Thread: Pulley Drop Vs Higher Timing (Custom Tune)

Timing should peak at the top of the power band and drop off as you redline. Most people just run the same the entire way thru

Originally Posted by matt5112

Apparently increasing timing as you go up is a better way to do it.

that's just asking for knock up top.

but whats the point of running higher timing up top than in the mid range when you can more easily run it there? therefore, that point of running a static WOT timing.

by my unerstanding, timing doesn't necessarily equal power. it just makes sure all your fuel combusts at TDC. you have to spark the fuel earlier when the piston's moving faster, and i guess at lower rpm's there's less pressure, meaning it would take longer for the fuel to burn. so if you run boost, you can spark it later since it's pressurized and it'll burn quicker. we're also talking about degrees of timing, i bet if you look at time in seconds between the the spark and TDC it would be roughly the same.

or i'm way off and talking out of my ass

I once made a spreadsheet once that translated spark timing into actual time. All I remember is that as RPMs increased the time was smaller even with spark advance climbing as Roma went up. Makes sence as the Rome climb the total time is less for each cycle. But IIRC denser fuel and air is harder to light off as you want time for it to burn and not explode! If pressure is too high it will explode rather then burn and that's when you get Kr. It is ok to raise and lower spark thru out the table. But to be sure u are making more power a dyno is the only sure way. But a few deg here and there on a stock table will do the trick fine. If you are going far away from stock u deft need some real data.

Depends a lot on the fuel your are running as well. When guys are trying to get the most out of their car, they are running 100-110 octane fuels, lean as hell on small pulleys. If people ran 21* timing across the board they started popping head gaskets, so they would run 18* at 4500 rpms and go up in steps from there, some would even go past 24. Obviously you could not do this on 91 octane, but some of the same theories may apply. Also 4000 rpms is about the range that the car is under the highest load, so timing there is not going to be the highest.

I asked the guys at ZZP and told me I would chip a piston with 20* of timing with my setup...guess I'm gonna see someone who has a dyno and can custom tune my car safely based on my mods.

This thread is getting interesting, thanks for all the info!

Originally Posted by FoSHO99

Depends a lot on the fuel your are running as well. When guys are trying to get the most out of their car, they are running 100-110 octane fuels, lean as hell on small pulleys. If people ran 21* timing across the board they started popping head gaskets, so they would run 18* at 4500 rpms and go up in steps from there, some would even go past 24. Obviously you could not do this on 91 octane, but some of the same theories may apply. Also 4000 rpms is about the range that the car is under the highest load, so timing there is not going to be the highest.

Not only will octane be a factor but, with ethonal being thrown in there, its gonna matter what KIND of fuel you run aswell...

Since i switched, I cant MAKE my car knock...

Originally Posted by gtpsleeper

Not only will octane be a factor but, with ethonal being thrown in there, its gonna matter what KIND of fuel you run aswell...

Since i switched, I cant MAKE my car knock...

e85 has some crazy cooling properties and allows some stupid amounts of boost and timing without much more effort. i really wish i would have committed and done the switch instead of backing out.

I wish e85 was more redly available in the rural communities and interstates. There's a station a block from my house that sells it but i'm too afraid to convert. I don't want to be stranded somewhere.

i would only do it on a car that i drove around town and i would constantly be topping it off at known stations with it. i wouldnt want it for a car that i took on road trips (all of them).

Saying flat out that 20 deg of Timing will chip a piston is bad advice in my opinion. It deals more with AF ratio I would say then with the specific timing. If your too lean yeah you could have issues... Unless the pistons are that brittle? And the combustion makes too much pressure... But if that were the case everyone would be chipping pistons on higher HP setups and. Don't think this is the case.

Originally Posted by Z34Phoenix

Saying flat out that 20 deg of Timing will chip a piston is bad advice in my opinion. It deals more with AF ratio I would say then with the specific timing. If your too lean yeah you could have issues... Unless the pistons are that brittle? And the combustion makes too much pressure... But if that were the case everyone would be chipping pistons on higher HP setups and. Don't think this is the case.

They start popping headgaskets before they chip a piston on 110 leaded. People can see their timing easily so they like to focus on that, but a wideband is what few have, so street cars running 91 pump and trying to run 20* timing year round is what they label as unsafe and prone to chipping a piston. If people have no idea what their actual AFR is, then it's most likely good advice saying 20* is unsafe year around. Some can get away with it, some don't.

Originally Posted by rynoman03

I wish e85 was more redly available in the rural communities and interstates. There's a station a block from my house that sells it but i'm too afraid to convert. I don't want to be stranded somewhere.

where do you drive your car? If you usually stay around the Topeka area we have stations EVERYWHERE...?

Originally Posted by FoSHO99

They start popping headgaskets before they chip a piston on 110 leaded. People can see their timing easily so they like to focus on that, but a wideband is what few have, so street cars running 91 pump and trying to run 20* timing year round is what they label as unsafe and prone to chipping a piston. If people have no idea what their actual AFR is, then it's most likely good advice saying 20* is unsafe year around. Some can get away with it, some don't.

im wondering if e85 guys can get away with the higher timing as long as there is no KR?

this thread is getting interesting

Hey guys, I sent my question at Will from Overkill and got a very detailed answer. Here's how it goes :

"I would do the headers and the pulley.
I don't like to increase timing advance too much on the street for a couple of reasons. First is each degree of timing advance above 17* in my experience is worth 1.5 each, so not very much. In order to run close to 20*, you need about 8-9psi non-intercooled. You'll gain more power if you pulley down and get back to 10-11psi.
Second is high timing on a forced induction car and on our 3800s included reduces that buffer zone of engine safety. In order to run 20* of timing, I need to increase the engine knock attack rates to safely run it. This is because the computer hears a certain amount of engine knock and is programmed on how much KR it will introduce to control it based on how much it hears. If you think of 17* of timing advance and the engine hears enough engine knock to introduce 3* KR, you're down to 14* timing advance. If you have 20* of timing advance and the computer hears the same amount of engine knock, it introduces 3* but you're only back to 17* now (20-3 versus 17-3). There's a big difference in engine safety when its knocking the same amount and running 14* vs 17*, so I need to tell it to reduce by more than 3*. This causes higher KR numbers and can result in more inconsistent performance as KR is introduced and then removed as needed.

#1 it gives less horsepower than running more boost, if you don't have a good solid 10-11psi of boost. Each degree above 17* is worth roughly 1.5 wheel horsepower with no KR. Each psi of boost is significantly more.


Fuel wise, more boost = more air = more fuel, so you will use more fuel under boost with the 3.6 versus the stock 3.8.

Hope that helps explain why I recommend you go for the 3.6 pulley!"

very interesting