Porting and stufing 175 2.5

[SJD1974]

This build is for a 2600lbs 18.5 Bass tracker fiberglass boat.
This boat currently has 2.0 150 that we built 5yrs ago and now has 6800 hard HS bass fishing tournament miles on it which 95% of were at WOT. This current motor we did chest work stuffing and head cutting and...... It pushed the boat along at 55 with three people and full gear, this weight was not figured in the 2600lbs. It would hit 60 with just my son in it. we plan too keep as a spare.
We plan to prop the 2.5 to run at 6500 if possible and make it as efficient as possible to help with fuel consumption. Plan to do all that we did on 2.0 to the 2.5.
My son has started the chest work. Not sure how much can be removed, don't want too get die grinder happy. we have CC reed stuffers for it.
So looking for some assistance on where to do some stuffing and porting.
Any help would greatly bee appreciated.
Here are a few pics. The pic with the arrow pointing at transfer port if that is correct. Can I remove material from there to make for better flow. We have pics of a 260 block that we have been looking at as a reference as to where to port. Not removing that much material though. Any help would be greatly appreciated.
Sorry about it being so long winded just wanted to get as much information in so everyone new the application of the motor.



This is the boat its going on and the 150 that has taken a lickin and keeps on tickin.

[LakeFever]

Curious does your block have the notch in the sleeve or no?

The pic with the arrow is the rod slot and opening that up works great. I copied the promax slot on mine which looks like a half moon cut in that area to aid flow around that awkward transition. I also opened up the exhaust dump and base plate to the large hi perf metal reinforced base gasket size promarine sells. I added some small chamber 135 heads which bumped the compression up 15 psi or so. Runs on pump premium. I smoothed out all casting flash in the block and lapped the reeds. Smoothed out all the intake flash as well. Removed the oil injection system and the brass bushing in the block. Filled that entire cavity with marine Tex to stuff better. Jay smith reeds and I think that was it. Took my stream to 93mph at 7200rpm this summer

[SJD1974]

All that you have mentioned we did on our 2.0. we just didn't have the transfer ports, so I was not sure how much I could remove from there and what shape. The exhaust dump has been ported to the size of the stock gasket that would be on there for the 2.0 that we have and everything under that. It does have the slots you are referring to.
Pic's would be nice if you have some.

[SJD1974]

We have a set of 2.5 heads, just need to figure how much to mill off to get the 140comp. Was thinking somewhere around 33cc.
Do you have a picture of your work?

[SJD1974]

Here is a picture of one of the cylinders.

[LakeFever]

Yep lots of pics in this thread

https://www.screamandfly.com/showthr...istakes!/page2

[108]

You can't cut a slotted motor for 140 psi cranking and expect it to live at bass boat loading weight on pump gas.

[SJD1974]

LakeFever thanks for the link.

108 I was not going for 140 at cranking I was going for total. I have recently learned that I have to check compression at a much higher rpm. I don't know how to do it exactly just yet, could you help me with that.

So I was doing more reading, i am thinking we will be getting more from this upgrade than i was originally thinking. We are going from a 150 2.0 running 54 at 5000 rpms turning a 23p Turning point prop. Being fulling loaded, people gear, fuel, everything, totaling 2600lbs. The boat wieghs 1080 bare bones so we have a lot of gear.

Going to 2400 lbs total with a 175 2.5 and with all the mods to the motor. We are loosing 1 person.
Am thinking correctly, in saying we will gain a fair amount of speed?

[SJD1974]

I'm looking for a safe zone to cut the heads to for some improvement to go along with the chest work and rod slot work.
This is kinda a Frankenstein motor. The heads that I have didn't come on it and the carbs are wmv 18 that came off a 200. It's going on a lower unit from the current 150 2.0 we have on the boat which more than likely is a 2 to1. It's all going under the 150 clamshell covers so I have a lot of to do getting it in there. Had 2.4 200 in there for a bit and it didn't fit in there very well.
I appreciate everyone for their help.

[LakeFever]

I did a lot to my motor and the biggest bang I got out of the whole deal was swapping out the large chamber 2.5L heads to the 2.0L fatblock heads. It produces 130 and change compression and runs great on pump 91. Keep the timing conservative imo 23 degrees is where to run it safe. Also this may be redundant but delete all black boxes too. If it’s a stock 175 it will be four petal front half which is what I would stick with for such a boat. I’m still running a four on mine and it winds up good, loads of bottom end though which your going to want with that weight.

here’s another thread that might be of interest about the small chamber heads

https://www.screamandfly.com/showthr...ds-on-2-5L-200

[SJD1974]

These are the heads i have to work with, im going to cc them today.
While cleaning i found this crack. My 150 had multiples of them but not that deep.
May be able to drill a small hole to stop the crack then fill the hole with jb weld or something.

Do you know the cc of the 2.0 fat block heads you put on.
I dont know how to check the compresion on this 175 , it has the slots near the exhaust ports.

[skialot2]

Compression gets checked on all motors basically the same. All spark plugs out. Block warm if possible. Fully charged battery. Throttle butterflies open. Crank until gauge stops moving.

[LakeFever]

488 2.5 fishin motor heads 38CC. My 135 2.0L heads are bone stock and they are 34cc I verified with a burette.

[SJD1974]

Just cc them come up with 39cc with plug not spark plug in there.
With a spark plug in there it was 43cc. Crazy how much fluid goes in the spark plug.
So it seems i need to cut the heads. Good that i have a friend just down the road that does that for me.

[SJD1974]

The exhaust idle relief slots don't come into play when checking the compression at cranking speed?