Author Topic: power loss through heat (Read 6055 times)

udontknowme · « **on:** August 08, 2014, 02:30:58 AM »

i been thinking about this. whats the best way to reduce the temp. move the water faster ? fans ? single large row radiator instead of 2 smaller rows ? not sure what to make of this but some people are claiming as much as 10-15% power loss between 140f and 180f. hey jerry does this percent of loss seem consistent with what youve seen ?

rsss396 · « **Reply #1 on:** August 08, 2014, 08:08:27 AM »

i have defiantly seen power loss around 180, they say over 150 power starts to drop off, in the case of your motorcycles with a large cc motor usually its radiator surface area that hurts you.
IMO moving water faster is a good thing but I have not tested it, but i have tested running a fan and not running a fan on my snowmobile powered bike that had 1100cc and a radiator that was not big enough to keep it from running over 200.
A simple 7" fan I bought off ebay that ran off the lighting stator cooled it over 30 degrees better than without it. problem is most bikes do not have a lighting stator or a very weak one if they do. Snowmobiles have very large lighting stators for hand warmers and lights.
But still I would attempt a small low wattage fan on one of the radiators to help, i believe I have seen guys use small computer like fans used on the power supply with positive results.

Bio86 · « **Reply #2 on:** August 08, 2014, 09:08:28 AM »

What is contributing to the power loss? Increased friction in the internals from expansion, higher intake temps? Just kind of curious what's hurting it the most. If the motor is going to be ran for long cycles couldn't the engine be set up so it's making peak power at any temp? Still goes back to being able to cool it consistently at that temp I suppose.

udontknowme · « **Reply #3 on:** August 08, 2014, 12:49:24 PM »

i would assume the intake mixture gets heated alot more before it reaches the cylinder top and then its less dense so i guess this is where you see the power loss. ive always known there was a loss of power as the temp goes up but i was never sure how much loss. most anyone can see this loss if riding sand first thing in the morning then later in the day when its alot hotter. it always seems like the bike gets alittle or alot slower. atleast thats what ive noticed

the challenge is how do you make the engine stay at 140f or below in july going up large sand hills :congratulatory:. hell even below 150f would be quit a accomplishment i would think. normal for mine seems to be around 200f. im sure a few guys around here have access to cnc machines. they should try a different angle on the impeller fins and see what that does. fan would be good idea if you have a decent ign to power it. but like you say most bikes dont have any option of a high powered stator. atleast not much available for the hondas that ive seen. service honda stuff in the past wasnt worth a shit. maybe the new stuff is better

JesseA420 · « **Reply #4 on:** August 08, 2014, 12:53:38 PM »

Quote from: udontknowme;40592

different angle on the impeller fins and see what that does

i always wondered about this, several other models have high flow impellers for them, never seen one made for these trx250rs

udontknowme · « **Reply #5 on:** August 08, 2014, 01:14:18 PM »

a big chunk of alluminum is cheap. anyone with cnc experience should have no problem making a few impellers with various fin angles. ive wondered about this also. anyone with boat propeller experience probly realises similar affects from different props pitches

JesseA420 · « **Reply #6 on:** August 08, 2014, 01:27:30 PM »

one hard part would be measuring the various increasingly changing radiuses on the fins, would probably be easiest for someone with a 3d scanner. also need the capability of cutting the inner splines.

Bio86 · « **Reply #7 on:** August 08, 2014, 01:51:45 PM »

Would just need an internal spline broach made there. Need a little flow bench and just start experimenting! And of course a 5axis cnc mill to do it right. Speeding the flow up doesn't always help if it's not in the radiator long enough to effectively cool though.

Alky!! :congratulatory:

rsss396 · « **Reply #8 on:** August 09, 2014, 12:24:01 AM »

power loss would be from a few things such as pumping losses, a cooler denser mixture will push more fuel/air mixture into the cylinder. as the motor heats up so does the fresh intake charge that has plenty of time to absorb engine heat do to the fact it can take multiple strokes for this fresh charge to find its way in to the combustion chamber from the crank area.

The less fuel'air mixture that is introduced in to the combustion chamber the less BTU's to push the piston but also the weaker pulse signal the pipe receives thus weakening its effect on cylinder scavenging

I also have to believe detonation occurrences happen more frequent even though it may not be audible or traces be seen on the plug. Honda sells a detonation counter for there RS125R/250R, a acceptable amount of detonation was in the area of 10 per Kilometer of racing. My guess is as temps start to rise these detonation occurrence increase and power output starts to suffer

http://world.honda.com/HRC/products/kit/data_logger/

udontknowme · « **Reply #9 on:** August 09, 2014, 03:08:56 AM »

ive heard it can take 4 cycles for mixture to reach the cyclinder. not sure if thats a well designed race engine or a crappy old run of the mill version. it enters at somewhere around ambient temp i would think unless you have a black tank thats heating it before it even hits the reed valve. be interesting to find out how hot it is when it enters the cylinder. doesnt air heat up when its compressed ? and if the cases are 200*. the charge must be around 200* by the time it hits the cylinder

rk88r · « **Reply #10 on:** August 09, 2014, 09:19:31 AM »

Maybe some coatings along the intake path?

udontknowme · « **Reply #11 on:** August 09, 2014, 12:05:25 PM »

im sure some kind of rubberised coating would work good. but what kind to use that can withstand the heat and gas exposure ? if you get the engine real hot and feel the carb it is still fairly cold from the rubber insulator. a coating would have similar affect inside the engine im sure.

rsss396 · « **Reply #12 on:** August 10, 2014, 08:34:19 AM »

Coating will not help, allot heat is introduced into the transfer tunnels at higher rpms because the pressure of the cylinder is still higher than the transfers. Some times you can actually see burn marks in the transfers or burnt reeds from this happening.
a well designed cylinder will have good flow around the exhaust port along with the tops of the transfers, some cylinders go as far as cooling the inner radius of the transfer port also.

christph · « **Reply #13 on:** August 11, 2014, 02:29:43 AM »

I think a hot carburetor can contribute to power loss as well. I have a 1988 GSXR 750 that has an air-oil cooled motor. Back in the day, they used to make heat damns that redirected the air coming off the cylinders and away from the carburetors. Cooler fuel means more power, and when fuel sits in a hot bowl for a while it obviously heats up. This is also why they sell the heat reflective tape for tanks and fuel hoses.