but woon's is a street car with stock interior, radio, etc. not a dedicated track car.


my compression tester reads 300

 

? the evo has a 4g63...always has...the evo has been around since the early 90s in japan with a 4g63 in it....we always had dsms with the 4g63, then they brought the evo here and kept the 4g63...i think they are changing it for the evo X though. what smaller engine are you talking about?

 

He is referrring to the Evo engine being smaller than the Supra engine.

 

ever look at a diesel's cylinders or rods, they're friggin huge! they have to be cause they make a lot of torque down low which stresses the internals hard.

boost is a measure of restriction, your engine can handle as much cylindrical pressure as the properties of the components can handle.

 

I agree with what you're saying. If you have a pressure driven flow then yes twice the pressure with half the flow area would be the same cfm.

What I was trying to say was that if you take an engine cylinder as a quasi sealed container (which it is more or less after the intake valve closes) then...the more positive pressure a turbo can supply (before the intake closes) than the more molecules of air that will be in the engine to combust with fuel so...it would be a measure of air (in a closed container aka an engine cylinder). The more pressure in a sealed container, the more air molecules it contains. An engine is an air pump with air flowing in and out but combustion does take place in a closed container (at least it can be modeled as such because combustion takes place so rapidly it's modeled as a fixed volume with a rapid pressure increase). So..if you take two identical ls1's one that runs at 15psi and one at 20psi, if BOTH have IATs at the same temperature, the one at 20psi will have more air molecules in the cylinder at the time of combustion.

Everybody is right when they say it's psi versus cfm. The power required by a pump is equal to the flowrate times the pressure drop/rise across it. A turbo will have a fixed amount of power being delivered to it in the form of the exhaust. So it has to have a tradeoff between the two.

 

So, everybody saying that PSI is "just a measure of restriction" would rather see 0 psi on a boost gauge then with their forced induction setup? Hmm.

Where do you think the pressure comes from? Two identical engines, ie. same displacement, breathing characteristics and rpm range. One engine is fed by atmospheric pressure alone, the other is fed by a supercharger of some type either turbo or belt driven centrifugal for example. The naturally aspirated engine will flow a max of say 650 cfm. The centrifugal supercharger is driven to move say 1000 cfm. As the 1000 cfm is roughly 1.5 times the volume that the N/A engine can ingest pressure will increase in the intake manifold over atmospheric as the airflow stacks up and increases in temperature due to compression. If you have 1.5 times the volume * of air in an area then it stands to reason you have 1.5 times the oxygen and therfore can burn 1.5 times the fuel to make more power.


While you most deffinitely may see a decrease in a boost gauge reading after doing exhaust work, cam swap and or cylinder head porting what you are doing is increasing the volumetric efficiency of the engine and allowing more airflow to be used. This may come from more exhaust being evacuated which basically makes the engine larger or from allowing more of the intake charge to make it in the cylinder. At some point there will be no more improvements that can be made in the VE% from traditional hotrodding modifications at your rpm level and making more power will come solely from driving the compressor to higher airflow levels and improvements in intercooling.

SpeedDensity formulas calculate air density from basically airpressure / temperature with a known displacement and constant for the air the engine breathes.

Pressure with temperature is a measure of air density, and therefore power potential.

Never compare different sized engines and or rpm ranges with "boost". There is no correlation as boost is determined by airflow of the compressor / the airflow the engine is capable of using without the supercharger's help.

A smaller engine may operate with more boost, but less overall airflow due to its lower capacity (cubic inch displacement and VE %)

Likewise a larger lower rpm engine may also operate with more boost but comparable airflow the the smaller higher rpm package.

Take a Cummins diesel for example. 360 cubic inches / 3200 redline stock max boost 32 psi. Estimated CFM 1070

1070 CFM into a 6900 rpm LS2.......9 psi.

Both engines would have roughly the same fuel volume requirements. The diesel would be more effiecient as for one there is no throttle and it operates at less rpm.



* In this case I want to make a clarification. By volume I really mean weight here. I make the assumption that the air entering the supercharger is the same density as the air being naturally aspirated and thus weighs the same and contains the same ammount of oxygen. 1.5 times the volume of the same temperature air will contain 1.5 times the ammount of oxygen. The excess volume that is ingested into the supercharger will compress into the available volume of the intake system.

 

All I can say is..................DAMN!

 

You gasser guys crack me up.. My street driven diesel sees 50 psi on a daily basis.. Try huffin' 120 psi through 2 turbos and 359 c.i. with almost as much fuel flowing as a top fuel dragster...

 

We build diesels running anywhere from 75psi to 250psi depending on the application.

 

just think what A V8 would run on 31 psi

 

Just look at outlaw 10.5 cars. Our customers run well north of 30psi+

 

Anderek,
I never knew that's how speed density worked. so basically it just uses the ideal gas law
(Pressure)/density=(Gas constant)*Temperature to constantly figure out the density for the incoming air?

gotta love diesels and practically no pumping loss at part throttle!

 

Here is a good description of what's going on inside for speed density calculations:

http://www.megasquirt.info/v22manual/mfuel.htm

 

A couple cars on here do run that kind of boost.......

restriction of flow........

Look at Dave Underwoods car.... 7.69's @ 15 psi...

 

You do know that TF cars are running 90+ GALLONS per MINUTE at over 500 psi when full throttle right? Not slamming you at all, because I don't know anything about diesel performance, but I wouldn't imagine a lightduty truck diesel (even when turned up to the max) could be flowing that much fuel!

 

My Turbo T-(Sold) and Grand National have seen 30+ PSI on numerous occasions and the new motor in my GN will most likely see the same with a TE-63 turbo. With better heads I wouldn't have run quite as much boost in the past to run the numbers I was after. But now...........

Jim C.

 

500 psi..uh hu ..exquise me...bacon..i thought you said 500psi!!!

 

He's talking about fuel pressure. Boost is more in the 60-80 psi range with alcohol screw blowers running up to 100. 1:1 AFR on nitro.

 

But the boost level on TF and Funny cars is actually closer to 50-60 psi, as they are limited to a max of 50% overdrive on the blowers, and we all know a conventional roots blower can't move that much air!

You are right on the Alcohol cars though, they do run up to 100 psi of boost with the screw blowers that they are allowed to run.

 

You're referring to the NHRA - No Hardware Replacements Allowed, or No Hardware Research Allowed, New Hardware Requires Approval, No Hotrodders that Resist Authority, blah blah. Hey, is that your car on Super Chevy's website?