Car falls flat , exhaust?
06-13-2014, 10:05 AM
#1
Thread Starter
Car falls flat , exhaust?
Just got a call from my tuner. He has been working on the car and for some reason it flatlines at high rpm. People with my kit usually make power in a straight line all the way up the graph, mine hits 6800-7000 and falls flat. If it did follow the straight line it would get to between 330-340 at the wheels but once it hits 300, game over, it stops climbing. He said it won't take anymore timing for some reason an suspects the exhaust. Fuel pressure is fine, injectors are new, nothing from any sensor looks out of the ordinary.
The tuner is pretty good, it is LJ at full blown and he said from his experience the problem is being caused by backpressure in the exhaust. I have a Mugen header, Berk Cat, and stock exhaust. There should be nothing in the header, the cat is nearly new and I thought the stock exhaust was supposed to be great at flowing but don't know what gives.
I don't want a 70, 63mm or whatever stock is would be fine. I tend to understand single have been shown to manage a little better than duals on an SC'ed car.
But I don't really know what is fairly OEM sounding besides Mugen and that is more than I want to spend on the car unless I find a good used one. Custom unit LJ recommended Magnaflow, but everyone has a different idea of what sounds good. I am an old fart who will drive this to work. I don't want it to sound un-OEM like below about 5000 rpm. At full trottle louder is OK but don't want obnoxious. Drone is not to be tolerated.
I don't suppose there is a good way to test the stock exhaust for restriction? FWIW the exhaust pretty much all comes out the passenger side until a certain rpm before it will flow from both sides, I don't know if that is normal but the passenger side is the shortest path so I thought that was typical. At idle it comes out one side only.
I don't know if anybody knows at what point a working stock exhaust becomes a restriction, but I thought it was much higher that 300.
The tuner is pretty good, it is LJ at full blown and he said from his experience the problem is being caused by backpressure in the exhaust. I have a Mugen header, Berk Cat, and stock exhaust. There should be nothing in the header, the cat is nearly new and I thought the stock exhaust was supposed to be great at flowing but don't know what gives.
I don't want a 70, 63mm or whatever stock is would be fine. I tend to understand single have been shown to manage a little better than duals on an SC'ed car.
But I don't really know what is fairly OEM sounding besides Mugen and that is more than I want to spend on the car unless I find a good used one. Custom unit LJ recommended Magnaflow, but everyone has a different idea of what sounds good. I am an old fart who will drive this to work. I don't want it to sound un-OEM like below about 5000 rpm. At full trottle louder is OK but don't want obnoxious. Drone is not to be tolerated.
I don't suppose there is a good way to test the stock exhaust for restriction? FWIW the exhaust pretty much all comes out the passenger side until a certain rpm before it will flow from both sides, I don't know if that is normal but the passenger side is the shortest path so I thought that was typical. At idle it comes out one side only.
I don't know if anybody knows at what point a working stock exhaust becomes a restriction, but I thought it was much higher that 300.
06-13-2014, 11:52 AM
#2
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I only made 320whp with a 2.5" duel exhaust, switched it out for a straight 3" and made 355whp. This was on a comptech supercharger. Tell him to unbolt the exhaust and see if you see any gains.
I also have the Mugen header. but I had a test pipe, and then switched to a straight 3" back from the header.
I also have the Mugen header. but I had a test pipe, and then switched to a straight 3" back from the header.
06-13-2014, 01:47 PM
#5
Thread Starter
As an aside, S2000 exhausts have become ridiculous as far as prices go. Custom would be much cheaper.
The only ones I really would do that are aftermarket would be Mugen, Fujitsubo or ASM but all of those are high priced new and hard to find used. The car gets daily-ed so I don't want it silly loud, cheap sounding, or drone.
06-13-2014, 03:33 PM
#7
I'm guessing a "berk cat" is a high flow cat correct? Can you not use a test pipe? Are you sure the belt isn't slipping? I would hope LJ would catch that, boost plot pulls full psi all the way to redline?
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06-13-2014, 05:48 PM
#8
Thread Starter
Full boost, no belt slip, new injectors, fuel pressure good, the high flow cat is Berk, plugs are fine, new coils, temps are where they should be but if the tuner's hunch is correct, the exhaust will flow 300 and no more. There are stock exhausts on the power chart that are making more than 340.
Setup is a roots blower, SOT kit but I switched to a TVS blower and modified the kit.
Had this thing dynoed three different times with two different blowers and have tried everything EXCEPT the exhaust so that makes a lot of sense. I never heard of a stock exhaust getting plugged before, but I did try two other exhausts for short periods that I did not like and sold and put stock back on. Maybe taking it on and off a few times loosened something inside, no rattles though.
I did find a local shop that does cutom work and says they have "backpressure testing". Not sure how they do that but I will inquire when they open on Monday.
Listening to clips I kind of like the reviews on this board and sound clips of the Borla. I wonder if I could just buy two Borla mufflers and cut the stock ones off. It would make it lighter and get rid of the one that I think is plugged.
