Ha, I never finished my last post for some reason, I just deleted that last part becuase now I am not sure where I was going with it...
Sadly not a whole can be done to promote even better breathing...I was a little misleading the first time I posted that...
A stock FS-DE breathes like s***, everyone knows that...The engine bites it at just over 6,000 rpm. If you use the J-spec cams it will help immensely on a harder pull to redline despite only giving a couple more horsepower...That is what is really hard to explain to people...It is not just how much hp you are making but also where you are making it. With the cams you only make about 7-8hp more than stock, but that only illustrates a total peak gain of 7-8hp. if you compare the dynos back to back you see that the stock DE's power drops considerably at 6,200rpm and it peaks with about 102hp at 6,100 rpm on average...With the cams you will be making like 109hp at 6,500rpm but the significance is that it maintains that power all the way to redline, rather than dropping off. So the cam'd DE has 109hp at 6,500 were the stock DE is making more like 90hp at that particular rpm...Hopefully this is clear enough to see the significance...you only gain a few hp but you signifcantly lengthen the powerband, which definately helps situations where you need the engine boiling (Drag racing etc.)...
So more aggressive cams are a must for NA...The intake manifold on the stock DE seems to be ok...The runner length is pretty good for lowend torque and high end breathing. The breathing problem most likely is a combination of the fixed cam timing/lift head, undersquare engine properties, and the con ratio's...Like a lot of people have said you need to rev to make power NA. A FS will safely rev to about 7300 (The stock ECU rev limits around 7,000rpm, but most of us don't spend any time there becuase the power sucks), with the right mods the engine will make power considerably higher but you need to change the ECU to something that will be able to control the rev limit i.e. Stand Alone...Notice that the j-spec ecu for the FS-ZE revlimits at more like 7400 rpm, so our low redline is becuase Mazda figured us North Americans want lowend torque and would not rev the engine at all...and not that the engine physically can't handle those rev speeds...In short, if properly built an FS will easily pull a few hundred rpms above 7,000rpm. After that piston speeds become to great and engine tolerances will give in...
Obviously this is not high enough to promote crazy NA gains...The FS's block itself is very strong but it would take a lot of money to reinforce the bottom end to tolerate extremely high speeds...This is one reason why the Speed Touring cars FS's are so expensive...A lot of money on forging cranks and connecting rods is spent...And becuase of the fixed head you will get an annoyingly peaky, un-streetable engine (imagine making 225whp only between 7500-9300rpm, virtually no lowend torque, and cams aggressive enough to need a 3,000 rpm idle)
OK so here is the slews of mods...There is no single mod that will give big gains NA. Look at it like a turbo, you don't just buy a Turbocharger and gain 70whp, you have to buy a turbo and a bunch of misc pieces to make it work...The same applies with NA...start buy getting air to the engine...Do some research on building your own intake, if you get the diameters right 10hp is not too far out of the question...I have never had good experiences with polished or honed intake manifolds. They usually create more turbulence and in turn give less hp than before...If you are unlike me and want to stay 100% NA get a good header. IF anyone has seen the stock down-pipe you will know why this is a must...Then get a decent diameter exhuast (if staying NA and not planning on reinforcing the engine to speeds above 7300 rpm, no bigger than 2.75")..the Racing beat Cat-back seems to be one of the best for NA gains (remember bigger diameter is not always better, to big and you get exhuast pulses hanging around in the pipes, and they love to rob lowend torque) Then raise the compression, get a good ECU (stand alone seems the only way to go, but check E-Bay I have seen brand new E6K's going for less than $1,000 lately), and get the cams...These don't have to be done in any order really accept the ecu has to be in before the raised compression...And also each one of these mods gives more or less puny gains by itself, but all of these mods working together will be right around 165whp(figuring ZE spec compression ratio and ZE cams, more is attainable with more aggressive cams and a higher static compression ratio...custom pieces are the only way to go for that though)...Not to bad at all...doing the work yourself will make it a worthwhile route for some...
I am sorry this is so ridiculously long...tried to answer a bunch of question in one post
