AEM tuning help for fuel octane change.

[OnceBitten]

Hello all. Figured I would post up here for any more pointers I could get from the knoledgable folks of this forum. I recently purchased an AEM viper from florida where the pump gas is 93 Octane. Now that I have it here in Oklahoma I can only get 91 Octane from the pump (unless I'm willing to drive well out of my way for every fill up)

My question is. How should I alter the fuel/timing map to allow for the lower Octane rating fuel without any detonantion issues? This is my first time tuning an AEM that isnt on a turbo car. Let alone a car without a knock sensor. Normally I would just dial back the timing, find the baseline knock value, and increase the timing agan until I started seeing detonation. Of course then back slightly off of that number and verify that AFR is still good through all loads and RPM. This car has a pretty good tune on it as it is. I dont want to have to start from scratch if I dont have to.

[Dajerseyviper]

Hello all. Figured I would post up here for any more pointers I could get from the knoledgable folks of this forum. I recently purchased an AEM viper from florida where the pump gas is 93 Octane. Now that I have it here in Oklahoma I can only get 91 Octane from the pump (unless I'm willing to drive well out of my way for every fill up)

My question is. How should I alter the fuel/timing map to allow for the lower Octane rating fuel without any detonantion issues? This is my first time tuning an AEM that isnt on a turbo car. Let alone a car without a knock sensor. Normally I would just dial back the timing, find the baseline knock value, and increase the timing agan until I started seeing detonation. Of course then back slightly off of that number and verify that AFR is still good through all loads and RPM. This car has a pretty good tune on it as it is. I dont want to have to start from scratch if I dont have to.

It a N/A Viper correct? There is not a huge difference in the tuning of an N/A car with 93-91 octane. I would say the AFR is similar to the point you likely wont have to change a thing. I would be happy with a 12.5 AFR under WOT (or whatever these cars like) and basically pull 2 degrees of timing globally for starters. Then for added safety you could pull an additional degree where the car makes peak TQ numbers which is around 3600rpms to about 4200 rpms.. I would leave the fuel map alone.

If you are going to detonate it is going to be due to the timing..

[ICPREY]

I would go to a dyno and see where you're at, data log the pulls, and send them to a competent Viper tuner with AEM experience.

[Dajerseyviper]

If you have tuned an AEM before, just do it yourself and knock a few degrees of timing out, its not rocket science. You could do it on a dyno if you want to be sure of everything..But Im willing to bet if it was tuned perfect on 93 octane the 91 shouldnt be that far off except for the timing.


I have however seen an N/A car loose 25 HP on the dyno cause the owner accidentally filled with 89 octane instead of 93..

[OnceBitten]

Thanks for the input guys. It was fully tuned on a dyno. I still have the sheets. I did a datalogging run on half and half 91-93. everything looked good. Ran the tank down and filled it with 91and datalogged again. It looks like there was built in safety margin from the original tune. Just had tweak the timing map just a little bit. Runs a little too rich for my liking. Its at about 12 AFR almost all the time. I need to lean out the table and do some work with the accel fuel. This thing was tuned for the track not the street. I will keep at it and confirm on a dyno in a few weeks.

[Dajerseyviper]

Thanks for the input guys. It was fully tuned on a dyno. I still have the sheets. I did a datalogging run on half and half 91-93. everything looked good. Ran the tank down and filled it with 91and datalogged again. It looks like there was built in safety margin from the original tune. Just had tweak the timing map just a little bit. Runs a little too rich for my liking. Its at about 12 AFR almost all the time. I need to lean out the table and do some work with the accel fuel. This thing was tuned for the track not the street. I will keep at it and confirm on a dyno in a few weeks.

Also keep in mind the car was tuned in Florida at sea level correct? Hotter and more humid dense air at the time. The main thing I have seen with every AEM and most "tuned" cars was that most of them were tuned only for WOT and the drive ability was god awful. How modified is the car that it needs an AEM standalone??

[plumcrazy]

Also keep in mind the car was tuned in Florida at sea level correct? Hotter and more humid dense air at the time. The main thing I have seen with every AEM and most "tuned" cars was that most of them were tuned only for WOT and the drive ability was god awful. How modified is the car that it needs an AEM standalone??

tuning the driveability is as important as WOT, its take a lot of time to get it right though under a lot of different conditions

[OnceBitten]

Its a never ending cycle. Every time I take my VR-4 out on a joyride I datalog. Always end up tweaking something.

tuning the driveability is as important as WOT, its take a lot of time to get it right though under a lot of different conditions

[Dajerseyviper]

Its a never ending cycle. Every time I take my VR-4 out on a joyride I datalog. Always end up tweaking something.

I used to Tune Fcons and had one in my 350Z making 850hp, and one in my 450hp Evo8. I had both of them fine tuned in perfect, but it took a good amount of time on the Dyno and the street. If you can find a real load based Dyno like a Dynapack or DynoDynamics that's the way to go. The AEM also should have an auto tune feature that will get your near your target AFR range providing you have a wideband hooked up to it.

It could also just be such a nasty and aggressive head and cam combo that it just wont drive like a normal car on the streets.. I would expect bucking and breaking up on a race car at low RPM's.

[Dajerseyviper]

tuning the driveability is as important as WOT, its take a lot of time to get it right though under a lot of different conditions

I know, that's the point I was making.

[OnceBitten]

hennesey heads, gen 3 intake and fuel system, larger throttle body, fairly aggressive cam, hennesey headers, no cats, mopar 3" exhaust with X-pipe. It could probably have been done without the AEM just not quite as well. No idea really. I have barely any experience with Vipers. It is definitely only tuned for WOT at this point. Driving it on the street leaves A LOT to be desired. Haha

[OnceBitten]

I just finally sat down and looked at the entire cal file. Its beyond me at this point. Im not sure where to start. I just dont know enough about tuning a Viper to feel confident enough. I also believe there is a vac leak somewhere to track down. Changes I made didnt give me what I was expecting. Couldnt get idle below 1000 rpm. Couldnt even get it to stall out with what should have done it. Fun stuff. There is so much timing advance across the map that i can only assume it is because of the cam.

[Dajerseyviper]

I just finally sat down and looked at the entire cal file. Its beyond me at this point. Im not sure where to start. I just dont know enough about tuning a Viper to feel confident enough. I also believe there is a vac leak somewhere to track down. Changes I made didnt give me what I was expecting. Couldnt get idle below 1000 rpm. Couldnt even get it to stall out with what should have done it. Fun stuff. There is so much timing advance across the map that i can only assume it is because of the cam.

Sounds like and intake leak or the Throttle is open too much. for starters, i would check for the leaks first before you start messing with the map.

[OnceBitten]

Im leaning towards throttle. The values arent matching up to the voltage sent from the TPS (shows 100% before pedal is fully to floor). I think the cable needs to be adjusted so I will start there. I completely agree though. I saved the .cal file before making any changes. I loaded it back on the ECU before I called it quits last night. Quick question, It shows about -1.xx psi static with the engine off. It was pretty cold last night though. Is that normal for a gen 2 MAP sensor? Also, is 26 degrees of timing at idle normal? 26 is the lowest value across the entire ignition map. Highest is 46 I believe.

Sounds like and intake leak or the Throttle is open too much. for starters, i would check for the leaks first before you start messing with the map.

[Dajerseyviper]

Im leaning towards throttle. The values arent matching up to the voltage sent from the TPS (shows 100% before pedal is fully to floor). I think the cable needs to be adjusted so I will start there. I completely agree though. I saved the .cal file before making any changes. I loaded it back on the ECU before I called it quits last night. Quick question, It shows about -1.xx psi static with the engine off. It was pretty cold last night though. Is that normal for a gen 2 MAP sensor? Also, is 26 degrees of timing at idle normal? 26 is the lowest value across the entire ignition map. Highest is 46 I believe.

Not really sure on a Viper to be honest, Ill look through the service manual later and see if it says anything about the timing at idle. I know On my Camaro I ran 24-26 at idle with the big cam.

[OnceBitten]

Thats what I was thinking as well. The cam was driving the higher ignition timing. I didnt think to check the service manual. That would have been a good place to start.