Cooling / water flow

[4l04ever]

I have seen on some of the big bore engines that the water flow through the engine is reversed, so that the exhaust side of the engine gets the most cooling. I wonder if this would work on standard LC/YPVS engines? May be worth a test to see which routing is most efficient...

[midlifecrisisrd]

First thing to do would be to measure the inlet and outlet temp to see if it is worthwhile

Sounds to me like a way of trying to get more out of a cooling system that isn't coping

Steve

[4l04ever]

I think the exhaust ports were overheating and causing seizures on the big bore engines, so they re-routed the water flow to hit the exhaust side first, which would be the hotter then the inlet side. I would think this should make more efficient use of the coolant...

[Tobyjugs]

I think the standard cooling water flow on a 4LO is more than good it could be too much. At 7000+ rpm the Delta T is almost 1 degree over the engine. This seems extreme but my field of expertise is diesel engines, so not quite the same.

The problem with the big bore engines is the lack of flow around the exhausts ports as Rob pointed out. I believe a lot of this is to do with the design of cool heads used on big bore engines.

A standard Yamaha cylinder head channels all the cooling water through and around the bores, a cool head will divert more over the combustion dome giving less flow around the liners. I haven't seen too many styles of Coolhead but i did like the Chariot coolhead and i think the Wicked head is pants

[bare]

Could be gains in restricting water flows. More than a few race engines have restrictors judiciously fitted.
When Water circulates Too quickly, hot spots can develop.... with ugly result.

[marrcel]

Sept 9, 2020 4:20:44 GMT 1 bare said:

Could be gains in restricting water flows. More than a few race engines have restrictors judiciously fitted.
When Water circulates Too quickly, hot spots can develop.... with ugly result.

This can’t be right.
High velocity liquid is turbulant. Slow is laminair flow in the law of Reynolds. Turbulant flow gives more heat transfer.
Adding a restrictor to a pumping system is usually done to bring the overall resistance in line with the pump curve of the impeller. This reduces the chance of cavitation on the inlet.

[jon]

+1

Fluid dynamics is a very complicated subject, and I don’t pretend to understand it all, just schoolboy stuff.

For instance fluid is different to gas, but not too dissimilar.

If it’s hot you may put a fan on. The ‘cooling’ air will seem more cool the faster the flow.

In a cylinder even if the flow over the head is increased, thus cooling it more; surely the heat transfer of the pockets within the jacket is equalised through thermal transfer?

Jon

[midlifecrisisrd]

I don't know, I always thought flow speed was a fine balancing act as the water need to be in the engine long enough to absorb heat and in the rad long enough to get rid of it

Steve

[muttsnuts]

the differences in temps from front to rear on the head tends to be around 6 degrees, the reverse flow helps alot on the big bore engines, I am currently making a cylinder head that reverses the flow with stock pipe work, so it all looks neat and tidy as normal, but the flow goes to the front of the cylinders first, hitting the exhaust port area first, this helps reduce seizures on the big bores.

Once I've got the prototype head sorted I'll do some testing and then I'll know for sure, what i do know is running the big bore engines much cooler results in a much better reliability and geenrally more consistent BHP

I am running one of my bikes with a seriously big radiator and it generally runs between 45 to 50 degrees, it has improved everything massively, but it is pushing circa ~110bhp so keeping it "chilled" is important when pushing it hard.

The extra large radiators I do have proven to be a massive help on all of the bikes they are fitted to and everyone has noticed a big difference in how the bike performs, whether this is true for a stock LC or YPVS I can't say as not really tested it on them, but heat and air leaks are 2 of the biggest killers of 2 stroke engines, so in my eyes getting it right is extremely important

HTH

[Tobyjugs]

Sept 11, 2020 11:27:03 GMT 1 muttsnuts said:

the differences in temps from front to rear on the head tends to be around 6 degrees, the reverse flow helps alot on the big bore engines, I am currently making a cylinder head that reverses the flow with stock pipe work, so it all looks neat and tidy as normal, but the flow goes to the front of the cylinders first, hitting the exhaust port area first, this helps reduce seizures on the big bores.

Once I've got the prototype head sorted I'll do some testing and then I'll know for sure, what i do know is running the big bore engines much cooler results in a much better reliability and geenrally more consistent BHP

I am running one of my bikes with a seriously big radiator and it generally runs between 45 to 50 degrees, it has improved everything massively, but it is pushing circa ~110bhp so keeping it "chilled" is important when pushing it hard.

The extra large radiators I do have proven to be a massive help on all of the bikes they are fitted to and everyone has noticed a big difference in how the bike performs, whether this is true for a stock LC or YPVS I can't say as not really tested it on them, but heat and air leaks are 2 of the biggest killers of 2 stroke engines, so in my eyes getting it right is extremely important

HTH

I think one of your big radiators would help a 4LO as it would have an over capacity for cooling. This used with a proper thermostat would keep the engine temperature very stable.

It's a pity i didn't know about your large radiators as it might have fitted my Bakker project. Much easier than all the faffing around measuring different radiators etc.

[YZR654]

I dont know if this is any interest to anyone on this subject, i am building a second bike YZR replica using 350 heads and barrels on a RD 500 bottom end, knowing that 500s have a rear cylinder over heating problem, i have welded the water inlets on the rear cylinders into the barrels instead or entering through the head, in five years of running the first bike i have never had a overheating problem, so i have done the same on the second bike and is very easy thing to do

[4l04ever]

I run a modified Thundercat radiator on my tuned 4L0 and it runs bout 20 degrees cooler than the standard rad. Even on track on a hot day it only gets to 80. Usually runs at about 55 to 65 for fast road use.