mike_rudy

I am wondering if anyone actually runs the MFR PP housings 12a or 13b i have never heard one run or seen any dyno pics or vids or info on them i am mostly looking for 12a ones because i have some of the housings sitting in my basement if anyone could tell me any good links/website is would greatly appreciate it, Thanks,Mike

z8cw

Check Vosko's videos.



http://www.cityperformancecentre.com/custo...stairs_rx-7.htm



The link shows a three rotor PP.



CW

Lynn E. Hanover

I have one in a first gen tube frame GT-2 car. If you have the lite rotors and don't mind going to 10,500 RPM you can get (I am told) 310 HP. We never went over 9,500 RPM so I don't know. This is the only car that we ever had that the driver had to pay attention if the car was not straight on the 2-3 shift. The 2-3 was weelspin limited. Overall we were not competitive, and SCCA is owned by Toyota and Nissan so they were not about to do anything about it. It idles like a normal piston engine. No brap-brap-brap, like a bridgeported 12A. Actually the port timing is less all the way around on the Pport. Sounds good at full tilt, just like a bridgeport.



Picture is from long ago running the Pport 12A.



Lynn E. Hanover

mike_rudy

lynn, just wondering why on all your race cars you never go above 9,500 rpm??? it seems on lots of the engines with wicked timing and huge ports 9,000 rpm is not getting its full potential. I know with revving up higher then that you need hardened stationary gears and balancing is more critical , Thanks, mike

Lynn E. Hanover

We have all of that stuff, except for the lite rotors. So the rev chip is a 9,600.



I could probably go a bit higher with what we have. Race bearings all around, bone stock rotors, dry sump oil system with a solid 100 PSI through 9,600 RPM and good cooling numbers. We could have any oil pressure we want with the turn of a screw, but the engine builder said that 100 is plenty so long as it is 100 at top revs, and we have that just fine.



On the dyno best power is at 9,400 RPM so going way above 9,600, that just costs time, because the rate of acceleration is falling off. With a very close ratio trans there is less of a need to overwind very far to get a leg up on the next gear. The most overlook factor in hopping up the engine is to do it without reducing the bottom end power. So, you figure out the avarage HP through the usable range, and with special attention to the lower end of the range, and if you tune reduces that number you are going backwards.



It is of no value to have a monster HP number if you have to spend to much time below that number after each shift.



So look at the gear chart for our trans and the 4.86 rear gear.



We shift at 9,600 RPM in first and that drops the engine RPM to about 7,600 RPM.



The actual RPM loss is a bit more due to the aero drag and some time spent passing through neutral.



But lets say it is 7,600 RPM. Our first store bought race engine had 216.2 HP at 7,600 RPM. The second engine had 221.5 HP at 7,600 RPM.



Note also, that the ratios are closer together as the speed goes up. Aero drag becomes so high that the car slows quickly between shifts. The worst case is the

4-5 shift. So on the chart it looks like that shift makes little speed difference, this is not the case. This is the most critical shift, speed wise, and makes the biggest difference in the top speed of the car. If you blow this shift a little bit your top speed can be way off at the end of the longest straight.



The second engine made the car much faster. even when peak power of both was the same. 245 HP at 9,400 RPM.



Lynn E. Hanover

j9fd3s

as always, great stuff! we spent some time with our race car (86 its rx7) and we didnt find any peak power but we really fattened up the bottom end, and it helps! we dont really have the chassis/driver to take advantage of it, but its strong on the main straight!