More Horse Power

[brodie123]

My Mercruiser 165HP is running great

I just went to a 19" pitch prop as it seems to give best over performance

but I need just a couple extra HP to get my RPM's right

I already converted to electronic ignition

I've been told to change the jets in the carb from 67 to 69 - a little wasted gas is ok for more HP - is this a good idea??

I have a 4 barrel rochester to replace my 2 barrel but I need some kind of riser plate for it - where can i gt one?

Is going up to a 4 barrel a good idea?

I don't expect night and day - but an extra 10hp would put me on the mark.

It's a 165 HP inline 6 - 250 chev engine

Thanks!

 

[ziggy]

Re: More Horse Power

My Mercruiser 165HP is running great

I just went to a 19" pitch prop as it seems to give best over performance

but I need just a couple extra HP to get my RPM's right

there's nothing ya can do to yer 165hp L6 to soup it up. it is what it is. good that it's running great. but if ya can't get yer rpms just right. something is amiss. i'd think yer lookin for 3900-4300. my L6, w/ a 19P aluminim wot is 4300-4400. my L6 is runnin on the edge of 20% vairiation compression between cyl. all within spec. though. still, not the tightest engine ya ever seen. anyways. here's good list of things that can cause ya to not achive wot..... list provided by dons....

List of possible causes of low WOT.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation (Full tuneup done recently)
• Remote control cables and linkage for proper travel to open throttle plates fully.

__________________
Don S.

go thru that list. ya'll likely find out why ya can't get yer wot. one by one too. check em off.

 

[brodie123]

Re: More Horse Power

thanks for the feedback.

I'm getting 4100 RPM on WOT - thought it should be closer to 4300.

I just had the engine completely rebuilt and have been advised that by a couple mechanics to open up the jets a bit.

Any feedback?

 

[JustJason]

Re: More Horse Power

increasing the diameter of the jets isn't going to help

Lean is mean

running a richer mixture will not increase HP..... i have no idea why some people think that.

4100 sounds like right around where your supposed to be, as long as you verify that with a known good tach.
What kind of goals are you looking for here? More top end, more low end pulling, more holeshoat? You only get 1 out of those 3... you don't get all thee.

 

[ziggy]

Re: More Horse Power

Any feedback?

i ain't no mech. but i'd think, leave them oem. no idea even what that is. but the carter 2bbl. in stock form is just right for the 250 L6. only reason i could think that'd justifiy changeing the jets, would be altitude issues. what it boils down to, is ya ain't gonna gain nothing, so why reinvent the wheel.... mercruiser already did it for us......
so what kinda boat ya pushin with the 165?
when i got mine, i was turning bout's what ya are, 4100, maybe a little more. had a fan blade style 21P ontoit..... i agree with ya. ya need to get the next 200.....

 

[Tail_Gunner]

Re: More Horse Power

You are limited by cam profille. no matter how you tune the engine valve over lap will kill a marine motor,,,aka a hot cam great air iduction means nothing if the motor sucks water into the engine.....and thats the first last and the end of all discussion....ya i am a prick.......

 

[brodie123]

Re: More Horse Power

lol - thanks for the replies.

I totally get that it's hard to up the HP in these things - and replacing the cam now is not an option.

I'm going to see about a larger flame arrestor to minimize air restriction and a hotter spark ignition coil.

The manual says WOT should be 4300 and I'm getting 4100 w/19". I get over-rev'd with a 17".

Would a 4 barrel help a 'little' - just to make sure the 2 barrel isn't restricting the current cam at all?

 

[paulrfrancisco]

Re: More Horse Power

Just some suggestions...
What size 19 in prop...? Is it stainless or aluminum? 14x19, 13.5x19, if its aluminum 19 maybe go back to the 17 in stainless. Or drop a 1/2 inch off of the diameter....Also, is it a "cupped" prop or a standard prop. If its standard, go down a size but in a cupped version.

 

[brodie123]

Re: More Horse Power

it's a 14.5x19" Aluminum prop Cupped

the 17 was the same as above only 17 vs 19

Would a 4 barrel help a 'little' - just to make sure the 2 barrel isn't restricting the current cam at all?

 

[ziggy]

Re: More Horse Power

ya might find this thread of interest.
http://forums.iboats.com/showthread.php?t=236243

 

[brodie123]

Re: More Horse Power

Thanks for the replies - and the other thread was a good read.

I do have the manifold (attached pic) already - so I'm really hoping that a new carb will bring it up even if only a little.

My challenge is that the 4 barrel Rochester Carb that I have does not fit. Even with a riser it's questionable and I have not been able to find one.

What 4 barrel carb would fit? What is this 'fat' 2 barrel and where can I get one?

Thanks!!

 

[fishmen111]

Re: More Horse Power

I had a quadrajet on mine. Don't laugh, but my first boat had a 250 bored 30 over with a high lift cam, triple valve springs and Offy manifold with q-jet. I do not suggest you do the same. It was a good motor and a lot of fun, but not cost effective. She would jump when the secondaries kicked in, but fuel usage skyrocketed. Once you hear the "moan", it is hard to throttle back. You will fight to get this motor above 4500 rpm and 10-20 hp will not allow you to step up to a 21" pitch very well.

 

[brodie123]

Re: More Horse Power

thanks - I don't need a 21" prop - just simply adding an extra 100RPM would make me happy. Plus, it's fun to do! lol

 

[ziggy]

Re: More Horse Power

so what kinda boat ya pushin with the 165?

???

if she's in good tune. maybe ya just need to do a little adjusting of prop pitch. or design....

 

[paulrfrancisco]

Re: More Horse Power

it's a 14.5x19" Aluminum prop Cupped

the 17 was the same as above only 17 vs 19

Would a 4 barrel help a 'little' - just to make sure the 2 barrel isn't restricting the current cam at all?

OK, what condition is the 14.5 x 17 alum prop? Is it new, or an old or original one that has been reworked several times... it could be flexing flat and causing an over rev, when a new 19 might be too much. Go to a reputable prop guy and see if you can test drive a 14.5 x 17 alum. cupped prop, same geometry of the old one but it will not flex or flatten out under high load... Old props tend to get mushy...

 

[Hitech]

Re: More Horse Power

Well, has anyone thought of trying smart tabs? They should give just a little more top end and lots more bottom end, so to speak. It's the most cost effective performance improvement I can think of.

 

[MikDee]

Re: More Horse Power

The Chevy 250 can be modded fairly easily, with the right parts. Probably one of the easist ways to gain 20 - 25 HP is to replace the intake manifold with one made for a 4 BBL carb by Offenhouser. (About $250) For that engine you will want a carb in the 400 - 500 CFM range. (Larger than that will make it very finicky.)

Maybe a carb that would fit is an early design Chevy 4bbl with matching primaries, & secondaries, like they used on the old 283 Chevy, & 250hp/327. I think it was an early rochester? That would probably be the perfect size.
Years ago GM had a factory low rise aluminum 2- 4bbl manifold on their 283/270hp power pack, & corvette motor that was made to use these carbs. I used to own one of these manifolds many years ago, till my old landlord threw it out, without my knowledge, thinking it was junk!
I know that Holley makes a small 4bbl, if you've got the money.

 

[brodie123]

Re: More Horse Power

thanks guys. A motor shop is making an adapter - I'll let you know how many extra rpm I get - if any lol.

What are the tabs? How do they work?

 

[Hitech]

Re: More Horse Power

What are the tabs? How do they work?

Here is a link to the ones I have (I haven't installed them yet):

http://www.nauticusinc.com/smart_tabsSX.htm

If you search for "Smart Tabs" on here you will find a lot of infomation. Basically what I have found reading here is that the claims of the manufacture, while they seem extreme, are accurate.

 

[paulrfrancisco]

Re: More Horse Power

thanks guys. A motor shop is making an adapter - I'll let you know how many extra rpm I get - if any lol.

Seems to me the 14.5 x 17 stainless is the easiest option.. I think you'll be pleased with the results... It may only be a temp hold for the cost of the prop on a credit card to try it out... if you like, you trade the other 2 you have in for credit.