rz350 cooling system

have any of you current or former rz350 racers found the need to swap the stock radiator for a different one? or has your experience been that the stock radiator was adequate even in the hot summer season with water wetter?

cheers

 

I have always used the stock radiator even when I ran my cylinders that were bored to the max. I know Mark Marrow used a larger one on his. Joe Pomroy owns that bike now, so you could contact him to see what it came off of.

 

Anything over about 60rwhp and you're gonna have trouble with the stock one.

 

ran a stock one with stock cyls 30mm carbs toomey pipes with no problem(race bike). my current barlow motor with double the stock core thickness is barley doing the job. i will be upsizing soon.

 

I've got Marks old RZ (not old anymore ). The engine in my bike is over 60 HP. Mark installed a Honda CX500 radiator since the stock unit could not displace the heat efficiently enough. The CX radiator fits very nicely where the stock one was. The length and height is almost the same. But, it is probably twice as thick which gives it the superior cooling ability. The only downside to this radiator is weight - it is not aluminium. But, since it works so well I won't change it.

For example, at North Florida Motorsport Park last July 20th, it was 101 degrees in the shade according to one WERA official. My bike never got over about 74 degrees celcius. My main problem is the bike staying too cool when the ambient temperature drops below 70. Then, I need to use some well placed duct tape.

I hope this helps.
Joe Pomeroy

 

That bike needs some well placed duct tape over the carbs, not the radiator!

 

Kyle, just wait. It's now even better than before! Last night I just finished going completely through the engine. New crank bearings, new seals, complete new top end, etc, etc. Also, I decided to take the extra time and paint the upper engine case, polish the lower case, clean the cylinders extra well, polish the cool head, and paint a few other bits and pieces. Now, it's even nicer. It's almost too pretty . I've even got some more ideas for over the winter. And no, she's not for sale .

 

Painting cases, polishing the head...I think this bike should go to the Barber museum before it gets a little dirt on it Guess you and Jim Johnson need to pit together so you two can wash the bikes after ever round of practice Hope to see you and the gang at Tally next week. I'll be there with "Old Dirt" with new secret squirrell go fast stuff.

 

Kith, Jon J. and I will be at TGPR arriving Friday night. If you want to bring "Old Dirt" up to the Jon and Joe specs, let me at your bike over the winter. I've been thinking of contracting out my services during the off-season and do racebike restorations. I enjoyed doing the RZ and since I won't be doing it again this winter I was thinking one or two projects might be fun. It keeps the boredom away.

 

uummm...I'd rather it be fast than pretty. We'll talk at TGPR. I'll also be there Fri evening.

 

thanks to everyone for the replies. i'll see how hot my bike gets on track days first and then contemplate the necessity of replacing my stock radiator.

cheers.

 

If you are seeing more than 75 deg C on the track, you should think about getting more cooling. It may go up hotter than that when you first shut it off in the pits- don't worry too much about that. It's just residual heat.

 

Carl, the OEM thermostat on an RZ350 doesn't open fully until 85 degrees C.

 

I know, that's why I wouldn't run a race bike with that piece of junk in there. As I understand it, the engine was kept hot to help reduce emissions that might clog the catalytic converters. If you really wanted a thermostat, a colder one from a Euro TZR would be the way to go. I advocate removing the thermostat entirely in a tuned RZ. Of course, then you've got to warm it up like it's a TZ...

 

Great info I didn't know about the thermostat guys. I don't run one, and sometimes it takes awhile to warm it up. I've got a Cool Head on my bike and I think running a thermostat with it is not possible. The one thing I don't like about a thermostat is fear of a failure during a race. I'm not sure if this is a well founded fear or just ignorance on my part

 

Wouldn't it be better to retain a thermostat (with a lower opening temp) to keep engine temps at a constant for a more consistant performance level? Wouldn't a regulated engine temperature also make jetting easier to get spot on ?

 

I've been told to retain the use of a thermostat, strictly for the purpose of keeping the coolant flow constant. However, that reasoning really doesn't jive as the thermostat actually regulates, and changes, the flow as the temp changes. I don't know what the "right" answer is, nor do I know if removing a thermostat is truly "wrong."

Modern GP bikes do not have a thermostat ... you control the coolant temp by adding or removing strips of tape on your radiator.

 

I was always under the impression that the thermostat controlled engine temperature by regulating the amount of coolant getting to the motor from the radiator. Whether the coolant circulating through the radiator is 25c or 85c, the motor's temperature will always be regulated at the temperature of the thermostat's rating and will remain there as long as the radiator coolant temperature doesn't exceed the motor's.

With an "open system" the motor's temperature is directly dependant upon the radiator coolant temp. I believe the fluctuation in temperature would be pretty dramatic and is dependant upon too many variables such as changes in weather conditions or the reduced air flow through the radiator while drafting behind someone.

Then again if you're a damned good sprint rider and are consistant in how hard and fast you ride the bike, the temp fluctuations may be negligable and warrant removing the thermostat to do away with just another component that could fail.

 

In a system that's designed to operate that way (like a modern fuel injected 4 stroke) I think that's the case. But in the case of the RZ350, the stock thermostat is way too hot for max power ( GP bikes shoot for something like 55-60 deg C to make best power, but that's probably near cold-seize territory for an RZ ). Why don't the GP guys then have a 55deg thermostat? I don't know that one. The tape method has always been the way. Perhaps the get so much insight into how the motor is running that they don't want the temp rigidly controlled, but prefer instead to watch the temp gauge and use tape?

I don't race bikes with water any more...

 

When the thermostat fails you will DNF.

Phil Shilling {Schilling ?? } did some dyno { Water brake } tests on some Rotax 125 and 250 rr motors in the 80's and in back to back tests 70C lost several hp over 60C.

Ray