<VV> What is squish?

[Joel McGregor]

2-strokes do make the most power with the leanest possible mixture.  I guess that is another way they behave differently from 4-strokes.  More questions...

-----Original Message-----
From: Jim Davis [mailto:jld at wk.net] 
Sent: Tuesday, August 11, 2015 10:58 AM
To: Joel McGregor
Subject: Re: <VV> What is squish?

Just a guess but I would say it is because of the port design.  Two cycles are designed for undercharging to prevent to help with fuel economy and excessive lean charges.  The transfer ports are designed to promotes swirl in the chamber.  Squish  increases tumble and the tumble probably defeats the effects of the intended swirl.  Of course that was before active intake valving and rotary valving.

In my old racing days, I remember the EXTs always ram the best on the edge of lean detonation.  Sometimes to win the race, you had to sacrifice a couple pistons.
Jim Davis


  8/11/2015 9:59 AM, Joel McGregor via VirtualVairs wrote:
> Does anyone know why squish decreased detonation in 4 strokes and increases it in 2 strokes?  Is it because the symmetrical way a 2 stroke head is generally made causes everything to collide in the middle?
> I know from experience that it's very easy to get too much squish velocity in a 2 stroke and have serious detonation problems.
> Joel McGregor
>
> -----Original Message-----
> From: VirtualVairs [mailto:virtualvairs-bounces at corvair.org] On Behalf 
> Of Matt Nall via VirtualVairs
> Subject: Re: <VV> What is squish?
>
> To add to what mark wrote.....which by the way is "Compression ratio".......
>
>
> "Squish"  in a Corvair head with the STEP  in it...as do most  engines  
> versus an "open Chamber" [ in our case  Smog heads with domed pistons  
> and some early low hp engines ]
>
>
> Is the distance between the "step"  and the top of the piston....... factory is usually approx. 0.080"
>
>
> By  decreasing this to approx 0.040"   you  get less pinging......yet have higher compression!  win win!
>
>
> Matt Nall
> Charleston, Oregon
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