LSK lobes...
12-30-2005, 02:15 PM
#41
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Originally Posted by Beast96Z
DAPSUPRSLO, I understand exactlly what your saying, but, in your applcation, you have the intake as a limiting factor. You will maximize your under curve power, but with the smaller cubes, it'lll want to rev, which it won't be able to, because it is intake limited. The motor will peak far before it could because of lack of being able to get the proper amount of air. So, I ask, why would you want to limit yourself in the intake department? Kinda like ya'll asking me why I would limit myself in the cam department?
Keep this stuff coming guys, it's very informative, and I'm enjoying the conversation.
12-30-2005, 03:44 PM
#42
Originally Posted by DAPSUPRSLO
Actually I don't think I will be intake limited nor does HPE. My intake is a fully ported cut up re welded etc. etc. sb2 manifold that more then likely flows more then my heads, lol. My throttle body flows 1550 cfm as well. If you do the math my motor should require around the 1000-1150 cfm range at 7500 I believe (just off the top of my head, not put in the formula) so I should be able to feed it more then enough with my current intake setup. The plenum in my intake is much bigger then any of the normal single plain setups people are used to seeing and even bigger then most of the sb2 intakes most people are seeing. That beeing said it is still not as good as what you are going to be running. I'm not sure but I believe the setup like you have's superiority comes from two things. First off the world is the plenum of an intake like that, lol. I would imagine that means no more turbulent air in the plenum. Second, you can tune the lengths of the runners and equalize them to maximize pressure wave induction in whatever rpm you want it. Anyone have any input on why the individual runner intakes work so well?
I was refrencing a LSX intake. I PM'd J-rod to see if he would join in on the conversation. Maybe he can enlighten us some on why they do what they do.
12-30-2005, 09:20 PM
#43
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DavidNJ wrote: "Throttle response will be fantastic. The throttle plate is just a few inches from the valve. However, the overlap is within a single cylinder. What is the theory behind individual TBs affecting idle? "
I'm sure it's on a thread somewhere, but when you have a plenum with an upstream throttle, at low RPM with a high overlap cam it's easier for a cylinder to suck in a charge of exhaust from an adjacent cylinder at overlap than fighting to get fresh air past an almost closed throttle, hence its charge is badly contaminated with exhaust, resulting in lumpy, rich running and poor throttle response.
PS, David: Yes, Dynomation does merge collectors, e.g. a 3" 'throat', on a 14" megaphone, opening to a 4" tip. It doesn't (at least my old DOS version) do reverse cones except on individual stacks.
I'm sure it's on a thread somewhere, but when you have a plenum with an upstream throttle, at low RPM with a high overlap cam it's easier for a cylinder to suck in a charge of exhaust from an adjacent cylinder at overlap than fighting to get fresh air past an almost closed throttle, hence its charge is badly contaminated with exhaust, resulting in lumpy, rich running and poor throttle response.
PS, David: Yes, Dynomation does merge collectors, e.g. a 3" 'throat', on a 14" megaphone, opening to a 4" tip. It doesn't (at least my old DOS version) do reverse cones except on individual stacks.
12-31-2005, 12:10 PM
#44
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Originally Posted by Beast96Z
Well, you didn't say anything about a SB2 intake to start with. I was refrencing a LSX intake. I PM'd J-rod to see if he would join in on the conversation. Maybe he can enlighten us some on why they do what they do.
I was refrencing a LSX intake. I PM'd J-rod to see if he would join in on the conversation. Maybe he can enlighten us some on why they do what they do.
12-31-2005, 04:50 PM
#45
Originally Posted by MadBill
DavidNJ wrote: "Throttle response will be fantastic. The throttle plate is just a few inches from the valve. However, the overlap is within a single cylinder. What is the theory behind individual TBs affecting idle? "
I'm sure it's on a thread somewhere, but when you have a plenum with an upstream throttle, at low RPM with a high overlap cam it's easier for a cylinder to suck in a charge of exhaust from an adjacent cylinder at overlap than fighting to get fresh air past an almost closed throttle, hence its charge is badly contaminated with exhaust, resulting in lumpy, rich running and poor throttle response.
PS, David: Yes, Dynomation does merge collectors, e.g. a 3" 'throat', on a 14" megaphone, opening to a 4" tip. It doesn't (at least my old DOS version) do reverse cones except on individual stacks.
I'm sure it's on a thread somewhere, but when you have a plenum with an upstream throttle, at low RPM with a high overlap cam it's easier for a cylinder to suck in a charge of exhaust from an adjacent cylinder at overlap than fighting to get fresh air past an almost closed throttle, hence its charge is badly contaminated with exhaust, resulting in lumpy, rich running and poor throttle response.
PS, David: Yes, Dynomation does merge collectors, e.g. a 3" 'throat', on a 14" megaphone, opening to a 4" tip. It doesn't (at least my old DOS version) do reverse cones except on individual stacks.
If I understand correctly, when cylinder 4 is at TDC, cylinder 3 is at TDC+90 in the intake stroke, cylinder 2 is at BDC, and cylinder 1 is at BDC+90 on the compression stroke, slightly after IVC. In this scenario, the vacuum from cylinders 2 and 3 would be sufficient to reverse the flow in cylinder 4's intake port, sucking exhaust gas into the plenum.
This how often does this happen?
P.S.
The Dynomation Advanced Pro Tools product looks very similar to the Performance Trends Engine Analyzer Pro. Similar price. Although it does have nicer graphics. It looks like ProRacing Software focuses on these simulations while Performance Trends has been focusing their data aquisition, flow bench and flow bench accessories (they measure tumble and swirl), cam analyzer, etc. I don't think Dynomation had the same flow model when I looked in '02.
12-31-2005, 05:36 PM
#46
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Originally Posted by DavidNJ
This how often does this happen?...
12-31-2005, 06:52 PM
#47
Yes, and sucking exhaust gases in is common and at times desirable. However, how often does it actually cause a reversion of the intake track, sucking exhaust up one intake track and into another? That seems much more extreme.
12-31-2005, 08:19 PM
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The exhaust doesn't have to make it all the way to another cylinder; just getting sucked say halfway back up a long LSx runner would be enough volume to pollute that cylinder's upcoming intake cycle.
01-10-2006, 12:26 PM
#49
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Sorry to get back to this thread so late.
A 242/242 106 on an ITB intake idles very smoothly. Much more so than it would in a common plenum intake. In fact I drove a 273/273 104LSA/103 ICL cam in a 346 behind an auto while I was in Australia. It had a 4000 stall and had lots of grunt down low.
The 242/242 106 cam is a grocery getter cam. With an ITB and Sd tuning its drivability is 1000X better than anyhting you'll ever see stateside.
As for why ITB is superior to a common plenum. See this thread.
https://ls1tech.com/forums/generation-iv-internal-engine/350199-ls7-c6r-velocity-stack-induction-injection.html
A 242/242 106 on an ITB intake idles very smoothly. Much more so than it would in a common plenum intake. In fact I drove a 273/273 104LSA/103 ICL cam in a 346 behind an auto while I was in Australia. It had a 4000 stall and had lots of grunt down low.
The 242/242 106 cam is a grocery getter cam. With an ITB and Sd tuning its drivability is 1000X better than anyhting you'll ever see stateside.
As for why ITB is superior to a common plenum. See this thread.
https://ls1tech.com/forums/generation-iv-internal-engine/350199-ls7-c6r-velocity-stack-induction-injection.html
https://ls1tech.com/forums/showpost....&postcount=293
The independent runner stuff with the small independent throttles before each port with the constantly pressurized near 100 kpa "mega plenum of the world" above those same little throttle bodies are just less affected by the exhaust reversion that affects a plenum car worse since the whole intake system on these setups is at very low pressure and the exhaust is at such a higher pressure. The exhaust reversion can and does fill up the whole plenum behind the central TB or carb and the whole runner of each cylinder with exhaust diluted air that causes the repeated and erratic misfiring that we hear as the cool loping sound some people love so much.
With enough overlap the IR systems will also lope too and turn black under those cute little throttle bodies from idling with all the same vacuum under them when they are closed and idling but they have less of the total runner to become as contaminated since the higher pressure is close at hand right above them and in the rest of the runner. You will sometimes, with really big cams in these systems see the exhaust and regular reversion in the form of standoff above the runners with some of them at lower engine speeds.
Also when you crack the throttle instead of an entire manifold plenum having to pressurize up slowly instead, now the port sees full atmosheric pressure and density basically almost instantaneously so the throttle response is WAY better. In fact some people need a progressive linkage or it's too jerky for them! Also just realize that Australians ARE crazy and they all drive cars with blowers and NOS and have mohawks. They also like cubic inches in a lot of their racing and RWD but that's finally coming back to the USA too as people here have had their fill of the FWD crap.
The independent runner stuff with the small independent throttles before each port with the constantly pressurized near 100 kpa "mega plenum of the world" above those same little throttle bodies are just less affected by the exhaust reversion that affects a plenum car worse since the whole intake system on these setups is at very low pressure and the exhaust is at such a higher pressure. The exhaust reversion can and does fill up the whole plenum behind the central TB or carb and the whole runner of each cylinder with exhaust diluted air that causes the repeated and erratic misfiring that we hear as the cool loping sound some people love so much.
With enough overlap the IR systems will also lope too and turn black under those cute little throttle bodies from idling with all the same vacuum under them when they are closed and idling but they have less of the total runner to become as contaminated since the higher pressure is close at hand right above them and in the rest of the runner. You will sometimes, with really big cams in these systems see the exhaust and regular reversion in the form of standoff above the runners with some of them at lower engine speeds.
Also when you crack the throttle instead of an entire manifold plenum having to pressurize up slowly instead, now the port sees full atmosheric pressure and density basically almost instantaneously so the throttle response is WAY better. In fact some people need a progressive linkage or it's too jerky for them! Also just realize that Australians ARE crazy and they all drive cars with blowers and NOS and have mohawks. They also like cubic inches in a lot of their racing and RWD but that's finally coming back to the USA too as people here have had their fill of the FWD crap.
