Adding fuel and pulling advance for dry nitrous

Give input on tuning as well as any tips and tricks you may have. Also feel free to share base mapping files for various engine types.
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Jon K
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Adding fuel and pulling advance for dry nitrous

Post by Jon K »

Hi all -

So I have a direct port wet nitrous kit on the shelf (Nitrous Express) that I never got around to reinstalling after having my new intake manifold created. I was thinking that since I am looking to run a small shot to help spool up a turbo, perhaps direct port is a waste of time and increased number of fittings/plumbing to leak/fail. Perhaps I'll go back to direct port and run a bigger jet setup - for now, I want to keep it simple and see how it goes.

Was thinking of going to a single port dry setup for a 50 - 75 shot. I plan on using my DTA S80 Pro to handle the nitrous control. I have a spare output (AUX1) on the ECU that can be triggered by two input (RPM and Throttle Position). I can program it such that fuel is added and timing is pulled. I contacted Allan to see if he can change the advance/retard from a percentage to a value (1 degree, 2 degree, etc) since I run a turbo setup my timing is different at 35 psi vs 20 psi, so 12% at 30 psi is a lot more timing pulled than 12% @ 20 psi. Here is an example of my config:

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Question is, how can I ballpark my added fuel? I am targeting around 11.5 - 11.7 AFR. If I am adding 50 shot what is a safe guess at added fuel percentage? What about 75? Is there an easy way to calculate without guessing? I know a 50 - 75 shot is not big by any means, and maybe I will increase it once I get more familiar, but I don't want to turn it on and be too lean. I mean, I could err on the side of caution and dump a bunch of fuel in but that has its negatives too.

Thanks for any input - nitrous is relatively new to me I ran a wet 75 shot a few years ago and it was OK but I wasn't controlling it properly and had mixed results. My setup is a lot more sophisticated today.

This is on a 2.8L 6 cylinder 76mm turbo setup by the way.

Thanks all!

Jon
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lumley32
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Re: Adding fuel and pulling advance for dry nitrous

Post by lumley32 »

i dont no any thing about nitrous, having said that.......

if you add a none amount of NO2 then surely you can work out the amount of oxegen that will be released and be able to calculate the amount of fuel needed?

its along time since i have done any chemistry but a little googling about molar amounts should give you the mass of oxegen in the NO2 then just add an appropriate volume of fuel.

should get you close?
Jon K
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Re: Adding fuel and pulling advance for dry nitrous

Post by Jon K »

I thought so too - but I am not a scientist - I was hoping to find a known "you're adding X jet size, you need Y fuel added" baseline.
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lumley32
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Re: Adding fuel and pulling advance for dry nitrous

Post by lumley32 »

how about this?

am i correct in thinking that a 75 shot of nitrous is meant to give you 75 hp? if so you can just work out the percentage increase in power and add that much more fuel?

ie 100hp NA + 25hp with no2 = 125hp this is a 25% increase in power there for it will need 25% more fuel? this is just a theory but might get you close?
stevieturbo
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Re: Adding fuel and pulling advance for dry nitrous

Post by stevieturbo »

Simple terms as lumley says.

You have 500hp and add a 50 shot. That's a 10% increase, so sensibly a 10% increase in fuel would be reasonable.
Jon K
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Re: Adding fuel and pulling advance for dry nitrous

Post by Jon K »

Stevie - right, except that at 3500RPM on point I am not making 500 HP.
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Roverdose
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Re: Adding fuel and pulling advance for dry nitrous

Post by Roverdose »

i would...

if you have a dyno plot you could see what power you have and estimate what percentage +50bhp is. use that for the added fuel % at those revs.

Drew
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Re: Adding fuel and pulling advance for dry nitrous

Post by Jon K »

I have a larger turbo on a smaller motor - I did 685 rwhp but its from like 5500 - 6900 RPM mostly. But I want to wake her up by spraying at like 3300-3500 RPM. I think I might just ease into it with a fat guesstimate.
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Roverdose
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Re: Adding fuel and pulling advance for dry nitrous

Post by Roverdose »

I contacted Allan to see if he can change the advance/retard from a percentage to a value (1 degree, 2 degree, etc)
there is a check box in the general engine settings that changes that to degree's. you run map based i guess then? as i would have changed that for map comps into dgr's already.

so lets say you have 200bhp at 3k? add 25% fuel.

Drew
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Re: Adding fuel and pulling advance for dry nitrous

Post by stevieturbo »

Jon K wrote:Stevie - right, except that at 3500RPM on point I am not making 500 HP.
I just used 500hp and 50 shot for easy maths :)

You'd need a rough idea of the power you are making at the turn on point, and work from there really.

Although if it then spools the turbo much earlier, it could have knock on effects to the main map too, and as the enrichment is % based, it might get a little more complicated to sort all the tuning again.
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