Hot Rodding an A4 - SailNet Community
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post #1 of 34 Old 11-02-2011 Thread Starter
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Hot Rodding an A4

Has anyone here ever done any hot rodding of an A4? Since that little engine is so simple and agricultural I imagine it would be pretty easy to get a significant increase in it's output without threatening its reliability and smoothness. Those attributes could well be increased since, considering its intended uses, I doubt much of anything about it was optimized or very precise when it was constructed.

What I'm thinking of is this;

First, stripping it for a rebuild
Next, adding the Moyer stuff - electronic ignition, oil filtration etc.
Next, shaving the cylinder head and block to raise the compression to, say, a whopping 8.5 to 1.
Then, having the mains line honed.
Then, cleaning up the intake and exhaust ports with a carbide burr and die grinder (port & polish). Since it's a flathead, I expect relieving the area between the valves & combustion chamber may be necessary. Also, matching the intake & exhaust openings with their respective manifolds. Also as part of this process, checking and matching the volume of the combustion chambers.
Next, having the rotating assembly carefully balanced.
In other words, basic balancing and blueprinting.
Next, painting the inside of the engine - all non machined surfaces, with Dolphinite to promote rapid oil return to the pan.
Last, possibly having the cam reground to increase its lift & duration a little. A good cam grinder will know how to shape the lobes to maximize low RPM torque

All basic, tried & true performance enhancements that, if done with moderation should increase its performance without degrading reliability. I figure getting 45 or 50 horses and a comparable increase in torque should be easily reached and it would be fun albeit a bit eccentric to do.

Anybody done anything like this?

Any opinions, theories, catcalls, shouts of derision or admiration & encouragement?

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #2 of 34 Old 11-03-2011
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I don't know anything about performance mods. I assume if this was done it would be to re-purpose the engine to a bigger boat. I have an A4 in a 27' boat that is probably overkill. Goes nearly hull speed at idle.
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post #3 of 34 Old 11-03-2011
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I have nrver owned one but have read they are pretty reliable in stock form, possibly because they are not stressed very hard? Do you want to swing a bigger prop or get more revs? From what I remember, flat heads used to be subject to heat issues, burnt valves and seats, high head temps, and pinging, not something you want in a continous heavy load situation. If you do it let us know how it worked out.

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post #4 of 34 Old 11-03-2011
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Look at the "Spruce Goose". If you throw enough money at something, you can make it fly.

I'm thinking you are joking, but in case you aren't, I'd recommend starting off simple. Start with the ignition, and maybe some carb work to see what the improvements are.

A rebuild certainly won't hurt, but I wonder about all the machining.
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post #5 of 34 Old 11-03-2011
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I think the crank bearings are limited in what they can handle. It is an interesting idea. The A-4 is probably right where it needs to be in its unaltered state.

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post #6 of 34 Old 11-03-2011
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Since it's a 30hp engine that, with the direct drive, will only put out about 18 hp (someone correct me if I'm wrong), your next move would be a Hurst 6 speed tranny with 4:11 posi traction rear end.

Nothing like a tranny with a good rear end.

Or you could simply get a prop from Indigo, atomic4.com Just make sure you use a zinc...don't ask me how I know.
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post #7 of 34 Old 11-03-2011 Thread Starter
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I'm not planning on doing it, I don't even own one, it's just curiosity. I've seen A4's in some pretty big boats and it won't swing much of a prop so I figured a torque increase could be useful in many cases. Overheating was a problem with Ford flatheads because the exhaust ports went through the water jacket - I don't know if that's the case in an A4. A bigger prop would be the nautical equivalent of a set of gears, so yeah - a set of 4:11's

I fully understand about the durability value of an engine being lightly stressed. That is why I stated several times that I'm talking about MODERATE modifications - things like line honing the mains, balancing the rotating assembly, improving oil drainback and so forth actually increase durability while they enhance performance. Pretty well everything I mentioned would add little or no cost to a normal "bolt it together" rebuild as well - it's mostly just craftsmanship.

I'm not talking here about throwing a blower or dual 4's on it, just a careful and precise build with a few bits of performance enhancing technology.

For those who think it is already optimized, think of the original Chevy small block - wonderful engine, IMHO the overall best engine of any kind ever made BUT it was extremely easy to improve everything about them simply by improving them from a mass production build standard to a precise "machinist" standard - with no decrease and usually an increase in durability.

Keep those responses coming in.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #8 of 34 Old 11-03-2011
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As an exercise in "What if", I would recommend tossing the cash into a non-fresh water cooled system (like in a car), and running a small Japanese 4 cylinder car engine with the required custom bell housing. Those things reliably go for hundreds of thousands of miles in a state of comparative neglect. Limit the RPM to about half of max and with normal maintenance the thing should outlive the boat. When it does finally give in, you've got a bellhousing that will fit a mountain of spit cheap replacements. Parts should also be sufficiently cheap to reduce the fear associated with maintaining marine engines.
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post #9 of 34 Old 11-03-2011
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Quote:
Originally Posted by SloopJonB View Post
I'm not planning on doing it, I don't even own one, it's just curiosity. I've seen A4's in some pretty big boats and it won't swing much of a prop so I figured a torque increase could be useful in many cases. Overheating was a problem with Ford flatheads because the exhaust ports went through the water jacket - I don't know if that's the case in an A4. A bigger prop would be the nautical equivalent of a set of gears, so yeah - a set of 4:11's

I fully understand about the durability value of an engine being lightly stressed. That is why I stated several times that I'm talking about MODERATE modifications - things like line honing the mains, balancing the rotating assembly, improving oil drainback and so forth actually increase durability while they enhance performance. Pretty well everything I mentioned would add little or no cost to a normal "bolt it together" rebuild as well - it's mostly just craftsmanship.

I'm not talking here about throwing a blower or dual 4's on it, just a careful and precise build with a few bits of performance enhancing technology.

For those who think it is already optimized, think of the original Chevy small block - wonderful engine, IMHO the overall best engine of any kind ever made BUT it was extremely easy to improve everything about them simply by improving them from a mass production build standard to a precise "machinist" standard - with no decrease and usually an increase in durability.

Keep those responses coming in.
My experience was with Ford and Continental flat heads. You mentioned a compression ratio increase, more heat to get rid of?

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post #10 of 34 Old 11-03-2011
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Car engines are designed for light load. Pushing a boat under power is like driving a car uphill forever. That's why automotive engines are "marinized" using heavy duty truck engines. I'd stick with a real marine engine myself.
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