compression question

[hydroholic]

I have a merc 2.4 200 with some minor mods. Compression is 125psi across the board. I don't know what cc my heads are but I would like to bump up my compression some. What cc head would I need to raise my compression to around 140 or 145. I have been told that I could put on thinner head gaskets on and achieve more compression. How much more would that give me and does anyone have a part #? Also I still want to be able to run on pump gas, premium is fine but no additives or race fuel, so is 140 or 145 to much? If so how much is the max I can run on premium pump gas? Mods include bobs tuner, velocity stacks ,relieved exhaust (bobs offshore housing), low water pickup, bobs lightweight cowling ,6 inch jack plate and running a 26 small ear on a vector.Barely breaks 80 mph. I have run it with jack plate at different heights and also with no jack plate. Have went as low as 21 and as high as 28 on pitch. Fastest is with 26 small ear and jack plate all the way up. I see where people are running 2.4 200's on vectors and are running in the high 80's low 90's and have been told mine is also capable. My question is how? I have everything that I think I should have ( dual cable steering, solid mounts, hot foot, trim on wheel) and still just breaks 80. motor comes out of the hole strong and pulls strong all the way through with all props 26 and under untill it tops out at about 81. Whats wrong,and how can I get more speed without major mods or bigger motor, or is what I am being told a crock? Are those speeds not possible with a basically stock 200? Boat is dry and not overweighted. Has tank in rear, small cranking battery, two lightweight captains chairs in the front and small bench seat in rear. Please help , need more speed!

[sosmerc]

Sounds like everything you have done is in the right direction. I think you should go to thinner head gaskets with your goal being 135 PSI. If you can afford it, I'd also recommend a new stator and 2 new switchboxes and new Merc plug wires. Ditch the spark advance module and set your timing at 23-25 degrees. I'd also recommend checking your carb main jets to be sure you are running at least .082 mains. Do all your mods in stages and test along the way...otherwise you don't learn anything.
Prop for 6200-6400RPM.
Always post your engine block serial number when asking for part numbers or recommendations.
Have fun!!

[sosmerc]

Ya know, if you're really break'n 80 with a 26pitch, you are already doing less than 8% slip if you are presently turning 6400 or less with a 1.86 gear ratio. Not too shabby!!

[Fish]

Sounds like everything you have done is in the right direction. I think you should go to thinner head gaskets with your goal being 135 PSI. If you can afford it, I'd also recommend a new stator and 2 new switchboxes and new Merc plug wires. Ditch the spark advance module and set your timing at 23-25 degrees. I'd also recommend checking your carb main jets to be sure you are running at least .082 mains. Do all your mods in stages and test along the way...otherwise you don't learn anything.
Prop for 6200-6400RPM.
Always post your engine block serial number when asking for part numbers or recommendations.
Have fun!!

What he said. Also, to answer the other Q, I beleive heads cut to 34cc will give you around 140-145 psi and still allow 93 pump gas.

[hydroholic]

Thanks guys for the info, will try some of the things you suggested. Already have new switch boxes and stator, but probably need to change plug wires. Will do away with spark advance and re-set timing. Any one know where I can get a set of 34 cc heads for a 2.4 200 fairly cheap?

[mod25]

You could send your heads to Jay Smith and have them cut to 34 CC and have them back in a week or less.

[T-REX]

My stock 88 chrome bore 200 haz 34cc heads and it has 135#s...If Your ports are raised, then your comp may rise slower with the same cc's....30cc heads usually put me rite at 150#s...and that is straddl'in tha fence!!

[Jay Smith]

I target 145 and most of the time 34 CC with the thicker 44 series head gasket works on a 2.5 the 2.4 seem to need more cut off to achieve that 145 target. I would think 32 CCs would be on the money !

[rock]

I have run 2.4 motors with 30cc heads and they live for a while. I think 32 would be safe for 93 octane. Is your 200 a verticle or a horizontal motor?
Rock

[hydroholic]

Motor is a horizontal. Wanting to stay around 140 psi , no more. Not wanting detination problems.Use mine to joy ride with the very often haul but runs.

[T-REX]

140#s...33cc's should do what U want...Thats a lot ov action for 5#s ov squeeze...I don't thank U will see much(If any) differnce wit 5#s, at leest not for tha money spent....If your motor sealz good, U may even see 138 to 140#s wit the 34cc heads...Use the thinner Head gaskets on the 34cc headz, and see what U git.,..The differnce between the thick and thin gaskets wuz worth 10#s(+ / -) on my motor...juss food fer thought!! :confused: