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Old 12-08-2011, 06:21 AM   #15
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Old 12-13-2011, 01:04 AM   #16
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Here's a question. What is the strength of head gasket? At what psi does the life and durability of the head gasket become shortened.

Given the car's compression ratio you multiply that by the boost with the 13.7 atmospheric pressure to get a rough guess of the cylinder pressure working against the head gasket. I know that this does not include additional presure from ignition, timing etc.

Just rough numbers but an idea.

Stock gti will hit around 14lbs of boost so that s roughly 263 psi of force. (13.7+14)x9.5
And a stage 2 gti can hit 21 lbs of boost so that is roughly 330 psi.

So, is there a know limit of pressure the headgasket can take? Not that I have seen or heard of a lot of headgasket failures, just curious.

If this is highjacking your engineering thread, or my math is wack, I apologize.
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Old 12-13-2011, 01:47 AM   #17
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Old 01-18-2012, 04:12 PM   #18
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Some Drivetrain Loss Fun

Quote:
Originally Posted by Banshee View Post
sorry... I meant a constant amount of power lost regardless of how much horsepower or torque the engine makes. Example: a constant 25hp lost whether the engine is making 200 or 300 hp. But I suppose that point is moot because more power usually means higher temps which would increase drivetrain loss.

I really should stay away from these technical questions...
No no, I see what you mean. I think I have a fair answer for you.

In regards to the question, both instances you described are roughly the same thing, except one is a percentage function of the power provide which would increase with power increases and the other is just a constant 25HP off.

200 HP at assumed 10% loss = 180WHP
150 HP at assumed 10% loss = 135WHP
200 HP at 25HP constant assumed loss = 175WHP (12.5%)
150 HP at 25HP constant assumed loss = 125WHP (17%)

However, lets get technical with it:

What makes the power? The force pushing down on the piston which turns the crank. This force is generated by a number of things (Cylinder Pressure, Temperature, Fuel Heating value, Bore, Stroke, etc. etc.)

The engine power is roughly described, in theory, like this. Taken from another thread I did this in:

Quote:
Brake Horsepower (Watts) = N*Displacement(in cubic Meters)* (RPM/2)* nc*nm*nth*nv*Qhv*(F/A)*Air Density

N = Number of cylinders
Displacement = Bore*Stroke*pi/4
RPM/2 = Must be placed in Revs/Second = RPM/2 * (1/60 {s/min})
nc = Combustion efficiency = about .98-.99 on newer cars (can be calculated further, but these estimations are fine)
nm = mechanical efficiency = Function of RPM/heat/etc range of about .8-.93 (can be calculated further, but these estimations are fine)
nv = volumetric efficiency (what percentage is your TB open?)= 100% at WOT (Possibly a little more depending on the flow. Most I've seen is 108%)
nth = thermal efficiency = 0.8*(1-[compression ratio^(-.35)])
Qhv = Heating value of the fuel = 43,000,000 J/kg

Air Density = Pressure Entering / (287.2 J/kg-K * Intake Temperature)
Pressure Entering = Atmospheric Pressure * Pressure Ratio (This is a function of RPM) - J/m^3
Now that you have the power the engine makes you can determine how much force can be placed on the crankshaft to provide the neccessary torque at the flywheel. This is a function of material properties and mechanical efficiencies which decrease/increase throughout the rev band due to fluids heating up and metal expanding when hot.

Nevertheless........what an automaker displays as their "specific output" is what it has been measured at on the engine dyno and calculated through various equations and testing.

NOW...onto Driveline loss

Now that you know what your engine makes how do you quantify it through the wheels?

Easy: Power = Difference in Kinetic Energy over the amount of time it takes

Easiest way to do that is to dyno it in a controlled enviorment. Normally, this "constant" weight and constant air temp and etc. etc. is propelled by your wheels. This is a great indication of the power through your wheels...but it doesnt really coorelate to what your engine is making because of the weight of the driveshafts, gears, wheels, tires, hubs, etc. etc.

You could do a velocity run with a certain scan rate in VAGCOM but that accounts for drag forces which will make your power output significantly lower.

So how can you relate wheel HP to crank then? Well....you can theorhetically calculate it, but that leaves room for error (Plus it gets really confusing quick. Fluids dynamics + thermodynamics + variating degrees of freedom, frictional factors, stress analysis, plastic yielding effects with respect to temp), or you can do a very long process:

1) Dyno your engine
2) Using the same dyno, dyno your engine + Trans (1 for every gear since the mass changes for different gears
3) Using the same dyno, dyno your engine + trans + driveshafts
4) Using the same dyno, dyno your E + T + DS + Hubs
5) Using same dyno, dyno your E + T + DS + Hub + Wheels

This will take various fixtures to mount the dyno to...but would be one of the most accurate ways to relate your efficiencies together and finally provide a coorelation between brake and wheel horesepower.

Whats easier? Assuming constant percentage difference calculated from factory dyno and vendor dyno? or the process described above? Remember, no dyno is the same. All calibrations are different for various altitudes and temperatures and etc. etc.

1/4 Mile times are a good indication of power. Its as simple as how long did it take to propel this 3000lb vehicle in a 1/4 mile and what was its final speed?
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Old 01-18-2012, 04:21 PM   #19
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Quote:
Originally Posted by Kal-GTI View Post
Here's a question. What is the strength of head gasket? At what psi does the life and durability of the head gasket become shortened.
So, is there a know limit of pressure the headgasket can take? Not that I have seen or heard of a lot of headgasket failures, just curious.
Please refer to this thread about head gasket strength:
http://www.golfmk6.com/forums/showthread.php?t=30807

K04 = ~22-23PSI
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Old 01-18-2012, 04:33 PM   #20
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Quote:
Originally Posted by grambles423 View Post
You could do a velocity run with a certain scan rate in VAGCOM but that accounts for drag forces which will make your power output significantly lower.
i did something like this with VAGCOM. full third gear pull and logged speed from 2000 to 6000 rpm back to 2000 rpm (just losses due drag/drivetrain), with the associated time stamp. with that info, i found the KE associated with accelerating through the rpm range, and the KE associated to decelerating. assuming that the engine is overcoming the same losses between the accel and decel. a couple curve fits and derivatives, subtract the one from the other, and poof... HP. my test did not work though because i need a completely flat road. in my test, i was accel down a slight hill, and my HP calc ended up being 277 HP... i wish.
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Old 01-18-2012, 04:38 PM   #21
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Quote:
Originally Posted by GTIwannagofast View Post
i did something like this with VAGCOM. full third gear pull and logged speed from 2000 to 6000 rpm back to 2000 rpm (just losses due drag/drivetrain), with the associated time stamp. with that info, i found the KE associated with accelerating through the rpm range, and the KE associated to decelerating. assuming that the engine is overcoming the same losses between the accel and decel. a couple curve fits and derivatives, subtract the one from the other, and poof... HP. my test did not work though because i need a completely flat road. in my test, i was accel down a slight hill, and my HP calc ended up being 277 HP... i wish.
lol But at least you're on the right track! I'm gonna give it a shot when VAGCOM comes in on Friday. Hopefully I'll have 100 logs or so this weekend with my new toy!
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Old 03-01-2012, 02:11 PM   #22
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Interesting.......5000RPM looks like there is something going on. I would have to analyze it much further

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Last edited by grambles423; 03-01-2012 at 02:21 PM.
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Old 03-05-2012, 12:22 AM   #23
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Hi all,
i am james frenkline, new here. hope this is a nice experience for me to being with you.
Nice information.... keep it up ...
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Old 09-30-2014, 12:39 PM   #24
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I can't believe this thread hasn't received the attention it deserves...

This is some amazing information. I'm going to have to put some time aside and try to decipher everything.

Thank you so much for sharing!
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Old 12-25-2014, 03:04 PM   #25
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Quote:
Originally Posted by steemax View Post
I can't believe this thread hasn't received the attention it deserves...

This is some amazing information. I'm going to have to put some time aside and try to decipher everything.

Thank you so much for sharing!
Fully agree on this !! Great stuff !!!
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Old 01-20-2015, 02:10 PM   #26
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Can somebody point me to the thread that was on here awhile back that discussed 2.5 vs 3" exhaust sizes and the benefits of each (like how much air you can move vs how quickly you move it, etc.)? I've been searching all morning and can't find it..

Found it.

Last edited by KVipers; 01-23-2015 at 09:45 AM. Reason: Found what I was looking for.
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Old 01-20-2015, 02:55 PM   #27
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Originally Posted by KVipers View Post
Can somebody point me to the thread that was on here awhile back that discussed 2.5 vs 3" exhaust sizes and the benefits of each (like how much air you can move vs how quickly you move it, etc.)? I've been searching all morning and can't find it..
heres a little info i got from a thread i made on vortex

http://forums.vwvortex.com/showthrea...on-help-please
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