Go Back  R/C Tech Forums > General Forums > Nitro On-Road > Onroad Nitro Engine Zone
Crank timing advice, please? Still trying to wring more power out of a HPI .12R SS >

Crank timing advice, please? Still trying to wring more power out of a HPI .12R SS

Crank timing advice, please? Still trying to wring more power out of a HPI .12R SS

Reply

Old 12-12-2016, 12:21 AM
  #1  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default Crank timing advice, please? Still trying to wring more power out of a HPI .12R SS

One of my cars runs a HPI .12R SS engine. Using the awesome power of elementary-school math, I calculated based on the top speed, tire size, and gear ratios that the engine is peaking at about 30,000rpm. I did a little grinding and polishing on the sleeve (and the hole in the side of the piston) to improve breathing through the transfer ports, and testing showed the car gained ~1mph, i.e. ~600rpm. Not a huge improvement.

I've been doing more reading and it looks like the next thing to try is modifying the intake port timing on the crankshaft. The general rule seems to be "opening earlier = more low-end power" and "closing later = higher max RPM". I wouldn't complain about more low-end power, but it's really the max RPM I want to raise. This engine just doesn't rev as high as I think it should, and it has the same conrod as HPI's .18 engine from the same time period, so there should be no concern about the conrod breaking from increased stress.

Having said that, I'd like someone with more experience to look at the pictures below and tell me if they think there's actually room to improve the intake port timing. If air had no inertia, then the answer would obviously be yes, because the intake port closes well before before the exhaust port and transfer ports open -- but of course air *does* have inertia, *and* it's elastic too, and I don't have enough experience to account for those effects at 30,000rpm.

Here are the crank positions when the various ports open and close:



What do you think? Is there enough room to have the intake port close later, to get more max RPM out of this engine? Or do the port timings suggest a different approach that would work better? Or am I S.O.L. and I should accept the engine as-is?

Also, I should mention that I recently got a Novarossi .12-.15 pipe tuned for higher max RPMs, but I haven't had a chance to test it compared to the stock HPI pipe, so take that into account if you think it will matter at all.

Last edited by fyrstormer; 03-29-2018 at 04:27 PM.
fyrstormer is offline  
Reply With Quote
Old 12-12-2016, 01:36 AM
  #2  
Tech Elite
iTrader: (1)
 
30Tooth's Avatar
 
Join Date: Sep 2010
Location: My house.
Posts: 3,411
Trader Rating: 1 (100%+)
Default

That's not crank timing. That's sleeve timing. Roleof I think said there's a .1mm on closing crank timing available to grind as a first approach, I would start there.
http://www.rctech.net/forum/onroad-n...t-modding.html
30Tooth is offline  
Reply With Quote
Old 12-12-2016, 01:40 AM
  #3  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default

I intend to modify the intake port on the crank, so by the definition in your own thread, it's crank timing. I provided pictures of the transfer and exhaust port timings as well, because the port timings have to all play nice with each other. I have no intention to modify the shapes of the transfer and exhaust ports unless someone says it would be a significantly better idea based on the information I provided.
fyrstormer is offline  
Reply With Quote
Old 12-12-2016, 01:51 AM
  #4  
Tech Addict
 
Join Date: Dec 2010
Location: Sweden
Posts: 592
Default

You need to get things measured up the right way, at least degrees on everything.
Eyeballing things from a picture will not give you any answers that's useful.
NitroVein is online now  
Reply With Quote
Old 12-12-2016, 02:36 AM
  #5  
Tech Elite
iTrader: (1)
 
30Tooth's Avatar
 
Join Date: Sep 2010
Location: My house.
Posts: 3,411
Trader Rating: 1 (100%+)
Default

I was talking about the pics, I could get a visual of durations because I'm accustomed to see them that way and I wouldn't touch sleeve timing, at least for now. Measuring with a rig should be easy for you.
30Tooth is offline  
Reply With Quote
Old 12-12-2016, 02:44 AM
  #6  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default

I would make accurate measurements before actually cutting anything. The photos are just to get a rough idea from someone who's modded crankshafts before whether it's even worth putting in the effort to build a degree wheel to use on this engine. I'm happy enough with the performance of my other engines that I would only start modding their crankshafts if I ran out of absolutely anything else to occupy my time, so a degree wheel would almost certainly be used for this engine only. Therefore I'd rather not build one at all if it's unlikely I could actually use it to improve this engine.

For example, if someone were to say "yes, it looks like the intake timing is very conservative and you could keep the intake valve open for an extra 5 degrees and get a lot more top end", then that would make it worth my time to measure things carefully. Whereas if someone were to say "no, this engine is already optimized from the factory, mediocre though it is", then there would be no point in pursuing this project any further.

Last edited by fyrstormer; 12-12-2016 at 02:55 AM.
fyrstormer is offline  
Reply With Quote
Old 12-12-2016, 03:11 AM
  #7  
Tech Elite
iTrader: (1)
 
30Tooth's Avatar
 
Join Date: Sep 2010
Location: My house.
Posts: 3,411
Trader Rating: 1 (100%+)
Default

Then do the same for the crank, take off the carb and take a pic of where the crankpin is at crank closing and revealing the opening. I know most if not all RTR engines are strained in the crank, not so much the sleeve.
30Tooth is offline  
Reply With Quote
Old 12-12-2016, 04:01 AM
  #8  
Tech Champion
 
Roelof's Avatar
 
Join Date: Aug 2007
Location: Holland
Posts: 6,917
Default

The problem with cranktimings with your crank size (12mm?) is that about 0.1mm shaving of the edge of the crankshaft is equal to 1 degree. Ofcourse you can remove something visable but there is a chance it will be too much.
That is why those pictures with positions does not tell a thing.... (athough I suspect the timing is very mild and has some room to enlarge)

The most simple thing to do is use a dremel and a caliper.
Take a caliper and measure the diameter of the crankshaft on the opening of the crankshaft. That is probably arround 9 to 10mm
Use a dremel to touch one edge at the opening so the diameter will be 0.05mm smaller. Do the same on the other edge so the total will be 0.1mm smaller.
In that way you have changed the opening and closing with both 1 degree, it should be noticeable.

Here a pic how to meassure
http://www.euronet.nl/users/tooms/ftp/meten_krukas.JPG
Roelof is offline  
Reply With Quote
Old 12-12-2016, 04:12 AM
  #9  
Tech Addict
 
Join Date: Dec 2010
Location: Sweden
Posts: 592
Default

+1 Roelof

You could use something as simple as a CD, I even think there is a picture on the web (Google it) that you just glue on to a CD.
Or go by calculating from piston movement, that's how I usually do it.
NitroVein is online now  
Reply With Quote
Old 12-12-2016, 04:19 AM
  #10  
Tech Elite
iTrader: (58)
 
1/8 IC Fan's Avatar
 
Join Date: Jan 2012
Location: North America & Europe
Posts: 3,122
Trader Rating: 58 (98%+)
Default

Originally Posted by 30Tooth View Post
That's not crank timing. That's sleeve timing. Roleof I think said there's a .1mm on closing crank timing available to grind as a first approach, I would start there.
http://www.rctech.net/forum/onroad-n...t-modding.html
30Tooth, do you still have that motor from your link? how did it do, perhaps your thread can be updated with your findings, as I am sure this thread too will be updated after the mods.
1/8 IC Fan is offline  
Reply With Quote
Old 12-12-2016, 02:00 PM
  #11  
Tech Elite
iTrader: (1)
 
30Tooth's Avatar
 
Join Date: Sep 2010
Location: My house.
Posts: 3,411
Trader Rating: 1 (100%+)
Default

Originally Posted by 1/8 IC Fan View Post
30Tooth, do you still have that motor from your link? how did it do, perhaps your thread can be updated with your findings, as I am sure this thread too will be updated after the mods.
Yeah still have the engine, I ground a bit too much on the crank and am afraid to run it, it's the ring close to the outer bearing.
30Tooth is offline  
Reply With Quote
Old 12-12-2016, 04:20 PM
  #12  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default

Originally Posted by 30Tooth View Post
Then do the same for the crank, take off the carb and take a pic of where the crankpin is at crank closing and revealing the opening. I know most if not all RTR engines are strained in the crank, not so much the sleeve.
??

That's what I did. The picture labeled "intake port opens" was taken after aligning the crank so the leading edge of the intake port was just barely visible at the base of the carb socket, and the picture labeled "intake port closes" was taken the same way except based on the trailing edge of the intake port instead.
fyrstormer is offline  
Reply With Quote
Old 12-12-2016, 04:22 PM
  #13  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default

Originally Posted by Roelof View Post
The problem with cranktimings with your crank size (12mm?) is that about 0.1mm shaving of the edge of the crankshaft is equal to 1 degree. Ofcourse you can remove something visable but there is a chance it will be too much.
That is why those pictures with positions does not tell a thing.... (athough I suspect the timing is very mild and has some room to enlarge)

The most simple thing to do is use a dremel and a caliper.
Take a caliper and measure the diameter of the crankshaft on the opening of the crankshaft. That is probably arround 9 to 10mm
Use a dremel to touch one edge at the opening so the diameter will be 0.05mm smaller. Do the same on the other edge so the total will be 0.1mm smaller.
In that way you have changed the opening and closing with both 1 degree, it should be noticeable.

Here a pic how to meassure
http://www.euronet.nl/users/tooms/ftp/meten_krukas.JPG
Thanks, I'll take the appropriate measurements. It sounds like the diamond-coated hand files I own will come in handy for this project.

Would I want to change the leading edge of the intake port, though? I'm looking for more top-end, not more bottom-end. I thought top-end was adjusted by changing the trailing edge of the intake port?

Also, how do I determine how much adjustment is actually useful vs. how much will cause damage?

Last edited by fyrstormer; 12-12-2016 at 04:35 PM.
fyrstormer is offline  
Reply With Quote
Old 12-12-2016, 10:36 PM
  #14  
Tech Champion
 
Roelof's Avatar
 
Join Date: Aug 2007
Location: Holland
Posts: 6,917
Default

More top end needs power, so the total opening needs to be larger. But with your enginge also the top-end is limited by a low exhaust port, just do not expect wonders with your engine, some small steps are noticeable.
Roelof is offline  
Reply With Quote
Old 12-13-2016, 03:32 AM
  #15  
Tech Elite
Thread Starter
 
fyrstormer's Avatar
 
Join Date: Mar 2014
Location: Maryland, Near DC, USA
Posts: 3,403
Default

Fair enough, thanks.
fyrstormer is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Terms of Service