supercharger

[65ShelbyClone]

Its pretty hard to estamate how much power increce a supercharged

It's really not. Atmospheric pressure is 14.7psia at sea level. Put 14.7psi of boost on top of that and power will effectively double minus losses from increased intake air temperature and parasitic loss from driving the supercharger. Figure about a 70% power increase for 15psi of boost. Intercooled turbocharger systems can reach 100% for 15psi, sometimes more depending on how the system is designed.

I’m trying to work this out in my head.. So let’s say 4 pounds of boost.

All before 3,800 rmps that the governor limits the engine to?

What pulleys would you run to spin/overdrive the pump up enough while the engine is only spinning 3,800rpm’s? And if you remove the governor to get more engine speed that makes spinning the pump up easier but the magnet is held on by glue!

I’m just pointing out (I can’t find The post) someone was saying something about a 2” pump pulley and a 32” crank pulley?

Search, read, and learn about blower drive ratios. If you have a 300cc/rev blower and a 150cc/rev four-stroke engine, how much boost will a 1:1 drive ratio make?

question could I do a 90% nitromethane and a 10% methanol engine?

Conceptually yes, but a blown nitromethane engine is the last thing you should be thinking about at this stage. Aside from the pool of knowledge being very small because so few people use it, a misstep with nitro can actually get you hurt. It is very expensive to run, both buying the fuel and replacing broken parts.

 

[Denny]

Besides you need a special permit from the ATF to buy nitromethane thanks to Timmy McVey who blew up the Oklahoma Federal building. Yes, nitromethane, diesel fuel and ammonium nitrate mixed with a small starter charge did that.
Now once you get past all that there are so many other things to consider, timing, chamber shape and volume, compression ratio, blower boost, mix ratios, and other stuff I have probably forgotten. Can it be done? Yes. But not by you successfully until you gain a lot more much needed knowledge.

 

[Rat]

We have told you the gov delete is #1 cause of overrev flywheel explosions right?

As I flog a stock chunk of iron to 6k on my 208 cringing about the actual accuracy of my induction tach... holding a nice idle at around 1250 like a champ. I know I'm good but is that even really a thing with these engines?

 

[bob58o]

nitro requires less air but if you drill out your jet you will need a bigger carb. Typicaly 28 to 32 mm

Let me think about this out loud….
You drill a jet larger to flow more fuel.
Increasing Venturi size slows the air, reduces the pressure difference (signal), reducing the flow of fuel.

Are you trying to decrease the air to fuel ratio?
Drill jets, then changing Venturi size is definitely not the correct order of steps to tune a carb

 

[bob58o]

Search, read, and learn about blower drive ratios. If you have a 300cc/rev blower and a 150cc/rev four-stroke engine, how much boost will a 1:1 drive ratio make?

In my head,
300cc per blower revolution
300cc 4 stroke engine = 150cc per rev on average.
300cc / 150cc = 2
2 * 14.7 psi = 29.4 psi
29.4 psi - 14.7 psi = 14.7 psi of boost

This is same math I applied before.
Stuffing double the volume of air into a chamber will double the absolute pressure. I think. If I ignore changes in temperature for now.

if looking for 4 psi boost, you want absolute pressure of 18.7 psi.

18.7 / 14.7 = 1.27

For a 4 stroke engine… divide displacement by 2 to get displacement per revolution.
Then multiple that “half displacemt” by 1.27.

for example…. 212 cc
212 / 2 = 106
106 * 1.27 = 135 cc

you need 135cc per blower revolution.

135cc / 300cc = 0.45

1 / 0.45 = 2.225

you need the crankshaft to turn 2.225 times per blower revolution.

2” driver pulley * 2.225 =
4.45” driven pulley.

2” on the crankshaft
4.45” on the blower

Then there’s the VE, bliwer leakage, heat and other various variables.

 

[bob58o]

32” on crank and 2” on blower?
YES!!! Lol
16:1 overdriven roots blower.
60,000 rpm
For 106cc engine displacement per revolution…
Stuff 300cc x 16 = 4.8 Liters of air. Equivalent to a 9.6L 4 stroke engine.

Just kidding. Don’t do that.
A 212cc thumper plus a 300cc blower does not make a V-12 engine.

2” on crank and 3.2” on blower is something more reasonable. At least the correct order of magnitude.

 

[bob58o]

Besides you need a special permit from the ATF to buy nitromethane thanks to Timmy McVey who blew up the Oklahoma Federal building. Yes, nitromethane, diesel fuel and ammonium nitrate mixed with a small starter charge did that.
Now once you get past all that there are so many other things to consider, timing, chamber shape and volume, compression ratio, blower boost, mix ratios, and other stuff I have probably forgotten. Can it be done? Yes. But not by you successfully until you gain a lot more much needed knowledge.

You can’t say that on the internet.

 

[Denny]

You need to jet it richer because nitromethane contains extra oxygen. It burns so much slower so you need around 50-60 degrees of advance timing. You need to pack fuel into the cylinder to the point of almost hydraulic locking (hydraulicing) the cylinder. That’s on about 80% nitro, 10% alchohol, 10% caster oil.

 

[Denny]

You’re going to need about 45lbs of boost also to pack it all nice and tight. About 2 seconds into the run the electrodes of the plugs will be burnt completely away. At the finish line a few seconds later if you didn’t blow the engine to little bitty pieces, just throw it away. Everything will be deformed already beyond repair. If you did blow it up we’ll see you at your funeral. Because most of the engine will be imbedded in your body. It will be a closed casket because you’ll look like you were shreaded and then barbaqued. Because you were!

 

[Rat]

Going Fast on cheap gas is more impressive than any race/drag mix that WILL destroy an engine IMHO

 

[65ShelbyClone]

Besides you need a special permit from the ATF to buy nitromethane thanks to Timmy McVey who blew up the Oklahoma Federal building.

No you don't. You don't need to do anything for quantities under 44 gallons. Above that and you have to fill out some paperwork for Homeland Security. The other stuff, the main component used in that incident, is more heavily regulated. Nitromethane by itself is not easy to use for those purposes.

You’re going to need about 45lbs of boost also to pack it all nice and tight. About 2 seconds into the run the electrodes of the plugs will be burnt completely away. At the finish line a few seconds later if you didn’t blow the engine to little bitty pieces, just throw it away. Everything will be deformed already beyond repair. If you did blow it up we’ll see you at your funeral. Because most of the engine will be imbedded in your body. It will be a closed casket because you’ll look like you were shreaded and then barbaqued. Because you were!

I know where you got that information and it was hogwash even decades before it was written to be more entertainment than factual. Top Fuel teams have been reusing their parts since Top Fuel began. Even current teams with huge budgets can't afford to replace the engine every run. And they don't.

Then there’s the VE, bliwer leakage, heat and other various variables.

Most of which the average hobbyist won't be able to quantify and doesn't really need to worry about. Boost and blower outlet temp are the main things and there's not much to be done about the temperature in a draw-through carbureted system.

I also want to address something that came up earlier. An engine's volumetric efficiency (VE) is completely unaffected by boost. It doesn't change without specific efforts to improve it like a cam, porting, exhaust, etc. Boost only changes the mass of air going through the engine. The pumping efficiency of an 80% VE engine stays 80% even with 15 or 30 or 60 or 100psi of boost.

Boosted engines respond very well to improvements in VE because the more power an engine makes without boost, the larger the boost gains will be. For example, a stock 200hp engine getting 15psi of boost and making 400hp. Picture that same engine upgraded to make 300hp and now add 15psi of boost. It's still a 100% gain in power, but it represents 300% of the stock engine's power. Boost is a power multiplier.

The letdown is that we're talking about engines that make 8hp stock, so

 

[Denny]

I’m talking about using a 6 hp industrial engine block. Not a TF engine. I know they reuse most parts and only change out what’s needed. Even you would have to admit a stock predator block or even a Honda would be all twisted out of shape under those conditions.

 

[A Manco Dingo]

Let me think about this out loud….
You drill a jet larger to flow more fuel.
Increasing Venturi size slows the air, reduces the pressure difference (signal), reducing the flow of fuel.

Are you trying to decrease the air to fuel ratio?
Drill jets, then changing Venturi size is definitely not the correct order of steps to tune a carb

no I met like if you are constantly drilling out your carb the venturi needs to be bigger with unless you get a good air fuel ratio thats why nitro is used on small engines. Before i got into go karts I worked on nitro and tiny 4 stroke engines for rc vehicles. the average air to fuel ratio is 1.7 (1 fuel seven Oxygen). the reason for this is because nitro has oxygen inside of it (you already know this). top fuel cars use this fuel to get more boom and less air (they still have to use superchargers to get more air but 11,000 hp is better than the average 1,400 hp camaro) and rc plane use this so that they could fly higher but from your experience it sounds like your getting to much fuel and not enough air that why i said either get a bigger carb or just stop drilling your carb, and its better if your drilling your carb then get forced induction like a supercharger or a turbo (i am not as similar with 4 strokes than with 2 or just nitro engines the most common problem i have ever had with these nitro engines it that they are not getting enough air )

 

[65ShelbyClone]

I’m talking about using a 6 hp industrial engine block. Not a TF engine. I know they reuse most parts and only change out what’s needed. Even you would have to admit a stock predator block or even a Honda would be all twisted out of shape under those conditions.

Fair enough, I must have misunderstood.

 

[Denny]

no I met like if you are constantly drilling out your carb the venturi needs to be bigger with unless you get a good air fuel ratio thats why nitro is used on small engines. Before i got into go karts I worked on nitro and tiny 4 stroke engines for rc vehicles. the average air to fuel ratio is 1.7 (1 fuel seven Oxygen). the reason for this is because nitro has oxygen inside of it (you already know this). top fuel cars use this fuel to get more boom and less air (they still have to use superchargers to get more air but 11,000 hp is better than the average 1,400 hp camaro) and rc plane use this so that they could fly higher but from your experience it sounds like your getting to much fuel and not enough air that why i said either get a bigger carb or just stop drilling your carb, and its better if your drilling your carb then get forced induction like a supercharger or a turbo (i am not as similar with 4 strokes than with 2 or just nitro engines the most common problem i have ever had with these nitro engines it that they are not getting enough air )

A 2 stroke small nitro engine is way different than a 4 stroke. Its needs are totally different. Add in a supercharger and things change even more. Also why mechanical fuel injection becomes necessary because a carb just can’t keep up with fuel needs.

 

[65ShelbyClone]

Mechanical injection is also used, AFAIK exclusively, on non-supercharged nitro engines at least in part because the fuel can be shut off if for some reason the engine starts dieseling. They also run magnetos for 1.) the extra ignition power and 2.) the ability to absolutely kill the ignition.

I was going to use a GM LS inductive coil with integrated igniter for a little nitro engine that was going to have EFI. In the process of setup and testing the ignition, I discovered the coil has built-in dwell control and will fire automatically if it doesn't get a trigger signal soon enough. If that happens when the valves are closed and the cylinder is flooded with nitro, the engine explodes. That's what I was talking about by a misstep getting you hurt.

 

[A Manco Dingo]

Mechanical injection is also used, AFAIK exclusively, on non-supercharged nitro engines at least in part because the fuel can be shut off if for some reason the engine starts dieseling. They also run magnetos for 1.) the extra ignition power and 2.) the ability to absolutely kill the ignition.

I was going to use a GM LS inductive coil with integrated igniter for a little nitro engine that was going to have EFI. In the process of setup and testing the ignition, I discovered the coil has built-in dwell control and will fire automatically if it doesn't get a trigger signal soon enough. If that happens when the valves are closed and the cylinder is flooded with nitro, the engine explodes. That's what I was talking about by a misstep getting you hurt.

Like i said i am better with 2 stroke not forced induction but i worked on nitro engins alot

 

[A Manco Dingo]

Got my self a gift

 

[BaconBitRacing]

Happy Birthday!

 

[bob58o]

Inspiring people ‘cross the globe to eat birthday cake on random Wednesdays