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AEM How much timing reduction for 9.0:1

88BB8B

Proven Member
143
8
Oct 14, 2016
Coldstream, BC_Canada
Hey everybody. I'm about to get my car started for the first time after building the motor with 9.0:1 compression pistons. I'm running straight 94 octane for now, with an HX35. I don't have the map available right now, but I had the car running well on stock 8.5:1 pistons up to 12 psi on a fairly conservative timing map that I built off of a stock evo 8 map. AEM infinity 506 ECU.

I'm wondering where I should adjust my timing map and by how much roughly to start safely. I'm assuming the low load portion of the map will probably be fine knock wise? But I'm not sure.
Is there anything else with the tune I should expect to adjust for the higher compression like fuel?
What about startup timing and fuel, any tips? I was having a bit of trouble getting the startup tune right before. (Crank, crank, fire, crank, crank, fire)
 

dustyboner

DSM Wiseman
1,940
1,049
Mar 13, 2016
abq, New_Mexico
if all that changed was the compression, you should be able to use the same map. check your a/f, adjust as necessary and tune out any knock you get.
 

dustyboner

DSM Wiseman
1,940
1,049
Mar 13, 2016
abq, New_Mexico
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DSMPT

DSM Wiseman
1,743
1,301
Jun 12, 2014
Japan / Mexico, Arizona
Hey everybody. I'm about to get my car started for the first time after building the motor with 9.0:1 compression pistons. I'm running straight 94 octane for now, with an HX35. I don't have the map available right now, but I had the car running well on stock 8.5:1 pistons up to 12 psi on a fairly conservative timing map that I built off of a stock evo 8 map. AEM infinity 506 ECU.

I'm wondering where I should adjust my timing map and by how much roughly to start safely. I'm assuming the low load portion of the map will probably be fine knock wise? But I'm not sure.
Is there anything else with the tune I should expect to adjust for the higher compression like fuel?
What about startup timing and fuel, any tips? I was having a bit of trouble getting the startup tune right before. (Crank, crank, fire, crank, crank, fire)
Like @dustyboner said above, it should be OK with the same map as long as the CR was the only change. Plus I remember that you have Supertech pistons. IIRC Supertech's number is calculated as head gasket thickness is 1.0mm, so actually you would have a little bit lower compression if you have one of major brand's head gasket, I think it would be approxi 8.8:1.

As for the startup, you have a standalone ECU, you have so many parameters that affect the startup beside maps, so you should play with it. But I don't recommend to do that until you finish to break-in the engine.
 

Kryndon

Proven Member
779
437
Jan 10, 2014
Bulgaria, Europe
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Am I reading this right? Let's say I'm running 22 psi selected boost via controller. And let's say my ECR is around 8.5:1. Does that mean my actual FCR will end up being 21.22psi? If so, that would make sense, and it really does show that CR isn't all that big of a deal in terms of tuning so long as you tweak timing properly. I ran a stock N/A 7 bolt block with a T25 for 3 years (10.5:1) without failure at 11 psi, with slight improvements in spool up and fuel efficiency.

However, based on the graph, we can see that the effect really becomes dominant if you're swapping from say 8.5CR to 11CR at very high boost levels. At that point you'd be better off dropping your target boost while raising timing until knock limit is found. Just some food for thought.
 
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