Power plenum vs reed valve?

[mrfubs]

Whats your opinion on which performs better.

Fred uses his power plenum on all of his builds i see and with excellent performance and on the other hand dave over at arrow motorized cycles uses reed valves and i have not seen the way his perform speed wise.

To me i think either or will be just fine but i think the reed valve has a little more advantage by not allowing any intake charge escape out of the carb.

Tell me what you think, iv not yet used a power plenum and am cerious if it is worth the money sense fred has some pretty smooth running bikes.

 

[Venice Motor Bikes]

My logic is this... If the power plenum was truely better?, all the motorcycle companies would be using them instead of reed valves!

 

[mrfubs]

smart and simple theory you have there haha

 

[MotorBicycleRacing]

smart and simple theory you have there haha

It's the same theory why boost bottles don't work.

Sent from my SCH-R720 using Forum Runner

 

[mapbike]

I've never run either one but I know that some very fast bikes have been built just using a short straight intake, Im sure there may be some advantages on better engineered engines but I dont see any major benefit to either on the negines 90+% of people run, I've seen 48mph on one of my bikes running a manic style intake with a well tuned NT carb, the bike will cruise for miles and miles at 42mph nice and comfortable runjing a Puch hi hi 70cc head and a free flowing straight pipe exhaust, im hoping to devise an expansion exhaust on this bike that doesnt take away from the top speed but so far everything I've tried took several mph off the top end so I always go back to my straight shorty pipe and my top speed comes back....

If I went with either on one of my engines I'd go the plenium proba ly jusy because I think the only time the reeds make that much difference is went they set up like the arrow engines which puts the fuel and air mix directly into the case instead of the jug, just my thoughts and opinion, not the gospel by any means.

Map

 

[MotorBicycleRacing]

[QUOTE="mrfubs]

Fred uses his power plenum on all of his builds i see and with excellent performance.

To me i think either or will be just fine but i think the reed valve has a little more advantage by not allowing any intake charge escape out of the carb.

Tell me what you think, iv not yet used a power plenum and am cerious if it is worth the money sense fred has some pretty smooth running bikes.[/QUOTE]
Fred is flying from the East coast to be at the race on April 12th.

Awesome opportunity to meet Fred in person.

 

[Theon]

I've heard most people say reeds are likely to loose you a little top end, unless properly set up as case induced.
However from most reports a properly set up reed conversion will gain you quite a bit of low to mid.
A correctly chosen intake volume will gain a little at chosen revs without so much top end sacrifice, so the intake plenum is likely to have some benefit.

 

[mrfubs]

i will keep u all posted

 

[mapbike]

I made my own Case reed engine, hopfully it works awesome. It took me a couple hours to hog out all of the metal to fit in the reed block and i also had to grind a bunch off the reed block.




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Looks good to me.... dont see any reason why that wont work great...

Ill be waiting to hear what your results are once you get-ur running.

Map

 

[mrfubs]

Looks good to me.... dont see any reason why that wont work great...

Ill be waiting to hear what your results are once you get-ur running.

Map

my hold up at the moment is finding some one to true my crank. this engine will be going on a cranbrook with a 32t sprocket and another yz80 pipe to fab, although i need to find a less restrictive header i need one that matches the bore of the exhaust im thinking ill have no choice but to make one. not sure how but i know i can figure something out. and also im going to possibly run a 26mm mikuni

 

[Theon]

Nice job.
Did you give it a third transfer?

 

[16v4nrbrgr]

My take on the "power plenum" is that it allows you to port match a thin piece of billet to the engine easily with a file, if the intake is port matched all the way through to the carburetor then its a great idea. If there is a big step in the intake with the large diameter part of the intake on the inside when installed, then the "plenum" part of the intake is a disturbance of smooth airflow. Reed valves are great for the intake pulse reversion at lower revs, at high revs the reversion is negligible in the powerband so in order for a piston ported intake to be a performance intake, port matching is most important, all the way from the filter inlet on the carb to the inside of the port in the engine.

My 2 cents on the matter, and if you go reeds, you need the proper cylinder porting to allow for longer intake duration, IE boost ports, which compensate for reduced airflow by having the reeds in the intake, and fill the cylinder with air for the longest duration afforded by the intake system. If you put a reed intake on an unmodified piston-ported engine, you will reduce airflow overall, which will hurt the mid and top end flow since it is an intake flow restriction.

 

[mrfubs]

Nice job.
Did you give it a third transfer?

my current cylinder has a 3rd transfer and i will be using a new cylinder on this one i have not bought yet i will be doing a better design transfer

 

[rogergendron1]

I've never run either one but I know that some very fast bikes have been built just using a short straight intake, Im sure there may be some advantages on better engineered engines but I dont see any major benefit to either on the negines 90+% of people run, I've seen 48mph on one of my bikes running a manic style intake with a well tuned NT carb, the bike will cruise for miles and miles at 42mph nice and comfortable runjing a Puch hi hi 70cc head and a free flowing straight pipe exhaust, im hoping to devise an expansion exhaust on this bike that doesnt take away from the top speed but so far everything I've tried took several mph off the top end so I always go back to my straight shorty pipe and my top speed comes back....

If I went with either on one of my engines I'd go the plenium proba ly jusy because I think the only time the reeds make that much difference is went they set up like the arrow engines which puts the fuel and air mix directly into the case instead of the jug, just my thoughts and opinion, not the gospel by any means.

Map

WOW >>>> NAIL ON THE HEAD MAN !!!!!

i run the same setup !!! dax f80 with 16mm id intake and a yamaha pw80 carb, lots of porting and piston raming transfer port fixing and a puch 70 hi hi head with .4mm head gasket and a light deck on the jug to get the right squish clearance, also i run a 7/8ths strait pipe and let me tell you ...... the strait pipe has the highest top end speed of any ... any exhaust i have tried !!!! it just lets the motor rip wide open and get up to a way higher rpm and it does it faster too ! of course the x chambers have there advantige and yehh the bike would be quite a bit more tourqy with one on but it always kills the top end speed by a good 5-10mph depending on the chamber !!! besides you can tune a straite pipe too lol all you do it make it long and keep trimming 1 in off at a time till you reach max speed and power, it gives a short but powerfull power band right at the top end.

i no longer am willing to waste money on reed valve setups and x chambers cause my bike does 38mph - 42mph max with a 44t sprocket !!! depending on fuel and temp and terain with just a long large bore intake and a straite pipe exaust lol
i have a buddy with the arrow jug and reeds and a sha carb and a fred head he paid out the arse for along with the sbp x chamber and i smoke him off the line and at the top end ! all he has on me is fuel ecomomy and midrange power but in a race my bike wins every single time

 

[spanners]

This is new to me a chamber making the bike 5 to10 MPH slower . Every two stroke race bike I ever seen runs chambers I don't think they would be doing that if they were getting less speed than a stock pipe. A good chamber made a world of difference on my bike I lost no top end.

 

[mapbike]

This is new to me a chamber making the bike 5 to10 MPH slower . Every two stroke race bike I ever seen runs chambers I don't think they would be doing that if they were getting less speed than a stock pipe. A good chamber made a world of difference on my bike I lost no top end.

Expansion chambers are great and on a high end 2 strokes they make a nice difference, but these engines aren't high end and most of the chambers out there aren't worth using as they are on our china girl engines unless the engine isn't capable of very high rpms and low to mid torque is desired above high speeds.

I have two bikes that have expansion pipes on them and they do good because the engines only run smooth enough to cruise comfortable at 30-32mph the expansion pipes do help with torque on those engines but on my fastest bike so far every chamber ai ised has reduced top sped but the. Low to mid remains good, I keep trying different pipes, header pipe size and length hoping that I can find that magic pipe that will keep the torque but also give me my top cruising speed back which is 42+mph.

I know there are some racers who have made some good pipes for there bikes and they work great for them, but but bairdco for example has had some of the fastest bike on this forum and none used an expansion chamber, to each there own and all I have to go by is what my personal results have been and the results of others who have been building these bikes for several years, im gonna continue to tinker a while more to find a chamber Im happy with but I know if I dont I have another home built pipe that does a nice job.

Map

 

[spanners]

Expansion chambers are great and on a high end 2 strokes they make a nice difference, but these engines aren't high end and most of the chambers out there aren't worth using as they are on our china girl engines unless the engine isn't capable of very high rpms and low to mid torque is desired above high speeds.

I have two bikes that have expansion pipes on them and they do good because the engines only run smooth enough to cruise comfortable at 30-32mph the expansion pipes do help with torque on those engines but on my fastest bike so far every chamber ai ised has reduced top sped but the. Low to mid remains good, I keep trying different pipes, header pipe size and length hoping that I can find that magic pipe that will keep the torque but also give me my top cruising speed back which is 42+mph.

I know there are some racers who have made some good pipes for there bikes and they work great for them, but but bairdco for example has had some of the fastest bike on this forum and none used an expansion chamber, to each there own and all I have to go by is what my personal results have been and the results of others who have been building these bikes for several years, im gonna continue to tinker a while more to find a chamber Im happy with but I know if I dont I have another home built pipe that does a nice job.

Map

I have played around with chambers myself I have three.I agree some are better than others. The one I'm using now has it all over a stock pipe speed wise .I watched a lot of motorized bike raceing on utube all the fastest two stokes are all running chambers I don't think I've seen one with out a chamber. As you say each to there own.

 

[Theon]

A good expansion Chamber makes a big difference.
Banana Pipes and the like are a gimmick.
Maybe small improvement somewhere in the rev range.
A good pipe will give a proper powerband that if timed right could be the difference between 45Mph and 50!
Sticking a standard pocket bike pipe on one of these is not going to do much.
They don't do much for a pocket bike!
If your looking for power from a pipe, it has to be designed right, and the engine set up to match the pipe.
I have no experience with SBP pipes or any of the banana contraptions, cause there not right, wouldn't waist my money.
I'm sure there are some improvements to certain parts of the rev range.
I havn't tried a big bore open pipe either, and can imagine this also works well and over a wide rev range, but probably loud.
A properly designed straight through silencer should not impact performance much, still give a nice note and please your family and neighbours!

 

[mrfubs]

I am pretty confident on my new build going everybit of 55 to 60 i would actually bet on that.

I pressed my crank apart to do some balancing and found a local shop that is pressing it back together truing and welding the crank pin for 55+10 to weld the pin.

I have a good feeling on the porting iv done advancing the exhaust a decent amount and other add ports, it will be done in a couple months.

 

[mapbike]

Expansion pipes are good on a 2 stroke engine no doubt, buy if its to restrictive like most all of what is being sold for our bike it only helps performance in the low to mid rpm range and then peters out on the top end, I personally choose not to spend more on an exhaust pipe than I did for my engine, I do know that bairdco had one of the fastest bikes being run on this forum and he never used an expansion chamber on any of his bikes, he was gps'd at 54mph and blew one engine up doing over 60mph while drafting a truck, on a track the expansion pipes are gonna give better low to midrange torque out of the turns and better acceleration but for someone that rides like I do those things are not that important, I like to have a good cruise speed above torque and not a bike that hits its plateau short of its top cruising speed and so far all the chambers I've used have been a disappointment on top speed performance, probably just not getting things matched up right andnprobably wrong pipe.

By the way some of the fastest race bikes are running pocket bike pipes also, some are running the fatty pipes like the one jnmotors sells, not sure how they are setting them up but they run a very short header pipe and I assume they're ditching the silencer and using the correct length stinger on the back side.

All I care about is having a good cruise speed in the 40-45mph range, for me that is plenty fast on a bicycle.

Map

 

[Theon]

A good pocket bike pipe is a good pipe. and getting good mid range on the track is probably what you want, what I'm talking about is a pipe that gives reasonable low to mid with a big header pipe, but starts to work around 7000. I find the standard pipe starts to become a problem here, and no doubt an open pipe has it's big advantage around now.
But a good expansion chamber with motor tuned to suit, can start to run really nice around 8000, even with a 'silencer', and give a real 'push' all the way above 9.

 

[slayer60973]

A good pocket bike pipe is a good pipe. and getting good mid range on the track is probably what you want, what I'm talking about is a pipe that gives reasonable low to mid with a big header pipe, but starts to work around 7000. I find the standard pipe starts to become a problem here, and no doubt an open pipe has it's big advantage around now.
But a good expansion chamber with motor tuned to suit, can start to run really nice around 8000, even with a 'silencer', and give a real 'push' all the way above 9.

You want a pipe that does that get a torquer 2, I have it and low to mid range is pretty good, as soon as I hit 29 the power band hits hard and rockets up to 40, I'm sure I can go faster but reliability is more my thing, so I usually cruise around 30-33- but it can be hard to keep the mph steady within the band of POWA! Oh and I run a disc mounted 38t