Technical So school me on Nitromethane

A few truths, a bunch of wives tales, some B.S.
Great stuff if you learn/know how to use it.
Just remember, it's expensive as it goes into the tank, it's expensive as it goes down the track...

Mike

 

Trials and tribulations of a Pontiac nitro funny car racer. Just one of the little guys prying his wallet open often to go nitro funny car racing using an off-brand engine. Interesting reading for sure.

Engine autopsy:

http://forums.maxperformanceinc.com/forums/showthread.php?t=792707

Success, 6.027 @ 231.64 MPH, video included:

http://forums.maxperformanceinc.com/forums/showthread.php?t=793763

In-car video of 6.027-second run:

http://forums.maxperformanceinc.com/forums/showthread.php?t=798712

Solid aluminum aftermarket Pontiac block cast with added material for nitro use, a nice upgrade from the previously successful iron aftermarket block:

http://forums.maxperformanceinc.com/forums/showthread.php?t=791117

Special block oiling mods for nitro use:

http://forums.maxperformanceinc.com/forums/showthread.php?t=754296

Insight on connecting rods and bearing fit for nitro use:

http://forums.maxperformanceinc.com/forums/showthread.php?t=799237

 

If you do decide to try it one of the main problems will be getting good info on running smaller percentages. Most fuel racers are knowledgeable in 90 plus percent only. Timing,compression,pumps,etc are all different on the smaller percentage engine.

 

My knowledge comes from experience only like Plan 9. 1/4 mile "squirt" racing teaches a lot less the leaning on the nitro pedal for 3 to 5 miles which very few have done in the scheme of running it. In my opinion all the photos are blown engines. I choose naturally aspirated and found it not only the best thrill on the loud pedal for us but the most fun too. With up to 80% we never ever had a bearing problem just changed them because I thought I ought to. Hurt some valves the first time because of being a little lean but learned quickly don't do that again. If common knowledge says to run a 110 bypass start with a 60. The most notable learning came from getting a more powerful magnito. We always ran oil for nitro, liked Torco 60, changed after 2 runs, and used a System 1 oil filter with the corse screen. Our engine did not like much rpm so the remedy was a biggest gear I could get for my Pontiac rear end with the tallest tire I could buy and found I could still use more. I would do it again in a heart beat but my son and I both have the Red Hat of the Bonneville 200 mph Club and felt we had done enough since it took 5 yrs. Nitro is good stuff that requires respect and likes compression when treated right. Good luck.

 

Well EXCUSE us! A professional what? Nitro user / expert?

 

I will preface this by readily admitting I don't know the first thing about running nitro, never done it. But I have "heard" for whatever that's worth, that nitro engines work better if they are loaded harder, IE pulling a taller gear then you would otherwise normally use in a given application. Any nitro guys want to respond to this?

 

Some very good information and some entertaining wives tales here for sure.

We just fired up our injected Early Hemi FED, 25% Nitro, what a rush. We both thought the engine loved it, she reved way faster than straight methanol, and the sound, "priceless". It is a 365" Chrysler, and the plan from the start was to run nitro, and the entire build was planned around high percentages of nitro. Think 1960's Jr. Fuel set up. Aluminum Rods, Arias Pistons, big cam, well prepped steel crank, big bearing clearances and 50w oil.

Dead winter here, so we pre-warmed the oil, fueled her up and pushed it out side when ready. Funny thing seeing nitro flames in the pipes and snow in the back ground. I will have to figure out how to post video. Too bad we don't have "smell-O-vision".


Compression ratio and camshaft selection weigh heavily with Nitro, you want lots of overlap and watch the opening and closing events. This is no place for the typical low comp. tight cylinder pressure building cam grinds, so if you are one of the many on here that are squeamish about BIG Cams, best to move on.

A very good source for information is Spud Miller, Fuel Injection Enterprises. Go to his web site and start reading, good stuff but it is going to take some study and thought, you are not going to rush into this shit and keep the short block together. http://fuelinjectionent.com/
And his race page http://www.onehotchilipepper.com/
Read, re-read, and learn, it's the best free advice on the web.

I sent our entire fuel system and magneto to Spud for service and calibration. He flows the pump, which is critical to determine the the fuel system details (nozzles, bypass jets, high speed by pass, etc). He included very detailed tune up suggestions specifically for our set up. I set it up as he instructed and it fired right up and only needed minor playing around with the idle mixture.

My advise, "just do it"

 

No Gary.but started using it before 1960..and have better sense than to advise anyone here on its use
As I stated in my first post,there is some bad information on this thread..I'd rather not mention names.

 

"I have always been intrigued with it, but have never been around it much."
The poster says it's just curiosity, he states he has no plans to run nitro, just want's to be "schooled" on it.
No plan. No car. No goal. So exactly what are "experts" supposed to impart? Interesting stuff, but the OP has no specifics, not even close. HE DIDN'T EVEN ASK FOR ADVISE ON IT'S USE! He just seems to be "wondering"!
JEEEEEEZ!

 

Nitro engines like to get pulled down hard off the line. A lower gear in the rear end or trans or a combination of both if a trans is used helps do this
Nitro makes so much power and torque a car can begin to launch in a unpredictable violent way ultimately slowing the car down.The lower gear helps calm down the launch. They just dont need alot of gear. You hear nitro guys talk about reading the pipes. For the most power the pipes should have a slight wet look inside at idle. Too much barrel valve and raw fuel comes out. Too lean the pipes look dry inside. Getting the correct gear ratio and the right barrel valve settings can make a car really 60 foot. On a gas engine when the plug fires there is a instant big explosion snapping the piston down the bore. Its basically coasting down the bore. With nitro the fuel burns so slow it forces the piston the whole way down the bore. It will continue to create pressure as it burns. When it gets near the bottom the exhaust valve has to open to relieve the pressure. If it didnt work that way the engine would get damaged. Thats why nitro cams are ground the way they are. Thats also were the flames come from and the big exhaust noise. The fuel is still burning with the valve open. The valves need to be made of inconel for them to survive. Close examination of the back side and stems can give a good indication of the tune up. If its too lean piston spray will settle there. If it gets too high up the stem the valve can get stuck in the guide with the predictable results that would follow. In a lower percentage combo the plugs shouldnt have the ground straps burned off. If they are its very lean. A bigger nozzle is needed for that cylinder. Its normal to have a different size nozzle in each cylinder. Some crew chiefs run different pistons or head gasket thicknesses from one bank to the other. A leak down test should be a regular part of servicing the engine if the heads dont come off. Everyone does things different. In no way am i saying this is the only way. Its just my way and the way i was taught. But however its done its alot of work. Proper maintainance performed in a regimented and disiplined way is they key to success. Some of mine shown.

 

Some i crew on. The dragster has set a low et of 5.60/263mph. It has runnered up at the march meet. The altered won the march meet last year also setting highest mph. These cars have and continue to teach me how to do it. Look for my nitro street coupe on the cover of the upcoming nitro madness magazine. Out next week.

 

@jimmy six brings up good points and has more experience with the stuff than me, a Red Hat isnt an easy to get, congrats! Things were running pretty good until we swapped a new motor in with about 15 extra cubes.. I think a couple things killed the motor... a) it was a little lean and i ran anyway, b) my block relief was too deep... when we went to 30% the increased cylinder pressure found thin spots in the relief area and formed a crack. Autopsy revealed as much... live and learn!

@falcongeorge gear swap did happen.. more power to the rear wheels and a lot of mileage to cover.

The oil we used is called Z-ALT, expensive but they gave us a number of cases - Im not sure if this outfit is around anymore. I do recall changing oil after every couple runs, methanol/nitro will dilute oil if you idle for long periods.



racer-x, nice info, good to get the drag racing perspective.

 

What I remember about running our dual 327 Chevy SB (364" each engine) on 98% was the tremendous amount of cylinder pressure. The blocks were dry, the water jackets were full of cement (or whatever they called that stuff in the '60's). We could not run water in the heads after about two to three runs, the heads showed cracks between the valves, so we ran dry. The cylinder pressure would blow unburned fuel past the rings into the pan, turning the oil into "milk", we had to change the oil after every pass.

 

Amen. One thing not mentioned; Nitro is addictive. A couple of my friends ran nostalgia funny cars, it ate a ton of funds so they finally dropped out. But not for long.... They are back. Both said, " the smell, the feel of the power, the sounds - once you run it, it's hard to stay away" I've never run it but I totally understand.
Great thread. Thanks Racer-X for sharing your experiences.

 

It refers to another thread, but a while back, some millennial asked about running nitro with 3 bolt carbs. He got all snotty and pissy with wbrw32, which I thought was kinda funny, considering that he is probably one of a very small handful of guys left with actual experience running nitro through 3 bolt carbs...

 

It all depends on what yr are try to accomplish !!!
Nitro is not forgiven, its either right or wrong ,It will let you know ,
To many are Are focused on a HEAVY tip of the can !!!
Nitro is manageable but you need to study and learn on how it works ,
NOT A JUST ADD fuel .
You do not need a Mag 44 or twins Unless you are wanting to Make 4,000 hp and North , 44 mag came out mid 90's
But you need $$ to play ,
There A site all about Nitro and tune ups , from Flatty's 60's to Mid 90's tun ups,
I use to hang on site , lot of neat Ideas and information , but been some time , I will look up and post

 

I did recently talk to a guy at a recent vintage racers get together and he said it wasn't even produced in the US anymore. It was all coming out of China. I think there are only 2 major vendors now. VP fuel was one of them and someone else, but I can't remember who.

 

Yes ,, CHINA !!!!

 

White Punk on Nitro wrote the following. It will be in my memory banks until they stop working

A Few Moments in HELL

"I Was Held Captive By A Fuel Altered"

So help me, this is the truth. When I was growing up in New York City, I had three dreams. The first was to drive a fuel car. The second was to become a hot shot automotive journalist and write for big car magazines. The third one, of course, was to see my ride in the pages of HOT ROD.

I've been messing with fuel cars most of my adult life. I've sucked clutch dust and tweaked, tuned and built enough stuff over the years that you could say I've got a well rounded background within the world of cars that go boom. The only thing I hadn't done was actually sit in the seat and steer one down the strip. Why? Because my empty pockets run pretty deep, and as you all know, in the world of professional drag racing, it's the billionaires who have the fun.

Like anyone else with as loose a grasp of reality as I exhibit so professionally, so often, I wasn't about to let a trivial detail like an utter lack of resources stand in my way. So I built me a fueler.

It's A Hot Rod


No kiddin', you don't even need to have a passing interest in pro drag cars to appreciate my ride. Why? Because it's not a race car, it's a hot rod!

To me, race cars are really nothing more than tools; devices to be used in the quest for making money and/or satisfying ego. Hot rods are also tools, but they are used within a much more spiritual realm. Hot rods exist only to please the soul. This is why I chose to package my hot rod in the form of a AA/Fuel Altered. Given my East Coast, growin' up street racin' in Brooklyn roots, a Fuel Altered is about as far removed from my native culture as you're ever gonna get. Anyway, had I gone with a more conventional machine like a Funny Car or digger, people might have gotten the impression that I was trying to be serious.

No sterile alloy replica was gonna do my hot rod justice, so I whipped up a cast-iron 426 Hemi. Stock bore, stock stroke, stock cylinder heads, 6.0:1 compression, and an 8-71 blower. So help me, if you topped the things with carbs, it'd be mild enough to drive to LA. On 90 percent and 60 degrees in the mag, it'll make an honest 2,000 hp, which on paper is just enough to cram my 1,600-lb. sled through the lights a pulsebeat under 6 seconds . . . on paper.

The neat thing about Fuel Altereds is that they have no contemporary science of their own. Dragster wings don't function very well on such a machine, and it has none of the aerodynamics and thus directional stability of a Funny Car. The Fuel Altered is an entity unto itself.

Preparing To Die


They say you never forget your first ride in a fuel car. Well, I'll attest to that. What influences me even more are the days, hours and minutes preceding my first attempt at riding the beast. Anyone who says they'd attempt a contraption as uncivilized and hyper-rude as a Fuel Altered and not be scared witless is someone you don't want to spend too much time around. The machine would be just as willing to snuff you out as it would to whiz you safely through the lights.

I managed to keep my fear well-covered until I went for the required "AA" physical a couple of days before the ride. I clearly remember the doctor wrapping my arm in order to take the blood pressure readings, and the thought popping into my head, "I wonder if they do this to the pig right before they stuff the apple in it's mouth?" Hey, I knew I was in trouble. Still, I kept it under wraps while I pondered the pyschological implications. About then, I experienced the grand realization of a drag racing lifetime --- you don't drive one of these things you want to . . . you do it because you have to! It is a disease.

Nailed To The Cross


I'm sure the feelings that twisted my gut as the shoulder harness was being cinched against my chest weren't all that different from those one might experience while awaiting the executioner's cold hand. We've all had "butterflies in the stomach," but I'll tell you, those suckers felt more like wombats on angel dust! My anxiety was checked by the knowledge that I could disband the firing squad by simply lifting my right foot. The adrenaline high was awesome, and we hadn't even towed from the staging lanes yet.

When we imagine ourselves thundering the ground and storming the big end, we tend to leave out the details that compromise the tangible experience. We'll leave out the discomfort and the claustrophobia. In the name of safety, the NHRA mandates a multitude of devices.

First, there's the itchy fireproof underwear. Then the thick fireproof pants, the bottoms of which are tucked into fire boots, which, in turn, are duct-taped to the pants so that they don't get snagged during a hasty exit. The jacket goes on next, and then your head is swallowed up by a fireproof sock. Since I don't have a firewall between my face and the engine, I wear an old-style breather mask and goggle setup, which in my estimation is a whole lot more insulation than a 1/16" inch thick sheet of Lexan. The helmet is the last thing to go on.

Race cars are usually quite comfortable when you try 'em out in street threads, but climb in looking like Captain Orbit and "tight fit" takes on a whole new meaning. Once you get scrunched into place, your crew begins the strapping-in process. A pair of 3-inch-wide belts run from the seatback over your shoulders to 3-inch lap belts; all four intersect at the middle of your gut and are then cinched tight. The final blow to freedom is the anti-submarine, or "crotch-strap," fitted to the buckle. In case you have a modicum of mobility left, three more devices ensure sensory deprivation: flameproof gloves, arm restraints, and --- my personal favourite --- the neck brace. Then you're ready to rumble.

Hey Dude (Don't Be Afraid)


You feel incredibly isolated, but the next few minutes of utter silence allow an exercise in automotive Zen: Become one with the machine. Feel the controls. Run through all the motions. Contemplating your fate is no longer an option.

Find a comfortable grip on the wheel with your left hand, which is so swollen out of proportion by the bulky glove you can only fit three fingers around the grip. Right hand on the brake, you tug back, then reach down to operate the reverser with your left. You feel for the clutch pedal, which is way forward in the cockpit. Since the car is equipped with a centrifugal clutch, the pedal is only used to help release tension going in and out of reverse. At all other times, you drive the car essentially the same way you would an automatic.

Finally, you practice the run itself. Left hand firmly on the wheel, you brace yourself against the seatback, pull hard against the brake, then peg the throttle. As soon as your right foot stops, you let go of the brake, reach down between your knees, and pull the shifter into High gear. There's only one strategy involved in shifting a two-speed fueler. Do it is as quickly as possible! The only motion required from this point on, aside from steering, is deployment of the chute. You acclimate with your right hand, running it over the chute lever, and letting it fall back to the brake handle.

Suddenly, your mind shatters like a plate-glass window as the tow rope jerks the car forward. Reality grabs you by the spleen --- the moment of truth has arrived! You do the best you can to keep your head together as the crew maneuvers the car into the fire-up zone. You watch, somewhat detached, as one of them puts the starter to the blower drive and rests the gasoline squirt bottle atop the injector.

You are no longer a human being. You are a component of the machine. This feeling is exacerbated by the fact that no one is paying attention to or even looking at you, because they're all focused on their individual roles. Somehow, this instills an odd feeling of confidence.

An official signals that it's showtime. You crack the throttle as your man gives the injector a healthly squirt of gasoline. Close the throttle. The starter spins the motor up to cranking speed. You point to another crew member who's poised with the magneto ground wire in his hand, and he rips it away as if trying to start a balky lawn mower. The sleeping elephant roars instantly, as if a red-hot poker has been shoved through it's guts.

Electricity vibrates through the framerails. You tug the brake handle tightly and watch as your crew hustles to get out of the way. Idle speed is high for the first couple of seconds as the engine swizzles it's gasoline primer shot, but once it's fully involved with the nitro, the beast hunkers down with a hammering lope. All vestiges of fear and apprehension are erased by a level of lust only nitromethane can inspire.

Aside from the deceivingly gentle rocking generated by the motor's 2500 rpm idle, you are quite unaware of the noise it's making and this is somehow unnerving. You watch the crew scurry, cupping their hands over their ears, flinching as nitro fumes corrode their sinuses. You are in the eye of the storm and it's eerily peaceful, and ultimately surreal. With the tow vehicle away, you ease off the brake and roll toward the water box.

You goose the throttle to give the tires a full spin in the wet stuff. The monster at your feet bellows as the slicks freewheel for an instant, playfully bobbing the back of the car skyward. Everything seems right. You glance down at the oil pressure gauge: 100 pounds of pressure. You keep rolling. A crew member motions you to a predetermined point. He gives the high sign and you dig deep into the throttle.

The motor comes on like a chainsaw, the back of the car rises up as the tires sling outward. Visual perception changes to one of looking down on the motor and front tires. From where you sit, there's no indication that you are actually smoking the tires. No clouds, no deafening noise, no indication of anything radical other than a slight skating and drifting sensation, as if driving through thick snow with the hammer down. You gently saw the steering wheel in response to the car's subtle movements.

As you watch the Tree pass from your peripheal sight, you ease off the throttle to keep the motor out of valve float. Everything feels so smooth and easy that you want to keep the skins lit for the whole quarter mile and call it a day, but the plan is to vulcanize 100 feet or so and then get it stopped.

The first licks of ferocity begin when you back off the throttle at the end of the burnout. For an instant, the tires leech the pavement while the motor is still generating, and it shoots you forward at a rate oddly out of synch with the seeming tameness of the burnout itself. It's an enormous rush! You grab the brake, pull the car to a stop, and begin fumbling it into reverse.

A moment or two later, a crew member begins relaying hand signals to bring you back to the burnout tracks. You gently twist the steering wheel as you reverse into the freshly generated fog bank, occasionaly glancing at the oil pressure gauge, then the headers, just to make sure everything's still lit. Fifteen or 20 feet behind the starting line, you go for the clutch pedal and pull the reverser handle back. In the same motion, you put the transmission into low gear by pushing the shift lever forward.

It occurs to you that the only thing that's more fun than a sliding high-C burnout is hammering the throttle and grabbing at the brake for a quick blast of dry-hop g-force. Whap! The machine lurches like it's been rear-ended by an 18-wheeler. The shock compresses you in the seat, and you feel your internal organs wrapping around your spine. Dude, you're livin' large now!

The chirpie puts you right in the beams. You inch ahead and the top light flickers on. You linger with the pre-stage bulb for a moment as you gather up and prepare for battle. The irony is that your competition isn't in the other lane, it's the Nazi doktor's bed you're strapped to, ready to scare you half to death if not complete the job outright. Sure, you're the one at the controls, but the beast-thing howling in your face is the boss. You ease off the brake and the stage beam lights up. Tug the brake, take a deep breath, and get ready to do it for real.

Everything turns to gel and kicks into slow motion. You look toward the Tree. Yellow flashes. You slam the throttle, and for the slightest part of an instant, nothing . . . then boom! The docile idle becomes a fury. The clutch comes in and you feel the frame distort around you in an unnerving reaction to the awesome torque.

Acceleration is sudden and violent, yet smooth and efficient in it's application, and you rocket forward, aiming the front of the car at any large object on the horizon. You're shoved ahead by the tires, but the sensation is more like being sucked through a tunnel by an immense magnet . . . but everything is still happening in slow-mo.

Your brain has gone into severe trauma mode. As far as it's concerned, you're in the middle of a horrible accident. The first 100 feet or so of strip seem to take an eternity to cover, and during this time your analytical mind has gone into some sort of hyperdrive, a thousand inputs being absorbed and processed simulatenously while you weed out the critical decisions necessary for control.

You grab for the shifter and yank it back, aware of the extra load placed against the motor because you can feel it's pitch change deep in your bones. At the same time, you're aware that the car is drifting to the right, and you counter it with the steering wheel.

It was too little a move, too late into the drift, and now the finish line markers in sight an instant ago have become a yellow stripe and a white blur. You've just received an invitation to dance with Mr. Guardrail. No thanks, man. Bring the hot rod home intact. You reel in your right foot, and like a slot car, the toy falls right into line and motors down the strip with the deliberation of a cat drawn to a bowl of tuna.

@!#**&@!


Well, see, we'd love to take you along for the rest of the ride, but truth is, we haven't been there yet. We've put about five runs on the "Bomb Squad" so far, and the most she's gone is to the eighth-mile . . . and that was a struggle. Severe tire shake put an end to one run, and landed yours truly in the hospital for one lap of the CAT scan. That's a story in itself: I made it to the hospital before I made it to the finish line! With a best of 11.08 at 42 mph --- try that in your street car --- we've got a long way to go, but we're having fun every inch of the way. And we're doin' it on nitro!



written by Tony DeFeo
from HOT ROD Magazine
page 42-48 - June, 1997
© HOT ROD Magazine 1997

 

This one?
http://classicfunnycarboard.com/CFB/index.php/board,34.0.html?PHPSESSID=8i5dtuis8ecmeq8ksbf14ttb54

 

Tony Defoe, Hunter S Thompson for car guys!

 

tony is here on the hamb. cool guy. he has a unique writing style that i like.

 

371 ci SBC 16 nozzles 2-80A pumps 50+ in the mag 90+ Nitro....thats how to do it on a budget....

 

I was a HUGE fan back in the Cars Illustrated days. the "12.99 for $1299" series was a hoot! I really love his writing style, kind of reminiscent of Car Craft in '73/'75.

 

This Why I built a Altered in January 1998 !!!

 

Roothawg I am" just a dipshit on the Hamb" But I have owned and run 3 fuel bikes over the years and will tell you what I can.I never had any money so I never ran over 60%.It wasnt the cost of the nitro,it was that I couldnt afford to replace the engine. I dont know who makes it now but I always used Francisco racing fuels nitro as it seemed cleaner and more consistent.First be sure your fuel line is big enough,1\2" id is minimal,3\4" is better-note that all my experience is with gravity feed carbureted bikes-you need a carb with as much float bowl capacity as possible and brass floats .I am sure there are methanol proof synthetics now but I have never seen any. Methanol is IME the best possible thing to mix with your fuel,it greatly reduces the tendency of the nitro to detonate and helps control temperature,it will also help give you some sort of plug reading.Obviously I cannot help with jetting since I dont know what sort of engine,mixture etc you propose to use .On a 77" sportster at sea level running 60% my main jet size started at 3\16" emulsion tube was 3\ 8". When you build your engine dont go nuts on compression ratio.I usually used 9-1. I saw lots of folks run big CR numbers and often helped them sweep their engines off the track.You WILL have enough cylinder pressure.Change your oil a lot,the nitro gets past the rings and dilutes the oil.I changed oil after every run-of course the bike only held 30 oz. I used both Torco 60 and Kendall 70 I could get.Use the hottest ignition you can devise that is 100% reliable.If you have an ignition stutter you are likely to hydraulic a piston head. NEVER try to start the engine with any nitro in the cylinders! The procedure we used was when you went through the eyes you shut the fuel off,slowly close the throttle,pull in the clutch and let the engine run out of fuel.If you snap the throttle shut and hit the kill button you will blow the engine right there .Before restart we filled the float bowls with methanol,pulled the plugs and spun the engine over.On startup we filled the bowls with methanol,started the engine and turned the fuel on.Try hard to avoid getting on and off the throttle during a run-if you have to get out of it abort the run and go through the shutdown process. A lot of people used to use up to 20% nitro with correctly jetted gas carbs and it seemed to work.I found that nitro will not mix with some gasolines.Put a little in a jar of the gas you are using,mix and set it aside.If it isnt going to work in a few minutes it will look odd,sort of one layer on top of the other.DO use a fuel hydrometer-do not mix by volume.I did that when I was a kid and it is not a good idea! RH I hope this has been of some small help,I am not exactly sure what you are doing and so tried to stay with general safe info.PS- stay away from additives! PO is useful in VERY small percentages-1-2 % if the weather is cold and you are running a heavy load.Please do not attempt to use whatever the latest "power additive" is.Ask anyone who lived through the Hydrazine period why.

 

Yep

 

Ha. That's amazing. I love science. So much more to know. So much faster to go.

 

Hey Guys
I'm an RC pilot and some of my planes were glow fueled(electric is the preferred fuel now). Glow fuel is caster and synthetic oil, nitro from 5 to 15 % and maybe some alcohol, not sure about the alcohol, haven't used the stuff in a while. low rpm engines run 5% and high performance ones use 15% or more. High performance means 20,000 to 23,000 rpms. I don't know anything about the properties of nitro, but always prefer at least 10% for a quick starting and good idle. If an engine goes lean at high rpm's it becomes a grenade. Engines are tuned at max rpm and made rich to drop rpm a few hundred and avoid the grenade effect. Always had several gallons in my garage, was a great fire-starter. Sorry I couldn't resist tossing in a pic of one of my planes.