Gas props on nitro rigger

[Ray Sametz]

Better chance at hitting the Lottery. Charles.

 

[Jim Allen]

Thanks Mr. Jim. Just one more question....will you build me an engine for christmas, I will not tell anyone.

Charles

I see your humor is still in working order. Have a Merry Christmas & A Happy New Year.

Jim

 

[Ray Sametz]

Thanks Mr. Jim. Just one more question....will you build me an engine for christmas, I will not tell anyone.

Charles

I see your humor is still in working order. Have a Merry Christmas & A Happy New Year.

Jim

Jim, you and yours have a great holiday season, maybe we can pull you out of the "Man Cave" for a race at the Internat's in Charleston, be great to hang out and smell some Nitro. B)

 

[Joe Warren]

28000.
Julian

Julian as long as you have a Boat, Engine, Props & are Setting Records. You are way ahead of the guy that is still reading props Charts & trying to figure in the prop slippage @ Speed. It requires a Total Package of Great Equipment & Driving Skills. Even the prop tip speed that ABC & Octura post are Estimated speeds. Even the slippage is Estimated. There is nothing that Will Replace Pond time........ it is Our BEST DYNO...... There are Experience Model Boaters that offer Good Engine Service, Excellent Boat kits,& Good props can be Purchased you can tweak them to your spec....Good Fuel can be purchased, But the Boater himself Must bring it all together to get it to Peform!!! Previous years we could by Engines that performed well with Known Pipes & with the correct prop.... You Could buy on Monday & Win on Saturday......After CMB took over the Nitro Engine Business We all went back thru a learning curve to Find the Best Engine set up With the Best Pipe. Today you can Buy Again Known Engines & Products... that if Used together Can Guarantee Performance on the Water.

 

[DaveMarles]

Thats correct. Compare an exhaust that is oval shaped at the top with one that is flat across the top & it can easily been seen which one has the greater time area number in the blow down area. You will definitely want this if the tuned pipe is really doing its job.

I do make the top of the ex flat but the different angle sounds real nice. I was always on the mind set that the ex should come out all at once to get that high pressure wave moving all in one shot. So 80% of the timed area should be the number of the wide area that is above the transfers and the the rest of the window should make up the rest? With a total area of the ex to be 30% of the combined transfer and boost area? Just got my new mill set up to day will mess with some old sleeves and do some test cutting. The bottom of radius on the piston should line up with the bottom of the ports. what kind of transition to the transfers would work best. Should the sleeve be a sharp edge on the OD or should this be a transition radius? then again the piston dose not spend much time at the bottom.

I think we have a little misunderstanding here. The 80% number shows the relatonship between the exhaust width at its widest point & the engine bore diameter. For example; a K-90 has an exhaust width of .895" & a bore of 1.0635", which equals 84%; OS MAX .91 has a .902" wide exhaust & a bore of 1.090" which gives 83%; CMB .90 has a .968" wide exhaust & a bore of 1.102" which gives 88%; Rossi 1.05 has a 1.096" wide exhaust & a bore of 1.1425" which gives 96%. Whats interesting here is that some of the most powerful piped engines such as K & B .40 & .82, Nelson .45 & Picco hydro .90 have exhaust widths that do not exceed 75%. Could excessive exhaust width & poor exhaust port shape coupled with poor transfer geometry restrict the main transfer areas & cause HP killing short circuiting? Dyno testing says the answer is a definite yes!! The radius is applied to the top edge of the piston only. Jim Allen

Jim, I don't think the KB40 KB82 and Picco 90 hydro are some of the most powerful piped engines and probably the reason is that the exhaust width is too little. You talk about trying for maximimum blowdown time area without increasing exhaust duration but the only way to do that is to either widen the exhaust port or narrow the transfers. Are you suggesting we narrow the transfers? I don't think thats an option or the right way to go. Most of the regularly used marine motors have gradually had the exhaust width increased over the years and power has steadily gone up.

Dave

 

[dwilfong]

Ok well here are the first test results. the 2818 was the fastest prop at 85 MPH top end at 20200 RPM.

The modded 1667 78 MPH at 26000 RPM.

Still going over the charts but I tested lots of props and the surprise prop was the AB CNC 7025/3 at 78 MPH and was the best handling of them all. Hooked up all the time and could turn in side at will.

Will give the 3020-20 a try next week when we get the profiling done.

The pitch dose give speed but have to work on the blade OD, area and some back cutting to unload the eng.

All the testing was done with the same set up just changing the props. 50% nitro.

It seams that the props MPH is right in line with the leading edge pitch at that RPM.

Will nail down the calculations and see what is needed to get it done.

And yes at 85 the boat is a hand full.

Will see where this leads.

David

 

[dwilfong]

Thats correct. Compare an exhaust that is oval shaped at the top with one that is flat across the top & it can easily been seen which one has the greater time area number in the blow down area. You will definitely want this if the tuned pipe is really doing its job.

I do make the top of the ex flat but the different angle sounds real nice. I was always on the mind set that the ex should come out all at once to get that high pressure wave moving all in one shot.

So 80% of the timed area should be the number of the wide area that is above the transfers and the the rest of the window should make up the rest?

With a total area of the ex to be 30% of the combined transfer and boost area?

Just got my new mill set up to day will mess with some old sleeves and do some test cutting.

The bottom of radius on the piston should line up with the bottom of the ports. what kind of transition to the transfers would work best.

Should the sleeve be a sharp edge on the OD or should this be a transition radius? then again the piston dose not spend much time at the bottom.

I think we have a little misunderstanding here. The 80% number shows the relatonship between the exhaust width at its widest point & the engine bore diameter. For example; a K-90 has an exhaust width of .895" & a bore of 1.0635", which equals 84%; OS MAX .91 has a .902" wide exhaust & a bore of 1.090" which gives 83%; CMB .90 has a .968" wide exhaust & a bore of 1.102" which gives 88%; Rossi 1.05 has a 1.096" wide exhaust & a bore of 1.1425" which gives 96%. Whats interesting here is that some of the most powerful piped engines such as K & B .40 & .82, Nelson .45 & Picco hydro .90 have exhaust widths that do not exceed 75%.

Could excessive exhaust width & poor exhaust port shape coupled with poor transfer geometry restrict the main transfer areas & cause HP killing short circuiting? Dyno testing says the answer is a definite yes!!

The radius is applied to the top edge of the piston only.

Jim Allen

Got the picture now. total with strait across the diameter not the circumference.

 

[Terry Keeley]

Good stuff!

Post some graphs when you get a chance, I'm very interested to compare them to mine...

 

[dwilfong]

28000.
Julian

Julian as long as you have a Boat, Engine, Props & are Setting Records. You are way ahead of the guy that is still reading props Charts & trying to figure in the prop slippage @ Speed. It requires a Total Package of Great Equipment & Driving Skills. Even the prop tip speed that ABC & Octura post are Estimated speeds. Even the slippage is Estimated. There is nothing that Will Replace Pond time........ it is Our BEST DYNO...... There are Experience Model Boaters that offer Good Engine Service, Excellent Boat kits,& Good props can be Purchased you can tweak them to your spec....Good Fuel can be purchased, But the Boater himself Must bring it all together to get it to Peform!!! Previous years we could by Engines that performed well with Known Pipes & with the correct prop.... You Could buy on Monday & Win on Saturday......After CMB took over the Nitro Engine Business We all went back thru a learning curve to Find the Best Engine set up With the Best Pipe. Today you can Buy Again Known Engines & Products... that if Used together Can Guarantee Performance on the Water.

You are right on the money Joe. Its all BS till you put a prop on it and throw it in the water.

David

 

[dwilfong]

Good stuff!

Post some graphs when you get a chance, I'm very interested to compare them to mine...

After dinner I will give it a try.

 

[shoboat]

David,

Do you have the numbers on the AB 7025/3? Pitch? and RPM?

The 1667 had 25% slippage

The 2818 had 11% slippage

Did not have enough numbers to calculate the slippage on the three blade.

The 7025/3 sound like it is a great heat racing propeller so far.

David give me a call if you have some time tonight.

Thanks For Sharing,

Mark Sholund

231.590.3023

 

[Ian Inverarity]

Ok well here are the first test results. the 2818 was the fastest prop at 85 MPH top end at 20200 RPM.

The modded 1667 78 MPH at 26000 RPM.

Still going over the charts but I tested lots of props and the surprise prop was the AB CNC 7025/3 at 78 MPH and was the best handling of them all. Hooked up all the time and could turn in side at will.

Will give the 3020-20 a try next week when we get the profiling done.

The pitch dose give speed but have to work on the blade OD, area and some back cutting to unload the eng.

All the testing was done with the same set up just changing the props. 50% nitro.

It seams that the props MPH is right in line with the leading edge pitch at that RPM.

Will nail down the calculations and see what is needed to get it done.

And yes at 85 the boat is a hand full.

Will see where this leads.

David

David,

The RPM difference between the 2818 and 1667 with the same pipe length is surprising, almost 6000 rpm. Was the 26000rpm sustained or peaks when the prop was hopping?

 

[Jim Allen]

"You talk about trying for maximimum blowdown time area without increasing exhaust duration but the only way to do that is to either widen the exhaust port or narrow the transfers. Are you suggesting we narrow the transfers? I don't think thats an option or the right way to go. Most of the regularly used marine motors have gradually had the exhaust width increased over the years and power has steadily gone up".

Dave

What I'm suggesting is a change to the shape of the exhaust so that small front transfers could be placed under its outer most edges, allowing very large rear transfers & a small boost. All of the transfers would have different upward angles & large ducts with a radius. A typical example is the 125 cc Aprillia engine.

Jim

 

[Ian Inverarity]

Is that a 7025CL3? 3.38" LE pitch, 6.55" TE pitch, Orlic gauge @ 5 degrees. I bought one to try on a gas mono and it wasnt so good, never tried it on a rigger.

 

[Ian Inverarity]

What I'm suggesting is a change to the shape of the exhaust so that small front transfers could be placed under its outer most edges, allowing very large rear transfers & a small boost. All of the transfers would have different upward angles & large ducts with a radius. A typical example is the 125 cc Aprillia engine.

Jim

Jim,

Altho it doesnt have the large radius ducts, do you mean cylinder porting something like this with transfer porting under the sub exhausts and small boost port, Novarossi 35+:

https://www.intlwaters.com/gallery/displayimage.php?album=930&pos=14

 

[dwilfong]

Here is a pic of all the props tested. 2818 1st and last 7025/3 2nd from last.

Will break them out more. still going over it.

The power supply took a crap at the pond could not get them in a diffrent named file.

Still trying to remember which ones are witch :wacko: Dumb ass didn't wright it down.

 

[Jim Allen]

Altho it doesnt have the large radius ducts, do you mean cylinder porting something like this with transfer porting under the sub exhausts and small boost port, Novarossi 35+:

I'm suggesting something like this.

 

[Ian Inverarity]

Jim,

Are you suggesting that porting is better? Specifically what do you feel is better and why? Thanks.

 

[aaron alberico]

Just shoot me a number. Never thought it would be free.

Just remember this is a toy boat not a NASCAR team. :lol:

Unless you want to sponsor the first 100MPH heat racing boat.

David

David

so how fast are you going now?

regards Aaron

only a estamat rite now. still have to get the gun on it . so lets just say fast.

I will hook up the eagle tree next week to get some data loged.Getting the new V4 with the power panel this week.

If you do the math 4.56 lead in pitch at 23500 RPM=101 MPH

O and this is right now not soon

 

[Tom Foley]

Here is a pic of all the props tested. 2818 1st and last 7025/3 2nd from last.

Will break them out more. still going over it.

The power supply took a crap at the pond could not get them in a diffrent named file.

Still trying to remember which ones are witch :wacko: Dumb ass didn't wright it down.

Add 3-4 oz of weight near the engine bay and see if it handles better but does not slow down . i think it will .