displacement -vs- turbo(s)
ok, so i've been planning my next build and in doing so, discussing a lot about displacement and turbo selection. i've done some math's but i'm still undecided. so i figured i'd ask some questions here. to get this going, i'll ask the main quesiton:
#1. how much does an increase in displacement affect turbo spool/sizing/boost characteristics? for example: would 360 ci drive X turbo the same as 380 ci would drive Y turbo. Y being a larger turbo. hope to incite some further discussion on this so i'll leave it at that for now. cheers |
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just not sure how this correlates to turbo drive/efficiency, however you want to put it. |
CI and SCFM are linear. so it may be more simple than I'm making it.
5% more CI moves 5% more air. just curious how it affects the turbo. was hoping some folks that have gone up in displacement could edumacate me. |
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20 cubic inch is a fairly small jump though, but I know from a 360 to a 402 makes a huge difference.
Chris |
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In theory, you should be able to burn % more fuel with % more air for % increase of cubes. These numbers are exponential, not linear, so the more cubes, the greater the benefit becomes. |
I believe he is referring to the difference between a 5.9l and a 6.7l.
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There are so many variables to that can change turbo spool up. I think you are trying to oversimplify. Compression, porting, cam, injection rate, quantity, convertor stall, etc.
What is your end goal? Are you trying to balance dollars spent to HP? Trying to get max HP at any price or? |
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More cubes moves more air, but usually more cubes also means more fuel, which is more heat, which is more air...see how this goes. But, all things equal, the bigger engine will like a bigger charger more than a smaller one, but I would not really call anything linear. Chris |
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im not even going to mention end goal at this point, planning phase and the compD wrath of hell would descend upon me if I did. but i will say that it's somewhere between the 2 options you mention, not max HP at any price, but also don't want to shoot down the build based on the "cost outweighs the benefit" mindset, because "it's not worth it" has a tendency to kill some good shyte. Quote:
more air + more fuel = more heat. i agree this is not linear. and all thing equal, charger difference, that is EXACTLY what i'm talking about here. just curious to what degree. i'm starting to feel that i will have to share my plans eventually to get some other answers. i want to run bigger than "normal" chargers so exploring more cubes as the answer. |
Turbo are similar air/gasous flow driven period.. anything that increases efficiency or volume of air in/out of the Engine...drives the turbo better,
If turbo/RPM limit remains constant. increase in displacement will have a greater effect on turbo response than anything else.. camshaft, head design, valves, intake plumbing, exhaust plumbing, bowl design, spray pattern, etc all compliment displacement. Take NA motors for example.. take a camshaft stick it in 283ci V8 and a 427ci V8 the 427 will be much more drive able and responsive than the 283. Same thing with a turbo 1500cfm is 80% efficiency at 3800 rpm.. a 402 will acieve that easier than a 364 |
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my only question is with your last statement as I may be doing my math's wrong. but for calculation SCFM I was using this equation 360ci x 3800 rpm x .80 VE / 3456 = ~317cfm 380ci x 3800 rpm x .80 VE / 3456 = ~334cfm 402ci x 3800 rpm x .80 VE / 3456 = ~354cfm so i'm not sure what the 1500cfm you are mentioning is? |
PR or pressure ratio..
4:1 PR is 45 psig or 60psia if we round 14.7 to 15psi for easy math and sake of debate.. Round to nearest "10" for debating... If you're shoving an additional 1500cfm Into an engine that does 350cfm the Engine is moving 1850cfm at PR of ~4.3:1 1500cfm is roughly 91lb/min air flow S480 will push ~120lbmin or ~2000cfm I talked about this in my FL60 thread in getting a better turbo to put on my 8.3 12V |
Hopefully I did this right.. quoting stuff page 4/5 is turbo talk
99 FL60 mutt/conversion/repower project build - Page 4 - Competition Diesel.Com - Bringing The BEST Together Quote:
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also, my maths a little different but i'll use the actual numbers and 4:1 PR. for the 6.7 its 1416 CFM to lb/min, 1416 x .076 = 107 lb/min. so to efficiently fill a 6.7L air pump at 3800 rpm and 60psi, you'd need 107 lb/min of air. (is this a fair mathematically conclusion?) and for a 6.2L air pump at 3800 rpm and 60psi, you'd need 100 lb/min. 5.9L = 96 lb/min |
I was using a .061 factor for hotter/thinner air. Which Common knowledge Engines regardless NA or FI run better with colder/denser air.
Example setup up a truck that is at it limits at sea level can't even light turbos at elevation.. DPC showed that many times.. Also look at turbine flow charts as well.. I read somewhere that there was rough 1:2- 1:3 ratio of expansion from cold air in to hot exhaust going out volume wise.. |
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Does this somehow tie into the "Does my engine think its bigger" thread I started? |
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