Topic: Target CR for NO2

[afkrejci90]

First off, I have the bottom end for this (Carrillo's).  Looking to run a NO2 setup for the occasional track day.  Using a 1000cc engine and getting custom pistons made.  What compression ratio should I be shooting for?  I want to keep it on a small shot.  Can I get by with using a higher octane fuel for a track day to combat the the detonation from the increased heat?  11.5:1 is what I want to be at for street use.

[Jim F]

you might want to see if David Fletcher  can answer this better than I can as he races a bike
with NO2. I can tell you that his bike off of NO2 runs low to mid 9,s and on the bottle runs low to mid 8,s
and he pulls timing out when on NO2.
On my turbo bike I would like to run 10 to 12 lbs of boost and I also have a way to pull timing out to keep the motor together
there are a lot of combinations out there for all of the above.
good luck


Jim

[afkrejci90]

do you have his username?

[Jim F]

I'll call David and get him on
I can't remember his user name
Sorry
Jim

[Jim F]

Just remembered
It's fast bike
J

[Fastbike]

afk,

Sorry, been real busy.  I will need more info on your setup.  What are you using the bike for: ie. dragracing, roadracing track days, stop light racing?  What do you consider a small shot? 

Just so you understand, I don't relate well to "shots", such as 50hp, 100hp.  I tend to deal with jet sizes instead.  I don't believe most manufacturers claims of this or that for horsepower.  Too many variables.  Tune the bike to do what you need to accomplish.  For example, I will install certain size jets in the foggers to do what I want it to do.  I may install very small jets to just make an index number in a flat out run, or I may install bigger jets and delay the start of the nitrous down track.  This make huge mph and screws with the other guy, as he thinks I had a problem being so slow at the start, but come flying by him with 20mph in the bank. 

One thing you need to remember is not to jet rich.  The proper AFR is just that, and you should retard the timing more than everybody else tells you.  Nothing kills a nitrous engine faster than too much timing.  I have run as much as 20* of retard with only 20 nitrous jets and watched the bike go into the 8.20's on a marginal track.  Keep in mind my engine is a 1075cc 2-valve Kaw.  Ask Jim French about it.  In closing, shoot me some info and I will be happy to give you my opinions.  I am not an expert, but I know what does and has worked for me, and (knock on wood) have yet to hurt my engine. 

[afkrejci90]

PM sent

[dusterdude]

Fb,curious question,what happens if one jets rich


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[Bill/BentON Racing]

Mark, I'm guessing just one jet but through the manifold. Sam.

[dusterdude]

Bill,im wondering if its bad for the engine


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[dusterdude]

Sam


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[Fastbike]

Dusterdude,

I'll try not to make this too long.   The first thing to remember about nitrous is it the same as normally aspirated, meaning if 12.8-13.2 afr is where your engine makes it's best power, so it will with nitrous.  You are not forcing the air-fuel mixture in under pressure like turbocharging.  You are just introducing more fuel and oxygen to the engine than atmospheric pressure does on its own.  The chemical reaction is still the same. 

The car guys are way ahead of us on nitrous use.  They found out several years ago that running rich mixtures (too cool the cylinder down and reduce detonation) was detrimental.  They didn't get the horsepower increase they were expecting so they would advance the timing to give the richer mixture more time to burn.  What they would do is cause detonation, rattle the piston rings unseating them, letting oil into the combustion chambers, and detonating even worse.  Oil in the chamber is a huge no-no, as I read the octane rating of oil is in the neighborhood of 45!  So mix that with the gas and your octane rating drops probably into the below 70 range.  Instant burned pistons.  You can see the problem with that. 

So, tune the nitrous and fuel for optimum afr and dial the timing down.  The only downside is losing a few horsepower if you go too far.  How far?  Start with more than you think you need.  If you know someone who takes only 2 degrees per 50 hp, start YOUR engine with at least twice that.  I remove more than that myself.  Now remember, I'm not running a heads-up class, so I won't run it on the ragged edge.  If I did run such a class,  I would start with pulling more than enough timing and add 1 degree back at a time and record my mph.  Mph is horsepower.  If I add 1 or 2 degrees back in and the mph picks up, I'll add another.  If the mph doesn't improve, then you are working the engine against itself BTDC on the compression stroke.  It's not as efficienct.

You also need to learn to read the spark plug.  There are several good articles out there on how to do this, but really, you have to just do it.  It helps to have someone who knows how to help you.  I took a set of plugs one time to George Bryce at a AMA-Dragbike race in Valdosta to show him (he offered) and told me they looked too lean.  I appreciated his advice ( I kept my tuneup the same as I was running better than ever ), but people are willing to help.  I know this was long winded, but there is alot of info to share.  I will try to answer anyone's questions too the best of my knowledge.  Thanks.

[scottly]

I thought a lean condition with laughing gas was more or less instant death?

[MRieck]

I have limited use with nitrous BUT the first thing is do not believe HP figures put out by the (especially old NOS). I have broken baskets etc in m FJ with that #$%* on the street. Nitrous requires stages and.....knowledge. It is no fun to do 100 MPH...hit a button...and spin the tire like you hit an electric motor.
 My past experience Dave. I bought a progressive unit years ago but I did not have the time or the want and uninstalled the nitrous. My Busa is NA at 190 HP....fine for me on the street.
  I will say....nitrous is very cool....everybody should try it.

[Fastbike]

Scottly,

I remember one time at a race,  I forgot to turn the fuel pump on, so the motor was running just nitrous with no added fuel.  It was a dog, but no fuel, no heat.  Now you can run alittle lean and possibly hurt it, but IF you have enough timing pulled out, it's not likely.  Ask Jim French about this;  2 years ago at the NOPI race in Atlanta, I had changed fuel from C16 to NO2.  It was warm during Saturday qualifying and the bike was fast.  On Sunday, the weather got cooler and dryer and the bike was slower.  We found the nitrous jetting was slightly too lean for best power, but since we pull so much timing, didn't hurt a thing.  Actually won the race. 

I do maintenance about every 3 races, depending on the amount of total passes.  I will do a leak-down and compression test.  Got alot of nitrous passes, haven't had the head off in over a year.  Leak-down is 4% or less on all four holes and compression is within 5 lbs. difference.  You can run nitrous reliably.  Keep in mind I don't run ProMod amounts of nitrous, but with small jets, we can run almost 1 second quicker than on just motor.  It's all in the tune-up.

[Jim F]

And I might be mistaking but I think he
Pulled almost 20 degrees total
And the bike kept getting faster

[Hondell]

Listen carefully to Fastbike. Especially pulling out timing. I've run through many bottles with no engine problems on my streeter. Reading plugs is important too. Mine look scary white but you have to know where to look. My N2O system is custom built and I don't now what HP "shot" it is. Everyone asks that but when I tell then what jet I'm running , their eyes just glaze over. As far as CR I run 10.5 but almost anything will work if your tuning is correct. So pull back the timing-watch the plugs for overly rich- control the oiling and you'll be successful.

[Fastbike]

Hondell,

Thanks for the backup.  That picture you posted is beautiful.  That engine looks like it never left the showroom floor, just immaculate!  Questions:  I see no foggers in the intake boots, so I assume you have the spray and fuel being introduced somewhere before the carb slides, such as in the air filters.  The only thing giving it away is the bottle.  Is this the case?  Do you mind giving jet sizes?  If not, I understand .  And last, how does having the bottle mounted sideways work for you.  I have only seen bottles mounted upright or upside down depending if the bottle has a siphon tube or not.  Thanks.

[Hondell]

Fastbike
The nozzles are custom-made and are actually one tube within another (N20 on the outside-Gas inside it). The tubes extend right up to the carb slides. Everyone comments that I'm doing it wrong but don't reallize how far they go into the carb. There are also rapid prototype velocity stacks inside the air cleaners. Few years now and a move later and I'll have to look it up. The internal pickup tube in the bottle was repositioned towards the rear (side) of the bottle so when you accelerate the tube is always in the juice. Not a race bike - just something to show the cruiser types in the work parking lot. Totally in agreement on all your comments. My bike is proof they work! 

[Greg H]

Using gas reliably is all about using self restraint ,and not being  too greedy . All the negative stuff I've read or been told over the years about the shortcomings of Nitrous say more about the guy using the stuff rather than any inherent problems with Nitrous . It's all about control , we always sacrificed max power for reliability when we ran a Busa over the mile( thats what I mean about not getting too greedy) . If you set up the bike on a dyno, using a guy with lots of Nitrous experience is a must .