Engine Shim Tuning
 

Okay guys onto the black art of engine tuning ! How does one actually go about tuning an engine by shimming it ? What do you gain/lose etc. I am talking particularly about performance on track - not about shimming it to match nitro percentages or to decrease/increase compression to solve pre-detonation or other problems.

Also does anyone know what nitro fuel % the Novarossi RS and NS .12 series came originally shimmed for ?

In my experience I have found that just by lowering the head you gain more power especially in lower rpm range, idle quality can suffer, the engine also ran cooler. I've ran my deck height really low before and didn't have idle problems but every engine is different. I don't run any big tracks so I am not sure how it effects top end performance but would assume that a higher deck height would be faster for top rpm speed on bigger tracks. With the copper shims for me I'd lose .001" head clearance for every .004-.005" in the shim(s) after the head was tightened. The guys with a lot more on-road experience than me should know how it effects the top end speed better than I do.

Yes you are right a decrease in head shims or an increase in compression ratio will increase torque because as the compression ratio goes higher the actual ignition timing occurs sooner. This is the same effect that happens with a colder plug except in the instance of a colder plug the ignition is slowed until a greater point of compression build occurs. however there is a point of diminishing returns where detonation occurs or engine temps can soar this is where a colder plug can also help.
Consequently the same effect occurs when you increase the head clearence. top end is enhanced as the ignition timing is retarded and occurs later. generally a hotter plug is needed to advance the ignition cycle so the timing does not occur to late in the cycle as at this point you end up overleaning the engine to get it to rev properly and the engine life will suffer dramatically.

on a 12 engine I would only advise going .004 thousanths over or under .018. so that is .014 or .021. I have run as low as .008 but this was with tremendously increased exhaust timing and to regain static compression ratio. to little and the piston can hit the head as you have to take into account rod and piston growth relative to their tempratures.

On marine engines we could get away with .003 on a 21 but we were water cooling it. that won't fly consistantly on a car engine without a special head that has a larger combustion chamber to start with.

Savant you can safetly use 30% on the stock head clearence. using an odonnel 99 plug you can go 40% If you dont overlean it the engine life will not suffer dramatically.

I should also comment that my comments with regards to plugs and head shimming are when both are used together. used alone a hotter plug will rev harder and a colder plug will make more torque.

there you have it.

I just bought an STS D3 and tore it down before running it. I Noticed That it had no Head shims. I went ahead and Broke it in like that and Ran it today first time. After a Few more Tanks I had it turn ON, Switch action that I've Heard about, is that from being too Far advanced and How much do you think I should shim it? I was Thinking .2 mm .008" I think thats the conversion.After awhile I was able to get it regulated back but Had to Really richen it up then had problems with it being too rich. Is a very fine line between the switch action and being too rich. Do you guys think the shims are the answer?

when you say switch action do you mean the temp soared?

you need to physically measure it. guessing won't get it take it apart again and look for the head shim again. sometimes it fits so tight to the head button it looks like it is part of it. I would bet it is there if not you need to measure it and set it to about .018 thousanths. measure the shims, never trust the package.

Duh.... ok it looked like a machined alum step. .012" alum and
.008" Brass shim so .020".
The switch action that I was taking about was a High rpm idle that I couldn't decrease with the idle adj or end point on my radio.
and yes it was followed by soaring temp.Low end mixture too lean? Sounds right now that I'm on the keyboard. I was trying to Richen the High end because the rpm's were so high then it would die on accelleration (bogged down) Too Rich....
I think I got it now Just hadda Read it and look at it a few times to see.
So here is my mistake I think...... I leaned the low speed too much causing it to Rev High then trying to compensate and mistaking the high rpm for idle adj or too lean High end I had a mental breakdown and screwed up what I should have left alone and left alone what I should have screwed up. Therefore Screwing up everything that I have been learning......
Thankfully I was able to run one more tank through it after I turned the right screws the right way and my motor will live. I tore it down after bringing it home and everything looks ok.no scoring, pits or discoloration.

sounds like your on the right track.

one last comment.never assume that the head shim that is on the engine is the actual head clerance. in many cases you will find that the engine actually has .006 to.oo8 without any head shim. Novarossi's are .008 without one and the factory installs an additional .010 giving the engine .018 stock. this has not always been the case but 99% of the time it is. when in doubt measure the head button register and the piston to the top of the liner at top dead center and subtract. this is the only way to really know.

I did that after i found the step was actually the shims.... D3 has a flat Head no step then has 2 shims .012" & .008" Measured them on my Dial caliper seperatly The buttonhead goes into the combustion chamber .050" then shimmed .020" back out.

On my P/S sets I am able to run engine from .125mm (.005) to .15 mm (0.006) shims and with 20% or less fuel with dramatic power increase overall, temperatrure will stays within 210-220 and no any detonation was seen so far ( ones by my mistake was hell of detonation in Texas, but there was my mistake with tuning). The engines has defenetly different timing setting from stock version, but I have never faced piston hit the botton.

Detonation
 

When you guys say detonation...does that mean the plug is turning black because of retarded timing due to extra shims?
To turn off the switch do you remove shims to speed up timing?

Please advise.

Engine Shim Tuning
 

Guys;

I'm new to running Novarossi engines (I'm normally a Picco fan) and would like some advice.

Several People at the track told me that NR based engines will detonate on 30% and anything less than about .024 Head clearance. On my Picco engines, I have always set clearance to .018-.019 on 30% and they ran great. I would like to increase the compression to get a little more grunt, but don't want to damage a almost new engine by too little head clearance.

Any suggestions or comments are welcome.

Re: Engine Shim Tuning
 

My sugestion is:If you want to increase compression ratio, you will need to use lower nitro content and you will have better power output with no detonation.:nod:

I read all the above and just measured my engines. My NS3 has a clearance of 0.018" at TDC where the Rossi Pixy Black has 0.028"

I am having all sorts of problem with the Pixy overheating. Will removing the shim and reducing the head clearance help?

Cheers

Re: Engine Shim Tuning
 

You can go down up to .021" with a 30%, but plug selection will be critical (you're on the ragged edge for 30% Nitro). Better to go with a Nova 7Tf with those nitro percentages. You can go down up to .018, but will be quite risky and will be quite weather sensitive.

Ziggy
This is a problerm on the pixy drop it to .018. That is exactly why it is overheating the CR is to low. The thing is you cant go that low withoug machining the head button to get it to go there.


I've been keeping my mouth shut for a long while but I have to say somthing.
TG you need to let go of the marine mentality man. If it works for you great but I know I can make more power than you on 30% at .018 and 40% at .021 with zero detonation at 4.5 mm exhaust height. we do it every day no problems. What you shouldn't be doing is spinning people off towards unrealistic head clerance on their production motors. If its a hand built thats a different story but you do them a disservice by directing then toward toward a global meltdown of their hardware.

If you feel inclined to take .008 thousanths head clerance advice do so at your own risk that is all I have to say.

Thanks a lot for your input.
Motorman, you know, I made strong respond, but decided to edit it. We will see who is right!!!!!!!!!!:D
but your post is very promissing to me, I love it. It means, I am on right way even from your point of view!!!!!!!!!!!:lol:
4.5mm-154.41 degreese:weird: 164 degreese is better! :nod: :lol:

Hey TG

Just take it easy, things is going good.

Re: Re: Engine Shim Tuning
 

Corse,

I usually run my NR based engines with 0,3 mm shims, 30% nitro and the shortbody 5TF plug without the slightest problems.

That is in Georgia weather where the temperatures reach 100F with 95% humidity.

Never had detonations or premature wear on my engines.

and Illegal too.

Whats the use TG if you can't race it in a real event?

Thanks for the advice. The engine is the USA ver with a normal head and 3 ports. I run with 16% nitro. the head has 2 copper shims at 0.004 each so removing these will give me 0.020, which might be ok.

I have just receved the turbo button for the pixy and plann to put this in. What plug should I use?

Chees

step up to 30% fuel it will help you and the engine will run better at .020 head clerance. I would use a 5tf like was recommended on the 12's you need a hot turbo plug. In my opinion the 5 is just barely hot enough.

Motorman. Whats CR when you say "The CR is too low"?

His engine might leak or not seal up right if he takes all of his head shims off to get it down to .020". Or is there not a problem with not using any shims as long everything else is good to go?

it might if the machining is not smooth enough. he will have to try it. I turned my head button down on a lathe so I could still use one. its not a problem if it don't leak
I guess I should be saying TCR
TCR=Compression ratio=trapped compression ratio

No, you wrong, it is totaly legal! :D read the roar ruls!:D
There is nothing about timing!!!!!!!!!!!:D
Just to give you an idea how it can be done one of the way. If you make conrod lenght not 25 mm, make 17 mm you timing will be 164 degree. It is just one of the way to do higher timing on exhaust and styas within ruls. Marine mentality!!!!!!!!!!:D
Just don't look on issue ordinary, be creative!!!!!!!!!!!:nod:
I have offered my help, but was regreted. I can be very helpfull with my marine mentality.:D I want to be very helpfull for everybody! I want to share my ideas and expirience!:nod:

It is totaly legal and can be use on any sanctioned event ( ROAR, EFRA, IFMAR etc).:nod:

Ok, from what I know about Engines. Displacement and timing are basicly what determine HP. Stroke effects the powerband.

If you shorten the stroke, then restore the CR. Won't this create an Engine with a even narrower powerband? Wouldn't that counter any gains from the timing change?

Just curious?

I didn't talk about the strok, I was talking about conrod lenght. On Novas based engines it is curently 25 mm between centers of the holes. If we make conrod lenght 17 mm, it will give us 163.5 degree timing duration on exhaust without changing anything else. It is just one of the way to work this issue out. there are much more, not ordinary but very interesting solutions.
Just we need to be creative and use non common sence.:nod:

Let's see if we can shed more light on your comments.

Transfer height (linear measurement) determines timing on a 360 degree wheel. 164 degrees of total timing for the exhaust port determines a height on the exhaust port. If is ROAR legal or not is an issue that should not bother anything. When your engine is teched, the exhaust transfer height is measured on milimeters, not timing degrees and if is higher than 4.5mm, you're deemed illegal and you're out of race.

Reducing on 7mm the conrod lenght is a no no. Shortening the conrod makes to collide the piston skirt with the counterweight of the crankshaft and you need to remove more material from the piston (still, doubt if current pistons can accept to radical material remove) this piston will be weakened up to a point that will be unstable into the sleeve and will rock into the sleeve, scratching it and making it ovalized.

Marine mentality is fine for boats that only rely on high rpms to produce power not for cars that run on a closed track (probably are fine for tether cars or planes too), hence here their exagerated exhaust timings along to ultra-high compression ratios (or ultra small combustion chamber heights - name it as you prefeer) that rely on the extreme timing to control what occurs into the combustion chamber. As a plus, those engines run with a water cooling system, so their temperature never reaches the extreme temperatures you can find in a .12 engine with a closed body.

Edward, probably this is your worst problem, you're directly extrapolating what works on boats to cars, and this doesn't work on all cases. Some of your ideas are interesting, others don't apply, others simply... well.

Here, many people works and make 1:1 engines for a living (Engineers, motor builders, mechanics), others simply are gearheads (like me, have their own experience building their own engines, but their money is earned in other places), other simply rely on the experience of other people because they don't want headaches with engines.

Some of your advices aren't questionable are directly dangerous and harmful to people with light or no knowledge of our engines (0.008" of chamber height is a fine example, another is to make propaganda that for making power, the best is to reduce Nitro on their fuel).

If you're right, all the guys that run on Funny cars or other Top fuel categories are doing a complete nonsense burning a mixture of 90% nitro and 10% of Methanol, running 100% Methanol is much cheaper to run their multi hundred thousands cars burning thousands of dollars on each weekend they run.

On this last assumption, you're extrapolating what happens on FAI categories that are limited by rulebook to low or no Nitro percentage on their fuels to car engines, who can run and are designed from the ground for the use with fuels with Nitro (trying to carb an engine running with no Nitro is a bitch to do...).

Nitro is vital and necessary for the chemical process that happens into the combustion chamber one of their actions is to give Oxygen and Hidrogen during the combustion, other less known is to slow the flame speed of the methanol burning, needed to control the explossion on the combustion chamber and help to give more power making the burning of the fuel and the explossion longer in time hence producing more overall power.

I just talked to the guy who runs the local model shop and he says a good guide is to have 0.001" head clearance for every 1% nitro above 16% so 16% is 0.016" where 25% is 0.025"

Is this a good guide?

Cheers

Wow, Alfonso. It looks like big smart book for me! Half of it I got check in dictionary.:D
Well this is the point about the rod-just to say it will hit counterweight and don't look for different design-it just nonsence. This is what called ordinary way. The second thing is I sad it is one of the ways to make timing for exhaust higher, but also I have mentioned there are more then that. It seems for me you are not interesting in it, so I will not go deeper.
About the real car, well I have slightly idea how the 4 cycle engine works, so I feel have no right to discuse them.
About marine mentality, well, did you ever run RC boat, FSR-V or FSR-H. If you did, you will know-we don't use there only TOP RPM, we have the same issues with panch and acceleration as well. The only difference is cooling. Well it is realy interesting point and can be dicuse forever. I have tested my motors on a lot of places around the world and nowhere people faced temp problem at all.
I sugested to try no nitro, yes I did, but before I sugested it, I tryed on my own engine and tortured very well. So I safe to say so, but again, if you never try don't say it will not work. Try and tell us what did you find, please!!!:nod:
About the power output. I would love to put my work on dyno but unfortunately I don't have one and don't know anybody who has it. I am sure i will find one iventualy and will do the test.
What do you mean is dangerouse to say you can run lower content Nitro with smaller head volume-is this dangerouse. I think more dangerouse to run 40% Nitro even with high head volume-Nitro is burning hotter, costs much more money etc.
Seems for me, like, you guys don't even want to try anything, beside what you did always. To move forward you need to be proactive and try a lot of stuff or one day it might be too late and can be way behind the line. I love to try, I am not afraid to work on engines, I am not afarid to experiment, but you can stay where you are right now, I have no problem with that at all.
So you stay on your way and I will stay on mine. But in the mean time I will put any post I want to here as long as I don't brake any rulls of forum. I think it is fair. I saw so much dangerouse info and can prove it easy by posting it, but will not do it. I just don't accepting it , that is all.
Have fun and run the hobby.:nod:

Is a very conservative guide, 0.021" is fine for running a 30% Nitro fuel. Going down to 0.015 to 0.018 if you're going from 16 to 25%, read some posts before this regarding this issue.

that sounds familiar, hey, where is my bottle of Smirnoff?

:ha: :ha: :ha:

Jedi has a good memory !!!

Maybe TG will send the smirnoff once you're legal age? :lol:

I have a good memory too.

Hey, I was at CP many times and never see you there!!!:sneaky:
Come for big race on KZ next weekend, I will give something better then Smirnoff.:D Will you come?

Its all good... you will find after you have spent all your money trying stuff, that some bigger fish takes your ideas, and produces an engine that we will all buy. Its the nature of the beast. People want an engine from a brand that has a good history. Not a backyarder.

Engine Shimming and Boost chambers
 

Does anyone know if a boost bottle/chamber are the same technology as shimming. Will using a boost bottle just expand the chamber just like adding shimms.
Is it good for the engine to use one?

Please advise.

I will be happy on this end too.:D and you will know you are running on somebodys good ideas. Don't worry about my money!
:lol:

maybe you have good memory too but i am sure you are confused about who is underage here.