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Old 14-05-2006, 04:35 PM   #1
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Skimming heads

Is it worth it?? What sort of gains do you think I could get and how much would I need to take off?

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Old 14-05-2006, 05:16 PM   #2
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only done it to a four stroke, made the tiniest difference, not sure about the power increase youll get out of a 2 stroke. The question you gotta ask yourself is that do you want to spend hours going back and forth over a sheet of glass and wet dry paper? or are you gonna get someone to do it?

oh and the max I skimmed this four stroke was just under a mm. I am not sure how a 2 stroke would react to that. I would like to know myself for interests sake what people say on here.


Oh and I am assuming you mean the head to your engine block right? you could mean skimming milk for all I know but I thought I would go off on one
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Old 14-05-2006, 05:41 PM   #3
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Quote:
Originally posted by divertom
only done it to a four stroke, made the tiniest difference, not sure about the power increase youll get out of a 2 stroke. The question you gotta ask yourself is that do you want to spend hours going back and forth over a sheet of glass and wet dry paper? or are you gonna get someone to do it?

oh and the max I skimmed this four stroke was just under a mm. I am not sure how a 2 stroke would react to that. I would like to know myself for interests sake what people say on here.


Oh and I am assuming you mean the head to your engine block right? you could mean skimming milk for all I know but I thought I would go off on one
Are you mad!!
If you think I`d sit doing it with wet and dry for ever and a day you must be!
I would get it done properly if I could gain anything from it.
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Old 14-05-2006, 05:50 PM   #4
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1mm is alot aint it?
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Old 14-05-2006, 05:52 PM   #5
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Dan, I'm sure if you looked up "performance heads" for Merc 2.0,2.4,2.5L on Google;

you'd get some specs to compare std ones ton and then you'll be able to make an educated choice as to "skimmings" merits.

I always thought the "done thing"was to bung XR2 heads on a 2.5................ as to why? I have no idea!
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Old 14-05-2006, 06:08 PM   #6
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Raising the compression on your engine is the cheapest mod you can do to get more hp.
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Old 14-05-2006, 06:15 PM   #7
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Quote:
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Raising the compression on your engine is the cheapest mod you can do to get more hp.
Any idea how much should come off? And what gain (hp/mph) I could expect to see?
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Old 14-05-2006, 06:22 PM   #8
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Quote:
Originally posted by Dan
Any idea how much should come off? And what gain (hp/mph) I could expect to see?
You could raise compression upto 150 psi and still run pump gas, depends on how long you want engine to last, could add 20hp.
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Old 14-05-2006, 08:40 PM   #9
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Quote:
Originally posted by roofer
You could raise compression upto 150 psi and still run pump gas, depends on how long you want engine to last, could add 20hp.
Thats good enough for me Roofer
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Old 14-05-2006, 08:44 PM   #10
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i wouldnt go above 145psi
you need to see what compression you are running at mo and then work out how much you need to take off
you could just get some aftermarket thin head gaskets
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Old 15-05-2006, 06:10 PM   #11
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You know you want to skimm yourself, its so much fun!!!! Just think....you, the head and a couple of lit candles and wine. Then wet/dry paper dipped lightly in water and placed on a glass table. Remember to caress in a figure of eight too, you dont want an uneven head :P
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Old 21-05-2006, 05:59 PM   #12
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Quote:
Originally posted by Dan
Any idea how much should come off? And what gain (hp/mph) I could expect to see?
Cylinder Heads

Pending Research

You can drop the cc's in the 200 heads to 31 cc's and still run 93 pump gas. It will do a lot for all around performance. (14)


Difference between 2.4 and 2.5 head gaskets: They are different. The cylinder holes are bigger on the 2.5 and the 2.5 has dowel pins. I would get the right gasket. There will be a very poor seal around the cylinders. (15)
I have cut 2.4 as tight as 28CC and folks are happy on pump gas.....Our suggestion on 91 octane on the 2.5 is no tighter than 34CC with thin head gaskets. (16)


The rule of thumb is anything over 145 cranking PSI with a good strong battery is beyond pump gas. (17)
Stock heads on a 200 fishing motor and hi-po motor, where typically 38cc. The first 245/260 motors were even as generous as 42cc, but this was later reduced. (19) Performance heads and stock heads share the same casting. Primary difference is CC's and the fact that stock heads have black paint, while performance heads are "natural".



As far as just taking the time and added expence to convert to a thin head gaskets VS thick, it is not measurable, some of the heads we cut have to have A LOT of material removed to achieve the desired pump gas top compatable compression. ( 145 ) This amount as I have atested to MANY times vary from head to head , and combustion chamber configuration to combustion chamber configurations. Going from the absolute thickest ( .061 ) to absolute thinnest ( .041 ) ( Hi Per gaskets ) would NOT raise compression enough to even fool with. Maybe 3 to 6 lbs at best and when one is trying to get the max out of a pump gas motor this amount is not measurable. (29) "MOST loss foam embrelled 1 piece heads that are stock and NOT A DRAG or F1 motor the formula for cutting is as follows :

For every .010" that is removed from the head surface the cc 's will be deminished by .7 cc's
Example: .040" removed will diminish the CC's by 2.8

This is ballpark and not exact but I have found after cutting a zillion heads this to be the norm ! My max that I will cut a pump gas motor with the thin head gaskets is 35 cc's , I will go 34 cc's with the thicker ( drag motor gaskets) and 33 cc's with the very thick fishing motor gaskest! My target is 145 max lbs anything higher your asking for a problem and will end up at the sleeving shop with your wallet a bunch lighter ! " (37)

2.5L Pro Max : "32 cc's is to tight for pump gas especially on a Pro max. I have found 35.5 cc's will live but that as tight as I have the experience that will live on pump gas on that motor !" (36) When more compression is added more BTU's are created, which along with more power comes more heat - with more compression being generated more fuel must be added to slow or stop detonation and make a safe HP gain..(39)

To CC your heads, follow the following procedure from Jay Smith

"I don't know but one way to CC a head and that is with a 100cc buret , a flat pulg ( to screw into the plug hole ), a piece of 1/4"thick plexiglas ( with a filler hole drilled in it ) some heavy grease to smear on the sealing surface to prevent the liquid from OZZING out the edges and I use methonol with some red food color mixed in so my blind ass can see the levels. The rest aint rocket science."


see http://www.hydrostream.org/ArticleArchives/CCHeads.htm aswell



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Old 21-05-2006, 08:31 PM   #13
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cut and paste from big hammer by any chance?
plus dans is a 150 so no help really
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Old 21-05-2006, 08:34 PM   #14
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yep
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Old 27-05-2006, 12:46 AM   #15
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145 is as high as one wants running pump gas. Thats 34 CC's with a 44 series thick merc gasket on a 260. I cut HUNDREDS of heads a year and thats what has worked for me. All 260's / 245's came with 38 CC heads. Most can be cut .045" and your in the ball park. The Mercury loss foam head ( Umbrelled style ) ratio is as follows, for ever .010" of an inch that is removed off the head you will diminish the CC by .7.... Example: cut .030" off you reduce the CC by 2.1CC's.

Unless you guys premium pump gas is better grade than the states 31 CC's with a thin or even a thick 1MM head gasket will eventually "get" a piston. Pump gas Fuel simply is not consistant. Not only do I own JSRE my second job is I am a fuel blender at EXXON...Also the more populated a city the more oxygen additives are added to prevent emmissions, this makes the burn HOTTER and can cause detonation...Motor gasoline has a "shelf life" of only 2000 HOURS from the time of its conception until it starts loosing potiency and octane..

Also all the Mercury motors have thier own quirks. The 260 deck height is different that the Drag . The pistons on a 260 are .004" recessed in the deck and Drags are .004" pretrudes out of the deck or a difference of .008". That is the reason a Drag motor comes with a 27- 822844-1 head gasket which is 1/4 MM thicker than the stock 260 /245 thin OEM gasket 27-814658-1.

Compression is indeed the BIGGEST bang for the buck one can do to an outboard without getting intrusive int the engine....

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Old 27-05-2006, 10:19 AM   #16
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Quote:
Originally posted by Jay Smith
145 is as high as one wants running pump gas. Thats 34 CC's with a 44 series thick merc gasket on a 260. I cut HUNDREDS of heads a year and thats what has worked for me. All 260's / 245's came with 38 CC heads. Most can be cut .045" and your in the ball park. The Mercury loss foam head ( Umbrelled style ) ratio is as follows, for ever .010" of an inch that is removed off the head you will diminish the CC by .7.... Example: cut .030" off you reduce the CC by 2.1CC's.

Unless you guys premium pump gas is better grade than the states 31 CC's with a thin or even a thick 1MM head gasket will eventually "get" a piston. Pump gas Fuel simply is not consistant. Not only do I own JSRE my second job is I am a fuel blender at EXXON...Also the more populated a city the more oxygen additives are added to prevent emmissions, this makes the burn HOTTER and can cause detonation...Motor gasoline has a "shelf life" of only 2000 HOURS from the time of its conception until it starts loosing potiency and octane..

Also all the Mercury motors have thier own quirks. The 260 deck height is different that the Drag . The pistons on a 260 are .004" recessed in the deck and Drags are .004" pretrudes out of the deck or a difference of .008". That is the reason a Drag motor comes with a 27- 822844-1 head gasket which is 1/4 MM thicker than the stock 260 /245 thin OEM gasket 27-814658-1.

Compression is indeed the BIGGEST bang for the buck one can do to an outboard without getting intrusive int the engine....

Jay @ JSRE

Thanks for that Jay. So Divertom was right then, I`m looking at 1mm? (0.04")?
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Old 27-05-2006, 10:43 AM   #17
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don't know dude cus Jay is talking about the 260's your 150 black max might be different
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Old 22-07-2006, 08:17 PM   #18
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Done a compression check today in preperation to skimming the heads. All six cylinders where at 140psi. I'm sure I have seen on here that normally they are around the 120 mark so does this point to the heads may have already been worked????
This brings me onto my next question, the safe figure as far as the heads go and using pump fuel seem to be 145psi, will 5psi make any noticable difference?
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Old 22-07-2006, 11:26 PM   #19
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if you're confident that your gauge is correct and thats a genuine 140psi the I'd leave em as is!!!
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Old 23-07-2006, 03:49 PM   #20
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is you,re 150 a sleeved down 2.5 to make it a 2.0. if so i think the heads about 26cc
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