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Thread: Two valve crossflow, wide angle combustion chamber design. Which design is superior?

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    Two valve crossflow, wide angle combustion chamber design. Which design is superior?

    Hello all,

    This is just for learning purposes. All photos stolen online.

    This here is an 18rg combustion chamber. As you know, it the legendary twin cam 8V wide angle Toyota engine from the 70's. The other one being the 2TG (also pictured).
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    2TG
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    If you only had a pic of the combustion chamber alone, you might be hard pressed to tell them apart. In short, they share the same smooth dome, hemispherical heads.
    (2tG)
    Click image for larger version. 

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    Also apparent is how they have a perfectly circular squish area all around the chamber.

    In order to get high compression out of these hemi heads, you need a fairly large dome on a piston. Like so.
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    Fast forward to the late 70's and early 80's, and Toyota comes up with the 5MGE. Still a DOHC 2valve per cylinder wide angle design (for a total of 12 valves on a six cylinder), but notice the different combustion chamber.
    Click image for larger version. 

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    Up close you can see how it is not hemi, with ridges and much larger quench areas.
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    Still, the wide angle of the valves means that you still need a fairly large dome on a high compression piston. However, it is visibly smaller than an 18rg or 2tg high dome piston.
    Click image for larger version. 

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    These were advertised as Venolia high comp pistons.



    So here's a question:

    For all out NA, and you have to stick with 2 valve per cylinder (let's say it's for vintage racing, so no engine swaps that were never factory offered anywhere in the world), and you could either machine out the 5MGE's ridged and quenched cylinder head to smooth it out so you could run an all out NA 5MGE Supra with giant ass domed pistons... OR weld up and cnc machine an 18RG Hemi head so you could run an all out NA 18RG Celica with a more subdued dome on the piston, which is the better chamber design?

    Why?

    Pls. mention advantages and disadvantages of each design regarding valve shrouding, quench, piston dome height quench, susceptibility to detonation and whatever else you can think of.



    Welding and remachining chambers is a thing I just learned. He does explain why quench is superior to giant domes. But he uses capslock...

    https://www.facebook.com/BenAlamedaR...type=3&theater
    Last edited by randedge; 07-14-2018 at 06:22 PM.
    I am Randy's desire to go faster.

    1988 Toyota MR2 Hardtop NA - Sold and sorely missed
    1992 RHD Mitsubishi Lancer Evolution 1 disguised as a III - I'm not actually that big of a JDM fanboy.

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