Choosing the right injectors for E85 high-compression build

[PolloLoco]

Buy a stand alone fuel injection first. You're wasting your time with the stock stuff.
Rule of thumb is .5 pounds of fuel per hour per HP.
Add 20-30% more for E-85.

Again using calculators on this page:
http://kgparts.com/index.php?page=fuel-calc

I googled around and found that E85 BSFC ranges from 0.60 to 0.65, which is 20-30% more than the gasoline BSFC assumption of 0.5.

From more of my google-fu skills I found that the average stroker makes about 60 horsepower more than the stock 190-ish horsepower I6. I assumed 260 horsepower at the flywheel for a basic stroker. It turns out that 27lb injectors are "ideal" for my assumed basic stroker.

base_stroker.gif

Here is how I guess my E85 stroker could be modeled. I assume 300 horsepower for fun's sake, that and the higher compression has got to do something, and I use the .65 BSFC assumption. It turns out that 42lb injectors are not so insane.

e85_stroker.gif

So I have arrived at the same answer using two different methods. 42lb injectors seems to be the right answer, but I just want another opinion on this.

TurboTom brings up another topic: the stock fuel injection system is crap. I am not building a badass turbocharged racing machine, I'm building a trail-rig. For my application could I use the stock fuel injection system with a piggyback computer such as an Apexi that SilverXJ is using?

[SilverXJ]

Those calculators are consistently wrong. 27lb is not the optimum size for a stroker.

Also, I wouldn't recommend the Apexi. I would look into something that can dial back the timing too if needed.

[PolloLoco]

Those calculators are consistently wrong. 27lb is not the optimum size for a stroker.

Also, I wouldn't recommend the Apexi. I would look into something that can dial back the timing too if needed.

You had recommended the PSC1 to me in another thread:
http://www.splitsec.com/products/calibrators.htm

I also found the FTC1:
http://www.splitsec.com/products/fueltime.htm

With E85 I can also advance the timing without pinging so I thought that it would be a good idea to do use something like the FTC1.


I'm still lost on what size injectors to use. I know that I want larger injectors but I don't know if I should go with 36lb or 42lb.

[SilverXJ]

There is also this: http://perfectpower.com/Products/smt6.asp The FTC would probably work better for you then the PSC. However you are just fooling the stock PCM, as said previously your best bet would be a complete aftermarket fuel system such as megasquirt or fast.

As for injector size I can't say. I know that 27lb is a bit too much for a stroker, but it may also be too little for an E 85 built. Maybe base it on 24-25lb injectors then add 20%?

I don't know much about E85, but 42lb injectors seem very large.

[PolloLoco]

I think 42lb would be too large too. 36lb might not be too extreme, 30lb is 20% more than 25lb. I'm not really into totally redoing my fuel injection system; a piggyback computer would suffice for me. Cost-wise I'm not going cheap with this build but I do not have unlimited funds.

Silver, if you could do it again would you get a megasquirt?

[gradon]

Yeah I don't know about those calculators either. Read up on Comanche91's dyno with the Unichip ( viewtopic.php?f=5&t=387&hilit=unichip )and see that he got 261hp and 345lb-ft (at the wheels!) out of 23.2# injectors defies those formula's(unless 95-100% duty cycle, bfc of .45, to get the ~300-310hp at the crank). I did buy the Uni on Friday. . .

[SilverXJ]

Silver, if you could do it again would you get a megasquirt?

Probably not on a 98+ vehicle as you would have to replace the whole gauge cluster. Then you have to take into consideration emissions checking in your area. On my 2000 Xj, no I would replace the Apexi with a PSC or FTC. Now, on my 74 V12 Jag I may go with a 96-97 engine and megasquirt. There is also a steep learning curve with the Megasquirt, not as easy to setup up or operate as an PSC or FTC or Apexi.

[gradon]

The Jag v12 would be an interesting rebuild project. Have you rewired it yet?

[SilverXJ]

Nope, it is all original currently.

[PolloLoco]

Buy a stand alone fuel injection first. You're wasting your time with the stock stuff.
Rule of thumb is .5 pounds of fuel per hour per HP.
Add 20-30% more for E-85.

Yeah I don't know about those calculators either. Read up on Comanche91's dyno with the Unichip ( viewtopic.php?f=5&t=387&hilit=unichip )and see that he got 261hp and 345lb-ft (at the wheels!) out of 23.2# injectors defies those formula's(unless 95-100% duty cycle, bfc of .45, to get the ~300-310hp at the crank). I did buy the Uni on Friday. . .

300 HP * .5 lb/hr / HP = 15 lb/hr

150 lb/hr / 6 cylinders = 25 lb/hr / cylinder

Myeh, the rule of thumb works close enough. Now how the hell do I forecast the HP for my future build? I suppose that I could get 300 HP at the crank. That would tell me to use 25 lb/hr injectors, add 30% and get 32.5 lb/hr, next step up would be 36 lb/hr injectors. I also think that the plus 20-30% is a bit conservative. E85 has an AFR of ~9.7 so I would need 50% more fuel than gasoline.

[Plechtan]

I just got back from a 2 day class at Haltech http://www.haltech.com They make aftermarket engine managment systems. I will be using one on my Bonneville Truck. Here is some of what i learned:

1. You can use way oversize injectors and program them for the proper pluse width.

2. The Haltech has 2 fuel and timing maps, so you can switch between 2 different types of fuel.

3. You can leave the stock ECU in place and disconnect the injectors and ignition. The stock ECu will still think it is controlling the engine and send the proper signals to the transmission and information to the ODB2 port. The Aftermarket ECU will actually be controlling the engine.