NovaRossi 21 5 port mods

[John Seybold]

Hi,

I'm interested in performing some mods to my motor, I've been reading some articles posted many years ago. While I'm sure the principles may be the same, I'm willing to bet that stock motors have evolved some as well. My question is where is a good place to start with modding a motor? I certainly don't expect anyone to give out their secrets, just hoping for a point in the right direction. Lastly, in the articles it mentioned use a dremel tool for mods, is this still the tool of choice?

Thanks for any help and advice

 

[Kevin Krogness]

Steve Wood I believe is the man to talk to... Dremel is one way to do it but not always the best..

 

[anthony_marquart]

In my opinion the dremel is not a good tool for mods at all,. but many use it. I have run the 5p alot. Steve woods will do a very professional mod for about $100,.. BUT,.. this motor in my opinion needs just a few things. I new head button, maybe brass with a volume of .17cc,.. Rodney, that is the right volume correct? Woods sells these for $40,. then you need to set the head clearance at 0.006-0.008,.. run 65%,.. S pipe works well..

Then get a few props and work on the setup,. you can run high 60's to 70 mph,.. If you want to buy one of the after market carbs you can get another 4-5 mph,.. but man,, those last few mph get real expensive!!!

 

[Tim_Duggan]

As anthony has suggested - The head button / head clearance and carb mods will net very good gains on the 5 port and no need for the dremel..... in fact you can even raise the sleeve timing a little with a sleeve shim before resorting to the dremel.....

If you have the burning desire to dremel something - use a grinding stone and CAREFULLY set the inlet timing in the crank window to close at 65 ATDC. It only takes 1 slip of the dremel to ruin a crankshaft.

 

[John Seybold]

Thanks, question about the head clearance, is this set with just adding or removing shims or is there more to it. I know I have a lot to learn.

 

[Glenn Quarles]

John, Anthony is pretty much right on, the motors don't need a lot to get hop them up. Unless you have a really good idea on what timing numbers work well together and are experienced at cutting the different metals in the motor, you stand a better chance at making the motor run worse than you do making it run better. I have not seen any performace advantage with a brass head button, but reducing the stock volume is a definite plus (yes around .17cc works well with the dished piston). To do this I would cut about .015" off the depth of the squish band and then the same off the shoulder to get the head clearance back down. Set the head clearance to .006 - .008 and you will be in the ball park. If the stock carb has the mod the remove the low speed needle and 1/2 the srpaybar, then I don't think you will find any more speed in any of the aftermarket carbs (I do like the remote needle on my Orlick carb a lot better than the Nova one, but it runs the same speed. And I have never been able to get a ZOOM so I can't comment on performance of that one).

If you want more performance I would send the motor to one of the good motor guys that have some good number combinations worked out and have the tools needed to make the precise cuts.

Have fun!!!!

Glenn

 

[John Seybold]

Thanks, I'll put the dremel away

 

[John Seybold]

Thanks Glenn, it does run good stock, but like everyone else always trying to get a little more out of it.

 

[steve wood]

As anthony has suggested - The head button / head clearance and carb mods will net very good gains on the 5 port and no need for the dremel..... in fact you can even raise the sleeve timing a little with a sleeve shim before resorting to the dremel.....

If you have the burning desire to dremel something - use a grinding stone and CAREFULLY set the inlet timing in the crank window to close at 65 ATDC. It only takes 1 slip of the dremel to ruin a crankshaft.

for the last 2 years i have had to lower the liner on all the novas i have worked on.raising the liner is the wrong way to go.i probably do more work on the novas than any other motor i work on.i do use a grinder some,but it's a 60,000 rpm turbine air grinder,not a dremel

 

[anthony_marquart]

I rebuild an engine recently Glenn and the new piston is not dished. Should I not use the low volume head? I have 5-6 break in tanks through it,.. seems fine... no real power yet though..

 

[David Murany]

Leave the sleeve alone and set the head clearance to what the guys mentioned earlier. The important thing is the induction timing numbers. 65 degress ATDC is real good. Also knife edge the crank. Pipe length at 8" and the right propeller will get you some speed. Good luck.

 

[Glenn Quarles]

I rebuild an engine recently Glenn and the new piston is not dished. Should I not use the low volume head? I have 5-6 break in tanks through it,.. seems fine... no real power yet though..

Anthony, with the flat top piston I use a head volume around .19cc. If it is working with one smaller than that then leave it...it will make more power!

Glenn

 

[RodneyPierce]

Anthony, that button will be fine. Keep it rich, and load the motor to burn the fuel instead of leaning on it. It will turn on just fine!

 

[Marty Davis]

As anthony has suggested - The head button / head clearance and carb mods will net very good gains on the 5 port and no need for the dremel..... in fact you can even raise the sleeve timing a little with a sleeve shim before resorting to the dremel.....

If you have the burning desire to dremel something - use a grinding stone and CAREFULLY set the inlet timing in the crank window to close at 65 ATDC. It only takes 1 slip of the dremel to ruin a crankshaft.

for the last 2 years i have had to lower the liner on all the novas i have worked on.raising the liner is the wrong way to go.i probably do more work on the novas than any other motor i work on.i do use a grinder some,but it's a 60,000 rpm turbine air grinder,not a dremel

Steve:

I do the same. I like a low exhaust timing with 30 degrees of blow down time on all my engines (all sizes). I use the pipe to get the rpm that I want, not by increasing the exhaust duration. Most of us are still in the "crude" stages of engine development. A detailed time/angle/area analysis might change my mind about all of this. Just not an easy way currently to do such an analysis.

 

[aaron alberico]

As anthony has suggested - The head button / head clearance and carb mods will net very good gains on the 5 port and no need for the dremel..... in fact you can even raise the sleeve timing a little with a sleeve shim before resorting to the dremel.....

If you have the burning desire to dremel something - use a grinding stone and CAREFULLY set the inlet timing in the crank window to close at 65 ATDC. It only takes 1 slip of the dremel to ruin a crankshaft.

for the last 2 years i have had to lower the liner on all the novas i have worked on.raising the liner is the wrong way to go.i probably do more work on the novas than any other motor i work on.i do use a grinder some,but it's a 60,000 rpm turbine air grinder,not a dremel

Steve:

I do the same. I like a low exhaust timing with 30 degrees of blow down time on all my engines (all sizes). I use the pipe to get the rpm that I want, not by increasing the exhaust duration. Most of us are still in the "crude" stages of engine development. A detailed time/angle/area analysis might change my mind about all of this. Just not an easy way currently to do such an analysis.

Marty

what do you call low and high for exhaust timings?

Regards Aaron

 

[Marty Davis]

Aaron:

This is just what I like and have found works well for me. I did do some Time/Angle/Area analysis in the past that led me to this preference. I like an exhaust timing below 184, prefer 182. High timing for me is anything above 185.

If you will consider these small engines, any raise of the exhaust window making it close later will effectively reduce the trapped charge. This has the effect of making the engine smaller since it has a smaller trapped charge.

I have found that I can get RPM based on pipe length rather than having to raise the exhaust timing. I also run large diameter props and don't turn rpm over about 35k in my .21 engines.

I have found that having a blow down time of 30 degrees is much more important to power than exhaust timing. Dave Marles, who I respect greatly in his attention to .21 engines, put me onto this a long time ago and I have followed it since. I have proven the 30 degrees of blow down time on the dyno as well as the lower exhaust timing makes more power in the .21 engines. I also do all my testing with .21 engines and apply my findings to my larger engines.

Have been spending most of my time recently on head button shapes, squish velocity parameters and head volumes recently. I am finding a ton of performance in this area. Probably more than you really asked, but I thought I would offer what I have been trying.

I am also starting a project based on the discussion on engine balance and hope to see some gains as a result of this area of study. Ordered the drills to be able to slug cranks, which I believe is necessary to get a handle on the balance issue. This is a really new area for me and I am anxious to see what I can learn. I have picked Ackerman's brain about it, as he was very active slugging cranks in years past.

Would appreciate your thoughts on this....

 

[John Beardslee]

Hi Marty,

If you can get depleted uranium for the slugs it is better than mallory metal that we originally used. I did have access for a few years as we did the extrusion dies for the 5/8" dia pyrotectic (depleted uranium) projectal that went in the bullets of the Vulcan gun in the nose of the A10's. I mention this as with small cranks it it nice to not have to drill large holes and our best results were using the 2 hole/slug method.

Thanks, John

 

[Marty Davis]

Hi Marty,

If you can get depleted uranium for the slugs it is better than mallory metal that we originally used. I did have access for a few years as we did the extrusion dies for the 5/8" dia pyrotectic (depleted uranium) projectal that went in the bullets of the Vulcan gun in the nose of the A10's. I mention this as with small cranks it it nice to not have to drill large holes and our best results were using the 2 hole/slug method.

Thanks, John

John:

I have a bunch of Sintered Tungsten (MAllory) so I will just use that.

Thanks,

Marty

 

[dwilfong]

Aaron:

This is just what I like and have found works well for me. I did do some Time/Angle/Area analysis in the past that led me to this preference. I like an exhaust timing below 184, prefer 182. High timing for me is anything above 185.

If you will consider these small engines, any raise of the exhaust window making it close later will effectively reduce the trapped charge. This has the effect of making the engine smaller since it has a smaller trapped charge.

I have found that I can get RPM based on pipe length rather than having to raise the exhaust timing. I also run large diameter props and don't turn rpm over about 35k in my .21 engines.

I have found that having a blow down time of 30 degrees is much more important to power than exhaust timing. Dave Marles, who I respect greatly in his attention to .21 engines, put me onto this a long time ago and I have followed it since. I have proven the 30 degrees of blow down time on the dyno as well as the lower exhaust timing makes more power in the .21 engines. I also do all my testing with .21 engines and apply my findings to my larger engines.

Have been spending most of my time recently on head button shapes, squish velocity parameters and head volumes recently. I am finding a ton of performance in this area. Probably more than you really asked, but I thought I would offer what I have been trying.

I am also starting a project based on the discussion on engine balance and hope to see some gains as a result of this area of study. Ordered the drills to be able to slug cranks, which I believe is necessary to get a handle on the balance issue. This is a really new area for me and I am anxious to see what I can learn. I have picked Ackerman's brain about it, as he was very active slugging cranks in years past.

Would appreciate your thoughts on this....

Marty on the 30% blow down I have bin doing that from you advice. So to get a 30% you will need to have the transfers at 124 with a 184 ex. Most eng are well over that from the get go. heck the new VAC .91 comes in at over 136.

Lowering the liner is the only way to get lower # or have a custom piston made with a higher comp distance.

you can only lower the liner so much or the piston will sub-port the ex.

I have got around this in two ways with two eng. one is the VAC91 by boring the case out and using the RS P/L in it.

The VAC91 is over 136 deg trans to start. but with this mod it will come in at 130. not as low as would be perfect but much better.

With a custom piston it lowerd it eaven more to 126.

Also with the MAC21 with the valvola P/L have some custom pistons with a higher compression distance.

Just thought I would share some of my building techniques.

David

 

[John Beardslee]

Hi Marty,

If you can get depleted uranium for the slugs it is better than mallory metal that we originally used. I did have access for a few years as we did the extrusion dies for the 5/8" dia pyrotectic (depleted uranium) projectal that went in the bullets of the Vulcan gun in the nose of the A10's. I mention this as with small cranks it it nice to not have to drill large holes and our best results were using the 2 hole/slug method.

Thanks, John

John:

I have a bunch of Sintered Tungsten (MAllory) so I will just use that.

Thanks,

Marty

Hi Marty,

How are you holding the Mallory metal in? Sometime it would crumble.

Thanks, John