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Compression Ratio On A 266 Cam


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#1 Minigman

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Posted 27 November 2019 - 06:55 PM

What’s the max compression ratio you can run with a 266 cam please?

#2 ACDodd

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Posted 27 November 2019 - 07:02 PM

I would build it to run at 9.75:1.

Ac

#3 Minigman

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Posted 27 November 2019 - 07:36 PM

If I end up having the head chambers changed to that CR I’ll buy your RS one AC. Having just spent a small fortune on it I’m trying to lessen the cam effect whilst keeping the CR at 10.5:1. Sounds like it could be mission impossible.

Edited by Minigman, 27 November 2019 - 08:18 PM.


#4 Moke Spider

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Posted 27 November 2019 - 10:08 PM

What Engine have you got ?

 

And what fuels are you happy to run with?



#5 dotmatrix

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Posted 27 November 2019 - 10:25 PM

I build a 10.5:1 998cc with a kent 266 and it was very pingy. took about 1cc out of the chamber after this which brought the compression down to where it was more acceptable regarding ping



#6 DeadSquare

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Posted 27 November 2019 - 11:01 PM

45 years ago, before "Secret black boxes" did things to the engine, we could buy 105 Octane petrol at any garage which could take 11.5:1 in a race engine, but with today's unleaded stuff, 10:1 is pushing it.



#7 Minigman

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Posted 27 November 2019 - 11:53 PM

What Engine have you got ?

And what fuels are you happy to run with?


It’s a 1330. I run RON98 with an additive booster.

#8 Moke Spider

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Posted 28 November 2019 - 04:51 AM

 

What Engine have you got ?

And what fuels are you happy to run with?


It’s a 1330. I run RON98 with an additive booster.

 

 

Assuming you have the Cam Timed to 106 Degrees, I've calculated the optimum Static CR to be 9.69:1.



#9 luismx123

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Posted 28 November 2019 - 06:56 AM

 

 

What Engine have you got ?

And what fuels are you happy to run with?


It’s a 1330. I run RON98 with an additive booster.

 

 

Assuming you have the Cam Timed to 106 Degrees, I've calculated the optimum Static CR to be 9.69:1.

 

 

how does one calculate an optimum CR? Im really interested as my 998 is going in for a rebuild this winter with a 12g295 ported head and possibly a SW5 or ac dodd Rs/rs+ (lets see) and since the 295 head is unskimmed it would be good to know whats ideal. Planning on using 98-100 gas here in Austria. Yes I know i should consult the engine builder but its good to get other inputs ;)



#10 andyapanel

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Posted 28 November 2019 - 08:41 AM

I ran a 1098 with a 295 head and 266 cam with 9.5 CR

It was very torquey, but a bit thirsty. 

No probs with pinking or running on.



#11 DeadSquare

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Posted 28 November 2019 - 09:58 AM

I ran a 1098 with a 295 head and 266 cam with 9.5 CR

It was very torquey, but a bit thirsty. 

No probs with pinking or running on.

 

I once heard LJK Setright give a wide ranging talk about engines, and Octane/Pinking was one of the subsequent questions asked.

 

He espoused the idea that the piston speed of a long stroke engine made the combustion gasses less likely to pre-ignite.



#12 Minigman

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Posted 28 November 2019 - 10:27 AM


What Engine have you got ?

And what fuels are you happy to run with?

It’s a 1330. I run RON98 with an additive booster.

Assuming you have the Cam Timed to 106 Degrees, I've calculated the optimum Static CR to be 9.69:1.

So days of the 10+:1 CR is well and truly over then. I’ve never had an engine built below that before. I think the head will have to be sent off again for further chamber mods. I’ve calculated to go from 10.5 to 9.75 is 3.1cc difference, so quite a bit to be ‘scooped’ out.

#13 DeadSquare

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Posted 28 November 2019 - 10:44 AM

 

 

 

What Engine have you got ?

And what fuels are you happy to run with?

It’s a 1330. I run RON98 with an additive booster.

Assuming you have the Cam Timed to 106 Degrees, I've calculated the optimum Static CR to be 9.69:1.

So days of the 10+:1 CR is well and truly over then. I’ve never had an engine built below that before. I think the head will have to be sent off again for further chamber mods. I’ve calculated to go from 10.5 to 9.75 is 3.1cc difference, so quite a bit to be ‘scooped’ out.

 

 

Just fit two best quality gaskets.



#14 OzOAP

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Posted 28 November 2019 - 10:48 AM

I would build it to run at 9.75:1.

Ac


Spot on

#15 Moke Spider

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Posted 28 November 2019 - 10:53 AM

 

 

 

What Engine have you got ?

And what fuels are you happy to run with?

It’s a 1330. I run RON98 with an additive booster.

Assuming you have the Cam Timed to 106 Degrees, I've calculated the optimum Static CR to be 9.69:1.

So days of the 10+:1 CR is well and truly over then. I’ve never had an engine built below that before. I think the head will have to be sent off again for further chamber mods. I’ve calculated to go from 10.5 to 9.75 is 3.1cc difference, so quite a bit to be ‘scooped’ out.

 

 

Not necessarily.

It depends on the Cam and the Crank Angle that the Inlet closes at.

 

Longer duration Cams need higher Static Compression Ratios.






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