Trivia question for the day!
If you have two cars....same weight, same engine displacement, same turbo etc.... one car is running 35psi of boost pressure, the other car is running 25psi of boost pressure...yet both cars run the same e.t. and trap speed.... Why?

Boost doesn't mean anything except for a measurement of the air NOT getting into the engine!!

If both cars weigh the same and trap the same, then RWHP is similar.

The reason for the difference in boost could be many..... back pressure, cylinder head flow etc. Bottom line is that both cars are flowing the same volume of air.... just that the one at 25 psi is doing it much more efficiently.

Boost doesn't mean anything except for a measurement of the air NOT getting into the engine!!

If both cars weigh the same and trap the same, then RWHP is similar.

The reason for the difference in boost could be many..... back pressure, cylinder head flow etc. Bottom line is that both cars are flowing the same volume of air.... just that the one at 25 psi is doing it much more efficiently.

Both turbos are the same....so it's not in backpressure! Your on the right track, I am looking for a bit more specific of an answer though. So by "the same volume of air" are you saying both engines are under the same cylinder pressure?

Both turbos are the same....so it's not in backpressure! Your on the right track, I am looking for a bit more specific of an answer though. So by "the same volume of air" are you saying both engines are under the same cylinder pressure?


Am I then to assume that both engines have the same VE characteristics, same CR, same cams, same head flow, same backpressure?

Am I then to assume that both engines have the same VE characteristics, same CR, same cams, same head flow, same backpressure?

No...same CR... V.E. is Obviously different..otherwise...they wouldn't be running the same mph with less boost!

Trivia question for the day!
If you have two cars....same weight, same engine displacement, same turbo etc.... one car is running 35psi of boost pressure, the other car is running 25psi of boost pressure...yet both cars run the same e.t. and trap speed.... Why?Is this a real-life scenario, or hypothetical? If it's an actual example, what about other factors not related to horsepower, such as tires, launch technique, driveline loss, suspension, etc.? Are they all exactly the same too? Even if they are, depending on the tires, more horsepower might simply buy you more wheelspin. ...and was either car running nos?

Even if the example is hypothetical, if the turbo is the same...but that turbo has a relatively small exhaust housing...the extra boost may not translate into significantly more horsepower. As EightSecondSupra said, "Boost doesn't mean anything except for a measurement of the air NOT getting into the engine!!". Iow, a small exhaust housing can introduce so much extra backpressure that the additional air+fuel doesn't get into the cylinder...in addition to a higher % of inert exhaust gasses getting mixed with the air+fuel (reducing the VE).

Trivia question for the day!
If you have two cars....same weight, same engine displacement, same turbo etc.... one car is running 35psi of boost pressure, the other car is running 25psi of boost pressure...yet both cars run the same e.t. and trap speed.... Why?


Are both cars running on the same track at the same level above sea?

Are both cars running on the same track at the same level above sea?

Knowing Jason, Id assume same track.... he is questioning our ability to think inside of the engine.


SO Jason.... V.E. being different could be caused by many things. Cams, valve size, intake manifold design, head porting etc.....

Maybe the car at 25 psi is running a triple stage NOS kit like you have!

What about the transmission and final drive?

And the driver??? :aiwebs_01

What about the transmission and final drive?

And the driver??? :aiwebs_01

If that were different, I doubt the ET and trap would be the same.

No nitrous....same track....same day....tires and launch won't affect mph. Basically I am asking you to think what inside the engine is going to affect this type of difference. This particular example is hypothetical, but I can give you several real world example. Just changing valve size alone isn't going to make this much difference. Work with me a bit on this....it's just a fun little exercise....:)

No nitrous....same track....same day....tires and launch won't affect mph. Basically I am asking you to think what inside the engine is going to affect this type of difference. This particular example is hypothetical, but I can give you several real world example. Just changing valve size alone isn't going to make this much difference. Work with me a bit on this....it's just a fun little exercise....:)

Obviously then it is the overall flow of the engine. The head flows better, the cams are more aggressive etc. Each stroke of the cylinder, it can ingest a larger volume of air therefore making more HP. Therefore the boost in the intake is less because more air is actually ingested into the cylinder. The turbo is still moving the same volume of air.

No nitrous....same track....same day....tires and launch won't affect mph. Basically I am asking you to think what inside the engine is going to affect this type of difference. This particular example is hypothetical, but I can give you several real world example. Just changing valve size alone isn't going to make this much difference. Work with me a bit on this....it's just a fun little exercise....:)


Internally, I mean engine wise the only thing that can effect final results so much on such a huge difference of boost(10psi) is timing.

Obviously then it is the overall flow of the engine. The head flows better, the cams are more aggressive etc. Each stroke of the cylinder, it can ingest a larger volume of air therefore making more HP. Therefore the boost in the intake is less because more air is actually ingested into the cylinder. The turbo is still moving the same volume of air.


Right on the money!

Internally, I mean engine wise the only thing that can effect final results so much on such a huge difference of boost(10psi) is timing.

Wrong!....sorry!

Right on the money!


Im pretty smart huh?


What is tomorrow's quiz?

Internally, I mean engine wise the only thing that can effect final results so much on such a huge difference of boost(10psi) is timing.


I cannot see timing make that much difference! Think about it.... we are talking 10 psi of boost..... even for a relatively small turbo that is usually 200 HP difference. Timing wont make that much difference. Unless your tuner is ..... an idiot!

More possible reasons...

At 35psi of boost, that particular turbo could be well outside it's efficiency range heating up the air considerably but still making enough power to keep up with the same turbo at 25psi. The hotter air is less dense and less fuel can be injected. Timing will also have to be retarded to make up for the high pressure / hotter air which will further reduce power.

Another reason... The turbo also may create 35psi of boost but with a tiny exhaust A/R there could be substantial back pressure choking off peak power.

Chris.

More possible reasons...

At 35psi of boost, that particular turbo could be well outside it's efficiency range heating up the air considerably but still making enough power to keep up with the same turbo at 25psi. The hotter air is less dense and less fuel can be injected. Timing will also have to be retarded to make up for the high pressure / hotter air which will further reduce power.

Another reason... The turbo also may create 35psi of boost but with a tiny exhaust A/R there could be substantial back pressure choking off peak power.

Chris.


Chris, Jason stated that both cars have the same turbo, same backpressure.....

Chris, Jason stated that both cars have the same turbo, same backpressure.....

Yes, I was assuming the turbo would be the same, but would be too small to efficiently move 35psi.

Excuse me.....

Weren't we assuming that the engines were identical internally?

Excuse me.....

Weren't we assuming that the engines were identical internally?

No, if you read the first post, it was stated, same displacement, and post or two later, same compression ratio (I forgot to list that one).

So...same turbo, fuel, exhaust, weight, trap speed, e.t., boost pressure, hell let's say same tuner!

Eightsecond Supra hit the nail on the head. Pressure is irrelevant to airflow when it comes to power. If you take a turbo charger capable of making 30psi of boost on a 3.0 liter engine with a head that flows 'x' at 'x' lift, and put it on a 6.0 liter engine that has heads that flow the same, you will effectively achieve half the pressure, yet the same power. Like wise if you have two identical combinations with the exception of one having a cylinder head that flows significanly better, pressure for pressure, the better cylinder head will produce significantly more power!

So the next time you ask someone what boost their running, keep in mind.....that number doesn't necessarily mean Squat!:)

No, if you read the first post, it was stated, same displacement, and post or two later, same compression ratio (I forgot to list that one).

So...same turbo, fuel, exhaust, weight, trap speed, e.t., boost pressure, hell let's say same tuner!

Eightsecond Supra hit the nail on the head. Pressure is irrelevant to airflow when it comes to power. If you take a turbo charger capable of making 30psi of boost on a 3.0 liter engine with a head that flows 'x' at 'x' lift, and put it on a 6.0 liter engine that has heads that flow the same, you will effectively achieve half the pressure, yet the same power. Like wise if you have two identical combinations with the exception of one having a cylinder head that flows significanly better, pressure for pressure, the better cylinder head will produce significantly more power!

So the next time you ask someone what boost their running, keep in mind.....that number doesn't necessarily mean Squat!:)

Although I agree fully with the theory you are proposing, and that in effect is real.

I am not agreeing with your subsequent 6.0litre example, where you are stating that effectively pressure achieved will be half of the 3.0litre example.

If pressure is 35psi in the intake tract, it will be 35psi on cylinder 1 and 35 psi on cylinder 8, on the opposite head! And all other cylinders for what it matters! This is based on the same principle you are using that boost(pressure) is irrelevant to flow.

Although I agree fully with the theory you are proposing, and that in effect is real.

I am not agreeing with your subsequent 6.0litre example, where you are stating that effectively pressure achieved will be half of the 3.0litre example.

If pressure is 35psi in the intake tract, it will be 35psi on cylinder 1 and 35 psi on cylinder 8, on the opposite head! And all other cylinders for what it matters! This is based on the same principle you are using that boost(pressure) is irrelevant to flow.

What you are missing is the turbocharger is only going to flow "x" amount of air, so if it is all in at 35psi on a 3.0 liter, with a 6.0 liter with heads that flow the same, the turbo will still only be able to flow "x" amount of air, therefore since the engine is processing twice as much.......pressure will be cut in half!

BTW, this isn't theory, I have tuned 6.0liter cars with a 76mm turbo and they are capable of making about half the boost I can get out of the same turbo on a 3.0 2j.

What you are missing is the turbocharger is only going to flow "x" amount of air, so if it is all in at 35psi on a 3.0 liter, with a 6.0 liter with heads that flow the same, the turbo will still only be able to flow "x" amount of air, therefore since the engine is processing twice as much.......pressure will be cut in half!

BTW, this isn't theory, I have tuned 6.0liter cars with a 76mm turbo and they are capable of making about half the boost I can get out of the same turbo on a 3.0 2j.


All makes sense....but man, if the turbo can achieve 35psi on the 3litre, I still think that it can achieve them on the 6litre(perhaps even with a lesser effort). What I think is that the 35psi peak once achieved on the 6litre will drop quicker than on the 3litre(twice faster if we consider the same specs as used in the previous examples).

???

Dude, Mind you, I am not in anyway questioning your knowledge when answering(questioning back) it's just nice to talk with someone with a better know how.

Lets pick the maximum boost level that a turbo can hold steady to redline on the 3L..... on the 6L it will be significantly less. Sure the turbo one the 6L motor might be able to make more boost in the lower RPM band where volume is less, but if you compare the max boost that the turbo can hold steady to redline on both motors, it will be WAY less on the 6L.

Lets pick the maximum boost level that a turbo can hold steady to redline on the 3L..... on the 6L it will be significantly less. Sure the turbo one the 6L motor might be able to make more boost in the lower RPM band where volume is less, but if you compare the max boost that the turbo can hold steady to redline on both motors, it will be WAY less on the 6L.

That's exactly what I meant.

Agree !

That's exactly what I meant.

Agree !

Sorry, I guess i should have been a bit more clear... These are discussions, so don't sweat it! It's more for fun, and sharing info than anything else.

i think one was manual and the other was automatic, yaa yaa