Hypothetical tuning questions

[james]

I've been looking around since I saw a couple of the Nelson Racing vids where they had a dual fuel setup with pump gas and ethanol/race gas. For me it is more of a hypothetical since I'm no where near close to doing this, but we can dream right?

Say you're running an EFI v8 street/strip car such as a mustang with a huge turbo or two, lots of boost, and capable of well over 1000 to the wheels. You've got essentially two fuel systems: 1- a mild upgrade to your factory system (Walbro 255, 42lb injectors) which pumps 93 octane and provides enough fuel for the idle and low boost, and the second, a fuel cell, giant pump of your choice, big lines, and whatever size injectors are necessary (120 or 160lb) and you keep it full of E85/E98 so that as you get into boost your high octane fuel system kicks in. Good so far?

1 - As you get into boost, your ethenol injectors start firing but what do you do with the gasoline injectors? Ramp them down as the ethanol injectors come in? Keep them firing at at least some duty cycle? Obviously when they can no longer support the hp level, you need to have the ethanol injectors already firing, but how do you know when to turn down/off the gas injectors?

2- If you reach the upper limits of your ethanol injectors, can you add in your gasoline injectors and make more power? With all 16 pumping at 80% duty cycle, is there a calculation to figure out how much hp they can support? At 80% duty cycle, say 42lb injectors support roughly 400rwhp and 120lb injectors on E85 support roughly 1000rwhp, do all of them at once support 1400rwhp at 80% duty cycle?

3- Would you change anything if running race gas instead of E85/E98?

[modscotty]

This sounds like a completely over-complicated system. There are plenty of 1000hp systems that work great with one fuel source....or at least different maps for different fuels (ie: a map for 93oct and a map for race gas or E85).

The addition of a completely separate fuel system not only adds a whole new bunch of potential problems, but a complete nightmare as far as tuning. Sure, you could tune it enough to have it not blow up on the track (1/4mi), but having any kind of drivability on the street would be an enormous challenge.

If multiple maps aren't enough to support the desired hp levels, there is also the concept of additional injectors. Many tuning solutions accommodate additional injectors, and would allow you to only turn them on during periods of higher fuel demand.

I guess I just really don't see any benefit of this kind of setup. Mind explaining why these guys are using it?

[james]

People are using them for race setups that get driven on the street and they don't want to be running high octane ($$$) fuel all the time, plus putting the wear and tear on big dollar fuel pumps. Most of the stock/stockish stuff would get ripped out anyway, this way they put it to good use and don't have to listen to a couple giant fuel pumps whining away while sitting at a stop light.

Some EFI systems let you run multiple maps, either manually switching between them or having a predetermined switch (e.g. 5psi boost or x-amount of calculated load) either switch the map or add in the second set of injectors.

Its "supposedly not hard to tune"* because the stock setup is already close to the low end and idle, and from there you tune the stock setup until your injectors start running out of capacity. from there, your secondary setup rolls in which is really going to be a high-load, wide-open throttle setting.

The advantage would be not having to drain your tank or hope you added enough extra high octane fuel, and being able to wack open the throttle whenever you feel like it. Moreover, you can tune it for your fuel (buy a 55 gallon drum of E85/C16 etc. and keep it in the garage) rather then having to tune it to what you can get at the pump or fuel trailer (is this the summer seasonal E85 blend... well we're out of C16, but we've got Q16). Additional injectors are good too, but are limited to the same as I just mentioned. Running an extra somewhere in the intake can lead to fuel puddling and boom(!), andwith running 16 93octane injectors, you're throwing a whole lot of fuel down in there to fight the detonation and have to worry about washing the cylinder walls.

*thats from people that have tuned it... not me... their idea of what is hard to tune may or may not be what we thing considering we haven't done a lot of that

[modscotty]

You could always just have two fuel tanks (or race cells), like in some of those 90's Ford pickup trucks (probably a lot of years/brands have them). It'd be really easy to set up, with a manual switch, two fuel gauges, etc. Combine that with multiple fuel maps, and it seems like you can have the best of both worlds.

Personally, I'd rather just build an all-out race car, then waste all the time/effort/money trying to make a street-able one.