borka

iTrader: (1)

I admit, I could be wrong... but I've never seen a miata dyno sheet with 300hp at 9psi.

thumpetto007

iTrader: (15)

There are turbos larger than your house. Millions of hp at low psi. So....

Any turbo that flows more than 60lb/min can easily make 300whp at single digit psi.

Especially with headwork.

concealer404

iTrader: (3)

Because why would you do such a thing?

jonboy

Apart from the slightly odd rear muffler design, with the 'side entry' into what looks to be an expansion chamber, the rest of the system is 'straight through'. I just stuck a borescope up the tailpipe in the name of science (don't we all claim that? ) and it looks like a standard non baffled silencer...

18psi

iTrader: (76)

that sharp corner is a significant restriction, and so is the catalytic converter that most (all?) of their systems run. And by significant I mean measurable and repeatable, not some astronomical number.

That's why the big Maggie "MT Approved" exhaust setup is so good: it's quieter, AND free-er flowing.

superchargers, esp centri superchargers, basically need to do this to make up for all the power/efficiency they're loosing by spinning the blower.

turbo's don't have this problem, and most people would never want to give up delicious torque for that "flat" power curve peaking at redline.

jonboy

Has anyone done a back to back comparison on it? Not arguing, just wondering how much of a difference it is...

When I bought the FM setup in 2009 (!!) there weren't a lot of alternatives available off the shelf, especially in the UK... I've hacked the front half around recently for the tubular mani and V band setup, if there's significant free power I may hack the back half around, as it looks like you can get Magnaflow mufflers over here now...

borka

iTrader: (1)

right, but what i originally meant was that i never seen a turbo in a MIATA that made 300hp at 9psi, in reply to K24MADNESS that his supercharger made 300hp at 9psi.

concealer404

iTrader: (3)

Right, because Miata motors are terrible and people here tend to size their turbos properly.

Full_Tilt_Boogie

iTrader: (1)

The only way a BP is making 300hp on 9 psi is going to have to be at around 8k rpm or more, and that is probably going to be with cams to make it hold its torque better above 6k rpm where they normally start falling off.

The idea that a really huge turbo is going to make more power for the same amount of boost is a bit of a fallacy. Just because the turbo can flow more doesnt mean that it does, it flows what the engine flows, not the other way around. The only reason you ever do see a big turbo improving power on the same pressure is due to decreased back pressure from the larger turbine and better compressor efficiency; at a higher rpm. More torque at high rpm equals more power.

The torque output is based on the engines displacement, volumetric efficiency, pressure ratio, and charge air temp. Turbo flow is not a factor in the equation, it only influences the other factors.

hi_im_sean

iTrader: (3)

Savington

iTrader: (31)

Peak power is dictated almost entirely by airflow. Boost is a measure of restriction. The two do not correlate linearly. 300whp at 9psi in Tom's setup (which I tuned) is a result of his custom cams and overall system performance which allow for more flow than the stock cams do at the same boost level. In supercharger setups in particular, if you add custom cams which increase airflow (i.e. less flow restriction), boost (a measure of said restriction) will fall every time. Put the same cams in an engine with a large turbo (something like an EFR7163) and you'd see similar power at similarly low boost levels.

k24madness

iTrader: (6)

pdexta

iTrader: (17)

Not quite what you were asking for, but I thought it was an interesting datapoint. When I first put my car together I ran a 3" exhaust necked down into a tiny MSM muffler to see what kind of power I could get out of it.

MSM datalogged 283/236 @ 200kpa


3" datalogged 335/283 @ 210kpa


~50whp gained from a MSM muffler to 3" magnaflow. Just the fact that the MSM muffler would make 283hp makes me feel like a 2.5" can't be too terrible of a restriction at realistic stock motor power levels.

codrus

Intuitively, the sharp corner seems like it should be a significant restriction, but empirically it's not. I did backpressure measurements on it and it barely registers at all. I've done 360+ rwhp through that muffler, it's not a problem.

The cat I agree on -- the first FM 3" cat I bought was a Magnaflow metal core cat, and flowed very nicely. The warranty replacement for it was a ceramic core cat of a different design and was a significant restriction. Backpressure measurements for all of this are in my build thread.

​​​​​​--Ian

DNMakinson

iTrader: (3)

Codrus gets a POSCAT because, 1) he is always helpful; 2) I like him; 3) He signs his posts; 4) This makes an even 400.

Scaxx

Some shitty person took it away, but I got you Ian.

Also to add to the slightly off topic ls3 comment, since my car is a single exit when I take the burns off (super small 4" muffler, very free flowing) and put on my custom one for the street (triple the volume, about twice the length, and 3" inner diameter) the low end and mid range is noticeable fatter. Seat of the pants, but it is noticeable. Sadly I don't have a dyno sheet to back it up but I may bring my other muffler to the dyno when I go this spring/summer. Just for *****, and science.

18psi

iTrader: (76)

Here, have another

y'all very well might be right. what I've noticed personally is that you feel the torque more with quieter exhaust, and less with loud. but if you end up testing this on the rollers you'll get ALLTHECATS

Full_Tilt_Boogie

iTrader: (1)

It could also be that the exhaust restriction helps the too-big collectors and too-big primaries work better at low RPM than they do with a free flowing muffler.

Note: When I say "too big" I mean not optimized for low RPM.