12.5 mph

[sastanley]

joe, I think you're right, but I'd be afraid the motor would self destruct if it spent any length of time at those RPMs.

Anyone wanna try an Indigo prop on their 2:1 reduction drive?

[Ball Racing]

High Rpms

Yeah, for you guys that may have to cruise for hours on end,
and hull speed can be acheived at as little as under 2,000 rpms for some.
There is no good reason to want to buzz it to the moon.
You want it to last, and be reliable.

But,,,,
Now I guess I want to "hot rod" it a little, as most of the places I plan on going are under 5 miles away, I feel I can risk more rpms, as I will not be doing it for hours on end.
I can go 5 miles in under 30 minutes. So even at WOT thats only half hour at the time.
So one hour a day of run time under those conditions max.
Then lots of time at hull speed just looking good, and cruising....

But speed is like most any drug, you get some, you want some more, then you want a little more, then a little more etc.....

[joe_db]

I doubt it. 30 HP from 60 cubic inches at 3500 RPM is not exactly "highly stressed". Going to New England in flat calm, we left Cape May, put the throttle to 100%, and added gas underway all the way to New York. No harm at all. When I was at flight school the airplanes pretty much all got flown at "rental power", which is full throttle, and they lasted their 2,000 hours between overhaul with no issues.

joe, I think you're right, but I'd be afraid the motor would self destruct if it spent any length of time at those RPMs.

Anyone wanna try an Indigo prop on their 2:1 reduction drive?

[sastanley]

Joe, I come from the 100 HP per litre camp. My current every day car is a 2007 Civic Si that makes 197 HP from a 2.0 (rounded up from 19xx)cc motor, and my "project car" 1991 Civic has a Japanese spec motor that makes 130HP from 1.6 litres.

So...as you said, after a little bit of math, 30 HP from 60 c.i. is not much.

Daniel, go for it...let's hot rod that bad boy! (just remember it only has two bearings!!!!

[ILikeRust]

Let's keep in mind the significant differences between the Honda Civic engine and similar more modern engines and the Atomic 4. Just because an engine is similar in displacement to another doesn't at all mean that it is deisgned or even capable of putting out similar HP.

As already has been pointed out, the A4 has an unsupported crankshaft - only two bearings, one at each end. Second, and significantly, the more modern engines are overhead cam engines, which are much higher-revving than our old flatheads.

Another issue is stroke vs. bore - a lot of the modern OHC engines are oversquare, with a very short stroke.

And on and on.

Although the Atomic 4 is a robust wee beastie, methinks you might be asking a bit much of it to try to get anywhere near 100 h.p. out of the poor devil!

[Ball Racing]

Years back when I was building Flathead Briggs & Stratton 5hp Engines for kart racing, I was getting about 1.75Hp per cubic inch and turning them 11,000 rpms.
We used big tillotson carbs, alky, sometimes nitromethane fuels.
Billet Aluminum Connecting Rods,
Billet Camshafts
Billet Lifters
Billet Flywheels
Billet Stroker Cranks
Hot Coils
Dual Valve Springs
Huge Oversized Titanium Valves
Welded up Ports
Multi Stage Headers
Briggs even had for a while, a motorsports division, and they had a block purpose cast out of 356t6 aluminum, angle ports, thick cast everywhere.

If I had more bearings in this A4 block I could make it a killer.
As the briggs 5 hp had the same bore, similar sized valves.

[Dave Neptune]

Power

Daniel, I too have a bit of flathead experience on the performance side. Although as you say the A-4 is not suited for a lot of RPM's with a 2 bearing crank the crank is quite strong and it is a forged steel one at that. I have recently played with a guy who has a nice lil 32 chop top roadster. He has been using a 350hp 327 SB in it for years. Then I didn't see him for a while and he shows up at rod gathering and I was shocked. Where the SB was sitting was a Ford flathead. I saked him why he went to the flatty and his answer suprised me~he said it was quicker and more fun to drive????. Well it had 3 strombergs on an Eddlebrock intake and Eddlebrock old school copper heads. The engine was polished up and looked really cool in the 32. Where he was getting the power was from a roller cam set up. That flatty has a great deal of bottom end power due the intake profile allowed with a roller and spins to around 5600 RPM's. It also sounds like an almost stock unit and when you stab the throttle it goes strong from the bottom end all the way up.

I have talked to a few about the possibility af a roller in an A-4 not so much for a great deal of power at higher RPM's but for more power up to 2500 would be great~say around 30+ at 2500 would easily be achievable in my humble opinion. If I had the money and time I would be talking to the boys at Iske or Cam Dynamics about grinding one. The lifters would be the issue for change over. That might just get your beautiful launch on a plane.

Dave Neptune

[Ball Racing]

More Speed!

Well max speed WAS 13.1mph
Today, I tied a dock line from the Port stern cleat, Under the boat to the Starboard Stern Cleat as tight as I could get it.
This acts like a trim tab of sorts.
Well, I went 13.3 mph, and it was too much lift to me, as it was driving the bow down.
It's amazing how much it lifted the stern.

I was able to cruise then at 2,200 and keep the boat on top, with little load
So then I took the alternator belt off and went 13.5 mph
I think I just need a smaller diameter line, and "could" pull off more as I was wetting up the boat, and causing too much drag...

[sastanley]

So, Daniel...is that piece of line getting wetted surface area from the bow out of the water?

Is there anyway to re-trim the motor/shaft combo itself to trim the boat better?

[Ball Racing]

14.4mph

Well, the tide was rolling fast today at the mouth of the creek and I decided to run with it at, doing a speed test.
14.4mph
That was with the altenator belt ON, so I maybe could have pulled off 15 mph in all that current if I had taken the belt off.....
Oh well, it was fun for a few seconds, and as the creek broadened the current effect was less and I slowed down...

Now, triming the boat, is best suited to trim tabs like alot of fiberglass boats use or "planing wedges" that alot of the wooden chesapeake bay commerical boats use.
I just needed a touch of lift in the stern.
I heard only this year of guys tying a rope under the boat at the stern, from port to starboard, not for and aft.As this diverts the water and causes lift.
So I said okay (not thinking that would do anything),, and it DOES work....
So now I just need to try a small diamter line, as I don't need as much lift as it's now giving me.

Trim tabs would be the answer as you can adjust them as you go, but they are just not the traditional look I am going for on this boat.

[sastanley]

Daniel,
Gotcha...makes sense...so the trim adjustment gives enough of a speed increase that it compensates for the additional drag the piece of line makes as well I guess.

[Ball Racing]

Indigo prop


Well I put the Indigo prop on today and tried it.
Before I had a 3 blade 11x7 wheel, and 2,500 max rpm and 12-13 mph.
Today it buzzed up to 2,800 rpm, and same speed.
I have less speed at idle than I had.
It does not have the docking authority, nor instant reponse to steering I had.

Plus:
I used to think my reverse was bad,
it is now SO much worse.
I also seem to have torque steer ahead now too, as now I have to keep pressure to the port side, if you relax the steering she starts turning starboard pretty quickly..

I hate to think I had another 15ft of boat under me to control....
And I really went backwards turning 300 more rpms to do the same speed.

Also: they say 1,975 rpm max tied to the dock. I can turn 2,500 rpm.
My old wheel tied up would only go 2,000 rpm.

[ArtJ]

The Indigo prop is designed to provide additional RPM and resulting thrust
for a sailboat to punch thru a chop.

It is not designed to provide higher
overall speed.

Best Regards

Art

[Ball Racing]

If I had more thrust , I would have more speed....
And in a sailboat, it can only push hull speed anyway, so you couldn't see a gain there.
Also I have less foward push thru high winds than the other prop..
Just not enough blade area for planing out applications.

[joe_db]

Props for planing and displacement boats are quite different. The Indigo prop is about opposite of what you need. OTOH it works fantastic on my boat

If I had more thrust , I would have more speed....
And in a sailboat, it can only push hull speed anyway, so you couldn't see a gain there.
Also I have less foward push thru high winds than the other prop..
Just not enough blade area for planing out applications.