cutting exhaust chest

[MERCing]

what is the purpose of cutting the exhaust chest, pros and cons ???

[Raceman]

Kind of a broad question, but basically some V6 mercs have considerable restriction, or lack of volume in the chest to enhance low end. The first 175 Mercs (2 liter engines) in the 70's were very open in the chest and bottom of the block. The 2.4 liter engines introduced in 1978 had much of the volume filled and the holes at the bottom of the block were considerably smaller too. These engines responded especially well to having the chests cut similar to the older 175's.

Pros: increase in horsepower in upper mid range and higher RPM's.
Cons: possibly some loss in low end.

In most any performance application the pros would outweigh the cons in this case.

It's not necesarily a good process to take on blindly and without experience. It's very easy to cut into water passages in the area, and just like a lot of other things, too much can be worse than not enough. If you're considering it I'd let someone who has experience with it do it for you rather than taking it on as a home project or lettin' Bubba the dirtbike porting ace take it on. Blocks are too expensive to experiment with when there's a 25+ year state of the art knowledge pool available. Jay Smith is a good place to start.

[T-REX]

Lemm'e add my 2 centz...I have leerned that most people(include'in myself in tha beginn'in) thank cutt'in tha exhaust chest iz HP...WRONG!!...It allows a rise in HP, if your application needz tha extra exhaust flow!!!...I have cut tha exhaust chest outta a stock 2.5 200...tha gain wuz:...LOSS OV BOTTOM END!!! ONLY...I actuall lost a few RPM on top!!!...Cutt'in tha exhaust chest should only be considered with other more extinsive modifications...A re-directing ov exhaust outlets WILL help sum, but tha less material removed, tha better....

A stock 200 2.5 fish'in motor exhaust chest iz capible ov flow'in enuff exhaust to turn 9000rpm!!!........A stock 200 2.4 exh chest iz capible ov 8500rpm!!!...Tha differnce in rpm is because of behind tha liner, vs piston port'in, not exhaust chest size!!...

My brother haz a 2.4 200 on a 17' Laser Basser...He wanted sum extra HP...I told him what to do and not to do, but anuther guy talked him into cutt'in tha exhaust chest!!!...With all tha other mods, he lost bottom and it ain't reel spunky below 4500...He wish he could put it back, but it's easier ta lissen to a buddy, than ya bruther!!!...REX

[Earl Murchison]

Listen to T-Rex If i was going cut I would try to copy a 260 Hp or 225 Pro Max cleaned up . There is a little dog leg right in the top (with the engine sitting on the boat) of the exhaust port that I reshape And NO more. MY opinion Is if you cut any on the rod slots you have ruined the engine .US1 has a port map posted somewhere that should be good .
Earl

[MERCing]

thanks Guys,
This is a 225 Pro Max project block. Looks like I'll leave the exhaust chest alone and focus my attenton eslewhere.

[GPI Racing]

T-Rex,

EXCELLENT post! Thank god I'm getting used to your "speakage" as it doesn't take me as long to transcribe them in to regular english. :D

Randy

[T-REX]

dammm Randy, I juss type like I reely wanted to back when I wuz sett'in ther look'in out tha winder, while my english teacher wuz dump'in all dat proper kinna junk on us...pronounz, nounz, agitive'z(I did leern quite a few ov them!!)...My english teecher knw I wuz a loss kauze, so we juss got along till klass wuz over...I bet she would turn over in her grave ta no they ain't many ENGLISH speek'in people leff in this country!!...Hell, I don't have a problemo(did ya catch dat spanish??) understand'in what I said...sumtimez!!

[Jay Smith]

Agree with Raceman and T-Rex ( I think , LOL ) The chest mods should only get wild and "gutted" if your motor is on a VERY light hull and running a ton of compression , OR you utilize a mechinical advantage such as a low gear or a low pitch prop to allow the motor to transisition from the the lower RPMS to the powerband.......The 225's and 260's if on a recreational boat should stick to clean ups in the chest areas and maybe drag the "ant trail" with a little bit larger ball nosed end mill , if the boats not too heavy , then do the clean ups. I just did a guys 260 last week on a Bullet Bass Boat ( Pump gas motor ) ( not a potato chip hull a REAL fishing rig ) and he loved the whole increased power range , but I did alot of intake side work along with increased the crankcase compression to increase the air speed .

[Raceman]

Rex we all no dad duh sekunt grade wuz da hardess foe yirs of yo life but if'n yu'd pade mo atenshun fore yo gramma skool graduation whin yu wuz ninteen din yu wud be simpla to undastand now. Yu shudda studdied mo insted uv spendin yo time winnin all dem ugly kontests.

Now I bleeve yu probly did git wunna dem 2. foes ta turn up dat 9000 revs widout no hoggin', but Ima bettin dat whin you put dat prop bak on an stuckit in da watur it took it a lot lownga time ta git dere din it did on dat flushin hoze. I dont juss like dem RPMs, I like dem RPMs in a rush.

[Earl Murchison]

REX
I hope you are not going to let Raceman get away wit nsultn yr edukshun GO REX make it good.

[popslavaz]

T-REX

Tell your brother(If he will listen lol ) to install a casting #87321 2.4
exhaust divider in that motor.It will help cure his problem. It is designed
to stuff the chest.If you cant find one let me know. I use them to cure
that problem on motors often.

pops

[T-REX]

Popz, we did put one ov tha thick dividers in it(a 2.0 one I thank)...I have several ov them...an ole Guru told me about them...I had a couple and didn't even know it...even wit tha divider, it didn't git back to square one!!...He shoulda lissened!!

Ye UGLINESS, Seemz ta me ya knew what I wuz say'in, so U mussa been bored in english class too...Now U juss jelous kuz I kin talk better then U and U iz mo UGLY than me...Now, put ya damm glasses on, an ya hed out ya azz, an U'll see I neva said a 2-fo would turn no 9000...I said 8500!!!...Now, korse I ain't never got mine ta turn mo than 7900, but I know ov several that will hit tha 8500 mark, an are legally stock!!

Earl, He'z juss too old an UGLY ta try an teech anythang...I ain't got dat much spare time...REX

[Mark75H]

At least Rex can read Yankee english, even if the can't speak it :rolleyes:

[Promax1R]

PopS, T-Rex? I have a ProMax that is completely gutted and polished in the exhaust chest. I run it on a Bullet bassboat, I didn't notice a drop in holeshot after the porting. Do you guys suggest trying a 2.0-2.4 plate? Does it hurt on top? I only turn it to 7500 lite loaded. :confused: :confused: Which divider plate is the best?

[T-REX]

If U didn't feel a loss, then U'ze iz one lucky dude!!...But, ever motor iz differnt...Tha other divider I'm familiar wit iz only for tha 2 piece exhaust cover, and won't fit a 2.5!!...U must still have tha promax tuner???...AND, ya still one lucky dude!!! ;)