s2000Junky

The pressure your pushing in the cylinder has everything to do with reliabilty since that is directly effecting stress on the engine mechanics, to say power is the cause of reliabitly issues is a very broad general statment and not really true. You can have a 370whp f20 that is pushing 14psi with stock internals and exhaust be more harmful on the engine then a higher flowing stock f20 that is pushing less boost of 11psi but still making the same power of 370whp. Its about stress on the internals of the motor, not how much power the engine makes. On an FI engine, having a higher flowing intake and especially exhuast increases power wile reducing the boost or internal pressure in the motor. The headgasket or low comp pistons is another mechanical measure to do the same thing, however this has an effect on other things as well.

Sellout

Your broad, general statements aren't any more true than his were.

s2000Junky

really? I disagree, maybe you misunderstood. My point to Camerons (seattle2k)statment was a high power output number doesnt mean its less reliable then a motor with lessor power would be, I gave some examples of how and why. Cameron means well but he has never owned a boosted car to my knowlege. Boost pressure does have a direct link to how reliable a motor performs, power output doesnt mean anything, its just a number. So how do you figure? You seem to be the knowlegable one here. School us please

s2000Junky

Becuase a centrifugal blower only hits max boost at redline, just for a fraction of what turbo does. You could have a turbo making 12psi from 4k all the way to redline, its not only the duration but the 12psi at 4k that is the issue. Requires allot more retard in timing and fuel managment. The threshold for failure is much tighter.

I have run a centrifugal blower with a 10.5 psi pulley with the stock timing map with no detonation. The reason why is becuase the sc is belt driven as builds boost as the motor increases revolution, a 10psi pully on an sc only puts out 4psi at 4k rpm and thats still withen the factory ecu abilty to retain proper cobustion as long as there is proper fuel delivery.

s2000Junky

Well maybe we can go through and clean it up someone revived it from the dead

Sellout

The problem is that boost pressure is an arbitrary number. Two cars making the same power at slightly different boost levels are both either perfectly safe, or they're both on the ragged edge of blowing up.

To say that one is automatically less safe than the other because it's running a little more boost to hit that same whp number is way too much of a generalization, and in many cases completely untrue.

s2000Junky

Sure there is several factors involved, and we may just have to disagree on this, but i think it is safe to say with all else being the equal between the two motors, the motor that is pushing higher boost pressure to maintain the same power output isn't going to be as strong, reliable, safe, longevity, whatever then a lower boosted motor that breaths better to maintain its same power output. The ideal to shoot for if you can afford it, is to have as free of flowing motor as possible to reach your power goals with the least boost pressure, its less strain on the internals of the motor, particularly the rings, pistons, head gaskets which are all in direct relation to the amount forced pressure felt in the consumption process, also with a motor that is freer flowing it will reduce the amount of cylinder detonation tenancies which kills motors. Just throwing more boost at a motor to produce more power is the easiest and usually the most strait forward, so this gets focused on most, but its not necessarily the best choice when you get to a point, knowing that point and having some understanding of tuning all helps, but again with all else being equal I stand behind my position on this. So again if you would explain to me a bit more in depth how boost amount doesn't matter or mean the same to you? I fail to see your logic, maybe I will learn something and some of these companies as well that have set up tuning packages based around a specific psi level to be within a safety margin

Sellout

[QUOTE=s2000Junky,Apr 9 2009, 04:48 PM] Sure there is several factors involved, and we may just have to disagree on this, but i think it is safe to say with all else being the equal between the two motors, the motor that is pushing higher boost pressure to maintain the same power output isn't going to be as strong, reliable, safe, longevity, whatever then a lower boosted motor that breaths better to maintain its same power output. The ideal to shoot for if you can afford it, is to have as free of flowing motor as possible to reach your power goals with the least boost pressure, its less strain on the internals of the motor, particularly the rings, pistons, head gaskets which are all in direct relation to the amount forced pressure felt in the consumption process, also with a motor that is freer flowing it will reduce the amount of cylinder detonation tenancies which kills motors. Just throwing more boost at a motor to produce more power is the easiest and usually the most strait forward, so this gets focused on most, but its not necessarily the best choice when you get to a point, knowing that point and having some understanding of tuning all helps, but again with all else being equal I stand behind my position on this. So again if you would explain to me a bit more in depth how boost amount doesn't matter or mean the same to you? I fail to see your logic, maybe I will learn something and some of these companies as well that have set up tuning packages based around a specific psi level to be within a safety margin

s2000Junky

1) Right but maybe what you are not realizing is when you make the engine move and expel the flow more efficient, the boost pressure drops but the volume does not. Hence the same power output but with a lower boost pressure, and many times its an increase in power. I dont use turbos for sake of comparison because there is too many variables. I run a centrifugal SC, so lets say you have a fixed rated 10psi 3.6" Comptech pulley, it has been replicated time and time again with all things equal, ie elevation, head gasket ect that this boost pressure fluctuates even though it is a fixed belt driven system. It is common knowledge even with my own friends in the neighborhood that have the same system, that guys with a bigger free flowing exhaust have a reduced boost pressure of say 9psi with the 10psi pulley but many times are making more power then the guy running the more restrictive exhaust system with the same pulley and boost pressure. I know for myself I took that pulley and was making 10.5 psi, I also had a stock size exhaust.


2) I agree this is true except for the part about the pistons and rods only seeing 330whp, the piston is still seeing boost, the rods are not so you are right there, they are isolated by the compression rings. But those rings see the boost pressure.


3) I never said connecting rods, boost pressure never touches the bottom end, I said the piston and rings, head and gasket.

So again with understanding this, I will use my motor for example, the motor with the 10.5psi of 350whp and stock size exhaust flowing to its efficiency range is going to be under more strain and build more heat, -- less reliable) then say the same motor that flows better at 9 psi making the same power or higher say 360whp

Sellout

I understand that very well. What you're ignoring is that the load on the bottom end is coming from that volume, not from the pressure behind the air as it flows in around the intake valves.

The pressure on the pistons, rings, head, and gasket cycles from a deep vacuum to utterly hellish pressure a thousand times a minute every time you start your car in the morning. The amount of pressure behind the intake valves is completely irrelevant. The amount of air making it through those valves while they're open and the piston is pulling down (with vacuum, not boost on top of it) is what creates the load that the piston sees when that mixture is ignited on the next power stroke.

The example you gave in point 1 explained exactly why what I'm saying is the truth. Did you think that when you got more power at less boost pressure that you suddenly had less load on the motor? You'd be dead wrong if you did...