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Thread: 18RG destroking...

  1. #1
    Forum Member
    Join Date
    Apr 2016

    Default 18RG destroking...

    Hey guys,

    I've finally got my hands on an 18RGU for the 71 Corona, and I've been tossing an idea around in my head, and wanted some advice.

    The car currently has a 6R (1700cc) which is a destroked, debored 18R. I was thinking of using the crank and rods from the 6R in the 18RGU with 92.5mm pistons. This would keep the engine almost 2000cc, but should be much more rev happy.

    I've done the calculations, and piston speed would be the same at 6500rpm as a normal 18R at 6000rpm.

    Any thoughts on whether this would be a good idea, or a stupid waste of time?

    Also, if anyone knows if the piston pins are at the same height on both motors. I heard a rumour once that they kept the same conrods, and moved where the piston pin was on the piston, which would make the whole expedition pointless...

    Thanks for any ideas or info!!!

  2. #2
    Junior Member Backyard Mechanic
    Join Date
    Sep 2007

    Default Re: 18RG destroking...

    I believe that you are on to something, however, the 8R and 18R use the same crank different bore, same stroke.

    You would need to measure the length of the front of that 6R crank and the sizes of the turn down to see if it is long enough for the 8-RC or 18RG application.

    How about the 6R crank specs, what is the stoke on that engine?
    Found it 86.0 x 73.5 for the1700cc DX model and 1700 SL
    1.707 liter engine.

    Now I took a 8R block and bored it up to the standard size for the 18RG stock pistons, but not as high as you are going. I have also had my 18RG block bored to 92mm which is currently still on the engine stand awaiting installation. I do know that I as warned about the walls being too thin now and that it could be porous.

    8R bored to 88.5mm

    18RG bored to 92mm

    Last edited by 73GTV; 22-11-2019 at 01:41 PM.

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