8.8 or 9.5 CR
 

Building two 454's for my heavy ass Formula 302SR1. Original 330hp now more. Is 9.5 too much CR for todays gas 90 octane? Should I stick with 8.8CR or less. Is the small difference even worth considering. Flat top Kieth Black with 100 cc chambers at 9.5 CR, flat top Power Plus pistons, same chamber size 8.8CR.

Re: 8.8 or 9.5 CR
 

8.8 to 9.5 isn't exactley a small diffrence, It's not huge but it aint small. I would go with the 8.8 and run cheap fuel for now. When your ready for more just add vortechs or whipples and there ya go.

Re: 8.8 or 9.5 CR
 

I rebuilt my 500's this winter and went with a little ove 9.5 CR and will have to run 93 all the time but the torque is incredible.

Re: 8.8 or 9.5 CR
 

The engines in my Bullet are 9.6 to 1 502's and I run 93 octane in it with 36 degrees total timing.

Re: 8.8 or 9.5 CR
 

Of course it is YOUR choice, but if you are running cast iron heads I would run the lower (8.8cr) as compared to 9.5cr-----especially while running cast iron heads! Use good fuel----the gas should be the cheapest part of boating, especially if you're thinking about skimping on using good fuel, and take the chance of burning your engine(s) down! That's when it REALLY starts costing you money!!! :(

Re: 8.8 or 9.5 CR
 

my 454's are 9.5 to 1 and I run 89 octain fuel...no issues.

Re: 8.8 or 9.5 CR
 

Are you running aluminum heads Dyno?

BT

Re: 8.8 or 9.5 CR
 

Its probably important here for us "motor heads" to remember that octane numbers alone are not always a good measure of "better fuel".I have tested and seen lots of fuel being sold as 91 or 92 octane that tested no better than 87 to 89. It really depends on the refiner and blending of additives in your particular region or supply chain. As an engine builder and developer I will tell you that almost every different combination of BBC motors depending on not only compression differences, cams, stroke, bore, piston type, combustion chamber type and size and ignition systems can see entirely different results on different fuel types and octane levels. Remember that octane level tends to control how fast the burn takes place and not always whether you will have knock or ping. Compression ratio changes can have significant affects on power and you can still have knock issues with 8.5 to 1 compression ratios even with 91 or 92 octane fuel if other engine factors are creating the issue. You will have to cross check with others who have been running a very similar engine spec.in your "fuel zone" such as actual cylinder head used. cam spec and timing settings needed for good power before you just make a compression decision based on octane "numbers"
Just my thoughts,

Ray @ Raylar

Re: 8.8 or 9.5 CR
 

Dyno has iron Merlin oval-port heads and his combination gives him a touch over 9.5:1. He sets the timing at 32 degrees and hasn't had any issues with 89 octane fuel. Same with his friend SuperV, who has the identical engine components except for forged pistons and Lightning headers. SuperV's engines turned 505 chp on the dyno with 89-octane fuel.