Daily drive with that much? what's the specs on your cam? 245/245 on a 112 would get you 21 degrees of overlap 
Valve overlap
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From: Fuquay-Varina, NC
Valve overlap OK, this isn't shown in most cam specs unless you see the cam card or cam doctor report I guess. I would think this is a fairly important spec that I don't often see discussed. Could someone tell me what the difference is in one with say 9 degrees versus 5-6? I would imagine the higher degree of overlap also affects the fuel coming out of the exhaust. I know with my cam, it affected PTV clearance and we couldn't machine the heads. What is ideal for a street car with heads, if there is such a thing? I know there are valve event timing, lobe type, ramp speeds, and other things that come into play, just looking at this from a more generalized point.
@050 int dur+exh duration divide by 2 subtract lsa twice= overlap
the more positive you have the more its gonna lope the more negative the smoother it will idle and be easier to tune....the more positive usually means that it will create more cylinder pressure.....hope that helps theres a few good threads on here in the stickies..lots of reading but educational
the more positive you have the more its gonna lope the more negative the smoother it will idle and be easier to tune....the more positive usually means that it will create more cylinder pressure.....hope that helps theres a few good threads on here in the stickies..lots of reading but educational
@050 int dur+exh duration divide by 2 subtract lsa twice= overlap
the more positive you have the more its gonna lope the more negative the smoother it will idle and be easier to tune....the more positive usually means that it will create more cylinder pressure.....hope that helps theres a few good threads on here in the stickies..lots of reading but educational
the more positive you have the more its gonna lope the more negative the smoother it will idle and be easier to tune....the more positive usually means that it will create more cylinder pressure.....hope that helps theres a few good threads on here in the stickies..lots of reading but educational
Not to hijack but my uneducated question is this: at 0 degrees overlap the intake and exhaust valves are not open at the same time correct? Or, is it wiht an overlap of 0* that they are just not open at .050 but they are both still open at the same time at a lower lift like .006? Once they are both closed and not open at the same time and there are no degrees of overlap, it shouldn't matter how much negative the overlap is, right?
Negative overlap is undefined. There's no such thing.
Here's a link with some good examples.
http://members.uia.net/pkelley2/Overlap.html
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Verdad Gallardo 0 degrees means the intake and exhaust valves are never open at the same time. 0.050" durations will not give the correct overlap, you need to use advertised durations.
Negative overlap is undefined. There's no such thing.
Here's a link with some good examples.
http://members.uia.net/pkelley2/Overlap.html
Negative overlap is undefined. There's no such thing.
Here's a link with some good examples.
http://members.uia.net/pkelley2/Overlap.html
It seems the main thing with measuring the duration at .050 versus the advertised duration are the opening and closing ramp rates.
Mine is 9 degrees overlap figured at .050
I just checked the cam card from COMP and did not see any advertised duration, only duration at .006 and .050and it listed the valve events at .050 from which I figured up the overlap (INT opens at 8* BTDC and EXH closes at 1* ATDC so 8* + 1*= 9* overlap which is the same overlap as just figuring the overlap from the durations at .050
So, I have no idea what my real overlap is.
I just checked the cam card from COMP and did not see any advertised duration, only duration at .006 and .050and it listed the valve events at .050 from which I figured up the overlap (INT opens at 8* BTDC and EXH closes at 1* ATDC so 8* + 1*= 9* overlap which is the same overlap as just figuring the overlap from the durations at .050
So, I have no idea what my real overlap is.
For a daily driven street 346 ci LS1, you can have perfectly acceptable street manners with almost no issues up to 7 degrees of overlap at .050". You will continue to gain power with more overlap, but once you pass 15 degrees of overlap, the gains begin to diminish quickly. With 25 degrees of overlap, you will need a very skilled tuner to make this cam enjoyable with an EFI setup.
Here are some popular cams and their overlaps.
TR 224/224 on a 112LSA = 0 degrees at .050"
228/230 F-13 on a 112LSA = 7 degrees
G5X3 on a 112 LSA = 14 degrees
T-Rex = 25 degrees of overlap at .050"
Here are some popular cams and their overlaps.
TR 224/224 on a 112LSA = 0 degrees at .050"
228/230 F-13 on a 112LSA = 7 degrees
G5X3 on a 112 LSA = 14 degrees
T-Rex = 25 degrees of overlap at .050"
__________________
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
It is not a good time for me to take up the art of tuning. But, I have it running pretty well. I'm not a cam expert but this thing is fairly smooth for the amount of overlap. I can idle through a parking lot in first gear the majority of the time. More tuning to come...
For a daily driven street 346 ci LS1, you can have perfectly acceptable street manners with almost no issues up to 7 degrees of overlap at .050". You will continue to gain power with more overlap, but once you pass 15 degrees of overlap, the gains begin to diminish quickly. With 25 degrees of overlap, you will need a very skilled tuner to make this cam enjoyable with an EFI setup.
Here are some popular cams and their overlaps.
TR 224/224 on a 112LSA = 0 degrees at .050"
228/230 F-13 on a 112LSA = 7 degrees
G5X3 on a 112 LSA = 14 degrees
T-Rex = 25 degrees of overlap at .050"
Here are some popular cams and their overlaps.
TR 224/224 on a 112LSA = 0 degrees at .050"
228/230 F-13 on a 112LSA = 7 degrees
G5X3 on a 112 LSA = 14 degrees
T-Rex = 25 degrees of overlap at .050"
How does increasing cubic inches affect this? Lets say a 408. Since with the larger bore you typically have larger valves. The amount of overlap you need reduces as there's a greater area for flow. You can end up diluting the intake charge with too much overlap. Semi educated guess.
__________________
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
Increasing cubic inches without increasing valve area makes the engine "undervalved" and it will want more overlap. Increasing valve size area while increasing displacement keeps overlap from having to increase as much, but as a general rule, you want to add 8 degrees of duration (and overlap) for every 50 cubic inches of displacement increase. A 408 is 62 cubic inches larger than a 346 so it will want around 10 degrees more duration to have the same street manners and power range as the 346 (62/50 = 1.24 x 8 = 9.92 duration increase).
Increasing cubic inches without increasing valve area makes the engine "undervalved" and it will want more overlap. Increasing valve size area while increasing displacement keeps overlap from having to increase as much, but as a general rule, you want to add 8 degrees of duration (and overlap) for every 50 cubic inches of displacement increase. A 408 is 62 cubic inches larger than a 346 so it will want around 10 degrees more duration to have the same street manners and power range as the 346 (62/50 = 1.24 x 8 = 9.92 duration increase).
The amount of split between the intake and exhaust is mostly a function of getting the valve events where you want them. We'll want the intake valve to open at a certain point and close at a certain point to work best with our rpm range and the tuned resonance of the head/intake manifold combo. The exhaust valve will want a certain opening point depending on its flow, the exhaust header size, the rpm range, and whether there's a power adder involved.
In your case, you are running a smallish exhaust port with a smallish exhaust header (1 3/4") on a large engine (416) with a 200-250 shot of nitrous. The larger split was my approach to extending your rpm range without having to run too big of an intake lobe. It's all about balance.
__________________
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
