Before you ask, I have searched. Surprisingly little info on J ports here...

I am building a Lotus Seven-inspired car from scratch in my garage, using s4 donor parts like engine, trans, LSD, halfshafts, uprights, brakes, etc...

My question is about the engine I have. It is a rebuilt (not even run yet) s4 13b, that has been J Ported. The porting and assembly was done by a reputable builder. I am using a 4-port Star Mazda intake manifold under a Weber 48 DCOE carb, MSD 6AL ignition and a pair of MSD coils, run by an old-school distributor/cap/rotor. All of this is to keep the entire engine management as simple as possible. The car will only weigh 1300 lbs, so I can sacrifice a few HP for the sake of simplicity.

I was looking at gear ratios today, and got to thinking... Is the J Port powerband too narrow for the relatively long gear ratios?? I'm VERY interested to see or even hear approximate peak HP torque RPMs, and where the power starts to build. I have heard the idle pretty high (like 1800 RPM), I assume because of the increased overlap, and drivability isn't so great either. But keep in mind, this is a track/autoX car first, and occassionaly Sunday driver.

Any help is greatly appreciated! Thanks.

PS- On a side note, the gear calculator I plugged the factory gear ratios and final drive gave me a top speed of 199 mph @ 8,500 RPM in fifth gear.
OVERDRIVE FTMFW!

 

It's unlikely you'll find any j-port dyno sheets because most people aren't crazy enough to build such an engine.

J-port are about the most unreliable form of porting around due to the fact you need to cut into the water jacket. Most of the time those engines last under 5K, with the normal failure mode being water leaking into the intake area. Certainly not idea for a street engine.

A peripheral port will give you more power and a wider powerband, but may be banned by your racing class.

 

^why would they ban it??

 

Because it makes a lot of power for a small displacement engine. When you stack up a Rotary P-Port motor to majority of the major car manufacturers the Rotary is the best bang for your buck. Most people know this already that is why banning it makes sense to other people, but not Mazda Rotary owners.

 

Because they're scared of the BRAP BRAP BRAP !!!

 

lol....i know it sucks for rotary owners but still competition is competition...right?? i see no neccesity for being banned...