Reed Valves

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aaronbentzel

New Member
May 2, 2012
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York
Can someone talk about Reed Valves? Many people have said they are a very good upgrade. I have a Grubee Skyhawk GT5 engine. Some of my questions are as follows:

What do they do differently?
How hard are they to install?
How much increase in performance can I expect?
Do they come with instructions?
Are they universal or will I have to modify them for the engine?

Thanks ahead of time for any information!!.xx.
 
BigBlue

BigBlue

Member
Nov 29, 2011
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California
aaron,

welcome to the board. Look in the Intake & Exhaust and High Performance sections of this forum or do a Google search.

Good Luck,

Chris
AKA: BigBlue
 
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ivan H

Member
Oct 8, 2011
622
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australia
Adding reeds 2 a HT motor stops reversion blowback thru the carb resulting in a bit better crankcase compression ratio. They r a bolt on mod, c Rock Solid Engines or Arrow Cycles. I cant give u a real answer 2 how much increased power, I'm waiting on a manifold from RSE to fit Mikunl 2 reeds but figure like 15 percent without porting the piston & boost or boyesen porting the cycinder, & up to 30 percent if u do. Cheers
 
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ivan H

Member
Oct 8, 2011
622
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australia
U can use reeds without porting the piston/jug, how well they work depends on design & wot they made of. Metal or carbon fiber r stiffer so can restrict flow but resist flutter at hi rpm. Fiberglass r more flexible so arent so restrictive but will flutter at hi rpm. Portwork involves lowering intake port floor, raising piston skirt on intake side & cutting a port in the intake side of the piston so the motor intakes thru 180 degrees instead of 60. Then a boost port can b cut above the intake port to the height of the transfers. Cheers
 
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ivan H

Member
Oct 8, 2011
622
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australia
BTW, these Chinagirls dont produce anywhere near the sort of rpm that will cause reed flutter. Adding reeds without doing portwork can increase crankcase compression ratio by eliminating reversion blowback. How well they do this depends on design & wot they r made from. Cheers
 
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ivan H

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Oct 8, 2011
622
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australia
I havent really been able 2 test yet, 1&1/2 weeks rain since fitting & still raining. The RSE reeds protrude into the port a little so dont increase crankcase volume over stock, & use thin fiberglass reed petals. Every1 I've spoke 2 reports a good low/mid increase without other mods after downjetting a little, but I guess I'll find out 4 sure when this freakin rain finally stops. Cheers
 
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ivan H

Member
Oct 8, 2011
622
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australia
I plan on running it without all the piston/intake/boost port mods 4 a bit, then doing the mods 2 compare the gains. Cylinder reeded motors can b "Boyesen" ported 2, where ports r drilled from the intake port floor thru 2 the transfers (usually rear transfers), but on these they would need 2 b surface cut into the cylinder wall & care with positioning would b needed so as not 2 hang up ring ends. Cheers
 
Fuji Moto

Fuji Moto

New Member
Jan 17, 2010
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Canada
the porting doesnt seem too difficult, so basically the rock solid reeds are the ones to get? i assume the high compression head and better carb such as the dellorto would also be crucial to get the most from everything? all i have going on now is a stock slant head, which is old but has really good compression still, shift kit sbp pipe tuned some what, custom short intake, iridium plug, ngk wiire and the nice chrome filter, impressive, but I want to get this motor to crank as much power as possible , i geared it low and it has made it way more useable its crazy in tight trails and climbs pretty steep hills, and i can dump the clutch sitting still right into a wheelie no prob its amazing what this motor can already do but i feel it can be better
 
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ivan H

Member
Oct 8, 2011
622
1
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australia
I cant comment on which reeds 2 get, as I havent tried others. Yeah the porting isnt overly difficult, make sure u get the timing of piston ports right if u utilize the full 180 degrees. Low/mid IMHO, is where 2 look 4 gains as the port split is best suited 4 this. Using RSE reeds with 60 degrees of intake requires downjetting a bit but if u mod for 180 degrees of intake u will needs 2 upjet a fair bit due 2 much reduced intake velocity, & dont go 2 big with the carb. I've got 16mm mikuni & thats probly on the limit for a not hi reving reeded motor breathing thru 180 degrees. Cheers
 
Fuji Moto

Fuji Moto

New Member
Jan 17, 2010
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Canada
so what type of porting do u reccomend? it seems easy enough to lower intake floor, raise skirt on intake side of piston, now as far as the port you put on the intake side of piston, is that just one round hole? or a bunch of small ones? and the boost port above intake goes as high as the top, or bottom of transfer ports? im new at this it would help if i were looking at a jug
 
Fuji Moto

Fuji Moto

New Member
Jan 17, 2010
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Canada
yeah im not too sure about the port timing and how high and low to grind but i gotta try something i got a few older engines with decent cylinders that i dont mind messing up is 60 degrees stock timing?
 
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ivan H

Member
Oct 8, 2011
622
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australia
The port in the piston can b any shape u like. I was thinking of using 2 long thin side by side ports like old yamaha's had 2 keep structural integrity in the piston,, kinda like "ll" shape. The piston port has 2 b essentially closed at Bottom Dead Center, just about 2 open. The boost port is exactly 2 the height of the tops of transfers & exit angle is very important. It should discharge towards the rear of the head, & not forward towards the exhaust port. Cheers
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
check out Macdizzies Technology Exchange (forum) for a good primer on this topic. Check "cylinder mapping" on that site, or alotta other threads. Cheers
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
Hi Fuji Moto, u will also need a feeder port in the piston above the intake port, that will feed the boost port in the cylinder. The feeder port should b fully open to the cylinder intake port at BDC, so the inertia of transfer can draw fresh charge in. I said last night that the piston port must b just close at BDC but that is incorrect. (I was bit under th weather). The main piston port can b open a little also so fresh charge can also draw thru it. Cheers
 
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ivan H

Member
Oct 8, 2011
622
1
16
australia
Hi Fuji Moto, when porting the piston or raising the skirt is is important 2 radius any edges, both inside & out, for strength & because sharp edges r stress risers. Also, u dont wanna lower the whole intake port floor as any metal removed is essentially lowering crankcase compression ratio, so only the inside say, 5mm. I was thinking of starting by removing around 2.5mm or 3mm from both skirt & port floor & seeing how that went, rather than just hoging heaps out in 1 go, do more later if I think it will benefit from. A steeper angle will mean less turbulent flow into the crankcase. Maybe rabius this angle into the port floor. Cheers
 
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