuel mileage. I have a comp 218-224 on a 114 LSA in a 383 LT1 that is just a little choppier than what I am looking for. If I remember right it has -3.5 degrees of overlap (at .050" lift). The stock Z06 (2004 model) is somewhere around -11 on overlap. I'm considering something like a 212/216 on a 113 LSA for about -6 on overlap. Just haven't run anything in this overlap range. Anybody run a cam with similar overlap? If so I'd really appreciate some info on how smooth it idled, what RPM you used at idle and how it affected your fuel efficiency. Thanks for any help here, Michael.
Last edited by grammerman; Oct 5, 2009 at 12:27 AM. Reason: typo
yeah that cam and the afr heads. put down good numbers. but it sounds like tuning issue maybe. my cam tr226 drives fine even though it has a shitty tune by a sponsor on here. but yeah ull be fine with the cheatr n afrs
You should be able to get that cam to idle pretty close to stock. Add some timing to smooth it out and dial in your over and underspeed spark table. Raise your idle up a bit and even tinkering with your injection timing can tame the idle.
Thanks for the input. Not sure from the replies if any of you have actually used that cam in your own ride? Definitely looking for direct feedback about idle quality and fuel efficiency from peeps that have hands on experience (ran and/or tuned a cam with similar overlap). Regards, Michael
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I have ran a 220/220 114+4..which is ~-8 overlap. While idle quality is 'good', if what you are asking did it sound stock..not really. Yes, it had more of a muted lope, but with a catback and headers, it still had a small lope.
Obviously compared to the +10 cam overlap I now run it seemed mild, but it did not sound perfectly stock. I mean it was smooth, but even it required tuning.
As far as gas mileage, in all honesty the idle characteristics were not such that it contributed to a loss in gas mileage. Especially if you are running closed-loop. It will normally get trimmed to ~14.7 AFR anyway. Any cam that pushes your usable RPM past stock will use more fuel if you push your right foot down! But for normal day to day driving I think I somehow even picked up another 1-2 mpg on highway (multiple mods simultaneously ..so no total claim there).
I don't know if this answer totally addresses your question. But from experience only a stock cam or very close to stock will sound stock. With the caveat if you are running headers and a good exhaust. If you are keeping stock manifolds, maybe you can not notice.
Good luck.
..WeathermanShawn..
Obviously compared to the +10 cam overlap I now run it seemed mild, but it did not sound perfectly stock. I mean it was smooth, but even it required tuning.
As far as gas mileage, in all honesty the idle characteristics were not such that it contributed to a loss in gas mileage. Especially if you are running closed-loop. It will normally get trimmed to ~14.7 AFR anyway. Any cam that pushes your usable RPM past stock will use more fuel if you push your right foot down! But for normal day to day driving I think I somehow even picked up another 1-2 mpg on highway (multiple mods simultaneously ..so no total claim there).
I don't know if this answer totally addresses your question. But from experience only a stock cam or very close to stock will sound stock. With the caveat if you are running headers and a good exhaust. If you are keeping stock manifolds, maybe you can not notice.
Good luck.
..WeathermanShawn..
Thanks very much for the detailed reply 
Wouldn't your cam be -4 on overlap with 4 degrees of advance ground in? If so that's pretty close to the 218/224 comp cam with -3.5 overlap I have in the LT1. Definitely won't pass for stock but a fairly mild chop in a 383. Really appreciate the feedback on your highway mileage. Any other first hand experience is welcomed.
Michael
Wouldn't your cam be -4 on overlap with 4 degrees of advance ground in? If so that's pretty close to the 218/224 comp cam with -3.5 overlap I have in the LT1. Definitely won't pass for stock but a fairly mild chop in a 383. Really appreciate the feedback on your highway mileage. Any other first hand experience is welcomed. Michael
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Well, someone please double-check my math/program. I am using the DCR Calculator by Pat Kelly. I just popped in the numbers pretty quick, and came up with the same numbers on repeated calculations. (for a LS1).
The amount of advance does not change the overlap. It does change the IVC and EVO, but it takes a manipulation of the duration/exhaust and/or LSA to change the overlap.
One can always make a mistake, so unless I am inputting the wrong numbers..I keep coming up with a -8 overlap. I originally got it as a smog cam, so I know I was trying to keep the overlap at -6 or less.
Let me know if I made a mistake..Hopefully the description of it's manners made sense.
..WeathermanShawn..
The amount of advance does not change the overlap. It does change the IVC and EVO, but it takes a manipulation of the duration/exhaust and/or LSA to change the overlap.
One can always make a mistake, so unless I am inputting the wrong numbers..I keep coming up with a -8 overlap. I originally got it as a smog cam, so I know I was trying to keep the overlap at -6 or less.
Let me know if I made a mistake..Hopefully the description of it's manners made sense.
..WeathermanShawn..
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The formula I have always used is average duration - two times lobe separation angle ([intake + exhaust] /2) - (LSA x 2).
[(218 + 224) /2] - [114 x 2] = 221 - 228 = -7
[(204 + 218) /2] - [117 x 2] = 211 - 234 = -23
[(212 + 216) /2] - [113 x 2] = 214 - 226 = -12
and Weatherman's calc's
[(220 + 220) /2] - [114 x 2] = 220 - 228 = -8
Shawn is correct, advance or retard has no effect on overlap. Hope this helps!
I see where the difference is Being a little rusty on this cam math I was calculating overlap in degrees of cam rotation vs. the standard numbers calculated in degrees of crankshaft rotation. Makes 'em half as big the way I'm doing it. Valid when using only my own overlap calcs from different cams to compare idle quality, but non-standard no doubt. Thanks for clearing that up 
We were on the same page about the +4 being 4 degrees of advance ground in, this doesn't affect the lobe sepearation angle.
Some more reports on cams near the "ahem" corrected overlap range of -12 to -16 at .050" would be awesome. Later dudes, Michael.
Being a little rusty on this cam math I was calculating overlap in degrees of cam rotation vs. the standard numbers calculated in degrees of crankshaft rotation. Makes 'em half as big the way I'm doing it. Valid when using only my own overlap calcs from different cams to compare idle quality, but non-standard no doubt. Thanks for clearing that up We were on the same page about the +4 being 4 degrees of advance ground in, this doesn't affect the lobe sepearation angle.Some more reports on cams near the "ahem" corrected overlap range of -12 to -16 at .050" would be awesome. Later dudes, Michael.
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Thanks Hammer!
I was beginning to doubt myself there! To the OP..As Hammer-Time indicated, doing the calculations can be learned fairly easy.
Quite honestly, even with the stock cam, I could always hear a slight lope when I added headers and a catback. Do you absolutely want stealth? Or are you just trying to maximize you power band?
As a fan of cam lope, I am just trying to understand what you are after..
That 220/220 cam was not bad. While I really like where I am at now, a 224/224 to a 228/228 112 +2 in general is a winner.
If you go too small, you willl never be able to rev past 6000 Rpm's. Let us know what our goals and combinations are, and I am sure we will get you close!
Good luck.
..WeathermanShawn..
I was beginning to doubt myself there! To the OP..As Hammer-Time indicated, doing the calculations can be learned fairly easy.
Quite honestly, even with the stock cam, I could always hear a slight lope when I added headers and a catback. Do you absolutely want stealth? Or are you just trying to maximize you power band?
As a fan of cam lope, I am just trying to understand what you are after..
That 220/220 cam was not bad. While I really like where I am at now, a 224/224 to a 228/228 112 +2 in general is a winner.
If you go too small, you willl never be able to rev past 6000 Rpm's. Let us know what our goals and combinations are, and I am sure we will get you close!
Good luck.
..WeathermanShawn..
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Thanks Hammer!
I was beginning to doubt myself there! To the OP..As Hammer-Time indicated, doing the calculations can be learned fairly easy.
Quite honestly, even with the stock cam, I could always hear a slight lope when I added headers and a catback. Do you absolutely want stealth? Or are you just trying to maximize you power band?
As a fan of cam lope, I am just trying to understand what you are after..
That 220/220 cam was not bad. While I really like where I am at now, a 224/224 to a 228/228 112 +2 in general is a winner.
If you go too small, you will never be able to rev past 6000 Rpm's. Let us know what our goals and combinations are, and I am sure we will get you close!
Good luck.
..WeathermanShawn..
I was beginning to doubt myself there! To the OP..As Hammer-Time indicated, doing the calculations can be learned fairly easy.
Quite honestly, even with the stock cam, I could always hear a slight lope when I added headers and a catback. Do you absolutely want stealth? Or are you just trying to maximize you power band?
As a fan of cam lope, I am just trying to understand what you are after..
That 220/220 cam was not bad. While I really like where I am at now, a 224/224 to a 228/228 112 +2 in general is a winner.
If you go too small, you will never be able to rev past 6000 Rpm's. Let us know what our goals and combinations are, and I am sure we will get you close!
Good luck.
..WeathermanShawn..
Just looking for first hand reports on mild overlap cams and how they idled and if mileage was affected. The goal is increased midrange throttle response without losing any peak hp. Gaining a few at peak would be fine too With about 440 hp with mods it's already plenty fast to break ugly on the occasional Mustang or dispatch traffic on the Interstate. Thanks for the reports. Any others are appreciated, Michael.
With about 440 hp with mods it's already plenty fast to break ugly on the occasional Mustang or dispatch traffic on the Interstate. Thanks for the reports. Any others are appreciated, Michael. 
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you can get all the usable street perfomance you can handle AND have an idle that is hard to pick up without a lot of extra idle related tuning required, the key is to get one with 0* overlap.
listen to this, is this too much of an extreme loap? Don't be fooled it IS an extreme cam!
DMH_oval_cutouts.wmv
(.614/.607) custom ground with radical lobes to my own recipe, stock heads, super extreme springs that were a SOB to install WITH the special tool, slightly different cromoly pushrods. I gave up a touch of top end power and moved the power curve down to where I can use it on the street and have fun once in a while on the track. I couldn't find what I wanted off the shelf, so don't be afraid to get one cut special for what you want instead of something the speed shops tell you that you want. There are a few guys that are on these forums and work for the sponsers that will take the time to help you if you know what you want your car to do and have done some homework before you call and bug them. I got mine through Thunder but I could have ordered it direct from comp but since they spent the time on the phone and through emails I special ordered it thru them.
just my two cents, you don't have to find the "closest" one to what you want off of the shelf and the thing that was kinda surprising is that mine was about the same price as all those other "hot" cams, I just had to wait a little longer.
listen to this, is this too much of an extreme loap? Don't be fooled it IS an extreme cam!
DMH_oval_cutouts.wmv
(.614/.607) custom ground with radical lobes to my own recipe, stock heads, super extreme springs that were a SOB to install WITH the special tool, slightly different cromoly pushrods. I gave up a touch of top end power and moved the power curve down to where I can use it on the street and have fun once in a while on the track. I couldn't find what I wanted off the shelf, so don't be afraid to get one cut special for what you want instead of something the speed shops tell you that you want. There are a few guys that are on these forums and work for the sponsers that will take the time to help you if you know what you want your car to do and have done some homework before you call and bug them. I got mine through Thunder but I could have ordered it direct from comp but since they spent the time on the phone and through emails I special ordered it thru them.
just my two cents, you don't have to find the "closest" one to what you want off of the shelf and the thing that was kinda surprising is that mine was about the same price as all those other "hot" cams, I just had to wait a little longer.
