bond-o, Don, some others with omc experience... please

[wca_tim]

I know this is an oddball question, especially for this forum, but some of you on here are a wealth of knowledge and have good sense as well. I appreciate any thought you give this.

running a merc alpha drive with a long duration camshaft, one of the biggest problems is setting the idle low enough that you don't beat the drive to pieces shifting into gear. (after dealing with exhaust, low end power, general usability, etc... talking about small, light i/o for going fast). Someone told me that one could use an omc shift assist module and connect it to the merc shift interrupt switch. I've been thinking about it a while, and have done some reading and digging. I understand that the omc module basicaly drops cylinders a lot like an electronic ignition rev limiter does, and that for many of the applications on stringer and cobra drives the module basically drops cylinders for a few seconds on a timer. It really sounds like a great way to ease the going into gear if you're required to run a little higher idle... sorry for the overly long explaination... so my questions are;

1. is there a good reason that i couldn't do this?

2. which drive system would be the best candidate for the kind of interrupt module i'm talking about?

I know i would need one made for a v8 and of course no matter what would happen, the responsibilit y for what I do or don't do is entirely mine... it;s not your fault if i smoke my ignition system or light myself on fire doing something silly... note also that i can figure the electrical connections part out...

Thanks!

 

[JustJason]

Re: bond-o, Don, some others with omc experience... please

The thing about shift interrupters is this. They work comming OUT of gear, they don't do anything going INTO gear.
You really should do what you can to get your idle speed down.

 

[Fun Times]

Re: bond-o, Don, some others with omc experience... please

What engine set up do you have??? Do you have a bravo or a alpha??? If you have a V 8, And it lookes like you do then You might want too look into using maybe a mercruiser V 6 IGN module, They do this with V8 blower engines to get more base timing at Idle to help lower the hi surge they get at idle in and out of gear, And helps controll the idle much better. You would just set your total advanced timing too where your engine needs to be for best performance at top end and adjust your idle down as needed with a higher base timing, And you should be fine. That would be a easy thing too try first. Here is a list of modules merc has. http://www.mtboats.com/mercuryignitionadvancemodules.html. Maybe you might have a freind with a V 6 that might let you try his out for a Quick test first before buying one. This is Just a different way to look at it is all I am saying Good luck.

 

[wca_tim]

Re: bond-o, Don, some others with omc experience... please

The thing about shift interrupters is this. They work comming OUT of gear, they don't do anything going INTO gear.
You really should do what you can to get your idle speed down.

Thanks jason

that's because the microswitch on the original omc application is set up to start the module when you're coming out of gear right? putting the omc shift assiste module inline with a merc interrupt switch will drop cylinders for a short period after the click through the typical interrupt on a merc set up and let you get into gear without banging it. the idea is to momentarily lower the idle so you can put it in gear without chipping a gear or the like, but not for long enough for it to die. Same general concept as the merc set up, just stretching out the time the engine is not turning as fast. Note that I'm thinking about a situation where you're running enough cam duration that the only other viable alternative is to bypass the neutral safety switch and start it in gear...

 

[wca_tim]

Re: bond-o, Don, some others with omc experience... please

What engine set up do you have??? Do you have a bravo or a alpha??? If you have a V 8, And it lookes like you do then You might want too look into using maybe a mercruiser V 6 IGN module, They do this with V8 blower engines to get more base timing at Idle to help lower the hi surge they get at idle in and out of gear, And helps controll the idle much better. You would just set your total advanced timing too where your engine needs to be for best performance at top end and adjust your idle down as needed with a higher base timing, And you should be fine. That would be a easy thing too try first. Here is a list of modules merc has. http://www.mtboats.com/mercuryignitionadvancemodules.html. Maybe you might have a freind with a V 6 that might let you try his out for a Quick test first before buying one. This is Just a different way to look at it is all I am saying Good luck.

hear you. good thoughts. I'm currently running a mild enough cam that the engine in wil lidle down with the v8-22 module. I'm also running an old style crane cd box (uses the advance curve from the merc ign module) which helps with idle quality. I funny you should mention the v-6 module thing... I've got a spare v-6 module. when I set the v-6 module up for best total timing (ca. 34 deg), it was too much for the starter to turn it over... The v8-hp would probably be ideal, but for the cost, I'll upgrade to a newer version of the crane ignition with the programmed advance curves. ...383 about 10:1 compression...270/286 cam right now, but I'm going to step it up, maybe quite a bit, for a while to see how much power I can get out of it. Just playing... Oh, and alpha drive - wouldn't worry about it if a bravo.

 

[n2ostroker]

Re: bond-o, Don, some others with omc experience... please

What kind of shifter are you running?

You could always put a momentary push button switch to a relay for the ign module power on the shifter to manually push.

You could also put a micro switch on the shifter mechanism like the merc switch. You would have to fab up some sort of cam or something to ride on the switch for when push it into gear though which might be quite a pita.

 

[SuperNova]

Re: bond-o, Don, some others with omc experience... please

Thanks jason

that's because the microswitch on the original omc application is set up to start the module when you're coming out of gear right?

No, the merc steup and the omc setup have the same basic goal and only work coming out of gear.

putting the omc shift assiste module inline with a merc interrupt switch will drop cylinders for a short period after the click through the typical interrupt on a merc set up and let you get into gear without banging it.

No.

the idea is to momentarily lower the idle so you can put it in gear without chipping a gear or the like, but not for long enough for it to die. Same general concept as the merc set up, just stretching out the time the engine is not turning as fast. Note that I'm thinking about a situation where you're running enough cam duration that the only other viable alternative is to bypass the neutral safety switch and start it in gear...

I have two ideas for you, only because I've already done what you are getting ready to attempt. 1. At one point I was running a cam with 236 degrees at .050" lift and didn't have any problem shifting due to a high idle speed. I did run the V6 module. 2. There really is no point in putting a big cam in and revving it to hell because the Alpha doesn't survive long much above 5500 rpm. Stick with the 383 and cam it for a power peak about 4700-5000 rpm. A good offroad 4x4 cam will work wonders. This is coming from 3 years of playing around with different combinations and learning the hard way.

Also, unless your valve train is top-notch and completely bullet-proof, you WILL break stuff after about 10 or 15 minutes of running at a steady elevated rpm. I ran edelbrock performer rpm heads on a stock-ish 355 with a small marine cam and broke the included screw-in rocker studs edelbrock gives you after about 15 minutes of steady 4500+ rpm and that's nothing compared to what you are talking about.

 

[wca_tim]

Re: bond-o, Don, some others with omc experience... please

Thanks a bunch for the great input! I appreciate your time and opinions. Didn't have a good enough understanding of omc side to havea good handle.

currently running the older style crane ignition box, but could go to msd if really needed.

have the valve train to handle it.

current duration at 0.05 already 226/236 or so.... max horsepower somewhere around 5200-5500 and can idle at 500 rpms. that I should be able to get by with anything sane and still shift is clear at this point.

also clear that unless go with a bravo drive, larger chamber heads and a blower, I need to be satisfied with incremental gains for the curent combo and not try to get out of hand...

really, it sounds like its...

...time for a bigger boat, bravo or better drive and a whole lot more cubes...

 

[jtybt]

Re: bond-o, Don, some others with omc experience... please

I've found the 350 just doesn't have the torque to push my piggy boat(7660 lbs) so I've gone up to the 400 SBC. Plenty of torque at SBC prices for building.

Too much cam sucks water at idle RPM's.(seems like you've run into that)

You've also seen the practical limit to what you can do with and alpha drive...mainly, all gears constantly rotating while engine is running and having to slam dog gear on prop shaft into rotating dogs on drive gears.

Automatic crunch time at increased idle speeds.

 

[SuperNova]

Re: bond-o, Don, some others with omc experience... please

Thanks a bunch for the great input! I appreciate your time and opinions. Didn't have a good enough understanding of omc side to havea good handle.

currently running the older style crane ignition box, but could go to msd if really needed.

have the valve train to handle it.

current duration at 0.05 already 226/236 or so.... max horsepower somewhere around 5200-5500 and can idle at 500 rpms. that I should be able to get by with anything sane and still shift is clear at this point.

also clear that unless go with a bravo drive, larger chamber heads and a blower, I need to be satisfied with incremental gains for the curent combo and not try to get out of hand...

really, it sounds like its...

...time for a bigger boat, bravo or better drive and a whole lot more cubes...

If you're not spinning a 26" pitch prop out to 5000 rpm.....well then I won't agree that you have hit the limit for your combo yet. I could do it with a fairly tame but blueprinted 355 in a 21' '86 Wellcraft.

 

[JustJason]

Re: bond-o, Don, some others with omc experience... please

and can idle at 500 rpms.

uhmm... if your motor idles at 500 that's plenty low enough.

 

[wca_tim]

Re: bond-o, Don, some others with omc experience... please

If you're not spinning a 26" pitch prop out to 5000 rpm.....well then I won't agree that you have hit the limit for your combo yet. I could do it with a fairly tame but blueprinted 355 in a 21' '86 Wellcraft.

hear you and agreed - don't think have hit the limit yet, just meant would play more with gear, prop, intakes, carbs and set-up for a while to see what works best and think about a little more cam and some more head work, but stop there. I can hit the 5600 rpm rev limiter with a 28" 4 blade or a 27" mirage plus now (1.8 gear).

your welcraft sounds like fun. that's hauling

 

[SuperNova]

Re: bond-o, Don, some others with omc experience... please

your welcraft sounds like fun. that's hauling

Thanks, and it did, but it had to be fairly smooth out or it was a real hell ride. With the outdrive trimmed up for max speed, there wasn't a lot of anything left in the water. I sold the boat to a friend of mine who now wants a big-block jet boat. It's NEVER enough, you know?