Posted By: JoesMopar
School me on Open Chamber VS Closed - 02/06/11 04:23 AM
I know that closed chamber heads usually give you the compression and quench that you need/want. But mainly my question is, what is the point of running an open chamber head? It seems to me a closed chamber will do everything you want, so why ever use an open chamber? For example, I can see using it in a later 70's model car where they used lower compression ratios to run on lower octane gas etc....but why were they using them on performance cars in the 60's? Why use them today?
Posted By: ahy
Re: School me on Open Chamber VS Closed - 02/06/11 04:29 AM
One reason may be they are not too sensitive to manufacturing variation. Quench depends on precise tolerences. If you can't control deck height very well, for example, the open chamber design is more forgiving. MOPAR block machining in the late 60's/70's wasn't the best.
I believe the open camber head was also part of the emission reduction strategy of the day. Lower NOX perhaps.
Posted By: JoesMopar
Re: School me on Open Chamber VS Closed - 02/06/11 05:14 AM
But I thought a closed chamber would reduce emmissions more because of the more complete combustion?
Posted By: JoesMopar
Re: School me on Open Chamber VS Closed - 02/06/11 07:17 AM
I see, that makes sense. I didn't think they worried about that in the 60's though. So basically the point to open chambered heads is strictly emissions and nothing performance orientated whatsoever.
Posted By: superbeedave
Re: School me on Open Chamber VS Closed - 02/06/11 04:50 PM
So with that being said, The 10.1-1 compression that was advertised in 69 & 70 on the 383,440's with the 906 heads really wasn't true? More like 9.5-1. Would this be a true fact?
Posted By: DJVCuda
Re: School me on Open Chamber VS Closed - 02/06/11 04:54 PM
i measured 8.8:1 on an original 383 magnum motor we pulled out for rebuild.
Posted By: superbeedave
Re: School me on Open Chamber VS Closed - 02/06/11 05:11 PM
Could you imagine that back in 69 you bought a Superbee with a 383 magnum and you were under the impression that it was a true 10.1
engine only to find out it really was 9.0. They probably wouldn't
have sold as many as they did!
Posted By: joewhite440
Re: School me on Open Chamber VS Closed - 02/07/11 02:17 AM
Actually the 69 383Hp engines had a Positive deck. In other words the piston actually was above the block deck surface. I do not have my book in here but I believe the 67 440HP Pistons with the 915 closed chamber heads were at a lower deck than the 1969 and 70 440's with the open chamber heads. I am sure someone will chime in with the numbers. The deck differences is what kept the compression up on the 68/69/70 engines with the open chambered heads. if you punch the numbers into a Compression Calculator (Bore,Stroke, Head volume CC, +/- Effective Dome CC, Deck Clearance, Compressed Gasket thickness, number of cylinders). You will see the factory numbers are real close.
Posted By: can.al
Re: School me on Open Chamber VS Closed - 02/07/11 02:44 AM
..Was the manufacturers rating an NHRA limit?
i.e a 383 could be built to 10:1 for competition.
i think 10.5 340's were really around 9.5 if you do the math?
