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rex
Needs a Life!!!
Joined: 09/29/2005
305 Posts |
 Posted - 07/12/2010 : 08:48:28
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quote:
Originally posted by Steve Kramer
Well, rex, I may have been a little off on how I phrased that, so I checked with the chief....Mikey..."I can't tell you what the exact %'s of the Injector pulse time is made from.....but at WOT it is water, air temp and RPM....in a small part Mas Air signal and baro psi." So, there is no consideration of A/F ratio. Therefore, to alter the A/F ratio, you could alter the FP, since the rest of the values would be illegal to alter as you would be modifying a sensor or the computer.
Steve you need to go back to the chief "Mickey" because this is still totally wrong. Pull the hose off you MAF or unplug it and see how it runs.
More to Jeff's question however. I don't think you would want to mess with the FP much, even if you could, and then only if you were a little lean at high RPM and high load ... like 4th coming up on 4200 RPM (around 90% load). The injector slopes are setup in the ECU to deliver the proper amount of fuel, based on the correct fuel pressure,at a given load and RPM with a fuel pressure of 42 PSI in the case of the SRF. Moving it 1-2 PSI either side will move the AFR about 0.1-.2 point.
The SRF is setup to hit 12.35 at high loads - >60% load and RPM above 3000. This is typically the WOT range.
02 sensors are not used in open loop which is WOT.
MAP sensors (baro), instead of MAF, are used in some cars, especially turbos, to sense absolute manifold pressure ... the SRF does not have one.
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Tray
Needs a Life!!!
Joined: 08/14/2003
USA
308 Posts |
Posted - 07/12/2010 : 12:37:35
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The 02 sensor on the SRF is a narrow band one, only used for close loop. (Not WOT) You can install a wide band one that can help tune the car for WOT if you choose. However, if you do, be ready to do something about it or its just another useless gage.
Fuel and weather can have a major impact on what your actual AFR is on any given track. (I don't just mean "HOT" fuels, there are major differences in your average pump gas.) If you want to know what works best, test it. Take your car to a local chassis dyno and see what fuel works best. Or you can test fuel for water and start with the one that contains the least. Since ethanol has an affinity for water, by testing the fuel for water you are also testing it for percentage of ethanol. All you need is a graduated cylinder.)
By varying your FP you can move the MAS curve up or down. (You can lean the entire curve or richen the entire curve...) And, a 2 psi change is large to me and should affect the WOT MAS curve more then .2
You can also buy (off Ebay) an adjustable fuel pressure regulator. This helps when at the dyno to vary the FP and look for differences. Be careful... Your not looking for 10 HP with a FP change. The most you can do here is to optimize your car for the fuel your using and the weather conditions that day. Most dynos don't have the accuracy to even see this with out averaging several runs and plotting them later. But,its still a good idea to have some data on your car so you know where you need to see the AFR for the most power on your gage. And this gives you a baseline to come back to when you feel your down on power.
Tray |
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Adam Brouillard
Ready to Write a Book
Joined: 07/10/2006
USA
74 Posts |
Posted - 07/12/2010 : 12:50:42
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| Out of curiosity what kind of gas do most people use regularly? I have to get a new fuel cell and the alcohol resistant kind is significantly more. It seems like if you can get a FP regulator that is a little high to compensate for what the richer mixture pump gas E10 likes, it would be fine. Or do most people use AVGAS or racegas and just get the regular fuel cell. |
http://adamstechshed.com/
www.hollingsworthrg.com |
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Steve Kramer
Needs a Life!!!
Joined: 04/03/2002
775 Posts |
Posted - 07/12/2010 : 21:53:40
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rex: the person I was referring to was our Technical Manager or whatever we call Mr. Davies these days - that was a direct quote from an email we exchanged. Since I did not perhaps phrase my original post on the subject correctly, I checked with him to ensure my info was accurate. Tray's post was perhaps better phrased than mine but that is exactly the point I was trying to make - varying FP varies the AF ratio at WOT. And it is an open area for engine tuning as the regulator can be modified for different pressures.
Now, if you want to tell Mikey he is wrong, you know how to find him.
Steve |
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rex
Needs a Life!!!
Joined: 09/29/2005
305 Posts |
Posted - 07/13/2010 : 08:17:47
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quote:
Originally posted by Steve Kramer
rex: the person I was referring to was our Technical Manager or whatever we call Mr. Davies these days - that was a direct quote from an email we exchanged. Since I did not perhaps phrase my original post on the subject correctly, I checked with him to ensure my info was accurate. Tray's post was perhaps better phrased than mine but that is exactly the point I was trying to make - varying FP varies the AF ratio at WOT. And it is an open area for engine tuning as the regulator can be modified for different pressures.
Now, if you want to tell Mikey he is wrong, you know how to find him.
Steve
Steve, I beleive I said varying the fuel pressure will change the AFR in the first post ...LOL.
Not trying to be argumentative; however, if that was a direct quote from Mr. Davies ... what can I say. It is totally inaccurate and not even close. |
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Ed Cavalier
Forum Hermit
Joined: 12/20/2006
USA
114 Posts |
Posted - 07/13/2010 : 09:16:39
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| In reference to Adam's question: I only run at two tracks and both have ethanol free gas available. At TWS, it's 96 octane. At Houston MSR, I'm not sure whether it's 96 or 98 octane. Regardless, I try to avoid ethanol. |
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rex
Needs a Life!!!
Joined: 09/29/2005
305 Posts |
Posted - 07/14/2010 : 07:40:47
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I know Adam runs at VIR and I finally got them to mark their pumps for Ethanol. All of Sunoco fuel has ethanol and even the 100 has 9% ethanol everyplace.
It is about impossible now to find any without it around here and like Tray said ... try to find one that works and stick with it if possible. |
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Adam Brouillard
Ready to Write a Book
Joined: 07/10/2006
USA
74 Posts |
Posted - 07/14/2010 : 07:51:27
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| Oh so even race gas has ethanol now? Isn't avgas ethanol free? I live right near a small airport so that could be an option. Maybe I should just get the alcohol resistant fuel cell. |
http://adamstechshed.com/
www.hollingsworthrg.com |
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specdoc
Needs a Life!!!
Joined: 04/02/2002
USA
234 Posts |
Posted - 07/14/2010 : 11:51:51
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| I have said this before. If you go to your nearby fuel tank pipeline farm where the transport trucks go to fill their loads you will get the REAL information. Each driver blends his load for the stations he is going to deliver. If it has ethanol it is because he put it there. It might take a while to get to talk to someone that will talk back with the real info but it is worth the trip. DO NOT ATTEMPT to go through the gate, they get really pissed off about that. I have found a few stations around here that I can get ethanol free fuel that way. Always 91 octane. |
Steve Fenske
CSR, Midwest Division
Midwest Spec Racer, Inc.
(785) 862-2777 |
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Slug
Ready to Write a Book
Joined: 05/14/2007
USA
60 Posts |
Posted - 07/14/2010 : 17:16:06
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Try this site:
http://pure-gas.org/index.jsp
It lists all the gas stations in the country that sell ethanol-free fuel. It is updated frequently, too.
We used to be able to get all three grades (87-89-91)in the KC area, but just this month we are only able to get the 91 anymore. Bummer.
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Joe Bob |
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OregonSRF73
Needs a Life!!!
Joined: 04/04/2002
390 Posts |
Posted - 07/27/2010 : 17:42:04
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quote:
Originally posted by Adam Brouillard
Oh so even race gas has ethanol now? Isn't avgas ethanol free? I live right near a small airport so that could be an option. Maybe I should just get the alcohol resistant fuel cell.
Avgas may be ethanol free but even the 100 low lead avgas has too much lead in it and our O2 sensor won't like that. FF and Club Fords are quite happy on 100LL avgas.
For the record, the official fuel of SRF Pro, Sunoco 260GTX is ethanol free.
http://www.sunocoinc.com/site/Consumer/RaceFuels/UnleadedFuels/
Lowest octane unleaded w/ no ethanol Sunoco makes. |
Todd Butler
SRF73 OR/SFR Regions
Chassis #308 |
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Fuel pressure and the GCR
