Optimum Timing

I hope it's not low class to quote myself, but I posted the below in a thread in another forum. Any input to add to my understanding of timing would be welcome.

A number of factors play into optimum timing. What you are trying to achieve is maximum cylinder pressure at ~14-18 degrees after TDC. Sometimes, you can't add enough timing to do this without causing detonation. With a higher compression ratio, the motor will tolerate less timing before detonation occurs. Ditto for high intake air temps. A combustion chamber which is smaller, and more efficient combustion chamber (the GMPP "Fast Burn" is a good example) needs less timing to achieve max pressure at the correct time as does a smaller bore. Fuels which burn faster need less timing. The higher the rpm, the more timing is needed. A leaner mixture needs less timing (it burns faster), and so on.

In any case, no matter what, optimum timing has to be determined empirically and can't simply be calculated in advance. I doubt even the OEM's have a sufficiently detailed model of each combo to simulate it. Contrary to what you often see on the board, optimum timing cannot be determined by simply continuing to advance the timing until you experience knock and then backing off. More timing, even without detonation, is not good if it advances max cylinder pressure too far towards (I used the misleading word "beyond" in the other thread) TDC.

This is one of the many reasons why tuning is best done on a dyno. You can tell if you are making more hp or less with each change and you also can instrument so you know what the conditions are (IAT's, etc.).

One other point just FYI. The less timing needed to achieve max cylinder pressure at the optimum point the better. That's one reason why those GMPP "Fast Burn" heads work well, they need very little timing to make hp. The earlier the spark, the earlier the cylinder pressure starts to rise. Keeping in mind that this begins before the piston reaches TDC, you can see how power is lost as the piston is forced up against the already igniting fuel/air mixture. In an ideal world, instanteous complete combustion would occur with the piston at ~14-18 degress ATDC. Of course, this is impossible. But the closer you can get, the better.

Rich Krause

Hey Rich,

I'm doing as much digging on info before I make my first dynotune. I'm gald you posted this. After I set the baseline A:F, how should I go about dialing in timing? Should I be very concerned with adjusting A:F as I dial in the timing?

(This probably requires a long reply - skip down if you don't wanna type a bunch! :))

Optimum timing = most power?

IOW, the right timing to use would be the timing were the ___ (Rwhp? Rwtq? Both?) is greatest at that MAP/RPM?

I don't think its low class ;).

Ryan

Nice post Rich.

For my non technical response to the last reply:

best timing = best HP on the dyno or highest MPH at the track.

Simplified tuning guide:

Warm engine enough to bring oil temp up before WOT runs, try to have water temp about the same at the start of each run. Water temp should be in the 165-170 degree range. The point isn't to show a big number but to make the runs reproducible. Begin with 28 degrees of timing. Make a run and check the AF ratio. Adjust AF to ~13:1. Make AF ratio adjustments after to each run to try to bring it back to ~13:1. Add two degrees of timing on each subsequent run. Once you see the hp begin to drop, or stop increasing you are almost done. At that point, lean it out a little (to 13.2-13.3:1) and take out a degree or two of timing. You can then try adding the little bit of timing you just took out back.

Keep in mind the effect of density altitiude. If you are tuning with bad air, the motor will be leaner and tolerate less timing on a day with good air. So err on the rich side if the air is bad when you tune and subtract a degree or two of timing.

Rich Krause

Rich:

I'm assuming that you keep a close eye on all parts of the graph (hp). After a few pulls you can begin to decide which individual rpm points make more power with a little higher (leaner) than 13:1 and which points make more hp with less than 13:1 (richer). Am I on the right track?

Thanks Rich :thumb:
Ryan

Timing is really only dialed in well on a dyno like Rich said. I can't agree more. Track times or MPH are really not a accurate way to do it, but sometimes the only option. I would tune the car for the max coolant and oil temps you plan on running it at. The heat from them will make the motor detonate on a timing curve that was at the ragged edge on a lower temp motor.

Engines that are sensative to timing will make optimum power at the right timing, 1 deg +/- optimum will drop power and 2 +/- will kill it. Some motors you can run at 36 degs, and then drop to 32 and nothing happens.

Fast burning fuels are really not a option for us. Street gas is going to burn at about the same rate, and things like Alcohol and Nitro are completely different. Nitro doesn't really burn but "crakel" and it gets like 60degs of timing just to try to get there. The burn rate is really related to the chamber and dome/dish shape along with the quench areas.

Winston Cup guys run as little as 25 degs of total timing. From what I have heard that only happens in Fords at events like the Winston.

People forget that it's not a explosion but a burn and burns take time. One reason why I can't emphisize paying close attention to the quench area.

"IOW, the right timing to use would be the timing were the ___ (Rwhp? Rwtq? Both?) is greatest at that MAP/RPM?"

If you adjust the whole curve, or the area where the timing is maxed (max total timing) a degree or two you will see that part of the curve drop or raise. If it drops, meaning probably RWTQ and RWHP are down then you need to go back to where you were. It's mainly trial and error.

One thing that makes me laugh is guys who tune by ear. That's just crap. If you listen for knock you are doing the wrong thing unless you have too much compression. Then you should get better gas because the lower timing hurts you more than the higher compression helps. I've tuned motors to have slight detnonation in the low end to bring up the power, but it's only to get good numbers on the dyno. On a street car you should never tune it to have any detionation.

Bret

Originally posted by 96-speed
Rich:

I'm assuming that you keep a close eye on all parts of the graph (hp). After a few pulls you can begin to decide which individual rpm points make more power with a little higher (leaner) than 13:1 and which points make more hp with less than 13:1 (richer). Am I on the right track?

Thanks Rich :thumb:
Ryan

You will basically find that the motor will like to be leaner (make more power) untill it burns a piston. Leaner or richer at any RPM is not really optimum for performance and engine life. A blower motor might be different because it might like the cooling properties of the fuel, so more fuel will make more power at a point.

Shooting for a flat A/F table is a good idea. A carb doesn't really get that option unless you are really good. With EFI you should shoot for a flat curve.

Bret

Originally posted by SStrokerAce
You will basically find that the motor will like to be leaner (make more power) untill it burns a piston. Leaner or richer at any RPM is not really optimum for performance and engine life. A blower motor might be different because it might like the cooling properties of the fuel, so more fuel will make more power at a point.

Shooting for a flat A/F table is a good idea. A carb doesn't really get that option unless you are really good. With EFI you should shoot for a flat curve.

Bret

Ok..makes sense - thank's for explaning it it :).

How do guys know that they are ok to disable the knock sensor? If my A:F is dialed in at 13:1 across the board and my timing is dialed in (power curve is looking good), would it be perfectly safe to turn the knock sensor off when I'm at the track?

I think I understand the idea of leaner is meaner. Am I correct to assume 13:1 is the point of diminishing returns for the A:F? IOW, any leaner and your risk of damage goes way up, while your power increase goes up very little?

You guys are helping me out big time! :bow:
Ryan

Originally posted by 96-speed
Ok..makes sense - thank's for explaning it it :).

How do guys know that they are ok to disable the knock sensor? If my A:F is dialed in at 13:1 across the board and my timing is dialed in (power curve is looking good), would it be perfectly safe to turn the knock sensor off when I'm at the track?

I think I understand the idea of leaner is meaner. Am I correct to assume 13:1 is the point of diminishing returns for the A:F? IOW, any leaner and your risk of damage goes way up, while your power increase goes up very little?

You guys are helping me out big time! :bow:
Ryan

Lean is mean.

13:1 is safe and will make power. High 13's is riskier and will make more power.

If you could get the motor to live at 16:1 and it made more power there you would run it there.

One of the reasons that NASCAR boys get such awesome fuel mileage is that they work on making the motor burn every ounce of fuel. Or optimizing the BSFC which is the lbs per HP per Hour of running. the lower the BSFC the better it is burning what it has and usually the lower the A/F ratio.

I know there were some sick readings in the Engine Masters last year on A/F ratio, like 17:1 at the low end. That's in the highest detonation area too, that's a bit iffy!

Bret

I'm guessing there's only way one way to know for sure what A:F the motor can take and last. Since I'm not anxious to find out myself I'll shoot for 13:1...lol

Thanks Bret.
Ryan

Originally posted by 96-speed
I'm guessing there's only way one way to know for sure what A:F the motor can take and last. Since I'm not anxious to find out myself I'll shoot for 13:1...lol

Thanks Bret.
Ryan

Yeah a mid 13's will work. As long as you don't run stupid compression.

Holing a piston is the way to find if it's TOO lean.

Bret

Good points raised. You got the "simplified tuning guide" 'cause there is obviously a lot more to it if you care to get into it.

For the kind of basic tuning I was talking about, leave the KS on. It won't help you find the optimum timing for the way your car is usually driven to turn it off. You will end up with "optimum" timing, but as soon as you turn the KS back on, your timing will probably change and negate your efforts.

Doing a run at high-normal operating temp is not a bad idea, to verify a safe operating mode. But OEM LT1 and LS1 programming already adds a lot of fuel and takes away timing at high operating temps (as well as high IAT's), so it almost certainly going to be safe. It will probably be too rich and have too much timing, but that's a nice safety margin. And I am assuming that someone with a high performance car will operate it with some common sense. Just like you wouldn't do a WOT run on a cold motor, you wouldn't put it in high gear at 2,000rpm and crack the throttle when it's 95 degrees and the water temp is already at 210 degrees. Of course, people do this kind of stuff, that's why the factory tune for these types of conditions are so conservative.

There is more power in certain combos by going leaner, and as Bret said, optimum AF ratio for forced induction is much richer. We can get into this at some point, but just one thing. It gets more complicated, risky, and time consuming (expensive) to start pushing the limits. If you want to experiment with lean AF ratios, you need to monitor exhaust gas temps for each cylinder and have the capability to tune fuel for each cylinder. You are flirting with major engine damge as the EGT's start to approach 1650 degees. What is optimum? It's like with timing, it takes experimentation. Mainly, the role of EGT is to help determine "how lean is too lean?" Keeping in mind that leaner - hotter. If you are making more power as you lean it out, and the EGT's are getting to the 1500-1550 range, I'd stop leaning it out at that point. But if you still have one or more cylinders that are cooler, there may be more hp to be found by continuing to lean out just those cylinders.

A nice thing about using a dyno for tuning is the ability to tune for different fuels. If you use one kind of gas at the track, and another on the street as I do, you need to different tunes to get optimum performance. Think about the density of the fuel for a minute. A 5% difference between fuels is common. If you already have your motor on the ragged edge of lean, if you put in a fuel that's 5% less dense, your AF ratio may well be too lean. And then ther's octane, burn rates, O2 content, etc. So don't just assume that everything will be fine if you put in a tank of race gas at the track. It should be safe, but you may not gain anything without a tune for that fuel. And, of course, for your base tune you must tune with the same fuel you are going to be using on an everyday basis.

Rich Krause

Take care with the idea that "lean is mean". If you are a little to the rich side your car will probably not slow down much. If you run too lean you will kill it. Remember that a dyno does not take things like drag into account.
I have spent quite a bit of time dynoing different combos and then testing them at the drag strip. I have found my best results by running leaner at the start line and richer towards the traps. On the timing I run about two degrees more on the bottom end than the top.
I will add that LT1's seem to love a bunch of timing.

Best Regards,

Daren

Great post guys!!! I love tinkering on the dyno (friend owns one) with timing and air/fuel. Rich are you sayin that you need to dial in the a/f ratio first and then the timing? Should the a/f change at all when changing timing? Whats the first indication of too much timing? (less torque?, less horsepower?, both?) Is more timing needed with bigger duration cams? Just trying to learn!!! Thanks again guys. :bow:

Thanks for the information, it's very helpful!

One question/comment: isn't tuning timing on the dyno a bad idea, if you plan on drag racing, since there is less load present on the dyno? Then when you get the car on the real road, the higher load will tend to cause detonation earlier with the same amount of timing, correct?

Originally posted by JSK333
Thanks for the information, it's very helpful!

One question/comment: isn't tuning timing on the dyno if you plan on drag racing a bad idea, since there is less load present on the dyno? Then when you get the car on the real road, the higher load will tend to cause detonation earlier with the same amount of timing, correct?

Basically you can tune the wide open throttle portions of the table and for LT1 edit and timing that's the 85-100Kpa section. The dyno can easily load the engin down enough for that portion of the table. A dyno can actually load the motor more than the strip can in most cases, because the slower acceleration rates will raise the the power. A higher acceleration rate of the motor will lower the power output because some power is being lossed in the moving of the parts faster.

Bret

Originally posted by Shankels94TA
Great post guys!!! I love tinkering on the dyno (friend owns one) with timing and air/fuel. Rich are you sayin that you need to dial in the a/f ratio first and then the timing? Should the a/f change at all when changing timing? Whats the first indication of too much timing? (less torque?, less horsepower?, both?) Is more timing needed with bigger duration cams? Just trying to learn!!! Thanks again guys. :bow:

Timing will change AF ratio as measured by an exhaust gas analyzer. Obviously, it doesn't change what's going into the motor. The way I usually do it it to monitor the AF ratio on each pull. Make adjustments as needed to keep AF where you want it if it changes with each timing change. Make sense?

As far as load, Bret said it well. If you want to simulate very high load (going up a hill) you can use the brake on a chassis dyno. An engine dyno may have a myiad of possibilities depending on how sophisticated it is. The drums on a Dynojet wieght something over 3,000lbs and have a lot of inertia. A typical F-body pull will take 4-7 seconds in 4th (3rd for an automatic).

Rich Krause

On the data logger NA the EGT's are 1200 to 1300 and the motor is very responsive and with 300 to 400hp nitrous tuneup the EGT's are in the 1600's. Timming on the bottle will start usually 32 to 36 degree's under normal tuneup but for the big tuneup timming will be at 28 and down per each stage. Motor is working HIGH compression.

The problem with at least going by EGT'S with nitrous motors the timming is retarded so much not to mention using designed nitrous fuel with slow burn properties what ends up happening is the fuel/air/nitrous mixture is still burning even in the primarie's of the header. This will show false EGT reading's. This is where many people go wrong and end up putting more fuel back in and then causes a fuel wash in the cylinder. With out giving out to many secretes LOL! It's not uncommon to have a motor using timming in the single digts when at WOT in a run.

Just be aware that different motor combinations will require different timming. I seen a apples to apples combination but the only difference was valve angle of the heads and alumn block and heads comapred to cast block/alumn heads. The alumn motor made more power and liked to be at less timming compared to the cast block motor on the dyno.

That's my heads up for the day and good luck in the tuneup search!

Originally posted by rskrause
You are flirting with major engine damge as the EGT's start to approach 1650 degees.

Now this I find very interesting. I used to keep 1600 deg. F in my head as a practical limit for EGTs until I started working on the engine program I'm currently on. As an example of a production engine going right up to your limit at WOT, the 5.7 Hemi will consistently get 1650 deg. F exhaust temp near peak HP. The EGTs are monitored in durability just before the cats, and they're close coupled right behind the exhaust manifolds. On the engine I'm currently working on we will see excursions to 1670-1680 deg. F. At that temp we can't use normal cast iron exhaust manifolds very easily because the manifold material just can't take the heat. As a result, we're moving to stainless steel headers - better durability and more HP, can't beat it. ;)

Some of our high EGTs are influenced by the detonation sensitivity of our engine. We have to back off MBT at peak TQ by about 8 deg. to save the engine on 93 octane. Even at peak HP we're about 2 deg. off MBT. If we had time to do some more combustion work we could get some of that back, but we don't, so we live with higher EGTs.

WRT EGT's, keep in mind I am talking about street OHV V-8's with at least the potential for decent, if not OEM level, reliability. A drag race motor intended for a few seconds at WOT and frequent rebuilds is something else.

I tune for 1450 in a street motor.

Rich Krause

VERY COOL POST:thumb:

1-What would a nice timing cure look like at wot.
I no every car is diff for timing but just ie: would be nice from old files or what you like see.

2- Where should you start the timing for wot, 85kpa,90kpa,95kpa,100kpa full timing

3-ie: if you start wot timing at 85kpa say you have

4000 rpm/85kpa-39.0 timing in tuner cat do you make 90/95/100kpa timing the same or do you advance it

4- is it the higher the rpm the more timing you put in +1-2* or is it more.

my timing at 100kpa
rpm/kap-timing
400-22
600-22
800-22
1000-23
1200-24
1400-26.5
1600-27
1800-28
2000-29.5
2200-31.5
2400-32
2800-35
3200-35
3600-35
4000-35
4000extended spark adv table-36.5
4500-36.5
5000-36.5
5500-36.5
6000-36.5
6500-36.5
7000-36.5
i have 7* kr at 4000rpm up to 5500rpm this is the fixed table i pulled out 5* just to start

thx

Originally posted by rskrause
WRT EGT's, keep in mind I am talking about street OHV V-8's with at least the potential for decent, if not OEM level, reliability.

Referencing my post above, so am I. Since we can get a production engine with an annual volume in the hundreds of thousands to live at 1650 deg. F exhaust temperature, can I ask where you normally take your EGTs? How far from the cylinder head port generally? Are you talking individual cylinder EGTs or a bulk EGT from each bank, perhaps with long tube headers?

Originally posted by 94bird
Referencing my post above, so am I. Since we can get a production engine with an annual volume in the hundreds of thousands to live at 1650 deg. F exhaust temperature, can I ask where you normally take your EGTs? How far from the cylinder head port generally? Are you talking individual cylinder EGTs or a bulk EGT from each bank, perhaps with long tube headers?

I'm talking individual cylinders ~3in from the exhaust port. I am suprised you take them so high. Mayber I need to be more agressive in my tune?

Rich Krause

i never much undestood timing and tuning- just took in the facts. I guess this is a good time to question why.

first off- let me verify everything i'm basing my readings off of.

what is meant by "30 deg of timing." how is it measured?

second- why do you want max pressure at 14* after TDC of the compression stroke? how is that possible?

this is what is playing in my head

intake opens towards the end ofof the "exhuast stroke" staying open in the intake stroke and closing somewhere in there. the piston hits TDC. should that not be MAX pressure? the piston goes down 14* anf you have max pressure?

or are you saying that after the the "burn" starts- you want max pressure at 14*?

whats so great about 14* after? wont you get the best power if it ignites at TDC? thats where the most pressure is (pre combustion).

not doubting, just questioning.

Trey: I am not one of the engineers here, but I think the key to understanding the points you raised is to keep in mind that combustion is a process that takes a finite amount of time. The combustion process begins at the spark plug electrode and propagates through the combustion space. While this process is occurring, the piston is moving. The amount of time for combustion is pretty much independent of rpm, but the distance the piston travels is not. So, as rpm rises, spark must be "advanced" (occur earlier relative to TDC) so that combustion occurs at the right time relative to piston position. Too early, and a large rise in cylinder pressure (due to combustion) occurs while the piston is still travelling upward toward TDC. Obviously not desireable. Too late, and the piston is already moving rapidly down the bore, increasing the size of the combustion space and decreasing efficiency of combustion.

I believe that the empiric fact that best power occurs with peak cylinder pressure occurring ~14-18 degrees after TDC is related to the interaction of these various factors. The speed of the combustion process and the acceleration of the piston away from TDC and how this effects the size of the combustion space. Perhaps it is also related to mechanical advantage at different rod angles? Anyway, again you can see how timing must change with rpm to achieve the desired result.

Just to be clear on how timing is typically expressed. It is where the plug fires defined as crank degrees before TDC. "Advancing" the timing means earlier, for example: if ignition occurs at 25 degrees (before TDC) that is more "advanced" than ignition occurring at 20 degrees. IOW, that would be "adding" 5 degrees of timing. Vice versa for retarding timing.

Rich Krause

What Rich said.

Originally posted by rskrause
I'm talking individual cylinders ~3in from the exhaust port. I am suprised you take them so high. Mayber I need to be more agressive in my tune?


I just find it interesting. That's all. We are obviously higher than most engines since we were having great trouble getting a cast exhaust manifold to live, but we've done a simple change in materials to stainless steel, and switching to headers (almost free at that point) and it appears to be no problem. Very few large volume production engines would take the hit going to stainless steel but we have different constraints. The 5.7L group went right to the limits of the cast exhaust material at 1650 deg. F and did a few months of development to design a manifold that would work. However, for racing you don't have the constraints of a cast exhaust manifold so I definitely believe you could raise your exhaust temps if it proves to be beneficial to HP.

can anyone explain what the deal is with 14*?

the ONLY thing i can think of is that 14* is the end of the piston dwell- but that seems like a long dwell no?

my stab in the dark...

Coming from an OE perspective here:

Burning the charge in the chamber takes a certain period of time. For a decent pushrod engine a 10-90 burn is in the 25 crank degree range. That means the number of crank degrees it takes once 10% of the charge is burned until 90% of the charge is burned. If you burn much faster than that the NVH guys at work will come down on you like a ton of bricks because the customer will actually hear the knocking, even though it's not detonating. If you burn much slower you're not burning the charge efficiently and are losing potential HP.

Since burning the charge takes a pretty good number of crank degrees you have to start the burn before TDC, but if you start too early you increase the pumping work. If you start too late, you send a lot of heat out the exhaust valve and it's lost HP. 14 deg. for peak cylinder pressure is not a hard and fast rule. It's just about where it usually works out for a well-timed engine.

From my experience dealing with a few LT1s and LS1s the sign of detonation is not necesarily the limit for timing...

When tunning on a dyno I have always tried to reach max timing at around 4k and lower a degree towards the end trying to achieve a smooth curve... From experience I have found that too much timing and you loose smoothness in the curve and not necesarily power.

I think also that tunning for the best smoothness of curve and power combo is the fastest on the street.

I try to achieve a nice round curve (maybe logarithmic) to get to max timing, not just a straight line and then lower and make the car keep a straight timing all the way to shift...

I dont like relying too much on EGT unless it is to measure the difference between pistons... AFR is a bit safer. As said before with the hemis and 1650F, probably there is where it likes it... and have the same AFR that I have on the LT1 with a EGT of 1500, or somewhere in the vecinity... SInce each engine is particular, even those with the same combo, EGT will have the same pattern although you can follow the rule of the thumb...

The shape of the timing curve has helped me improve a lot more than total or max timing.

Originally posted by Schurters LT1
VERY COOL POST:thumb:

1-What would a nice timing cure look like at wot.
I no every car is diff for timing but just ie: would be nice from old files or what you like see.

2- Where should you start the timing for wot, 85kpa,90kpa,95kpa,100kpa full timing

3-ie: if you start wot timing at 85kpa say you have

4000 rpm/85kpa-39.0 timing in tuner cat do you make 90/95/100kpa timing the same or do you advance it

4- is it the higher the rpm the more timing you put in +1-2* or is it more.

my timing at 100kpa
rpm/kap-timing
400-22
600-22
800-22
1000-23
1200-24
1400-26.5
1600-27
1800-28
2000-29.5
2200-31.5
2400-32
2800-35
3200-35
3600-35
4000-35
4000extended spark adv table-36.5
4500-36.5
5000-36.5
5500-36.5
6000-36.5
6500-36.5
7000-36.5
i have 7* kr at 4000rpm up to 5500rpm this is the fixed table i pulled out 5* just to start

thx


Coming from a non-CC racing side, I find it odd that you would add timing at a higher RPM.

The weekly motors we deal with are pretty basic, 355 with flat tops, 390-410 stock camshafts up to .550 lift solid lifter, 500 two barrel with a performer. Every engine builder and dizzy builder locks a HEI up making it take total timing out, in the range of 2-5* through the RPM range.

The idea is more timing equals more TQ on the low RPM side and lowers those numbers as RPM comes up and vice versa. Ever try taking timing out as the RPM range comes up?

The timing numbers that you see there are my frist try ever on the dyno with me doing the tuning so there will be abit of a learning curve here,

That timing cure is also what i have seen posted on the board and people sayed it was not a bad set up . i no my car is diff and needs are diff just try to see what people do how fast they bring in the timing, max timing and so on

yes i thing i need less timing going back soon

Your timing map looks backwards to me also. I have maximum timing in by 3000 and retard it two to three degrees on the top end.
You will probably find a lot more response if you put more timing in on the bottom end. If the car is making good HP on the top end I would leave that part of the map alone.

Daren

Gump,
so youre timimg would be ie:

0-3000 36* and start taking out 1-2* so on up to 7000rpm

rpm/kap-timing your timing
400-22 36
600-22 -
800-22 -
1000-23
1200-24
1400-26.5
1600-27
1800-28
2000-29.5
2200-31.5
2400-32
2800-35 36
3200-35 -
3600-35
4000-35
4000extended spark adv table-36.5
4500-36.5
5000-36.5 34
5500-36.5 34
6000-36.5 34
6500-36.5 33
7000-36.5 33
like this:confused:

It all depends on how well your car ran with the timing set at 36 deg at 7000. It also depends on what gas you are running and you if your A/F ratio is good (A little too rich is better than a little too lean).
My application is drag race only, so I run VP fuel exclusively.
I have my timing at 41 deg about 500 rpm below where I stall my converter (@ 3000 rpm). I begin to take timing out at about 5000 rpm. By 6000 rpm my timing is at 38 deg.
If your car ran well at 36 degrees why take out timing?

Hope this helps,

Daren

This is just in the wot part of the timing table 85kpa-100kpa
or are you saying to do the hole timing table from 0-100kpa

thx for the help

do you have tuner cat and if so could i see youre file on the timing
thx

As I said, my application is race only. I run my opti spark like it is a conventional distributor(x timing at x rpm). It is much easier for me to work with and I am not interested in emissions and other daily driver type issues. Both of my cars have Accel DFI.


Daren

So my under standing with timing is

(all this done on the dyno)

-Eng temp allways the same 170-190 range

-bring in timing as fast as you can and have full timing in by 3000rpm, take that through the rpm range taking out 1-3* timing to peak rpm.

(Why do you want to take timing out as rpm go's up)

WOT timing starts in the 85kpa-100kpa & the is the same from 85 -100kpa (my car is a na set up)

Afr in the 13-13.3 range with +1-2* timing and -1-2* timing to find what the car likes.

What is bad air? this is mid Oct sould you leave full timing in or take out 1-2* timing because of the air. then what will happen in mid summer when air temp is bad will this hurt the car or will the
iat/map/eng temp/ pull timing out
thx

I warm up my oil first and then cool my motor back to about 100 deg. I try to never stage above 140 deg (we normally push the car down the staging lane).
More timing will get you out of the hole better. When you take out a little timing you will pick up mph.
I do not adjust my timing for bad air, only my fuel. You can run more fuel when the air is denser.

Daren

Should youre timing cure stay with youre tq cure

i.e

my tq peaked at 5500rpm so should i have full timing untill5500rpm then start to drop it off as the rpm go's up to 7000rpm

Timing is usually taken out at higher rpms because the unburned air/fuel mixture is more turbulent (in the chamber) as rpms go up. The more turbulent mixture burns faster, requiring less advance.

Something else worth mentioning... The other factor is that the engine is less likely to have detonation at higher rpms. Since there's less time to complete the burn cycle, there's also less time for the unburned mix to be pre-heated by the flame front moving towards it. Lower temps= further from pre-ignition, which means more timing *can* (not must) be run without knock.

I think these cars need a good bit more timing on the low end, especially after adding exhaust. Low rpm timing will improve torque, which is why they say it will leave better. If you've ever seen a mustang do the locked distributor without the spout connector and run faster, you can do the same thing in principle. It just requires us to change the maps in the computer instead of twisting a distributor. I've seen a car pick up 5 mph in the 1/4 from this. Granted, it was a h/c car, but it works. Mustang boys say its worth 2 - 3 mph. A benefit to doing it in the ecu as opposed to the distributor, is our cars will still be easy to start. Just don't change the map down that low. The more timing and compression, the harder it is to start. I have yet to do back to back testing on my car at the track with that, but will be shortly. I'll let you know. Drivability definitely improved after I added some timing down around 1500 - 3000. I kept the topend the same since I don't have a cam or heads, yet.

At what point do you stop the advance of the timing, should the timing cure and Tq be the same
ie: if my Tq cure stops at 5500rpm is that the point where hp takes over and i should start taking out timing