I'm in the market for a new exhaust for my mini. I currently have a highly modified 1380 running stage 2 maniflow LCB extractors and single box RC 40. I seem to have some crazy pressure coming out of the exhaust at idle. Plus a typical fart sounding exhaust note. What exhaust would be recommended? I just see the performance of the exhaust being that great if there's a large amount of pressure coming out of the muffler which can be felt a meter or a meter and half back from the tip.

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If its yours, customize it !

Firstly, it is normal for a bigbore mini with a decent cam and exhaust system to have large pulsations out of the exhaust at idle. It isn't a a modern efi motor running on bugger all throttle and fuel drops at idle.

I run a 2" system on my 1360, specs are in my sig below. 2" OD pipe fits straight over a Maniflow med bore LCB) with a 2" `turbo' diagonal pipe straight through muffler.
A while back I fitted a 2" hot dog resonator in the tunnel in front of it. That reduced it's bark without hurting its bite. So, is more Mr Plod friendly.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Okay so I was on the right track. I was wanting this one but they are out of stock. http://www.minisport.com/mini-parts/exh ... e-box.html

Minispares have them but they are out of stock of 8.4 alloy calipers which I need. Just my luck

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If its yours, customize it !

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No need to go that far and get Mini stuff, I went to Parramatta Exhausts, bought a 2" muffler, 2 bent pipes [30°]and some U-bolts. An hour or so later it was all piped up and hung.
[edit] It uses std Cooper S brackets and mounts.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hmm yeah maybe I'll just see what the exhaust shop can do

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If its yours, customize it !

I recently had a good scout around for exhausts - talked to a few of the dons down south, Swiftune and Maniflow in UK and local performance exhaust fabricator. Result:

Don't use RCM (reverse cone megaphone) on road car (Nick Swift) - increases mid-range torque but too noisy
ID of 1.75 inch OK for most engines, but 1380s+ can use 2 inch
Finish end of exhaust just shy of rear bumper - get some extraction effect from vortex behind car (!!!??) but too short and you'll gas yourself
Get better dispersal behind car with side exit than centre exit - less fumes in cabin
Twin box system (hot-dog with perforated - but not the old 'cheese grater' raised perforations - core and straight through oval box muffler widely recommended (RC40/Maniflow twin box)
Build your own with optional hotdog and oval Lukey Turbo muffler
Vizard rates Maniflow and another american system (not available here)
Some say Mini engine very sensitive to back pressure - need some for big overlap cams to help trapping - others say go for lowest BP possible within noise limits. I don't know.

For my money (and it was significantly cheaper to buy from Minisport UK) the Maniflow 2" twin-box side exit got the nod -plenty loud enough but haven't had it on the road yet - partnered with my Brownrigg headers makes a sweet growl with no mosquito buzz.
Looks good and just a bit lairy - 2.5" chromed tail pipe, but then I was never that fussed about concourse standard - run 'em scruffy and every damn day! They're not museum pieces....

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Min - 1970 MkII S, 119hp Dave Anton 1380, SH Engineering belt drive, 1.5 rollers, 123Tune ignition, 48 DCO SP Weber, HP Headers, MSD, Maniflow ex. Swiftune SC/CR 3.7 + ATB, all KAD front, antiroll bars and gas shocks, 6 inch Minilites with Dunlop Sports

I would really like to see something that explained why back pressure is desirable. I'd also like to see it quantified more accurately than "a little bit" or "not too much". Not aimed at you cranky, you even said in your post that you weren't sure and had been told.

I have a suspicion that people are referring to the positive results of back pressure when they are actually finding results through resonance tuning and reflected pressure waves. Unlike back pressure (at least as far as I'm aware), these have measurable and predictable results, and can be calculated through complex algorithms.

I now have a `cheese grater' hotdog muffler in the front pipe to reduce the `bark'. They work fine IF the perforations point to the rear, I have noticed no power loss. But if put round the wrong way you will get significantly reduced flow.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Good point! My mistake Dr.
P

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Min - 1970 MkII S, 119hp Dave Anton 1380, SH Engineering belt drive, 1.5 rollers, 123Tune ignition, 48 DCO SP Weber, HP Headers, MSD, Maniflow ex. Swiftune SC/CR 3.7 + ATB, all KAD front, antiroll bars and gas shocks, 6 inch Minilites with Dunlop Sports