Something I noticed that may help explain the difference in power increase between the two models is that apparently the OEM headers are the same between the 250 and 350. In looking at the parts manual, I'm showing the following part numbers:

RWD exhaust manifold:
R 17140-31120
L 17150-31120

There are separate part listings for the AWD exhaust manifolds, but my manual shows the 2.5 and 3.5L engines use the same headers. In fact, they only pieces in the entire exhaust system that are different between the 250 and 350 are the center exhaust pipe (which has the last two cats) and the rear exhaust pipe.

Javier

 

whoaa didnt know that is250 and is350 have same headers...

 

The AFR graph looks surprisingly lean for the baseline run too. Definitely leaner than any stock car I've ever seen. If I recall, mine was running close to 11:1 at WOT.

What I think would be very helpfull at this point is a plot of your timing curve via OBDII.

 

I agree, It would also be nice to see the EGT's on it also. I'd bet its getting close to 1600-1800 degrees. Which wouldn't be bad if there were more fuel. But 14.0 " I smell burnt valves"

 

they key to making power on this cars is getting rid of all the cats

 

why do you say that? wouldn't that be the "key" for every exhaust system? lol

For all I know, you want to reduce bends and restrictions for less back pressure. I'd want to keep the exhaust street legal by installing a set of 100 cell high flow cats. I'm just wondering what the diameter of the piping is for our stock exhaust and the mazzuri headers.

 

Thanks for the second dyno.

I have to say the results are not what I though they would be and I will go over the numbers one more time to see if anything else can be changed maybe.

With that said, over all I am happy with everything. What I mean by that, the header made power in all RPMs. Made good TQ down low which will be noticeable and looking at the A/F a tune will defiantly help in finding more power. Also, any exhaust mods you do after the header will be a lote more noticeable with the header.

Looking at the Tu-jen ,or what ever the name is, header they seemed to make great power from their header and exhaust on the IS250, which make sense with my results. Maybe this is why they (or no one else) make a set of headers for the 350, the gains are not as big.

I think with an exhaust and a good tune, the gains will be a lot better.

 

^^^^agreed. just need to find a way to get more fuel to the engine.

I'd be very interested in seeing what a cat back, or even axle back will do for this.

Just curious, caus I'm a 250 I already intend to get one.

 

Isn't there a 350 owner with the headers in FL?

I'd be willing to swap my exhaust with his for testing purposes. My exhaust has the secondary cat's removed and its 2.5" piping, to an x-pipe, to 2 mufflers. It's a true-dual.

 

I just looked a little closer at the graph, too bad its auto and we can't see what is going on in the low RPMs, but the dyno seems to "start" at around 3800 RPM and if you notice on both hp and tq, there are great gains, about 15 wtq and 10 whp. I think 2 things are happening here:

1. The car is running out of fuel up top (which can be seen from the A/F).. actually as a matter of fact, on the 250 up top it was in the low 12s for A/F.

2. The headers may need to be a step design, where they are a little bigger on the ends.

I don't think we are seeing the whole picture here. I think there is a good amount of power still in there.

 

yes there is a decent amount of power in there.. just no where near what was expected.. atleast not right now.. maybe after some tuning to the A/F... but the gains still wont be as good as the 250

 

This picture says it all. Up to 3800 the stock ECU runs lean with the stock header, same with my header and the gains are there (maybe leaning it out a bit may make even more) after the 3800 mark the stock header starts to go rich while with my header it's still super lean all the way to redline almost. It's a clear picture that the engine needs fuel that it's not getting... I really would love to see the timing graph, I bet it's pulling the **** out of it up top.

 

Looking at my dyno:



Around 3800 I made almost the same power, a gain of about 15 whp with the 250.

I wish there was an easy way to add fuel.

 

There's no way that this 350 was "running out of fuel". At his altitude, the stock injectors would be totally capable of delivering much more fuel than needed. I think that there has to be something wrong with the dyno's WBO2 or the car's primary O2's. The results are also being taken from behind the secondary cats, which will skew the readings a bit.

 

Isn't there a 350 owner with the headers in FL?

I'd be willing to swap my exhaust with his for testing purposes. My exhaust has the secondary cat's removed and its 2.5" piping, to an x-pipe, to 2 mufflers. It's a true-dual.

Where in FL are you? I live in Naples...