I made the X-over my self. It also includes lukey mufflers and resonators. I you give me your email address I will send some piccys
ok i think 2.5 too but yeah the exhaust there now is only 2 inch Tube is measured on the inside diameter 2 inch. Outside is 2 1/4 correct, but the tube would be sold as 2 inch.
I still don't see how a 2" exhaust would be the cause of this. You should have at least seen some gain. 2" is still able to flow quite a lot!!
Exactly I fully expected to see some gain also even with stock exhaust But to why there was none has me dumbfounded.
Heres the photos The x-over section is about 250mm long, fabricated from 2 pieces of 2-1/2' tube I can't tell you what power its producing as I'm away at work and I don't have the info with me
i think the problem would be that the headers are flowing a nice 2.5 inches of airflow. then you are trying to cram that excellent 2.5 inches worth of flow into a 2 inch pipe. obviously the flow is going to slow down. i think this slow down in air flow is significant enough to cancel out the increase in flow from the headers. have you checked your cats? also do you have a graph with the A/F ratio on it? another cause might be that the ecu is richening the mixture to the point that it is cancelling out the increase in power from the headers
Re: What the....exhaust problem, headers = 0kw Not having optimal exhaust size and flow will decrease potential but there should be some gain. Thinking back, when I changed exhaust systems on performance motorbikes I had to modify the carby to tune the engine. I wonder if the ECU should have had the self learning cleared to allow it to adjust to the change created by the headers? Also if the 02 sensors are iffy then It may not know that the A/F is not optimal. Just a thought but I am scratching to give you a logical reason. :unsure:
I still put it down to retuning the a/f ratios to utilize the extra flow, n ot the change in exhaust size, that really doesn't do much I don't think as 2" should flow really well, and even though its dropping .5", it still should be flowing more than enough to get a gain.
Something I just noticed This is the dyno run before installing headers. Note the timing at the bottom IT 30 This is the dyno run after installing headers. Note the timing at the bottom IT 26 I'm assuming IT is maximum advance over the rev range. Note all weather conditions in the second dyno should yeild higher hp eg. Cooler air and lower humidity So I have a feeling that 4 degrees over the rev range could be holding her back, to spite the fact it may only equate to 1 degree @ idle.
the problem is the cat-back as others have siad, going from 2.5" into a 2" cat-back not only creates a restriction, but causes turbulence. this turbulence breaks the nice flow that NA's need for it all to make power as for the dyno graph... AT = ambient temperature IT = intake temperature the problem exists when the intake temperature is much higer than the ambient temperature, as that creates false dyno figures. there is no problem between your graphs as they were on separate days (i assume) whre the ambient temps are different, and this has been reflected by the changes in intake temp also. at a minimum i would suggest to go back to a stock exhaust, or consider a 2.5" as others have said cheers, Warren
RE: the problem is the cat-back I recall reading somewhere that in order to make an exhaust for optimum flow, the exhaust size must decrease throughout the length of the exhaust (So 2.5 at headers, 2.5 at cat, then taper down over some distance to a 2.25 closer to the tips). The theory behind this being that as the exhaust gasses leave the chamber, into the headers the gas temperature is very high, as it progresses past the cat gas temperatures drop dramatically, so the gasses contract in size becoming more dense. Because the pipe decreases in diametre, the volume that the pipe can hold is less (If it were a greater volume the engine would need to "work harder" to push the gasses out the pipe). Any thoughts on this anybody?
If this theory is correct then increasing cat-back pipes to 2.5 inch and leaving the stocky mufflers on should produce more horsepower right? Not that this helps macman's problem.
well it apprears some of you may be right after getting the a/f of the dyno it clearly shows the car using a lot more fuel and the same power so I think as some of you have said time for a chip of sorts. I'm thinking 2.5 inch ss all the way and then a chip. you can see the a/f below.
Try and get your hands on a Apexi SAFC. No need for series 2, but the older model 5 button type. They are cheap and you can sort out your A/F mixtures. Tidy these up, along with your new headers and you should see results. As far as your exhaust diameter is concerned, I was under the belief that back pressure was essential in an NA.
yeah back pressure is essential and at the moment I have plenty So long as i keep all the same bends as the original exhaust that should be enough to keep plenty off back pressure, yet allow better flow. Here is a clearer image, what sort of numbers do other NA cars run for their a/f, higher or lower than mine?
i agree that you should get a safc will help you get the missing kw plus adds a little bit extra to the interior,cause i think they do look good:thumbsup:
