no shims = Horsepower gain?

[bigsouljaslim13]

I was just reading some website on tuning and i saw something that said you can gain horsepower by removing the shims between the cylinder head and the sleeve they say it will make the combustion chamber smaller and will increase the engine's compression.. does anyone know if this is this true and if its safe or not?onder2:
heres the site i found it at> http://www.storacingproducts.com/rc-cars-planes/html_templates/storacing_templates/horsepower.htm

 

[sweetdiesel]

it is true, but if you have too much compression you can experience glow plug failure. Folks I know who have done this use lower nitro content fuels. I run 30% and in most cases have had to add a shim to reduce compression.

 

[bigsouljaslim13]

I run 20% so if i wanted to remover the shims should i go lower % ?

 

[racin_38]

yeah but there wouldn't be any benefit ,just that your motor wil run right on the lower % but no power gain ,you can remove 1 shim to compensate for the motor getting run in to recoup some loss which will regain the power loss due to being used ,IMO
i may be wrong but that is my thoughts

 

[rocknbil]

I'm with S.D. on this one, I am no "engine guru" but have read a lot of stuff. When you go fiddling with shims, you change the compression ratio for the engine. This affects not only the overall compression but the pressures on the con rod and many other factors. Engines are generally designed for a specific compression ratio in combination with a suggested range of nitro percentage.

Generally you only need to fiddle with changing shims when you are using very high nitro contents, like 40%. In either case, unless you really know your stuff, it is not a good idea to chnage shim clearances. But the worst that could happen is a blown engine, so if you're feeling adventurous . . . .

Here amd here are a couple good articles I always bring up when people ask about shims, it's a boat site but the concepts are the same.

 

[NSantana]

yeah but there wouldn't be any benefit ,just that your motor wil run right on the lower % but no power gain ,you can remove 1 shim to compensate for the motor getting run in to recoup some loss which will regain the power loss due to being used ,IMO
i may be wrong but that is my thoughts

HUH?


Now I'm no pro or anything, but shouldn't there be at least SOME sort of power increase in relation to the nitro % change? Otherwise, what would be the point in changing it (other than sharing between 2 or so different types of vehicles)? I'm not being a smart-$$, I just would like someone to explain this because it sounds a little odd to me. Thanks

 

[olds97_lss]

I didn't see where anyone said higher nitro doesn't give you higher power. All I saw that was said is that less shims doesn't necessarily mean more power.

You should always have at least one shim to create the seal between the head and the crank case. It's a soft brass and forms itself to the imperfections of the two surfaces to help create the seal.

In most cases, to run a higher nitro % you need to add shims or it doesn't run right. Early detonation, blow/compressed coils in the plugs. Reason is, higher nitro gives it a bigger bang, which means more compression at the time of detonation (I believe). You do get performance gains with higher nitro, but you also need to shim the head more.

 

[supercharged]

i'v removed 2 shims and run 25% there is a slight power gain but nothing really noticeable

 

[CorradoPsi]

there is powergain, but slight and not always worth the risk for backyard and light track running. most engines come shimmed for 20% fuel. race engines come shimmed for 25% fuel. when running 30% on an average engine its usually a good idea to add a thin shim. race engines can usually get away with stock shimming. a good indicator of too few shims is an engine that runs hot with good to excessive smoke, and the proper plug for the weather. in thice scenereo, one thin copper shim usually drops temps considerably, and allows you to lean the engine out to its fullest power potential.

 

[Monkey Wrench]

Just a follow-up question to this thread. Are shims manufacturer-specific? I mean, if I need a shim for, say, a HPI .15FE and find an Ofna shim that has the same diameter and thickness, am I potentially doing more harm than good? I wouldn't necessarily think so, but then again I may not be thinking of something.

 

[CorradoPsi]

nope, not specific. you want to measure, the shims ID, OD, and check for the desired thickness

 

[Monkey Wrench]

Thanks! Just wanted to be sure. Good to know.

 

[Plaidfish]

If you can tune your mill now, Buy a shim kit and try em...just be real careful how you're running....monitorthe temps closely..like was said you can have all the smoke and still be running hot....that's the big gotcha when trying new stuff...but unfortunately there is no nitro RC bachelors degree so it's school of hard nocks and low cash for ya buddy......never learn it less ya do it, right???

Corrado...I thought you went full on autocross on us (like sargent Blamo did)......ar eyou going to race again this year or do the real car thing now?