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I assume you meant RR (R1R is 200TW)? I have been using the RR on both the RX7 and my Spec Miata (until I sold it, anyway). They are good, although not as fast as Hoosier SM7's at their peak. I assume R7's are even faster. The SM7's seem to drop off pretty quickly compared to the RR's. It seems like 15-20 HC's is about what I can get out of the RR's before they drop off. Because they start out with pretty thin tread (~3mm), a little booboo or aggressive track (T8-T9 at Willow Springs), they can get corded pretty quickly. The R888R's (100TW like old RA1's) have interested me as they are $136 for 205-50-15. The goodyears look also like an interesting option.
The endurance race groups I race with require 180TW tires, so I am using Hankook RS-4. Based on my son's performance in the car (he is more consistent than me), they are 1-2 seconds slower than Toyo RR's. I kind of wish SCCA IT race groups would require 200TW.
I need new tires very soon (I am sure my remaining Toyos will be done by the end of a Willow Springs test day on Friday).
Yep meant the RR's. Let me know what you think of the R888Rs.
I think the way to get IT on a 200TW tire is add a weight penalty for running a softer tire. It could be graduated where 200TW = no penalty, 100TW = 100lbs, less than 100TW = 200lbs. Or something like that. Taking weight off of a car for running a harder tire is a harder sale because most cars can't get to minimums.
What I have heard/read is that the SM7 and SM7.5 are not as fast as the R7 of the same size. I had planned on using SM7.5s this year but based on the former I decided not to. But factoring the cost of R7s....holy bankruptcy Batman. I wanted to run on new rubber this year not take offs and with the Goodyears I can do that. I will have 2 new sets at the Runoffs.
Last edited by mustanghammer; Jul 6, 2021 at 09:27 PM.
Yeah I know what you mean about take-offs. I did that with the SM7's for quite a while with my Spec Miata. I finally realized that the take-offs, especially after a couple more heat cycles were not any faster than 200TW tires. Switched over to RR's then and ran SMT. The R7's are a different compound (faster and shorter life) than the SM versions. Almost $300 a pop is crazy. Goodyears sound like a good option. I don't have any aspirations for nationals and in SoCal, IT and ST classes are generally not that well subscribed so I don't need the fastest tires. Just enough to keep me racing with some other cars.
The closest I can come to any advice is what some friends saw running an IT7 and now IT7R car. They were limited to Toyo, either RA1 or R888, they can probably run the R888R now, but I am not sure. Most people in the class run the RA1, but they found that the R888 was very competitive, but the trick was to run much lower tire pressures. They were down to 25-28 hot to get them to work well.
Didn't get the R888R's tested yesterday, because only 3 turned up in time. Did find that late 2020 date code Toyo RR's with 16HC's were no faster than Hankook RS-4 (2 w/ 15-20 hours and 2 with 1-5 hours). The Hankooks were full tread depth and were easier and more comfortable to drive than the RR's. I think what that shows is that maybe the RR's don't last as long as people (including me previously) think.
On the oil cooler side, I have some thoughts on ducting to the cooler. I relocated the cooler, but mainly it just was moved up 3-4 inches. Otherwise not much difference in physical location. I did see what appears to be 25-30 degF reduction in oil temperature from a month ago when the air temperature was over 10 degrees lower (~95 a month ago, compared to 105-110 yesterday). That apparent difference was with the uncorrected gauge, so hopefully comparing apples to apples. At the end of the day, I added the 15 ohm resistor to the sender and water temp was just barely over 200 deg. I also tested the gauge with the resistor installed in boiling water and it was indicating about 210, so within accuracy of the gauge.
When I was relocating the oil cooler, I was looking for different options and came across the "divergent" inlet duct, "converging" outlet duct concept to increase airflow through the cooler. I guess it goes back to airplanes in WWII. I had a little problem finding lots of info on the internet, but this website explains the concept pretty well http://avstop.com/ac/Aviation_Mainte...eral/3-39.html . If you believe Bernoulli's equation (which I do), the diverging duct on the inlet increases the static pressure at the face of the oil cooler (in our case). The converging duct on the outlet decreases the static pressure on the outlet side. The higher pressure difference increases the airflow through the cooler. Someone on an FSAE forum said they tested their oil cooler in a wind tunnel and found that reducing the inlet and outlet ducting to 80% of the oil cooler face provided the highest air flow through the cooler. The diverging/converging angles are supposedly optimum at about 7 deg to avoid the wrong kind of turbulence that would reduce the airflow. The following picture kind of shows what I am talking about for the inlet side. I found it somewhere on this site.
So the "best" is what I did. I didn't have room for the converging duct on the outlet, so my install doesn't have that. Anyway, since I didn't really change the location alot, I kind of have the feeling that the diverging duct may have been the main contributor to the significant reduction in oil temperature, despite higher ambient air temperatures (did I add enough qualifiers to that sentence?). Anyway, something to think about.
I also added an airdam before testing, that one would expect to significantly help the cooling. As it turned out, I pulled it off at the end of the day (still somewhere between 105-110 deg) and it had absolutely no effect on the oil temperature. The water temperature might have increased a couple of degrees, but I can't really say. I will test the w/ and w/o the again in a couple of weeks, but currently having a hard justifying the difficulties it adds (getting up my driveway and in and out of my alley). Has anyone else documented any significant improvements (to anything) when adding an air dam.
Anyway, maybe some more info for cooling oil in rotarys.
Kurt, if you haven't thrown it away and aren't going to keep it, I could maybe use your oil cooler and put it in a wind tunnel to test the idea. Not sure of the details, but seems like I probably have enough airmovers to do it.
Scott, if you would prefer that I start another thread for this kind of stuff let me know.
So I tried a ducted cooler in like 05-07 or so when the Runoffs were at Heartland Park and they let us lowly Regional Racers have a group in a Double National. it made a small improvement but nothing like adding a second cooler. Which is what I did next.
No experience with an RX7 and no air dam. The word on the street was the Kamei style air dam I had provided some down force so it was always on the car.
I am going to build ramp to keep air from going under my current oil cooler and maybe around it. Good info here, no problem with having in this thread unless you feel like there would be more utility with a separate race car cooling system thread
Ah the good old days when my car ran consistently and I was getting Kumho Bucks.
“Has anyone else documented any significant improvements (to anything) when adding an air dam. ”
I recently watched a youtube video from an East coast STU? Honda? guy that did a comparison of his car with and without a low buck air dam/splitter. No improvement in slow stuff but slightly higher top end. Just did a quick look but could not find the link.
Carl, you are welcome to the cooler but it is bent and cracked. I believe a also have a another cooler that someone JB welded the cracks at the fitting sockets. You are welcome to both.
Kurt, I was interested in the cooler just to do some air flow measurements, so cracked and bent don't really matter. I did figure out in the meantime that I can use a pitot tube with a good cooler without damaging it, so I don't need it. Thanks for the offer though.
If I were you I wouldn't throw the JB welded one away. It can be TIG welded up and AN fittings can be added. I have done that to both the 1st gen coolers I have and they worked fine.
On the airdams, I am kind of thinking that for endurance racing they might not be the greatest plan, because a normally innocuous off could end up with some unwanted time in the pits to remove splintered fiberglass. It does seem easy enough to remove that I could use it for sprint races.
I like the first picture of the LeMans car. That oil cooler is huge and with the vented hood just above it, the airflow and cooling must be really good.
That is actually the article that originally set me down the divervent ducting path, but I couldn't find it again. Seems kind of weird that their aren't more articles discussing that concept.
so you have a point, i wonder what is going on between the bumper and the intake/coolers in the Lemans car, its just got two brake ducts, and one big one for intake/oil/water. its not like the Kent style where there is a separate intake section.
gas tank looks HUGE. hope you guys don't mind the picture dump, but the oil cooler is mounted on those rubber dinguses, like stock.
There are some advantages to putting the oil cooler up there. A big one is that it is less likely to get hit by track debris. The cumulative state of the SCCA STU rule set would allow me to configure my car like this but not 6-7 years ago. So pro-tip.....pick a class with an established and stable rule set.....if that is even a thing.
Carl, what kind of protection do you have in front of your radiator/cooler? I have seen an unlucky rock take out an oil cooler and then an engine. Below is what I was running in IT7 and wish I could get away with on my car now. Had the advantage of being flexible and not getting grass clogged if I had an off
In the past I have used 1/4" welded wire mesh. After cleaning out the oil cooler I just installed I realized that there are lots of smaller pieces of dirt and gravel that block the fin area, so I am going to use the mesh in the attached pic. There does not seem like there will be an noticeable restriction to airflow.
In California we do not have any grass at race tracks so that is never a problem. Just dirt and gravel. Also the only thing I have ever needed to use windshield wipers for is to clear a thick layer of dust from the windshield so I can see to get back on track after a spin.
Okay that makes sense. I found out that alfalfa sticks to grills in when you drive off track in Nebraska.
Registered for the Runoffs today.
The question of the day is this: How much more power can I make with 44-45mm chokes on a 13B Street Port as apposed to the 42mm Chokes I run now. I have the weight to work with as my car currently weighs 2460 with me in it. Carb is an IDA with 51mm throttle blades.
Adjusted weight with 42mm chokes on a street port: 2250 (base weight) + 5% for advanced aero -50lbs for the solid rear axle = 2312.5lbs
Adjusted weight with +42mm chokes on a street port: 2400 (base weight) +5% for advanced aero -50lbs for the solid rear axle = 2470lbs
I mean, unless you want to put everything on a diet, bigger chokes are worth a shot? I think supposedly Rob Warcocki is close to 300hp at the flywheel on unrestricted streetport in GT3... but the frontrunners are running bridges with 42mm chokes and more weight. But again, if you're only 10lbs underweight, makes a lot of sense to just try the chokes with what you have.
Ok, I have 44 and 45mm chokes due in Friday as well as main jets with bigger holes that I ordered late last week. But i have been waffling back and forth on this part of my prep plan trying to determine if it is worth it. Plus the reality of needing to pay attention to car weight hit me when I was registering today, because this is something I haven't had to worry about before. If I can get some testing in August then I will give them a shot or set up some dyno time.
My guess is that Warcocki has a street ported 4 port motor.....
Probably; Dave Lemon had a throwaway comment I saw somewhere of being around 290 with an over-ported Prod motor with big chokes though so... thinking the better irons may definitely have broader powerband, but may not matter that much for peak numbers.
In a nutshell (of my opinion), the Toyo R888R's are a bit slower (o.5 to 1.0 sec per lap) than Toyo RR's when both are new. New Toyo R888R's are faster and more predictable than 16HC RR's. 16 HC RR's are 1-2 secs per lap slower than new RR's. Hankook RS-4's are surprisingly fast for 200TW tires, not really much slower than new R888R's or high HC RR's. This info is almost all relative to Willow Springs track.
Will see how R888R's heat cycle out. Also plan on trying the new Goodyear tire mentioned previously by Scott.
Here is another option I stumbled across the other day - https://bspectires.com/ 205/50/15 for $165.00. Tell them you have a Mazda......a Mazda 2.....yeah that's it a Mazda 2....that's the ticket.
Those Hankooks look like a great idea. I used them a few years ago in 225-45-13 when they were still available. I loved them then. I checked out comments on the B-Spec Facebook page and the feedback seems really good. Fast and last a long time. Looks like $165 through B-Spec and $195 direct from Hankook. They also have a 225-45-15, which appears to have the same dimensions as the RS4's that I endurance race with.
Thanks for the heads-up.
Carl
PS Just so I understand, this is Mazda2Club.com right? Or did I make a wrong turn somewhere? ;-)
In a nutshell (of my opinion), the Toyo R888R's are a bit slower (o.5 to 1.0 sec per lap) than Toyo RR's when both are new. New Toyo R888R's are faster and more predictable than 16HC RR's. 16 HC RR's are 1-2 secs per lap slower than new RR's. Hankook RS-4's are surprisingly fast for 200TW tires, not really much slower than new R888R's or high HC RR's. This info is almost all relative to Willow Springs track.
Will see how R888R's heat cycle out. Also plan on trying the new Goodyear tire mentioned previously by Scott.
Carl
The 200TW tire wars are producing some amazing tires, the Hankook RS4 is considered dated and slow in that field nowadays. Another thing that is of interest to us is that many of the new tires are coming in 245-40-15 size, with 275-35-15 DOT approved “street” tires on the horizon.
It’s causing a tizzy in endurance racing circles, where teams who can afford to change tires every 4 hours or so can bolt on seconds a lap of performance.
Fortunately most of my endurance racing is with Lucky Dog and they have the RS4 as their spec tire. It definitely is not the fastest 200TW tire, but it lasts pretty easily for two enduro weekends (about 28 hours). At that point it is not typically corded, just seems to get slower. The number of heat cycles seems to make a difference too. We have had some bad luck lately with finishing endurance races, so the last set got past about 20 hours over 3 or 4 weekends, thus a lot more heat cycles than normal. They seem to have lost more grip than would normally have happened with that many hours on them.
As you can see from my search for cheaper race tires, our team is not going down the road of changing tires every 4 hours ;-)
