Mercruiser OEM to performance????

[18WCmerc]

Im a very experienced engine builder...automotive wise; I'm a pretty new marine engine guy.

here is where my question emerges. when can factory/aftermarket automotive parts interchange with marine engine parts? First, a little more information into my situation.

I have a 188hp mercruiser ford 302/351 mutt. Now, I have all intentions of putting on performance intake/4bbl carb/ignition system/cam&lifters/fuel pump on my merc. However, i broke the points last boating trip, figured I could snag up some cheap ford points/condenser kit from my local autozone...mmmm not so much. spent 30 bones on a special mercruiser site for just the points! necessary but crazy. Whats a homie to do right? so before i start dumping money into cool aluminum and shiny parts that promise 10 hp to the wheels...i mean prop lol, what is really interchangable?

at a quick glance it seems as though intake would have its snags...special throttle cable mount on a 2bbl carb, circuit breaker/harness connector mount, what else could be different?

Just gonna check before i carelessly toss my hard earned cookies away...

If no one has been down this road before, I'm going for it, then ill make a write up about how it just doesnt work lol. or a mercruiser to ford/chevy conversion chart.


thanks everyone

 

[18WCmerc]

Re: Mercruiser OEM to performance????

just one more thing... ive seen a lot of posts around here about guys wanting more power out of there motor and what not, i know it takes a lot to get more speed per hp on marine application. This is a grade-A waste of money want a winter project kinda thing, i understand that im throwing money at something to gain 10 hp that will help me gain 1mph. This is more an aesthetics thing and bragging rights, and boredom. just to squash any shinanigans before they start.

Thanks again...

 

[Howard Sterndrive]

Re: Mercruiser OEM to performance????

one common issue I hear/see with car engine guys moving to boat engines is the lack of understanding in this one area:

most V8 automotive performance parts are all about making power at high rpm's

roller rockers, ported intakes, better flowing heads... all designed to make torque when the engine is revved above 5000 rpm's

well, guess what... boat engines NEVER turn that fast.

So, it is all a total waste of time and money.... guys put on $2000 worth of parts and there is no HP gain at 4600 rpm, which is the maximum you can safely rotate your outdrive, ujoints, and gimbal bearing

Stock heads, intake, exhaust... it is all more than adequate for 4600 rpm

So, the bragging rights you earn amongst your car buddies might earn you snickers, giggles and jeers at the dock... there's nothing funnier to me than a K&N flame arrester on a boat engine

 

[wire2]

Re: Mercruiser OEM to performance????

one common issue I hear/see with car engine guys moving to boat engines is the lack of understanding in this one area:

most V8 automotive performance parts are all about making power at high rpm's

roller rockers, ported intakes, better flowing heads... all designed to make torque when the engine is revved above 5000 rpm's

well, guess what... boat engines NEVER turn that fast.

So, it is all a total waste of time and money.... guys put on $2000 worth of parts and there is no HP gain at 4600 rpm, which is the maximum you can safely rotate your outdrive, ujoints, and gimbal bearing

Stock heads, intake, exhaust... it is all more than adequate for 4600 rpm

So, the bragging rights you earn amongst your car buddies might earn you snickers, giggles and jeers at the dock

I have to disagree, Howard. I made several changes over the years to my once stock 1984 260 hp 5.7; alum hi rise intake, alum heads, cam, roller rockers, ss headers. Had to change original 21" ss prop to 23, (after mods, was running 5500 rpm wot). It now planes in under 1 second, throws your head back from 30 to 60 mph, all under 5000 rpm. Do I need that kind of performance? No. Would I do it again if I lost that boat? YES!

 

[Bondo]

Re: Mercruiser OEM to performance????

Im a very experienced engine builder...automotive wise; I'm a pretty new marine engine guy.

here is where my question emerges. when can factory/aftermarket automotive parts interchange with marine engine parts?

Ayuh,... Ya wanta build a real Stump Puller,... Idle to 4800rpms is the window....

Any thing Fuel, Spark, or Electrical Must be Marine rated...
Internal hard parts are interchangable...

You had the problem with the points, because Ford didn't use a Marine rated distributer...
Mercruiser did...

You probably already know that your starting with 1 hand tied behind yer back,...
Ford has left the Marine market, Years ago...
Chevys are easier,+ Cheaper to build...

 

[Philster]

Re: Mercruiser OEM to performance????

Odds are likely that you'll get worse performance, but since you seem reckless about this, all I can offer is this:

You can't drop in an overly aggressive cam. Doing so will cause water in the exhaust system to be sucked back into the cylinders, because of valve overlap. Water reversion is common with cam upgrades. During the exhaust cycle, there is a moment when the long duration creates a sucking action, which works water back into the cylinders. It is most likely at low RPMs.

It's not uncommon to hear about water reversion with cam 'upgrades'. I'm trying to save you the grief of spending the winter working/spending only to take her out and then slowly learn you have problems only to come back and post about it.

Go like a banshee on it, but you can't go hog wild on a cam.

Anything that boosts breathing by going wider/bigger runs the risk of throwin' torque out the window. Boats like torque. They got one gear. Imagine trying to manage acceleration and top end in anything with one gear.


Ain't boating fun?

 

[18WCmerc]

Re: Mercruiser OEM to performance????

Wire2 Thanks! that was actually the kinda info im hunting for. I had to put up my second post/disclamer because i foreseen the flaming coming on fast on this post.

philister, i kinda understand you cam logic, but not really, valve overlap isnt going to suck water into the engine. sorry champ---this is the cam thats in it right now...Comps Cam Mag. 306 Has 260 dur@.050 and 592 lift on int. and exh.

what you need to also factor that the 5.0 merc alredy has a 351 cam and heads which is comparable to a lot of mild bump sticks with some 2.02-1.60 heads.


I dont really need help justifying what im doing or even if its a bad idea, i just need to know whats interchangable. i found out about the merc distributer what i had to pick up some points. curious as of now about about intake compatabilities, sooooo to make this very very simple for everyone i will ask one simple question:

Has anyone ever put an aftermarket aluminum intake on a 1975 5.0 mercruiser?

 

[75TowerOfPower]

Re: Mercruiser OEM to performance????

What if we ported the stock one out? I mean yeah we wold be out a couple hours and if it doesn't work oh well we can buy an aftermarket one.

Also the miss you had ealrier in the year may go away with these new points but we always saw in under the load.

 

[18WCmerc]

Re: Mercruiser OEM to performance????

thanks canuck, i didnt even think about that. picking up an intake is super duper cheap, worse case scenerio is we have to build custom brackets for throttle cable and engine harness bracket, which is too easy and gives us a job for the winter. should have a wicked hole shot with that 21p prop too. now i just need to make my steering handle that prop torque. I think mid winter im going to invest in a no feedback system, maybe it will only take one guy to hold the wheel on hole shots.


p.s. your lucky i didnt have to beat you with a stick for your info...watch out jeepforum tards.....

 

[mkast]

Re: Mercruiser OEM to performance????

If you are talking about a "seat of the pants feel" when you push the throttle, you might consider a 351 instead of the 302.
The old Offenhauser Dual Port intake manifolds are designed for torque instead of RPM, I have used them on big block and small block Ford's and GM's.
Your throttle linkage is available at Summit.
Holley Part numbers
hly 717-7
hly 717-11

 

[18WCmerc]

Re: Mercruiser OEM to performance????

thanks mkast! good stuff more specifically what am i looking at in a mercruiser 188hp ford, heard a lot. is it a 302 with 351 cam and heads? its a 1975 if that helps, cant get a straight answer on what it really is

 

[45Auto]

Re: Mercruiser OEM to performance????

philister, i kinda understand you cam logic, but not really, valve overlap isnt going to suck water into the engine. sorry champ---

Sounds like you already know everything about overlap, reversion, and marine cams. No point in you wasting your time here. Maybe you could contact some of Philster's buddies below and straighten them out?

Crane Cams Marine Tech Tips:
http://cranecams.com/?show=newsLetters&no=92

Marine Tech Tips

Camshafts with a wider centerline like 112 - 114 are better for marine use because they idle better during docking or shifting in and out of gear.

Also wider centerline camshafts have less valve overlap, so you have a lesser chance of water reversion in the exhaust system (i.e. water sucking back into the engine at idle).

Mercruiser Service Bulletin 2001-13
http://www.boatfix.com/merc/Bullet/01/01_13.pdf

Water Ingestion
Engine cooling water mixes with the exhaust at the end of the exhaust elbow to go overboard. Under certain conditions, a fine mist or droplets of water can be drawn backward into the exhaust passage of the exhaust elbow while the engine is idling.
1. All engines have valve overlap, even 4 cylinder engines. Gen+ V6 and V8 engines have more valve overlap than the older engines. The higher horsepower big block V8 engines have more than the base big block engines. This ?valve overlap? coupled with the ?tuning? of the boat?s exhaust system can cause water ingestion. Valve overlap is more likely to cause water ingestion at idle or low engine rpm than it is at higher engine rpm.
2. Extended idling before shutting the engine off.
a. This affects an engine with thru-hull exhaust outlets more that thru-prop exhaust models. Because of ?No Wake? zones and other conditions, engines that idle 30+ minutes prior to being shut off, tend to be more likely to have water ingestion. Quiz the boat operator about their idle times. One way to stop or minimize this condition is to increase engine rpm (in neutral gear) to 1300 for 45 seconds then slowly return throttle to idle position and shut the engine off.
3. Throttle ?chops?.
a. Doing ?throttle chops? can cause water exiting from the exhaust elbow to be drawn backward into the engine on either thru-hull or thru-prop exhaust engines. Also, it can happen with the boat in the water or on a trailer with a flush device. Caution technicians and boat owners about doing ?throttle chops?.
4. Missing internal shutters in exhaust tips (sterndrive engines only).
a. Sterndrive engines with thru-transom exhaust are more likely to have water ingestion if the internal shutters are missing. The exhaust hose length is short on these installations. The internal shutters help break up the ?tuning? effect of the short hoses. Install exhaust tips that have internal shutters that will not burn out or break off. Installing exhaust tip silencers is another option. If there is room in the exhaust hose, installing the Exhaust Resonator Kit will help correct this condition also

Lightening Performance Marine:
http://www.boatheaders.com/reversion.htm

• REVERSION ​

Reversion is simply the exhaust gases momentarily flowing backwards during the overlap phase of the camshaft at low cycling rates. During the overlap phase the engine is on the exhaust stroke and the piston is pushing out the last of the exhaust gases. Prior to reaching top dead center the intake valve begins to open. At low cycling rates the intake charge and the exiting exhaust pulse have yet created any momentum. Thus the piston pushes some spent exhaust gas into the intake manifold. This is why engines with big camshafts idle and sound radical. Not a problem until you add water into the exhaust stream. Concerning headers, reversion can be severe enough to add water to oil (milky oil), rust valve seats, even stall the engine. This effect only happens at idle, but engines encounter their greatest reversion pulse at shut down.
THE ONLY TRUE TEST FOR REVERSION IS TO IDLE THE ENGINE WITH THE HEADERS ATTACHED AND WATER GOING THROUGH THEM, SHUT IT DOWN, REMOVE THE HEADERS AND IF YOU HAVE WATER RESIDUE LAYING IN THE EXHAUST PORTS, YOU HAVE REVERSION.


Lightning Performance Marine makes many options to reduce or totally eliminate reversion.

• ANTI REVERSION TIPS

1. Header selection The tip to header selection is to choose a design that will introduce water into the exhaust stream as late as possible. For example our 40340 header is actually made to replace a Mercury manifold with a 3" riser block. This header is 4" taller than a standard Mercury header plus it rocks forward 2" thus were able to add a 2" longer collector. If the height is not a concern you just added 6" of dry length to the header.
2. Collector selection If you have room to add dry collector length do it. Collectors are available in a variety of lengths.
3. Cubic inch displacement The tip here is simple, the bigger they are the harder they suck back. Either reduce the duration of the cam or start add some anti reversion options.
4. Camshaft selection With regards to headers the only thing your concerned about is how much piston movement in volume takes place while the exhaust valve is open on the intake stroke. A wide lobe separation angle actually advances the exhaust valve timing event which will close the exhaust valve sooner, but the down side is it also moves the horsepower and torque curve up the RPM range. Rhoades style bleed down lifters will deduce the cam duration by as much as 20 degrees. Available only in standard hydraulic these lifters are a great choice.
5. Connecting rods Marine engine builders rarely think of connecting rod ratios effecting reversion, but it does. A longer than stock connecting rod will make the piston dwell at the top during the overlap cycle thus less piston movement with regards to crank rotation.

Boat Exhaust.com:
http://www.boatexhaust.com/faq.html

What is reversion?
Reversion is the pulling back of water from the riser where water enters the exhaust. The water is pulled back into the exhaust part of the head and into the cylinders of the motor. Reversion occurs with the exhaust systems that utilize short stock type risers when a cam change has been made in the motor and duration of the cam exceeds 230 degrees. Stock motors do not have a problem with reversion. To eliminate reversion long stainless steel risers are utilized for systems with altered cams. These are jacketed and inject water into the exhaust at a point much farther from the motor thus eliminating reversion.

 

[18WCmerc]

Re: Mercruiser OEM to performance????

i completely understand that could happen with a huge bump stick, however with 112 lobe seperation thats not a worry. we are talking mild cams


I always have to tread lightly here...some people search iboats to start arguments.

 

[45Auto]

Re: Mercruiser OEM to performance????

http://www.boatexhaust.com/faq.html

Reversion occurs with the exhaust systems that utilize short stock type risers when a cam change has been made in the motor and duration of the cam exceeds 230 degrees.

this is the cam thats in it right now...Comps Cam Mag. 306 Has 260 dur@.050 and 592 lift on int. and exh.

Your boat, your choice. Maybe you're the lucky type . A lot depends on the exhaust configuration (riser height, thru-hull vs prop, etc). There's more to it than just lobe separation.

 

[mkast]

Re: Mercruiser OEM to performance????

thanks mkast! good stuff more specifically what am i looking at in a mercruiser 188hp ford, heard a lot. is it a 302 with 351 cam and heads? its a 1975 if that helps, cant get a straight answer on what it really is

A 188 is in fact a 302 block with 351 heads and a 351 cam, your engine uses a 351 firing order. Look at your intake manifold. At the rear of the manifold the firing order has been ground off and the 351 firing order has been stamped on the manifold.
If you are planning on spending some money on an engine, consider spending it on a 351 instead of the 302. All you need is the short block, distributor, flywheel, water pump and intake manifold, (as I remember it). You might also look at NAPA for your marine parts.

 

[Philster]

Re: Mercruiser OEM to performance????

In post number one, you didn't mentioned the cam specs, so I was just warning you.

All good.

 

[18WCmerc]

Re: Mercruiser OEM to performance????

you gents wernt kidding, transitioning from automotive to marine is quite the undertaking.

thanks for all the input thus far

 

[haulnazz15]

Re: Mercruiser OEM to performance????

He wouldn't need a flywheel/harmonic balancer since the 302's didn't go to the 50oz unit until the late 80's. 302/351w share the same balancer/flywheel up until that point. If you were looking at messing with the points/condenser, I would have just gone with an electronic unit since you dizzy is 30+ years old and is likely going to have a bit of slack in the tolerances. Personally, I wouldn't run any cam with more than .500 lift on the SBF's for marine use. Find a cam that is good from 1000-5000rpms or less, which is usually a 4x4/Truck cam. I have an Edelbrock performer aluminum intake on my 351w, and I can help you with any of the miscellaneous parts you would need. The exhaust manifolds can be changed to the center-riser style for a few more ponies. The 302 w/4bbl carb/intake will put out 220HP or so. You might be able to squeeze 230-235HP with a cam and new manifolds. To put it in perspective, the 2bbl 351w was at 233HP, and 260+ with 4bbl, so it's up to you where you want to go.

Reversion is a real issue because the water from the manifolds/risers exits just a few inches from where the exhaust is coming up from the center of the riser, so it doesn't have to travel far to get sucked back into the the exhaust manifold in between exhaust pulses. There is obviously less frequency of pulses and water flowing slower closer to idle, so a cam with a lot of lope at idle stands a good chance of introducing water into the exhaust/cylinders. I'm just saying don't write it off as a possibility, although 112 LOA shouldn't put you in too much danger.

 

[wca_tim]

Re: Mercruiser OEM to performance????

There are ways to deal with reversion... depending on what your exhaust manifolds look like, you can for example weld extensions onto the inner tube of the risers to more the point back wher ethe water is mixed with the exhaust. Also it's important to realize that reversion is a funny thing and not always so predictable just by looking at cam duration. to be safe, if you add much duration, you have to check once you get it running.

I'm not a ford guy, so I can't comment too much on specifics here, but I do humbly, respectfully disagree with the folks who say it's not worth doing. or that if you make more power you'll kill the bottom end. My experience is that if you pay close attention to what you're doing, do the homework and design the build so it has a nice flat torque curve, you can get great results!


Cheers!

http://www.youtube.com/watch?v=EHoXsQc6644

 

[18WCmerc]

Re: Mercruiser OEM to performance????

as of this weekend im going to put on a intake and hunt for a 4bbl carb. does it have to be a marine carb? where can i find a flame arrestor to ride a 4bbl and on the 188 do i need to find a 302 or 351 intake? the cam will wait till next winter after further research.

thanks all!