16LikesHelp polishing a turd (HPI 15FE)
05-25-2018, 11:32 AM
#1
Help polishing a turd (HPI 15FE)
I have a HPI 15FE. In my RS4 2, it will reach 47mph. I would like it to reach 50mph. I've tried everything I can think of, and the top speed doesn't change at all:
- Raising the cylinder by 0.2mm to increase the transfer and exhaust port timings
- Lowering the shim-stack from 0.5mm to 0.3mm, and then to 0.1mm
- Running a hotter plug
- Clearing obstructions near the transfer port channels in the crankcase
- Rounding the lower edges of the cylinder under the transfer ports
I haven't tried:
- Filing the upper edge of the exhaust port to make the exhaust port taller, because raising the entire cylinder didn't make any difference
- Filing the edges of the intake port on the crankshaft, because they're already nice and clean
The engine makes noticeably better torque, and revs-up faster than it used to, but the top speed hasn't increased even a tiny bit. Obviously I could just get a different engine, but the challenge is to see how much I can improve this engine. It's not inherently a bad engine, it's inherently a pile of metal parts. Those metal parts just need to be shaped right, and the engine will run faster. Anyone have any more suggestions for things I can try that don't involve replacing the engine?
- Raising the cylinder by 0.2mm to increase the transfer and exhaust port timings
- Lowering the shim-stack from 0.5mm to 0.3mm, and then to 0.1mm
- Running a hotter plug
- Clearing obstructions near the transfer port channels in the crankcase
- Rounding the lower edges of the cylinder under the transfer ports
I haven't tried:
- Filing the upper edge of the exhaust port to make the exhaust port taller, because raising the entire cylinder didn't make any difference
- Filing the edges of the intake port on the crankshaft, because they're already nice and clean
The engine makes noticeably better torque, and revs-up faster than it used to, but the top speed hasn't increased even a tiny bit. Obviously I could just get a different engine, but the challenge is to see how much I can improve this engine. It's not inherently a bad engine, it's inherently a pile of metal parts. Those metal parts just need to be shaped right, and the engine will run faster. Anyone have any more suggestions for things I can try that don't involve replacing the engine?
05-25-2018, 12:07 PM
#2
……………………….……in how many sections are you going to post this?? its 2 now probably more..
Last edited by the rc guy; 05-25-2018 at 02:23 PM.
05-25-2018, 12:07 PM
#3
Some piles of metal parts just suck and some piles are just better. Then of course you have your royalty class of metal piles.
05-25-2018, 03:48 PM
#5
Tech Fanatic
First of all you need a colder glow plug, not a hotter one, if you want more top end.
All engines have their bottlenecks, finding them is a matter of many things, but start by looking on the timing numbers you got now and see if it makes sense to increase them any more. If not, you got to work in other areas, and it's not always as straight forward as some like to think.
I've never seen one of those engines so I can't help you with any specifics unfortunately...
All engines have their bottlenecks, finding them is a matter of many things, but start by looking on the timing numbers you got now and see if it makes sense to increase them any more. If not, you got to work in other areas, and it's not always as straight forward as some like to think.
I've never seen one of those engines so I can't help you with any specifics unfortunately...
05-25-2018, 08:43 PM
#6
It's basically an old Toki-manufactured airplane engine that HPI slapped a bigger heatsink on and called a "car engine". It didn't even have a twin-needle carburetor until I fitted it with one from a HPI 3.0 engine. I cleared a bunch of crud out of the crankcase that was partially obstructing the transfer ports, and I cut some bits off the crankshaft on either side of the conrod journal to make it a little better balanced for a wide range of RPMs. (airplane engines basically run at full throttle the entire time the airplane is in the air, and the propeller acts like a huge heavy flywheel, so having a properly-balanced crankshaft is less important. The engine stopped making the entire car buzz after I did this mod.)
It would seem that increasing the transfer port and exhaust port timings wouldn't make any difference, because raising the entire cylinder changed all of those timings at once and the engine didn't go any faster. I haven't tried anything with the intake port on the crankshaft yet, though.
I tried a medium plug and a hot plug, and I saw no difference in top speed. I might be inferring too much, but if a cold plug were going to make a difference, wouldn't the medium plug have performed better than the hot plug? There was no difference whatsoever. Also, I thought cold plugs were only necessary for racing, when the engine is at high RPM almost constantly for minutes at a time. This is a basher engine in a basher car, it spends most of its time in the middle of its RPM range.
It's just very puzzling that I tried so many different things thus far and the top speed has remained exactly the same. No variation at all, no faster than before, and no slower than before either. It makes me think there's a single huge bottleneck that I don't know about, and all the other changes I've made are irrelevant because of that single huge bottleneck. But what could it be? In its current state, the engine has higher compression, a bigger and more-tunable carburetor, unobstructed airflow paths through the crankcase, a mandrel-bent exhaust header, ceramic crank bearings (because I'm apparently a madman), and a pullstarter that spins on ball-bearings to eliminate the drag that pullstarters usually cause. What else is there to improve?
It would seem that increasing the transfer port and exhaust port timings wouldn't make any difference, because raising the entire cylinder changed all of those timings at once and the engine didn't go any faster. I haven't tried anything with the intake port on the crankshaft yet, though.
I tried a medium plug and a hot plug, and I saw no difference in top speed. I might be inferring too much, but if a cold plug were going to make a difference, wouldn't the medium plug have performed better than the hot plug? There was no difference whatsoever. Also, I thought cold plugs were only necessary for racing, when the engine is at high RPM almost constantly for minutes at a time. This is a basher engine in a basher car, it spends most of its time in the middle of its RPM range.
It's just very puzzling that I tried so many different things thus far and the top speed has remained exactly the same. No variation at all, no faster than before, and no slower than before either. It makes me think there's a single huge bottleneck that I don't know about, and all the other changes I've made are irrelevant because of that single huge bottleneck. But what could it be? In its current state, the engine has higher compression, a bigger and more-tunable carburetor, unobstructed airflow paths through the crankcase, a mandrel-bent exhaust header, ceramic crank bearings (because I'm apparently a madman), and a pullstarter that spins on ball-bearings to eliminate the drag that pullstarters usually cause. What else is there to improve?
05-25-2018, 09:29 PM
#7
Hm...comparing the 15FE crankshaft to the 12R SS crankshaft (both made by Toki, using essentially the same engine block, but the 12R SS is higher-performing), I see that the 12R SS' crankshaft has the intake port area ground-down 0.4mm more to increase the intake timing by about 2.3° on both the leading and trailing edges of the port. It also has a ramp at the end of the intake bore, whereas the 15FE crankshaft has a blunt reversion dam at the end of the intake bore. (I've read things that suggest intake ramps both do and don't have any effect. Gotta love the internet.) Those differences seem to be good for giving the 12R SS an extra 2500rpm over the 15FE.
Interestingly, I could just put the 12R SS crankshaft into the 15FE to test, but the 12R SS crankshaft's intake port is a little too long (though I suppose that isn't super important -- it would matter more if it were too short), but the 12R SS' crankshaft is harder than hell to find and I don't want to use my only spare for this test.
EDIT: Wow. I was just looking at a spare sleeve for my Losi 3.4 engine, and the exhaust port opens waaaaaay before the transfer ports open. The exhaust port is twice as tall as the transfer ports. I would've thought that would make the engine a pig at low RPM, but it has no trouble hauling ass from a standstill. I don't know how many extra degrees of exhaust port timing that translates to, but no wonder I can wring-out the Losi 3.4 to 38,000rpm.
Interestingly, I could just put the 12R SS crankshaft into the 15FE to test, but the 12R SS crankshaft's intake port is a little too long (though I suppose that isn't super important -- it would matter more if it were too short), but the 12R SS' crankshaft is harder than hell to find and I don't want to use my only spare for this test.
EDIT: Wow. I was just looking at a spare sleeve for my Losi 3.4 engine, and the exhaust port opens waaaaaay before the transfer ports open. The exhaust port is twice as tall as the transfer ports. I would've thought that would make the engine a pig at low RPM, but it has no trouble hauling ass from a standstill. I don't know how many extra degrees of exhaust port timing that translates to, but no wonder I can wring-out the Losi 3.4 to 38,000rpm.
Last edited by fyrstormer; 05-25-2018 at 09:44 PM.
05-26-2018, 01:55 AM
#8
Tech Fanatic
It's hard to say exactly why you didn't experience any difference between a medium and a hot glow plug, could be that your already to cold or that it wasn't that big difference between them.
There are several things that makes them hot or cold, wires, size of hole, material etc. An engine that runs more at full throttle might not need a thicker wire but a body that dissipates heat quicker, for instance.
Airplane engines usually doesn't run with a pipe, and that changes A LOT. So crankshaft timing is one thing to start looking, just like you noticed.
Without a pipe they run less exhaust timing as well, like you noticed.
You need to compare timing numbers (at the very least) to see what's different between engines and finding the potential bottleneck.
There are several things that makes them hot or cold, wires, size of hole, material etc. An engine that runs more at full throttle might not need a thicker wire but a body that dissipates heat quicker, for instance.
Airplane engines usually doesn't run with a pipe, and that changes A LOT. So crankshaft timing is one thing to start looking, just like you noticed.
Without a pipe they run less exhaust timing as well, like you noticed.
You need to compare timing numbers (at the very least) to see what's different between engines and finding the potential bottleneck.
05-26-2018, 04:28 AM
#9
It's hard to say exactly why you didn't experience any difference between a medium and a hot glow plug, could be that your already to cold or that it wasn't that big difference between them.
There are several things that makes them hot or cold, wires, size of hole, material etc. An engine that runs more at full throttle might not need a thicker wire but a body that dissipates heat quicker, for instance.
Airplane engines usually doesn't run with a pipe, and that changes A LOT. So crankshaft timing is one thing to start looking, just like you noticed.
Without a pipe they run less exhaust timing as well, like you noticed.
You need to compare timing numbers (at the very least) to see what's different between engines and finding the potential bottleneck.
There are several things that makes them hot or cold, wires, size of hole, material etc. An engine that runs more at full throttle might not need a thicker wire but a body that dissipates heat quicker, for instance.
Airplane engines usually doesn't run with a pipe, and that changes A LOT. So crankshaft timing is one thing to start looking, just like you noticed.
Without a pipe they run less exhaust timing as well, like you noticed.
You need to compare timing numbers (at the very least) to see what's different between engines and finding the potential bottleneck.
I have a 15FE engine. It’s an ABN turd alright. The one I have (in really nice shape) is gonna get turned into a desk fan.
. It serves no other purpose.
Last edited by RCTecher12; 05-26-2018 at 04:55 AM.
05-26-2018, 06:42 PM
#10
I dunno, mine already goes 47mph and can make my RS4 hold a sustained low-speed drift pretty nicely. It's not an inherently bad engine, it's just really not optimized for car use. For all practical purposes the car is already fast enough for bashing, but I want that feeling of satisfaction that comes from making it work better if I can.
I guess I'll try increasing the intake timing next. I just really don't look forward to having to completely disassemble the engine to do it.
I guess I'll try increasing the intake timing next. I just really don't look forward to having to completely disassemble the engine to do it.
05-28-2018, 07:46 PM
#11
I modded the crank this afternoon, increasing the intake timing by a few degrees and widening the port to match the width of the carb throat. Oh, and I replaced a notchy bearing. The engine felt a little more responsive in the mid-RPM range.
Top speed? 47mph.
LOL, this freaking engine, man. If nothing else I have to give it points for not self-destructing from all the modding attempts I've inflicted on it. Vintage RS4 enthusiasts have told me the 15FE is a super-reliable engine that will chug along for damn near forever, and that certainly seems to be the case.
My last idea is to make the exhaust port taller. I added 0.5mm to its overall height, from 3.9mm to 4.4mm. It still idles properly, but I'll have to wait until tomorrow to see if it goes any faster. At this point my expectations are pretty low.
I guess I could also fill the reversion dam at the end of the intake bore with silicone, to make a nice smooth ramp, but I haven't been able to figure out what kind of silicone can hold up to being spun at 30,000rpm while being doused with oil and alcohol.
Top speed? 47mph.
LOL, this freaking engine, man. If nothing else I have to give it points for not self-destructing from all the modding attempts I've inflicted on it. Vintage RS4 enthusiasts have told me the 15FE is a super-reliable engine that will chug along for damn near forever, and that certainly seems to be the case.
My last idea is to make the exhaust port taller. I added 0.5mm to its overall height, from 3.9mm to 4.4mm. It still idles properly, but I'll have to wait until tomorrow to see if it goes any faster. At this point my expectations are pretty low.
I guess I could also fill the reversion dam at the end of the intake bore with silicone, to make a nice smooth ramp, but I haven't been able to figure out what kind of silicone can hold up to being spun at 30,000rpm while being doused with oil and alcohol.
Last edited by fyrstormer; 05-28-2018 at 08:07 PM.
05-28-2018, 09:25 PM
#12
Filling and stuffing the crank...
Have you tried leaning it out a bit for more RPMs? Maybe the carb is too big.
Can you play with the gearing or tire size? If you think it's making better power but you just can't spin it faster...
Sean
05-28-2018, 10:50 PM
#13
Higher gearing is an option, but I want that tiny F1 sound dammit! Also the 2-speed clutch bells for the RS4 2 are long-discontinued and hard to find.
It's definitely making more torque than it used to, at least at low-to-mid RPMs, because I can blip the throttle and spin the car around on-the-spot. Couldn't do that with the stock setup.
I've tried leaning the carb, all it does is run hotter. There's a nice wide adjustment range on the HSN where the only effect is the engine temperature, not the performance, which normally makes me think the compression ratio is too low, but when I increased the compression ratio it still didn't go faster. On every single WOT pass, the engine sounds exactly the same. It's very perplexing.
I'll order a tube of that 3Bond stuff for the hell of it. Does it flow before setting, or do you have to smoosh it just-right to make a smooth surface? If you have to smoosh it, how to you get it perfectly smooth?
Also the 2-speed clutch bells for the RS4 2 are long-discontinued and hard to find.It's definitely making more torque than it used to, at least at low-to-mid RPMs, because I can blip the throttle and spin the car around on-the-spot. Couldn't do that with the stock setup.
I've tried leaning the carb, all it does is run hotter. There's a nice wide adjustment range on the HSN where the only effect is the engine temperature, not the performance, which normally makes me think the compression ratio is too low, but when I increased the compression ratio it still didn't go faster. On every single WOT pass, the engine sounds exactly the same. It's very perplexing.
I'll order a tube of that 3Bond stuff for the hell of it. Does it flow before setting, or do you have to smoosh it just-right to make a smooth surface? If you have to smoosh it, how to you get it perfectly smooth?
05-28-2018, 11:07 PM
#15
See above. I can't just bolt on a bigger pinion gear on this car, unfortunately, and my options for smaller spur gears are very limited. The car requires an even-tooth 1st-gear spur and an odd-tooth 2nd-gear spur, and I already have the smallest even-tooth 1st-gear HPI ever made. So either I have to find a discontinued clutch bell with a wider gear range, or I have to make the engine run faster. There's a few extra RPMs in there somewhere, I just have to find where they're getting stuck. I can hear them in there when I blip the throttle with the wheels in the air, I just can't seem to get them when the wheels are on the ground and the engine has actually do work.