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Old 07-06-2017, 10:48 AM   #1
j.fondler

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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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Old 07-06-2017, 11:34 AM   #2
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What's "math's"?....
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Old 07-06-2017, 11:58 AM   #3
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Quote:
Originally Posted by blackmega3500 View Post
What's "math's"?....
just the scfm per displacement using a standard VE of .80 and rpm of 3800.

just not sure how this correlates to turbo drive/efficiency, however you want to put it.
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Old 07-06-2017, 12:01 PM   #4
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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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Old 07-06-2017, 01:10 PM   #5
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Quote:
Originally Posted by j.fondler View Post

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
Yes, that is a fairly easy question.
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Old 07-06-2017, 02:03 PM   #6
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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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Old 07-06-2017, 03:07 PM   #7
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Originally Posted by Signature600 View Post
20 cubic inch is a fairly small jump though, but I know from a 360 to a 402 makes a huge difference.

Chris
When you say huge difference, can you elaborate? That's about a 10% increase in cubes.

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.
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Old 07-06-2017, 03:13 PM   #8
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I believe he is referring to the difference between a 5.9l and a 6.7l.
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Old 07-06-2017, 03:21 PM   #9
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Originally Posted by jlbayes View Post
I believe he is referring to the difference between a 5.9l and a 6.7l.
I'm fine with using those 2 displacements for this discussion. 360 and 402. it's easy to math backwards to to any lesser displacement i want after that.
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Old 07-06-2017, 03:25 PM   #10
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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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Old 07-06-2017, 03:35 PM   #11
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Quote:
Originally Posted by j.fondler View Post
When you say huge difference, can you elaborate? That's about a 10% increase in cubes.

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.
Lot's of other variables come into play with fuel burn and efficiency.


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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Old 07-06-2017, 03:47 PM   #12
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Quote:
Originally Posted by zstroken View Post
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?
sorry, i should have mentioned that we're in a hypothetically perfect disney land where the rest of the setup is perfect. maybe i am oversimplifying but just pretending all else is "perfect" with cubes being the only factor. meaning the entire setup would be "perfect" for both displacements.

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:
Originally Posted by Signature600 View Post
Lot's of other variables come into play with fuel burn and efficiency.


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
this^^^^ is right up my alley here.

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.
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Old 07-06-2017, 04:54 PM   #13
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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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Old 07-06-2017, 05:06 PM   #14
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Quote:
Originally Posted by malibu795 View Post
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
thank you as this is a lot of what i was looking for.

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?
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Old 07-06-2017, 05:32 PM   #15
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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
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Old 07-06-2017, 05:37 PM   #16
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Hopefully I did this right.. quoting stuff page 4/5 is turbo talk
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Quote:
Originally Posted by malibu795 View Post
8.3 cummins 500cid at 2500rpm and 200%VE =725cfm
6.6 duramax 403cid at 3500rpm and 200%VE = 816cfm
CFM*.069=lbMN
CID*RPM*VE/3456=CFM

723*.069=49lbmn
816*.069=56lbmn

300% be or essentially 3:1 pr
500cid is 1080cfm/75lbmn
403cid is 1224cfm/81lbmin

The GT4088R is what I currently have on my dmax.. and a s362sxe I'm told flows more than the GT4088R which is a 63.5
On paper the is Question run a 364 and lose low-end response or 362 and risk overspending at the top end?
Can the AFC be adjusted to pull fuel above X psi?
Or setup an external WG with a 362..
Quote:
Originally Posted by Signature600 View Post
Set it up for Bottom end and cruise speed, wastegate the top end, I would really doubt you will be having to pull hills at 2500RPM with 505 cubes anyway.

AFC setup is backwards in operation from what you want, but I'd have to think of a way to cut fuel back with boost....I know you could wire in a Valet switch to kill AFC signal once a pressure switch is hit, but that would be almost instant once you hit that pressure limit.

On a 5.9L at 400hp with full AFC travel, killing AFC with a valet switch dropped about 140-150hp...depending on injectors, I would imagine the difference would be similar with the bigger engine, as fuel is fuel out of 12mm plungers to a point. Injectors could change that some.

My S360 is wastegated at 38psi, I don't see any reason pushing farther than that, and I'm pushing the little 5.9 to up around 425hp in that big chassis....F1 Mach 4's and an Edge EZ, should be in that ballpark at the wheels in a pickup....


IMHO,
Chris
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Why do you need an external gate? Can't get a internal dual port gate?

Chris
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Originally Posted by malibu795 View Post
While I'd like an internal gate, for plumbing/simplicity reason..it might not be an option for a S300/with a 76/68 turbine.. I'm not that familiar with turbine housing options for s300 platform

Planned cruise is 1500-2100 range at 70mph basically top 3 gears of a 13sp..

500cid with 2-3:1 PR
1500rpm 30-45lbsmn
2100rpm 42-63lbmn

2-3:1 PR is 15-30PSIG for those following

With fixed the problem I see me running into is either being under the turbo running light, or over speeding with heavy high sail load and head wind

On paper this gt4088R in my truck with a .83 WG housing would work pretty good... Only problem it's a T3 foot vs T4 I don't really want to put a T3/T4 adapter on the truck

Though seams I can get a WG housing for a 74 turbine vs a 76.. maybe have someone like Zach machine the housing for a bigger turbine
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Old 07-06-2017, 06:01 PM   #17
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Quote:
Originally Posted by malibu795 View Post
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
ok, you're taking into account the forced induction. so would we need to change the VE to a hypothetical 2.8(?) instead of the .80?

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
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Old 07-06-2017, 06:30 PM   #18
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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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Old 07-06-2017, 06:56 PM   #19
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Quote:
Originally Posted by blackmega3500 View Post
What's "math's"?....
, give it to him.

Does this somehow tie into the "Does my engine think its bigger" thread I started?
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Old 07-06-2017, 07:21 PM   #20
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, give it to him.

Does this somehow tie into the "Does my engine think its bigger" thread I started?
never heard of her. have a link?
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