OzVMX Forum
Marque Remarks => Spaniards (Bultaco, Ossa, Montesa etc) => Topic started by: montman on September 15, 2010, 08:23:13 pm
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Just wonderd if anyone has converted a 250/414 cappra to reed valve and if so how and was it any good.
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It'd be a pointless exercise. The biggest thing I've learnt from my time in VMX and especially with the Montesa's is that the engineers actually had an idea of what they were doing. Especially when it comes to cylinders, porting and pipes. Once you start screwing with them you throw the balance out and lose the magic of these great bikes. Usable power, great handling and a bit of harmony.
When I first started out I was changing this and that and trying to improve things and begrudgingly, at the end of the day, I had to admit that things were no better.....
So now my motto is
"If you want them to rock, leave 'em stock". ;)
Leave that sort of thing up to the Maico 490 and Honda guys......
* On the advice of a race tuner and engine builder whom I implicitly trust, I have a poofteenth taken out of the heads of my bikes to lower the compression due to the low octane that we run today in fuels. :)
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I like Ross's advice. I think it is particularly applicable to Monties. Monties were designed and set up for European MX - either deep sand tracks or muddy tracks. In these situation a stable but quick turning, easy steering bike with lots of mid range excels.
My understanding is that reed valves add bottom end and mid range to what would otherwise be a high hp high revs piston port engine. If a piston port engine is a grunt master I can't see putting reeds on is gunna change anything. If things change it would probably be to the determent as the reeds interfere with the airflow.
Lozza will be along in a mo and tell you 'go for it' :D. But then he'll say 'you just have to open up this port here, lift the exhaust port, increase the transfers here, here and here' etc ;D ;).
You'll probably produce more hp (and suck more juice) but if you produce more useful hp will probably be argumentative or dependent on where you ride.
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Amen, brothers.....
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Just wonderd if anyone has converted a 250/414 cappra to reed valve and if so how and was it any good.
Depends how it's done. When completed correctly the reed engine will have more and a far better spread of power.Very helpful in preventing spit-back or reverse flow into the carb.Just post a pic of the cylinder.
I'll leave you with the words or Ramon Forcada, if you got to ask he's Jorge Lorenzo's crew chief, he started with Eduardo Giro at Ossa and went through working on every fast Spanish two stroke ever built and with just about every fast Spanish rider that ever raced(and a few others).His words still ring in my ear when he stated 'Even on a GP level factory bike I see things that can be improved"
Ramon spends his 'spare' time prepping enduro and supermoto bikes.
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Despite Ramons wise words, I agree with my learned colleague yet again.... but from a Maico perspective.
Back in the early vintage days I tried to perfect the reed valve conversion on Maicos. I tried modifying a Gem reed with no obvious improvement then adapted a Yamaha MX250 reed block to the Maico barrel. It took many hours of welding and porting and reed material trial and error but the end result was that the engines performance improved two fifths of FA. I now run them basically stock, even down to using Bing carbs. The only major mods being a more modern pipe design and PVL ignition. As Gary Treadwell ( a tuner who knows his shit once told me, "some engines work better the way they were created, Maicos don't seem to respond to reeds". It seems Montys are in the same boat.
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As a wise head once told me; if you want hp on a 4t concentrate on the inlet side; if you want hp from a 2t concentrate on the exhaust side. ;) ;D.
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Yes at GP level I'm sure there's room for improvement in my engines but I'm a long way off being a GP rider (except when I've got Black Sabbath's Neon Knights pumpin' out the stereo and no one's home ::))
On the track I was racing on last Sunday there's a step-up jump just out of a corner which you have to be gassin' it to make the leap. At first I was shifting from 2nd to 3rd and making it easily but the thought of finding one of the many neutrals in my gearbox dictated that making that gear change was going to be folly when I hit the ramp in neutral sooner or later. So....
I decided to leave it in 3rd gear through the corner and hope it would come on the pipe when I hit the jump. With just a hint of clutch when it straightened up and the roar of something close to primal I was happily soaring through the air again. :P
That's the sort of power a lowly C grader like myself needs on a race track.
Not a time bomb that won't track or steer where I want it to....... :-[
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Hey 414, when you say a pooftenth out of the head, i think you'd be upping the comp not lowering it.
or are you messing with the squish and shape to create more volume in there ????
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No doubt that almost any motor can be improved if you throw enough money and time at it.
Big bore Montesa's seem to have plenty of power without the addition of reeds. In 1974,
EC Birt, the reed valve master, tried to make a Rickman VR 250 faster with the addition of
extra boost ports in the piston, a reed setup and custom pipe. On the dyno, the stock
motor produced 26.5 hp at 7,850 rpm (rear wheel) With the reed setup 28.4 hp. He did
say at the end of the article "To improve over the stock Montesa engine is very hard to do
and it should not be messed with unless you really know what your doing. So ride it!
With this kind of horsepowe curve, you can win with it stock"
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I have taken a 414 cylinder to the local go fast guy who had
computer controlled air flow testing equipment and he does work
on modern mx and flat track bike. He took one look at the 414's
transfers and the intake tract and just rolled his eye's and wondered
how the bike even ran. Just told him that it's the combination that counts.
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or are you messing with the squish and shape to create more volume in there ????
Yeah Freaky. He gives the head a little more volume (takes some out of the dome). I've had him to it with my 2000 YZ as well. ;)
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interesting, i have only heard of guy decomping a motor to run off hot events, such as long flat out racing like dirt track and enduro stuff. NEver seen it on mx type on/off throttle events.
might have been cheaper just to add another base gasket ........... :D
PS...do the nanna party dance Nimmo, you know you want to........ :-X
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It has to be your most annoying avatar yet...... ::)
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Success !!!!!!
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(http://i323.photobucket.com/albums/nn458/mx250syd/icons/shooting.gif)
Success !!!!!!
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A lot of interesting comments i was not intending to try to reed valve my monts but with all the talk in the UK of reed valve,more horsepower,better throttle responce it does make you start to think.Its also interesting to hear comments like great handling and great bikes and while i agree with all things 414 on that not a lot of people in the UK will agree they all think they are camels in the handling area and were out dated when they were new.I can remember in the early to mid 1970's along with bultaco they were the bike to have (in the UK anyway) then after 1975 they started to go downhill in the riders views what with the maico's and jap bikes coming through even now in what we call the twin shock class its nearly all maico's i can not recall seeing a mont in a lineup for ages(pehaps its time i stoped riding modern bikes and gave my monts another blast)so is it down to what shocks you have OHLINS/BETORS as from factory/AVAX(any body heard of them)or what do you sugest also forks while i think MAZOKS were the best at the time do you just run with stock settings or has anyone moded or added anything to them.One thing that annoyed me more than anything with a mont was the bogging on bottom end this used to happen when the bike was a few months old(6 or more)even after new piston/ring timing correct carb jets correct and clean in fact every thing you could check replace we did apart from a new carb and yet you could still sit there throttle open with the bike not picking up for a good few seconds any one else come across this?.
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Can't say I've discovered that problem Montman (thank gawd!). I run everything standard apart from the slightly lower compression. I have the timing set at 3mm BTDC. 40mm Bing with factory jetting. I am having problems with suitable crank seals and I've been made aware that I should use gaskets on the seal carriers instead of Three Bond (I had the clutch case preasurising on the weekend due to this).
I have a set of YSS shocks on the rear with adjustable pre-load and rebound damping (we can run them over here) and a set of YSS emulators in the forks. The only thing I did was shorten the shocks to 360mm as I'm a bit of a short-arse but this doesn't seem to have changed the the way it steers that much. It hooks up very well.
I reckon' they'll run with anything else out there. :)
There's a big gap between this one and the rest of the field..... :P (pics thanks to Yamatragic)
(http://i235.photobucket.com/albums/ee74/All_things_414/IMG_7209.jpg)
(http://i235.photobucket.com/albums/ee74/All_things_414/IMG_7210.jpg)
(http://i235.photobucket.com/albums/ee74/All_things_414/IMG_7215.jpg)
(http://i235.photobucket.com/albums/ee74/All_things_414/IMG_7216.jpg)
(http://i235.photobucket.com/albums/ee74/All_things_414/IMG_7217.jpg)
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I don't see how you could use more low/mid and mid/high rev power than the Monties make standard. My VB360 was setting quick times at the Canberra track last Saturday (before the bloody Motoplat let all the smoke out) using two gears 2nd and 3rd ;D. I can assure you it must have been the bike because the riders nothing special ::)
The H7 250 has a reed valve and to be honest I think it was only put on to satisfy the fashion gods.
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Yeh it took another 2 laps before '48' lapped you ;D ;D ;D ;D Sorry Ross
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firko get Treaders to explain what the relationship is between the reed and the pipe at BDC.That will explain how piston ports just cannot compete with reed valves. I don't think the 250 Maico is probably the best example to use either, the scavenging on that cylinder is not very good that's the first thing to address .Big trap with reed conversions is to go too big and next is removing those 'restrictions' like stuffers followed by bending the stops back as far as possible.. Big bores are a bit of a law unto themselves, the abudence of torque wallpapers over lots of issues.Go down to 125's and a reed engine is far more enjoyable to ride than the piston port.
When dyno figures are mentioned there is little talk about the shape or the 'area under the curve' which is far more important than the peak figure.