Ideal Drag Car Fuel & Timing Curve?
Moderator: Team
Ideal Drag Car Fuel & Timing Curve?
I'm not a tuner but, would like to know what to shoot for on an EFI Drag application. The car has a C4 and is Vortech Supercharged. Would I go for a flat Air/Fuel Ratio during a pass? Can I run more timing at lower RPM vs high RPM? My timing is adjusted based on boost and the fuel pressure regulator is boost referenced. Are there any publications or websites out there that will help me get a better understanding of what to do?
There's no real "ideal" air/fuel or timing curve. Every engine is different and needs different amounts of both. Combustion efficiency, air temperature and several other factors all play a role.
Plus, you can never trust a wideband 02 meter, you never truely know whats going on without reading the plugs. The wideband should be used as a tool, and thats its, just like several other tools you use.
A "rough" target air/fuel ratio on pumpgas to shoot for would be around 11:1 to be on the safe side. I wouldn't go much over 12:1 without good fuel.
On race fuel you can get away with a litle bit leaner mixture, I would shoot for 12-12.5:1. 13:1 is OK probably for a drag application, but its pushing it. There wont be much power gained after that point.
Timing really is something that needs to be done on a dyno. Start with a ballpark low advance number and gradually work your way up every pull. You will see a noticeble increase in power every degree, then you will get to a point where you will either hear knock or see the power curve flatten off. Then back it off a degree and you should be there.
Cylinder pressure in a force-inducted engine is generally really high in the lower to mid rpm range, so you usually cant give the engine a whole lot of advance. In the upper rpm range you can give it more as cylinder pressure will decrease allowing more timing without knock.
Be very carefull, this isn't something you just jump into. Get some help from somebody with a good background in performance efi tuning to help you on the dyno. An incorrect key stroke could toast your entire engine. Hit up some forums online to get you some starting points for your particular engine. Good luck!
Bo
Plus, you can never trust a wideband 02 meter, you never truely know whats going on without reading the plugs. The wideband should be used as a tool, and thats its, just like several other tools you use.
A "rough" target air/fuel ratio on pumpgas to shoot for would be around 11:1 to be on the safe side. I wouldn't go much over 12:1 without good fuel.
On race fuel you can get away with a litle bit leaner mixture, I would shoot for 12-12.5:1. 13:1 is OK probably for a drag application, but its pushing it. There wont be much power gained after that point.
Timing really is something that needs to be done on a dyno. Start with a ballpark low advance number and gradually work your way up every pull. You will see a noticeble increase in power every degree, then you will get to a point where you will either hear knock or see the power curve flatten off. Then back it off a degree and you should be there.
Cylinder pressure in a force-inducted engine is generally really high in the lower to mid rpm range, so you usually cant give the engine a whole lot of advance. In the upper rpm range you can give it more as cylinder pressure will decrease allowing more timing without knock.
Be very carefull, this isn't something you just jump into. Get some help from somebody with a good background in performance efi tuning to help you on the dyno. An incorrect key stroke could toast your entire engine. Hit up some forums online to get you some starting points for your particular engine. Good luck!
Bo
I do have a base tune that works pretty good and run VP C16. I normally can't push it past 12:1 AFR with 22 degrees going through the traps or the plug tips start dissappearing. I think there is some power in the rest of the tune but, I'm not sure what the limits are. I do tune off the dual widebands on the car. Sounds like I need to get back on the dyno. It's hard on the C4 though so, I try to do it at the track.
-
airflowdevelop
- Guru
- Posts: 2011
- Joined: Tue Oct 12, 2004 1:19 pm
- Location: Dillsburg, PA
- Contact:
Bob, Do you have a system that can data log? I have found that feature to be the key for track tuning EFI.
What are your intake charge temps. through the traps?
With my setup I have found that intake charge temps really dictate the amount of advance I can run. I,m pushing a 4cyl. Mopar to 35 psi on C16 with no detonation. 23 dgrees max advance through peak torque, then after peak torque I add about three more degrees through peak RPM.
I have found alchohol injection to be VERY usefull in lowering charge temps., My system injects Isopropyl alky at manifold pressures above 26psi, one alky nozzle (@ .09 gpm-60psi ) mounted in the intake between the Intercooler and the manifold lowers charge temps 100 degrees!.....on a hot day around 95 ambient my charge temps will stay about 135 degrees.
without the alcohol inj. this 2.2 would be on the verge of detonation and head gskt. failure, could only manage 25 psi manifold pressure.
as for A/F ratios, God only knows....somwhere between 11.5 and 12.5..... my makes best power at 12.65 to one.
Like advance, I change A/F ratio after peak torque. slightly leaning it out at higher rpms...........
A good web site is at Simple Digital systems http://www.sdsefi.com/tech.html
Warren
What are your intake charge temps. through the traps?
With my setup I have found that intake charge temps really dictate the amount of advance I can run. I,m pushing a 4cyl. Mopar to 35 psi on C16 with no detonation. 23 dgrees max advance through peak torque, then after peak torque I add about three more degrees through peak RPM.
I have found alchohol injection to be VERY usefull in lowering charge temps., My system injects Isopropyl alky at manifold pressures above 26psi, one alky nozzle (@ .09 gpm-60psi ) mounted in the intake between the Intercooler and the manifold lowers charge temps 100 degrees!.....on a hot day around 95 ambient my charge temps will stay about 135 degrees.
without the alcohol inj. this 2.2 would be on the verge of detonation and head gskt. failure, could only manage 25 psi manifold pressure.
as for A/F ratios, God only knows....somwhere between 11.5 and 12.5..... my makes best power at 12.65 to one.
Like advance, I change A/F ratio after peak torque. slightly leaning it out at higher rpms...........
A good web site is at Simple Digital systems http://www.sdsefi.com/tech.html
Warren
Wow! 300F, thats a hot intake charge. Do your rules allow fuel coolers? If you could inject COLD fuel it could help a bunch.
Are you trying to tune in closed loop?
Do you have knock sensor capability?
would you/could you run pure methonol?, ( would drastically reduce charge temps)
I guess what I'm getting at is that you really need to lower the intake temp to get full potential from a pressurized engine......on my turbo 4cyl. with a good flowing intercooler my charge temps were at aprox. 185F, at 28 lbs boost I was lifting the head, added alky inj. and charge temps dropped dramatically and I was able to add 5 degrees timing, went to 35 lbs. boost and head STOPPED lifting. no more detonation, cars ET dropped 4 tenthes! Just by lowering charge temps.
you might want to try VP "Import" fuel, I believe it has higher MON #s than C16. I think it is rated at 120+ MON....it has a higher specific gravity so you would probably have to lean it down a bit.
Warren
Are you trying to tune in closed loop?
Do you have knock sensor capability?
would you/could you run pure methonol?, ( would drastically reduce charge temps)
I guess what I'm getting at is that you really need to lower the intake temp to get full potential from a pressurized engine......on my turbo 4cyl. with a good flowing intercooler my charge temps were at aprox. 185F, at 28 lbs boost I was lifting the head, added alky inj. and charge temps dropped dramatically and I was able to add 5 degrees timing, went to 35 lbs. boost and head STOPPED lifting. no more detonation, cars ET dropped 4 tenthes! Just by lowering charge temps.
you might want to try VP "Import" fuel, I believe it has higher MON #s than C16. I think it is rated at 120+ MON....it has a higher specific gravity so you would probably have to lean it down a bit.
Warren
The PMS is running in stand alone mode. Can't run alky or any type of cooler. Also, no cooling of the fuel. I looked into the VP Import fuel but, it would not pass the fuel check. It will lift the head with another degree or two of timing depending on the weather. Just wondering if I can put more timing down low with more fuel or up high with more fuel? Maybe run leaner at lower rpm? There are alot of ways to go it's just hard to try them all at the track. I'm looking for someone that can give me some direction to start with. Don't think the system can use a knock sensor directly connected to it but, I have looked at a few standalone systems that are out there. Any recommendations on those?