ColinRX7

I understand what heretic is saying, and teknics





More rotating mass on the flywheel side results in more work for the driveline to slow the engine down. Working on the same scale as how much more power it takes for the engine to turn the heavier mass.



Slip 1st from a stop on a 30lb flywheel, and on a 10lb flywheel.



Less opportunity for engine bog before the car moves on the 30lb, more bog on the 10lb.



Consequently, take into account what heretic mentions AFTER the car is already moving. Engine revs slower in general with the 30lb, 10lb will walk through revs easier.



It's all about inertia!

R.P.M.

There is a guy near Barrie Ont who make PP engines for aircraft...

I was just going to send him a pair of rotor housings and let him have his way with them, so I'm not really sure what size they will be. He told me its the same port as the 787B engine.



Dave, How heavily built is the Genie header compared to Racing Beats? What size are the primaries and the collector? Some pics would be awesome!!

The protege is the daily driver for now...its a fun car to drive!!





So what do you guys think, is a mid-high 11 sec quarter mile time possible with a setup like this?

superdave

Its built similarily to the rb. The flange to pipe surfaces are much smoother though. Primaries are the same size...(will measure tomorrow if you'd like) and there is no collector... I took a pic today but forgot to bring the damn camera home. I'll post it up tomorrow.



The protege IS a fun car. Which is why I never got around to building another rx-7. lol.

laundryhamperman

If you are drag racing, i would assume a lighter weight flywheel would be more beneficial than a heavier one due to the increased accleration you will get with the lighter one. True the heavier flywheel will prevent the engine from bogging, but for racing you will want to launch with a high initial RPM. The energy from the inertia of the flywheel will increase from the higher rotational speed of the engine. Comparing to a street application, low RPM startups will reqire a heavier flywheel to prevent bogging, as the speed is much lower than holding several thousand RPM and dropping the clutch.



If your interested in learning, the equation for the energy of a rotatin mass is E = (1/2) * I * w^2



Energy is equal to one half times the Inertial value of the rotating object, times the angular speed squared. So if you double the rotational speed of a rotating flywheel, the energy stored in the rotating mass is quadroupled.



The Inertial value is related to the mass, and mass distribution of the rotating object. I = M*R^2

Mass time the radious squared from the center of rotation. This isn't an easy thing to calculate becase most objects require calculus and the knoledge of the mass distribution to determine the Inertial value.



hope people can learn from this

R.P.M.

http://www.rx7.com/accel_calculator.html



I typed this info into the 1/4 mile calculator:



HP: 300 Weight: 2100 Shifts: 3 Tire height: 28 Gear: 4.88



And it gave me this for ET: 11.34 and a trap speed of 125mph





Now I totally guessed on the tire size, so not sure how accurate it is.



What do you guys think?

mazdaspeed7

The aircraft PP engines Ive seen are designed to peak at around 6500 rpm, while making around 200-220 hp at the crank. It would be a poor choice for an all motor drag car. You really need to discuss your power and rpm requirements with the builder, and make sure he is not only aware of that, but knowledgeable enough to accomplish your goals.

R.P.M.

Port size will be 2" I.D. of each sleeve.



I am the one who will be building the motor itself, I'm getting this guy to machine and sleeve the housings for me.



Heres what I plan to use for internals: Cosmo RE stationary gears (supposidly uber hardend from factory), 3 window main bearings, high pressure oil regulator, the e-shaft oil jet mod

I guess I may use a set of S5 N/A 9.7:1 rotors instead of the renisis, just a little less costly to begin with.



My goal for the motor is 9000rpm shifts and 300+ HP....my PP guy says easy....what do you think?

mazdaspeed7

All the stationary gears from 89+ engines are hardened. Personally, Id go with the 13B-REW stat gears and engine bearings. Basically the same stuff as the "race" parts for earlier engines, with a more livable pricetag. But everything aside, 9k rpm shifts are easily tolerated by a s5 rotating and oiling system with only minor mods.



Personally, I think the jet mod is overrated. The stock ball and spring doesnt fail, period. It flows perfectly adequately, and it doesnt screw your oil pressure at idle. The ball and spring only limits oil flow to the rotor at low rpm conditions. You will never be at high load and low rpm conditions for long enough to cause heat problems that could be avoided by the oil jet mod. BUT, you are more likely to have oil pressure problems which could result in bearing failure at low rpm, especially as the throttle is opened and the rpm's climb rapidly before the oil pressure has a chance to catch up. I think the oil jet mod is a solution for a problem that doesnt exist, and is ultimately taking a step back from mazda's engineering aproach.



High oil pressure is definately a must in a high revving engine, but Id recommend using a 13B-REW oil pressure regulator and oil pump, as both were designed for 100 PSI operating pressure. The REW pump supposedly is designed for that pressure, as opposed to the 60 psi operating pressure of the s5 and earlier pumps. And the oil pressure regulator is like $30 new from the dealer, which leaves little reason to spend more from someone such as racing beat.



I dont think you will make over 300 hp below 9k rpm. I think you will be looking at a power peak closer to 10k rpm to make over 300 hp, and as high as 11,500-12k if you really want to make good power. That may seem very high, but the engine will only see peak power for fractions of a second before shifts anyways. Even in the highest gear you will see in a 1/4 mile, you will only be within 1k rpm os redline for 1-2 seconds. That changes the requirements for reliability a lot from a track car, that see's redline hundreds of times a race, and is likely to spend more time close to redline.



Its been rumored that Jesus Padilla's all motor 13B drag car makes 360 rwhp. I dont think he's making that below 10k rpm(or probably even 11k).