WOT Tuning

[mrand]

Originally Posted by Starman

Guys, as I recall the LT-5 is programmed for a 12:1 fuel/air ratio with the secondary injectors on. It will be faster if you lean it out (ideal stochiometric ratio for gas is 14:1), but it is programmed rich to protect against detonation. Let's face it, the 90-92 cars have 2nd generation ECMs and only read every 25 RPM. With Speed Density control and batch fired injectors there is not much to work with here. You can detonate the hell out of the car without it responding enough to prevent it, just on a bad tank of gas.

The 93 up cars have the P8 ECM that read every RPM. I've often thought that there would be more driveability there but have not found anyone that has made the change.

I'm sorry to say that, regarding LT5 applications, there isn't much correct in this quoted post.

"Ideal stochiometric ratio" describes a chemically balanced mixture - it has nothing to do with best performance. Leaning out the AFR of a performance engine at WOT to anything approaching 14:1 is a recipe for disaster.
Has has been pointed out, the LT5 injectors are not batched fired.
The computer runs plenty fast to respond to rpm changes. The post makes it sound like the computer sits around and once every 25 rpms does something. That isn't correct. And while a bad tank of gas could cause a little detonation, there is a knock sensor which will prevent "detonating the hell out of the car." And really - do people get "bad" tanks of gas any more? Lastly, the computer used in 1993 was not noticeably different than the one used in previous years.

Marc

[Tyler Townsley]

Buy a WB with recording capability and have it plumed into the collector. I am all for reading plugs but having a actual track picture would pay for itself in the end. Marc is right, 14.7 is not anywhere near your target AFR for load based tuning. Not sure what Marc uses as his baseline for WOT but it would be a good start. I would think money spent on suspension improvements would have a better return than trying to find additional HP through calibration changes.

Tyler

[tpepmeie]

Originally Posted by Tyler Townsley

I would think money spent on suspension improvements would have a better return than trying to find additional HP through calibration changes.

Tyler

Tyler, you keep that logic up and we'll have to award you a Beacon of Reality award. Can we do that on the forum?

Seriously, Marc has spoken the truth also. There has been this urban legend posted before about the mysterious "P8" ECM in 93+ cars. It isn't true, at lease to the best of my knowledge...still got the good ole P4.

Todd

[XfireZ51]

Originally Posted by Tyler Townsley

Buy a WB with recording capability and have it plumed into the collector. I am all for reading plugs but having a actual track picture would pay for itself in the end. Marc is right, 14.7 is not anywhere near your target AFR for load based tuning. Not sure what Marc uses as his baseline for WOT but it would be a good start. I would think money spent on suspension improvements would have a better return than trying to find additional HP through calibration changes.

Tyler

Not certain if this was directed to me or someone else. I think I previously stated that I do have a ZT-2. Used it for 2 years on my old 84. Haven't installed it yet on the ZR deciding how to route it into the cabin. As for finding additional HP from calibration changes, so far with a change of plug heat range ($1.50/plug) and modifying both SA and VE tables(FREE) where it counts, I've been able to pick up about 2- 2.5 mph in trap speed. IMO, pretty good bang for the buck and I don't think I'm done yet. I'd agree that tires should be on the short list.

[Tyler Townsley]

Originally Posted by XfireZ51

Not certain if this was directed to me or someone else. I think I previously stated that I do have a ZT-2. Used it for 2 years on my old 84. Haven't installed it yet on the ZR deciding how to route it into the cabin. As for finding additional HP from calibration changes, so far with a change of plug heat range ($1.50/plug) and modifying both SA and VE tables(FREE) where it counts, I've been able to pick up about 2- 2.5 mph in trap speed. IMO, pretty good bang for the buck and I don't think I'm done yet. I'd agree that tires should be on the short list.

Kind of both. Repairing a broke LT 5 can be expensive. There is a lot of collective wisdom on this forum that hopefully can help. I do not know your knowledge level on the calibration tables so I am urging caution. If I were to race a ZR-1 the first thing I would address is the radiator bypass and how it functions. In stock configuration this system starts routing water around the radiator at 5200 rpm and by 5800 you have almost no water being cooled unless you slow the revs back down, leaning the motor only increases the likelyhood of blowing a head gasket in this situation. The fix is simple but does call for a heavy duty radiator and cutting the thermostat pressure spring and blocking the bypass.

It is obvious you are comfortable with data monitoring so there is no reason to fly blind. Take the laptop and record a session then look at temps and rpms then look at the AFRs from your WB O2 to see just what fueling is doing throughout the run. What happened to spark? As previously stated the computer will pull timing out and you will never notice without going back over the data. Oh yeah start the session with enough fuel so you will have at least 1/4 tank at the end of the session. The dual pumps suck a lot of fuel and it does not take much to lean out the motor when a turn or stop pulls fuel away from the pickup.

Tyler

[XfireZ51]

Originally Posted by Tyler Townsley

... If I were to race a ZR-1 the first thing I would address is the radiator bypass and how it functions. In stock configuration this system starts routing water around the radiator at 5200 rpm and by 5800 you have almost no water being cooled unless you slow the revs back down, leaning the motor only increases the likelyhood of blowing a head gasket in this situation. The fix is simple but does call for a heavy duty radiator and cutting the thermostat pressure spring and blocking the bypass.

Interesting. Thanks for that bit of advice.

It is obvious you are comfortable with data monitoring so there is no reason to fly blind. Take the laptop and record a session then look at temps and rpms then look at the AFRs from your WB O2 to see just what fueling is doing throughout the run. What happened to spark? As previously stated the computer will pull timing out and you will never notice without going back over the data. Oh yeah start the session with enough fuel so you will have at least 1/4 tank at the end of the session. The dual pumps suck a lot of fuel and it does not take much to lean out the motor when a turn or stop pulls fuel away from the pickup.

Tyler

Last year I datalogged a number of runs at the track. That led me to re-curve spark avoiding the knock retard. Trap speed went from 111 to 115mph.
The most recent changes I made were based on datalogs from my dyno runs a few weeks before. Having done some plug cuts, I began to suspect that the WB used at the dyno may have been reading lean although the dyno charts showed a pretty
steady 12.8 - 12.9 AFR up thru 7000rpm.
Hoping to go to track one last time this weekend. Back to your point however, if I lean it out any more, I will be datalogging looking for any knock. I'll keep you posted.

[Tyler Townsley]

Originally Posted by XfireZ51

Interesting. Thanks for that bit of advice.



Last year I datalogged a number of runs at the track. That led me to re-curve spark avoiding the knock retard. Trap speed went from 111 to 115mph.
The most recent changes I made were based on datalogs from my dyno runs a few weeks before. Having done some plug cuts, I began to suspect that the WB used at the dyno may have been reading lean although the dyno charts showed a pretty
steady 12.8 - 12.9 AFR up thru 7000rpm.
Hoping to go to track one last time this weekend. Back to your point however, if I lean it out any more, I will be datalogging looking for any knock. I'll keep you posted.

Here is a picture of which spring to cut. When you cut the thermo like this it is always open for water flow as long as the bypass does not open to pull the water around the radiator which is why I put a 1 in plug in the hose to block the bypass. Do not do this unless you have upgraded the stock radiator.

http://deliquescence.net/~tyler/misc/Thermo.jpg

Another point to consider is that the best HP in a LT 5 is made when the water temp is between 160-165 deg. This was tested some years ago by a tuner and I asked Graham B directly and he agreed that the test was accurate. He also made the point that OEM water temp was a compromise between emissions and power with emission winning the day. If you go back and look at your earlier data runs I would be interested in what you see when you compare rpms to water temp. IE what happens when you hold a rpm over 5800 for a period on time.

Tyler

[XfireZ51]

Tyler,

Thank you for that. I will review my datalogs altho I think the main issue is maintaining a 160F temp before a run. You know you just sit there waiting to get up to the line.

Originally Posted by Tyler Townsley

If I were to race a ZR-1 the first thing I would address is the radiator bypass and how it functions. In stock configuration this system starts routing water around the radiator at 5200 rpm and by 5800 you have almost no water being cooled unless you slow the revs back down, leaning the motor only increases the likelyhood of blowing a head gasket in this situation. The fix is simple but does call for a heavy duty radiator and cutting the thermostat pressure spring and blocking the bypass.

Tyler,I have no problems running my car at the track with a Ron Davis and a 170 Therm. I double stinted the car with Dwight at the track this past summer and the coolant temps were never a problem. The oil temp was a different story though.

[Tyler Townsley]

Originally Posted by Jeffvette

Tyler,I have no problems running my car at the track with a Ron Davis and a 170 Therm. I double stinted the car with Dwight at the track this past summer and the coolant temps were never a problem. The oil temp was a different story though.

The bypass works by pressure. The stock radiator has a low (restriction)flow rating and once the water pressure gets to a certain point (5200 rpm) the spring on the thermo begins to open and water goes around the radiator. The Ron Davis has a higher flow rate (less restriction) which raises the flow needed to open the bypass spring. With the cut thermo I could run 160 deg-165 deg with A/C and outside temps of 95+ as long as I was moving.

Lane Goldstein (Fastlane) used a switch in the cockpit to turn on his fans with engine off to cool down his motor between runs. You can do the same thing by turning off the motor but leave the ignition on and turning on the A/C both fans should come on.

Tyler