Doing nothing at all! Same engine/turbo setup, same fuel, same Dyno, no changes to the tune whatsoever. Made 38.3 more HP at peak than I did back in May. (And 14.7 ft/lbs) Only physical change I've made to the car was in the exhaust, and that was just a muffler change. (Thermal 3" cat back, switched muffler/axle back section to a Borla Boomer) but I highly doubt that is the reason for the increase. Anyone have any insight?

 

If it's pump fuel, it wasn't the same fuel. There are inconsistencies between different stations, and even the same station from month to month. Was the temperature the same? How about the humidity? Wheel/tire size? Transmission?

No two dyno days are the same.

 

Didn't think the temp/humidity would make THAT big of a difference but I suppose your right. Wheel/tires were the same, I always use my stock wheels with all seasons for inspection and Dyno so that's concistant. I only run Shell fuel in it, but not always the same station. I guess it's just a bunch of little factors adding up to the difference. I was just amazed at how BIG a difference with all(read most lol) things being equal. **** back in my NA days I'd spend two graNd or more for 40hp and now I got it "free".

 

Here today, gone tomorrow, though, and yeah, the little things can add up, especially on an FI motor. Hell, I used to have an MBC with my build, but my ECU was set to do a hard (and I mean HARD) cut when it saw 10 PSI. I could have my MBC dialed in perfectly to peak at 9.98 PSI in the morning, but that night, when it got colder, suddenly I would get cut because I was hitting 10.1. All this because it was a little cooler outside. The weather is a fickle bitch with FI.

There are other things that'll affect your BHP, though, too. Let's say it's a BRAND NEW, freshly rebuilt motor, seeing it's first start on the dyno. The rings aren't sealed. Your BHP will increase if it's broken in properly. That's a very narrow window, though, so unless you literally slapped the brand new motor on the dyno, did a pull, and called those your numbers, I doubt that has anything to do with it.

I'm sure there are a hundred other little things that I'm forgetting, but yeah. It all adds up.

 

Post photos of the old muffler and the new...

If the new muffler is less restrictive then that would explain the power gains. Tubocharged engines are very sensitive to post-turbine back pressure (exhaust system back pressure). If you've ever done something as simple as removing a catalytic converter and putting a test pipe in its place then you know what I'm talking about.

To give you some hard numbers on exhaust system efficiency I give you the following example:

MKIV Supra, stock internals and stock cylinder head 2jz, basic popular single turbo conversion, methanol injection, full 3" exhaust from turbo back (no cat)

This car was used to do a direct dyno comparison between a 3" and 3.5" turbo back exhaust. Test was done at two different boost levels to get good data at different power levels.

At 19psi the 3" exhaust made 527hp. The first pull with the 3.5" exhaust was done with no revisions to tuning where it made 567hp. After adjusting the tune power output jumped 103hp over the 527hp baseline.

At 29psi with the 3" exhaust baseline power was 699hp. The 3.5" exhaust was installed and again a pull was made with no tuning corrections where it made 740hp. After tweaking the tune it made 70hp over the baseline.

Another good side effect is better turbocharger response (ie less lag). Watching the datalogs they saw that the turbocharger responded about 200rpm faster. They were unable to go any further as they had but the safe limits of 93 octane and methanol injection. On E85 or race gas the gains would be even higher.

One thing also worth noting is the 4" exhaust showed similar gains over the 3.5" exhaust. Those results should give you some idea of how minimizing back pressure AFTER the turbine wheel can result in not only more power but faster response and better fuel economy. Removing a restrictive muffler entirely or replacing it with one that is less restrictive has the same effect as a larger diameter exhaust system.

 

Wow yea that is crazy. This is only my second personal turbo setup so I'm not super well versed yet. I always knew back pressure effected spool characteristics but I didn't know how drastically things would change. On that case, changes in air temp/humidity plus the small exhaust change could easily account for the increase. Thanks for the knowledge guys!

 

And how do you post pics on here that aren't hosted somewhere? But the new muffler is a Borla Boomer series 4" tip and the old was the standard Thermal R&D muffler that came on my 3" cAtback from them for my EM1 chassis. Piping was kept the same just took my recip saw to the old muffler that had seen better days and had my buddy tac on the new one.

 

if you car had some mileage on it and a fair share of backfires, rev limiters, etc... the perforated tube inside the muffler can collapse and it's hard to detect unless you really look through it in detail.

If the car was first tuned on a fresh build, then the numbers will be lower on a completely fresh engine. Later down the road, it will make more power.

If the boost slightly higher, like a PSI more, and the setup is efficient, that can account for about 20 WHP already by itself.

If the car ran leaner + combination of more boost and leaner, that could account of 30 WHP or more, depending how rich it was initially tuned, and then how lean it went. Could be from 10.8:1 AFR and leaned out to 11.8:1 AFR, still safe, but unexpected power gains.

Cars with good amount of mileage would be susceptible to running leaner later in its life, from things like more restrictive/clogged fuel filter, weaker fuel pump / older wiring, or MAP sensor getting stretched overtime (same boost, but ECU sees less) and so forth.

That's the pattern I find on my own cars, after owning and driving them for the past decade or so. And for 1000+ WHP cars, I think if a dude farted beside my car during a pull, I would gain or lose 100WHP or even if I looked at the turbo at a funny angle.

 

Methane injection, you say?

 

Lol. Didn't ever think about the collapse inside of muffler. It is nearly 5 years old. The engine itself has seen about 40k miles but only been boosted for a little under 9k miles. This was the same engine I ran NA for 3+ years. The turbo and all related components were brand new when I went boost though. Who knows what the exact cause is, probably all of the above. I was just surprised at how easy the power levels change on a boosted setup. Would take quite a bit of effort to see a 40hp gain when I was NA so I guess I was basing it on that logic, but now these things make a lot more Sense.

 

Lmao