boost vs cfm

[OkieRichard]

Is the purpose of making more boost to produce more cfm? With two different set ups with equal cfm's, will increasing boost increase hp? Does increasing boost help flow more cfm at lower rpms?

 

[1gDSM4g63]

Yes, running higher boost will simultaneously increase the air flow (CFM), but running a higher boost will not help the CFM flow at lower rpms. If the turbo isn't spooling in your low rpm then the CFM will stay the same whether or not you are running a higher boost. And yes if tuned correctly running higher boost will generate more hp. What are you trying to do?

 

[OkieRichard]

I am just trying to understand the physics/whatever behind it. I've got a 60-1 on there and the new engine will be broke in by tomorrow. I was looking at the compression chart and I was trying to understand what it is that actually makes power, CFM or boost or both? I realize that you can't have one without the other but if your CFM is maxed out for that turbo is there a reason in pushing more boost? The reason I was asking about CFM being increased with increased boost at lower engine RPM's (not necessarily for off boost applications) is because I guess that I'm trying to ask something different. I guess I'm trying to ask, if you are making full boost is your CFM rate going to be the same throughout the engine RPM's that you are making boost? It seems by the maps if you make more boost you have a little more guarantee that you will be maxing the flow of the turbo and maybe that would be beneficial for lower engine RPM's where flow might not be as high as with higher engine RPM's.

I have 9:1 with an FP Red and by the chart you can be flowing the same cfm at 30 psi as you would at 35 psi. So would increasing the boost above 30 be of any benefit?

 

[pboglio]

Read this: TurboByGarrett.com - Turbo Tech103

Engine CFM is a product of boost pressure, air temps, engine displacement, volumetric efficiency, rpms, etc. Then on the other hand you have the turbo compressor map itself. Essentially you are comparing the "theoretical" performance of your reciprocating engine (air pump/compressor) to the "actual" peformance of the turbocharger (air pump/compressor).

You can put the engine airflow equation into a spreadsheet and run all kinds of cfm scenarios for your engine. BUT, it has to match or be below the top speed compressor line for whichever turbo your planning to run. The turbo is calling the shots on the engine's cfm basically.

This type of mapping can also help you determine the "theoretical" maximum spool rpm for that compressor using the compressor map "surge" line. You get all kinds of useful info out of the compressor maps.

 

[1gDSM4g63]

Exactly what pboglio said. CFM also incorporates boost pressure, air temps, engine displacement, volumetric efficiency, and rpms.

I don't where you're heading or the tuning device you're using, but I suggest you get a good intercooler instead of the generic one off of eBay because the intercooler is a huge factor in the CFM. The last thing you want to do is to lean out and/or not pushing as much boost your car is built for.

 

[toofast82]

Maybe this page will help some Compressor Flow Maps and Calculations

Here is a calculator to see what an engine will require at a given rpm/boost based on VE and displacement. This will help you plot your engines needs on a compressor map to see if the turbo is right for you. I plotted a basice 2.0/20psi/7k as an example:
http://cybrina.mine.nu:8080/WebModu...oost=20&maxrpm=7000&rpmstep=500&Submit=Submit

CFM Calculations

 

[OkieRichard]

So it is dependent on RPM, and I can see this on the example shown bytoofast82. So it seems logical that increasing boost could give more cfm at lower rpms and therefore increasing the hp "area under the curve". I'm using the maft pro with speed density and also have a zeitronix wideband. As far as intercooler goes it is a little bit late, I already bought a huge one off of ebay core of 28x12x4... so I hope that it won't hinder things to badly.

 

[toofast82]

So it seems logical that increasing boost could give more cfm at lower rpms and therefore increasing the hp "area under the curve". I'm using the maft pro with speed density and also have a zeitronix wideband.

Tuning is all a compensation game between boost/fuel/timing. With 1gs, you have to be careful because the timing curve is pretty aggressive as well as knock happy on when increasing boost on pump