.21 Engine Exhaust Timing

[DaveMarles]

Dave:

For example, a Nova Rossi 8 port .15 has an exhaust timing of 161 and transfers of 114 for a blow down of 23.5. How can this engine perform at 40,000 rpm? Another a Traxas .15 with 156 degrees of exhaust and 117 degrees of transfers for a blow down of 19.5. Or a OS 12TZ with 155 degrees of exhaust and 119 degrees of transfer for 18 degrees of blow down. All engines are high reving engines used in buggys and cars.

I have no idea why these engines have such a configuration...

Marty Davis

Marty, Without doing some calculations I have no ideas on those motors, maybe you need to do the TA calculations. Good luck..

Dave

 

[DaveMarles]

Dave MarlesSo what you are saying if you had 186 ext timing deduct 122 intake and divide it 2 would be 32 would that be 32 deg blow down.Or what would the 32 be.

Thanks

Dave Roach

Dave, That would be 32 degrees blowdown.

My first posting was just to explain that quoting exhaust numbers is really a waste of time. Many motors have their transfer timings changed by the manufacturers which will give completely different characteristics to that particular motor if the exhaust timing was one particular figure.

For example.

The CMB 91 RS first came out with 184 exhaust/124 transfers, the next version had 186/127, the latest 190/130. Each one had similar characteristics but if someone had found the last one worked well with 190 degrees and got his friend with an engine with the oldest liner to modify it to 190 exhaust with its original 124 transfers the motor would be a disaster, because the blowdown would be too high and it would never get away from the shore.

Hope this helps as an explanation.

Dave

 

[ids987]

The RPM vs pipe length angle of the original thread got me thinking.

If we accept that we are primarily tuning the pipe so that the reflected wave arrives just before the exhaust port closes (and ignore the other pipe effects), this clearly explains why a longer exhaust duration requires a longer pipe for the same RPM. But, whatever is left of this pressure wave will reflect back up the exhaust pipe, reflect, and return again (weaker of course). If the exhaust duration is significantly more than 180 degrees, the exhaust port will open again before the (re)reflected wave arrives back at the exhaust port - thereby (initially) opposing the flow of the gases from the exhaust port. At 180 degrees open time, the second reflection should arrive back just as the exhaust port opens. At this point, or perhaps at just less than 180 degrees open time, as it reflects again, the negative pressure should help to evacuate the exhaust gases. As the new pressure wave, and the reflected pressure wave are now in phase, we effectively have a standing wave scenario. I guess whether this is of any significance, depends on the power still remaining in the reflected wave.

Also, as we lengthen the pipe to maintain the same RPM with longer exhaust duration, the frequency of the other pipe effects will fall, so the relationship between the different pipe effects will change.

These are just thoughts / ideas on my part - written down in the hope that they may provoke further thoughts........

Ian

 

[DAN MCCORMICK]

MARTY,ROD,ANDY,DAVE AND MARK.

After reading these threads on exhaust and transfer timing seems conflicting. It sounds to me like lower exhaust and transfer timing can make a engine have overall more hp and go faster in a boat. Has it not always been said and taught by all engines gurus that a engine needs more time/area to increase the air and fuel to the engine to develope more HP and a higher narrower power curve. Then why would a lower exhaust and transfer timing engine put out equal to more Hp then a higher timed engine with all things set to optimum settings being equal.

My experience is that the engine is not putting out more Hp then it is in total setup of the boat. I would bet that lower timed engines run larger propellers of equal to or more pitch and the water stays on the propeller longer developing more forward thrust and less slip. Lowering the sleeve puts more torque in the engine and a flatter power curve and usually less HP. More torque allows bigger blades and more pitch giving the preception of more HP. Were in my option it is in the larger more pitch props that developes the speed.

If a lower timed engine with larger higher pitched props runs faster then a higher timed engine with smaller lower pitched props (more rpms) could it be that the setup of the higher timed high rpm engine was running to high of rpms with a lesser efficient prop and the lower timed engine lowerd the rpms just enough to operate at the peak of the power curve and thus a larger propeller can be run with more pitch resulting in faster speeds. Its in the setup .

I have never known any reputable engine builder that mods a engine that lowers transfer and exhaust timing to make more HP ON THE AVERAGE. Yes manufactures miss the setup sometimes.

Conclusion: A higher timed engine will always produce more Hp till it can,t produce anymore and you have a higher narrow power curve and a critical setup'.

Lower timed engines will run faster when the higher timed setup is off its optimum setup giving the preception that the gain is strictly in the lower timing of the engine. Rational comments please. DAN

 

[Marty Davis]

MARTY,ROD,ANDY,DAVE AND MARK.After reading these threads on exhaust and transfer timing seems conflicting. It sounds to me like lower exhaust and transfer timing can make a engine have overall more hp and go faster in a boat. Has it not always been said and taught by all engines gurus that a engine needs more time/area to increase the air and fuel to the engine to develope more HP and a higher narrower power curve. Then why would a lower exhaust and transfer timing engine put out equal to more Hp then a higher timed engine with all things set to optimum settings being equal.

My experience is that the engine is not putting out more Hp then it is in total setup of the boat. I would bet that lower timed engines run larger propellers of equal to or more pitch and the water stays on the propeller longer developing more forward thrust and less slip. Lowering the sleeve puts more torque in the engine and a flatter power curve and usually less HP. More torque allows bigger blades and more pitch giving the preception of more HP. Were in my option it is in the larger more pitch props that developes the speed.

If a lower timed engine with larger higher pitched props runs faster then a higher timed engine with smaller lower pitched props (more rpms) could it be that the setup of the higher timed high rpm engine was running to high of rpms with a lesser efficient prop and the lower timed engine lowerd the rpms just enough to operate at the peak of the power curve and thus a larger propeller can be run with more pitch resulting in faster speeds. Its in the setup .

I have never known any reputable engine builder that mods a engine that lowers transfer and exhaust timing to make more HP ON THE AVERAGE. Yes manufactures miss the setup sometimes.

Conclusion: A higher timed engine will always produce more Hp till it can,t produce anymore and you have a higher narrow power curve and a critical setup'.

Lower timed engines will run faster when the higher timed setup is off its optimum setup giving the preception that the gain is strictly in the lower timing of the engine. Rational comments please. DAN

Dan:

WOW, you are all over the place with this post.

How about 1 or 2 questions at a time?

Marty Davis

 

[DaveMarles]

MARTY,ROD,ANDY,DAVE AND MARK.After reading these threads on exhaust and transfer timing seems conflicting. It sounds to me like lower exhaust and transfer timing can make a engine have overall more hp and go faster in a boat. Has it not always been said and taught by all engines gurus that a engine needs more time/area to increase the air and fuel to the engine to develope more HP and a higher narrower power curve. Then why would a lower exhaust and transfer timing engine put out equal to more Hp then a higher timed engine with all things set to optimum settings being equal.

My experience is that the engine is not putting out more Hp then it is in total setup of the boat. I would bet that lower timed engines run larger propellers of equal to or more pitch and the water stays on the propeller longer developing more forward thrust and less slip. Lowering the sleeve puts more torque in the engine and a flatter power curve and usually less HP. More torque allows bigger blades and more pitch giving the preception of more HP. Were in my option it is in the larger more pitch props that developes the speed.

If a lower timed engine with larger higher pitched props runs faster then a higher timed engine with smaller lower pitched props (more rpms) could it be that the setup of the higher timed high rpm engine was running to high of rpms with a lesser efficient prop and the lower timed engine lowerd the rpms just enough to operate at the peak of the power curve and thus a larger propeller can be run with more pitch resulting in faster speeds. Its in the setup .

I have never known any reputable engine builder that mods a engine that lowers transfer and exhaust timing to make more HP ON THE AVERAGE. Yes manufactures miss the setup sometimes.

Conclusion: A higher timed engine will always produce more Hp till it can,t produce anymore and you have a higher narrow power curve and a critical setup'.

Lower timed engines will run faster when the higher timed setup is off its optimum setup giving the preception that the gain is strictly in the lower timing of the engine. Rational comments please. DAN

Dan, Its usable power that we need. If you were to put an engine on the test bench or dyno and play with timings, port areas, crankcase volumes, head shapes, pipes to just get more power you would end up with an engine that revved very hard with a high bhp figure but a power band so narrow that it would impossible to use it in a boat.

There is a balance of port timings/ areas that will give you the best overall performance for your particular type of boat and that is not necessarily the one with the highest timings. I run the highest rpm that the engine will stand i.e. I run just below the 'blowup' point but I don't run extremely high timings. To repeat, timings and rpm don't necessarily go together. For example a motor with high transfer timings will not allow the use of early opening induction timings and without adequate induction timing the motor will not produce power at high rpm.

As I explained earlier a motor with low transfer timings can still have peak hp at a higher rpm than a motor with higher transfer timings, also there comes a point with exhaust timing where the power stroke (which starts at ex closing) becomes too short to produce adequate torque. This can be overcome to a certain extent by pipe design, but then the powerband will be narrowed.

Its all a balance.

Then of course we could discuss pipes but lifes too short.

Dave

 

[Anders_Martinelle]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

 

[Marty Davis]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. http://engine-analysis-software.com/p5_1.jpg

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

 

[AndyBrown]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. http://engine-analysis-software.com/p5_1.jpg

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

So the bottom line is....learn how to set up an engine to produce a FLATTER power curve!

 

[Marty Davis]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. <a href="http://engine-analysis-software.com/p5_1.jpg" target="_blank">http://engine-analysis-software.com/p5_1.jpg</a>

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

So the bottom line is....learn how to set up an engine to produce a FLATTER power curve!

Andy:

I'll see if I can figure that out.. :lol:

Which one of these would you rather have?

http://engine-analysis-software.com/ob7.jpg

http://engine-analysis-software.com/ns6.jpg

The one with the peaky curve that produces 2.66 hp and has an "n" factor that is about as high as we have ever seen (1.26). BMEP is also about as high as we have ever seen at 12.46.

OR

The one with the flatter curve that produces 2.43 hp and has an "n" factor of 1.2. BMEP on this one is 9.37.

While the first look will indicate that the one with the high peak is much better, look at the useable range of "n" which shows that the one with the 9.37 BMEP keeps going and still has an acceptable amount of torque at 34,692 rpm while the other one falls off at 29739 rpm.

There are MANY things that contribute to a useable engine and these two screen captures show that.

By the way Andy, which one would you rather race with?

Marty Davis

 

[AndyBrown]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. <a href="http://engine-analysis-software.com/p5_1.jpg" target="_blank">http://engine-analysis-software.com/p5_1.jpg</a>

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

So the bottom line is....learn how to set up an engine to produce a FLATTER power curve!

Andy:

I'll see if I can figure that out.. :lol:

Which one of these would you rather have?

http://engine-analysis-software.com/ob7.jpg

http://engine-analysis-software.com/ns6.jpg

The one with the peaky curve that produces 2.66 hp and has an "n" factor that is about as high as we have ever seen (1.26). BMEP is also about as high as we have ever seen at 12.46.

OR

The one with the flatter curve that produces 2.43 hp and has an "n" factor of 1.2. BMEP on this one is 9.37.

While the first look will indicate that the one with the high peak is much better, look at the useable range of "n" which shows that the one with the 9.37 BMEP keeps going and still has an acceptable amount of torque at 34,692 rpm while the other one falls off at 29739 rpm.

There are MANY things that contribute to a useable engine and these two screen captures show that.

By the way Andy, which one would you rather race with?

Marty Davis

Marty that's nice, but I was thinking in terms of 3.0 hp with an "n" factor of 1.8 and with the peak power @ 37,000.

Of coarse that's not going to happen with the "currently" availible .21's.

 

[Marty Davis]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. <a href="http://engine-analysis-software.com/p5_1.jpg" target="_blank">http://engine-analysis-software.com/p5_1.jpg</a>

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

So the bottom line is....learn how to set up an engine to produce a FLATTER power curve!

Andy:

I'll see if I can figure that out.. :lol:

Which one of these would you rather have?

<a href="http://engine-analysis-software.com/ob7.jpg" target="_blank">http://engine-analysis-software.com/ob7.jpg</a>

<a href="http://engine-analysis-software.com/ns6.jpg" target="_blank">http://engine-analysis-software.com/ns6.jpg</a>

The one with the peaky curve that produces 2.66 hp and has an "n" factor that is about as high as we have ever seen (1.26). BMEP is also about as high as we have ever seen at 12.46.

OR

The one with the flatter curve that produces 2.43 hp and has an "n" factor of 1.2. BMEP on this one is 9.37.

While the first look will indicate that the one with the high peak is much better, look at the useable range of "n" which shows that the one with the 9.37 BMEP keeps going and still has an acceptable amount of torque at 34,692 rpm while the other one falls off at 29739 rpm.

There are MANY things that contribute to a useable engine and these two screen captures show that.

By the way Andy, which one would you rather race with?

Marty Davis

Marty that's nice, but I was thinking in terms of 3.0 hp with an "n" factor of 1.8 and with the peak power @ 37,000.

Of coarse that's not going to happen with the "currently" availible .21's.

I wonder what you have in mind.....

Marty Davis

 

[AndyBrown]

Then of course we could discuss pipes but lifes too short

Is it?

Don`t stop untill your 6 feet under Dave.

I agree with you totaly, it`s not easy.

RPM is mainly controled by the pipe.(in our application)

Marty, just because a engine can rev 40k that dosen`t mean that it produce some power???

Most 21 engines will rev 40k but you will not have any power left.

I have asked this question before but so far no one have give me a good answerd to it.

At what point does it take more power from the engine to turn it internal parts then you get out of it???

If you run a engine in a dyno and it reach it maximum hp rev if more and you will just loose power???

Anders

Anders:

On a dyno, the power curve JUMPS out at you. You can see the limit of the pipe, etc graphically. <a href="http://engine-analysis-software.com/p5_1.jpg" target="_blank">http://engine-analysis-software.com/p5_1.jpg</a>

This is a perfect example of the limit of rpm. If you moved the pipe shorter the ledge would be higher, but the point where you made max HP and Torque would also be higher. The problem would be the launchability. The point where max HP (28,320) and max torque (27,979) would move up. This is addressed in our test by the amount of "n" that is shown. That is an output that we include to show launchability. If "n" drops below a certain point, it shows that we have lost acceptable launchability. Also look at the useful powerband and the point where useful output falls below acceptable limits. That would show you where you would lose millability. We use BMEP as the comparison between engines (it will show output that is equivalent regardless of engine size). You can actually compare a .67 engine to a .21 engine in output using BMEP.

This probably more information than you wanted, but it shows graphically what you have said.

Marty Davis

So the bottom line is....learn how to set up an engine to produce a FLATTER power curve!

Andy:

I'll see if I can figure that out.. :lol:

Which one of these would you rather have?

<a href="http://engine-analysis-software.com/ob7.jpg" target="_blank">http://engine-analysis-software.com/ob7.jpg</a>

<a href="http://engine-analysis-software.com/ns6.jpg" target="_blank">http://engine-analysis-software.com/ns6.jpg</a>

The one with the peaky curve that produces 2.66 hp and has an "n" factor that is about as high as we have ever seen (1.26). BMEP is also about as high as we have ever seen at 12.46.

OR

The one with the flatter curve that produces 2.43 hp and has an "n" factor of 1.2. BMEP on this one is 9.37.

While the first look will indicate that the one with the high peak is much better, look at the useable range of "n" which shows that the one with the 9.37 BMEP keeps going and still has an acceptable amount of torque at 34,692 rpm while the other one falls off at 29739 rpm.

There are MANY things that contribute to a useable engine and these two screen captures show that.

By the way Andy, which one would you rather race with?

Marty Davis

Marty that's nice, but I was thinking in terms of 3.0 hp with an "n" factor of 1.8 and with the peak power @ 37,000.

Of coarse that's not going to happen with the "currently" availible .21's.

I wonder what you have in mind.....

Marty Davis

Marty,

I have lots of neat things in mind.........I just can't wait to turm them into Hard Alloy Steel and Aluminum!!

 

[Anders_Martinelle]

Thank`s Marty for the info but it`s not a answer to my queston.

The diagram ends at 32k, next time rev it to 40k and see how mutch HP it will produse as i ask in the question.

Just because you shorten the pipe the HP will go up, yes but you come to a point when it dosen`t do that anymore and were is that on a 21 engine?

As you self ask

Nova Rossi 8 port .15 has an exhaust timing of 161 and transfers of 114 for a blow down of 23.5. How can this engine perform at 40,000 rpm?

Who knows how mutch HP that engine has at 40k, close to 0.............?

Anders

 

[GrePower]

G/day Guys

This is the first time I've tried to post a pic.

It looks like there is only 13K left, so I'll try posting 4 links.

I want to say first that I am trying to help here. My Dyno is a NitroDyne model & certified from manufacturer. You cannot compare my figures with Marties. You can compare my figures with other NitroDynes, such as used by Xtreme Rc Cars magazine.

I also have to say that I ran John Ackerman engines in Marties Crapshooters from the 70's & have kept in touch with both having the highest admiration & regard for both.

I also have to say that for the last 11 years my primary interest is 1/10RC Drag racing, which are different engines & especially fuels again. Please remember this - our apples to apples & oranges to oranges can be worlds apart here.

Anders, you're requesting an answer of Marty, but it's not that simple. I've just spent a couple hours to come up with these graphs here. I have over 180 pulls of 21 & 29 engines logged & I can't find one with a 21 engine running boat fuel to 40,000 rpm., it's too excruciating & nerve wracking, waiting for the final spool up. There is a big difference in power at the top end between 20% oil & 8% oil !! Also difficult with most commercial pipes.

I know I could change the gearing, but my development work so far has been nearly all NovaRossi 28 engines for drag racing. I guess the closest to this is your SAWS, which I will be starting (again after a 14 year break) to run next year.

Here are the links :-

www.are.com.au/HobbyPics/Marine Dyno graphs&pics/2x28&2xCMBgraph.jpg

Pulls 32 & 69 are both NovaRossi .28 engines.

www.are.com.au/HobbyPics/Marine Dyno graphs&pics/2x28&2xCMBnotes.jpg

www.are.com.au/HobbyPics/Marine Dyno graphs&pics/2xCMB&1xMACgraph.jpg

www.are.com.au/HobbyPics/Marine Dyno graphs&pics/2xCMB&ixMACnotes.jpg

Hope this works & the notes explain enough. Sorry if you have to cut & paste. There must be a 200k limit per page.

Regards Richard...........& remember - apples to apples, oranges to oranges, please.

 

[GrePower]

G'day again

I didn't have the figures at work but here are the relevent exhaust timings.

Pull no. 32. NovaRossi .28 - 184 degrees.

Pull no. 69. NovaRossi .28 - 187 degrees.

Pulls no. 6 & 14. CMB .21 - Std & not measured.

Pull no. 5 Mac .21 - Modified in Aust by Paul Osmond - unknown, & engine has done heaps of work.

The Kamakarzee pipe referred to is alloy & fabricated by myself, much more a car pipe than boat.

Regards Richard

 

[Anders_Martinelle]

Thank`s Richard , that is what i would like to see how mutch power you loose over the peak.

At 40k you have only around 50% of the "total" hp..

Of course it`s easier to run a boat and engine that has a wider power band but that was not my question.

Set the pipe to 40k and i think you will see that it can`t produse as mutch power then around 32-34k.

Anders

 

[Mike Mooers]

So after reading all this, how does exhaust timing, and boost/transfer timing relate to intake timing? When you run higher numbers on the sleeve, can you open the intake earlier to take advantage of the suction created by the pipe? Is there a relationship here?

Mike

 

[DaveMarles]

So after reading all this, how does exhaust timing, and boost/transfer timing relate to intake timing? When you run higher numbers on the sleeve, can you open the intake earlier to take advantage of the suction created by the pipe? Is there a relationship here?
Mike

Before discussing this I think its important that we are all on the same page with the terminology. In the USA you have a lot of different names for the ports and some call the transfers the intakes and so I think its important to clarify this. In books I've read, intake and induction are the same thing. Transfers are not intakes.

Anybody ?

Dave

 

[Mike Mooers]

Dave, for clarity, boost and transfer ports I'm referring to would be in the sleeve, and the intake would be the drum/rotor/crank inlet timing. It seems to me that with high port timing in the sleeve, there is a possibility of having the pipe create a negative pressure in the crankcase near or before the point in the cycle where the piston begins its upward movement. Would there be any benefit to opening the drum/rotor/crank earlier to take advantage of that negative pressure and move more air/fuel through the motor?

Mike