How much can I advance my timing?

[WINDYCITYJOHN400]

thats the second time today i`ve seen someone mention "dune ported cub" wtf

 

is that what passion did to daves cub...dune ported it

Yes.

Full dune porting. LOL

 

For Trinity that = run a grinder against the transfer tunnel walls to make it look worked on.

But still ship it with domes that have a convergent shape. (AKA DETONATION SERIES)

 

For Passion that = Take 3-6 months and $1000 to grind away 5HP.

[trickedcarbine]

On race gas, if the domes are not GAY, and you don't have stupid compression......... I'd say 5-7 will be ok. Keep checking the plugs. Especially on the trinity motor. Leontief be surprised I that motor has a hard time with even +4 degrees.

[WINDYCITYJOHN400]

They are GAY......

 

It will have stupid compression.....

 

Plug checks are easy.

You can either look at them when they back themselves out....

Or look at them when you are replacing O-rings.

[trickedcarbine]

^ awesome

[tfaith08]

What compression are you running?

[BANSHEEBEEFM2M]

175 in my bike idk about other one

[tfaith08]

At that compression, I'd stay under 8 or 9.  Is the fuel oxygenated?

[Deadbeat]

175 in my bike idk about other one

are you running 110 octane through that beef

[trickedcarbine]

At that compression, I'd stay under 8 or 9. Is the fuel oxygenated?

Really? I am curious as to how you are able to get so much timing in your motors. Not trying to talk shit, but didn't you mention as much 15* timing? That's kinda gnarly on almost any motor isn't it? Isn't it safe to assume that if a motor needs that much advance to burn at it's most efficient point, it would have some set up issues? Also, how can you get a motor to still pull RPM like that? Or are you referring to motors that are running minimal compression on race gas with lots of timing? I've just never had much luck myself on these motors with much more then 7 degrees while still having a bit of compression.

[WINDYCITYJOHN400]

If you are running timing that high in a gas motor you have a combustion chamber issue.

Anything more than 7 degees on race gas is...... (insert negative statement here)

 

4-7 or start looking for a problem.

[fappy'97]

LIKE I SAID, ADVANCE ALL TIME FOR MAXIMUHM HORSEPOWER.

[tfaith08]

A lot of people think that more timing means more bottom end power, but I've never seen evidence of this in any realm of motorsports.  More timing means more time for the gasses to burn  before the downstroke at higher RPM.  That's why the Yamaha DT200 has 8 at idle and 30 at 8000rpm.  Timing that high isn't unheard of.

 

When I said 15 over stock, I mean that was the absolute maximum that I would run before he saw detonation on 112 and stock compression (didn't know he was upwards of 170), not what I'd recommend for efficiency and power.  With larger bores, the mixture needs more time to burn as well.  Add a bad dome to the mix and top end power would scream for more timing.  The higher compression packs the mixture into a much smaller area and the charge will burn quicker, reducing the need for more advance.

 

On that kind of compression, I wouldn't recommend anything more than 8 or 9 over stock.  That wouldn't be the setting at which the most power was realized, but that's likely the limit of the fuel.  The best way to look at timing is in 2 ways, with the first being "what is the limit on timing with my setup and fuel choice" and 2, "what setting makes the most power."  All of my answers were aimed at the first question.  If the second exceeds the first, you need to alter your setup or go to a higher octane gas or settle for a less than optimal setting. 

 

I set mine to around 4 for when I'm in the dunes and around stock for woods, but that's with aftermarket domes.

 

I never did understand why everyone goes straight to +4 anyway.  From what I understand, that was the setting that the stock head needed to see maximum peak power, which is why most companies market it as such.  IMO, it's kind of like the stage 3 jet kits.  Great for marketing, bad for your wallet.

Edited July 5, 2014 by tfaith08

[tfaith08]

Just to tap on setting timing...

 

Back in my car tuning days on standalones, we'd always set timing at TDC across the board.  After we got our AFRs in the ballpark, we'd start advancing the ignition.  If we saw an increase in power, we'd advance it more.  If we saw a drop in power, we'd set it back to the previous setting.  On the higher end (especially with boosted cars) we always, 100% of the time, had more timing than the lower RPM ranges. 

 

It was very often the case that the engine that we were tuning could make more power with more timing, but we were limited by knock, which was largely limited by the fuel that was going to be used. 

 

If we had this table for race gas (made up, but nonetheless within common occurrences):

 

1k   4°

2k   7°

3k   11°

4k   16°

5k   23°

6k   28°

7k   33°

8k   39°

 

and we switched to pump gas, we may have to set the timing cap to around 25° because knock would limit us.  Keep in mind that we could have set the timing to 180° BTDC or ATDC (effectively BDC), but we tuned for maximum power, not a claim of erroneously high timing numbers.  There were also instances where more timing did not result in knock, but the engine made less power with more than a certain setting, further contributing to the fact that more timing doesn't always mean more power, even if you have the octane to support it. More timing will always result in more pumping losses.  The key is to maximize downward force without excess pumping losses from too much timing.

 

With static timing systems (Banshee for example), you should choose a setting where you will see the most benefit.  That being said, advancing the timing will NOT benefit the bottom end range unless the entire combustion chamber is out of whack to begin with.  At this point, you are covering up a problem by advancing the timing. 

 

If you have aftermarket domes, the builder would be the best person to ask about the timing setting.  If you have PD domes, well... you should get custom domes.

Edited July 5, 2014 by tfaith08

[trickedcarbine]

Glad you touched on the bore size effect and pumping loss. Lots of fellas not thinking about either. The pumping loss is a real problem on the banshee as it's a twin so with a bad set up you can really get to the point where the cylinders are almost fighting each other.

[tfaith08]

I saw the effects of it when my banshee ran 96 with the stock head and timing and fresh tires, but ran 83 yesterday with 150psi and +4 timing with less than 1/4" of tread.  Thread loss doesn't account for 13mph.  I do get there fast as shit though lol.

Edited July 5, 2014 by tfaith08