Re: Vespa intake timing: let's talk numbers

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> Simon Nyi Wrote:

> -------------------------------------------------------

> The Bell book says that the intake port should close no sooner than ten

> degrees before the transfers open and vice versa. So take a port map,

> figure out when the transfers open and close, convert mm to degrees of

> rotation, give ten degrees on either side, and there's your safe

> maximum.

> just realized that might not be clear. the intake port should close at least ten

> degrees before the transfers open, no less, and the intake should open no sooner

> than ten degrees after the transfers close.

I tried to resist the urge to bump this ridiculously old thread but I couldn't. I figure I'm probably not the only one that ends up in threads like this to learn and figure stuff out . . . and I just wanted to correct some misinformation that threw me for a loop and most likely did for others returning to this thread for vespa knowledge.

Bell says in his book the exact opposite actually, regarding when the inlet port should open. And he never mentions anything about precisely when the port should close in relationship to the transfers because there is generally no amount of usable and reasonable transfer/intake timing that would ever bring the port close even within that range to the transfer open point. You'd have to be running ridiculously long intake period and even more ridiculously long transfer timing. I think? Either way I suppose on that half of the statement Simon was somewhat correct because it's good for the inlet to close a bit before the transfers open to build pressure while the mixture is in there.

Here is what Bell actually says:

"It is usual, when good low speed power is required, to open the inlet port about 5 to 10 degrees before the transfer port closes (ie 120 to 130 degrees before TDC) and to close the inlet port at about 55 to 60 degrees after TDC. This results in an inlet duration of around 180 to 190 degrees."

Cartsen does a good job of showing this math in practice in this video that I'm sure many of us have watched (he gets into this stuff right before the 27 minute mark).

This is also confirmed on Ciao NL. The translation is kind of crude but same exact idea:

"Graham Bell says in his 2-stroke tuning book that the coil ports can be opened up to 10 degrees flush with the inlet, I have adhered to that very strictly until I encountered many cases of more than 10 degrees where it just goes well. So it may be slightly more than 10 degrees. Suppose you close flush ports 124 degrees before TDC, then you may open inlet 134 degrees before TDC." (edited)

This single post is part of a larger thread. Start from the top or view this post in context.
Subject Written By Posted
Vespa intake timing: let's talk numbersTopic by: Simon Nyi 10/01/13 03:23PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 10/01/13 04:27PM
Re: Vespa intake timing: let's talk numbersRe: Adam Blickhahn 05/14/14 11:50PM
Re: Vespa intake timing: let's talk numbersRe: #CrazyWayne™ rocks. #CrazyWayne 06/22/14 02:34AM
Re: Vespa intake timing: let's talk numbersRe: Josh G 10/01/13 05:47PM
Re: Vespa intake timing: let's talk numbersRe: Josh G 10/01/13 05:52PM
Re: Vespa intake timing: let's talk numbersRe: Josh G 10/01/13 06:19PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 10/01/13 06:37PM
Re: Vespa intake timing: let's talk numbersRe: Simon Nyi 10/01/13 06:50PM
Re: Vespa intake timing: let's talk numbersRe: Graham Motzing 10/01/13 08:23PM
Re: Vespa intake timing: let's talk numbersRe: Simon Nyi 10/01/13 10:55PM
Re: Vespa intake timing: let's talk numbersRe: Allen Halk 10/01/13 11:25PM
Re: Vespa intake timing: let's talk numbersRe: Deadped Ryan 10/01/13 11:42PM
Re: Vespa intake timing: let's talk numbersRe: Simon Nyi 10/18/13 12:58PM
Re: Vespa intake timing: let's talk numbersRe: Jason ( ͡° ͜ʖ ͡°) 12/28/20 03:51AM
Re: Vespa intake timing: let's talk numbersRe: «tyler » 10/18/13 01:42PM
Re: Vespa intake timing: let's talk numbersRe: Simon Nyi 10/18/13 02:44PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 05/15/14 04:07AM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 06/20/14 01:16PM
Re: Vespa intake timing: let's talk numbersRe: Pete Puczasaurus 06/20/14 02:30PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 06/20/14 06:43PM
Re: Vespa intake timing: let's talk numbersRe: Graham Motzing 06/24/14 03:26PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/13/14 02:38AM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/13/14 03:33AM
Re: Vespa intake timing: let's talk numbersRe: #CrazyWayne™ rocks. #CrazyWayne 07/13/14 03:49AM
Re: Vespa intake timing: let's talk numbersRe: Pete Puczasaurus 07/13/14 02:09PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/13/14 07:10AM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/17/14 12:17PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 07/17/14 12:46PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/17/14 12:59PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/17/14 01:31PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 07/17/14 01:42PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/17/14 02:11PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 07/17/14 02:57PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/17/14 04:24PM
Re: Vespa intake timing: let's talk numbersRe: peter heid 07/20/14 10:35AM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 08/19/14 02:51AM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/14/14 02:59PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 07/22/14 03:30AM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/14/14 03:50PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/14/14 04:06PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/14/14 04:20PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/14/14 04:26PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/15/14 09:44AM
Re: Vespa intake timing: let's talk numbersRe: «tyler » 12/15/14 12:24PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/15/14 12:28PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 12/16/14 05:34PM
Re: Vespa intake timing: let's talk numbersRe: alex . 12/19/14 04:35AM
Re: Vespa intake timing: let's talk numbersRe: alex . 12/19/14 05:00AM
Re: Vespa intake timing: let's talk numbersRe: Walt W 12/22/14 08:35PM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/22/14 08:48PM
Re: Vespa intake timing: let's talk numbersRe: alex . 12/23/14 04:15AM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/23/14 01:12PM
Re: Vespa intake timing: let's talk numbersRe: Maciek Dub 12/24/14 11:48AM
Re: Vespa intake timing: let's talk numbersRe: «tyler » 10/02/13 08:46AM
Re: Vespa intake timing: let's talk numbersRe: Simon Nyi 10/18/13 01:52AM
Re: Vespa intake timing: let's talk numbersRe: «tyler » 10/18/13 09:31AM
Re: Vespa intake timing: let's talk numbersRe: Pete Puczasaurus 06/11/14 07:38PM
Re: Vespa intake timing: let's talk numbersRe: Pete Puczasaurus 06/20/14 01:09PM
Re: Vespa intake timing: let's talk numbersRe: «tyler » 12/15/14 07:52AM
Re: Vespa intake timing: let's talk numbersRe: Marc Friedman 12/15/14 09:19AM

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