Limits of a street ported motor
06-03-08, 02:54 PM
#76
the reason I say that the alum center plates are needed for the 12a is that the stock 12a center plates are a little odd and need to be changed for the motor to match the current design work. also the harder those plates are the less issue of flex at high rpms and the wear issue (the motor I designed is built to last a much longer time and higher stress then stock) you can build a car using 2 of 3 things:
1. cheap
2. safe
3. fast
which two do you want?
1. cheap
2. safe
3. fast
which two do you want?
Most flexing at higher RPMs are not in the Irons, but the E-shaft. They build 2 piece shafts with bearings to solve that, then you have the dowel pins, tension bolts, etc.
06-03-08, 02:59 PM
#77
the reason I say that the alum center plates are needed for the 12a is that the stock 12a center plates are a little odd and need to be changed for the motor to match the current design work. also the harder those plates are the less issue of flex at high rpms and the wear issue (the motor I designed is built to last a much longer time and higher stress then stock) you can build a car using 2 of 3 things:
1. cheap
2. safe
3. fast
which two do you want?
1. cheap
2. safe
3. fast
which two do you want?
06-03-08, 03:20 PM
#79
Respecognize!
06-03-08, 04:42 PM
#80
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lol, thats good.
As for my defending the side plates. I ment all side plates not just the intermidiate plate. The big thing I worry about is the flex from the eshaft true but to better the support eshaft the all hardened aluminum is a good choice(it helps with the flex on a different scale) as for the two piece eshaft i forgot about that, they are so hard to get your hands on that I do not consider them much anymore. I am thinking purely on a design level an all aluminum motor is better then a iron/alumiunum motor. Especially when your dealing with high revving/power etc.
As for my defending the side plates. I ment all side plates not just the intermidiate plate. The big thing I worry about is the flex from the eshaft true but to better the support eshaft the all hardened aluminum is a good choice(it helps with the flex on a different scale) as for the two piece eshaft i forgot about that, they are so hard to get your hands on that I do not consider them much anymore. I am thinking purely on a design level an all aluminum motor is better then a iron/alumiunum motor. Especially when your dealing with high revving/power etc.
06-03-08, 05:17 PM
#81
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Ok.........well I dont know a whole lot about my motor, other than its supposed to be a street ported 13b from a 74 pickup. Not sure who it was built by. It has a rotary engineering intake with dual 38mm webbers. Seems to run great, pulls hard on top end, smells a little rich but what rotary doesnt with headers and aftermarket exhaust. Based off a couple of cars I have played around with on the street, Im guessing I have a low 14 second 1/4 mile car. However it is more set up for auto cross. Im also guessing that I might be somewhere around the 175-200hp at the flywheel mark, based on my weight and 1/4 mile estimation. Of course all of this really doesnt matter till I actually get it to the track and find out 
I just wanted to know if this sounded about right for my set up.
I just wanted to know if this sounded about right for my set up.
06-04-08, 12:10 AM
#82
jjbrozak - since you are in the Midwest and close to Mid America Motorplex, take a trip over there and check out the SCCA Regional/National on August 16/17 and you will see at least 5-6 Street Port Rx7s running in E Production. At present we have 1 12A and 5 13B powered EP cars running in the Midwest Division . The engines are all pro-built from the likes of Prather Racing (Topeka KS), Tony Riveria and Roger Mandeville. Hp is in the 210-225 neighborhood (at the crank) depending on state of tune. Note that these engines are restricted to webers with 38mm chokes. The 12A motor holds is own by the way.
As far as RPM, I am familiar with the Roger Mandeville street port 13B and it is shifted at 9300 all of the time and the stock port Prather Racing 12A Improved Touring engine I own is shifted at 8300. The Street Ported 13B has lightened, balanced and clearanced rotors with ceramic seals and my stock port 12A has stock rotors (required) and carbon seals. Bearings and stationary gears are upgraded over stock. My engine 12A is 6 years old and has 30 plus races on it.
Regarding exhaust, I think you need to distinguish between racecar exhaust and street exhaust. E Production cars have 3-4" exhaust systems after the header and it works for them. Thats because they are allowed to run VERY close ratio transmissions so RPM's are kept high and in the power band so low RPM perfomance is not an issue. My IT car runs a long primary (110") header into a 2.5" exhaust. My car also operates primarily at a constant high RPM so the 2.5" pipe is not too big.
As far as the Mazda Trix car and exhaust that is pictured in this thread - don't doubt the setup on that car. I have seen that car run with that exhaust and it is FREAKING FAST and reasonablly quiet. I believe the double muffler setup is good for 95 db's. In fact that car, driven by Dave Lemon, set a track record at the June Sprints several years ago and has lead/been in the running at the Runoffs recently. You can bet that anything you see on that car or from that shop is dead nuts on and dyno proven.
As far as RPM, I am familiar with the Roger Mandeville street port 13B and it is shifted at 9300 all of the time and the stock port Prather Racing 12A Improved Touring engine I own is shifted at 8300. The Street Ported 13B has lightened, balanced and clearanced rotors with ceramic seals and my stock port 12A has stock rotors (required) and carbon seals. Bearings and stationary gears are upgraded over stock. My engine 12A is 6 years old and has 30 plus races on it.
Regarding exhaust, I think you need to distinguish between racecar exhaust and street exhaust. E Production cars have 3-4" exhaust systems after the header and it works for them. Thats because they are allowed to run VERY close ratio transmissions so RPM's are kept high and in the power band so low RPM perfomance is not an issue. My IT car runs a long primary (110") header into a 2.5" exhaust. My car also operates primarily at a constant high RPM so the 2.5" pipe is not too big.
As far as the Mazda Trix car and exhaust that is pictured in this thread - don't doubt the setup on that car. I have seen that car run with that exhaust and it is FREAKING FAST and reasonablly quiet. I believe the double muffler setup is good for 95 db's. In fact that car, driven by Dave Lemon, set a track record at the June Sprints several years ago and has lead/been in the running at the Runoffs recently. You can bet that anything you see on that car or from that shop is dead nuts on and dyno proven.
06-04-08, 08:01 AM
#83
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Ill say Im close, its about a 30 minute drive for me. You can be Ill try and be there to watch that too by the way. It would be cool to talk to some people who actually track race their cars. I have been on the track with my old 7, but not the one I currently own. I dont suppose you and your group have any extra wheels for sale? Im running on the stock LE wheels with victoracers for autocross. I would like something better. I have a set of MRT wheels, they are aluminum and carbon fiber, 15x10. Im a poor midwest boy and I cant justify spending $1000 for a set of tires though. Im looking for more a 15x7 or 8.
06-04-08, 11:08 PM
#85
Ill say Im close, its about a 30 minute drive for me. You can be Ill try and be there to watch that too by the way. It would be cool to talk to some people who actually track race their cars. I have been on the track with my old 7, but not the one I currently own. I dont suppose you and your group have any extra wheels for sale? Im running on the stock LE wheels with victoracers for autocross. I would like something better. I have a set of MRT wheels, they are aluminum and carbon fiber, 15x10. Im a poor midwest boy and I cant justify spending $1000 for a set of tires though. Im looking for more a 15x7 or 8.
A place to look for cheaper racing tires for the 15x10's would be www.americanraceronline.com. They make circle track bias ply racing tires in both DOT and non-DOT ratings. They have dirt and asphalt tires with prices that are less that Goodyear and Hoosier. They make an asphalt modified tire - 24x10x15 that would fit your wheels perfectly. Of course this would put you in F Prepared at a solo II.
Wheels are gold so no one is parting with any that I know of. That said, Konig Rewinds and B-Bombs are a good deal if you have the GSL-SE pattern. Rewinds also come in the 4x110.
Anyway come on over to MAM in August. There should be a few cars to look at. The same group will be at Heartland Park in Topeka over labor day for a Double National. Finally, the SCCA Runoffs are at Heartland Park for the last time this year in October. You can expect to see 10-20 Rotory powerd cars in E Production alone.
06-05-08, 07:31 AM
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Well unfortunately I am already in FP due to the *** clown before me gutting the interior. It doesnt really matter, I go out to have fun with the car anyway. I just know if I had a good set of 15s with stickies, I would be contener for FTD. I was running on a set of falken azenis. They were mounted to 15x7 snyper wheels. I was running within .2 of trailered FP cars in my class. Im about .5 off now with the worn out 14" victoracers now. I found a link to a site on here that has the rewind style in a 15x8 for 550 shipped. Ill probably end up going with those.
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