Michigan Boarder Engine Blueprint and Build

[formulaben]

Do you know your cup specs for each prop?

[WheelerWake]

Do you know your cup specs for each prop?

They are OJ non-cnc props. Don't know the cup specs. They don't have a part number on them, only dia, pitch, "cup" and the mfg date.

Cruising at 30 mph is ~3000rpm with the 18" and ~3300 with the 16".

Never really cared what top speed is...

[JB-FOOT]

a 1.5 : 1 gear reduction transmission and a 1:1 are TOTALLY different animals...

John, you have a 1:1 direct drive and as such will not be able to spin a 14x18 at all....you will hurt your motor and will not be able to get WOT up to your full rpms

[WheelerWake]

a 1.5 : 1 gear reduction transmission and a 1:1 are TOTALLY different animals...

John, you have a 1:1 direct drive and as such will not be able to spin a 14x18 at all....you will hurt your motor and will not be able to get WOT up to your full rpms

Yes, of course, this is the reason I pointed out mine has a 1.5:1 v-drive...

[sgt1970-442]

john, as for a prop. I would call acme as they are close to you and they let me try a couple different props to see which one was best for me.

explain to them the numbers we came up with on the dyno and see what they recommend.

[Oberon]

Prop selection on my setup has been backwards from what I expected. I have a home-brew stoker 350/383 also (mine has mefi though). We run ~2500 lbs ballast + ~1500 people, gear, fuel, etc.

I've tried 2 props, a 14x16 and a 14x18 (have a 1.5:1 v-drive). Wide open, from a stop, both stall at about 3900 rpm. I'll bet mine has a similar torque curve to yours, starts heading south around this rpm (looking at the graph's on the "just a little fyi" thread.

The interesting thing is, the 16" pitch prop takes 8 seconds to get to 20 mph with ballast, while the 18" is quicker at 6 seconds. I believe this is because the engine is able to spin them both to 3900 rpm "stalled" and the 18" pushes more water at this rpm.

I obviously run the 18, the 16 is my spare.

I've recently acquired a 14x20 but won't be able to test it until next season.

When you say your prop "stalls" do you mean it cavitates at 3900 rpm or that it maxes out at 3900? Either situation means you have the wrong prop but cavitating is a potentially damaging situation for your running gear.

A lower pitched prop will always accelerate better than a higher pitched prop because it can get the to peak torque curve faster and stays in it longer.

I don't know what the optimum WOT rpm is for your engine but it is certainly higher than 3900. There is a pretty good write-up on this sight somewhere that describes how to fit a prop. If memory serves, you want to load your boat to the max you will regularly run and find a prop that will run at the optimum rpm at WOT. Based on your description I think you may have too much prop on your boat.

Caveat; I'm no prop expert. I know what I know based on what I've read hear and the prop on my boat was a fairly simple match since my boat is stock.

[tvano]

i think this is the thread that Oberon referenced "Don't kill your engine" by enginenut

Edited December 1, 2014 by tvano

[WheelerWake]

When you say your prop "stalls" do you mean it cavitates at 3900 rpm or that it maxes out at 3900? Either situation means you have the wrong prop but cavitating is a potentially damaging situation for your running gear.

A lower pitched prop will always accelerate better than a higher pitched prop because it can get the to peak torque curve faster and stays in it longer.

I don't know what the optimum WOT rpm is for your engine but it is certainly higher than 3900. There is a pretty good write-up on this sight somewhere that describes how to fit a prop. If memory serves, you want to load your boat to the max you will regularly run and find a prop that will run at the optimum rpm at WOT. Based on your description I think you may have too much prop on your boat.

Caveat; I'm no prop expert. I know what I know based on what I've read hear and the prop on my boat was a fairly simple match since my boat is stock.

I am using the term "stall" to define the RPM the engine achieves about 1 second after going to WOT from a stop. It then stays at this RPM for a couple seconds before increasing to max RPM (5k+ in my case). "Stall" is a term used with torque converters in cars and trucks (especially racing).

The reason for my post is that mine accelerates better with the higher pitch prop, not the lower.

[formulaben]

The reason for my post is that mine accelerates better with the higher pitch prop, not the lower.

This is why I was asking what the cup was, as the advertised pitch may be very different from the effective pitch based on the cupping. For what it's worth, ACME says that you gain about 1" of pitch for each .050" of cup...

[WheelerWake]

This is why I was asking what the cup was, as the advertised pitch may be very different from the effective pitch based on the cupping. For what it's worth, ACME says that you gain about 1" of pitch for each .050" of cup...

I agree, but I think the cup on these props is similar because, while cruising, the rpm changes as expected:

Cruising at 30 mph is ~3000rpm with the 18" and ~3300 with the 16".

[Oberon]

I am using the term "stall" to define the RPM the engine achieves about 1 second after going to WOT from a stop. It then stays at this RPM for a couple seconds before increasing to max RPM (5k+ in my case). "Stall" is a term used with torque converters in cars and trucks (especially racing).

The reason for my post is that mine accelerates better with the higher pitch prop, not the lower.

Got it. I misunderstood what you were saying.

[sgt1970-442]

john,

do me a favor and lets just get with acme or oj and see what they recommend. hate to see a new mill go to crap because of suggestions.

we have some numbers that are not anything that indmar every built so we need advice from the people that build the prop and are in the know.

not saying the suggestions aren't going to work. I just would feel safer if we contact the people that build the props.

[shawndoggy]

Although... OJ and Acme have certainly been known to give some wack, kneejerk advice too.

[JB-FOOT]

john,

do me a favor and lets just get with acme or oj and see what they recommend. hate to see a new mill go to crap because of suggestions.

we have some numbers that are not anything that indmar every built so we need advice from the people that build the prop and are in the know.

not saying the suggestions aren't going to work. I just would feel safer if we contact the people that build the props.

Sarge...

That sounds like pretty "SOUND and SAGE" advice...

Especially with all of the time invested in getting it done...

Because I believe you said "After this one, you were DONE!"

JB-Foot

[Michigan boarder]

The prop is on hold 'till spring, as is the carb. I need to get thru Christmas expenses and work stuff, get the engine in the boat, fabricate an exhaust system, etc. etc. Come spring I'll work with Acme directly but will also factor any advice that I can get from JB or others that have an Echelon & similar power plant.

[Michigan boarder]

I have some time today so I thought I'd put up all of the dyno data.

I drove to Steve's place in an ice storm, left my house at 4am and got to his place around 7ish. Drove in front of his house at about 15mph and almost took out a tree, sheet of ice. We then took off to his friend's place (John) where the engine was located, had a coffee, loaded up the engine and went to the dyno guy. Jimkid Motorsports in Redford, MI, great guy, nice shop. This was my first experience but Steve and John seemed very impressed with his set up and how accommodating he was to us. We unloaded the engine and hooked everything up (dyno plate to flywheel, carb, fuel lines, water cooling lines, exhaust manifolds, throttle cable, etc.etc.). We finished up a little at about 11am and fired it up. Ran great at idle, and Jim ran it for about 20 minutes varying the RPM's from idle to a couple thousand, back down, back up, etc. Then we decided to do a "short pull" with the stock carb. This was a stock carb that had about a half hour run time on it from a rebuild before the engine failure. A short pull means only running it up to around 3500rpm. Here's the chart:

After that Jim suggested we grab some lunch, knowing that we'd be at this for a while. So we did, at Jest Omlettes. Had a chance to share some good "destructive testing" stories, and I had some Mexican thing that I would later regret.

Edit: so looking at that chart, at only 4000rpms we were hitting 453tq and 345hp. I was a very, very happy guy, but none of us really talked about what the data showed or where we might end up, knowing we had long pulls and bigger carbs to experiment with. All along as the build and season went on I was hoping to get 370 or 380hp, but on the drive across the state I set my expectations low. So after this pull to me we were already good, the fact that I had just gone from 265hp originally to 345hp, was going to be fantastic. Whatever more we got was going to be icing on the cake.

Edited December 3, 2014 by Michigan boarder

[Michigan boarder]

We got back to Jim's place, and after a brief talk about CFM's we put a manifold pressure guage in. Then we did two pulls.

So here we are now with the stock carb, hitting 460tq and 383hp. We were all smiles at this point, and the even better news was the manifold pressure went to 1.19hg, which means we were drawing a vaccum. Which means we need more air flow. Which means we need a bigger carb. Which means 383hp was not the limit, this engine was capable of more.

Edited December 3, 2014 by Michigan boarder

[Michigan boarder]

Next we took the carb off of Steve's boat, which had been re-jetted a bit, but believed to be 600cfm. Here are those pulls:

We were running well on manifold pressure, but air/fuel looked a little rich, which was keeping down the tq and hp.

[Michigan boarder]

Next we used the 850cfm Quick Fuel Technology carb that Steve normally ran on his hot rod. Timing at this point has been at 34 degrees BTDC on all carbs and all pulls.

On the second pull we got up to 389hp but more importantly went up to 486tq. Huge gain.

Then we moved the timing up to 36 BTDC

That got us into the 390's for hp and close to 490 on tq.

Edited December 3, 2014 by Michigan boarder

[Michigan boarder]

Next we advance the timing to 38 degrees BTDC.

Here it is with the 850cfm carb:

Then with a 750cfm carb that the shop had on hand:

And then we put my stock carb on it one more time:

[Michigan boarder]

Here are a couple of graphs that compare the output with the different carbs.

This is the 850cfm versus the stock carb at 38 BTDC:

And here is the 750cfm versus the stock carb at 38 BTDC:

[Michigan boarder]

So the stock carb at 34 BTDC means I can run 87 octane, and I'll be at 460tq and 383hp. I can do this right now, got a good carb, etc.

Or, I can buy a new carb, stay at 34 BTDC and I'll be at 486tq and 389hp.

Or, I can buy a new carb, advance to 38 BTDC requiring 93 octane fuel and hit 490tq and 395hp.

I still need to get a new prop, but those numbers are close enough that it probably doesn't matter too much which set up I go with, the prop will probably be the same. Other things I'd like to do to the boat are replace my old guages & add depth and hour meters and add a heater. A new rub rail would be nice too, the front of mine is all banged up. So that is the stuff I need to think about over the next couple of months.

Once again, thanks Steve for your help, it all turned out great!

[Woodski]

@Michigan Boarder: Adjusting the ignition timing to 34 deg BTC will allow you to run a lower octane fuel, although the dyno numbers may not be representative of the actuals using different fuel, assuming the same fuel was used for the timing sweep. Lower octane fuel will light off sooner and burn faster than higher octane fuel, thus the need to retard the timing. You may end up at the same power level, or it may differ depending on how things react although it should improve the power level as 34 deg. BTC is a better match for 89 octane fuel. It is pretty clear the increased airflow, improved mixing and/or better A/F ratio of the "better" carb offers a significant performance gain.

[WheelerWake]

john,

do me a favor and lets just get with acme or oj and see what they recommend. hate to see a new mill go to crap because of suggestions.

we have some numbers that are not anything that indmar every built so we need advice from the people that build the prop and are in the know.

not saying the suggestions aren't going to work. I just would feel safer if we contact the people that build the props.

I agree, my non-stock engine didn't respond well to conventional prop selection.

[sgt1970-442]

john,

I think after we get that slug of an engine back in your boat tomorrow,

we are probably going to need lunch at the yacht club.

who's in?