Power Pistons - Trimming Dome Makes HP Shown

The Thread Spread

-Power Pistons-

Trimming Dome Makes HP Shown

The Question - Has anybody used the Magic Racing Banshee Power Pistons? If so, did you see an increase of 6+ horsepower like the add claims?

The Response - I think that the power pistons are very similar to Trinities superlites. Six hp? I don't think you are going to see that. Quicker revs? Yes, definitely. I also believe that these pistons should be replaced more frequently(very

often actually)...

Is that 6 HP each or for the pair... <eg> With a twin cylinder there is some gain from just equalizing the weight of the piston/rings/pin/clip/bearing setups in each barrel. Additional machine work to lighten the part usually means increased maintenance. Though real benefits can be realized this way. The point is - how long do you need the pistons to last? A day? A week? A year?

Modified pistons can provide some substantial power gains, but usually at the cost of longevity. Every machinist who has access to a lathe and the right part(s), can cut a piston with special crown shape to alter compression AND cut increases in its port timing. There are several ways to lighten a piston by removing material from non critical areas and provide increased lubrication. This will make more power (most likely) at a higher RPM. That's no big deal - it's done all the time and has been for years. What maybe is a big deal is that someone NEW discovered it...

Rick

**** Section added about the bolt on 5 hp Blaster piston ****

For this complete Thread please click here. to access the BBS at Blaster Central.

OK - I saw the photo's (of the special Blaster piston).

Comments...

I suppose you know your engine was running very hot and coked the oil on the underside of the old piston not to mention wasting the ring land grooves and compression seal but that's another matter. Your jetting was way off.

The reason there's more height to the piston crown is to increase the compression a bit, though by nature that decreases its mechanical advantage - not good. The stock (crummy) combustion chamber shape allows for much improvement in this area - so the pop up dome helps reduce the squish clearance. The thinner head gasket accomplishes that even more.

As far as the top ring being further down the face of the piston, that's necessary because there are specific limitations as to how close the top ring can be to the top of the piston - it has to do with combustion temperature and its ability to seal when too close to the crown as well as its ability to dissipate heat. Too close and it will burn the top ring.

The .62 mm thick head gasket is .20 mm thinner than stock making it less than .010" thinner (.010" = .25 mm). According to my calculations the gasket will account for about a 5 psi increase ay sea level. However, the cut out in the area of the exhaust port reduces the compression, so some of it is a wash.

It is clear from the photos that the larger intake ports in the piston are more for appearance than performance - though they add to reducing the overall weight, so it's not all flash. The way to get fuel into the engine is through larger intake tract ports - not the pistons ports. As an example (if the pressure is constant like it is here), if you had to fill a swimming pool with water the faster way would be to increase the diameter of the hose, not the nozzle at the end of the hose.

The exhaust cut out will allow for more exhaust port timing and blowdown which should allow for more higher rev power - though these cuts also make the squish affect in that area less usefull than stock. Since the transfer port timing remains the same you'll not be able to take advantage of any benefits there. I'm surprised that there's not cut outs in that area as well.

Years ago when we did these modifications to pistons we called it pie cutting. It's what you do instead of cutting the barrel. That way if it doesn't work you don't have to trash the barrel or epoxy the mistake. It's well discussed in Gordon Jennings 1974 book "The Two-Stroke Tuners Handbook" (now I'm dating myself). Sometimes it worked very well - and when it did the ports of the engine were cut to match the change the pie cut piston made. Another thing we used to do is taper bore the wrist pin - to save a little weigh. After all, lighter pistons require less wrist pin.

To answer the question as to whether this piston will work in a ported engine - well it would be negative gain to add one. That is to say, if the porter did his job correctly in the first place there is no need for such a piece. The power available by the addition of this piston and its associated parts in no way compares to the power available from a properly ported engine. At $139 for the piston you're half way to my real porting and head modification which I charge $260 for. Add a replacement piston and it's not that much more.

These pricey bolt ons simply empty the wallet. You'll be way ahead if you have your engine ported properly in the first place.

I hope I haven't offended anyone by my remarks about this product or its new owner - Flyin Ryan you know I mean no disrespect. When you're ready to step up to a real power gain I'll schedule your engine build in and give you power that lasts and lasts - it won't go away when you need to replace that pricey part(s).

Rick

Though this doesn't completely apply in this case I never like it when someone is trying to sell something mentions the (supposed) higher resale value on account of buying - what ever it might be. It is a ploy to get the buyer to refocus and gather thoughts. Adding a statement about resale is supposed to be viewed as a positive thing by the buyer. Actually it is not something the buyer should be thinking about - we don't worry about the $50 our power windows will add to the resale value of the automobile 5 years down the road when they cost $400 up front.

The funny thing about that piston kit is... in order to make more power it must turn higher rpm's - there is no way to add the 6 hp from the installed parts otherwise. In fact since the exhaust port cut out is lower than stock a reduction of static compression is realized. The thin gasket can just account for the loss. Any additional compression has to come from the pop up dome. (I estimated the relief of the exhaust port cut in the top of the new piston to be 1.5 mm). If a stock Blaster puts out 17.3 hp @ 7000 rpm with a compression ratio of 9.5:1 (130 psi static) with its .82 mm thick head gasket then decreasing the gasket thickness to .62 increases the compression ratio to 9.76:1 (133 psi static) - power is now 17.8 hp @ 7000 rpm (+.5 hp). Unknown is the difference in volume of the pop up piston. The static compression lowers to 128 psi with the exhaust port timing change (cut out on top of piston). With these parameters in place spinning the engine to 8000 rpm yields 20.3 hp (+3 hp). The engine must spin to 9150 rpm to make 23.3 hp - the full 6 hp claimed. This is a fact related to the engines BMEP (brake mean effective pressure).

Unfortunately the engine does not have enough port time/area to make good power at that rev level. A mis match occurs between the exhaust port and transfer port timing (they become out of sync with each other) and the rev ceiling is reached at about 8050 to 8150 rpm - it's barely holding on with its increased blow down at that level as well.

It is because of the above data that I believe this piston and gasket do not increase power by the amount claimed. The 3 hp gain @ 8000 may be possible if the compression ratio is indeed increased by the pop up of the piston crown outweighing the cut out. It is unclear to me whether the stock Blaster exhaust system will allow the engine to rev that high since its tuned affect peaks at 7000 rpm and it would have to have enough wave amplitude left at that level to continue to make power.

Adding other bolt ons such as an after market tuned pipe, a reed spacer or a larger carburetor would alter the data tremendously (especially the rpm level the peak power is achieved) but the baseline is still set by the geometric compression ratio of the engine. No amount of add ons will increase the power of the engine to the tune of an additional 30% to 40% as outlined above in another post.

A two stroke engines peak power output can be defined by the amount of exhaust port area it has. More area = more power. If that port has enough area and there is not enough time between when the it opens and the transfer ports open a short circuit occurs. When the fresh incoming mixture collides with the hot spent gasses, not only does the new charge become diluted (weakened) but the suction wave of the pipe tries to draw more fresh mixture from the cases to mix it with more exhaust gasses (out of phase). Additionally, the return wave arrives at the exhaust port just before it closes and packs spent gasses and diluted mixture back into the engine making the condition even worse. In prime examples the return wave will send exhaust gasses back through the transfer ports and back out the carburetor.

More power is gained by increasing the compression ratio of the engine and its exhaust port area - and corresponding inlet and transfer ports than by any other means. Increases in compression ratio must be balanced by fuel that will not ignite until it is started by the spark plug (high octane gas). This is simple physics.

Building the above 9150 rpm engine to run 105 octane at a compression ratio of 14:1 yields 33.4 real hp.

**********S i de b a r **************

I mentioned in another post that there are limits relating to the distance a ring can be from the combustion. What I should add is that since the piston rings account for allowing the removal of heat from the piston crown to the tune of something like 85% to 95%, placing them too far from the crown can result in seizures due to the oil flash-burning (not an oil related problem - the flame is just too hot to come in direct contact with oil), collapsed piston crowns and any number of other heat related problems.

Building an engine using a base plate spacer raises the cylinder barrel up a specific amount which allows setting the transfer ports at the correct timing without having to carve the port roofs and possibly disturb their horizontal or vertical wall angles. The Exhaust port and inlet can then be set to their proper values.

Sometimes base plate spacers are used in combination with pistons to create hybrid engine designs.

The color of the oil spot on the under side of the piston tells its own story. Like spark plug reading - it's a bit of an art and science. Generally, flakey black is VERY not good - way too hot. Black is still too hot - it's burning the oil as if it were in a frying pan. Dark brown and a little sticky is still hot and can be improved upon - usually acceptable for recreational use. Medium brown is kind of warm still - but getting me excited. Tan to light brown is probably the best you can do. Light tan to gold - too cool, get on it more or find someone to race. No color - Fresh from the box - looking at wrong piston.

Since pistons are not all created equal some cast parts have thick or thin spots - that alters the heat path and the color. Carbon on the top of the piston is common due to the fact that most of us have to ride our vehicles slowly through a yard or parking lot or some other area before we put it away. Running at low rpm under no load can cause it.

Rick

* The Blaster engine shows 148 psi static compression after installation.

Ahhh... You have skimmed your head (milled it) at one time...Yes?!?

Rick

* It looks like someone took a "clean-up" cut on the head at one time, not much, but some.

Back to The Thread Spread index of articles.

Trimming Dome Makes HP Shown
The Question - Has anybody used the Magic Racing Banshee Power Pistons? If so, did you see an increase of 6+ horsepower like the add claims?
The Response - I think that the power pistons are very similar to Trinities superlites. Six hp? I don't think you are going to see that. Quicker revs? Yes, definitely. I also believe that these pistons should be replaced more frequently(very often actually)... Is that 6 HP each or for the pair... <eg> With a twin cylinder there is some gain from just equalizing the weight of the piston/rings/pin/clip/bearing setups in each barrel. Additional machine work to lighten the part usually means increased maintenance. Though real benefits can be realized this way. The point is - how long do you need the pistons to last? A day? A week? A year? Modified pistons can provide some substantial power gains, but usually at the cost of longevity. Every machinist who has access to a lathe and the right part(s), can cut a piston with special crown shape to alter compression AND cut increases in its port timing. There are several ways to lighten a piston by removing material from non critical areas and provide increased lubrication. This will make more power (most likely) at a higher RPM. That's no big deal - it's done all the time and has been for years. What maybe is a big deal is that someone NEW discovered it... Rick ** Section added about the bolt on 5 hp Blaster piston For this complete Thread please click here. to access the BBS at Blaster Central. OK - I saw the photo's (of the special Blaster piston). Comments... I suppose you know your engine was running very hot and coked the oil on the underside of the old piston not to mention wasting the ring land grooves and compression seal but that's another matter. Your jetting was way off. The reason there's more height to the piston crown is to increase the compression a bit, though by nature that decreases its mechanical advantage - not good. The stock (crummy) combustion chamber shape allows for much improvement in this area - so the pop up dome helps reduce the squish clearance. The thinner head gasket accomplishes that even more. As far as the top ring being further down the face of the piston, that's necessary because there are specific limitations as to how close the top ring can be to the top of the piston - it has to do with combustion temperature and its ability to seal when too close to the crown as well as its ability to dissipate heat. Too close and it will burn the top ring. The .62 mm thick head gasket is .20 mm thinner than stock making it less than .010" thinner (.010" = .25 mm). According to my calculations the gasket will account for about a 5 psi increase ay sea level. However, the cut out in the area of the exhaust port reduces the compression, so some of it is a wash. It is clear from the photos that the larger intake ports in the piston are more for appearance than performance - though they add to reducing the overall weight, so it's not all flash. The way to get fuel into the engine is through larger intake tract ports - not the pistons ports. As an example (if the pressure is constant like it is here), if you had to fill a swimming pool with water the faster way would be to increase the diameter of the hose, not the nozzle at the end of the hose. The exhaust cut out will allow for more exhaust port timing and blowdown which should allow for more higher rev power - though these cuts also make the squish affect in that area less usefull than stock. Since the transfer port timing remains the same you'll not be able to take advantage of any benefits there. I'm surprised that there's not cut outs in that area as well. Years ago when we did these modifications to pistons we called it pie cutting. It's what you do instead of cutting the barrel. That way if it doesn't work you don't have to trash the barrel or epoxy the mistake. It's well discussed in Gordon Jennings 1974 book "The Two-Stroke Tuners Handbook" (now I'm dating myself). Sometimes it worked very well - and when it did the ports of the engine were cut to match the change the pie cut piston made. Another thing we used to do is taper bore the wrist pin - to save a little weigh. After all, lighter pistons require less wrist pin. To answer the question as to whether this piston will work in a ported engine - well it would be negative gain to add one. That is to say, if the porter did his job correctly in the first place there is no need for such a piece. The power available by the addition of this piston and its associated parts in no way compares to the power available from a properly ported engine. At $139 for the piston you're half way to my real porting and head modification which I charge $260 for. Add a replacement piston and it's not that much more. These pricey bolt ons simply empty the wallet. You'll be way ahead if you have your engine ported properly in the first place. I hope I haven't offended anyone by my remarks about this product or its new owner - Flyin Ryan you know I mean no disrespect. When you're ready to step up to a real power gain I'll schedule your engine build in and give you power that lasts and lasts - it won't go away when you need to replace that pricey part(s). Rick Though this doesn't completely apply in this case I never like it when someone is trying to sell something mentions the (supposed) higher resale value on account of buying - what ever it might be. It is a ploy to get the buyer to refocus and gather thoughts. Adding a statement about resale is supposed to be viewed as a positive thing by the buyer. Actually it is not something the buyer should be thinking about - we don't worry about the $50 our power windows will add to the resale value of the automobile 5 years down the road when they cost $400 up front. The funny thing about that piston kit is... in order to make more power it must turn higher rpm's - there is no way to add the 6 hp from the installed parts otherwise. In fact since the exhaust port cut out is lower than stock a reduction of static compression is realized. The thin gasket can just account for the loss. Any additional compression has to come from the pop up dome. (I estimated the relief of the exhaust port cut in the top of the new piston to be 1.5 mm). If a stock Blaster puts out 17.3 hp @ 7000 rpm with a compression ratio of 9.5:1 (130 psi static) with its .82 mm thick head gasket then decreasing the gasket thickness to .62 increases the compression ratio to 9.76:1 (133 psi static) - power is now 17.8 hp @ 7000 rpm (+.5 hp). Unknown is the difference in volume of the pop up piston. The static compression lowers to 128 psi with the exhaust port timing change (cut out on top of piston). With these parameters in place spinning the engine to 8000 rpm yields 20.3 hp (+3 hp). The engine must spin to 9150 rpm to make 23.3 hp - the full 6 hp claimed. This is a fact related to the engines BMEP (brake mean effective pressure). Unfortunately the engine does not have enough port time/area to make good power at that rev level. A mis match occurs between the exhaust port and transfer port timing (they become out of sync with each other) and the rev ceiling is reached at about 8050 to 8150 rpm - it's barely holding on with its increased blow down at that level as well. It is because of the above data that I believe this piston and gasket do not increase power by the amount claimed. The 3 hp gain @ 8000 may be possible if the compression ratio is indeed increased by the pop up of the piston crown outweighing the cut out. It is unclear to me whether the stock Blaster exhaust system will allow the engine to rev that high since its tuned affect peaks at 7000 rpm and it would have to have enough wave amplitude left at that level to continue to make power. Adding other bolt ons such as an after market tuned pipe, a reed spacer or a larger carburetor would alter the data tremendously (especially the rpm level the peak power is achieved) but the baseline is still set by the geometric compression ratio of the engine. No amount of add ons will increase the power of the engine to the tune of an additional 30% to 40% as outlined above in another post. A two stroke engines peak power output can be defined by the amount of exhaust port area it has. More area = more power. If that port has enough area and there is not enough time between when the it opens and the transfer ports open a short circuit occurs. When the fresh incoming mixture collides with the hot spent gasses, not only does the new charge become diluted (weakened) but the suction wave of the pipe tries to draw more fresh mixture from the cases to mix it with more exhaust gasses (out of phase). Additionally, the return wave arrives at the exhaust port just before it closes and packs spent gasses and diluted mixture back into the engine making the condition even worse. In prime examples the return wave will send exhaust gasses back through the transfer ports and back out the carburetor. More power is gained by increasing the compression ratio of the engine and its exhaust port area - and corresponding inlet and transfer ports than by any other means. Increases in compression ratio must be balanced by fuel that will not ignite until it is started by the spark plug (high octane gas). This is simple physics. Building the above 9150 rpm engine to run 105 octane at a compression ratio of 14:1 yields 33.4 real hp. ******S i de b a r ************ I mentioned in another post that there are limits relating to the distance a ring can be from the combustion. What I should add is that since the piston rings account for allowing the removal of heat from the piston crown to the tune of something like 85% to 95%, placing them too far from the crown can result in seizures due to the oil flash-burning (not an oil related problem - the flame is just too hot to come in direct contact with oil), collapsed piston crowns and any number of other heat related problems. Building an engine using a base plate spacer raises the cylinder barrel up a specific amount which allows setting the transfer ports at the correct timing without having to carve the port roofs and possibly disturb their horizontal or vertical wall angles. The Exhaust port and inlet can then be set to their proper values. Sometimes base plate spacers are used in combination with pistons to create hybrid engine designs. The color of the oil spot on the under side of the piston tells its own story. Like spark plug reading - it's a bit of an art and science. Generally, flakey black is VERY not good - way too hot. Black is still too hot - it's burning the oil as if it were in a frying pan. Dark brown and a little sticky is still hot and can be improved upon - usually acceptable for recreational use. Medium brown is kind of warm still - but getting me excited. Tan to light brown is probably the best you can do. Light tan to gold - too cool, get on it more or find someone to race. No color - Fresh from the box - looking at wrong piston. Since pistons are not all created equal some cast parts have thick or thin spots - that alters the heat path and the color. Carbon on the top of the piston is common due to the fact that most of us have to ride our vehicles slowly through a yard or parking lot or some other area before we put it away. Running at low rpm under no load can cause it. Rick * The Blaster engine shows 148 psi static compression after installation. Ahhh... You have skimmed your head (milled it) at one time...Yes?!? Rick * It looks like someone took a "clean-up" cut on the head at one time, not much, but some.