Jetting and engine temperature

[avendlerdp]

Hello-

I have a honda cbr900rr powered race car (road race) and have a bit of trouble keeping it cool.

It uses a Geo Metro radiator that is about 12x16 and 3 core. Electric fan wired to run all the time. It seems like this should be enough capacity but under race conditions it runs up near the top of the stock temp gauge and boils over. Due to track rules I can't use any coolant, only straight water.

I have a 16lb cap but it still boils. I have heard that having the jetting wrong may cause overheating. The car runs well and has good power but may be jetted a bit rich.

Thoughts??

[nutz4sand]

I have heard many time that the CBRs run hot (especially the 1000's) But your 900 likely as well. Pop up a couple pics of your setup. Maybe someone will see something thats helping to cause your grief.

[nutz4sand]

Also the weight and gearing if you know both. Tire size too.

Lean jetting usually makes them run hotter. Rich should not contribute to overheating as much as help it.

[avendlerdp]

Thanks for the replies. Here are a couple of pix of the rig. Not a ton of airflow through the rad but remember, the speeds are a lot higher than on sand or dirt. Between 50 and 100 mph the whole time the car is on track. I will be installing a belly pan to help reduce the tendency for air to come up under the car and push the wrong way through the radiator.

Car weighs at most 1400 wet w/driver. Tires are 195 50 15. Front drive.

[nutz4sand]

I was thinking tiny race car. Those motors ran hot in the bikes. Your asking it to move a good bit more weight sooooo.

I see more air being moved up over the hood then thru the radiator behind the headlight bucket area.

You might look at some louvers or a scoop in the hood to help draw more air thru and could look at adding another radiator behind the motor. If there ever was an oil cooler on those motors do anything you can to increase it. I have seen a minibuggy with a cbr1000 and he had external oil tank. Cooling the oil would be easy and a big benefit. Just dont push it hard if you ever have to start it when its cold outside till it warms up.

Does it get as hot if you run with the hood off? Just for testing/practice. I doubt they let you race with it off.

[Bugpac]

I think the radiator is far to isolated myself..cant you put it in the oem position? them geos had 3 core radiators? I have yet to race were the car didnt get hot, I can run mine all day at 160-180, as soon as i put it on the track racing its 200...

[avendlerdp]

Stock Geo rads are 1 or two core. This one is a custom 3 cored one. I can't put the rad in the front due to the engine sticking out there. I am going to cut more access for air to the rad where it is though. Still under development. Racing does put tremendous stress on systems but then that's part of the fun.

[Bugpac]

Originally Posted by avendlerdp

Stock Geo rads are 1 or two core. This one is a custom 3 cored one. I can't put the rad in the front due to the engine sticking out there. I am going to cut more access for air to the rad where it is though. Still under development. Racing does put tremendous stress on systems but then that's part of the fun.

I agree...

[avendlerdp]

Just to follow up here. We got the car to run cool. There where two issues. One was just not enough open area for air to get to the rad.. One more hole cut in the hood solved that. The big thing though was that the air was not exiting the engine compartment. Air was getting packed in there from underneath and keeping air from going through the rad.. A belly pan was the solution. Now the air exits the bottom rear of the engine compartment and all is well.

I realize this does not apply to most of the user's rides on this forum but there it's good to be reminded that air has to not only get to the front of a radiator but it also has to be able to get out the back!

[K-fab]

Cool info. Good to hear that you got the issues figured out and fixed.

Sort of on the same thread of thinking - lack of flow through: Radiators that are exposed to extremely high speeds, like above 170 mph or so, suffer from a lack of flow through too.

As the air hits the rad and tries to separate and go through the fins, the turbulence gets high enough that it actually buffers the incoming air to the point of acting like a shield and the rad looses it's ability to work.

This was a problem on motorcycles (race bikes like F1 and World Super Bike) as they approached the 200 mph limit back a few years back.