More Exhaust questions

[Dingie]

When you look at a exhaust sys after it has been run a few hours and see carbon build up in a area would it a good idea to fill those areas in.Wouldnt that be a area that isnt flowing correct ? What could one use as a filler on a exhaust plate. Could you fill low spots on the intake side of the block to raise the crank case compression? What would be a good filler on the intake side ? Instead of grinding a area smooth on the intake side that has a edge would it help in more than one way to fill it in and level it raising crank case compression increasing intake flow and air speed.What kind of filler will hold up to temp changes and vibration ? Shouldn't the exhaust plate divider and tuner be flowing correct before any port work is done. Dirt bikes change exhaust by mm to fine tune power curves Has anyone tried trimming tuners very small amounts at a time to see what is gain or lost at what RPM's. I remember GPI saying to cut 1 3/8 '' off of the 115 tuner and it will make great power up to 6000 RPM . Do you remember what PN tuner that you cut down ?It seems to me that everyone is always talking about changing exhaust ports but not a lot of R&D is being done with the complete exhaust sys. Hard to change a port when the motor looses power from a modification that went to far,I would much rather change a tuner or exhaust cover. Thanks for any help

[Ray Neudecker]

Blending the entire exhaust from the port to the tuner does give a big boost. This is not a bolt on application though. When that divider is off, look down it and see if you don't see what I am talking about.

[Dingie]

Im still looking reading and asking exhaust questions.From what I have read and can see.Gradually increasing diameter gives more useful negative wave and helps pull exhaust out.This may be the reason that the exhaust plate on the 130 has a smaller Dia. than the 115 plate.Seems to me after seeing what exhaust plate tuner combination works best would be worth the trouble.Likely wont increase RPM's but should improve torque. The smaller dia at the exhaust pipe start (the 130 is smaller dia than the 115) at the exhaust plate going into a larger dia tuner ( the 130 tuner has a larger dia. than the 115),than exiting thru the same lower unit thru the prop.Is this normal for HP motors to have a smaller start of the exhaust than a larger center section.Has anyone fine tuned the tuner by trimmimg lenght to see what if any performance gains where made on a V-4 Yamaha ?

[GPI Racing]

Hey Joe,

Some food for thought. A V-6 exhaust system is basicly 2 three cylinder exhaust systems. These sonic tune themselves at all rpm. 120 degree spacing in each bank of cylinders. The V-4 cannot do this as the firing is either 180 degrees apart or 90 degrees if you use all the cylinders. This means that the motor is "in tune" only at a specific rpm. Everywhere else it is running with no real exhaust tuning. If you change the exhaust tuner or chest you effectively move that tuned "window" to some other rpm. (the book you just bought will explain this) Unless you have an instumented dyno it will be hard to find out what you did. This is a problem that has always been around and why the three cylinder and V-6 motors make more power per cube than multiples of two.

Just thought you'd get a kick out of the above.

Randy

[Dingie]

Would this mean that the hi torque tuner sold by Hydra Tec that fits V-4 and V-6 in therory shouldn't great work on both applications . This also means that when I put a bigger power head I should change the tuner again ?

[GPI Racing]

To be honest with you I never had any luck with the tuner they sell. It was derived off the pipe that Brian Daley and I ran on the tunnel boat motors back in the late '80s. Great for v-6's turning 9000 rpm, not much good for lake boats. The tuning deal is why the 115/130 pipes join the flow together towards the end. They are trying to get by the one rpm band deal. With the V-6 I'd have you run a real V-6 pipe. Kind of like we talked about..not everything is what is seems and sometimes things are sold to guys that really are a blind alley. The tuner works when mated to an engine that is way beyond anything we're talking about here.

Randy

[Markus]

Yes, that is what it means.

Although the V6 is much less sensitive than the V4 for the reasons GPI Racing described.

[W. Tripp]

The length of the exhaust - from the port, to the tip of the tuner - determines when the scavenging wave will reflect back through the exhaust and help pull fresh air and fuel into the cylinder. This scavenging occurs largely in the boost ports that are located opposite the exhaust port. The efficiency of these ports will determine how well the pulse tuning will affect the power of the engine.

A longer length takes more time to reflect back to the port and this causes it to produce peak results at lower rpm than a shorter length. The peak pulse tuning will happen over a given section of the power band. For best results, the length needs to be tuned for the power band of the engine and how it is used. Length tuning will move the peak results around by a few hundred rpm.

The angle of the difusion cone (tuner) changes how broad the pulse tuning will cover the power band. A narrow angle will give more peak results, but over less area of the power band. A wider angle will reduce the peak results, but widen the area that the pulse tuning will improve.

If you look at many of the performance tuners from Mercury, you will notice that the tuners have 12-14 degree angles - for good reason. Some of the "fishing" engines have little, if any, angle in the tuner.

Making sure the area of the exhaust passages is matched to the power, rpm, and use of the engine can produce slight benefits as well. If the passages through the exhaust adapter plate and tuner all are as straight as possible, and of a close to the same length on all sides, you can find small gains as well.

On a Mercury Drag engine, paying close attention to the details and tuning the system to the power curve, can make 3-4 hp through the most important part of the engine's power band. This may not sound like a lot, but getting this amount of additional power from other modifications can be MUCH more expensive.

I hope this helps.

[Dingie]

Thanks guys that's a handfull of good info. to look at test and study. Without changing props.Could RPM be increased by fine tuning exhaust tuners,plates, without raising exhaust ports or enlarging carb sizes ?Could RPM be gained on the top end if ignition timing was backed off 2 or 3 degrees ?

[Dingie]

Got on the water and tested the 130 exhaust plate. I noticed as soon as I started it that it doesn't sound the same has less of a ringing sound at idle than it did with the 115 exhaust plate. It does fell a lot more Crisp/Pep/Ballsy at RPM's 2000-4000 mid range really feels good, didnt seem to improve top speed but didnt loose any either.Maybe a little more RPM seems to reach top speed quicker.Randy the little red book got here today,it should be gold plated.