daveintexas

When you rebuild your BBC, what is your determining factor on what CR to go with? Fuel octane availability? Fuel price? More HP? Keeping it stock? Wear / tear issues?

How many here run 10:1 compression on their n/a BBC? Seems like most OEM marine engines are 8.75 or so and I assume that is for 87 octane and possibility of poor quality gasoline. Does higher compression have anything to do with longevity as long as the correct octane fuel is used along with correct timing?

If you have aluminum heads and 93 octane availability is there any reason not to run 10:1 instead of 9:1 or 9.5 9.6 9.8 etc? Pro's Versus Con's

Thanks,
Dave

mikebrls

not sure but i think it will just make more power and nothing to do with reliability . but you will need to use good 93 octane gas all the time and hope u don't get any bad gas when u fill up or you mite have a boooom . the lower compression n/a motor from what i understand is more of a safety issue with fuel .
i think if you stay in the low 9's with your compression and use high octane gas you will be running more safe if you do get bad fuel .
i mite be all wrong on this and im sure one of the motor builder's on this site will chime in and give you a better idea.

mike

t500hps

I had modified 500efi's: 540's, iron heads, 9.8 compression. Trailered it so 93 wasn't an issue but the engines were more suseptible to bad fuel than those running sub 9:1. Compression added some power, and it sounded awesome!!!

Raylar

With aluminum cylinder heads, a good cooling system and a good ecm or carb and distributor tune, 10.0 to 1 should be not to much of a problem with 93 octane in a N/A engine. We do it with 496's all the time, but you must monitor and know when you have knock so you don't detonate badly and destroy a piston or two. In a 500 cubic inch big block this increase over 9.1 to 1 will add about 50Hp just from the compression change.

Best Regards,
Ray @ Raylar

Best Regards,
Raylar

BY U BOY

I was at 10.7:1 with Aluminum heads. Did it just for the power.

Philm

I run 10:1 with aluminum heads as well. Timing is important, but proper setup is even more important. Quench distance is very important. Too much and you will have detonation.

ezstriper

I think in a normal marine setup 10-1 not a good idea...will make more power, but a marine engine under a load all the time so detination always a fear...around where I boat 93 non-existant, 89 hard to find..87 the norm, so if have to fuel on the water, not going to be good..my opinion is that more timing on a 9-1 going to be better than less timing on 10-1..sure lots will voice thoughts...aluminum heads and running temp will effect what will live and what won't..as well as camshaft design..Rob

Centsless

im curious..... are there good octane boost products and do they work
the other question can someone do the fuel cocktail? like use 2 gallons of high 110 octane aviation gas to so many gallons of 87 reg gas to arrive at X octane

Rookie

iTrader: (4)

http://www.easyperformance.com/Tech_...d_Content.html

blackboat

Some of them discolor your plugs making it hard to read them.
I used to mix 10 gal. of 94 octane Sunoco with 5 gallon 110 octane racing gas and ran a cold plug ,made plenty power.
I ran a 10:1 motor with iron heads in a Donzi on straight high test at 32 to 34 degrees total timing for 5 years or so until I sold the boat.
I run a 11:1 bbc with aluminum heads now with no issues You do have to be careful ,there are certain limitations like not running for miles with your trim tabs in the down position !
There are a lot of good cam and motor combinations now that make plenty of power in the 9:1 to 9.7:1 range and would be a lot more practical to run on todays gas.