LS7 manifolds better than headers?
Melting Slicks
Joined: Nov 2009
Posts: 2,536
Likes: 15
You ask these questions like they're some sort of stumpers 
Basic engine stuff dude. It sounds like you learned something on the internet and feel a compelling need to use it as a your "look how smart I am" badge. I haven't done powertrain stuff in a decade and didn't have to think for more than half a second. And I answered your question dead on.
The engine with the later valve closing will have a lower DCR because, like I said, DCR "starts counting when the valves are closed (you're not compressing anything with open valves). " Instead of using cylinder volume at BDC, you're using cylinder volume at valve closing. I'm not sure how much more clear I can make it to an internet scholar.
It's obviously possible to lower cranking pressure and increase HP for a multitude of reasons. One reason might be running more boost. Another might be that your CR is just too damn high for your octane and you're pulling back too much timing. You might also just be running a bigger cam (again, see my original answer. You're not compressing anything with the valves open during the compression stroke).
Basic engine stuff dude. It sounds like you learned something on the internet and feel a compelling need to use it as a your "look how smart I am" badge. I haven't done powertrain stuff in a decade and didn't have to think for more than half a second. And I answered your question dead on. The engine with the later valve closing will have a lower DCR because, like I said, DCR "starts counting when the valves are closed (you're not compressing anything with open valves). " Instead of using cylinder volume at BDC, you're using cylinder volume at valve closing. I'm not sure how much more clear I can make it to an internet scholar.
It's obviously possible to lower cranking pressure and increase HP for a multitude of reasons. One reason might be running more boost. Another might be that your CR is just too damn high for your octane and you're pulling back too much timing. You might also just be running a bigger cam (again, see my original answer. You're not compressing anything with the valves open during the compression stroke).
I see Dymanic compression as the medium that is trapped. The more you trap the more power you make. The dynamic calculators are misleading, they do not take reversion, exhaust scavenging, over scavenging, differential pressures...etc into account.
So the more you trap, the higher your dynamic is.....higher dynamic = more power, with more fuel of course. So when more medium is trapped the higher the dynamic compression. So when you add atmospheric pressure/ boost the dynamic has to go up. If dynamic did not increase with boost then timing would not need to be compensated.
Current A&P air craft technician. ...lol.
Instructor
Joined: Aug 2013
Posts: 187
Likes: 4
From: Austin TX
I was thinking when I do this swap that I would just take the x-pipe on my car now and the h-pipe off the Z06 to a muffler shop and have them neck down the 3" to 2.5" at the rear near the axle-back connection and put a flange similar to the factory to allow it to mate up to my existing 2.5" system.
Le Mans Master
Joined: Oct 2011
Posts: 7,079
Likes: 1,922
From: DFW, Tejas!
Lol....sorry for the elementary questions but the point was missed. If the larger cam has less dynamic then more power is made because of time...aka; RPM. Thats is where the cranking compression question comes in. You can lower cranking compression and gain power with time/rpm. Thats what the ivc question was about.
I see Dymanic compression as the medium that is trapped. The more you trap the more power you make. The dynamic calculators are misleading, they do not take reversion, exhaust scavenging, over scavenging, differential pressures...etc into account.
So the more you trap, the higher your dynamic is.....higher dynamic = more power, with more fuel of course. So when more medium is trapped the higher the dynamic compression. So when you add atmospheric pressure/ boost the dynamic has to go up. If dynamic did not increase with boost then timing would not need to be compensated.
Current A&P air craft technician. ...lol.
I see Dymanic compression as the medium that is trapped. The more you trap the more power you make. The dynamic calculators are misleading, they do not take reversion, exhaust scavenging, over scavenging, differential pressures...etc into account.
So the more you trap, the higher your dynamic is.....higher dynamic = more power, with more fuel of course. So when more medium is trapped the higher the dynamic compression. So when you add atmospheric pressure/ boost the dynamic has to go up. If dynamic did not increase with boost then timing would not need to be compensated.
Current A&P air craft technician. ...lol.
Dynamic compression ratio is constant with time/rpm (unless you want to account for flex in the cam and stuff like that). Dynamic compression ratio calculators aren't misleading. They're spot on. They're just not meant to calculate what you're getting at.
Last edited by village idiot; Jun 2, 2014 at 11:53 AM.
Race Director
Joined: Mar 2005
Posts: 11,549
Likes: 27
From: Southampton NJ
I think everyone is getting volumetric pressure confused with compression. I wonder if the compression is higher at ATCO in mine shaft air, no! but the volumetric is, and the maff tune takes advantage of it over speed density with no changes to the tune.
Melting Slicks
Joined: Nov 2009
Posts: 2,536
Likes: 15
I always associate dynamic with ve....and I know, by the text book term dcr is piston travel with valves closed. But the root word dynamic, is taking the big picture into consideration...imho.
I'm 12.2 SCR with a dynamic of 8.8.....what does that tell you other than its a big stick...lol.
Point is, a dynamic number is useless without contributing factors that effect cylinder pressure. And when I consider a discussion about dynamic events....thats is exactly what I consider. ..the word dynamic. We know its a moving target, look at your timing table, I run 6 degrees less at peak tq because of ve. So am I trapping 8.8 per stroke throughout the rpm...absolutely not. So what good is the number without contributing factors ??
....edit.....for the record. Dynamic compression does change throughout the cycle but the ratio stays the same.
.
I'm 12.2 SCR with a dynamic of 8.8.....what does that tell you other than its a big stick...lol.
Point is, a dynamic number is useless without contributing factors that effect cylinder pressure. And when I consider a discussion about dynamic events....thats is exactly what I consider. ..the word dynamic. We know its a moving target, look at your timing table, I run 6 degrees less at peak tq because of ve. So am I trapping 8.8 per stroke throughout the rpm...absolutely not. So what good is the number without contributing factors ??
....edit.....for the record. Dynamic compression does change throughout the cycle but the ratio stays the same.
.
Last edited by LSOHOLIC; Jun 5, 2014 at 08:09 AM.
Le Mans Master
Joined: Oct 2011
Posts: 7,079
Likes: 1,922
From: DFW, Tejas!
Dynamic compression ratio is pretty well defined. I mean, it is what it has been forever. It is a big misleading in that it's just as static as Static Compression Ratio.
DCR (and static) is useful to know when designing an engine for a multitude of reasons. Like anything else, it's not the end all.
DCR (and static) is useful to know when designing an engine for a multitude of reasons. Like anything else, it's not the end all.
Advanced
Joined: Aug 2013
Posts: 80
Likes: 0
From: Cedar Lake Indiana
What is this connection pipe you are referring to? I have a Z06 manifold, cats, and h pipe that I'm planning to put on my C6. Is this something to make it a bolt up operation to my existing 2.5" axle-back exhaust?
I was thinking when I do this swap that I would just take the x-pipe on my car now and the h-pipe off the Z06 to a muffler shop and have them neck down the 3" to 2.5" at the rear near the axle-back connection and put a flange similar to the factory to allow it to mate up to my existing 2.5" system.
I was thinking when I do this swap that I would just take the x-pipe on my car now and the h-pipe off the Z06 to a muffler shop and have them neck down the 3" to 2.5" at the rear near the axle-back connection and put a flange similar to the factory to allow it to mate up to my existing 2.5" system.
Le Mans Master
Joined: Oct 2011
Posts: 7,079
Likes: 1,922
From: DFW, Tejas!
so back on topic, what LS7 parts do I need to bolt them up to an LS7 and use as much of the factory exhaust as possible.
I don't want the extra noise or any emissions problems. It's a daily driver, don't care about leaving power on the table.
I don't want the extra noise or any emissions problems. It's a daily driver, don't care about leaving power on the table.
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