Happy Thanksgiving! Update on Joe's GT
- Thread starter QKSTNG514
- Start date
californiacuda
GT Owner
- Oct 21, 2005
- 919
Weird question for Torrie or Joe. Have you every checked exhaust backpressue compared to boost pressure?
Dwight
Well-known member
We keep saying we are going to, but we never have a chance to do so. It most not be bad seeing the power gains we are getting for every pound of boost we turn it up.californiacuda said:
At the level we are at I and others are concerned that the MAF size needs to be increased since that may be an inlet restriction.
TonY G
TonY G
californiacuda
GT Owner
- Oct 21, 2005
- 919
Tony, it is possible to run 2 seperate mafs and ground 1 into the other and the voltage readings are added together. An engineer I know explained to me how to do it. I could get a diagram if you would like.
californiacuda said:
We were going to do just that originally and decided to try the simple way first.
I think using the larger diameter housing may help in more ways than one.
TonY G
timcantwell
Le Mans 2010 Sponsor * Moderator
There are no words to express my reaction to the numbers Tony posted for Joe's latest dyno run, maybe dameihahahldiahidididliweijgbnothjnothlmfhuiohtowowowowowow!!!!!!!!!! :banana
californiacuda
GT Owner
- Oct 21, 2005
- 919
Dwight
Well-known member
californiacuda said:
The new set-up will be able to switch from a single MAF to a twin MAF with out any refabing of piping. The new layout will be a little different than the current one but still be easy to work on.
californiacuda
GT Owner
- Oct 21, 2005
- 919
californiacuda
GT Owner
- Oct 21, 2005
- 919
John B, can you tell us your method for coming with up with 293 mph, it is an interesting subject?
So far the Fuel Pump setup is holding up well! Pressure has not fluctuated and the voltage to the pumps is still less than 12volts at peak.
TonY G
TonY G
John B
GT Owner
- Jan 28, 2006
- 158
Sure CaliforniaCuda, it's really pretty simple.
I use the cube root of the ratio of "new" horsepower (HP2) to "old" horsepower (HP1) and apply that to the "old" speed or et variable I am trying to get an estimate on. Multiply for speed, divide by for e.t.. Obviously this is only an estimate, and necessarily assumes all else (weight, traction, barometric conditions, Cd, no rpm limited speeds, etc…) is held constant.
e.g. for Joe's GT
Stock GT: 550 RWHP, 11.9 et, 212 top speed (unrestricted, not quarter mile trap speed)
Estimates for Joes GT:
et: 11.9/(1453/550)^(1/3) = 8.61
top speed: 212*(1453/550)^(1/3) = 293
Drag increases with the cube of speed, so I initially used this only to estimate top speeds. I subsequently found it is also provides a reasonable estimate for et’s. For example, I used it to estimate the performance changes in the BMW 5 series as they went from the E39 540i sport, to the E39 M5, and then the E60 M5. The estimates proved to be quite accurate. I have owned, and derestricted, them all. I have verified the speeds of the first two, as have many others. I have not tested the E60, although the factory published a test of a unrestricted E60 M5 at 205 mph.
Actual performance data:
E39 540i sport: 282 hp, 14.7 et, 168 mph (unrestricted)
E39 M5: 396 hp, 13.2 et, 189 mph (unrestricted)
E60 M5: 505 hp, 12.3 et, 205 mph (unrestricted)
Estimates, working up from 540i sport:
E39 M5 et: 14.7/(396/282)^(1/3) = 13.13
E39 M5 top speed: 168*(396/282)^(1/3) = 188
E60 M5 et: 14.7/(505/282)^(1/3) = 12.11
E60 M5 top speed: 168*(505/282)^(1/3) = 204
Pretty cool huh?
I use the cube root of the ratio of "new" horsepower (HP2) to "old" horsepower (HP1) and apply that to the "old" speed or et variable I am trying to get an estimate on. Multiply for speed, divide by for e.t.. Obviously this is only an estimate, and necessarily assumes all else (weight, traction, barometric conditions, Cd, no rpm limited speeds, etc…) is held constant.
e.g. for Joe's GT
Stock GT: 550 RWHP, 11.9 et, 212 top speed (unrestricted, not quarter mile trap speed)
Estimates for Joes GT:
et: 11.9/(1453/550)^(1/3) = 8.61
top speed: 212*(1453/550)^(1/3) = 293
Drag increases with the cube of speed, so I initially used this only to estimate top speeds. I subsequently found it is also provides a reasonable estimate for et’s. For example, I used it to estimate the performance changes in the BMW 5 series as they went from the E39 540i sport, to the E39 M5, and then the E60 M5. The estimates proved to be quite accurate. I have owned, and derestricted, them all. I have verified the speeds of the first two, as have many others. I have not tested the E60, although the factory published a test of a unrestricted E60 M5 at 205 mph.
Actual performance data:
E39 540i sport: 282 hp, 14.7 et, 168 mph (unrestricted)
E39 M5: 396 hp, 13.2 et, 189 mph (unrestricted)
E60 M5: 505 hp, 12.3 et, 205 mph (unrestricted)
Estimates, working up from 540i sport:
E39 M5 et: 14.7/(396/282)^(1/3) = 13.13
E39 M5 top speed: 168*(396/282)^(1/3) = 188
E60 M5 et: 14.7/(505/282)^(1/3) = 12.11
E60 M5 top speed: 168*(505/282)^(1/3) = 204
Pretty cool huh?
californiacuda
GT Owner
- Oct 21, 2005
- 919
BlackICE
GT Owner
The power need to overcome wind resistance at top speed is to the 4th power not cube for estimating top end speed assuming ideal gearing. So Joe's car would do an est.
top speed: 212*(1453/550)^(1/4) = 270
BlackICE
top speed: 212*(1453/550)^(1/4) = 270
BlackICE
John B
GT Owner
- Jan 28, 2006
- 158
nah... you had me going there for a second but NASA agrees with my version.
http://space-power.grc.nasa.gov/ppo/projects/heva/appx_a.html#AERODRAG
http://space-power.grc.nasa.gov/ppo/projects/heva/appx_a.html#AERODRAG
BlackICE
GT Owner
The site you quoted is correct the drag goes up by the cube, but the power necessary to overcome the drag has the 4th power in relation to the velocity.
force = drag = lbs
work = force x distance, drag x miles, lbs x miles
Power = work/time = HP = 550 ft lbs / sec
power = (drag x miles) / time
Now note the the distance traveled per unit time is inversely proportional to the velocity. There is where the other power (to the 4th) comes from. The "time factor."
Example:
At 60 miles per hour the drag is X, then at at 120 mph the drag is 8X, but the time to cover 1 mile drops from 60 seconds to 30 seconds, then the power is:
60 mph X/60
120 mph 8X/30
To the 4th power!
That is why higher tops speeds are better achieved by lower the frontal area and drag coefficient (linear gain) rather that adding power (4th root gain).
BlackICE
force = drag = lbs
work = force x distance, drag x miles, lbs x miles
Power = work/time = HP = 550 ft lbs / sec
power = (drag x miles) / time
Now note the the distance traveled per unit time is inversely proportional to the velocity. There is where the other power (to the 4th) comes from. The "time factor."
Example:
At 60 miles per hour the drag is X, then at at 120 mph the drag is 8X, but the time to cover 1 mile drops from 60 seconds to 30 seconds, then the power is:
60 mph X/60
120 mph 8X/30
To the 4th power!
That is why higher tops speeds are better achieved by lower the frontal area and drag coefficient (linear gain) rather that adding power (4th root gain).
BlackICE