morris

iTrader: (2)

Can anyone explain to me how timing effects power in a FI engine. We all know that to little fuel kills an engine. Its my understanding that this is from increased cylinder temps and increased possibillity of detonation.

But besides retarding timing if you are getting detonation, I dont know how it affects the engine tuning process.

Anyone care to educate me?

SuprRunner

Well, we all know that we get spark...before top dead center and not after. This starts burning the fuel before the piston reaches the top...this does not mean that all the fuel gets burnt before this time, it will still continue to burn after TDC. This is where octane comes in to play. The higher the octane, the slower the fuel will burn. With higher octane fuel, you can increas your timing even more...or run more boost on a boosted application, because when boosted, the fuel will have a tendancy to ignite and burn quicker.

As for power...imagine a diesel engine, they have like 21:1 compression. It takes an incredible amount of force to compress the air in the cylinder, and it works extra hard to do so. When the fuel ignites, that force is mutiplied(I really don't know the math or physics behind this)...hence generating more torque.

The further you advance your timing, the more engergy it will take to compress the air, and the more engergy will be released to the downward stroke of the pistons, generating more torque. Too much timing advance will cause to much fuel to be ignited before the pistons reaches the top...it will pretty much be hitting a brick wall. This will cause rings to shatter, ring landings to break...or blow holes in your pistons.

This isn't only inherent to FI engines...but all combustion engines, and the heat is created by the engine having to work a little harder to compress expanding air after it has been ignited. And of course, the more air you shove in along with more fuel..the harder the engine has to work...again...generation more heat.

Methonal is a great way to help with this. Methonal will greatly reduce charge temps..and I think methonal has a pretty high octane rating...but I could be wrong.

morris

iTrader: (2)

Okay, I am getting a clearer picture but still its a bit foggy.

I think you have two separate topics here.

1. is Octane, which I thought was the fuels abillity to resist detonation (igniting due to compression in the absence of sparK). Are you certain the fuel or flame front burns any faster due to Octane?

2. the other is timing, are you saying that by advancing the timing the spark occurs later in the stroke or earlier in the stroke as it approaches TDC. My guess is later in the stroke but I dont really know.

I also have heard that fuel management keeps the engine from going poof, but that timing makes the power. Is this true? if so then how does timing effect power?

SuprRunner

1 .Yes, Octane helps fuel burn slower...so even if you were to get ignition due to compression...the octane will help the fuel burn slower so you don't get a full combustion before the pistons hits TDC.

2. Your timing is always BTDC, not after. Advancing your timing will cause ignition to hapen ealier...so say 15 degrees BTDC will spark earlier than 10 degrees BTDC. In both cases, you will get ignition before the piston reaches the top...so the fuel is combusting while it is still incompression stage. The sooner conbustion happens...the more energy it takes to compress, and the more engergy you will yeild in your down work stroke after the piston reaches TDC. Too much compression or too early of igntion will make the pressures soo great before the pitson reaches TDC, that you will get engine knocking. The lower the octane..the more prone you are to this.

Fuel managment does not allow you to control your timing. The factory ECU will retard and advance timing on its own depending on the load and RPM's of the engine. As your RPM's go up the scale, the ECU will tend to increase timing. If you trick the comptuter into thinking it is getting less air than it really is, and this will also increase your timing. This could eventually wind up in giving you too early of igntion causing engine knocking and damaging the engine. This is different than running lean. Running lean will cause the tempuratures to rise in the compustion chamber, causing excess heat and pre-detonation. This is different than advanced timing...and more dangerous.

I had already described how advancing timing will give you more power...but I am no pro on that matter, and only have limited knowledge on the subject..

morris

iTrader: (2)

Thanks in terms of fuel management and timing management, I was refering to a car with a standalone or emanage ultimate. not the stock ECU

Thanks.

SuprRunner

Ok...but you did say fuel managment...not engine managment.


Oh, and after doing a little more research on octane...it's primary function seems to be that it can be compressed more without igniting...but I have also read elswhere that it helps burn fuel slower...let me do a little more looking to verify that.

SuprRunner

Ok, good, my info wasn't bad...I hate giving bad info...anyway, here is a good link I just found about some truths and myths about octane.

http://www.state.mn.us/mn/externalDo...ctaneFacts.pdf

morris

iTrader: (2)

thanks and yea I realize I wasnt clear about it at first, English is my second language.

SuprRunner

And here is one I found about torque and combustion pressures on the pistons before and after ignition. Read the last 4 paragraphs to learn about gasoline engines...the rest is about diesls. I would read that too, as it is great info.

http://www.bankspower.com/Tech_somuchtorque.cfm

sockfocks

iTrader: (1)

I believe ideally you want the fuel/air charge to burn completely by TDC to maximize combustion chamber pressure for maximum torque. Factory timing is usually retarded from this maximum to decrease temperature for reduced NOX emissions and increase fuel efficiency. If your timing is too late, you can burn the exhaust valves and watch your exhaust manifold turn bright cherry red real quick. The information i found is that fuel burn is generally constant, but you may have found even more specific information. Spark timing advances as rpms increase because the fuel/air charge has less time to burn. Advancing the timing moves the spark earlier in the compression stroke. Too much advance and the engine will work against itself and raise combustion temps.

LMSguy

There is no magic percentage of timing advance that will make the most power.
EVERY engine combination will be a little different.
If two guys have the same exact engine combo except one guy has ported heads they will require a little different timing strategy to make the best SAFE power.
Thats where a stand alone engine management helps because you have such precise control over the timing and fuel events.That way a GOOD tuner can dial in your exact combo.
But YES you can hurt an engine by trying to run too much timing and causing pre ignition just like from running too low of an octane fuel.You get the same result, detonation/preignition which CAN be very harmful.Some rotating assemblies are able to deal with it better than others.
Take a 4.6 ford for example,they are hyper-eutectic (Sp?) pistons which are a great daily driver piston, but they tend to break very quickly with any hint of detonation.

So Morris, there really is no hard and fast rule.You talk to one tunner and they will tell you they like to use X amount of timing for a certain application and then another tuner might use a different amount for the same combo.