Cutting 2.5 225 Promax heads need cc advice please help

[woundedwarrior]

With 35cc heads and a .75 mm gasket and std bore on a fresh very low hour motor my compression is as follows below if looking at the back of the motor..
Port. Starboard
132. 135
130. 135
131. 135
I guess the easy way to explain and ask my question is I would like to gain 20 more lb compression...So how many lbs of compression do you gain per 1 cc reduction in chamber size.. Also if you notice there is only a 5lb or less total side to side spread but the left side is a little weaker could be in deck height variance or a combination of things so I'm gonna cut it slightly more to add 4 lb of compression but will cc the heads first to make sure the cambers are the same ...Also here is another wrench in the equation I'm going from a present .75 mm gasket to a 1 mm gasket tommorow because its the only set I have left until I can order some more..I've been told but want to make sure that there is a 4 lb difference in these to gaskets ....So that being said what ever compression I'm gonna loose try to figure that also. But I'm shooting for about a 20lb gain and150-155 lb compression.. Thanks for any help and p.s. I'm not lazy just to dumb to do the math lol

[jeff dunn]

Cut to 32cc and 1mm gasket, will give you around 145 to 150 on a pro max.
all v6 mercs are off from one side to other on compression numbers.
if your # don't come close to this after cutting heads you may wanna do a leak down on motor.

[woundedwarrior]

The bores look really good with the hone still very visible..not saying it isn't but I don't believe its a ring issue being the entire port side is within 2 lb of each other...I was just gonna cut it a little more to add about 4 lb to make up the slight differnce side to side for what ever the cause gasket crush or slight deck height variation..and was needing to know aproximatly cc less to cut it to make up roughly 4 lb...Thanks everyone

[woundedwarrior]

After doing some post research I've found that the difference in gasket size thickness is right at 5 lb from .75 mm to 1 mm and a total of about 10 lb from .75 mm to 1.25 mm That being said I'm gonna cut the heads the same cc and make sure the chambers are equal. And if the port side is still a little weaker than the starboard I will just run a .75 mm on it and a 1 mm on the starboard then the whole motor would be within 2 lb or less...I know they vary from side to side often and 5 lb side to side ain't really much and most say just run it. But if i can get um closer to harmony I would think it would be a lot smother and run more like a sowing machine and not a Harley so to speak...Nothing against a Harley just an example.lol

[tux974]

You really need to do a leak down. Your bores can look mint but if they are not true (round) you are chasing your tail on building compression. With 35cc and .75 gaskets if all is fresh and correct you should be around 145.
Have the heads been cc'ed correctly or just a guess from depth?
Like I have stated on your other thread, I would not run below a true 35cc on pump gas... 32cc... This is JMPO!

[woundedwarrior]

Its a factory built mercury power head .
The starboard side came out all equal at 135
The port side is from the top 132,130,131
I was told this could be a common variance in the crank and not deck height ...
But I have had heard a lot of different answers as to what It took different people to achieve 145-150 lb compression on just broke in or low hour motors. And the range was about 32 cc - 35 cc ....so wtf..
I guess Ill do a leak down this morning ....cc each pocket on the head and if all is good head to my machinist who will cut them on the spot while I wait...HHHHMMM I'm thinking screw it cut um to 24 cc and stop at the local airport on the way home .get some av gas and put my helmet and flack vest on head to the lake and go out like a screaming heathen ...lmao thanks yall

[tux974]

GL......borrow a parachute while at it....LOL

[woundedwarrior]

Its a factory built mercury power head .
The starboard side came out all equal at 135
The port side is from the top 132,130,131
I was told this could be a common variance in the crank and not deck height ...
But I have had heard a lot of different answers as to what It took different people to achieve 145-150 lb compression on just broke in or low hour motors. And the range was about 32 cc - 35 cc ....so wtf..
I guess Ill do a leak down this morning ....cc each pocket on the head and if all is good head to my machinist who will cut them on the spot while I wait...HHHHMMM I'm thinking screw it cut um to 24 cc and stop at the local airport on the way home .get some av gas and put my helmet and flack vest on head to the lake and go out like a screaming heathen ...lmao thanks yall

[patchesII]

The variance from port to starboard is nothing to worry about and it's not the crank

[woundedwarrior]

Well the local boat shop forman laughed his ass of when I called him and asked for a leak down test after I told him the above compression numbers on my motor said hell all even on the right and within 2 lb of each other on the left and only 5 lb side to side difference ...Said that's about as even a motor as I've ever seen but if you wanna bring her in shop rate for a leak down is $125....Then I called my machinist and he's coverd up today...Goes I'll just go fishing

[Jay Smith]

I cut and build dozens of V-6 steel sleeved mercury engines and heads a year I like 34 CC's with a 1 MM head gasket yields 140-142 ish at sea level and with stock timing is safe with pump gas super unleaded... If you test compression on a V-6 and get EXACTLY the same compression on all six check the accuracy of that gauge I find NON of them are dead nut the same on all 6....

Jay

[woundedwarrior]

Thanks everyone I wasn't trying to be an ass or anything ...just hoping y'all would get a good laugh on me to start you day...