Brett B

Jean,

Thanks for the all the great info. I will get some dyno numbers and track times with my current setup just for a baseline. In my opinion chassis dynos aren’t all bad as tuning tools when you have an eddy current load dyno that can exactly match road loading conditions. Everything I am discussing below is related to the built motor. I don’t plan on running anywhere near 1 bar on the stock high compression motor, I’m only driving it at 6 psi right now so I could enjoy it a bit this summer.

You are right about the compressor map. 1 bar at 70% efficiency puts me right around 55lb/min. However, as I mentioned, I will be doing a built motor over the winter, so I don’t exactly plan on running only 1 bar after that. Regardless, here is some interesting math regarding compressor efficiencies using some conservative numbers.

At 1 bar and 70% adiabatic comp efficiency, with an 80F ambient temp, the comp outlet temp is 247 F. With an 80% efficient intercooler, still at 80 F ambient, and at 1 psi pressure drop, the charge air temp at the throttle body will be 113F.
At 1 bar and 68% adiabatic comp efficiency, with an 80F inlet temp, the comp outlet temp is 252 F. With the same intercooler conditions, the charge air temp at the throttle body will now be 114F.
This is of course assuming the intercooler has not been heat soaked.

So looking at the compressor map, if I extend to the 68% efficiency island, I am already at ~60 lb/min at only one bar. The 1 degree F difference in charge air temp from the 2% efficiency drop will not be reflected significantly in power output. Of course this is all hypothetical and is dependent on actual engine demand. But it’s interesting none the less, and is the reason why I chose this turbo. Being able to datalog and monitor the intake air temps in real time with the AEM standalone is a nice plus.

Regarding the fpr. As I mentioned, I don’t just want a 5 bar regulator, I want an adjustable one. As in, I may want to adjust the fuel pressure down at idle slightly. This helps when running big injectors (much bigger then I currently have) as the pulse widths aren’t as short to maintain a lean AFR. For example, I just finished tuning a built Evo 8 with cams this past weekend. It is running 1200cc injectors with the base idle fuel pressure dropped by 5 psi, this helps with idle smoothness. So, having the ability to adjust it myself to my liking is what I am after.

Geoffrey

You have to remember that as you increase the fuel pressure you get a diminishing return on the fuel pump volume, so you have to look at the fuel pumps as well as fuel pressure. In addition, you need to think about the total fuel pressure at the injector. With a base fuel pressure of 5bar, with 1 bar of boost, the injector will realize a 6bar pressure. Bosch injectors are Ok, but some of the other injectors don't like high fuel pressures. Rochester 72lb injectors stick closed at about 68psi for instance. For the MoTeC stand alone setups I do, using 3.8bar base fuel pressure and a max of 85% duty cycle I'll use 44lb/hr injectors to about 480hp, 55lb/hr injectors up to about 550hp, and 72lb/hr up to about 700hp.

With the AEM you should be able to control large injectors, certainly the ones you'll use in your engine and should not need an adjustable FPR. Also, are you talking about an adjustable rate FPR or just a statically adjustable FRP? I would encourage you to stay away from an adjustable rate FPR and use the ECU to increase fuel as boost comes on.

Woodster

Geoffrey and Jean once again show why this board so great!!!

and congrats to the new guy for building something different!!!

Makes my 996TT with ECU tuning seem pretty mundane (although I still
like the potential of MY platform!)

cheers to you AirCoolers,

Marty K.

Brett B

Thanks for the great info Geoffrey. You may have missed my earlier response about pumps and injectors:

Once again, I have never stated that I wanted a 5 bar FPR, only that I wanted a statically adjustable regulator so I could set base pressure where I want it. I am not trying to raise pressure to account for undersized injectors or a poor fuel map. I can control the injector pulse width anywhere I want it. I can throw in any size injectors I want and rescale the entire map with a single function in the software. But once again, when running large injectors at extremely short pulse widths the idle can be poor. This is just the nature of the beast with all large narrow-spray-pattern injectors no matter what ECU you are using. I’m talking about being well below the 1% duty cycle range. Upgrading to a larger pump sometimes also requires the regulator be backed off a bit to set the correct base pressure. These are the reasons I would like to put in an adjustable regulator with the rest of my fuel upgrades.

chris walrod

Putting the bumper cover back on is like a woman that wears shorts but should be wearing a G-string Love the look of a turbo hangin' off the back of these cars

Geoffrey

"The 3.8 FPR is working ok for now, but I am having to increase injector duty cycles more then I should on the top end, so can tell I'm dropping rail pressure a bit."

This would not indicate a fuel pressure issue, but rather a fuel delivery issue. If you are increasing fuel flow (injector pulsewidth) and you are experiencing a drop in pressure, then it is likely the fuel system (lines, pump, filter, etc.) does not have the required flow rate.

"when running large injectors at extremely short pulse widths the idle can be poor. "

This was certainly the case with ECUs in the late 80s where if the injector pulse width was below about 1.8ms the ECU's injector drivers were not able to properly control the injector. With today's ECUs, this typically is not the case, and I've done a MoTeC Honda methonal engine with TWIN 1600cc injectors PER cylinder and an injector pulsewidth of .7ms and the engine idled stable at 800rpm. I've also had a fair amount of experience with AEM PnP units on STI and EVO cars and AEM is known to have difficulties with Idle and has about 9 different tables that have an effect on Idle stability and quality. I have found that if you adjust the injection timing to provide optimum fuel atomization based on intake air speed your idle improves.

There is nothing wrong with an adjustable 1:1 rate fuel pressure regulator, but if you are adjusting fuel pressure (mechanical) to effect an air fuel ratio change when you have an engine management system (electrical) that can more effectively with more stability control the engine then you have two systems doing the same funciton.

Brett B

Exactly. Which is why in the very next sentence I said this:

“I will be going with bigger injectors and a bigger pump in the near future, so I prefer to have an adjustable regulator once those are installed.”

Possibly poor wording on my part is causing the confusion?

I agree, I have also gotten plenty of AEM equipped Japanese cars to idle fine with large injectors in the 1000cc-1600cc level. I have tuned several maps with idle pulse widths in the 0.60 millisecond range that run great. The injector advance map (load and rpm based injector phasing) and the primary injector battery offset map make all the difference in the world. However, depending on the specifics of the application this is not always the case, which is the entire point I was making. Since you qualified your statements with “typically”, obviously you know this too. I’m sure you have also seen the cases where a large fuel pump will easily over-run a stock non-adjustable regulator, causing higher fuel pressure at idle then desired.

An adjustable regulator is very standard practice with upgraded fuel systems on just about all of the modded platforms I worked with over the years. I didn’t realize that requesting info on where to purchase one to support the rest of my fuel mods would cause such a response.

Anyway, thanks for all the great feedback guys. I always enjoy a good technical discussion.

Geoffrey

"I’m sure you have also seen the cases where a large fuel pump will easily over-run a stock non-adjustable regulator, causing higher fuel pressure at idle then desired."

I've actually not seen this, but I also don't do a lot with the FnF crowd that buys the biggest thing on the market...I am always impressed with the consistency and reliability of Bosch parts.

Bosch makes a 3.5bar to 5 bar adjustable FPR that is a drop in for the 993 style rail.