Nozzle size, fuel ratio and nitrous

Mike · 11-23-2008

My head hurts just thinking about it, but how can I calculate appx nozzle sizes when it comes to nitrous injection? Anyone know?

Nitrous is pretty much useless without matching it with fuel and this, hopefully, is where the alcohol injection comes in.

As it stands, I'm given a 2GPH nozzle size for my engine, max revs and boost but I assume I need to go larger if nitrous were injected.

How can I get some estimates as I don't want to be buying lots of different sized nozzles to find out.

To complicate matters, I'm planning a dual nozzle set up (pre-turbo and post-intercooler) and if possible, stage it for off and on nitrous?

Is there a rough formula I can use?

forcefed86 · 11-23-2008

A/F ratos won't change. If your turbo then shoot for mid 11's. I've found that a 5gpm nozzle is on the rich side of good for approx 70 hp of N20 @150psi. So if your given a 2gpm nozzle size and are spraying a 70 shot Use a 7gpm nozzle. Stick with a 1gpm nozzle pre turbo to keep the atomization/press high. So with the pre-turbo inj. I'd use a 1gpm pre and a 6 gpm post with a 70 shot. Also I'd turn your boost down 2-3lbs the N20 is going to make it spike a bit.

Good luck...

Mike · 11-24-2008

I'm not sure what you mean that A/F won't change with nitrous? And where does @ 150psi come into it? Another uncertainty I have is the Alcohol/Water mix. I read with diesel engines I need to go no higher than 40% alc to avoid pre-ignition but can that be safely increased when nitrous is added?

forcefed86 · 11-25-2008

Originally Posted by Mike

I'm not sure what you mean that A/F won't change with nitrous? And where does @ 150psi come into it? Another uncertainty I have is the Alcohol/Water mix. I read with diesel engines I need to go no higher than 40% alc to avoid pre-ignition but can that be safely increased when nitrous is added?

A/F stands for air fuel ratio. And you want it in the mid 11:1 range. Yes obviously the A/F will change if you add N20. But you still want it in the mid 11 range. Thats where the addition of fuel to the N20 shot comes in. I suggest using the methanol for your additional fuel. 150psi is the pressure of a standard devils own alcohol pump. I haven't read up on diesel myself so I'm not sure about the 40% rule...

sharkey · 11-26-2008

diesels are a little different to tune. first, their stoichiometric ratio is a bit different than gas (not much, diesel is 14.6 were gas is 14.7), however a diesel will make best power leaner that stoich, unlike gas. a diesel will also never actualy reach a stoich ratio because the fuel is what controlls the engines power, not a throttle body. typically diesels are tuned using EGT (exhaust gas temps) as a refference.

ive never played with nitrous on a diesel. however, nitrous is just adding more oxygen. that being said, it will likley cause a little lower egt and a bit more power, however adding fuel with nitrous will make the best power at the same egt as before. however thats just theory for adding more diesel, i have no clue on how itll act with meth in the mix and what you will need to do.

Mike · 11-26-2008

Sorry I wasn't clear, I know what A/F stands for and that was my point, that injecting nitrous will weaken the mix and give no benefit other than cooling unless it's matched with additional fuel. However, when it comes to diesels, A/F ratios aren't such a concern as they are with petrol cars and rather than utilise wideband (which isn't ideal either) I'll be watching the EGT's (and turbo boost) to tune mine by. For road use, I also have to be aware of the smoke.

The best advice I've been given so far is to add the nitrous then try to match it with the fuel but I don't really want to be forever buying dyno or drag strip time if I can help it.

I've now got a 1GPH, 3GPH and 7GPH nozzle to play with. Can any maths guru out there work out what power I can add in the way of alcohol as a fuel? Bearing in mind I might have to observe a max 40% mix?

forcefed86 · 11-26-2008

Yanno, now that I think of it. I don't think meth would offer as much to a diesel engine. Diesel fuel has good anti-detonation properties it's self. Most of the tractor pull engines I've seen use water only. And alot of it! Read up on the tracotr pull forums but I don't know if I'd even use meth. I think Banks drag truck uses straight diesel fuel to make it's ridiclious power. And if you've ever seen it run it doesn't produce any black clouds out of the stack. He called that wasted HP in an interview I saw. Also might want to look in to propane injection. Lot of them use that too...

Let us know if I'm ever feeling spendy I might buy that new straight six dodge diesel!

Mike · 11-27-2008

You're right that diesels can't take advantage of raised octane but I'm looking at it from a fuelling point of view to match nitrous.
LPG is another option I'm looking into. However, the cheapest kits I found so far are over £500 so I doubt I'll be getting one of them. I do have another LPG alternative to explore otherwise it'll have to be a diesel plunger to supply the extra fuel.

forcefed86 · 11-30-2008

HammerDownAuto.com: Do-it-yourself propane injection

;)

bruce-m · 12-10-2008

Hey mike, when i was tuning my 306 D-turbo for NOS, it did take a bit of dyno and road time to get it right.

But what i did is tuned the fuel pump perfect on the dyno for maximum bhp when the NOS was on, now obviously it massively over fueled when NOS was off, so i set up a valve to bleed boost pressure away from the on boost valve on the fuel pump so it would keep the fueling down.

Then when i hit the NOS on the valve would close increasing the fuel for the NOS.

With regards to the water/methanol injection i went with a 30% mix and used a EGT gauge to find which was the best size jet, i ended up using a 5gph which was to big for general driving but spot on for giving it some real heavy right foot or with NOS.