[Diy_efi] Combustion chamber question

[Tlsalt at aol.com]

Perry Harrington wrote,

> Here's a question for the gurus of the list.  I was under the impression
that
> hemi heads are the best WRT detonation and power.  However a response
countered
> that.
>
> So, here's the question:  How does Honda make 183HP per liter with 12:1 CR
> on the CBR600 engine?  I understand that RPM is more of an affect on the
HP/l,
> but running 12:1 on pump gas without detonation is impressive.
>
> Perhaps someone could shed some light on this?

Hello Perry,

The CBR600 is a 4 valve pent roof head not a hemi. The VIA is much narrower 
than on a hemi (30 degrees versus 70-90 degrees) resulting in a compact 
combustion chamber and high compression with flat top pistons. Hemi heads 
need high dome pistons to get high compression, resulting in a long narrow 
combustion chamber at TDC that is prone to detonation.  I have an injected 
hemi head Jaguar XK engine with 9:1 compression that has huge domes on the 
pistons that shroud the intake at TDC.  It ran 36 BTDC timing from the 
factory, but it will make power out to 44 if you live near an airport.  If 
you want to get big valves in a hemi you have to widen the VIA out toward 90 
degrees, worsening the problem. Honda published some SAE papers in the early 
sixties about combustion chambers, detonation and very high rpm (20,000rpm) 
that make interesting reading. 

Paul

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