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Post by southerner on Aug 20, 2014 22:37:28 GMT -5
Guys, i'd like to have a go at welding my own performance custom exhaust as much "by the book" as possible, the thing is my Justy came without any manuals and i can't seem to find info anywhere.. has anyone done the math about this ? or has the info (Valve diameter, opening point, duration, centerline) i need to calculate the header/exhaust ?
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Post by cvan on Oct 24, 2014 18:28:43 GMT -5
I was looking into this, there's Mag Flow (sp?) cherry bomb version in the relative shape of Justy muffler. I know you need enough back pressure to keep the torque up, but I don't think this engine needs fine tuned exhaust. Heard people with straight thru glass packs are quicker off the line but can't climb well compared to stock.
The stock muffler is HEAVY, it was super loud and when pulled a 3" x 8" hole was rusted out on top. I pop riveted on an old license plate and sealed with JB weld. It's now quiet like stock, but can't let go how heavy those things are. I am thinking of replacing with a restricted glass pack and make it fit, would drop 25 lbs off the car easily.
Took the spare, tools and passenger seat out (80 lbs?). It's much better off the line and you get a nice spot to put several bags of chicken/dog/horse food there instead
34 mpg, ECVT, GL
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Post by madmatt on Oct 25, 2014 0:14:56 GMT -5
Argh... Back pressure is NEVER a good thing... please folks stop spreading folk lore. Velocity is important, it helps to scavenge, but "back pressure" kills power. Big pipes kill velocity, slowing down the exit charge, somewhere, somebody said that the "drop in back pressure killed my bottom end. NO! the loss in velocity killed your bottom end. Take 2L motor and a 2" pipe, run a dyno, weld a washer on the end with a 1" hole. You're not going to get a better bottom end. PERIOD. Put a 4" pipe on... maybe it kill it. The difference is velocity, and the vacuum created after the pulse has passed. This in nicely put. www.dsmtuners.com/threads/exhaust-the-straight-scoop-on-backpressure.168578/Stop the spread of silliness. PLLLEEEASE
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Post by gearheadeh on Oct 25, 2014 10:12:05 GMT -5
Matt, You are Sooo right, love that link it is great!
Cvan, reducing weight is a great way to improve the performance and fuel economy of your car, When I had a classic Mini I took out the passenger seat and loved it. As far as the stock muffler being heavy I disagree, I have several stock 2 gen North American edition mufflers and they could not be lighter for a stock deal. They are round and I think from your description of your repair that yours is oval and not original.
As far as back pressure goes, When I converted my 1st gen to efi I swapped in a 2 inch pipe to the back, it ran like crap with no muffler and the only muffler I had was a stock one which had the same flanges to mount up to the 2 inch pipe. So when I put on the stock muffler just to get the car running to go to work with, it ran much better, more low end .. etc.
I think this is because the fuel curve set up from the factory can't handle the free flowing - no muffler exhaust and goes lean or something!
If I could hack into the stock ecu and recurve the fuel map for an open exhaust that would be the best for more power and bottom end!
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Post by Mato393 on Oct 26, 2014 12:48:22 GMT -5
I am thinking about build some stainless steel exhaust that looks like the oem one for my future project car... But I do not know how expensive will it be and how to make good locking manifold and muffler... And i do not have welder for stainless steel... Maybe I just make it from some standard steel.
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Post by indkid87 on Oct 26, 2014 14:08:01 GMT -5
You can weld stainless with a regular welder, but your welds won't be stainless. The front section of my exhaust is made from stainless milk pipe. I just made my own flanges.
-Dave
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Post by madmatt on Oct 26, 2014 21:24:10 GMT -5
Y The front section of my exhaust is made from stainless milk pipe. That has awesome written all over it!!!! And your from Wisconsin! (or at least live there...)
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Post by indkid87 on Oct 27, 2014 9:30:06 GMT -5
It worked pretty slick, nice heavy walled stainless tubing. Plus it was free, you've gotta work with what you've got (born and raised in the dairyland)
-Dave
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