The_Pipefather

iTrader: (5)

My exhaust is 2.25". Regardless, I am going to do a simple test with a mityvac pump to see when the wastegate starts opening. If that isn't enough, I want to hook up a string pot or a modified TPS to my data acq. and get a relationship of boost vs. actuator rod movement. That should help narrow down the cause of the slow spool: exhaust restriction or improperly set wastegate.



Which piping? Charge or exhaust? I am taking boost signal off of the compressor right now. Can you point me to more info about this?


Thanks, wouldn't have been possible without your help.


There is no dropoff? In fact there is creep I would imagine.


Revving to 7000. I am working on getting a constant AFR through the MLV VE analyzer. Will post a 4th gear WOT log and then it will be easy to see this.

Not sure since I clocked the turbo and disturbed the wastegate mounting, so I will hook up the mityvac pump and test this. The leakage angle is intriguing. Can you explain a little bit please.


Appreciate everyone's help in ironing all the bugs out.

AbeFM

iTrader: (3)

http://abefm.smugmug.com/gallery/116...54351231_aiCXV pics, a little explination. But, at low flow, the intercooler doesn't present much restriction. At high flow, there is a restriction in all those bends and the intercooler itself.

Take the signal at the turbo, it's constant boost there, minus a varying number across the IC set up. Take it at the manifold, and the wastegate stays shut even when the piping is at 22 psi, overspinning the turbo, overheating the air. Take it right ahead of the throttle plates, and the manifold will always see the same pressure anytime the turbo is capable of supplying it, and you vary what the motor sees with the throttel.

rb26dett

Nicely said Abe. I have a partly finished write up if you want. PM me for a link if interested.

Thinking about it again, leakage probably wouldn't do what you have in your logs. It would just push the knee point to the right, whereas creep does exactly what you show.

2.25" for the exhaust can't be much of an issue down low where there is stuff all flow, but it could hurt up top. If it's really bad I guess you could still see some improvement in bottom end spool by fixing it.

Fred.

AbeFM

iTrader: (3)

Well, if you want to stop messing around and find out what's going on - esp since I had the 2.25 ex and when I went to 3 it was night and day... Try this:

Pick a day you hate all your neighbors (a turbo quiets it down some, so it won't be that bad) and break the exhaust at the bottom of the downpipe - either leave the ex hanging there or remove it, but let the gas leak out. Drive around the block (I suggest doing this where it's not crowded, or simply wait till the car is warmed up to make the break.

Then you'll know what you're missing. If you really like it, get a dump pipe. More likely, build a 3" exhaust. And just live with the late spool, I did for over a year.

devin mac

iTrader: (2)

bah, all i did was send you something that you never got to put on your car ;-)

rb26dett

A 3" exhaust is overkill on even a 500+ hp engine. 2" is good for 150+ 2.25 more than 200 which is probably where he is on a b6t with 8psi. I've gotta ask Abe, did your 2.25 use some bodgy baffled-to-hell mufflers and a LOT of particularly sharp edged crush bends?

I know a guy making 400whp on a 2.5" system from a 2.5 litre v6 on 14psi, you just can't tell me that the size matters that much without backing it up with some context and physics.

AbeFM

iTrader: (3)

Here in a country where we don't make the rest of the world choke on our polution (ha!) the OEM exhaust has 2.25 diameter, with muffeler, resonator, catalytic converter, etc etc.

Presumably he didn't make a 2.25" system custom, he's referring to the OEM exhaust. I like 2.5", and it's likely what I would have made (2.75 without batting an eye)....

But... 3" is cheap. That's a big plus. More to the point, the volume of the muffler you use determines how quiet it is. And I'd read a lot of testing, and they said for the best reduction in noise, a bigger muffler is better. Since I wanted a straight through system, I had to go to 3".

Taking out the bends... will be where your gains are. Did I need 3" for performance? No. I went the 3" route because it was the best way to keep from waking up the whole neighborhood when I drive, and from getting eyed by cops, and to have the girlfriend actually WANT to ride in my car when we go somewhere....

rb26dett

My mates B6 NA mx5 had an oem 2" on it. it should still be suitable for spool purposes, if not top end, with the exception of the rear muffler, then again, US spec cars could be wildly different to his jap or NZ one.

http://i238.photobucket.com/albums/f...remounted2.jpg

The_Pipefather

iTrader: (5)

This is definitely a point for discussion: i have read here about people who went to a 2.5" or a 3" from an OEM exhaust (mine isnt OEM though, its levnubhin's old ebay exhaust, plus I don't have a cat) and noticed improved spool.

This is counter-intuitive because the smaller exhaust shouldn't hurt in the low end. Yet it seems to. Why is this?

rb26dett

The OEM rear muffler is probably pretty bad, that could easily be why, combined with even more hard core cat converters in some parts of the states it could make a big difference. The exhaust on my mates early car would be fine up to some reasonable power (enough to take it from slow to acceptable) because it is all straight through.

ZX-Tex

iTrader: (15)

I saw this when I went from the stock exhaust to a custom 2.5" with a metallic cat and straight through resonator and muffler. Changing nothing else, it made an immediately noticeable difference on a BEGI-S with a 2560 only running at 6-7 psi. I was smiling as I drove away from the exhaust shop with the new system in place.

AbeFM

iTrader: (3)

In some kits, with the 99-00 2 cat cars, there's actually a cat between the motor and the turbo - sapping all that energy!

But more likely, the further along cat is the problem - turbos would on differential pressure, a cat after the turbo ensures that the effective 'barometric' pressure is quite high. In a steady state things aren't that bad, but you need a high force to overcome the rotational inertia of the turbo.

I bet a 1.5" STRAIGHT through pipe would be better than a 2.5" pipe or even a 3" (if you could find one) that meets the worlds' strictest noise and pollution laws. And remember, a car that's NA needs a lot more muffler and resonator on it than a turbo one, so an NA exhaust is much more restrictive.

Anyway, trumping all this: Go for a ride with the exhaust off. If it doesn't make a difference, we're barking up the wrong tree. :-)