Exhaust question/ No power question
 

I have a 12a street ported engine (rebuilt 4,000 miles ago) with a racing beat intake manifold and holley 600 carb setup with a holley fuel pump (the "red" one) delivering 7 psi... The car has NO type of power... I'd go as far as to say if I went back in time and raced the original stock car 3 years ago as I bought it, it would beat me in the 1/4 mile by a car length... It doesn't have power, and there is an especially noticeable power leveling out after 5,000 rpms... My mechanic says it has to be the exhaust holding the car back, not allowing enough flow... I have headers and a prima flow muffler on the car right now... This upcoming weeekend he is going to extend the headers (they will not connect into 1 tube as they do now) and have 2 2" pipes running all the way to the u-bend over the rear before the muffler,,, he will then tune the car and raise the jet# that the carb has right now.... And after this long story that I just told, my question is, is it resonable that what could be holding my car back is the exhaust??? between the headers and muffler right now is a hollowed out universal cat and a stock pipe... Any suggestions, advice, or references to a knowledged (reasonably priced- I'm on a college budget) first gen mechanic in the northern new jersey area would be greatly appreciated... Thanks...

I'm sorry,, I need to clarify,,, when I say NO power,,, I mean no type of additional power to that of when it was stock...

Other gurus correct me if Im wrong, but when you move the collector back you shift the torque curve further on the graph. Meaning you move the torque to the higher powerband..

Id say cut the cat out, and weld a better pipe in there, I wonder if its loading up in the larger chamber and therefore somehow restricting flow?

Street ported with a better FP, carb and intake, should net you almost 190 hp or so. It ought to run very nice...

Everything else seem fine? Spark plugs, timing? coils?

Mike-P-28, always good to come across a fellow 80 owner... that 85 sounds like a beast....
the 2 2inch pipe project is scheduled for this weekend... the hollowed catalytic is going to be chucked as far as i can throw it.... the 2 pipes extending from the headers are going to come together just before the bend over the rear axel,,, and then is the primaflow muffler....
the plugs are 4 head ngk's,,, changed about a year ago (before the rebuild)... the wires are morrosso 8mm,, they are approaching 20k miles... timing was set by mechanic who did the job...
the mechanic that did the job has been working on rotaries since before the rx7 came out!!! he sais it has to be the exhaust,,, once that's done,, he put higher jets in the carb.... does it seem feasible that the exhaust would make the car run as if it were stock??? it's not even the whole exhaust,,, the muffler and headers are done already,,, it's just what's in between....
enjoying 190hp sounds nice,, considering a 115hp rx7 can keep up with me as it is now...

Oh yeah man, horsepower is only the amount and velocity of air/fuel you can put through the motor.. If theres a blockage in the exhaust it cant take any more fuel/air effectively... So therfore will run like crap.. Let us know how the cat throwing contest goes :D

yeah, moving the collector backwards will move the torque further up in the RPM range.

mike-p-28 is right, yor setup should give you about 190 HP, if it was done right.

were new seals used when the motor was assembled?

i guess the cat could be responsible, but i am a bit skeptical about the exhaust being the "only" thing responsible for your troubles. i get decent power throughout the rev range out of my setup with Dells and the stock exhaust manifold (stock port). my brother has a streetport 13B with an RB exhaust system and his is collected right after the headers dump out, and his car pulls HARD all the way to redline. could you describe what happens with a little more detail, like, talk us through what happens if you stay in the throttle from first through third.

i would second the advice to check the timing and the coils. changing the plugs can't hurt, but i doubt if they could be responsible for losing 70+ HP. are you sure the carburetor is jetted correctly?

if you don't mind crossing the bridge, i know someone in the Bronx that should be able to help you - don't know how much he would charge, but he knows rotaries!!!

New seals and springs were used in the rebuild, and the rotor bearings were bad, so those were put in new too...
I will have my mechanic check the coils and timing again this weekend when the exhaust gets done... I will update this thread with a reply after this weekend,, hopefully it will be a happy reply.... If not, I just might take you up on that mechanic in the Bronx... My mouth waters every time I read "190 hp".... I would say my car is using about 115 hp, so to say 70 hp lost is pretty accurate...
The plugs are 4 head ngk's and they are 1 year old,, changed about 4 months before the rebuild... Should I change them???
The wires are 8mm morrosso wires and are approaching 20k miles... How often should I change those???