• Welcome to the Checkmate Community Forums forums.

    You are currently viewing our boards as a guest which gives you limited access to view most discussions, articles and access to our other FREE features.
    By joining our free community you will be able to:

    » Interact with over 10,000 Checkmate Fanatics from around the world!
    » Post topics and messages
    » Post and view photos
    » Communicate privately with other members
    » Access our extensive gallery of old Checkmate brochures located in our Media Gallery
    » Browse the various pictures in our Checkmate photo gallery

    Registration is fast, simple and absolutely free so please, join our community today!

    If you have any problems with the registration process or your account login, please contact support by clicking here or by using the"contact us" link at the bottom of the page.

Compression

dreamer

dreamer

Member
I have an opportunity to buy a boat with a newly built 454. the boat is running in the mid 400's for horsepower. The boat needs to run 91+octane or it will have problems due to the high compression. What can I do to lower the compression the easiest. the boat is a checkmate enforcer. the moter is all balanced b.grumpy heads emi thunder captains call. edlbrock cARB. Boat is mint I just don't want SUCH a hugh maintenance motor. How can I tone it down.
 
Your best bet is to contact the engine builder and tell him what you want to do. If he's good, he can give you tips to modify the engine to do whatever you want.
 
Changing compression on a motor that is already assembled and running is difficult. At the very least, you would have to pull the heads and put thicker head gaskets in. This all depends on what the compression is now. There is only so much you can do by changing gaskets. It also depends on what gaskets are in there now. What is the compression?? You need to get the build sheet for that motor to know for sure what can be done.
 
Im going to buy the boat anyway so I wilkl deal with it when I get it. the guy has all the engine info., I just thought there might be some kind of quick or inexpensive fix. My other worry is that it has an alpha drive and we know that they don't handle horsepower well. I will baby it this year and then see what I or the engine builder can do. The motor was build by a company that builds racing motors so it was done right no expenses spared.
 
Not sure aluminum I believe. The motor has been used for two years with no problems. about 50 hours on the rebuild.
 
It is possible that this motor is detonating without you even knowing. Between the wind and engine noise, you may not hear it detonating. The best advice I can give you is to set the carb up rich, keep the timing reasonable, I would say no more than 33*. Keep an eye on the plugs. The addition of a knock guage may be a good idea as well.
I dont know why some builders choose to build marine motors with that high a compression. It doesnt make sense. The amount of power increase from the additional compression isnt worth it.
Aluminum heads are more forgiving to higher compression than steel. The reason being is that they suck up more of the heat generated by combustion than steel heads. Basically, they act as a giant heat sink.
 
Vinnie, Detonating? Do you mean miss firing. Im going to run this motor this summer and then see what I can do to tone it down. Would be more cost efficient to pull this motor and sell it then buy a new one?? Or just down grade this one. This thing also sucks gas like crazy a gallon a minute a wot. Runs to 5300 max. I need to get better gas milage.
 
My personal reccomendation... run it the way it is.. its well understood that gas is expensive, and only getting more expensive.. My experience with big blocks, (even stock) rely on quality fuel.. you can detonate a big block in a hurry running hard on poor quality fuel..

I don't see the compression ratio changing your maintenance cost, its not related to oil changes, tune ups, fuel filters, inspecting hoses, and all the fun stuff that comes along with performance boating. preventive maintenance is the key to keeping any engine running.. Unfortuneatly, most owners turn the key and run the dog crap out of em, then, can't figure out why there blowing drives, or dropping valves, and the best one is running 5000 rpm+ 2-3 qts of oil low..

heres what i would reccomend you do before you slam it in the water and go run...

1. drive service,,,,, change the gear lube, grease the prop shaft.. pull the drive, inspect the bellows, gimball brg, engine coupler, ujoints, and engine alignment. grease the engine coupler, ujoints, and gimball brg.. and in the alpha, inspect the h2o pump, or just change it out.. (that way you know its new for the season. )

2. inspect spark plugs, wires, distrib cap &rotor.. replace as necessary, look for running rust trails, or corrosion at hose destinations.

3. inspect the exhaust system, look for running rust trails. or pull the riser and look down inside the manifolds for water intrusion.

4. inspect all the belts,

5. inspect wiring harness make sure everything is hooked up, grounds clean and tight..

6. check your trim pump for proper fluid levels, and that the soliniods are not all corroded up..

7. Check battery level

8. engine oil and filter change... (fuel filter too)

This may seem a lil excessive, but not only will you learn your engine compartment... you'll find any lil problem that may turn into an ugly monster when your 20 miles away from the dock ... (and my luck have a nasty storm bearing down on me) Once this is done, however, you should be able to run the rest of the season trouble free.. with just routine inspection/maintanence...
 
NICE ADVISE GUYS!!!

They are on the money... poor fuel (87 or 89 octane) will cause pre-ignition (spark knock). It can and eventially lead to cracked rings, melted pistons or valves, etc. At 10 to 1, you are really on the edge with tuning for 91 octane, and jetting and timing are critical. I have done a few dyno pulls with a 10 to 1 502 motor running on 89 octane, but really had to play with jetting and timing to keep the EGT (exhaust gas temp) safe and no spark-knock under load. Interestingly, about 15 horsepower falls off on the 89 octane as well as crappier fuel economy! Your better off running good fuel and taking advanbtage of the better power, safer running (no knock), and getter fuel ecomony of a higher compression motor!
Good luck and enjoy that sweet boat! :banana: Jim
 
I wouldn't bet your motor on this but I believe some are adding Toulene to their gas to up the octane. I was reading a post (can't remember where) that toulene is added by the gas manufacturers to up the octane as it is, and it supposedely it is safe for the motor. I guess the stuff is fairly cheap and goes a long way, and is readily available at finer hardware stores. Food for thought, but I have no experience with it. Might be something you may want to keep handy in case you are out on the water and have no access to good fuel, and must use lower octane dock fuel.
 
Toulene you find in many paint/chemical stores as a paint thinner. It has an octane rating of 114 so thus when you mix it with gas in different quantities you can boost the octane level.
 
Yeah but the difference in price of 93 and 87 never makes it more cost efficient. If you don't need to boost into the high 90's it seems the only reason to use it would be if you are on the water and can only get 87.
 
CAREFULL...

That stuff can do funky stuff to PLASTIC fuel system parts!

We did that as kids to the snowmobiles we were "racing"...
now that I think of it, that was probably fatel to the 2-strokes we were running! Be safe and run the better gas! You can always do the 5 gallons of turbo blue to a tank of 87 for your own "blend" at the lake.
 
You must log in or register to reply here.
Back
Top