AmbyBomb

I don't believe that you lost nearly 20 ft lbs of torque by changing the mufflers.

How many runs did you do? Same conditions?

95bat

it looks like the graph is showing a change of 2.34 tq and 0.71 hp. Basically within run to run variance showing no benefit of adding axle back exhaust.

The headers look to have added around 50 hp though!

AmbyBomb

The low end has a big gap, almost as if the tester simply didn't go full throttle at the same time.

hotct

This makes me 100% want headers for my IS. Seems to be some low hanging fruit

konichiwa3

Normally axle back alone will not net you any gains if any. However, a catback exhaust will.

It will with Natural aspirated engine. A free flowing axle back and even a catback with no cats and or resonators will reduce back pressure to the point that the engine will loose that low end torque but gain on the top end.
This is quite common with Natural aspirated engines. I have seen this happen time and again even with the older Bmw M's when they were naturally aspirated. Turbo's and superchargers fare a lot better with a similar setup.

The runs are SAE corrected for any temperature and humidity changes. Dyno's were run on the exact same dyno each time. 3 runs every session.

Gains were at peak, the torque was a minimal gain whereas the delta in hp (0.71) was actually a loss but too marginal. The only benefit to the axle back is sound which in of itself enhances the driving experience.
Yes, headers is where the big gains are achieved. What was amazing to observe with the dyno is how the headers even without a tune made the torque and horsepower curves so much smoother with less severe dips. In stock form you see how much the torque and HP were undulating through the RPM range.

AmbyBomb

I don't believe that a 5L V8 lost power because the mufflers were replaced.

hotct

Do any of the RC F headers fit our cars? I assume nobody had made headers specifically for the IS

cp2

iTrader: (1)

after seeing the graph, it makes me not want to get an exhaust...haha. maybe just change out the mid pipe and keep the stock axel back? indeed the headers did real good though!

@konichiwa3 do you not have an intake system? if not, why not?

cp2

iTrader: (1)

I'm sure the headers fit on the engine, it's just finding out if the plumbing on the way out are similar.

AmbyBomb

Here's a thread by RR Racing with lots of dynos.

https://www.clublexus.com/forums/rc-...ispreloading=1

An exhaust doesn't lose power.

Kwilliams5

That is exactly what imma do but this wait is making me feel like I shoulda gotten an m3 or m4

Kwilliams5

If you find out please let me know as well

Kanpai

If exhaust note was such a big deal, then the IS500 was definitely not for you.

AmbyBomb

If you're this anxious about it and considering an M4, the IS500 wasn't for you.

95bat

Those are both super fast cars. If you want speed, get one for sure.
For pure exhaust sound I'd probably go with a Dodge, they sound pretty dang good stock.