Port Timing
03-20-2007, 08:45 PM
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Port Timing
I was wondering if I could get everyone and anyone’s advise on port timing numbers. The type of engines I am getting back into, are the Homelite's with out removable cylinders. I’m talking about 33's 38's and the 45's. It’s also the same setup as some Poulan's and Echo’s. I know with the 25 and 30 you can leave out the cylinder gasket and deck the block to move around the timing. On this style, if not familiar with, once the crank and bearings are bolted on with the cap, there isn’t anything that can be done besides grinding and massaging the ports. So I am back to my question ... What numbers are good, better, and best taking into account all engine RPM operation. I would like to get a bit more power without sacrificing idle and transition. I know opening the exhaust port width wakes these up for breathing so that will be a given. I was just wondering what every finds works for them. I will take all and any info anyone wants to give. I do have a saved thread where a respectable engine builder gave some numbers but that was for a 26.3cc engine, I think that was the size. I'm sure a lot, if not all those numbers will work so I have them. I'd like to thank everyone in advance for their time and info...
ALW
ALW
03-20-2007, 11:24 PM
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RE: Port Timing
ALW,
Most of the people doing saw conversions leave the port timing alone, since it is much more advanced then trimmers already. Homelite 33 for example has 150 degrees exhust duration, 116 degrees transfer duration and 140 degrees intake durations. Also making the exhust much wider may cause the ring to catch on the port edge.
Dave
Most of the people doing saw conversions leave the port timing alone, since it is much more advanced then trimmers already. Homelite 33 for example has 150 degrees exhust duration, 116 degrees transfer duration and 140 degrees intake durations. Also making the exhust much wider may cause the ring to catch on the port edge.
Dave
03-20-2007, 11:49 PM
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RE: Port Timing
Port timing is mostly art but part science and volumes have been written about the effects and consequences when building racing engines. There are no sound bite answers that will be of value. Sort of asking about how to get along with females.
Do you have a specific question?
Bill
Do you have a specific question?
Bill
03-21-2007, 02:22 AM
#4
RE: Port Timing
140 to 145 intake, 150 to 160 or 165 on the exhaust, and transfers about 20 less than the exhaust have been working pretty well for me on the Homelite and Echo/Kioritz engines I've done. The higher numbers are used with slightly smaller props and higher rpms, and the lower numbers for swinging slightly larger props for scale applications. If you are going to run a tuned pipe, then the exhaust numbers get into the 170's.
AV8TOR
AV8TOR
03-21-2007, 05:43 AM
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RE: Port Timing
Dave, thanks for the info. I will be sure not to go to far, just open it up a bit to square the port as much as I can with out the ring issue.
Bill, specific question? No not really, Just looking to collect data from people and their trial and errors. Im not looking to make reace engines, just looking to try and get the most out of a conversion across all RPMs.
Av8tor, thanks for the info. Thats what Im looking for, kind of like that chart you did in your one post. Just geared more towards the style of engines I mentioned. I know the port timing numbers directly affect it but anything on duration?
ALW
Bill, specific question? No not really, Just looking to collect data from people and their trial and errors. Im not looking to make reace engines, just looking to try and get the most out of a conversion across all RPMs.
Av8tor, thanks for the info. Thats what Im looking for, kind of like that chart you did in your one post. Just geared more towards the style of engines I mentioned. I know the port timing numbers directly affect it but anything on duration?
ALW
03-21-2007, 10:53 AM
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RE: Port Timing
ALW,
Since these saws are piston ported engines, you just double the port timings to get duration. Using this, you will see that the lower port timing numbers given by AV8tor are about half of the duration values that I listed for a stock Homelite.. If you use electronic ignition with some form of advance, you can get away with more radical timing while still retaining a decent idle. Everything is a tradeoff, when you gain something, you lose at the other end.
Dave
Since these saws are piston ported engines, you just double the port timings to get duration. Using this, you will see that the lower port timing numbers given by AV8tor are about half of the duration values that I listed for a stock Homelite.. If you use electronic ignition with some form of advance, you can get away with more radical timing while still retaining a decent idle. Everything is a tradeoff, when you gain something, you lose at the other end.
Dave
03-21-2007, 03:22 PM
#7
RE: Port Timing
Yeah... You raise the exhaust port and transfer ports, and lower the intake port to increase timing in a piston ported engine. The opening and closing times necessarily depend on the piston opening and closing the ports, and you don't really have much control over them. A rotary valve intake can have the opening and closing times varied.
AV8TOR
AV8TOR
