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

 

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!

 

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

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

 

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.

 

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.