Valve Overlap Discussion/Talk
Originally Posted by Billiumss
JRP, what cam are you running now with +15.1 degrees of overlap?
I know ramp rates can change overlap some but say you have a Comp Cams 224 cam and you have a TR 224 cam on the same LSA, how much of a overlap difference?
Are there pics of the different lobes somewhere on the net? (side view) Has anyone every done a overlay of different lobe designs?
Will shops tell you all the specs of a cam if you ask?
Does anyone have the 'full specs' on the MTI Stealth II cam? This might be my next cam.
I know ramp rates can change overlap some but say you have a Comp Cams 224 cam and you have a TR 224 cam on the same LSA, how much of a overlap difference?
Are there pics of the different lobes somewhere on the net? (side view) Has anyone every done a overlay of different lobe designs?
Will shops tell you all the specs of a cam if you ask?
Does anyone have the 'full specs' on the MTI Stealth II cam? This might be my next cam.
spec'd out a tad bigger on the cam doctor
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From: BFE
Originally Posted by DAPSUPRSLO
Do you mean a lobe intensity of 49 or 53, i.e. the difference between the advertised duration and at .050" duration?
in the case of Stealth II (273-224)int= 49 and (269-220)exh= 49
so both intake and exhaust lobes are true XE-R (since this is a Comp Cam grind)
So what makes more power: overlap or duration? Between these two cams, what would the power differences. 220/220 110lsa vs. 224/224 112lsa? I understand that overlap is the same only at .050, but then what point of reference is best to compare overlap, and is there a rule of thumb or ratio to get the same amount of power with less duration but have more overlap?
Last edited by Trojan T/A; Nov 16, 2004 at 10:51 PM.
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From: BFE
Originally Posted by Trojan T/A
So what makes more power: overlap or duration? Between these two cams, what would the power differences. 220/220 110lsa vs. 224/224 112lsa? I understand that overlap is the same only at .050, but then what point of reference is best to compare overlap, and is there a rule of thumb or ratio to get the same amount of power with less duration but have more overlap?
Duration and lobe separation determine your overlap so you really just can't ask the question which makes more power. Having a shorter duration cam with a lower lsa (in attempt to get more overlap) will make more low end power and not carry it very high in the rpm band. Ex. my old 224/224 106icl 110lsa cam made 405rwhp/406rwtq and was making 380 rwtq in the 2800 and up range.
A longer duration cam with the same amount of overlap of the theoretical above mentioned cam will make the same peak power but make it over a longer range. Overlap determines peak power, valve events caused by playing with your intake centerline and duration determine where it occurs and how long it occurs for.
A longer duration cam with the same amount of overlap of the theoretical above mentioned cam will make the same peak power but make it over a longer range. Overlap determines peak power, valve events caused by playing with your intake centerline and duration determine where it occurs and how long it occurs for.
So, for the average guy with a street car, having some negative overlap and a higher LSA will make more average TQ down low, right?
I'm thinking of these cam specs:
I - 226 E - 222 116 LSA
That should give me -8 degrees of overlap. It should lope a tad less than a TR 224 114lsa cam and be a tad easier to tune.
I'm thinking of these cam specs:
I - 226 E - 222 116 LSA
That should give me -8 degrees of overlap. It should lope a tad less than a TR 224 114lsa cam and be a tad easier to tune.
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Joined: Mar 2004
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From: BFE
Originally Posted by Billiumss
So, for the average guy with a street car, having some negative overlap and a higher LSA will make more average TQ down low, right?
I'm thinking of these cam specs:
I - 226 E - 222 116 LSA
That should give me -8 degrees of overlap. It should lope a tad less than a TR 224 114lsa cam and be a tad easier to tune.
I'm thinking of these cam specs:
I - 226 E - 222 116 LSA
That should give me -8 degrees of overlap. It should lope a tad less than a TR 224 114lsa cam and be a tad easier to tune.
I have MTI Stealth II 224/220, .581/.581 116+0 XE-R Comp grind.
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Advance is ground in for one of 2 reasons:
....
2) advancing a cam increases low end power
....
2) advancing a cam increases low end power
Thanks.
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From: BFE
Well they are advancing the cam to make it peak earlier, therefore bringing the powerband lower in the rpms, therefore making more trq earlier.
Unless truely they (grinders) assume that we all use stock T-chains and the stretch will retard it, making you loose power down the line with time.
Advancing or retarding a cam will make a difference in the powerband behavior. That is why a quick change timing cover allows you to play around with it to tune for maximum desired powerband output as per your set up.
Unless truely they (grinders) assume that we all use stock T-chains and the stretch will retard it, making you loose power down the line with time.
Advancing or retarding a cam will make a difference in the powerband behavior. That is why a quick change timing cover allows you to play around with it to tune for maximum desired powerband output as per your set up.
Say you have two identical cams but one has 2 degrees of advance built in and the other is "straight up", by having advance ground into the cam, does it affect overlap in anyway?
Bill
Bill
Originally Posted by Billiumss
Say you have two identical cams but one has 2 degrees of advance built in and the other is "straight up", by having advance ground into the cam, does it affect overlap in anyway?
Bill
Bill
All the pic shows is two completely different cam lobes. Where are they getting the 43.5 degrees of overlap form? Seems to be measured a lot more than at .050"
Here's another question for you guys: I know if you have a wider LSA, your idle will be smoother, and LSA affects overlap, having less of overlap will make it have less lope right?
So a cam with -4 degrees of overlap vs. one with -8 degrees, (same duration and lift) the -8 won't lope as much and have a tad smoother sound, right?
I just want to make sure I understand this whole overlap thing before I get my new cam this winter.
Thanks again for all your help and comments!
Bill
Here's another question for you guys: I know if you have a wider LSA, your idle will be smoother, and LSA affects overlap, having less of overlap will make it have less lope right?
So a cam with -4 degrees of overlap vs. one with -8 degrees, (same duration and lift) the -8 won't lope as much and have a tad smoother sound, right?
I just want to make sure I understand this whole overlap thing before I get my new cam this winter.
Thanks again for all your help and comments!
Bill
