Id have to see data logs that used calibrated MAP sensors and know that the timing was verified on both applications. Converter slip is probably different. The other guy is using alky also. There are to many variables to know the reason why one is using more power than the other. I wouldnt be running low boost like that either with those turbos either.
Pressure vs. Volume vs power output
- Thread starter Amelio
- Start date
No I am not running alky I did put a few gallons of 110 in the tank to help.....
The hp and tq figures are just made up I dont really know what kind of power my car makes but I imagine it is close to those figures.
FWIW . . . . I tried to back into the numbers.
If I am even close, on the 19PSI @ 118 MPH run, trap RPM was around 6100 with 9% slip (58 lb/min)
To run that number at 14PSI with alky, it is estimated at 6200 RPM, 0% slip (59 lb/min). With alky I would bet there is more timing in the tune as well.
Now, if I run the same numbers on the OP's car with alky, the estimated MPH is 119. With 5% vs 9% converter slip, it jumps to 121 mph.
Numbers are probably off, but it gives an idea of comparison.
There is definitely a BIG difference and I see why you are asking the question, which I am asking myself as well. I agree 110% with Bison though; It is NOT the turbo since that is not the constraint. Maybe the boost gages are off? (LOL!)
To me, this is pretty interesting and there is definitely more studying to do on my end . . . there is a reason Red runs 123 MPH through a stock IC/Elbow/Air box in TSA. Serious business!
So the numbers you come up with are probably real close.....I do not know my trap RPM because I was not logging but it has to be close to that because I have a non locking converter and was on 26" tire.
I think i would be at the 120mph mark if I was on 28" tire and had a locking converter which my friend does. I know that is costing me 2-3mph on the big end.Now with a locking converter and 28" tire I still dont think I could run an 11.3 on 16psi that just seems incredibly fast for such low boost.
The reason I am thinking this is because I primarily drive my car on the street...I want a strong mid to low 11sec car with 10 sec capability. I believe I have that now. But if I can achieve the same time or faster on the same or lower boost level by changing my turbo or converter then that is an option worth lookng into.
Now I do releaize I can most likely get in the lower 11 sec rang on the 19psi with a really good tune since the 11.54 was done with not much timing and god only knows where the fueling was......
So before I do anything my next step would most likely be to run a 28" tire to help drop my rpm and pick up my mph and have some logging files to dial in the tune. Then I can figure if I need a turbo change or converter change.....
My whole thing is if I can run faster on lower safer levels then thats what I want......
I just recently have been able to pick up another TR, so after 6 years I finally have another one to tinker with.
I am not trying to come off as an expert on internal combustion engines, and a lot of guys here have real world experience which always gives the best answer, but here is some food for thought. Below kind of summarizes what has already been posted with a few added pieces. I would be interested in hearing others thoughts to what I posted, and enjoy these kinds of discussions.
The manifold at a given pressure can only flow a specific amount of air. The amount is a fixed relationship between specific volume, flow area, pressure, and pressure drop. Other factors are involved to, but these are large drivers. It does not matter what is generating the 17 psi, the flow will be fixed for the two identical systems at 17 psi with two of the variables affected by the turbine and compressor selection. Charge temperature which is due to compressor efficiency. 40 deg F is equivalent to about 1 psi boost with regard to specific volume, but you do not get the effect of pressure increase just charge density. Residual exhaust and pressure in the cylinder also impact flow. This can be impacted by turbine selection, which will impact pressure drop across the intake port and manifold by increasing backpressure in the exhaust and hence the cylinder, not sure if this has any significant affect. The above only addresses the steady state question, behavior across the rpm range and turbo spool up are beyond my current ability to comment on.
The point made in an earlier post about back pressure for the posed question I would think is the most prominent driver. Increased back pressure is going to add to pumping losses in the engine. It takes power to pump the exhaust out against the pressure in the exhaust manifold. A typical engine has to actually pump out, using crank energy, the last 15% of the exhaust gases. All kinds of factors go into this and that number can change based on cam, headers, port…. I don’t know what that number is for a typical turbo engine, but you get the point. Higher manifold pressure means more work to get the exhaust out, less net horse power at the crank. If you can make 17 psi boost with significantly less back pressure per lb. of boost than the turbo making 26 psi, you will make proportionately more power for the boost level. Again, drivability and spool maybe effected.
Fuel, timing and detonation have also got to be significant to a question like this. If you are able to optimize timing and fuel for each due to the use of good fuel, I would think the advantage tends towards the 26 psi of boost. The optimal timing curves are looking to get peak pressure roughly in the neighborhood of 20 degrees past TDC. To early or too late and you are losing torque and horse power. Detonation you are losing horse power.
Glad to be back in TR world, hope this adds to the discussion. I see a lot of guys on the board making serious HP, looking forward to reading and learning what I have missed in 6 years. I don’t have any big HP goals at the moment, car is basically stock, excellent body, but needs all of typical TR maintenance items done, then we will see where to start with tuning and upgrades.
I am not trying to come off as an expert on internal combustion engines, and a lot of guys here have real world experience which always gives the best answer, but here is some food for thought. Below kind of summarizes what has already been posted with a few added pieces. I would be interested in hearing others thoughts to what I posted, and enjoy these kinds of discussions.
The manifold at a given pressure can only flow a specific amount of air. The amount is a fixed relationship between specific volume, flow area, pressure, and pressure drop. Other factors are involved to, but these are large drivers. It does not matter what is generating the 17 psi, the flow will be fixed for the two identical systems at 17 psi with two of the variables affected by the turbine and compressor selection. Charge temperature which is due to compressor efficiency. 40 deg F is equivalent to about 1 psi boost with regard to specific volume, but you do not get the effect of pressure increase just charge density. Residual exhaust and pressure in the cylinder also impact flow. This can be impacted by turbine selection, which will impact pressure drop across the intake port and manifold by increasing backpressure in the exhaust and hence the cylinder, not sure if this has any significant affect. The above only addresses the steady state question, behavior across the rpm range and turbo spool up are beyond my current ability to comment on.
The point made in an earlier post about back pressure for the posed question I would think is the most prominent driver. Increased back pressure is going to add to pumping losses in the engine. It takes power to pump the exhaust out against the pressure in the exhaust manifold. A typical engine has to actually pump out, using crank energy, the last 15% of the exhaust gases. All kinds of factors go into this and that number can change based on cam, headers, port…. I don’t know what that number is for a typical turbo engine, but you get the point. Higher manifold pressure means more work to get the exhaust out, less net horse power at the crank. If you can make 17 psi boost with significantly less back pressure per lb. of boost than the turbo making 26 psi, you will make proportionately more power for the boost level. Again, drivability and spool maybe effected.
Fuel, timing and detonation have also got to be significant to a question like this. If you are able to optimize timing and fuel for each due to the use of good fuel, I would think the advantage tends towards the 26 psi of boost. The optimal timing curves are looking to get peak pressure roughly in the neighborhood of 20 degrees past TDC. To early or too late and you are losing torque and horse power. Detonation you are losing horse power.
Glad to be back in TR world, hope this adds to the discussion. I see a lot of guys on the board making serious HP, looking forward to reading and learning what I have missed in 6 years. I don’t have any big HP goals at the moment, car is basically stock, excellent body, but needs all of typical TR maintenance items done, then we will see where to start with tuning and upgrades.
machinegun
Active Member
- Joined
- May 25, 2001
I want to first say that we dealing with assumptions here so lets say that the cylinder bore and stroke are exactly the same for both engines.
VE of any item pre or post the cylinder will affect the necessary flow of air however the cylinder will stay exactly the same. Remmember that boost is the stuck air not making it into the cylinders as fast is it is being pumped there.
To use an analogy.
2 5 gallon buckets.
Fill one with a 1 inch hose and fill one with a pressure washer.
In this case based on the original question asked, both buckets are still full at 5 gallons. They may even get filled at the same time, but they are still both filled at 5 gallons.
VE of any item pre or post the cylinder will affect the necessary flow of air however the cylinder will stay exactly the same. Remmember that boost is the stuck air not making it into the cylinders as fast is it is being pumped there.
To use an analogy.
2 5 gallon buckets.
Fill one with a 1 inch hose and fill one with a pressure washer.
In this case based on the original question asked, both buckets are still full at 5 gallons. They may even get filled at the same time, but they are still both filled at 5 gallons.
Kind of a bad analogy comparing a non-compressible like water to a compressible like air, which has an expansion ratio.
Yeahh. About as good as everyone that refers to mass efficiency as volumetric efficiency. Ive only ever heard 3 people say it correctly. All 3 were engineers.
