12.5 mph

[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]

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]

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]

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]

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

Originally Posted by 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.

[hanleyclifford]

Sounds like you should go back to your original prop. The numbers look a lot better. I am also dealing with this issue on Destiny. I have learned that vacuum also plays a role in prop selection. Dave Neptune may have some suggestions for you. Do you have a vacuum gauge set up so you can read it underway?

[Ball Racing]

Originally Posted by 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

I know displacement can call for different things,
I just tried the indigo because I had it, and several people said to try it.
I want to put a Michigan dyna jet on there..

I don't have a vacuum gauge installed at the moment, but I have one I can try.

Right now I am trying for all out performance, once I see what I can get the boat to do, then I will go back and see if I want to give up docking, reverse, or vacuum..

[Ball Racing]

Okay, heres some things I noticed.
With the engine out of gear, and trying to get it to run smooth smooth, I adjust the idle mixture just so,,,,,,,,, and then time it until it runs slick.
Now take that adjustment, and while tied to the dock, give it WOT and time it to get max rpms.
Okay, now it's still slick at idle, but maybe not as good as timed with no load.
Also, timed for max rpm tied to dock is not what produces max rpm under way, by about 150+ rpms.
Now, power timed for the max rpms under way yields a much rougher running engine at idle.
Amazingly enough max rpms under way is produced by maximum RETARDED timing.
Most of the time in other applications -cars- racing- anything OHV etc., advancing the timing yields the best results. Especially this low into the rpm band. In the car world, you may see a little less top rpm after 5,500 rpm with a touch high timing, and may run a retard box, also if you were running power adders.

One other note this motor gives me more max rpm after a rather long warm up or use. Not sure if it's the oil warming up, and getting easier to pump or if it combustion temp, as the block is warming.
And if I come down to dead idle and let things cool down for a few seconds, then go back to WOT I will reach max rpm, and then after about 20-30 seconds I begin to lose rpms- not many , but you watch the GPS numbers rise-rise,,, then stop, then start going right back down.
I can start out- and max 13.3 mph, and in 30 seconds I will go down to 12.7 mph. The longer you run it like that the more you gradually lose, say at total loss of around 100 or so rpms.
Not much to some but a ton to me.
I feel maybe the way the manifold is made the exhaust is heating up the intake runners , and then dumping hot fuel and air into the motor.
My motor does not seem to be as sensitive to high humidity as car engines I have had. you never make good HP when theres alot of water in the air.
But I guess this thing compressionis so low the water actually boost the compression.(old tractors, and even some forms of racing inject water).
Also the barometer make alot of difference in max rpms.
Low barometer, low rpms.
I think my numbers are way different then what you will see in displacement mode, as I believe I am unloading the motor differently being a planing hull, and not everyone is looking the the last 5 rpms or keeping it at WOT,,
But these are things I am noticing.

[Dave Neptune]

Daniel, have you tried a bit more fuel? I'd try a bit more preassure or a bit bigger orfice in the seat. You may just be pushing right at the limit of the carbs fuel delivery ability.
Also have you checked for full advance on the centrifugal adv. At what point does your engine reach full advance? I have seen a bit of a differance going to lighter springs that have brought mine to full adv below 2000 RPM's. I am using an EI so I don't have the drag of the points and am using the springs provided with the "kit".
My tied to the dock and running numbers vary too just not guite to the same extent as yours. On the lines she runs a bit rough but let her loose and she purr's just fine and very smooth.
Daniel, you may be a good candidate for trying a bit of porting/compression testing, as you are looking for more up top whereas most of us are looking for lower RPM torque.

Dave Neptune

[Ball Racing]

It may can use more fuel, as I have the adjustable jet needle, but you can loosen it a full turn open,from a good running spot and I see no change from where it was before I cranked it another turn.
I undercut and blended- polished the valve stems at the head like we have on race engines.
I cleaned - deburred the ports some, no enlarging. At such low rpm I can't believe it needs more air than the ports can deliver at their current size.
I have not put a light on it to see where full advance is coming in at, I have the Moyer EI stock springs.

I was thinking of removing one of the head gaskets to see it helps much.
(At this point I am not really worried about wear)

[Dave Neptune]

Daniel, as you probably know in a flatty like these it is a comporimise between breathing and compression as well as where it is open and where it is restricted. The single gasket will bump the compression I would guess a full half of a point or more. Might just be enough compression to make a lil' more HP up top. It would be interesting to see if you make a gain on the bottom as well.
Did the "springs" come in a kit or are they the stock units?
I think you have plenty of carb and manifold left for breathing a great deal more tnat she is a taking in now! I also found that when playing with the adjustable jet that it was not "big enough" to run rich enough to loose anything much RPM wise. As I recall it was .044 and the stock jet is around .042. I could lean it down OK but could not get it as rich as I could with an .046 jet. Are you getting more than 2.5 psi of FP? I think I read that the Zenith was good for 60HP (model A) at 4 PSI, but I am not sure if that app was using the same N&S feed restriction.

Dave Neptune

[Ball Racing]

Yeah, on the flathead you can only take so much of the head before there is no room left for good air and fuel flow to the piston.
But given the low lift of the cam, and the huge depth of the chamber,and lack of rpms, I believe you can shave it down and still be good for flow.
Or even a better place to get the compression would be to deck the block as the top ring is still a ways down the bore.
But the valve seats are flush at the top of the block, so you would have to re cut them back in.

In the early years on the briggs & strattons we used to race, we would put a 4hp head on a 5hp block to gain compression- as it had more wedged and shallowed chamber.(it was just the "IN THING" to do back then)
But it was no good above 5,000 rpms- just to restrictive.
I took a 4 hp head and cut about .060 off it,and ran a thinner head gasket and the motor was sounding like a serious hot rod at idle and when you reved it with no load.
I sat down on the kart, and it just would move , and started to instantly cook oils and dirt on the cooling fins as it was overheating that fast.
So we did away with that ole wives tale.
This was before I had my dyno- to test just how bad it was.
One thing I do like in the head is the intake valve side has a pretty straight shot across to the piston.You know how the exhaust is kinda shrouded in on the A4, well the briggs head was shrouded the same on both intake and exhaust side, and we would weld up the intake side head bolt holes, and then cut the head in the chamber to give a better shot of flow across.
Sometimes we cut a "fire slot" groove in the head, trying to get more bang directly on the piston center.
I wish the A4 had the valve slanted towards the bore like the briggs and fords
were.

[sastanley]

Daniel, awesome discussion. Are we talking about screwing up the "quench" area if we get the head to close to the block?

I could believe that in high-RPM (relatively speaking) that the manifold heating up could heat the intake charge. We need a seawater intercooler on the intake side!

[Ball Racing]

Kinda of, You only need as much space right on top the valves in the head as you have valve lift. That area being cut down won't hurt to bad.
But the area in front of the valves toward the piston is where we need the most space, or the best designed area to flow even if we have high compression.
Think of that area as the navagation channel- if you keep closing it up, the "fast high drafting ships carrying the big HP" can't get thru anymore, and only the row boats carrying limited supplies of fuel and air can move across.
But also there are like- locs (spelling)-waterways= (the valves) that open and close at a specific time, and if all the little boats can't get in time, there will not be supplies enough to sustain a good life.

AND even if you having a high "static" compression ratio that is what the math says the cylinder should have,
you also have the dynamic compression ratio which is what it actually is running.
You can cut the head so much that even though math shows big copression, so little air can actually make it across that you are losing dynamic compression.

Just like a nitrous car or supercharged car needs less of a compression ratio because the cylinder is being packed full by other natural means.

It's so fun putting little engines on the dyno, and buzzing them up to see what makes what happen...
I which I could get my A4 on my dyno..

[Dave Neptune]

Daniel. yeh it would be nice to be able to play with an A-4 on the dyno but I would want to be able to play with the cam first. I would like to find out if a bit of cam adv. would help the direct drives with their limited RPM's. Just somthin' I'd like to know. There have been many changes in cam profiles even on flat tappet configurations, a milder cam with steeper ramps and less duration can still have more "open time" off the seat. However in your case what RPM do you think she will perform the best?
Remember that the prop works almost like a dyno just without the nice read outs. With RPM's and vac readings you can still measure gains and losses. Just don't change the prop and the engine at the same time!
I have seen what a roller cam can do for a flatty and it was impressive, especially at the bottom end!!!
What are the specs to the prop you are now using?

Dave Neptune

[ndutton]

Originally Posted by Dave Neptune

a milder cam with steeper ramps and less duration can still have more "open time" off the seat.

There's a point where increased open time becomes a liability at least in terms of the exhaust valve. There has to be enough seat time to dissipate built up valve heat.

The original Honda 750-4 DOHC motorcycle engine had a reputation of burning exhaust valves. When rebuilding mine I was advised by a very experienced Honda mechanic to adjust the exhaust valves (adjusted with shims) considerably looser than the book spec. The resultant longer time on the seat allowed the valve heat to transfer to the head better and the burned valve syndrome disappeared.

This was a significant improvement considering the ceramic coated valves were $42 ea at the time and there were 8 of them.

[sastanley]

Thanks Daniel...makes sense! it is almost like you could mill the head, but then you gotta dredge a channel to get some volume back and keep some air flow!

[Ball Racing]

I know on the briggs flathead that I raced, which had the same bore size and valve size as the A4- you could run some UNbelieveable cam profiles, and hurting the valves or seats was non issue.
We did sometimes run titanium valves and copper berrilium (sp) seats.
Also ran stainless valves, and also regular steel stock ones.
I did see some ex valves take a slight warp from shutting the motor down hot, and not putting it on TDC and plugging the header.

On the briggs we had the same head diameter valves stock, but the stems were only 1/4"diameter where as the A4 is 5/16" so the A4 should handle heat a little better.

I don't see a reason to turn more than 3,000 rpm in my boat.
And thats what so hard for me,, ALL my tinkering on the briggs was for more and more airflow and more and more RPMS.
We could buzz them to 11,000rpms it was crazy.
We had cam companies make billet adjustable cams and gears so we could change the valve train timing.
Early on, we would advance or retard the cam a whole gear tooth...

The A4's torque curve is SO flat, I am not sure how much I can improve on it.
From idle to max rpm is in the 40 lb. ft. range of torque.

[Ball Racing]

Back in April I finally got around to putting the name on this thing.

Also I put a different distributor in it, the old one had tons of up and down play in the main shaft.
I put another accessory drive on it, as the old had lots of in-out play.
She runs better now, the timing is staying more true.

[sastanley]

Awesome pic. Trim tabs & everything!