Are adjustable regulators they worth it if I may go with forced induction in the future? I think my stock one has gone bad because it is very hard to start the engine, and when I checked the fpr by smelling the line that goes to the intake, it smelled like gas. Also, if I turn the key to "on" for a couple of seconds before starting, to let the fuel pressure build up, it starts right away. So I believe I need to replace it and I may as well get an adjustable if they provide any benefit in a FI application.
If you think there will be an advantage to using an adjustable, what do you think of the DFI and Accell brands?
Also, are there any downsides to using an adjustable? Do they hold a particular setting well, or are they known for needing to be readjusted from time to time?
Thanks.

 

Adjustable FPR's are really only a bandaid if your fuel system can't support the engine demands. It allows you to increase the fuel pressure to get more out of you undersized fuel injectors; but higher fuel pressure taxes your fuel pump. The better plan when you add a blower is to buy bigger injectors, not use a FMU, and have custom dyno tuning to dial in your fornula.

 

I had a feeling that might be the case, but figured I'd ask before buying the new fpr. Thanks.

So, I'll still be keeping my pressure around stock levels even after I go FI, just using a bigger pump and bigger injectors to suply extra volume. Is that right?

 

Stock pump should be good for at least 400 rwhp. It's the fuel injectors that you'll want to increase. 42# seem to be good for most guys; talk with your tuner about injector sizing.

 

What about rear wheel torque? I'm not looking for HP #s so much as TQ #s. It's a 96 Roadmaster and it weighs 4400 pounds. I'm looking to make as much torque as I possibly can, and not worry about hp. I'd be happy shifting at 5500 rpm. I'm planning 2 turbos with smaller than normal turbines to make them spool at a very low rpm. The higher rpm loss from that approach doesn't really concern me. The thing is, high torque levels need fuel, too. So how much rear wheel torque can I get from the stock pump at about 2600 to 3000 rpm?

 

Don't think of the pump in terms of how much it can or should support, think of it as a 10 year old pump and get a Walbro. No sesnse in having it go lean and crack a piston on you because you cheaped out on a $100 part in a turbo build. Have you found the Impala Forums, much more application specific info for you there though for motor stuff here is good too.

 

I'm over there, too. It's just that there are so many more people here that I can get a lot more info here, and I can usually get it a lot more quickly as well. At least non-model specific info. Thanks for the tip, though.

 

Generally people use HP to estimate PEAK fuel consumption. While torque may be more important to you, and you may want to be able to make more torque at much lower RPM, the engine is turning so slowly that it is not using the maximum amount of fuel. The maximum consumption is going to be closer to the peak HP.

The general formula for estimating injector size is:

(flywheel HP X BSFC) / (# of cyls X DC) = inj size in #/HR

....where BSFC is brake specific fuel consumption, and DC is the desired duty cycle. A VERY conservative approach is to use 0.50 #/HR/HP for BSFC, and 0.80 - 0.85 for duty cycle.

There's nothing wrong with designing a fuel system to operate at higher pressure than the 3bar (43.5psi) operating pressure used in the LT1's. GM went to 4bar (58psi) on the LS1 engines. Its not a band aid if the system is designed with the higher pressure in mind. There are some advntages to running higher pressure and lower duty cycle.

 

Your starting problem sounds like it could be your fuel pump getting weak anyway.

 

I agree wholeheartedly. I should have written "stock replacement" pump, as opposed to a mega-bucks pump that could feed an SR-71.

 

I guess the next question is how do I get a ballpark idea of what the BSFC would be? And how do I set it up to run on higher pressure? I imagine having tunercat or LT1edit would be necessary. Either that or I'd have to get someone else to take care of any programming issues. What else would I be looking at, aside from the pump and injectors?
Thanks.

 

The 0.50 #/HR/HP is a number that gives you a very conservative (read - maybe a slightly larger than you really need) injector size. I've seen well tuned engines with good combustion chamber design go below 0.45 #/HR/HP. I've got engine dyno tests on my own engine, and its around 0.45. If you don't know the exact number, it isn't important. Use 0.50. There is no problem with an injector that is slightly larger than you need.

As far as pressure, the system needs to be designed for a higher pressure if that's what you want to run. The popular Walbro 255 looks like it starts to lose volume fairly quickly as the pressure in the system increases. On the other hand, there are pumps that will operate more comfortably at the higher pressures. I run a Bosch 205LPH pump that will outflow many larger pumps at higher pressures. Its good for up to 100psi. My dual Bosch setup is good for 1,000HP at 58psi. I'm running injecctors that flow 78#/HR at that pressure, and with them spraying a 300 dry shot on a 500HP stroker, the duty cycle is still under 70%.

You also need to select an injector that is comfortable running at elevated pressures. The stock style ball/seat injectors do not like elevated pressures. The pintle style injectors (Bosch, Denso, SVO, FMS, etc) respond better. The Lucas disc injectors are good at elevated pressures, and fast too.

Your PCM needs to be programmed for the specific injector and the pressure its operating at, entering the flow constant and offsets for the injector/pressure combination.

If you are looking for a replacement for you current NA setup, why not just go with a stock pressure regulator, and select the injectors that will meet your current needs, and can still be used at higher pressures when you go to the forced induction setup.

 

Injuneer wrote: "You also need to select an injector that is comfortable running at elevated pressures. The stock style ball/seat injectors do not like elevated pressures. The pintle style injectors (Bosch, Denso, SVO, FMS, etc) respond better. The Lucas disc injectors are good at elevated pressures, and fast too."

Fred, correct me if I'm wrong, but it's my understand that the stock injectors are Lucas, disc style, and are prone to lock-up at elevated pressures (60+ psi).

 

This is why I like this site. I asked about fpr's and now I'm learning about BSFC values and different injector styles. Anything a guy needs to know can be found right here.