Reducing 4.6 RV8 compression ratio

General Chat About Exhaust, Cylinder Heads, Fuel Systems And Intake

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ratwing
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Post by ratwing »

sidecar wrote:Personally I would not use clay or anything like that when trying to work out the chamber volume, just use water and a plate of Perspex, you also need a burette, you can get plastic ones off ebay fro a few quid, I have a glass one and I can tell you that you only have to look at them in a funny way and they break!

You can also burette the pistons at TDC, use some grease around the top of the bore to seal the piston. Finally once you know the head gasket thickness its just some maths the work out the CR.
My plan was to make a plasticine head so I could see how much I can remove rather than just attack the actual heads with a die grinder and keep my fingers crossed, I realise it won't be accurate but hopefully it'll give me some idea if I can remove enough metal. Or if thicker gaskets would do the trick.
Before retiring I used to work in a lab and yes you're right, you have to be careful with glass burettes especially if they've got a glass tap.



ratwing
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Post by ratwing »

stevieturbo wrote:Are you sure spark timing is correct ?

Yes, has been checked by someone else and they agreed with my readings.

Are you sure valve timing is correct ?

Yes, double checked when building the engine - the cam sprocket has 3 keyways and I used the middle one which seems to give the same timing as the standard morse chain & sprockets. It's a standard 3.9 cam and I did have to shim the rocker pedestals up (but can't remember how much)

What sort of compression are you seeing on a compression test ?
I haven't tried this, I'll see if I can borrow a tester (mine broke and I've only had it 42 years) and see what I get.
Will it tell me anything useful though?

stevieturbo
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Post by stevieturbo »

ratwing wrote:
I haven't tried this, I'll see if I can borrow a tester (mine broke and I've only had it 42 years) and see what I get.
Will it tell me anything useful though?
If it's extremely high, then I'd expect compression pressure to also be a bit higher than might be normal for such an engine

But always confirm ignition timing is where you actually think it is, especially if something seems strange.
9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

ratwing
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Post by ratwing »

stevieturbo wrote: But always confirm ignition timing is where you actually think it is, especially if something seems strange.
Good point, wouldn't hurt to check it again.

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