Raising compression ratio

Greener101 · Post by **Greener101** » Fri Oct 19, 2012 9:00 am

I will soon start the rebuild of my 1962 CA77E 305.Upon completion I plan to utilize both fuel injection and a high energy ignition.I am considering raising the compression ratio to 9.0-9.5.Can someone steer me to the best path to this end?I would like to do this with just a piston swap.BTW, a PO has been in the engine previously so I plan a complete rebuild as I do not trust his competency.Greener

Greener101 · Post by **Greener101** » Sat Oct 20, 2012 4:13 pm

Is this change not possible?Does anyone know of a person who I can message directly?I was hoping someone else had accomplished this feat and knew of the best and cheapest route to this end.Thanks for looking.Greener

Ford Guy · Post by **Ford Guy** » Sat Oct 20, 2012 7:09 pm

Piston swap would be the easiest. May I ask why you would want to raise the compression ratio?

Greener101 · Post by **Greener101** » Sat Oct 20, 2012 8:37 pm

Ford Guy,Anticipated miles will be nearly all divided four-lane highway.I believe the higher compression will be more efficient, allowing a crisper response for passing(when necessary) .Greener

G-Man · Post by **G-Man** » Sun Oct 21, 2012 2:07 am

Greener

The CA combustion chamber is larger than the CB/CL so you cannot use those pistons to get higher CR. You need to find another similar 60mm piston with a higher dome. CB750 pistons are larger bore but have a flat top so they won't work.

British pistons will have a bigger gudgeon pin diameter and be heavier. Might be easier to skim a little off barrel or head but then you need to look out for clearance problems.

If you can find a set of the early 4-ring Dream pistons, they are supposed to give 9.5:1 so you might be lucky. Not sure why the 4-ring (266-010) piston was superseded but weight and friction would have been considerations.

Then again, you could try these......

http://www.ebay.co.uk/itm/NOS-Honda-CB7 ... 43b4b4fa66

Good luck.

G

Greener101 · Post by **Greener101** » Sun Oct 21, 2012 4:48 am

Thanks G-man for the information.The compression is a lot higher than I was looking for,but I will look into shaving the dome to reduce the ratio to something more to my liking.This will at-least give me somewhere to start.How early are the 4 ring Dream piston?When you use the term Dream,which Dream do you mean ?I ask this because some refer many bikes as Dreams just like many refer any Honda 305 as a CA77.Greener

G-Man · Post by **G-Man** » Sun Oct 21, 2012 6:43 am

Greener

The 4-ring pistons were used on 1960 C72 and C77, I think. May have been used on C71 / C76 too. I have a single NOS C72 one.

G

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Raising compression ratio

Raising compression ratio