Nitro And Superchargers!

[wobblywalrus]

This might help.  It is experience from the 1970's when we were trying to build British vertical twins capable of racing against Japanese four cylinder bikes.  The weaknesses of the brit bikes were poor machining for the most part, weak metal, and designs that were originally done before World War II.  The engines were naturally aspirated and running on gas.  The failures were like engines using fuel, i.e. cylinders pulling away from the blocks, cylinders breaking at the base flanges, rod big end bearings flattening, etc.

This is what I learned.  The combustion process produces a peak pressure a short time after ignition and this is not proportional to rpm.  The pressure spike, if it happens when the piston is too close to top dead center, pushes down on the piston when the rod has poor leverage on the crank.  This is hard on the rod bearings, everything else, and it hurts power.  The pressure spike itself, if it happens when the piston is too far down from TDC, is not as great as it can be - although the rod to crank leverage is better.  The pressure spike and piston position need to be optimal for the most power and engine life.  Spark advance timing can be used to keep the pressure spike and piston position optimal, to some extent.  So can choice of fuel.  The other factor is engine speed.  The piston is further past TDC when the pressure spike occurs at higher rpm.

One of my engines was built at the limit in regards to compression and the anti-knock capabilities of the gasoline I had.  The pressure spike and optimal piston position were within tolerable limits for a few thousand rpm.  My method was to roll on the throttle until the engine was within those rpm limits and then to open it up all of the way.  That is the only way I could get the engine to be powerful and reliable.

This is a long story.  The point is, it helps me a lot to be aware of what happens in the combustion cycle and when it occurs.  Some of this might apply to fuel use.  

[Stan Back]

Buddy --

Maybe changing your frontal area would be less expensive in the long run than going to nitro.  How about a 48 Crosley?  Here's my one voyage into nitro, be it 50 years ago.  We didn't use much and surely didn't learn much.

Gee -- this car might be just right for the new Roadster class!

Stan

[jl222]

Buddy --

Maybe changing your frontal area would be less expensive in the long run than going to nitro.  How about a 48 Crosley?  Here's my one voyage into nitro, be it 50 years ago.  We didn't use much and surely didn't learn much.

Gee -- this car might be just right for the new Roadster class!

Stan

  Does the tree come with it?

  Are those portawall white sidewalls on those slicks? We had them on our drag street roadster in the late 50ts   They would come off at high speed [for then].

     JL222

[stay`tee]

Gasoline runs at 14.7:1. Very stable, well known properties.
Methanol runs at 6.4:1. Also very stable, and you do need twice as much.

Nitromethane at 1.7:1 requires massive amounts of fuel compared to gasoline. Trying to pour that amount through a carburetor is a tough deal. Injection is the only way to go.





figures quoted are for "raw" fuel,, the actual A/F depends on the percentage you are going to mix, then take into account the variables, temp, boost etc, it aint easy but do the calculations, will save, or at best minimise brakeages,,

[Rex Schimmer]

Buddy,
My comment regarding running enough "pop" (nitro) to go from 570 to 800 hp is that I think you could convert to alcohol, increase your blower pressure and probably get very close to or exceed 800 without the risk of nitro. The great thing about alcohol is its' latent heat, i.e. its' ability to adsorb heat out of the incoming air and reduce the charge temp and therefore increase the air density. Properly done a good alcohol system can take 100 degrees out of the inlet air temp which of course means you can run more boost. When Indy cars were running turbos with unlimited boost the 159 inch Offies were making around 1200 hp on about 100-120 inches of boost, without an intercooler and they could run like this for 10 miles to qualify. You could even add a small shot of nitrous if you needed a quick 50 hp to make 200, and there are a lot of guys on this forum that have nitrous experience.

A comment about nitro: Nitro is very close to being an explosive and can be dangerous. A friend of mine, who runs a D fuel lakester, runs a 300 inch Chrysler on 90% and after a run several years ago he pulled back into the pits and did not realize that there was a fuel leak in the return system that allowed fuel, 90%!, to leak back into the engine. While sitting in the pits, right after the run, he accidentally hit the ignition switch which caused a spark in one of the front cylinders which set off the nitro. It did not crack the block or head it blew them off!! the complete front of the block and head on one side was completely blown away!!! Not something I would like to work with.

Rex

[wobblywalrus]

This is more about what I learned with the British bike fiasco.  Ignition timing in those days was by mechanical systems with counterweights and springs.  The typical setup in those days was to have the spark at full advance at about midway between idle and red line.  The advance curves I set were as linear as I could make them with full advance occurring at red line, and not before.  This was done after figuring out the relationships between combustion speed, rpm, and piston position.  I did this by putting heavy springs on the advance and lightening the weights.

Once the advance curve was set, I set the ignition to a setting I knew would be retarded.  Then I went out to a back road where I could do some testing.  I made runs and looked at the spark plugs.  The positive electrodes were what I examined.  I advanced the timing gradually until the outer 1/4 to 1/3 of the electrode length was shiny.  Then I had the timing set.  I put a timing light on the bike and made timing marks on the rotor so I would have a reference when I set the timing in the future.

In those days I was barely older than the teens.  I did not know jack rabbit on my own.  I could listen and take advice and the folks that helped me were familiar with fuel.  This is NA gasoline experience.  It might help. 

[38flattie]

Thanks Guys! Lots of good info here!

I guess we'll see how much HP we make on fuel, then decide which way to go.

Rex, I've blown a couple of engine up on nitrous, mostly because I got greedy! Still, it might be a better alternative than nitro.

Are guys using it the whole run, or just fogging it the last 1/2 mile or so? Simple push button fogger, or controlled electronically?

[jimmy six]

Jason...Your avitar has a bike so that may be your thing but I saw no difference in building a fuel engine versus gasoline and we used 75% as a goal. One time we started at Bonneville too lean and hurt some valves but that was it. Same expensive pistons, rods, valves, cam, steel main caps, etc. Yes the barrel of nitro costs $850 at the time and when we reched the limit of RPM (yes there was one) taller tires were bought twice but that had nothing to do with the engine.

Every year the engine was torn down, valves were checked, rings changed and bearings inspected. Maybe we were lucky in a way because we needed only 2 or 3 passes to bump up a record and we changed oil after every 2 runs. (unblown) but in reality I do the same with my gas engines with the execption of the oil. Winter is tear down. If you want to run at the top of your class this is all a necessity. Your competition is doing it to catch and pass you. Good Luck

[JasonS]

jimmy, bikes are actually new to me. I've always liked them but my wife finally changed her mind about being scared of me owning one and decided it's something we could do together. I'm still first and foremost a car guy, although if it has an engine, I'm probably going to like it.

I know the cost for a competitive race engine will be pretty much the same, just different specs (compression ratio, cam grind, etc.), I just don't have the money for either lol. You would be hard pressed to find someone who loves flatheads more than I do, but unfortunately I don't have any experience building them. I would LOVE to build a Vintage Fuel Competition Coupe out of a '33 Ford Sedan or a Fuel Modified Roadster, but I don't see it happening in the near future.

I'm glad to hear you didn't have any major problems with nitro, and I wish you the best of luck.

[John Burk]

My experience with nitro was with my unblown BBC dragster . 300 runs including getting the NHRA et record in 1968 . It was fairly easy on parts . 75% normally . Stock head gaskets and rods with small 3/8" bolts . Checked the bearings every week and never lost one . Singed one piston when a splinter partly blocked a nozzle. It made power with lots of spark and as much compression as possible . 12.8:1 was all you could get with a .060 over 427 . The only oil then with additives to prevent piston scuffing was 70 wt Penzoil . Probably not a proplem with lower % . Saw a friend's jr fueler make one of his best runs on 28% . One of the things I wished I'd tried was low % . With an unblown engine on high % it's very difficult to get the nitro to release much of it's oxygen . The only way I found was nough CR and spark lead to make it detonate which tuliped valves and ocasionally broke ring lands . Gene Adams did it far better by getting pistons with thick crowns and warming them well while staging . Tom Skinner ran a low % in his GMC's to stay competitive with the 480 ci BBC modifieds . Nitro is beautiful stuff , especially with small % . The stories of damaged engines and burned pistons I think come from running lean on high % . As I said my only nitro experience is with drag racing but I wouldn't be afraid of 10% or 15% with LSR with proper jetting .

[38flattie]

Thanks guys- good info here!

I talked to John Beck today, and we'll dyno and tune on gas.

We'll then change ignition, add a computer system and MSD box, and tune on alky. John feels nitro is more stable than nitrous, so if we still need more HP, and haven't used the kitty litter yet, we'll start adding the pop. John doesn't think we'll need much-10-20% max.

It would be real nice to have a good 'tuner' on the crew for B'ville!

Happy new year!

[stay`tee]

"nitro is more stable than nitrous",  x2,   

[flatman]

I tried adding 15% nitro to my Ford flathead at WOS on my backup run.  I only ran a little over a mile an hour over the record for my class the previous day and it was 46 degrees so it seemed like a good idea at the time to add some nitro.
I melted 3 of the outside pistons (1,5, & however the motor sounded like it was on steroids. Aftrward someone came to our trailer and asked if it was really a flathead (I run a 4th exhaust out the heat riser hole) because it sure didn't sound like one.
I'm running 21 pounds of boost and a 2 port Hilborn with direct port injection.  I ran the same size nozzles to all cylinders.
Ross has made me some heaver pistons and I plan to run larger nozzles to the outside pistons for 2013.
Just a little info from someone who has some experience blowing up flatheads but I think I'm getting close.

Happy 2013!

Jerry Wortman
#7472

[38flattie]

Thanks everyone!

I just got off of the phone with Rick Schnell, owner of 'Slider", the worlds fastest flathead dragster, with over 900HP.
 
Interestingly,he too only has 3 mains, Moldex crank, Crower rods, big crank girdle. He's running 60% nitro. He said sneak into the tune, and don't get gready. He says for every 10% nitro increase, he has to fatten the fuel return by .010. He says go .020-.030 to be safe.
 
Boys, if we don't go lean, I have to think we have a shot!
 
Forgot to mention, though, the block is aluminum filled.

[Dynoroom]

Also only run a 1/4 mile at a time. 

Have fun with the project!