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HipMF

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Hmm, almost 4 months with no progress? Time to get back to work on this thing now that I'm done fooling around with the compact.

Did a couple piddly things last weekend. Got started on building a new exhaust this weekend.

Since the subframe has moved up 2", there's no need to do the old over-the-subframe, under-the-half-shaft trick anymore. The exhaust that was on the car was put together at the 11th hour, and I never really liked it much anyway. It was fine for the grandpa-stanced, 13" wheeled version of the car, but it's time for something new...

Maybe my google-fu is weak, but I haven't been able to find a video of a 4-cylinder car that has a "true dual" exhaust (ie the exhaust from half the engine's cylinders travels to the rear of the car in one pipe, while the other half travels in another pipe). Both V8s and inline-6s both seem to sound better with this type of setup, but I don't seem to recall ever seeing it applied to an inline 4.

So, in the interests of science, I've decided to try it for myself. Obviously, 4-cylinders tend to sound like crap in general, so I'm not expecting miracles here, but here's what I'm thinking: 4-bangers tend to have a fairly mellow tone in general, but when they do get raspy it tends to be extreme, and in a narrow rpm range (unless, of course, they're forced through some terrible fart-can exhaust which just sounds raspy and terrible all the time...). By splitting the exhaust in two, I'm hoping that each half will hit it's raspyness at a different rpm, thereby cutting the intensity in half, but prolonging it over a larger part of the rpm range. I'm also assuming that lengths of straight-pipe tend to resonate at a particular RPM, contributing to raspyness, so I'm trying to make sure every straight section of pipe is a unique length. The idea here isn't to get rid of the raspyness, but to spread it evenly across as wide an RPM range as possible.

So, here's what I have so far:

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The M42 is a good candidate for this experiment, because the stock exhaust is a 4-into-2-into-1 system. The stock header already has each pair of cylinders each exiting through 2 separate pipes, so that's where my work starts.

Even "true dual" systems seem to sound better with an "H" or "X" pipe, so I've included one at the location where the stock exhaust would merge from two into one. This will also be a handy spot to put the O2 sensor so that it gets an average reading from all 4 cylinders and doesn't obstruct flow through the pipe. I'm using 2x1.875" pipe, which is way too large for a stock M42, but gives me some future proofing for when I finally put a turbo on this thing, or rip it out and do something completely different...

The glasspacks that I'm using are super cheap and don't seem like they'll be very effective, so if it does end up sounding like crap, I'll replace those with something that has a greater muffling potential. I've also got a couple stainless MagnaFlow mufflers for the rear of the car that should help quiet things down and look cool to boot.

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That's looking nice! I am interested to hear what it sounds like. I have a good history with working on Honda 4 cylinders and always thought cheap exhaust made them sound horrific. Because there is such a huge aftermarket for them, everyone buys these cheap exhausts, and now the whole world associates the terrible 4 cylinder sounds with Hondas.

 A nice muffler and correct resonator and piping makes a world of a difference. You look to be on the right track to making something that sounds good. Im all ears :)

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I've always wanted to try this, looks awesome so far! I saw someone post about doing something similar on an e36 318is on BF.c a while back using a stock 328i exhaust and a Y-pipe after the o2 sensor. I managed to dig up the link, but unfortunately the video isn't available anymore. It sounded way better than stock with minimal rasp. Here's the thread, not much info now that the video is gone:

https://www.bimmerforums.com/forum/showthread.php?1872648-328i-Exhaust-on-a-318is-(-video-with-sound)&highlight=318is+dual+exhaust

 

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Made some more progress. Not as confident about the rear section from a sound perspective. I think the long-ish straight sections aren't a good thing, but i chose the most direct route, rather than adding unnecessary bends.

Still have some tweaking, then hangers and weld the mufflers on. Fits nice and tight to the car, so I'll have to put some thought into the hangers to keep it from rattling. I think it will be fine though.

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3 hours ago, Jdesign said:

Doesn't it normally exit out the left side of the car?

I do what I want!

But yes, I moved the fuel pump to the drivers side since the fuel lines run down that side of the car. So I moved the exhaust to the other side.

The eE21s that I've seen corner-weighed are also a tad light on the rear right corner.

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21 minutes ago, HipMF said:

I do what I want!

But yes, I moved the fuel pump to the drivers side since the fuel lines run down that side of the car. So I moved the exhaust to the other side.

The eE21s that I've seen corner-weighed are also a tad light on the rear right corner.

There is a meaning to your madness. I like it!

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I bought some glass packs from http://www.heartthrobexhaust.com/glasspacksandflowpacks.htm The shell is much thicker than el cheapo ones, but they were very resonably priced, just call to order.  I think I paid under 60$ shipped for a pair of small ones.  I would never buy Cherry bomb or Thrush after using these.  Made in  Litchfield Minnesota too.

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  • 1 month later...

Got the car back together enough (barely) to take a couple beat-runs down the road in front of the shop. Can confirm that the exhaust is not just loud, but also obnoxious. Still no floor in the trunk, and no back seat, so the exhaust might as well be plumbed right into the cabin. It's the kind of loud that you can feel, as opposed to just hearing it. Also still missing one of the side windows. That combined with the not-car-culture-friendly temperatures this weekend, stiffer suspension, manual steering and general fear of things falling apart or exploding made for quiet a visceral first-drive experience. I survived, nothing broke, but there are more things left to do than I have fingers to count them.

I thought I did a pretty good job bleeding the brakes, but they didn't work worth crap (try rev-matching your downshifts when the brake pedal goes straight to the floor. It doesn't work well, but it's worth a laugh...). Bled the front, which made little, if any, difference. Will have to try re-bleeding the rears next weekend. May have a leak somewhere? Who knows...

Body roll is still substantial, even though my spring rates are 2-3 times stiffer than stock.

Also can confirm that Hankook RS-4s are no match for the mighty torque of a tired M42 when the temps outside are near freezing...

All-in-all it was a good time. Much work left to do, but definitely excited to get this thing out to an autocross or ten this summer.

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The front is shortened strut tubes with Bilstein mk-I Golf inserts. This is a pretty well documented "mod" on the internets.

The rear is...... "custom". The subframe mounting points have been moved up about 2 inches so that the car can be lowered about the same amount without effing up the geometry. The rear on e21s is already a coil-over, but the stock dampers are too long, so for the time being I've replaced them with some cheap Bilstein coil-overs that are intended for circle-track midgets.

From what I've read, I think what I need is a "digressive" damper (ie a lot of low-speed damping, with less high-speed damping). This helps control body roll, but still allows the suspension to absorb bumps. I've converted the rear to 1/2" heim mounting top and bottom, so I can swap that out for any 'ol coilover damper that I feel like. The fronts I believe can be modified to be take-apart shocks. Bilstein shocks, internally, are all very similar. So, once you can take them apart, and have a way to recharge them with nitrogen after you put them back together, you can have them re-valved to whatever damping you want, provided you can find a competent shop to do the work. I feel like my spring rates are in the right ballpark, so I'm thinking it's the dampers that are failing to keep the roll in-check.

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Question of the day: Is my car over-heating, or is my temp guage being an a-hole?

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The temp guage in the car occasionally bounces around for no reason, but seeing it way above middle is still disconcerting.

Top radiator hose is plenty hot. Have spent much time bleeding with no change in results...

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Nevermind. Finally got the courage to just let 'er bake. Head temp went from ~200 to ~210. Temp near thermostat shot up to ~190 and the entire radiator got hot, as opposed to just the area around the top hose.

So, apparently the T-stat opened. Guage still displayed ~3/4, so apparently that's my new normal.

My brake lights were also on constantly, and I had to adjust the switch to get them to turn off, so, apparently somewhere between 33 and 35 years old is when e21 electrical systems start to shit the bed...?

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