Timing vs. Boost

[Amelio]

I am sure there are lots of variables here regarding boost levels but my questions is specific to lower boost levels.

I am only running 17 psi because thats about all I can get away with on pump gas....depending on the air temp I can sometimes get 18psi but I definitely get zero kr on 17psi so I leave it there.

My question is would I get more power with my boost set at 17psi and more timing or leave the boost at 17psi and bump up the timing?

here is the comparison I just ran the car Saturday....17psi is where the car likes to be on the street with pump gas so I left it there......I then started to bump up the timing....I finally got to a point where I got about 2.0degrees of kr at the top of 2nd and 3rd. I did not make any pass after this one because the tracks traction started to get crappy. I did not have time to back the timing down and start upping the boost either.

So would I have made more power leaving my timing low and tried to get another pound or two out of it?

 

[JP112_89]

I'd leave it at 15psi with 93 octane. Timing 20/18

I wouldn't go above 19* in 3rd. You want the higher timing in 1/2nd as you increasing cyclinder pressures...

I am sure you will get knock on the top of 3rd with 17psi on 93 octane. I did... Not a WOT blast from 55-85mph.. I am talking WOT 55mph-102mph ish.

Joe

 

[bison]

Unless your out of turbo which I doubt you are it's likely the boost will make more power than timing. Timing heats the cylinder more.

 

[mgmshar]

Back when I was running a stock turbo and intercooler, I went to the drag strip and tested my car's response to changing these three variables:

1. Increasing boost.
2. Increase timing advance
3. Increasing A/F mixture (i.e. running leaner).

I made many runs with different combinations of the above, sort-of "Design of Experiments" style (for those engineering-types who do those sorts of things). I looked at how each of the above improved my MPH at the 1/4-mile. I didn't look at E.T. as closely because that is too much a function of traction at the launch. All testing was done with 94-octane Sunoco pump gas and no alky. This goes back to about 2002, so alky wasn't as big as it is now. Base boost was around the 16 to 17 psi range. Base timing was probably about 19-deg. in 1st/2nd and 17-deg. in 3rd.

The Results: the biggest "bang for the buck" seemed to come from increasing boost at the expense of timing and fuel. In other words, it appeared that I was better off running higher boost along with less spark advance and richer mixture. So, my data agrees with what Bison said above.

YMMV.

Hope this helps...

 

[Amelio]

ok makes perfect sense I kind of thought that but had no data to back it up.......so I should see better results in another pound or 2 if I can get away with it on the pump fuel instead of more timing......I did notice that the car was more explosive out of the hole with the additional timing...this resulted in a decent e.t but the mph was not as high as it usually is due to the low boost which goes along with your point.

 

[Amelio]

Unless your out of turbo which I doubt you are it's likely the boost will make more power than timing. Timing heats the cylinder more.

no not outta turbo at all if anything I am outside my efficiency range with this turbo running it so low.....next time I am at the track I will pull the timing back and try to run an additional pound or two and see how much it improves.

The car is completely different from 17psi to 22psi which I am sure you are well aware of that....


Thank s for the info!

 

[turbo nasty]

If you have the traction worked out i like to run higher timing and lower boost in first and second and then have lil more boost and less timing in third. The gearing in first and second seems to allow this to be done without knock showing up. But the car is gonna come out like a beast and youll spin it away if traction is there. This is based on the boost response being right with proper combo.

 

[we4Mateo]

My car has never responded as well with timing compared to boost. I helped a guy tune a very stock combo though and that car did pick up mph with timing when we couldn't get any more boost out of it without kr. We ended at 16psi and 22/18 timing. Outside of that though, every other TR I've seen, not THAT many, but all have picked up more with boost rather than timing. These were all bolt on up to wild cars though.

 

[Ttype6]

My question is would I get more power with my boost set at 17psi and more timing or leave the boost at 17psi and bump up the timing?

You're at the mercy of 93 octane.You're getting all you can out of it now. When we raise the boost,increasing the cylinder pressure,the flame front advances faster. If it advances too fast,we get spark knock. Advancing the spark event will also speed up the flame. We can slow down the speed of the flame by retarding the timing,cooling the air entering the motor,lowering boost pressure,or increasing the octane of the fuel as higher octane fuel burns slower. Since,both,boost and spark advance speed the flame front,you can't increase either if you do the other.

The one thing that might get you more is too bump the boost up and retard the timing. The thing we need to make power is oxygen. If we pump more air into the motor,we get more oxygen in the motor. Every time we add 11 parts of oxygen,we can add one part of fuel. The fuel contains the energy to create the power,but we can't extract that energy until we have enough oxygen. Why do our small motors make big power? Because we're forcing air into them. Generally,more boost is the power maker,but again,since boost increases the flame speed and you're already dangerously close to detonation,adding more boost will result in detonation if nothing else is changed. The best chance for you to add boost to make more power with 93 octane is to do it in conjunction with retarding the timing.

 

[Amelio]

If you have the traction worked out i like to run higher timing and lower boost in first and second and then have lil more boost and less timing in third. The gearing in first and second seems to allow this to be done without knock showing up. But the car is gonna come out like a beast and youll spin it away if traction is there. This is based on the boost response being right with proper combo.

Thats exactly what I was seeing....I believe the 11.80 pass I had 23.8 degrees in first and 2nd and 20 in 3rd......that was with a 6psi launch it ran clean the whole pass. The next pass I tried to leave at 10psi and traction was not there tried again and no go the track would not hold it. I think I maxed out my timing on the fuel I had because my next pass I backed my launch psi down it did spin a little but it was controlled. However I did get a little kr at the top of 2nd and 3rd the only thing that changed was it got warmer out.

 

[Amelio]

You're at the mercy of 93 octane.You're getting all you can out of it now. When we raise the boost,increasing the cylinder pressure,the flame front advances faster. If it advances too fast,we get spark knock. Advancing the spark event will also speed up the flame. We can slow down the speed of the flame by retarding the timing,cooling the air entering the motor,lowering boost pressure,or increasing the octane of the fuel as higher octane fuel burns slower. Since,both,boost and spark advance speed the flame front,you can't increase either if you do the other.

The one thing that might get you more is too bump the boost up and retard the timing. The thing we need to make power is oxygen. If we pump more air into the motor,we get more oxygen in the motor. Every time we add 11 parts of oxygen,we can add one part of fuel. The fuel contains the energy to create the power,but we can't extract that energy until we have enough oxygen. Why do our small motors make big power? Because we're forcing air into them. Generally,more boost is the power maker,but again,since boost increases the flame speed and you're already dangerously close to detonation,adding more boost will result in detonation if nothing else is changed. The best chance for you to add boost to make more power with 93 octane is to do it in conjunction with retarding the timing.

I gotcha....so next time out I may try to back the timing down to 18-19 degrees in first and 2nd and see if I can get 18 or so psi out of it and see if it equals the 17psi run with the timing turned up.

 

[Ttype6]

I gotcha....so next time out I may try to back the timing down to 18-19 degrees in first and 2nd and see if I can get 18 or so psi out of it and see if it equals the 17psi run with the timing turned up.

First and second should tolerate more boost and timing than third. You'll need to run less timing in third if you're gonna have any chance of running more boost as the motor is under more load. I'd try 17 degrees of timing in third and 19 in first and second. A mixture of 1 gallon of xylene and three gallons of 93 will net you 100 octane. Then you'll be able to run 21 lbs of boost.