Crank timing advice, please? Still trying to wring more power out of a HPI .12R SS
12-29-2016, 05:37 AM
#31
I ran the car with the body off today to see how much speed was being sacrificed to generate downforce. The car went 2mph faster, and was significantly harder to control. Obviously that energy is being put to good use keeping the tires stuck to the ground instead of making the car go faster, but damn I wish I knew where the extra power is hiding. I leaned-out the fuel mixture a bit and it *still* goes 45mph with the body on. It just seems implausible that all these changes I'm making could have no measurable effect whatsoever. Even the exhaust note is the same pitch at top speed, so the GPS speed readings are definitely accurate.
The only things I haven't tried at this point are:
- Hotter/colder glowplug (maybe advancing the ignition would help? I dunno, but I don't want to waste a new glowplug to test it; maybe I can get away with borrowing a hot plug from a different engine)
- Higher gearing (unlikely to do anything at all unless the engine is operating significantly above its power peak at its current top speed)
- Degrease all bearings and re-lubricate with oil (impractical for a basher vehicle)
- Replace the T3.0 carburetor with the stock carburetor (this would decrease the venturi size, which I'm pretty sure would *reduce* its top speed, unless there's something I'm misunderstanding)
The only things I haven't tried at this point are:
- Hotter/colder glowplug (maybe advancing the ignition would help? I dunno, but I don't want to waste a new glowplug to test it; maybe I can get away with borrowing a hot plug from a different engine)
- Higher gearing (unlikely to do anything at all unless the engine is operating significantly above its power peak at its current top speed)
- Degrease all bearings and re-lubricate with oil (impractical for a basher vehicle)
- Replace the T3.0 carburetor with the stock carburetor (this would decrease the venturi size, which I'm pretty sure would *reduce* its top speed, unless there's something I'm misunderstanding)
Removing shims is far more important then any of the mod work you did... leaving the engine at stock shimming cancels out everything you did, and if you increased exhaust timing you will lose power every time unless you increase compression to compensate. Truthfully just removing head shims will have a far more profound effect on power then any of the common mods you see online.. Also what manifold you use is super critical,want more power and speed go to a shorter manifold !
12-29-2016, 12:57 PM
#32
I did increase exhaust timing a little bit by raising the sleeve 0.1mm, though that means I also increased the transfer-port timing as well. I also dropped the total height of the shim stack 0.1mm, down to 0.3mm from 0.4mm. I could drop it further, down to 0.2mm, but that would leave only a single 0.1mm shim between the sleeve and the head since one of the shims is under the sleeve instead of above it.
I agree that increasing compression increases power, especially in the mid RPMs, I've seen that myself on other engines. Not on this one though, for some bizarre reason. I have no doubt that cleaning out the transfer-port channels must've helped somehow, because they were really badly obstructed before. But the effect on the engine's power output appears to have been academic.
Doesn't increasing compression have a negative effect on the top speed of the engine? I read that somewhere but I confess I have no firsthand knowledge to back it up.
I agree that increasing compression increases power, especially in the mid RPMs, I've seen that myself on other engines. Not on this one though, for some bizarre reason. I have no doubt that cleaning out the transfer-port channels must've helped somehow, because they were really badly obstructed before. But the effect on the engine's power output appears to have been academic.
Doesn't increasing compression have a negative effect on the top speed of the engine? I read that somewhere but I confess I have no firsthand knowledge to back it up.
12-29-2016, 01:51 PM
#33
I did increase exhaust timing a little bit by raising the sleeve 0.1mm, though that means I also increased the transfer-port timing as well. I also dropped the total height of the shim stack 0.1mm, down to 0.3mm from 0.4mm. I could drop it further, down to 0.2mm, but that would leave only a single 0.1mm shim between the sleeve and the head since one of the shims is under the sleeve instead of above it.
I agree that increasing compression increases power, especially in the mid RPMs, I've seen that myself on other engines. Not on this one though, for some bizarre reason. I have no doubt that cleaning out the transfer-port channels must've helped somehow, because they were really badly obstructed before. But the effect on the engine's power output appears to have been academic.
Doesn't increasing compression have a negative effect on the top speed of the engine? I read that somewhere but I confess I have no firsthand knowledge to back it up.
I agree that increasing compression increases power, especially in the mid RPMs, I've seen that myself on other engines. Not on this one though, for some bizarre reason. I have no doubt that cleaning out the transfer-port channels must've helped somehow, because they were really badly obstructed before. But the effect on the engine's power output appears to have been academic.
Doesn't increasing compression have a negative effect on the top speed of the engine? I read that somewhere but I confess I have no firsthand knowledge to back it up.
12-29-2016, 02:27 PM
#34
I generally break-in my engines with too many shims, because it reduces the risk of sudden overheating while the pinch is still tight, especially since I run 30% nitro.
The engine isn't getting to max RPM in 2nd gear, that's all I can tell at this point. Considering I have another RS4 that needs a .21 engine to reach 61mph, I should probably be happy that this one can reach 45mph with a .12 engine. The car is probably just too heavy, or something. But dammit, I want to wring-out this tiny engine to within an inch of its life. I suppose I can always try a .15 engine if this one refuses to cooperate.
I decided to go hunting for possible sources of drag on the car. I found a couple spots where parts were rubbing together slightly, and fixed them. It probably won't make any difference, but at least I can say I tried.
The engine isn't getting to max RPM in 2nd gear, that's all I can tell at this point. Considering I have another RS4 that needs a .21 engine to reach 61mph, I should probably be happy that this one can reach 45mph with a .12 engine. The car is probably just too heavy, or something. But dammit, I want to wring-out this tiny engine to within an inch of its life. I suppose I can always try a .15 engine if this one refuses to cooperate.
I decided to go hunting for possible sources of drag on the car. I found a couple spots where parts were rubbing together slightly, and fixed them. It probably won't make any difference, but at least I can say I tried.
01-01-2017, 12:40 PM
#36
Well, I finally had a bit of a breakthrough. I swapped the medium glowplug I was using with a hot glowplug from my dedicated winter nitro truck, and suddenly my RS4 gained 3mph in repeated testing. That's roughtly equivalent to 2000rpm, according to this car's drive ratio and tire size. As if to prove the increase in speed wasn't caused by removing drag in the drivetrain, it also idled higher, so I was able to close the idle gap a little bit. Enriching the fuel mixture 1/24t dropped the top speed to 47mph; leaning it 2/24t did not increase the top speed, only the operating temperature.
What do RCTech's nitro gurus think should be my next step, based on this info?
What do RCTech's nitro gurus think should be my next step, based on this info?
01-01-2017, 01:01 PM
#37
Well, I finally had a bit of a breakthrough. I swapped the medium glowplug I was using with a hot glowplug from my dedicated winter nitro truck, and suddenly my RS4 gained 3mph in repeated testing. That's roughtly equivalent to 2000rpm, according to this car's drive ratio and tire size. As if to prove the increase in speed wasn't caused by removing drag in the drivetrain, it also idled higher, so I was able to close the idle gap a little bit. Enriching the fuel mixture 1/24t dropped the top speed to 47mph; leaning it 2/24t did not increase the top speed, only the operating temperature.
What do RCTech's nitro gurus think should be my next step, based on this info?
What do RCTech's nitro gurus think should be my next step, based on this info?
01-01-2017, 01:48 PM
#38
I suppose I can try lowering the shim stack even further. I can only remove one more shim, though. Is it safe to run 0.2mm of shims on a .12 engine running on 30% nitro?
Also, am I correct in my assumption that switching back to the stock carburetor, with its narrower inlet, would reduce the top speed of the engine? I can't think of any reason why it would help, but maybe there's some detail I'm failing to consider.
Also, am I correct in my assumption that switching back to the stock carburetor, with its narrower inlet, would reduce the top speed of the engine? I can't think of any reason why it would help, but maybe there's some detail I'm failing to consider.
Last edited by fyrstormer; 01-01-2017 at 03:08 PM.
01-04-2017, 12:50 PM
#39
Lowered the shim stack from 0.3mm to 0.2mm. If I want to lower it further I'll have to remove the shim from under the lip of the sleeve, because there's only one shim left on top of the sleeve.
The car hit 48mph today with a medium glowplug. I swapped in the hot glowplug again and it made no difference. In my mind, that means increasing the compression further would have no beneficial effect. Does that sound right?
The engine temperature was cool, around 210F, but I don't want to go higher than that because I've been running in cold air and the engine is going to run much hotter when it's 90F outside instead of 45F.
The car hit 48mph today with a medium glowplug. I swapped in the hot glowplug again and it made no difference. In my mind, that means increasing the compression further would have no beneficial effect. Does that sound right?
The engine temperature was cool, around 210F, but I don't want to go higher than that because I've been running in cold air and the engine is going to run much hotter when it's 90F outside instead of 45F.
01-04-2017, 06:29 PM
#40
Lowered the shim stack from 0.3mm to 0.2mm. If I want to lower it further I'll have to remove the shim from under the lip of the sleeve, because there's only one shim left on top of the sleeve.
The car hit 48mph today with a medium glowplug. I swapped in the hot glowplug again and it made no difference. In my mind, that means increasing the compression further would have no beneficial effect. Does that sound right?
The engine temperature was cool, around 210F, but I don't want to go higher than that because I've been running in cold air and the engine is going to run much hotter when it's 90F outside instead of 45F.
The car hit 48mph today with a medium glowplug. I swapped in the hot glowplug again and it made no difference. In my mind, that means increasing the compression further would have no beneficial effect. Does that sound right?
The engine temperature was cool, around 210F, but I don't want to go higher than that because I've been running in cold air and the engine is going to run much hotter when it's 90F outside instead of 45F.
what pipe and manifold are you using ? do you have any tuning options for manifold ? quite often I have to trim the buttons on the engines I modify just to get them as tight as I need them.
01-04-2017, 10:11 PM
#41
Stock header (looks to be about 2" from the exhaust port to the tuned-pipe inlet if the header were straightened-out), Novarossi EFRA-2601 high-RPM tuned pipe. (I had to buy the freaking thing from Austria; Novarossi USA never officially carried the one that fits my car.) The header is port-matched to the engine, something I took care of when I first built the car.
If increasing the compression further were going to produce any benefit, wouldn't I have seen at least a slight speed increase from advancing the ignition timing with the hot glowplug? I didn't see any change at all, at least not on the GPS speedo.
Would I see any benefit from replacing the steel crank bearings with ceramic? I have no problem doing that, I've replaced crank bearings with ceramic before to protect against rust, but I don't know if it would make any difference in terms of performance. It seems like all the popular racing engines use ceramic bearings nowadays, but maybe that's just a gimmick to sell more expensive engines.
If increasing the compression further were going to produce any benefit, wouldn't I have seen at least a slight speed increase from advancing the ignition timing with the hot glowplug? I didn't see any change at all, at least not on the GPS speedo.
Would I see any benefit from replacing the steel crank bearings with ceramic? I have no problem doing that, I've replaced crank bearings with ceramic before to protect against rust, but I don't know if it would make any difference in terms of performance. It seems like all the popular racing engines use ceramic bearings nowadays, but maybe that's just a gimmick to sell more expensive engines.
Last edited by fyrstormer; 01-04-2017 at 10:29 PM.
01-04-2017, 11:41 PM
#42
No, ceramic will not add a noticable difference.
01-05-2017, 06:46 AM
#43
Stock header (looks to be about 2" from the exhaust port to the tuned-pipe inlet if the header were straightened-out), Novarossi EFRA-2601 high-RPM tuned pipe. (I had to buy the freaking thing from Austria; Novarossi USA never officially carried the one that fits my car.) The header is port-matched to the engine, something I took care of when I first built the car.
If increasing the compression further were going to produce any benefit, wouldn't I have seen at least a slight speed increase from advancing the ignition timing with the hot glowplug? I didn't see any change at all, at least not on the GPS speedo.
Would I see any benefit from replacing the steel crank bearings with ceramic? I have no problem doing that, I've replaced crank bearings with ceramic before to protect against rust, but I don't know if it would make any difference in terms of performance. It seems like all the popular racing engines use ceramic bearings nowadays, but maybe that's just a gimmick to sell more expensive engines.
If increasing the compression further were going to produce any benefit, wouldn't I have seen at least a slight speed increase from advancing the ignition timing with the hot glowplug? I didn't see any change at all, at least not on the GPS speedo.
Would I see any benefit from replacing the steel crank bearings with ceramic? I have no problem doing that, I've replaced crank bearings with ceramic before to protect against rust, but I don't know if it would make any difference in terms of performance. It seems like all the popular racing engines use ceramic bearings nowadays, but maybe that's just a gimmick to sell more expensive engines.
After compression the manifold is the next most critical...no matter what you do to the engine the RPM range of the powerband wont change much without a manifold change...So to find the sweet spot you would need to test multiple manifolds, likely needing a shorter one then the RTR manifold...As for compression you likely still have more to go, if the hot plug didn't lose power there is probably more in it.
01-05-2017, 07:04 AM
#44
Also you can run these engines without any shims if needed, they are only shims, not gaskets.