R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro On-Road > Onroad Nitro Engine Zone

Reply
 
Thread Tools Search this Thread
Old 04-08-2012, 03:32 PM   #1
Tech Addict
 
Bubblehead's Avatar
 
Join Date: Jan 2008
Location: Portsmouth, VA
Posts: 708
Default 16% Lean or 30% Rich

I was at the track yesterday and I was looking at the performance of three different engines [Touring Cars .12]. Each car was using a different percent of nitro 16, 20, and 30%. The car using the 30% was clearly the fastest car on the track and it seemed to go in order of the percentage of nitro. I know the 30% was a RB, 16% Murnan Modified, 20% [?] and two of the three cars were X-Ray's.

I have been doing some searching on using the different percentage of nitro one thing I have found that with 16% you can run leaner which improves run time and 30% provides better performance.

The question I have: What's better to run lean using 16% or 30% rich?
Bubblehead is offline   Reply With Quote
Old 04-08-2012, 04:59 PM   #2
Tech Addict
 
Bubblehead's Avatar
 
Join Date: Jan 2008
Location: Portsmouth, VA
Posts: 708
Default

I also found this in my search:

Engine Shim Tuning
By Dennis Richey

Experience dictates that just by lowering the head (more compression) you gain more power especially in lower rpm range, idle quality can suffer, but the engine also runs cooler . Also, that a higher head (less compression) will increase top rpm speed on bigger tracks.

A decrease in head shims (an increase in compression ratio) will increase torque because as the compression ratio goes higher, the actual ignition timing occurs sooner. However there is a point of diminishing returns where detonation occurs or engine temps can soar, and if this happens a colder plug can help. The colder plug will also increase torque, but ignition is slowed until a greater point of compression build occurs.

When you increase head shims (a decrease in compression), 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 that timing does not occur to late in the cycle, but at this point you end up over leaning the engine to get it to rev properly and the engine life will suffer dramatically.

On a .12 engine we would only advise going 0.10mm over or under 0.46mm, so that is 0.36mm or 0.56mm of total head clearance at sea level.
Generally on a .12 engine 0.10mm will change the compression ratio about 3/4 to 1 point..

We should also state that the 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.

One last comment. never assume that the head shim that is on the engine is the actual head clearance. When in doubt measure the head button register and the piston to the top of the liner at top dead center and subtract, to determine proper shim. This is the only way to really know.

You can safely use 30% Nitro with 0.56mm of real head clearance, and If you donít over lean it, the engine life will not suffer dramatically. For less Nitro % you can safely use 0.46mm of real head clearance.

Someone asked about plug fatigue the other day, plug fatigue can occur under high sustained RPM's, and this is where the plug stays shiny and the wire just fractures for no reason. When this happens it is usually not a carb. tuning or head clearance problem. If you see the wire start to pull out of the hole this means that the engine is scavenging really hard and when this occurs the engine is making serious power.

There you have it.
Bubblehead is offline   Reply With Quote
Old 04-10-2012, 03:17 PM   #3
Tech Elite
 
British Menace's Avatar
 
Join Date: Sep 2005
Location: Davenport, IA
Posts: 2,337
Default

Interesting stuff .... I know Mr. Richey so I know this info' will have been attained through his own knowledge and testing.

One point I would like to make is that the European engines such as the Nova Rossi's come shimmed for 16% so if you want to use these engines with higher nitro content, you would have to re-shim the head along the lines Mr. Richey outlines above.

Just my little input to an interesting question.

I would go for the 16%. You really can get some serious run time with that stuff. I found it a little easier to tune when I used it too.
I have seen engines make 10 mins on a tank .... and at race speed!!

BM
__________________
So enjoying building cars I sometimes forget to save some "man-time" to race them!?
British Menace is offline   Reply With Quote
Old 04-10-2012, 04:42 PM   #4
Tech Addict
 
Bubblehead's Avatar
 
Join Date: Jan 2008
Location: Portsmouth, VA
Posts: 708
Default

The performance difference I notice between the fuels 16% to 30%, could that have been a poorly tuned engine at 16%? I was ready to switch to 16% but after seeing the performance of 30% now I have questions.

British Menace, Do you notice any difference in performance where you race?
Bubblehead is offline   Reply With Quote
Old 04-10-2012, 07:58 PM   #5
Tech Addict
 
Bubblehead's Avatar
 
Join Date: Jan 2008
Location: Portsmouth, VA
Posts: 708
Default

I found this by: Joey Powell [Off-Road Forum]

It depends on what is going to win the race for you; run time, lap times, or both. Plenty of motors make good runtime on 30%. If going to 20% doesn't cut out a pit stop for you then there's no advantage in that regard. If you can put the extra power and crisper throttle response to good use then you'd probably be better off with the 30%. If the 20% is easier for you to drive and that is reflected in lower lap times then 20% might be a better choice. I'd recommend picking up a quart of both, and see what works for you. Do it with a lap timing system in place. Things to look for are lap time, run time, and overall feel on the track. Keep in mind that 20% will generally run a hotter plug than 30%, so make adjustments accordingly.

Also, let's say for argument's sake that the 20% allows you to eliminate 1 fuel stop in a 30 min. main in which your average lap times are 30 seconds and a fuel stop takes 6 seconds. Let's also say that you've noticed that you can go 0.3 sec. faster per lap with 30%. 30 sec. laps in a 30 minute main = 60 laps. 60 laps times 0.3 = 18. That's 18 seconds faster with the 30%. Deduct the extra fuel stop at 6 seconds and that's a net advantage of 12 seconds to the 30%. Btw, 0.3 sec. per lap is only 1% faster. Small increases make a big difference at the end of the day. That's why you need a lap counter.

After reading this I'm thinking of switching to 30%.

Last edited by Bubblehead; 04-11-2012 at 02:19 PM.
Bubblehead is offline   Reply With Quote
Old 04-12-2012, 12:48 PM   #6
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

More nitro makes more power, period.

There are only two reasons to run 16:

1. In most of the world outside the US, that is the maximum allowed.

2. You get better mileage.

So if mileage is no problem and the rules don't restrict it, run more.

If mileage is a problem, going to 16 is often faster than running more nitro but doing other things (like smaller carb restrictors) to make time.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is offline   Reply With Quote
Old 04-12-2012, 03:55 PM   #7
Tech Addict
 
Bubblehead's Avatar
 
Join Date: Jan 2008
Location: Portsmouth, VA
Posts: 708
Default

Well, I picked up a gallon of Sidewinder 30% Pro Blend switched to a medium glow plug. No track time yet, engine seems to idle better.
Bubblehead is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
The New Werks B5 .21 Racing Engine Werks Offroad Nitro Engine Forum 9312 11-08-2017 11:45 AM
V-ONE S Thread rhandee Nitro On-Road 4584 07-06-2014 07:19 PM
The Nitro Pit Dbackmasta Arizona-New Mexico Racing 18732 09-13-2012 09:27 AM
HK Talk Version 1.1 fai Hong Kong Racing 18317 05-13-2007 08:22 PM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 10:49 AM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net