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Discussion Starter · #1 ·
Alright fellas. Heres something I was pondering today. I know what the industry standard is but we all know the most common kits out there tackle the below in both ways:

Moderate compression with low boost vs. low compression and moderate/high boost.

As stated, almost all high performance cars and other motor vehicles are running low compression with a high amount of boost. I would like this subject elaborated on. I understand that overall with a lower static compression the lower end has less stress but a question that arises is the result in dynamic compression with the additive of boost. Wouldn't the resulting pressure be the same? You are compressing a fluid (air), mixing fuel, and finally combusting creating X amount of cylinder pressure or "push" on the piston hence creating horsepower. Whether it be low compression/high boost or the opposite, with the result in X amount of horsepower being equal you would have to assume the factor of "push" being the same.

Next lets talk about turbo efficiencies. No turbo is 100% efficient. Simply put, the higher the boost you would think these lacking efficiencies would stand out more resulting in even more boost requirements to gain the same amount of power progressively vs. the lower boost motor (e.i. a LC motor creating X amount of output with 14 psi may mathmatically be said equal to a HC motor with 7psi when comparing resulting cylinder pressures but this HC motor actually will make the same amount of power as the LC motor at 6psi). This efficiency issue brings me to lastly the intercooler/aftercooler which is also not 100% efficient.

Any time a fluid is compressed it gains energy (heat) hence the need for the after/intercooler. Lets say at 6psi and 85 degree ambient the air temps following the aftercooler are 98 degrees. 98 degree air has a certain amount of density which creates power potential. Now using the same intercooler with a 14 psi setup (turbo compressor now compressing more air) the temps following the aftercooler are now 115 degrees. Which air has the potential of more power?

I am in no way bias to either setup as I have ran both in cars and now RZR's and made great power with both with the right internals to hold. I understand the route most if not all the high performance applications go but wanted the subject elaborated on for learning and understanding purposes customers in the market new to boost and also us guys and gals getting a bit of a better grip on our machines. Thanks in advance for your know-how!
 
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Read up on Volumetric Efficiency..if you really want a detailed explanation and to talk for HOURS about it..I'll see if I can hook you up with a guy I know..he is a Scientist and a FI enthusiast..he will explain it too you until your head explodes.
 

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Discussion Starter · #4 ·
if you want to compare low compression with high boost, and high compression with low boost, do an internet search on "effective compression ratio".
Here is a calculator that you can play with that also factors in elevation: Boost Compression Ratio Calculator
Very good info to add Cliff! This calculates above where I explained the overall power output being said equal with both setups. I guess where I was going was the pro's/con's/reasoning with the variables getting to that power output but still good chart to use for calculations! The guy did talk a bit underneath about low/high compression with boost. One thing he stated was that higher boost/low compression can disguise poor flowing heads. There's a plus for that setup. Less flowing heads not much of a problem for LC/high boost.
 

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Sorry

You lost me when you said air was a fluid....it's a gas. Actually a mixture of gases, but who is paying attention. :rollfinger:
 

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Discussion Starter · #7 · (Edited)
Sorry

You lost me when you said air was a fluid....it's a gas. Actually a mixture of gases, but who is paying attention. :rollfinger:
By definition air is a less dense fluid as water is a high dense fluid. Alot of people mistake the word fluid for liquid. Water is a liquid but air is a gas yet both are fluids. :)

Edit - Cliff beat me to it lol
 

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Discussion Starter · #8 ·
Read up on Volumetric Efficiency..if you really want a detailed explanation and to talk for HOURS about it..I'll see if I can hook you up with a guy I know..he is a Scientist and a FI enthusiast..he will explain it too you until your head explodes.
Ahh, I did some reading up on VE in the past. May explain some of the masking effect of lower flowing heads that high boost has. Also, may get into having more overall combustion chamber volume to furnish more actual air and fuel. Somewhat like stating "You have a ballon filled with gas and air at X mixture and Y psi. Now you have a room filled with the same psi and same mix. Which makes the louder bang?" Sounds like this may be going somewhere.
 

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don't confuse fluid with liquid.
I'm not.

While I understand that he may have meant that in a turbocharger air is a "working fluid", it is not "A" fluid. It is a mixture of gases.

By definition. :)
 

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Discussion Starter · #11 ·
don't confuse fluid with liquid.
I'm not.

While I understand that he may have meant that in a turbocharger air is a "working fluid", it is not "A" fluid. It is a mixture of gases.

By definition. :)
All gases actually are fluids. By definition a fluid is any substance other than a solid that can take the shape of a containment area. Here you are:

What is fluid? Close
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... fluid any substance that is able to flow. Of the four states of matter , only a solid is not a fluid, since it has a definite shape that is not readily changed. Any liquid , gas , or plasma is classed as a fluid.
 

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Discussion Starter · #12 ·
I see where you are coming from though. My first fluid-dynamics class, I had to have the teacher point to the page (which oddly enough was the first page) and prove me wrong. Well, technically not wrong, I knew air was comprised of multiple gases, but that all those gases were actually in the catagory of fluids. It all makes since after you learn it. A fluid is not a state of matter but multiple stages and blah blah blah. Fun class:rofl3:
 
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