How much boost on 550s?

[talon187]

ok my profile is filled out all but the bushur race front mount im going to be using a safc2 and maft to tune with im wonder how much boost i can run on a big 16g and be ok... im also wondering if someone can give me some help with the tuning part ? what should i set the maft at and so forth...newbie at tuning... and i did some reading on the safc2 and im still like what ? anyway any help/advice would be great

 

[JayRolla]

Get yourself a wbo2 for tuning. Then get a logger. Start at around 15psi and tune to a low 11.0 afr on pump gas. Slowly turn up the boost and make sure the afr stays around 10.8-11.1 and watch for knock. Once you get some knock turn the boost back to the spot where there was no knock.

This will give you a safe tune. I dont recommend tuning without a wbo2 and logger.

 

[bpestilence]

A good approximation is:

HP = (F * duty * N)/ BSFC

F = flow of an injector
duty = maximum duty cycle of the injector (use 0.8 for high impedance, 1.0 for low impedence using the proper EMS and no resistor pack)
N = number of injectors
BSFC = brake specific fuel consumption. These values have to be assumed, and since I only know the values in SAE units, I also convert the flow from cc/min to lb/hour using the conversion 10.5:1 (respectively). BSFC is somewhere between 0.45 to 0.6, depending on the efficiency of the system. Using 0.55 for a turboed, fuel injected car is usually correct.

So, HP = (550/10.5 * 0.8 * 4) / 0.55 = 305 horsepower. The injectors will safely support 300 horsepower. Now just figure out how much boost (etc) you need to make that.

 

[95blackGsTurbo]

If you are good you can just tune with a logger. I ran 20psi on a Big 16g ported and clipped and was seeing about a half a count of knock with 88% IDC. I wouldn't go anywhere over 90% IDC but you should be able to run safely 19-20lbs depending on how good of pump gas you get.

 

[FFTec - jerry]

If you are good you can just tune with a logger. I ran 20psi on a Big 16g ported and clipped and was seeing about a half a count of knock with 88% IDC. I wouldn't go anywhere over 90% IDC but you should be able to run safely 19-20lbs depending on how good of pump gas you get.

Although I disagree with tuning w/o a wideband, I think the quality of gas you pump will make a big difference. Unless you have had some experience with tuning and can understand what's happening without using a wideband, I'd play it safe and get one.

jerry

 

[95blackGsTurbo]

Yeah I recommend a wide band highly if you are new but I'm sure you tune cars all the time Jerry without wide bands. I have yet to flash an EVO or Subie yet with a wide band and I have tuned quite a few of them. All about understanding what you are doing.

 

[FFTec - jerry]

Yeah I recommend a wide band highly if you are new but I'm sure you tune cars all the time Jerry without wide bands. I have yet to flash an EVO or Subie yet with a wide band and I have tuned quite a few of them. All about understanding what you are doing.

Actually, I dont tune at all, Sean is the tuner here. We use a wideband no matter what since we have one on the dyno. There's no need to second guess these things if they are readily available.

Jerry

 

[95blackGsTurbo]

haha cheaters. I only do road tuning since I don't own my own fancy shop . But when they go to the dyno to make their 3 pulls for $65 I am usually around the 11.3-11.5 area on race gas so I just do some minor adjusting to get it to around 11.7-11.9 and they are on their way. For some reason shops won't let me use their dyno's to tune on .

 

[zatomz]

Good stuff here, I have close to the same setup and This is good information.

 

[Boosted98gsx]

Injector flow needs to be colinear with airflow capabilities at a certain PSI. Boost doesn't mean anything, airflow and velocity at that pressure level does. Boost is a static measurement of back pressure on the head/cylinder. Airflow and fuel flow are dynamic quantities, and you cannot compare dynamics to statics.