engine compression

[toolsinbox]

What is the scoop with compression. what are the differences from a car to a boat. for example 10 to 1 .... is that not a good set up for a boat? 8 to 1 is what the manual shows for a 454. what would be the draw backs if you ran a higher compression?

Thanks

 

[HT32BSX115]

Re: engine compression

What is the scoop with compression. what are the differences from a car to a boat. for example 10 to 1 .... is that not a good set up for a boat? 8 to 1 is what the manual shows for a 454. what would be the draw backs if you ran a higher compression?

Thanks

Well, I read your other thread on the Scarab.....WOW. I am floored that the seller would pay for all the "fix"

Hi compression. Well, most boats don't use high compression engines because they're not "cammed" for a lot of torque at low RPMS. High compression engines like to run HI RPMS. Stern drives are good up to about 5000-5500 RPM.

Also, if that engine is "CAMMED" to make a LOT of HP at high RPM you *could* have a reversion problem. if so, You absolutely want to ensure that your exhaust doesn't get water in it from waves or you could suck some water into an exhaust port and hydrolock the engine.....

Maybe the engine builder thought of all this stuff when selecting the camshaft.....


I hate to be the one to tell you this but it sounds like you're going to put a seriously tricked engine in front of an Alpha drive.....

Several people will tell you that the Alphas are really only good for up to about 300hp +/-

A lot more than 300hp in rough numbers WILL break an Alpha if it isn't treated really "nice"....

Mercruiser put the (roughly 330hp) 454 in front of Alphas only for a couple of years or so and then came out with the Bravo. They stopped using the Alpha with the 454 in short order.

A LOT of people will tell you that they're running a lot of HP with an Alpha. Most will also say that they don't do full throttle starts or WOT (Wide Open Throttle) runs.

If you have 10:1 pistons you WILL HAVE to run premium gasoline. If you run regular you won't run it for long.......


There's more to this stuff....I've hit the highlights.....



Cheers,


Rick

 

[toolsinbox]

Re: engine compression

I was warned about that in my first post when I discribed my purchase. my two main upgrades for the future, captian call exaust and a bravo package. I think I am liking the "dial down" process that the engine shop is doing. There is a guy near me selling a complete bravo setup from the engine back with sea pump for 2500 bucks. Maby save my pennies this winter.

 

[HT32BSX115]

Re: engine compression

That might be your best bet I'm afraid.

Just be gentle with the Alpha and it'll still be worth something when you pull it!

 

[mkast]

Re: engine compression

What is the scoop with compression. what are the differences from a car to a boat. for example 10 to 1 .... is that not a good set up for a boat? 8 to 1 is what the manual shows for a 454. what would be the draw backs if you ran a higher compression?

One word, reliability.
I can put an 8:1 compression engine into the hull and NEVER worry about it.
The engine has adequate performance for the grandmother that only use the boat to go to church on Sunday, and the guy who wants to go cruising. This way both individuals are happy, an as the manufacturer I don't have to deal with the pain of broken engines.
The military used 6:1 compression four cylinder engines in their 3/4 ton trucks simply because they always started. You can't climb hills at 45 mph, but they always started and ran.
Mercruiser will sell how many engines in a year??? Of the ten or twenty that want more performance they are told to go to Mercruiser Racing, the rest will be more than happy with the engines offered. It's all about numbers.