Braineack

iTrader: (62)

I think I read somwhere (maybe Bell's book) that the best fuel can cool the intake charge is about 45°. After that it's simply wasting space in the cumbustion chamber.

but here's a good read:

Application Note: You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports
Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.

First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:

Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)

Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.

The latent heat values of different liquids are shown here:

Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kg

Most engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.

If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.

hustler

iTrader: (6)

so, is the lower a/f ratio required because of intake charge temp, or because of increased pressure in the combustion chamber? I've never understood why more fuel is required if an intercooler can get charge temps close to ambient.

magnamx-5

iTrader: (7)

The lower AF is not required at all. But alot of tunner's like to promote cylinder washing with 11-1 or less AFr's wich is bullshit if you can't get the job done at 11.8-13-1 then you have a frigin problem fix it and enjot the hp

Braineack

iTrader: (62)

what it says is, once you find your ideal AFR, dont go any richer, because they only thing gained is unburnt fuel that doesnt cool the air charge.

hustler

iTrader: (6)

I suppose EGT's tell you what your afr should be? I don't know this stuff. I know some tuners tell me they'll tune the car to 11.0, some say 12, none say anything intelligent other than "shut up and give me your money." At this point, I'm going to find a good book on this, and tune it myself.

Where can I find more, accurate, tested theories on AFR and EGT tuning for reliable applications?

Ben

iTrader: (33)

I learned a lot just watching Jerry and Scott tweak the fuel map on the dyno. That was more informational than any book or article I've ever read.

One of the lessons learned from that session: there is no 'magic' ratio that is right. Take a pull, see what happened, add a little fuel, take another pull, compare results. Tune by trial and error, essentially.

hustler

iTrader: (6)

so in this example are you playing with fuel for absolute power, or is there a safe range, where power output excedes "safe" regions?

btw, I made a *** forum in an attempt to rope FM and FFS into BDSM ecstacy.
http://forum.miata.net/vb/showthread...41#post2703241

1drum

iTrader: (1)

I know I'm jumping the gun since I haven't even started to turbo yet; but does anybody know if there is a good dyno in the Sacramento, CA area?

Ben

iTrader: (33)

Safety was always the first consideration.
It was more making small changes, always in the a good rich saftey range, to see what would happen. There were a couple times where adding fuel made more power. It surprised me. Our 'guide' range was like 12:1 going to 11.6:1 or so.

hustler

iTrader: (6)

Yes, everyone needs full EM, even if they don't think they do. Piggy backs are duct tape. PC Pro is trash.

Al Hounos

elesjuan

iTrader: (11)

I'm going to have to agree 100% with this. The Supercharged car we built has these stupid jackson racing piggyback pieces of crap and its impossible to get running correctly. Granted the car pulls good and hard it gives a huge smoke show everytime you apply the throttle.

On our dyno once the charger passed atmospheric and started to build boost the fuel curve shot straight to 10:1 which was WAAAAY too rich. Theres no way to adjust it with the powercard and o2 clamp. Car is run VERY VERY hard and still gets 23mpg though. :gay:

Its taken me months to talk the owner into a megasquirt setup, and I guaranteed him we could make an extra 10rwhp with nothing but MS. Finally worked and hes going to buy the PNP setup.

hustler

iTrader: (6)

I've been trying to explain this to a couple guys in dallas with blown cars. They run the cars at like 10:1 too "so it won't knock, but why buy the $700 MSpnp if its not going to ad any power?" Both cars make power from 5000-6500rpm...and talk **** about laggy turbos...lol.


I remember 2 vortech VR6 gti's from a few years ago. Both were stuck running 13's in the 1/4 on the vortech kit with the rising rate fpr. Then, one guy put haltech on the car, and ran low 12's right off, with no mechanical changes. The haltech car still runs, the piggy backed car is on another set of rings.

Ben

iTrader: (33)

the difference between running the BEGi FMU w/ MSD and the MS standalone was about 20 whp or so at equal boost

elesjuan

iTrader: (11)

Oh yeah, I believe that 100%.

We've got a local guy that had a bunch of piggy back bandage things (like, literally SIX of them..) and is building his third motor now. Yeah an FMU works but why not just spend the money for security and performance of a real controller?

I gotta say though, HKS, Greddy, apexi, etc have made a *TON* of money off that crap over the course of 10 years or so. Not saying everything they've made is junk, ie Emanage, but they've all got their bandaids.

Chiburbian

iTrader: (1)

Ok, for me the newb - I imagine you are saying the MS was the one that came out on top?

Ben

iTrader: (33)

Yes

Zabac

iTrader: (39)

i really like this noob, what a refreshing surprise eh, he uses the search function...yay we got us a good one

elesjuan

iTrader: (11)

P-P-P-P-P-POWERCARD!!

I should post in that thread asking how "autotune" is working with his closed loop security blanket.. Think its keeping him nice and comfy warm at night?



$950.00 for 2 PCPros and some junk *** bandaid for an 'intercooler' without ANY timing control STILL!

MSnSPNP- $700.00 + $189 LC-1.

Hmm.. Which to choose..

Really wish I had the money to spare. I'd build 2 identical miatas both with his supercharger systems on identical brand new motors. One with PCPro and "E-Cool" the second with Megasquirt and FMIC.. Tell him to roll those dyno numbers up and smoke em. That man is seriously a quack!



Wish I knew where he lived.. I'd love to leave a flaming bag of duck/chicken **** on his doorstep.