Am I maxing out my injectors with E85?

[SebringLX]

I have 750cc injectors (rated at 43.5psi). With 93 octane gas, I can run 24psi of boost and hold a nice 11.5:1 AFR. I don't like to run more than 22psi on 93 octane though, 'cause I'm afraid of running into detonation. With a mix of 93 and E85, I've felt safe going up to 26psi, but unless I get the mix just right, AFRs will start to creep up above 12:1 on the top end. I don't like the inconsistencies of trying to mix at the pump, not nowing exactly how much is still in the tank, etc.

Most people say you use approximately 30% more fuel when using E85 compared to regular gas.

Guessing at 20% drivetrain loss, it should take 711cc (rated at 43.5psi, but running at 58psi) injectors for 500 HP at the crank to make 400 HP at the wheels. So in theory I should be able to run enough boost to hit 400whp with the static stock 58psi fuel pressure and these 750cc injectors.

If we use the 30% more figure for E85, those injectors would now need to be 924cc @ 43.5psi. I have a rising rate regulator, lets say its set at 1:1, so now if I run 26psi of boost, the fuel pressure should raise from 58psi to 84psi. Those 750cc injectors should now be flowing 1042cc with that much pressure, which should be more than enough to make the same amount of power on E85.

What I think I am missing here, is the impact of fuel pressure on injector duty cycle. What is the impact? With that much pressure, am I pushing the IDC too far, and that's why it runs lean with more boost on E85?

When I built everything, I had never given a single thought to E85, I was thinking "Safe pump gas tune, and safe race gas tune if I can find some race gas". I think if I showed up at the track with an empty tank and threw a couple of gallons of race gas in the tank, I could safely tune for 26-30psi and max out my turbo.

E85 is a lot cheaper, and easier to get. I'd like to be able to hit that 26-30psi safely with E85. Am I correct in my thinking that my current injectors will not be enough for this? Would 1000cc injectors be enough?

[cordes]

in short, I believe you are running too little injector.


I also believe the way you are thinking of injector flow vs. boost pressure to be incorrect.

If your ~72s are good right now, I would go with something in the neighborhood of 1.5 times bigger at least.

I know that a lot of E85 guys shoot for that 30% number when doing fuel calculations. However, I've spoken with many people who have run alcohol and they seem to suggest that alcohol likes to be run much richer by way of comparison to gas and doesn't lose the power from being really fat like gas either. Those guys suggest running 50% more fuel than on straight gas. Granted, they are talking 100% alky, and there are guys who do tune for the 30% number in boosted aps. with E85 and get away with it.

[SebringLX]

I also believe the way you are thinking of injector flow vs. boost pressure to be incorrect.

Explain please.



If your ~72s are good right now, I would go with something in the neighborhood of 1.5 times bigger at least.

1.5x bigger would be 1125cc @ 43.5psi. Running at the stock 58psi fuel pressure, 1000cc injectors (rated at 43.5psi) should flow 1155cc (~110lb/hr)

I've been eyeing the Injector Dynamics 1000cc injectors, but can't find them for less than $450. Seems like a lot, but I guess the cost of filling the tank with E85 vs filling it with 100 octane race gas would pay for itself within about 5 tanks. Their next size up is a 1600cc, but the price jumps to $880 for a set of those!

Deatschwerks has 1300cc injectors for $450. The 750's I have now are Deatschwerks, I think I'd rather have the Injector Dynamics if I replace them, but I don't want to end up still not having enough injector with the 1000's, nor do I want to spend $880 for 1600's.

[shackwrrr]

what he is saying is that the 1 to 1 regulator doesnt change injector flow. the rise in pressure is only to overcome the pressure in the manifold trying to push the fuel back into the injector.

[cordes]

what he is saying is that the 1 to 1 regulator doesnt change injector flow. the rise in pressure is only to overcome the pressure in the manifold trying to push the fuel back into the injector.

That's exactly right. There was a thread which broke it down more a month or so ago now. It also got into how the SRT4 EFI stuff works too.

[SebringLX]

Source?

I'm going off this... http://www.rceng.com/technical.aspx

According to that math, flow increases as pressure increases.

[shackwrrr]

Source?

I'm going off this... http://www.rceng.com/technical.aspx

According to that math, flow increases as pressure increases.


Science, pressure differential.

Injectors only see Relative pressure. You measure absolute pressure at the rail.

The boost pressure is pushing at the tip of the injector and the fuel pressure is pushing at the other end. The fuel pressure has to overcome the manifold pressure before it will come out.

[jl93sundance]

1000cc injectors would probably be ideal and to keep it safe no matter what. What fuel pump are you running currently? I was told that a single walbro 255 would be maxing out at around 400whp running e85. In my srt that is

[SebringLX]

Walbro 190 feeding a Walbro 255. I have enough pump for more HP than this car will probably ever see.

[SebringLX]

Science, pressure differential.

Injectors only see Relative pressure. You measure absolute pressure at the rail.

The boost pressure is pushing at the tip of the injector and the fuel pressure is pushing at the other end. The fuel pressure has to overcome the manifold pressure before it will come out.

That makes sense. So if 750cc injectors flow 866cc at the 58psi base fuel pressure, they're still only going to be flowing 866cc when the fuel pressure increases to 84psi with 26psi of boost.

If it takes 711cc @ 43.5psi running @ 58psi to make 500 crank HP which should be close to 400whp. Then subtract 30% from 500 for the E85 estimate, that makes it 350 crank HP, which would be around 280whp, which is very close to what I put down running only 16psi of boost.

If I add 30% to the 500, that's 650, so like I said before I'd need 924cc @ 43.5psi running @ 58psi to flow enough for ~400whp on straight E85.

It looks like 1000cc injectors would actually be perfect then. That should be enough to max out the turbo right around 400whp, which at 3425lb race weight should get me the 11.9 I'm after.

[cordes]

That makes sense. So if 750cc injectors flow 866cc at the 58psi base fuel pressure, they're still only going to be flowing 866cc when the fuel pressure increases to 84psi with 26psi of boost.

If it takes 711cc @ 43.5psi running @ 58psi to make 500 crank HP which should be close to 400whp. Then subtract 30% from 500 for the E85 estimate, that makes it 350 crank HP, which would be around 280whp, which is very close to what I put down running only 16psi of boost.

If I add 30% to the 500, that's 650, so like I said before I'd need 924cc @ 43.5psi running @ 58psi to flow enough for ~400whp on straight E85.

It looks like 1000cc injectors would actually be perfect then. That should be enough to max out the turbo right around 400whp, which at 3425lb race weight should get me the 11.9 I'm after.

I can hear every part of your drive line sobbing in the corner as I rad the last sentence. Teehee.

[shackwrrr]

and 4th gear running away screaming.

[cordes]

and 4th gear running away screaming.

I LOLed. :)

[shackwrrr]

another thought I just had. Fuel pump flow drops with increase in head pressure so as you go up in boost and your fuel pressue rises to compensate the fuelpump has to work harder and flows less.

at 84 psi your walbro only feeds 140lph (http://www.autoperformanceengineering.com/html/fpspecs.html)

that is 140,000cc/hr or 2300cc/min, not enough for your goals even with pump gas.

[SebringLX]

another thought I just had. Fuel pump flow drops with increase in head pressure so as you go up in boost and your fuel pressue rises to compensate the fuelpump has to work harder and flows less.

at 84 psi your walbro only feeds 140lph (http://www.autoperformanceengineering.com/html/fpspecs.html)

that is 140,000cc/hr or 2300cc/min, not enough for your goals even with pump gas.

There are 2 pumps, a regular 190 in-tank running in-series with an external high pressure 255. Between the 2 pumps I should have ~314lph @ ~80psi. So that would be 314,000cc/hr or 5233cc/min.

[shackwrrr]

There are 2 pumps, a regular 190 in-tank running in-series with an external high pressure 255. Between the 2 pumps I should have ~314lph @ ~80psi. So that would be 314,000cc/hr or 5233cc/min.

running them in series does not increase the flow any more than the gains from the pump not lifting the fuel itself. You are probably slightly higher than the 255.

[SebringLX]

running them in series does not increase the flow any more than the gains from the pump not lifting the fuel itself. You are probably slightly higher than the 255.

You're right. It should be about 120% of the largest pumps flow rate running it like that. I think that should still be about enough.

I ran out of fuel pump with just the stock 190, it was very obvious when the pump couldn't keep up. After adding the high pressure 255, I haven't had a problem yet. I think injectors will still be the 1st step, and if the pumps can't keep up, I can always swap the 255 out for a Bosch 044. The Bosch 044 is a huge pump, and will flow over 250lph as high as 90psi on its own.