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Setting up meth using nitrous tables

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Hey guys,

I'm hoping to get some advice and info on the best way to set this up on my car. The setup is as following:

91 NSX USDM stock motor

CTSC 9lbs

AEM meth kit w/ 2x 130cc nozzles. 50/50

aem v1

93 usdm octane

I'm running the mainly to keep iats in check since that's a common problem with the CTSC. I have a on/off switch for my meth system and i'd like to set it up so that when i switch it on the aem will switch to the nitrous map to take out some fuel at wot to account for the extra fueling, and also to add a few degrees of timing (probably 3~). Here's a few questions i had:

1. For the nitrous map trigger, can i just run a wire to my on/off switch and then run it to one of the switched outputs on aem, and should i use ground off, or ground on if it's going to be triggered when the wire has grounding?

2. When tuning my iat fuel tables, should i be adding fuel to help prevent knock/detonation, or removing fuel since the air is less dense?

3. When tuning my iat timing table, what's a normal amount of timing to pull/retard as the iats increase? (ex. -2 degrees at 140F, -4 at 170?)

4. Since i'm not trying to push it to the max, just make a little more power and be safer, is +3 degrees at WOT with meth on, a good amount to start with?

Apologies if some of these questions have been answered elsewhere, i couldn't find much info.


1. I never spent much time with the AEM v1 so it's not a system I'm overly familiar with. The key point is to ensure that you are only in your nitrous maps when the system is active and spraying. If the nitrous maps are full 3D maps rather than a simple 2D trim then this should function adequately. I'd strongly recommend running AEM's failsafe gauge or similar too so that you can ensure you're only running a more aggressive tune when the water meth is actually functioning.

2. If you want to retain a consistent AFR as the IAT increases then you want to be removing around 2-2.5% fuel per 10 deg C increase in IAT. Of course you may find that at higher IAT the engine is less knock sensitive with a richer AFR and hence you could adjust the IAT trim table to accomodate this.

3. The amount of timing you need to pull will vary from engine to engine and will be dependent on how knock prone the engine is. If you can tune to MBT and the engine simply doesn't knock even with very high IAT (unlikely in your case) then you can ignore the IAT ignition trim. More often than not I'll leave the IAT ignition trim at zero until the IAT gets up around 50 deg C and above. At this point I'll start removing timing to ensure the engine doesn't knock. the best way to confirm how much timing you need to pull though is to do multiple back to back dyno pulls to get the IAT really hot and adjust the trim table to avoid knock. Sometimes blocking the IC or the radiator for a water/air IC is a good way to get the IAT hot for this sort of testing.

4. The best way to test your ignition trim with the water/meth spraying is on a dyno with knock detection equipment so you can audibly confirm that the engine is not knocking and also confirm that you're seeing a gain in torque/power from the extra timing. 3 degrees for a quality water/meth injection system is probably quite conservative.

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