DEFINITION OF A NERD?
#1
DEFINITION OF A NERD?
Would it be someone who checks the timing of a TD .049 on a Friday night?
BTW, I didn't want to junk up the AP .061 thread any more, so here are the timing numbers of a TD .049. Just in case you always wanted to know. The checks and results were taken a few times to verify the numbers.
Exhaust 136
Transfers 127
Crank ~ 180........taken with standard venturi installed, not easy to be super accurate.
The exhaust duration is lower than expected, but there are 2 ports. I doubt that Cox gave a hoot about the numbers during testing, I'll bet he had a bin full of blank cylinders and tried different set ups until he was happy. I wonder if he ever talked about R&D in public?
Oh man, these are the kinds of questions only a nerd would have on a Friday night, time to go listen to some Metallica and try to snap out of it! [8D]
BTW, I didn't want to junk up the AP .061 thread any more, so here are the timing numbers of a TD .049. Just in case you always wanted to know. The checks and results were taken a few times to verify the numbers.
Exhaust 136
Transfers 127
Crank ~ 180........taken with standard venturi installed, not easy to be super accurate.
The exhaust duration is lower than expected, but there are 2 ports. I doubt that Cox gave a hoot about the numbers during testing, I'll bet he had a bin full of blank cylinders and tried different set ups until he was happy. I wonder if he ever talked about R&D in public?
Oh man, these are the kinds of questions only a nerd would have on a Friday night, time to go listen to some Metallica and try to snap out of it! [8D]
#3
RE: DEFINITION OF A NERD?
Stewart, this piston had been shortened to obtain about .008" of SPI.
Joe Klaus [Kustom Kraftsmanship] used to sell liner shims to decrease SPI to a given dimension. I think he recommended .005"?
The intake overlap with the TD is similar to the Norvel and AP. The crank begins to open a split second before the transfer ports are closed.
Joe Klaus [Kustom Kraftsmanship] used to sell liner shims to decrease SPI to a given dimension. I think he recommended .005"?
The intake overlap with the TD is similar to the Norvel and AP. The crank begins to open a split second before the transfer ports are closed.
#4
RE: DEFINITION OF A NERD?
Did you get the readings of the crank opening and closing position besides the 180 degrees of duration?
As in does it open @30deg after bottom dead center?
As in does it open @30deg after bottom dead center?
#6
RE: DEFINITION OF A NERD?
Oh man, your not going to make go back out there []?
Just kidding, I got those numbers.
open at 225 ATDC [45 ABDC]
close at 45 ATDC......180 total
The chamfer at the top of the piston makes checking the exact moments tough. I use a flashlight, but actually the correct line of sight would be if you could position your eyes down in the liner, level with the top of the piston.
I also did a "zero slop" rod reset beforehand to eliminate variable timing.
I took another look at intake overlap with a better view [without the degree wheel in the way], and now it looks like the transfer ports close slightly before the crank opens. Bear in mind that it is practically a dead heat.
Just kidding, I got those numbers.
open at 225 ATDC [45 ABDC]
close at 45 ATDC......180 total
The chamfer at the top of the piston makes checking the exact moments tough. I use a flashlight, but actually the correct line of sight would be if you could position your eyes down in the liner, level with the top of the piston.
I also did a "zero slop" rod reset beforehand to eliminate variable timing.
I took another look at intake overlap with a better view [without the degree wheel in the way], and now it looks like the transfer ports close slightly before the crank opens. Bear in mind that it is practically a dead heat.
#10
RE: DEFINITION OF A NERD?
I'm still fooling around with designing an engine, and I plan to get my feet wet into making one. I figure if I pick an average of the various timings I can't go too far wrong.
#12
Senior Member
Join Date: Mar 2004
Location: BelvedereKent, UNITED KINGDOM
Posts: 766
Likes: 0
Received 0 Likes
on
0 Posts
RE: DEFINITION OF A NERD?
ORIGINAL: combatpigg
Would it be someone who checks the timing of a TD .049 on a Friday night?
Would it be someone who checks the timing of a TD .049 on a Friday night?
I last had an interest in modifying two stroke engines about 47yrs ago, I was padding the C/Case of a Villiers 197cc engine. After that time I became more interested in four stroke bike and car engines. I had all the equipment, degree wheels and plenty of measuring gear, air grinders etc. I built a number of modified car engines that produced significant improvements. Now I am no longer interested in Cars, simply model aircraft.
Recently a cousin gave me an engine that I mistook for an Arden, actually it was an Atom. I couldn't find the needle valve, in fact there was none. Reading up on the Atom I found that it has Port in Piston rather than Sub Piston Induction, I won't discuss the control of the mixture. Then this thread came along, upsetting my equilibrium and making me think of the unthinkable e.g. think.
So there you have it, I spent some hours after midnight reading up on the Atom, and looking at my 1/2A motors when I have no intention of modifying anything except perhaps making a silencer or two.
Please get out of my head.
old git - - - - aka John L.
#13
Senior Member
Join Date: Sep 2004
Location: Annapolis,
MD
Posts: 981
Likes: 0
Received 0 Likes
on
0 Posts
RE: DEFINITION OF A NERD?
When checking and comparing timings, don't forget that an air/fuel mixture has mass and it takes time to start and stop said mass. Often port (and valve) timings overlap to give the mixture a head start on flowing, and to give it a chance to finish filling (on it's respective cycle).
Obviously too much overlap is a bad thing too, but don't completely rule out the need for overlap(s).
The .PDF floating around the internet for the DIY Alpha diesel has a good write-up on port timings -vs- intended duty (i.e. sport/race). I have a copy of anyone is interested, just PM me...
-Joe
Obviously too much overlap is a bad thing too, but don't completely rule out the need for overlap(s).
The .PDF floating around the internet for the DIY Alpha diesel has a good write-up on port timings -vs- intended duty (i.e. sport/race). I have a copy of anyone is interested, just PM me...
-Joe
#16
RE: DEFINITION OF A NERD?
Relax PropTop, nerds don't own K&B 6.5s.
Remby, sorry I don't have a Medallion. I don't think you would be able to get a good visual reading since the venturi is so small. You would have to rig up air pressure in the crankcase and get your readings like that. That would probably be more meaningful than visually noting when the ports are open.
If you remove the carb body, the readings on the TD are more like 195 for crank duration. I don't think this is the effective duration if the port is masked by the venturi. I think Cox took a nice, quick, meaty cut into the case and into the crank without weakening the structure and came away with a working unit without worrying about exotic theories and numbers too much. I'm guessing the Medallion is just a low performance cylinder and smaller venturi in a stock TD case?
Remby, sorry I don't have a Medallion. I don't think you would be able to get a good visual reading since the venturi is so small. You would have to rig up air pressure in the crankcase and get your readings like that. That would probably be more meaningful than visually noting when the ports are open.
If you remove the carb body, the readings on the TD are more like 195 for crank duration. I don't think this is the effective duration if the port is masked by the venturi. I think Cox took a nice, quick, meaty cut into the case and into the crank without weakening the structure and came away with a working unit without worrying about exotic theories and numbers too much. I'm guessing the Medallion is just a low performance cylinder and smaller venturi in a stock TD case?
#17
RE: DEFINITION OF A NERD?
Interesting to compare these numbers to the numbers I built my little engine too.
Here are mine: 36/62 crank, 165/132 sleeve. The bypass and boost ports open at the same time. My crank numbers are determined by where the port opens on the case. no venturi installed.
I use a dial indicator on the piston to get movement measurements so I know exactly how much to take off to get to that magical number (take exactly 1/2 of reading for amount of material to remove) and I use a small light for visual indication of actual opening. My piston has a small barral shape to it as planned so getting port readings can be difficult if using a pressurized case method, plus my engines are so loose anyway the pressure method is just a head ache to me, not being very repeatable. A simple Mag-lite, a small one, taped to the rear cover hole works for me.
Edit. Yep I am just a nerd, ... a 300 lb one
Here are mine: 36/62 crank, 165/132 sleeve. The bypass and boost ports open at the same time. My crank numbers are determined by where the port opens on the case. no venturi installed.
I use a dial indicator on the piston to get movement measurements so I know exactly how much to take off to get to that magical number (take exactly 1/2 of reading for amount of material to remove) and I use a small light for visual indication of actual opening. My piston has a small barral shape to it as planned so getting port readings can be difficult if using a pressurized case method, plus my engines are so loose anyway the pressure method is just a head ache to me, not being very repeatable. A simple Mag-lite, a small one, taped to the rear cover hole works for me.
Edit. Yep I am just a nerd, ... a 300 lb one
#18
RE: DEFINITION OF A NERD?
Even the light can be deceiving, my BigMig is worn enough that light was showing up in the exhaust port with the top of the piston 1/8" from the port.
Toad, I took a Fox .36 out to those figures and turned it into a .15.......
Toad, I took a Fox .36 out to those figures and turned it into a .15.......
#20
RE: DEFINITION OF A NERD?
I am thinking for my next crank, the lefty one I need for a proto ship, will have 30/62 timming I see those numbers alot latly in the Profi series
and the masses seem to be gravitated to them, I havent been able to find out what Nelson is using on his new Long Stroke Quickie, I bet it is very close to that. seems like a good timming for non throttle applications. Someone on the delphi forum will tell the numbers soon on that engine. I hope. I want to copy it in an .050 size as far as timming goes.
and the masses seem to be gravitated to them, I havent been able to find out what Nelson is using on his new Long Stroke Quickie, I bet it is very close to that. seems like a good timming for non throttle applications. Someone on the delphi forum will tell the numbers soon on that engine. I hope. I want to copy it in an .050 size as far as timming goes.
#23
RE: DEFINITION OF A NERD?
DT, I might be able to save you some time. I just checked a OS.32, Os .15CV and OS .15LA. They are all nearly identical.
exhaust 140
transfer/boost 120.....110 for the LA .15
crank 192 [carburetors removed]
The .32 gets it's power from a high crankcase compression ratio, great fits and excellent transfer gas pathways. It also responds to full pipes very well.
The CV differs from the LA.15 obviously because of the ball bearings, but it uses a larger carb too. The LA is no slouch, it will turn a 8x3 about 17,000.....the CV is noticeably stronger but it costs twice as much. It responds to a full pipe pretty well, too.
All of these engine have overlap between the tranfer ports and crank port, with the crank opening before the transfers can close.
I was going to check a LA .40, but it was starting to get mo-not-i-nus
exhaust 140
transfer/boost 120.....110 for the LA .15
crank 192 [carburetors removed]
The .32 gets it's power from a high crankcase compression ratio, great fits and excellent transfer gas pathways. It also responds to full pipes very well.
The CV differs from the LA.15 obviously because of the ball bearings, but it uses a larger carb too. The LA is no slouch, it will turn a 8x3 about 17,000.....the CV is noticeably stronger but it costs twice as much. It responds to a full pipe pretty well, too.
All of these engine have overlap between the tranfer ports and crank port, with the crank opening before the transfers can close.
I was going to check a LA .40, but it was starting to get mo-not-i-nus
#25
RE: DEFINITION OF A NERD?
just had a very nice post timed out.........good idea to do this one, the one and only Norvel .074
exhaust 145
transfers 120
crank 184.....closes at 52
intake overlap, crank port opens before transfers close
No one has done a "Toad" on one of these, I'll bet. I've got one that is slightly past its' prime that might get flogged.
exhaust 145
transfers 120
crank 184.....closes at 52
intake overlap, crank port opens before transfers close
No one has done a "Toad" on one of these, I'll bet. I've got one that is slightly past its' prime that might get flogged.