super quick question how high can u rev an s4 na safely?? 8000 perheps?

 

With stock ECU? 7800. Rev limiters hurt more than they help.

Without stock ECU? I'd think twice about taking it past 8500-ish.
j9fd3s will probably chime in here about the destructive effects of rev limiters soon enough

 

not on a stock ecu, i have a ms1 and i have my ecu set for soft rev limit at 8000 and hard limit at 8500 and wanted to know if this is ok, i also have an s5 intake manifold and my ecu accuates my vdi with an electric air pump i got from a crown vic

 

no need to rev past 8k with stock intake.

 

+1 most na's make peak power around 6500rpm. When I had my custom intake manifold is when I made peak power at 8000rpm. Mind you that was also on a s4 na

 

pics? sounds good

 

i'm pretty sure he has a thread (with photos) floating around here in this section.

 

I can't find anything talking about custom intakes, can I get an explaination?

 

Twin80s' thread

what is it about custom intakes that you want to know?

 

That thread answered some of my questions. Thank you diabolical1.

 

ya too bad like half the pics are dead lol.....still have the dyno graph around here some where

 

lmao... yep, tis better to let it rev than to let it sit on the limiter for a really long time (30 seconds)

http://fc3spro.com/TECH/HOF/K2RD/k2rdhof01.html that's what happened when something decided to stop @8500rpm...

the next motor got revved to 9400, and the seals and springs are beat (it was a junkyard motor), but everything else looks nice

the current FC is an S4, lowering the exhaust backpressure, and leaning it out just a tad over 6500, and the power doesnt fall off over 6500 like it used to, peak is still 6500-6800ish, its broader.

on an s4/s5 block 8500 is no problem, but as peejay says, RPM stands for Ruins Peoples Motors, it'll last longer under 8...

 

wow no kidding ive never seen anything like that lol i got one more question lets say i make peak horsepower at 6800 what would be the best shifting point (not a drag question more of a on race track), im planing on building my self a budget exhaust i picked up a 12a rb header that im going to mod to fit my 13b, and imma build myself a expansion chamber out of some megaphones and some pipe, im going to use a rb presilencer and an rb muffler, as u can see here http://mazdatrix.com/e3.htm, my question is how loud will this set up be as i still street the car at the moment, i would think that the expansion chamber might work as a resonator as it would probably reflect some of the wave backward and cancel each other out, or should i add another presilencer or muffler.... i apologize if this doesnt make sense as im alittle tired
thanks
ismael

 

I'm not recommending but I hit the rev limiter all the time on my s5 and the motor never seemed to care. I mean, I really abused it cuz I couldn't help it and it just kept going. My motor was street ported with a huge exhaust port and the power just didn't die off. It didn't make all it's power at 8500rpms but close enough to make me hit the limiter sometimes. I drove it hard for 1 1/2 years until I seized the motor when my oil lines popped. Don't know how much longer it wouldve lasted but it ran fine up until than. But anyway, to the OP. You should only shift a little past where your cars power starts to die off.

 

Its hard to say with out knowing the whole power band, trans and gearset. On almost all stock manifold cars the power band is smooth enough to say 7k but on cars with a real narrow or top heavy power band you may want to rev a little higher to stay in the sweet spot.

 

noise is a bit hard to say.

we initially ran a custom header into a 3" pipe into a round magnaflow, this put us around 110DB if i remember correctly

we then put some baffled muffler in the center, and this dropped it to 103, but we had to keep rebuilding it, as it just couldn't handle the energy coming at it.

next we put the RB http://racingbeat.com/resultset.asp?PartNumber=16425P which lasted quite a bit longer, and dropped the noise even more.

 

how much quieter was it after u installed the presilencer, i wanna try and get it under the legal limit of 95db so should i install another presilencer or muffler?
thanks
ismael

btw do u have any sound clips or videos?? thanks

 

Your shift pointwill be determined by your gearing and your torque peak. For maximum acceleration you should be dropping back to within a few hundred rpm's of your torque peak.
I helped a friend calculate this at a race at Pocono and lowering his shift point by 600 rpm's resulted in a 2.5 second faster lap time with no other changes.

 

Technically, it will be the point at which the horsepower before the shift is the same as horsepower after the shift, in an ideal world.

 

Not necessarily. You're assuming that the power drops off at the exact rate that the power gains.

 

Well, it WILL give you the highest average horsepower, by definition.

 

I disagree. I'll post an example later tonight.

 

i don't recall how loud it was with the RB and magnaflow, and keep in mind this was measured at the race track, so like at infineon this is right after turn 11, so its WOT...

 

Torque is what accelerates you. Horsepower is an imaginary # derived from torque and rpms.

 

And when you divide by gearing, a given amount of HP will always equal the same amount of torque at the wheels at a given speed, by definition, no matter the engine RPM.

Making the math pretty, an engine making 300hp at 10,504 with 5:1 gearing makes the same acceleration as an engine making 300hp at 5252 with 2.5:1 gearing. The difference is the first engine has 150ft-lb at that point and the second has 300ft-lb. Do the math yourself, I'll wait. All gearing versus RPM cancels out by the time it gets to the wheels, by that point all that matters is how much horsepower the engine is making.