|I'm talking about the FJ1200 and the FJ1250 air cooled motors that are transplanted into the Legends Thunder roadster Baby Grand race cars. Let’s start with the simple and very obvious statement, these engines were never meant to be in a car. These engines need air flow going over the way the air did when the motor was mounted in the frame in order for them to survive. Without air flow the engine will not last very long. What BRG has found is when we tune them to run their best, they make a lot of heat. So what do you do? There are three things that can be done. Tune the motor fat (more fuel) so it does not make a much power. Do nothing which is what Innex would have you do, or get air flow over the motor i.e., around the cylinders and head.|
|Now that having been said, how do we get air flow on and around the motor since the motor was made to be sitting 90 degrees from where it is in a motorcycle frame. Should I use fans? That’s an idea. How much air will a good radiator fan move? Well a fan that we can get at your local car parts shore will be somewhere around 250 CFM. That’s like a 15 mph breeze. That's just not going to be enough air flow to cool a well tuned 1250 running full tilt. If anything, they may just get in the way. Now please keep in mind these engines are made to stay cool in the bike under “normal” riding conditions at about 35 mph. So where do we go from here? The motor is buried down in a hole that really has no outlet.|
|What does all this undisipated heat do to the motor?
Let’s start with what we all have seen, loose head bolts. Then there all
these wasters of time and money:
The blown head gasket.
Warped heads and in most case they're warped at least .010 thousandths.
Valves that are pounded into the head and are “dishing out.”
Valve seats that are no longer concentric.
Cams that will not turn in the head because the head is warped from too much heat.
In part broken cams, ring blow buy.
Out of round cylinder bores.
We have put motors together and then, after one race day, found the valve seats are out of round and not seating. All from heat.
|Here is what we have been doing. These are pictures of the cooling ducts we use to try and keep the ring barrels cool. There is 4” duct going to the front cylinder and a 4” duct going to the rear part. Please note it blows though the barrels, there is nothing in the way.|
|This helps a lot to keep the rings from collapsing and the cylinder round. On the head we need lots of air but it needs to be controlled going in and just as importantly going out. This is what we call the cool hat, designed and engineered by Steve Wilson from Livermore Ca. It take ram air coming in at least 60 mp and channels it down on the #1 spark plug then guides it through to the #2 plug where it comes out the exhaust hole in the hood. The back cylinders 3 and 4 are the same way. Now I need to take some time and explain on what data we are basing our results on. We monitor or head temps at the #3 spark plug with a cylinder head temp gauge. This cylinder is badly buried and gets next to no air flow. We have found that it runs the hottest. A lot of you may have noticed that the #3 cylinder head bolt next to the cam chain cavity is always loose. We use a thermal couple under the spark plug. Before the cool hat, our head temps where over 550 to 575. This is way over what can be tolerated for any length of time. All the bad things we have listed above are happening. You maybe wondering what we think a safe temp is? That would be 400 degrees. With the cool hat on, head temps at #3 dropped to 350 degrees. This is a temp range where the engine can make good power and last without ruining head gaskets, cams, heads, rings and all the stuff we have had problems with.|
|The conditions that we race under are all road race no circle track. I have no data on a circle track but, I feel the road racing a very good proving ground in that rpms are held longer and the throttle is open for a longer period of time. If we can keep a road race legends cool, on a circle track it should do even better.|
|Oil cooling, yes it is important, but I think it is only a small part of the cooling problem. If you can keep your oil temp in the 220 to 280 degree range, you're good. But if you think you can cool the motor only with oil, how long does it take to heat up gallon of oil? How long to heat up a gallon of water? How long for air? My point is oil takes heat in very slowly. The motor at full throttle is making a lot of heat a lot faster than the engine oil can take in. You can have all kinds of oil coolers on the car your oil temp can be 220 degree but you look at your cylinder head temp and you’re at 550\600 deg your cooking the motor down. That heat goes though the whole motor. This is the temp where ring relax and the aluminum under the head studs start to get soft, and the tension on the head bolt relaxes and the list of bad thing I talked about earlier. The best cooling medium would be water because of its ability to take heat in fast and get rid of it and the most efficiently with a consistent heat transfer. The next best thing is air and lots of it. But like I said it needs to be controlled. You want air flow where the heat is coming from. The cylinder head. Right at the spark plug. If you looked at the fJ1200 bike you can see where the engine has good air flow to the top of the head and just as importantly the cylinders.|
|There are 2 water cooled cylinders. The one from Innex which is legal for the Thunder roadsters and the one from Hank Scott. Both are good but I think Hank's is thought out a bit better but is expensive, $3000.00 for the whole kit whereas the Innex is $1500. We have worked with both and both work very well controlling the heat in the motor. Ring life has gone up significantly and the head gasket blowing out doesn’t seem to be a problem anymore. On the Thunder roadsters we set up, we have to tape up the radiator the get the motor up to temp. I like having that problem!|
|It does add about 45 pounds to the car though. What we have found is that if you control the heat at the head with some well thought out air flow to the head and cylinders you can get a couple of years out of the motors instead of a couple races. That’s a pretty good savings in time, effort and money and we all race on our wallets.|