"JeffFurbs" (jefffurbs)
05/29/2014 at 20:29 • Filed to: None
1
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"JeffFurbs" (jefffurbs)
05/29/2014 at 20:29 • Filed to: None | 1
| 14 |
So Oppo, just yesterday I had my exhaust replaced from the downpipe back on my 04 WRX. I found a CL ad for an 06 STI turbo back exhaust for 250. My situation was I had a crack in my catalytic converter (after the midpipe) and on top of that a lot of New England rust keeping everything "nice" and "snug". So anyways, now that the new exhaust is on I've noticed that high rpm shifts between 2nd gear and 3rd are no longer as jerky. By that I mean, as soon as I put the clutch in to up shift my whole car would bog down noticeably (like someone pushing it backwards) until I got back on the gas hard in 3rd. More rambling and some theories ahead...
Now when I shift in high rpm's (when the turbo is spooled) there is not as much bog it seems like. It feels incredibly more smooth. It may be because I don't often really go nuts with my RPM's and shifting. I may be just feeling a placebo affect because I except things to be better. Yet this feels different. It feels clean and smooth like how I envision a newer car to act (i've never had a new car).
So my theories as to why all of a sudden everything feels better. These are probably wrong which is why I'm posting this ramble. I like learning about things that confuse me and I figure that's where you guys come in.
1) There is no longer a bottleneck after the downpipe- on the wrx exhaust the downpipe is 2.5 inches then turns into 2.25 inches at the midpipe and stays that way all the way back. The STI exhaust however is 2.5 inches from the downpipe all the way back. Theory is that the turbo can breath a little better and is not getting forced so much
2) My Catalytic converter had a huge crack in it. Exhaust wasn't flowing cleanly through- This one I'm pretty sure has nothing to do with it but who knows.
3) I was told by the shop that put the exhaust on that my old Catalytic converter was an aftermarket one. So judging by the way that the previous owners took care of the car (lot of little neglect here and there) I'm guessing there was not a lot of money spent on upkeep. If the OEM CAT went I bet they did not replace it with a high quality one. So assuming I had a crappy aftermarket CAT on there I'm guessing that would inhibit good air flow.
So I'm probably wrong but would love an explanation as to what's going on. Hopefully I'm not just imagining things. Thanks for the lessons!
GhostZ
> JeffFurbs
05/29/2014 at 20:38 |
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Something something backpressure something that an engineer knows more than I do.
Brian, The Life of
> JeffFurbs
05/29/2014 at 20:39 |
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Beautiful '55 Fairlane! Here's my son's sedan:
RamblinRover Luxury-Yacht
> JeffFurbs
05/29/2014 at 20:48 |
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Broadly speaking your exhaust volume increased by about a quarter just going 2.25 -> 2.5. Which isn't nothing, but it's also possible you really tweaked some of the dynamics simply by altering what standing waves were possible in your exhaust. If there was a bottleneck, that would tend to form a wave chamber much shorter than going 2.5 all the way to the cat - which may mean you hit resonance at lower revs. It's also possible to likely that with the larger size in pipe comes a disproportionately larger size in another component in the system. Finally, if your cat was cracked, it may very well have been clogged first, or even could have become more clogged through your exhaust passing through the crack at low Rs and not evenly heating the element, causing it to be able to choke up. If you have a lot of area, but a rough edged shape, you pass more gas at low speed through it, but the drag increases phenomenally as speed increases - at which point the rest of your cat may not have been up to it. As soon as you'd hit sonic ranges through the crack, that's all she wrote.. until the cat heated up so much it opened up. Maybe.
IOW: maybe the cat, possibly any number of things or combination thereof.
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JeffFurbs
> Brian, The Life of
05/29/2014 at 20:48 |
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You have a lucky son! Or at least one with good taste.
I snapped that at my girlfriend's extended family's cookout two weekends ago. Those cars are gorgeous. In all honesty I thought it was a bel air at first
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JeffFurbs
> GhostZ
05/29/2014 at 20:49 |
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Well at least my theories don't seem so crack pipe after all!
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JeffFurbs
> RamblinRover Luxury-Yacht
05/29/2014 at 20:55 |
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So there's a good chance I'm not crazy or imaging things?
I believe I understand that pretty well. I never realized how complicated exhaust systems were until I started reading up on if I could make the swap to begin with and what the ramifications were. I like the explanation as to why it probably could've been cracked in the first place. Especially if it was a cheap aftermarket exhaust because everything I've read says stay away from those due to a multitude of issues.
I apprecaite the information!
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RamblinRover Luxury-Yacht
> JeffFurbs
05/29/2014 at 21:00 |
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I'm mostly spitballing, but past "bigger is almost always better", exhausts are devilishly tricky things in their impacts. I forgot in my discussion that the chokepoint was after the turbo, which means issues with standing wave frequency/etc. are less likely, but overall flow is more so - and with it being a turbo, any choking is bad, bad, bad.
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JeffFurbs
> RamblinRover Luxury-Yacht
05/29/2014 at 21:04 |
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I can see that now just by driving the car. I'm blown away. It's not the biggest difference in the world but it just makes the car feel healthier. Exhausts, I think, are magic.
Sidenote: I'd love to get a bigger downpipe (and up pipe) but what's involved with that seems scary (albeit better) and also out of my budget haha
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RamblinRover Luxury-Yacht
> JeffFurbs
05/29/2014 at 21:08 |
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I've got an excellent textbook around here somewhere on internal combustion engines that goes into depth on inlet runner and exhaust tuning. (Took a class on 'em.) I'm definitely going to have to make use of it for my hot rod because the exhaust's going to be a completely fresh slate - V8 instead of I6 with no shared routing or anything.
camaroboy68ss
> Brian, The Life of
05/29/2014 at 21:21 |
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Very kool, my grandfathers first car was a 55 Victoria hardtop. need to scan the pictures of it.
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JeffFurbs
> RamblinRover Luxury-Yacht
05/29/2014 at 21:31 |
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picture of the hot rod?
That's awesome man! That's got to be an interesting book. I was a psych major so my knowledge of cars is non existence. I do love reading up on things when I have random thoughts but putting things into practice is lost on me
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RamblinRover Luxury-Yacht
> JeffFurbs
05/29/2014 at 21:36 |
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'63 Ranchero, that in this picture I'm test-fitting a '60 grille and '71-72 Mustang front bumper to. To the right is the Jaguar rear suspension unit I'll be using (from an XJS).
Here's one like it being made at the San Jose/Malpitas Ford plant:
And rear (before I took the engine out of the back, just after I got it):
I've got a Rover 4.2 and Super T-10 four-speed to put in it.
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JeffFurbs
> RamblinRover Luxury-Yacht
05/29/2014 at 21:52 |
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Dude that is cool! I can't wait to see the finished project.
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JeffFurbs
> Brian, The Life of
05/29/2014 at 21:55 |
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also weird coincidence, my roommate came home with this today. Any relation haha?