how much hp can it take??
07-21-2004 | 03:53 PM
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From: waldorf,
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how much hp can it take??
a while ago i bought a sk27cc motor to put in my 1/4 scale car. stock it came with 3.5hp on gas. since then i've added a filter, tuned pipe, bigger carb, raised the compression, a billet head, and converted it to alcohol. im running 5%oil, 10% propylene oxide, 5% nitro, and 80% alcohol fuel. i'd have to say it putting out double the stock hp, 7 hp. my question is how much can it make? whats the weak link in these motors? thanks for lookin...PB
07-21-2004 | 04:12 PM
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From: waldorf,
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RE: how much hp can it take??
hey thanks. is there anything i can do about it? i'm not sure but i think it's forged. how much hp can i make before i have to worry about that?
07-21-2004 | 04:49 PM
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From: Mary Esther, Florida, FL
RE: how much hp can it take??
Mike:
You might be at 7hp, but if the engine is flexible enough to drive the car I doubt you're much over 4.
As a two stroke gets "Hotter" its power band narrows radically, at 7hp you would probably need a four speed transmissin just to get it off the line.
And why 10% propylene oxide? My experience has been that more than 2% or so is wasted. All it does is help in starting the burn. A little amyl acetate might help, though.
Bill.
PS: The highest specific output I've seen from a two-stroke is 6hp per cubic inch, your 27cc engine at the same level would be a hiar under 10hp. And the usable power band would be 14,500rpm to 15,000rpm. Not practical for a car, just barely usable on a motorbike with a six speed transmission. wr.
You might be at 7hp, but if the engine is flexible enough to drive the car I doubt you're much over 4.
As a two stroke gets "Hotter" its power band narrows radically, at 7hp you would probably need a four speed transmissin just to get it off the line.
And why 10% propylene oxide? My experience has been that more than 2% or so is wasted. All it does is help in starting the burn. A little amyl acetate might help, though.
Bill.
PS: The highest specific output I've seen from a two-stroke is 6hp per cubic inch, your 27cc engine at the same level would be a hiar under 10hp. And the usable power band would be 14,500rpm to 15,000rpm. Not practical for a car, just barely usable on a motorbike with a six speed transmission. wr.
07-21-2004 | 05:13 PM
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From: waldorf,
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RE: how much hp can it take??
hi bill! thanks for your input[sm=thumbup.gif] so after all that i'm only around .5 hp higher than when i started? i spoke with mr.hanson about adding a pipe to my ride and he told me that i'd gain at least 1 hp with that alone. also with the poly oxide, the man at the fuel plant just recommended that i not go over 10%. you are correct that my car is a lil slower off the line but not much more than before i threw all that stuff on the motor. when the power "hits" it doesn't matter where i'm at the tires break loose. i just compensate with the steering. it's still very drivable. the car is a blast
. also you obviously know a lil' something, i can have any fuel mixed up i want. what is your opinion on the best fuel? right now cooling is not a problem and keep in mind i'm able to raise and lower compression at will.
p.s. the 125's are making 42hp now. thats 3 cc per hp.
. also you obviously know a lil' something, i can have any fuel mixed up i want. what is your opinion on the best fuel? right now cooling is not a problem and keep in mind i'm able to raise and lower compression at will.p.s. the 125's are making 42hp now. thats 3 cc per hp.
07-21-2004 | 06:31 PM
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From: Mary Esther, Florida, FL
RE: how much hp can it take??
Mike:
My guess of 4hp is just that; a guess. Your noticing more difficulty coming off the line, and the sudden power surge as the rpm comes up indicates my guess was probably too low. The point I was trying to make is that with a really high specific output a two stroke becomes a royal pain to keep in the increasingly narrow power band. Again, my 14.5K to 15K is a guess. But you will have to crank some nasty engine speeds to get the power up, and the rpm will be your con rod limit rather than the hp developed.
On the fuel. Assuming it has a needle roller bearing on the big end of the con rod your 5% oil should be enough. The problem with decreasing oil to minimum is that you have to test to destruction. Then buy another engine and try again. Stay at 5% oil. A lot cheaper.
The methanol is what gives you the power, nitro methane allows more methanol to burn by sourcing more oxygen that the engine can get from the atmosphere. For a given power output you have to burn a given amount of methanol, by adding nitro you can burn more methanol and therefore increase the power of the engine. Nitro content up to 65% is available commercially, but remember you are going to burn 6 or 7 times as much as you will of a straight methanol/oil mix in the same run time. Gaining power through a fuel mix has a rather high price.
Propylene oxide is used with high nitro percentages, with high nitro the ignition can become erratic, the propylene oxide makes ignition more consistent. As I said in the earlier post, more than 2% generally isn't needed, it just raises the cost of the fuel.
Again, with high nitro percentages the fuel tends not to stay mixed. Amyl acetate, 2%, keeps the various components mixed nicely. Acetone or methyl ethyl ketone also work, but not quite as well.
I've been out of "Fuel" racing for quite a while, there might be better/later information available from a kart racing site, or someone racing two-stroke motorcycles. Think about a 500cc motorbike pumping close to 200hp.
Bill.
My guess of 4hp is just that; a guess. Your noticing more difficulty coming off the line, and the sudden power surge as the rpm comes up indicates my guess was probably too low. The point I was trying to make is that with a really high specific output a two stroke becomes a royal pain to keep in the increasingly narrow power band. Again, my 14.5K to 15K is a guess. But you will have to crank some nasty engine speeds to get the power up, and the rpm will be your con rod limit rather than the hp developed.
On the fuel. Assuming it has a needle roller bearing on the big end of the con rod your 5% oil should be enough. The problem with decreasing oil to minimum is that you have to test to destruction. Then buy another engine and try again. Stay at 5% oil. A lot cheaper.
The methanol is what gives you the power, nitro methane allows more methanol to burn by sourcing more oxygen that the engine can get from the atmosphere. For a given power output you have to burn a given amount of methanol, by adding nitro you can burn more methanol and therefore increase the power of the engine. Nitro content up to 65% is available commercially, but remember you are going to burn 6 or 7 times as much as you will of a straight methanol/oil mix in the same run time. Gaining power through a fuel mix has a rather high price.
Propylene oxide is used with high nitro percentages, with high nitro the ignition can become erratic, the propylene oxide makes ignition more consistent. As I said in the earlier post, more than 2% generally isn't needed, it just raises the cost of the fuel.
Again, with high nitro percentages the fuel tends not to stay mixed. Amyl acetate, 2%, keeps the various components mixed nicely. Acetone or methyl ethyl ketone also work, but not quite as well.
I've been out of "Fuel" racing for quite a while, there might be better/later information available from a kart racing site, or someone racing two-stroke motorcycles. Think about a 500cc motorbike pumping close to 200hp.
Bill.
07-21-2004 | 07:58 PM
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From: waldorf,
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RE: how much hp can it take??
thank you bill. your knowlege will be helpful in selecting my next fuel brew. it's rare to find someone who gives real 'helpful' information and not just an opinion...PB
. it's rare to find someone who gives real 'helpful' information and not just an opinion...PB
