Porting a reed valve saw

[bootboy]

I have an old poulan 2300cva that I tore into last night out of boredom. I never put a lot of thought into the design of this saw but turns out its a reed valve saw. I was thinking about opening up the exhaust port and smoothing out the transfers as my first porting expirement. It's open transfers I guess don't really lend themselves to smoothing out. I'll work on the exhaust but I was wondering with a reed valve saw like this, what kind of gains, if any can be seen with porting. Worth the time?
Like I said, this is an experiment, I'm not really concerned about trashing the saw, I just need some practice. Thanks for your help.

 

[Eccentric]

I have an old poulan 2300cva that I tore into last night out of boredom. I never put a lot of thought into the design of this saw but turns out its a reed valve saw. I was thinking about opening up the exhaust port and smoothing out the transfers as my first porting expirement. It's open transfers I guess don't really lend themselves to smoothing out. I'll work on the exhaust but I was wondering with a reed valve saw like this, what kind of gains, if any can be seen with porting. Worth the time?
Like I said, this is an experiment, I'm not really concerned about trashing the saw, I just need some practice. Thanks for your help.

Reed valve engines can have the same gains as piston port engines when properly modified. I have to laugh when people think that a reed valve engine must be a stodgy old low revving waste of time.............while a piston port engine is a modern, high revving masterpiece of engineering. The piston port system was in use long before the reed valve system became popular, especially in motorcycles. Piston port, rotary valve, and reed valve induction designs all predate handheld 2-stroke chainsaws. Many factors control how much and what type of power a 2-stroke engine can make. Being a reed valve engine (instead of a piston port engine) in and of itself isn't the issue...

A 'modern, high revving' piston port 2-stroke drag saw engine. Picture found in a google search.

Piston ported IEL Model K as introduced in 1939. Picture taken from Mike Acres site.

Model Profile: K

'Slow, low revving old fashioned' reed valve 2-stroke engine in a hotsaw. Picture found in a google search.

'Slow, low revving' (yeah right) reed valve I-4 Yamaha TZ750 engine. Absolutely breathtaking. Picture found in a google search.

Throw a good loop of chain on that little Poulan and shoot some 'before and after' videos. Let us know how your first porting experiment goes. Have fun with it.

 

[tdi-rick]

and the 100cc Italian reed kart engines I occasionally ran way back in the eighties were good past 18,000RPM at the end of a straight which would be equivalent to a saw in the cut, not free revving in mid air

 

[Eccentric]

and the 100cc Italian reed kart engines I occasionally ran way back in the eighties were good past 18,000RPM at the end of a straight which would be equivalent to a saw in the cut, not free revving in mid air

PCR?

 

[tdi-rick]

Long stroke PCR and TT65/TT75 Parilla's.

I raced SS20 rotary valve Parilla's but my mate in Junior International ran the reeds and I used to run the engines in for him as his and my engine builder, his Dad didn't trust him.
It was a tedious process to run them in, it took a few sessions, almost 45 minutes total run time before you could let 'em fully rip

 

[bootboy]

I never said anything about differences in their baseline performance, I was not operating under any such preconceptions. I just wanted to know if reed valve saws benefited from porting comparably to saws of other designs. Now here we are talking about go-karts.

Put a Suzuki gsxr 1000 on it and call it good...

 

[tdi-rick]

Now here we are talking about go-karts.

Not at all, we just added some high revving reed engines as examples

 

[cmarti]

Not at all, we just added some high revving reed engines as examples

Most AS threads get taken much further off the track than this one did. BTW, have you guys seen "Man of Steel" yet, great movie.:msp_rolleyes:

 

[moody]

I ported a reed valve eager beaver once. You can get gobs of torque and if you've got access to thinner reed types you'll gain rpms. I believe the reason we don't see more reed valve saws ported is based upon the fact that they're hard to come by parts for. Or they fall into the collectible side or aren't worth the investment. Who know but you should try it out.

 

[IEL]

Reed valve saws are monsters. Once again this will be me praising the best saw ever made, the homelite super ez. Only a reed valve 41cc could be that amaizing...... I seriously think it is more powerful than a ms290....

 

[MnSam]

I saw some good gains from exhaust porting and a MM on my saw similar to your 2300cva. I stopped short on the intake, wasn't sure where to go with the reed.

 

[bikesandcars]

I found some good gains on a similar poulan 2000 by doing a muffler mod and smoothing the transition from after the piston opening into the muffler (making it a little bigger).

I also used a more flexible fiber reed material instead of SS, but that didn't seem to net any power or RPM because I didn't change the porting, the reed in itself didn't seem to do much.

I then destroyed a 2300 in my 2nd round of experiments by opening up the piston side of the exhaust port. There is no center "rider" for the piston ring on those poulan's. Porting the cylinder side on those is very risky, you can easily swallow a ring and lunch the saw.... which then shears the flywheel pin... sucks

I suggest air cleaner (less restrictive) mods, muffler mod, and non-invasive porting / smoothing and stopping there. You can also remove the base gasket for more squish. It's more fun to destroy a cheap saw slowly with a high flow air filter than quickly with a bad port and yields better results.

These reed valve engines seem to make great torque

 

[tdi-rick]

I saw some good gains from exhaust porting and a MM on my saw similar to your 2300cva. I stopped short on the intake, wasn't sure where to go with the reed.

Cage mods and better reeds that don't flutter at revs, (aka carbon fibre ) but it's all in the transfers and boost port/s then the reed engine will give you the power and revs of a rotary valve engine and both start to leave the piston port engine behind, but we're talking real race engines not low revving industrial type two strokes and from the little I've seen there was some convoluted porting in the old saws.


[edit] I thought I better add this and sorry for being obvious, the reason a reed or rotary two stroke is ultimately superior to a piston port engine is you get better, more positive crankcase sealing and compression. Go too wild with your intake timing on a piston port engine and you end up with no bottom end/mid range and massive amounts of spit back through the carby

 

[Macman125]

I never said anything about differences in their baseline performance, I was not operating under any such preconceptions. I just wanted to know if reed valve saws benefited from porting comparably to saws of other designs. Now here we are talking about go-karts.

Put a Suzuki gsxr 1000 on it and call it good...

They are are just addressing the misconception that reed valve engines are old and slow technology. The fact is that reed valve engines can be quite competitive with piston port engines. Major gains can be seen in with both when properly ported. And I bet you a reed valve 1000cc four would whoop that gsxr 1000's arse.

 

[sawfun9]

Talk about old and slow, a few years back I believe Don Garlits and Chris Karmisines ran almost side by side at way over 300 mph and both men were either 80 years old or real close to it. Ironicaly these were the first two guys to calim to be the first over 200 mph several decades before. Old and slow Huh?

 

[bikesandcars]

since we're side tangenting I prefer peanut butter to chicken salad.

There's more than one way to skin a cat right? I don't care if my saw has a reed, I just care that it works good, and from my limited experience you can get a poulan 2xxx reed valve to perform very good for what it is

 

[67L36Driver]

PCR?

Is that a stodgy old Tilly HL on there?

 

[Eccentric]

Is that a stodgy old Tilly HL on there?

Yep. Nobody ever uses HL's on anything fast.

 

[tdi-rick]

Is that a stodgy old Tilly HL on there?

Yep. Nobody ever uses HL's on anything fast.

We considered little cube Walbro's sub-standard back in my karting days

 

[hillwilliam]

I have an old poulan 2300cva that I tore into last night out of boredom. I never put a lot of thought into the design of this saw but turns out its a reed valve saw. I was thinking about opening up the exhaust port and smoothing out the transfers as my first porting expirement. It's open transfers I guess don't really lend themselves to smoothing out. I'll work on the exhaust but I was wondering with a reed valve saw like this, what kind of gains, if any can be seen with porting. Worth the time?
Like I said, this is an experiment, I'm not really concerned about trashing the saw, I just need some practice. Thanks for your help.

I've done some hillbilly porting, etc. on several Pioneers. They were bad, bad saws in their time. They still run really well - except for the P42 that grenaded after a few years of hard use.