I dont mean to knock... Pressure is the energy impact on a unit area: force or thrust on a surface.. Thats straight out of my HVAC book...

Psi is the measure of force exerted on a area surface... Sorry if you already stated that...

again if its stated... but how much psi you have says nothing about how much air you're flowing as I think andereck was saying a 70mm turbo will flow less air at 8psi than a 76mm would flow at 8psi..

has all this been said already??

O and its not really fair to compare turbo diesels to gas engines running turbos... thats a diffrent story.. totally diffrent fields

 

well im no one to say, but honestly them supras are SICK!!!!!!!!!!!!!!!!! anything with a smaller engine displacement like that that runs way under 10's is very respectable

 

1895 RWHP 40PSI LS1

 

huh, well looky there, GOOD LORD!!!

 

Someone please help me I have a question.
I was told when you lower compression ratio you can actually run a little less boost and make the same amount or better horse power. I.E. a stock LS1 at 10.5 CR at #8 makes 550(example) and a built same displacement LS1 with CR of 8.5-9 at say #6 makes the same numbers, is this some what true? Does CR have anything to do with the amount of air you can fit into the cylinder without lifting the head. Inquiring mind wants to know.

 

 

That's not what I'm saying.

The point I'm trying to get across is that its airflow into the engine that makes boost. Excess airflow over what the engine can naturally inhale. Given a single engine tested with two different compressors the airflow requirement to make a predetermined level of boost will be nearly the same. Forget turbo exhaust configurations for a moment. While the smaller 70mm turbo will have to work harder (spin faster) to match a given airflow of its 76mm brother the volume of air required to make a specific power/boost number will be the same up to the smaller units capacity to move air.

In other words if it takes 1000 cfm to make 8 psi on an engine 1000cfm from one to the other compressor will make that 8 psi. Now turbo enthusiasts spec their turbos for many variables that include, but aren't necessarirly dominated by maximum airflow. But I'm not attempting to discuss that as its better left to turbo experts. One compressor will be better than another over a certain airflow range where it comes to thermal efficiency and the compressed air will be cooler and therefore slightly more dense. Proper intercooling and air control into and out of the engine compartment can easily level the field on that and provide larger dividends than agonizing over a 3% differennce in a compressor map.


For those of you that may still be holding to your "psi is only a measure of restriction" way of thinking consider the following: When the throttle is closed the engine pulls a vacuum. A vacuum is a lack of pressure. The engine still takes in say 346 cubic inches of air, but because this air is under less pressure its stretched out and the oxygen molecules are farther apart. Vacuum is often measured in inches of mercury or "HG. Roughly 2 inches of HG is 1 psi. An egine idling with 16 inches of HG has about 7 psi of pressure inside it - 29.92 "HG is an absolute vacuum. 29.92 -16 is 13.92" HG or 7 psi up from a perfect vacuum. Opening the throttle allows more air to rush in the engine, more oxygen, via the higher pressure outside air flowing into the lower pressure manifold. As air rushes in the pressure tries to equalize and squeezes the oxygen molecules closer together. With more fuel delivered to take advantage of the higher oxygen content and a higher dynamic compression ratio the cylinder produces a bigger bang and the engine makes more power. Opening the throttle increases the CFM of air entering the engine. A MAP sensor reads Manifold Absolute Pressure, with the pressure starting at zero, or a perfect vacuum. Why do you think this may be important? Because pressure is a variable in computing air density and oxygen content for appropriate fueling.

Boost is just an artificial atmosphere that pushes the oxygen molecules closer together so more oxygen fits in a given space so you can make more power by being able to burn more fuel.

CFM is the mechanism for creating the boost. The supercharger draws in a given volume of air for its speed (centrifugal superchargers belt or turbo). As is spins a low pressure area is created between its blades and it sucks in the air. This air is accellerated outwards and thrown into the volute. Because air molecules have mass they push againt the neighboring molecules and squeeze together. Think of one of those space age foam pillows and how you can squeeze the foam together tightly and then let it spring back. Its a kind of closed cell foam with air inside.
A higher rate of inducted airflow will throw more air molecules into the intake system pressurizing the system further. The pressure in the system is the molecules pushing apart from each other.


Finally, all pre maanifold induction side hotrod modifications are trying to do one thing. Increase air density by increasing the pressure in the intake manifold. A higher flowing air filter or throttle body is attempting to lower the pressure drop into the engine. Once you optimize this so no measureable drop is occuring no more benifit will be had by installing larger higher flowing parts.

 

its the opposite..more compression will give you more power on the same boost level with all things being equal. so high compression ratio will make more power, but has a better chance of having detonation.

 

hehehehe that thing is ace!!! any idea what turbos are being run on it??

also are there any problems with heads liffting or blow by?? i heard W2W say about about 1200lbst ft blow by gets bad!!!!

thanks Chris.

PS any links to this monster???

 

Been there, done that.....GM production block with only 352cid.....

http://www.w2wpowertrain.com/t-Casper-2.aspx

 

Hybrid GT42's

 

Old video, but still great. A Supra with a good driver and the right combination is deadly... Anyone notice the rear tires he was running?

 

by you by any chance Joe????? lol

Chris.

 

DAMMM forgot about you guys! sorry!

how was the blow by at that boost????

Chris.

 

Not sure about blow by. We did run a bleed-off pressure valve on the cooling system to release pressure. So it definitely pressurizes the cooling system at that level.

 

I think we already know that all turbos do is introduce more air into an engine.. an engines volumetric effieciency - naturally aspirated is only 80%.. meaning filling the cylinders with air.. 80%... with the introduction of forced induction... you can be well over the 100% since the i.e turbo.. crams air into the cylinder...

Cfm isnt a mechanism for creating boost... its just a unit used to measure airflow... cubic feet per minute.. psi is an unit used to express pressure unto a given area... they both are units... a turbo , supercharger are the mechanisms that create boost... which is just the air being crammed into the cylinders that produce the psi by being crammed with such force.. force onto the piston because it is being driven/ sucked in.. and the piston is moving up/down ... 0 psig is equal to atmosperic pressure which is 14.7 psi... 0 psia is perfect vaccum... psi absolute is guage pressure and atmosperic pressure...

 

I love Supras
ive got a 88 turbo, but i would like to have a mk4, its just a matter of time before i have one.
ive never seen any other car that can put down the power that the mk4s do on a bone stock motor. (for the money, under 40grand)
sad to say... but id trade my SS in for one lol

 

Without airflow there would be no boost. The rate of air entering the supercharger determines how much "boost" the system sees. Sorry if mechanism wan't used in the proper context for you. If the engine was demanding 700 cfm naturally aspirated and the supercharger was only capable of delivering 700 cfm at that point in time there would be no boost to the system. Boost is controlled by adjusting the airflow rate through the supercharger.

o psi gauge is equal to atmospheric pressure at the point of gauge installation which is rarely 14.7 psi. This applies to a pressure only gauge that is rated in pressure only.

Absolute pressure gauges, such as a vacuum/boost gauge or map sensor are indeed referenced off of total vacuum. This is why a typical vacuum or vacuum/boost gauge often doesn't rest on zero with the engine off. It acts as a barometer. The pressure conditions for the gauge are different than they were when the gauge was manufactured and sealed, which was supposed to be standard atmospheric pressure for the mechanical vacuum/boost gauge or zero absolute pressure depending on how it was built. Either would require a chamber to control conditions.

psi absolute is just that, it isn't corrected with a gauge pressure.

 

Im not saying your wrong.. but to just clarlify for some of the ppl reading through this gathering knowledge..

Well Psi absolute is Psi guage and atmospheric... psig + atmospheric pressure (14.7 or 15) = psia or absolute psi... psi guage is pressure within the system.. which I think is what you're talking about..

 

I always love this "boost is a measure of restriction" arguement.

If your engine were a fixed orifice, then yes, boost would be a measurement of restriction through the orifice. Enlarging the orifice would reduce the pressure drop and "boost" would reduce but airflow would increase. If you enlarge the orifice enough, then there would be no "boost" and airflow would be maximized.

However, a 4 cycle engine is NOT a fixed orifice. Only during overlap is there a clear path through the engine. During the engine's cycle, the cylinder traps the air in it to compress and burn. When the intake valve closes, you want the maximum possible mass of air in the cylinder. When you overfill the cylinder, you have positive pressure in it. If you build a really great naturally aspirated engine, you could achieve a couple psi positive pressure in the cylinder at BDC before compression. With a forced induction engine, you could get 15+ psi air trapped in the cylinder before the compression stroke. By doing this, you have double the normal amount of air to burn and will make double the power. No amount of head porting or exhaust improvements changes this. In order to get 15 psi trapped in the cylinder at BDC compression, you must have at least 15 psi in the intake manifold, aka "boost".

Mike