550s too small for my EVO3?

[tstkl]

i personally will be moving up to 1000cc injectors after I get dsmlink. there is no point in going any lower. I've maxed out my 450cc injectors on my 14b and I don't want to have to worry about maxing out injectors again for a long, long time. Might even pick up some 1600cc injectors, I'm just curious as to why they are cheaper than 1000cc injectors. is it a different design or something? pm answer as to not highjack thread

good to hear that the evoIII isn't to much better than us 14b'ers, since most of you guys use it for 15-20 psi anyways. Its also good to finally see someone on this thread talking about cfm's. When I came here from 3si.org, I went from only hearing about cfm's at different pressure ratios and such, to only hearing people talk about psi. reading stealth316.com is really what let me keep a level head and realise the truth. Most educational site on the internet in my opinion.

 

[danamo250]

So whats an ideal DC? I was told that you want to aim for about 80% when calcualting for injector size.

 

[dsm-onster]

Yes you'll want to calculate how much injector you need to reach your horsepower goal by figuring them to be open 80% of the time.

If you go much over 80% idc, several things happen. Because of the particular flow characterisitcs of a nozzle, the flow gets irratic and more or less like a pure stream instead of a pulse. The ecu can only calculate in pulses and so the right amount of gas to inject into the port is now anybodies guess as the ecu is up a creek.

Also, because the injector is on (current running through the solenoid) almost the entire time, the solenoid inside can burn up over time. High IDCs usually shorten the life of an injector substancially.

Third, getting closer and closer to 100% idc without an SAFC, MAFt, or other piggyback on while using a stock (unchipped) ecu means that the ecu is seeing mass airflow that is close to the mass airflow number at which it will cut fuel. 100% IDCs do not cause fuel cut. But where there is a mass airflow number that causes the ecu to calculate 100% IDC, then there is fuel cut. So, indirectly, you can use your % IDC to figure how "close" you are to fuel cut. Keeping lower % IDCs by using larger injectors coupled w/ a piggyback is one sure fire way to push back the likelyhood of fuel cut, other than actually programing it out with a chip or dsmlink or using another ecu such as AEM EMS or MegaSquirt.

So running higher than 80% IDCs screws around w/ the target air/fuel ratio in the mapping, prematurely wears out the injectors, and brings you closer to fuel cut.

Here's a great spreadsheet to properly size your injectors and do verious other calculations for you: DSM_Tuning_Sheet_v2.1.xls.

P.S. fuel cut is, of course, the ecu freaking out and cutting off ALL the injectors completely. It has been often coupled w/ many picking their teeth from their steering wheel. It is a sudden lean condition and the ECUs last ditch effort to remedy what it sees as a problem: too much airflow for which to give the proper amount of fuel. Don't hit fuel cut often. Running super lean frequently is a great way to bring the combustion chamber to welding temperatures and hole a piston or worse.

 

[ShapeGSX]

Assuming a relatively stock engine, you can see that the efficiency level of a 14B is actually greater than a large 16G at airflows that would equate to ~15psi at the intake. Stepping up the boost on the same engine, you can see that we even out at airflows ~20psi.

Now if you were to drastically increase engine VE (stroker, cams, intake) and take the engine to higher RPMs, the story would be much different and you'd see the larger turbo perform better at lower psi levels as the you'd be shifting those "dots" to the right in the below.

How did you pick the horizontal position of the dots in the first place? Your equations make it seem rather arbitrary.

 

[ShapeGSX]

BoostEst is a calculation that the ecu makes and then ships it the factory boost gage.

Bad information. BoostEst has nothing to do with the factory boost gauge.

Here is the calculation for BoostEst in the DSMLink Client Java source code:
float apr = aprCalc.next(vals);

// Take airflow per rev in gm/rev, and convert to boost estimate

float psia = apr * 13.0F;
psia = psia * 2.0F / displacement;

pressure = psia - 14.696F * altitudeCorrection;

The history is that they calculated a constant that would convert grams/rev over to boost pressure at ~5000RPMs. The farther away from 5000RPMs you get, the worse the estimate will be (but never too far off). If your BoostEst is way off, you should address the issues with your air metering, because it is likely that you have some.

 

[ShapeGSX]

good to hear that the evoIII isn't to much better than us 14b'ers, since most of you guys use it for 15-20 psi anyways. Its also good to finally see someone on this thread talking about cfm's. When I came here from 3si.org, I went from only hearing about cfm's at different pressure ratios and such, to only hearing people talk about psi. reading stealth316.com is really what let me keep a level head and realise the truth. Most educational site on the internet in my opinion.

An Evo III 16G is a lot better than a 14B in terms of airflow. But any turbo at 15 to 20psi is going to be roughly the same. Although the 14B is really starting to strain at 20psi and high revs.

Frankly, CFMs are a bad unit of measure for cars. You have to assume a particular density and temperature, and that changes with altitude and temperature (duh). A mass airflow rate (like lb/min or gm/sec) is a much better unit to use since it is temperature and density independent.

So, really, I think that all of the converted maps on stealth316 were taken in the wrong direction. There is a reason that the factory maps have a mass airflow rate on the x axis, and not CFM.

 

[DSM90AWD]

How did you pick the horizontal position of the dots in the first place? Your equations make it seem rather arbitrary.

I assume you read the link to Jeff's Site and the assumptions I was making in the picture?
Plug in those variables into his Turbo Temp/PR calculator and there you go

Pressure ratio has nothing to do with with compressor efficiency, so with the same intake, FMIC, boost pressure at the Intake, Outside temps/Pressure, the Pressure Ratio will be the same (I resized Jeffs Compressor Maps for uniformity in the compare)

Frankly, CFMs are a bad unit of measure for cars. You have to assume a particular density and temperature, and that changes with altitude and temperature (duh). A mass airflow rate (like lb/min or gm/sec) is a much better unit to use since it is temperature and density independent

Yes not optimal (as mass airflow is what the ECU actually uses to determine Fuel/Timing), but keeping temp and ATM Pressure constant in this example to compare diffeent turbos does not make the results any less accurate. Can convert CFM to airflow and post your own graphic if you want

 

[ShapeGSX]

I assume you read the link to Jeff's Site and the assumptions I was making in the picture?
Plug in those variables into his Turbo Temp/PR calculator and there you go

That determines the vertical position (pressure ratio) of the dots. I'm talking about the horizontal position. In other words, how did you pick the CFM?

 

[DSM90AWD]

Was it me or did the last two posts disappear and just came back

That determines the vertical position (pressure ratio) of the dots. I'm talking about the horizontal position. In other words, how did you pick the CFM?

I started at reasonable (yes arbitrary) HP Levels for these turbos (250 and 300) then using the math/assumptions illustrated in the pic, coverted to Lb-Min and then to CFM

 

[ShapeGSX]

I started at reasonable (yes arbitrary) HP Levels for these turbos (250 and 300) then using the math/assumptions illustrated in the pic, coverted to Lb-Min and then to CFM

Obviously this isn't really a valid way of performing this calculation. You are making an assumption about both airflow and power and the assumption that you are making for the x axis also depends on the value chosen of the y axis.

A 2.0L engine can only swallow so much air per revolution. I think that a better way to do this would be to figure out how much air an engine can swallow per revolution (in lb/min) at a given boost level assuming 100% volumetric efficiency. From that, pick an RPM that you think will provide peak power (say 6250RPM for these turbos with stock cams). Multiply the airflow/rev by 6500rev/min to get an airflow in lb/min. That gives you an absolute maximum airflow/rev. Now you have a coordinate for the x axis of the compressor map. Of course, 100% efficiency isn't going to happen, but this is just back of the envelope stuff.

This is essentially what the Stealth316 web site is trying to do, but with all VE points taken into account. I just wish they hadn't used cubic feet instead of a mass measurement. Using mass simplifies the math. Thank god Einstein used mass instead of cubic feet with his E=mc^2 equation. Can you imagine how confusing that would be?

Of course, the best way is to just plot it from a running engine, like I did:

You must be logged in to view this image or video.

 

[DSM90AWD]

Nice! Did you measure intake restriction and pressure drop on your run or did you uses a constant to determine PR? Any similar runs with a 14B?

Oh life would be so much easier if everyone had a dyno in their garage, could datalog +oo inputs/outputs and could swap turbos at the click of a mouse

 

[ShapeGSX]

Nice! Did you measure intake restriction and pressure drop on your run or did you uses a constant to determine PR? Any similar runs with a 14B?

I used the barometric pressure sensor in the 2G MAF and the intake manifold pressure to calculate PR. Yeah, I know, it isn't exactly right because the intercooler is in the way. So it is likely that the PR is actually higher than I am graphing.

 

[dsm-onster]

Bad information. BoostEst has nothing to do with the factory boost gauge.

Here is the calculation for BoostEst in the DSMLink Client Java source code:
float apr = aprCalc.next(vals);

// Take airflow per rev in gm/rev, and convert to boost estimate

float psia = apr * 13.0F;
psia = psia * 2.0F / displacement;

pressure = psia - 14.696F * altitudeCorrection;

The history is that they calculated a constant that would convert grams/rev over to boost pressure at ~5000RPMs. The farther away from 5000RPMs you get, the worse the estimate will be (but never too far off).

This makes total sense. Good info . So although the factory boost gauge is not a direct reflection of the BoostEst, it works on the same principle as the car's stock boost gauge. [dmertz]

It would be better to say that if your stock boost gauge is off relative to an aftermarket gauge significantly OR your BoostEst is off relative to an aftermarket gauge significantly then a number that the ecu uses to do a mass airflow calculations is probably off, which could be caused by a boost leak, bad maf, wrong maf or maf settings, incorrect intake air temp input, and/or incorrect baro input. That was a long sentence ! A factory boost gauge is not reliable for measuring boost because of possible boost leaks, possible maf inaccuracies (i.e. MAFt, hacked mafs, 2g maf in a 1g), possible baro or IAT inaccuracies...

If your BoostEst is way off, you should address the issues with your air metering, because it is likely that you have some.

Well, I did say:

1. Do you have a 2g maf in your 1G? becasue you have the 2g maf option active in your MAF compensation box.
2. Double and triple check w/ a boost leak test...

 

[dsm-onster]

Obviously this isn't really a valid way of performing this calculation. You are making an assumption about both airflow and power and the assumption that you are making for the x axis also depends on the value chosen of the y axis.

A 2.0L engine can only swallow so much air per revolution. I think that a better way to do this would be to figure out how much air an engine can swallow per revolution (in lb/min) at a given boost level assuming 100% volumetric efficiency. From that, pick an RPM that you think will provide peak power (say 6250RPM for these turbos with stock cams). Multiply the airflow/rev by 6500rev/min to get an airflow in lb/min. That gives you an absolute maximum airflow/rev. Now you have a coordinate for the x axis of the compressor map. Of course, 100% efficiency isn't going to happen, but this is just back of the envelope stuff.

This is essentially what the Stealth316 web site is trying to do, but with all VE points taken into account. I just wish they hadn't used cubic feet instead of a mass measurement. Using mass simplifies the math. Thank god Einstein used mass instead of cubic feet with his E=mc^2 equation. Can you imagine how confusing that would be?

The DSM_Tuning_Sheet_v2.1.xls does a great job of what you are mentioning here. It also takes into account turbo to intake mani presure drop, turbo efficiency, intake temps, and intercooler efficiency.

A couple of side notes using this sheet:

1. Where the variables are 20 psi, 1 psi pressure drop, intake temp of 80*, intecooler efficiency of 65%, 6250 rpms, 100% VE, 2.0L displacement; A compressor efficiency of 65% yields 30.57 lbs/min, and a compressor efficiency of 70% yields 30.88 lbs/min. Not very much. 0.31 lbs/min difference or approximately 3 hp. 6* aircharge temp difference. Those identical compressor efficiencies are even more negledgible as your intercooler efficiency goes up.

2. Keeping the turbo efficiency the same (at 70%) but changing the IAT from 80* to 70* (using the same turbo at a different time of day or a crappy cold air intake) yields an increase from 30.88 lbs/min to 31.46 lbs/min. 0.58 lbs/min difference or approximately 6 hp increase. 10* aircharge temp difference.

...this is some mathematical theory that goes against some opinions that compressor efficiency is paramount and a cold air intake is not important on a turbo car.