Reply With QuoteHi milkmoney ,I'll generalize a little. If your going to run pump gas your static comp ratio has to be low enougph (8.5-9.5 to1) to stuff er in. BTW WHAT DID YA BUY. Damn milk guys first our wives then they need a blower.
is it true that a 454 bbc with a blower can and or does run lower ratio like between 7to1 and 8to1 and runs on 91 pump gas .. i thought blower motors run highr ratio and use higher octane fuel..????? aliitle confused.. please help so i dont blow anything up thanks...
Hi milkmoney ,I'll generalize a little. If your going to run pump gas your static comp ratio has to be low enougph (8.5-9.5 to1) to stuff er in. BTW WHAT DID YA BUY. Damn milk guys first our wives then they need a blower.
didnt buy yet looking at this boat.. the guy said it has 7.75 to 1 is that real or true.. 871 blower.. thanks es we are still taking them all..
7.75 to 1, on pump sounds realistic to me. Let us know. pics!! How much boost?
Depends on how much boost the motor is making.
Boosted engines run lower compression ratios because the intake air is already under pressure. That way, the cylinder pressure at top dead center in a boosted engine is about the same pressure as a higher compression engine without a blower. The big difference is, the boosted engine has a larger volume of air and fuel waiting to be lit off. The high compression engine has just a little bit of air and fuel ready to be lit off, making a weaker pop. (That's why the high compression engine needs to turn lots of RPM to the power of a lower RPM boosted engine.)
So, the lower the compression ratio, the more fuel and air that can be stuffed into the combustion chamber under boost.
You can only have a certain amount of cylinder pressure at TDC with gasoline. If your boost is high, you want the compression ratio low.
If you have no boost, you can have the compression ratio high.
How high? That's up to the fuel. 87 octane burns really fast and it can light off just from the heat generated during the compression stroke. 87 octane in a boosted engine is a BAD idea. 92 octane burns slower, allowing you to run a little higher boost before the fuel lights itself off without the help of the spark plug. Alcohol burns even slower, allowing more boost or higher compression ratio.
Alky is the way to go with a blower because it is easy to tune.
7-8:1 should be fine for a blown 454 on 92 pump gas with aluminum heads but I would keep the boost low and the jetting a little rich until you get to know the engine well.
These are generalities. Cam, heads, blower drive ratios, timing, fuel blends, intake temperature and so many other variables come into play to make the setup work or not work.
We like to see about 8.5 comp, if you go too low,unboosted efficiency suffers. On a PROPERLY set up blower deal(carbs boost referenced and distributor curved for the blower), 8-10 lbs is fine with regular 87 octane pump swill. I run 11+ lbs, but mine is intercooled, still on 87 fuel. At 121+ mph. On your first rodeo, get help from someone knowlegable. Before taking advice, check out what the advisor HAS for a motor. TIMINATOR
We like to see about 8.5 comp, if you go too low,unboosted efficiency suffers. On a PROPERLY set up blower deal(carbs boost referenced and distributor curved for the blower), 8-10 lbs is fine with regular 87 octane pump swill. I run 11+ lbs, but mine is intercooled, still on 87 fuel. At 121+ mph. On your first rodeo, get help from someone knowlegable. Before taking advice, check out what the advisor HAS for a motor. TIMINATOR
And that's probably flat top pistons on a 454 with 118cc heads? Tim, that's good to know about the 87 octane! That's gotta be a nice recipe with a tight tune to boot. That's a bit risky for somewhat of a beginer, like myself. Most of my experience is with smaller car engines.
Tim, I'll be bugging you more when it comes time to decide on parts for my blown 496.
-Chuck
h20 i will let you know and will do pics, getting some this weekend... and to everyone else thanks alot that info is very helpful and i might be hitting you guys up for some more ? when i get closer..thanks agin..
I'd love to see it. A couple of weeks ago on blowers I started a thread in blower called ideal static compression ratio because I want to learn more before I take the "blower step". Sounds like the old school way is 8 or so to 1 and the new school is 9.5 or so to one. There was some pretty interesting points made IMO for both sides.
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