91 Octane...what size injectors

[jibberishballr]

I was just reading this:

http://www.roadraceengineering.com/eclfuel.htm

and they said something that stood out to me

"Bigger injectors allow you to run ridiculous amounts of boost on cheaper gas."

So i was thinking ive got an Evo III 16g and was planning on running it with 560's (stock on Evo) and was wondering if i should do this or run higher like 650's. I know there are tons of threads on 650's vs 550's but i was wondering if the fact i run 91 octane would affect it since im in Cali. Also would running 91 octane affect tuning with 650's? Would it be easier to tune 650's with an my SAFC than other higher octane gas? Because if tuning would be easier theres almost no point in not going with 650's.

 

[fourreGsixty3]

Go with the 650s, RRE knows what they are talking about, if you have crappy watered down 91 grade, get the 650s for running 15psi on that 16G. Tuning wont really change much, but you will be reaching the limits of the SAFC with those 650s, S-AFCs are generally thought to be replaced with a logger and DSMLink once you go past 660s.

Dustin

 

[andymoraitis]

If you're not maxing an injector or running above 85% IDC at a given boost level, you can throw 1600's at the motor and you won't be able to run more boost on pump. Pump gas suffers from low knock suppression, If the suggestion is that you buy bigger injectors and richen the tune to drown out the knock by dupming more fuel in the cylinders then this is way off.

What you'll have to balance on pump gas (especially 91) is the correct amount of timing relative the desired level of boost. As an example you can't run 25 psi on a 16G on 91 with 21-22 degrees of timing since the knock suppression capabilities of the fuel are poor. You may however be able to run that much boost on 91 by either:

1. Installing a methanol injection system to lower combustion charge temps.
2. Running less total timing advance

As a caveat, while running low timing will increase the detonation ceiling, cast parts will only take so much heat before they fail. If you have stock internals, it's generally a bad idea to go below 14 degrees of total timing advance.

On a turbo as small as a Big 16G, 650's are fine, especially if the motor will be cammed, however anything larger won't provide additional benefit or allow the tuner to run "ridiculous amounts of boost on cheaper gas". Between the 91 and the fact that small turbos generate a very hot intake charge the deck is stacked and adding more injector does nothing to alleviate the problem.

It's more important to have a tuning solution that will allow you to run A/F and timing maps that are correct for your setup (DSM link or a custom Keydiver chip). With the AFC, you'll always struggle with the boost vs. timing equation since the airflow correction for 650's will make you run higher timing advance. Unfortunately, this will limit your boost. I would consider another tuning option if you want to maximize your results on pump gas.

Hope that helps,

Andy

 

[DSM90AWD]

The "theory" behind RREs statement is that by running richer AFRs (cooling affect) you can run higher boost levels on pumpgas before knock onset, so a larger injector is needed as the fuel demands will be higher.

Unfortunately with a piggyback style tuning device and larger injectors, you have to add alot of (-) correction to get the injectors to work well the other 99.999% of the time you are not WOT. Because you are doing this correction outside the ECU, other calculations (namely timing which is also airflow based) will be affected.

Hence why DSMLink / EPROMs are such a popular mod, as they calibrate at the ECU level

In answer to your question, yea 650s (-30% correction vs stock inj) would be my recommendation with the EVO16G

 

[Kevin Jewer]

650s are also my recomendation with DSMlink or a chip (actually, might as well go 950s in this case and never worry about it again), 550s can be maxed out on a EVO 16g. To restate what Andy and others have said, I too would not run richer on lower octane fuel, but would lower timing. Removing 1 degree of timing will effectively avoid more knock than going from 11:1 to 10:1, IME. So that being said, injector selection is back to the usual process. And control over timing is the key. And of course that's the hardest part. You should stick to the 560s if you want to keep the timing down. And here is why this is such a heavily discussed and debated topic. The question becomes:

"Do I get the 650s and not have to worry about running at 95% IDC all day, or running out of fuel if a boost controller line melts, etc?"

Or, "Do I get the 560s so I don't further bollix timing with the AFC (or similar), which is probably more important in avoiding knock?"

Mathematically, 560s will support 41-42 lbs/min with a base pressure of 43 psi, specific gravity for typical pump gas, and a target AFR of 11:1. And sure enough, in real life my EVO 560s were at 101-102% IDC at 42 lbs/min at 11:1 on pump gas. Who says the math doesn't work?

Now, if you are one of those poeple that has a problem running 100% IDC (I've run them that way for a year or more, no ill effects, AFR is always exactly what it should be, etc) you could try a higher base pressure if you have a 255 and AFPR (a 190 is really not enough for an EVO 16g anyway). 50 psi will drop you to 94% IDCs at max compressor flow, and you'll need a global compensation of about -25-26% (instead of -19%) on a 2g ecu to adjust for it. I'm really not a big fan of changing fuel pressure from what the ECU expects, but to me the compromise in fuel pressure seems better than running too much timing on pump gas

Hopefully you find this helpful.

 

[jibberishballr]

650s are also my recomendation with DSMlink or a chip (actually, might as well go 950s in this case and never worry about it again), 550s can be maxed out on a EVO 16g. To restate what Andy and others have said, I too would not run richer on lower octane fuel, but would lower timing. Removing 1 degree of timing will effectively avoid more knock than going from 11:1 to 10:1, IME. So that being said, injector selection is back to the usual process. And control over timing is the key. And of course that's the hardest part. You should stick to the 560s if you want to keep the timing down. And here is why this is such a heavily discussed and debated topic. The question becomes:

"Do I get the 650s and not have to worry about running at 95% IDC all day, or running out of fuel if a boost controller line melts, etc?"

Or, "Do I get the 560s so I don't further bollix timing with the AFC (or similar), which is probably more important in avoiding knock?"

Mathematically, 560s will support 41-42 lbs/min with a base pressure of 43 psi, specific gravity for typical pump gas, and a target AFR of 11:1. And sure enough, in real life my EVO 560s were at 101-102% IDC at 42 lbs/min at 11:1 on pump gas. Who says the math doesn't work?

Now, if you are one of those poeple that has a problem running 100% IDC (I've run them that way for a year or more, no ill effects, AFR is always exactly what it should be, etc) you could try a higher base pressure if you have a 255 and AFPR (a 190 is really not enough for an EVO 16g anyway). 50 psi will drop you to 94% IDCs at max compressor flow, and you'll need a global compensation of about -25-26% (instead of -19%) on a 2g ecu to adjust for it. I'm really not a big fan of changing fuel pressure from what the ECU expects, but to me the compromise in fuel pressure seems better than running too much timing on pump gas

Hopefully you find this helpful.

Well heres some stuff i might have left out.

I cant get DSMlink for quite a while because of money so i will be running the safcII.
I cant run anything higher than 91 octane because im in cali.
I dont want to run over 90% IDC if i dont have to because its bad to run over that right (a little confused on that)? however i dont want to have lots of tuning problems.
I will not be running anything over 18psi and will most likely have a 190 rewired not a 255 and not raise fuel pressure. After telling you guys all of this what do you think i should do?

Also what level of boost am i going to be able to run on 91 octane without problems (no methanol, 560's or 650's)?

Also my goal for right now is low 13's

 

[Kevin Jewer]

You have to give somewhere. It's going to be a compromise between IDCs and timing. Personally, I'd rather not blow my shit up and run high IDCs, which seems to have no measureable negative side effects. I don't think anything is worth doing unless you're going to make some attempt to do it right. Of ocurse, this is all just my personal opinion based on my personal experience, you're free to do whatever you want to do.

Personally, I would do 560s and deal with the high IDCs. If the IDCs are a problem, do the 255 and reg, which you need to properly support an EVO 16g anyway, so it just plain makes sense. The pump and reg are a good investment for future upgrades anyway. At the least, do the 255 and no reg and deal with the non-linear FP curve. Again, it sucks, but it's better than taking unnecessary risks. When you don't invest in something to take control of timing, you have to take all of the necessary steps to avoid too much advance, IMO.

 

[jibberishballr]

You have to give somewhere. It's going to be a compromise between IDCs and timing. Personally, I'd rather not blow my shit up and run high IDCs, which seems to have no measureable negative side effects. I don't think anything is worth doing unless you're going to make some attempt to do it right. Of ocurse, this is all just my personal opinion based on my personal experience, you're free to do whatever you want to do.

Personally, I would do 560s and deal with the high IDCs. If the IDCs are a problem, do the 255 and reg, which you need to properly support an EVO 16g anyway, so it just plain makes sense. The pump and reg are a good investment for future upgrades anyway. At the least, do the 255 and no reg and deal with the non-linear FP curve. Again, it sucks, but it's better than taking unnecessary risks. When you don't invest in something to take control of timing, you have to take all of the necessary steps to avoid too much advance, IMO.

Ok so im going to go with the 560's then. I didnt want to go with the 255 because the 190 sounded so much easier (i think thats why most people go with the 190. the money doesnt bother me just having the fpr and one more thing to deal with). I guess i could go with the 255 and fpr and 560's. What kind of boost do you think ill be able to run with this setup on 91 octane and will this be enough for the typical driver to pull a low 13 timeslip. Also what do you think my IDC's will be at at 18psi of boost?