Cylinder pressure/boost
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Staging Lane
Joined: May 2014
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Cylinder pressure/boost Hi, I'm trying to get my head around cylinder pressure, take two motors, one lsx 427ci at 15psi boost make x cylinder pressure, if you had the exact heads intake cam tune psi on a 376, all else being the same only on smaller ci, would that mean much less cylinder pressure?
Boost being a restriction of air flow, is cylinder pressure a direct result of power. N/a or f/I ?
Boost being a restriction of air flow, is cylinder pressure a direct result of power. N/a or f/I ?
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From: Norn Iron
Is there more reason for the query ?
Dont think there is an easy way to answer that. Worst thing you'll do on an engine is suffer detonation, that will see massive cylinder pressure. And destructive too of course.
But boost is not directly linked to cylinder pressure as such. CR, fuel, timing as well as boost need to be considered.
Dont think there is an easy way to answer that. Worst thing you'll do on an engine is suffer detonation, that will see massive cylinder pressure. And destructive too of course.
But boost is not directly linked to cylinder pressure as such. CR, fuel, timing as well as boost need to be considered.
Thread Starter
Staging Lane
Joined: May 2014
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I just want an idea of it, does itincreases the smaller you go or decreases, I'm looking too build a small cube 261 ls to compete with the Lexus vh41, tt, I want to build it strong but not waste money. Every body I talk to says don't run more than 13-14 psi in a boat, due to the load.
I'll have a 4.000 bore so the heads will flow well, there fore I cannot consider boost as apposised to cylinder pressure.
So is 14psi bad heads = less cylinder pressure,
And good heads 14psi = more cylinder pressure?
I'll have a 4.000 bore so the heads will flow well, there fore I cannot consider boost as apposised to cylinder pressure.
So is 14psi bad heads = less cylinder pressure,
And good heads 14psi = more cylinder pressure?
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From: Norn Iron
I would guess cylinder pressure is more closely linked to power output. So using boost isnt really relevant.
As for not using more than 14psi because it's a boat....I cant see any sensible reason for that sort of generic statement.
As for not using more than 14psi because it's a boat....I cant see any sensible reason for that sort of generic statement.
You need to focus more on the power you want and how its delivered. If its not going to see too much RPM i'd opt for a larger motor with smaller than normal turbo. A bigger motor will give you much better low end, hit boost extremely quick and since its a marine app, the rpms are low enough that you probably wont have to worry choking the motor in upper rpms. But then again, i really dont know exactly what you'll be doing
I wouldnt concentrate too much on cylinder pressure to be honest with you.
I wouldnt concentrate too much on cylinder pressure to be honest with you.
On The Tree
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cylinder pressure is directly related to torque. How that translates to different size motors will take some math because a motor with a larger piston will do more work at the same pressures and a longer throw on the crankshaft allows that pressure to have more leverage. as said boost has a poor correlation to cylinder pressure in a general since. However when talking one motor with all other variables constant obviously more boost is more cylinder pressure assuming your supplying enough fuel to keep afr the same.
when tuning for max effort and so as to not lift the head you want to make the pressure curve wide and after tdc as possible. At some pressure x you know it will lift the head. So you can play with boost and timing (to keep it simple) and change where that number peaks. more power will be made the more area under the curve. so if you can keep the peak pressure at what it is now and move it later in the crank rotation the longer the pressure is supplied and the greater hp to be made. many times this is done by raising boost and decreasing timing, or using a higher octane fuel.
this is my opinion and experience with tuning I am sure others have much more experience and knowledge
when tuning for max effort and so as to not lift the head you want to make the pressure curve wide and after tdc as possible. At some pressure x you know it will lift the head. So you can play with boost and timing (to keep it simple) and change where that number peaks. more power will be made the more area under the curve. so if you can keep the peak pressure at what it is now and move it later in the crank rotation the longer the pressure is supplied and the greater hp to be made. many times this is done by raising boost and decreasing timing, or using a higher octane fuel.
this is my opinion and experience with tuning I am sure others have much more experience and knowledge
Thread Starter
Staging Lane
Joined: May 2014
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Thanks for the info, 261 is max cubes for me, I'm looking at a 4.000 bore 2.6 crank, ported ls9 heads, I would need to be close to 780hp (3 hp per ci) it will run between 4 an 6100 for long periods of time under constant load. I run 100 octane but have e85 available. I'm stuck on an intake manifold I was thinking a victor jnr/elbow, although I think I need longer runners to get my torque up above 5,
Thanks for the info I don't want to lift the head, reason I ask cylinder pressure is the heads won't be as much of a restriction compared to an 4.8/ls1 head, so cylinder pressure will be much higher?
Will I have problems with exhaust valves pushrods rockers?
Thanks for the info I don't want to lift the head, reason I ask cylinder pressure is the heads won't be as much of a restriction compared to an 4.8/ls1 head, so cylinder pressure will be much higher?
Will I have problems with exhaust valves pushrods rockers?
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From: Norn Iron
Build and tune it right and I dont see why you'd have any issues at all.
If you lift the heads, you've done something badly wrong. And at 4k+ rpm, the turbo should be taking care of any torque required.
If you lift the heads, you've done something badly wrong. And at 4k+ rpm, the turbo should be taking care of any torque required.
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