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View Full Version : SOME OMC OBSERVATIONS, IF ANYONE IS INTERESTED



Instigator
05-10-2001, 07:56 PM
Have finally gotten the time to inspect the motor for my project over a few beers and it looks very promising! Just bought a '87 Gt 200 in pcs. For those of you OMC guys that don't know, this is a 2.7 liter bridgeport motor that they only made for two ('86/'87) years. This thing has some serious exhaust ports in it! I just compared them to the 250 (same as a 225 H.O.) off my Sonic. The 250/H.O.'s are about .150" wider than a standard 225 (thats a big jump) and the bridgeport motor is .210" wider than those! The '86 versions had the biggest V-6 carbs they ever used on top of that! No wonder these things had a reputation of being sluggs! Here's the neat part though, the sleeves are thick enough to poke out to 3 liter specs! You thinkin what I'm thinkin?? Met with my tool maker friend, Mr. Wizard and think we have everything figured out for a bullet proof 15" mid. Had some hurdles to clear but I think we've finally got it. I'd be glad to share the project staus info with anyone interested but don't want to piss anyone off by talking about going fast in an OMC powered Stream. Oh, hell with that! Boat is almost to bare hull, just have a big black hemorrhoid to remove off the back then I think I can get it in my garage for rigging. Greg Moss helped me out with a set of wing plates to convert to cable/pulley steering, and about the only other thing I need is a foot throttle for the boat. Will be going balls to the wall once I get two other project motors out the door. Also looking at experimenting with the stock gear case to start with. Saw a Mod VP race way back when and they were running their motors jacked to the moon with stock gear cases!! I remember part of what I saw! Oh well, I'm geeked anyhow! Instigator

Rodney Nance
05-10-2001, 08:41 PM
Instigator back in the early to mid nineties we ran a OMC using the same block as you are going to run. At that time OMC had quit using the Bridgeport blocks and we bought 16 brand new "Service Blocks" from the factory. You are right about boring them to 3 liter spec's. One benifit of boring them is that you can get 6 straight hole's that will be parralell to the crankshaft. Dont be alarmed when you have it bored if one side of the sleeve is thicker than the other as you will have just corrected OMC's misalinged casting work. One thing you might want to do is put two small holes in the piston skirt to lubricate the bridge. If you can find a stator from a formula one v8 use crossflow switch boxe's and a good flex flywheel. Add some port work and compression, tune it right and you will have a pretty strong engine.

Instigator
05-10-2001, 09:08 PM
Soon as I finish porting, it's going out to get line bored to make sure everything is square.

Rodney Nance
05-10-2001, 09:23 PM
Are you going to add finger ports to the block?

Instigator
05-11-2001, 04:27 AM
Not this build.Not sure how much I would gain??

Ray Neudecker
05-11-2001, 08:21 AM
While it is apart, add the fingerports. The gain is awesome. First one I tried gained 800 rpms.

Rodney Nance
05-11-2001, 04:44 PM
Ray's right while it's down I would go ahead and fingerport it. The increase in midrange is awesome.

Instigator
05-12-2001, 07:16 AM
I will consider cost vs advantage on the fingers but you just told me one thing I was wondering about. The improvement is in mid range. I'm going WFO only.
This project is taking a life of its own and I may develop motor in stages??

Ray Neudecker
05-12-2001, 08:16 AM
The gain in finger porting is from start to finish. It is noticeable eveywhere.

Instigator
05-12-2001, 11:30 AM
You'r advice is much appreciated and respected! I just got back from picking up parts to screw my 250 back together and picked up a finger port donor piston to match to for the FrankenRude project.
I am having big fun with this project and am exicted about the potential that I see!
Lots of variables still exist that I will have to dial in. Probably get block back and start with mock up assemblies to figure deck height, ign. timing, combustion chamber cc etc.
Right now, working more on cleaning port runners than actual changes to timing. Plan is to go with more window area and only advance timing slightly.
Thanx again!
Instigator

LaveyT
05-12-2001, 04:32 PM
Come on Gary,cost is no object!Were counting on you!!!!!:)By the way,What are the dimensions of the H.O. Ex ports?You said they were wider than a stock 225,They are higher also?
On the low end issue (2.7),One of the OMC engineers objected when I commented on the lack of low end torque."Thats where SALES told us to put the powerband!"I guess sales was influenced by Mercs powerband.Also how much of the sleave will be left after boring?Enough to tolerate the lack of concentricity?Anyway,Sounds like a meeannn Fishhhhhhin motor!
P.S. Doctor says I gotta loss 20+ pounds,I figure this alone will mean more speed!Plus if I lose an inch or two of gut this will effectivly move the boats center of gravy/gravity back,this should have the same effect as more set back???????

Instigator
05-12-2001, 05:11 PM
Me too! Working on 25 lbs.
If I lose 25 lbs of body fat does that mean the JohnRude is 25 lbs lighter?? I thought so.
The HO/250 Exh. post is 2.370" wide, timing looks to be the same. Standard 225 port is 2.215" wide. Thats .155" or almost 3/16" of an inch! Bill Gohr may not think its much but I do!
Very difficult to get accurate port timing measurements (depth of ports in cylinder), but I checked everything several times.
On the 2.7 motor the sleeve will end up about the same thickness as a current 3 liter sleeve. Plenty there!
Gettin fun now!

LaveyT
05-12-2001, 06:23 PM
Plenty of room for boring?GREAT! I dont know why I havent heard about it before!Was it because someone with a black motor doesnt want OMC heads to know???Sounds like a vast right wing consp....................Gota go,two guys at the front door with black trench coats,SEE Yaaaaah

Instigator
05-14-2001, 07:48 AM
Local dealer just told me the same thing you did about adding the oiler hole for the port bridge.