View Full Version : custom exhaust?

10-09-2010, 06:24 PM
Does anyone think that my compression ratio will change much by taking the stock muffler off and run a 2.5" straight exhaust. Also will it hurt the motor by just running the header only.

10-09-2010, 08:42 PM
The compression ratio will not change, that is static set when the engine is built. But the back pressure in the exhaust system will. less or very little back pressure will mean that the ecm will have to be adjusted.

10-09-2010, 11:29 PM
how would I be able to do that with the stock one...and is that just for the header or will I have to after adding the pipe.

10-09-2010, 11:58 PM
You would want to do it if you did a custom exhaust.

ECM Spy is what you need to do a TPS reset, so basically reset the ECM for the new pipe. The software is free to download and there are DIY threads on the forum to follow.

You do also need this cable to hook up to the bike.
ECM Cable $50 (http://www.americansportbike.com/shoponline/ccp0-prodshow/A9317.html)


10-10-2010, 01:58 AM
Ok now ? what would happen if I dont do this...and can harley do this for me by chance instead of havin to order a cable?

10-10-2010, 02:03 AM
Your bike will run better.

10-10-2010, 02:05 AM
ok it will run better but any internal damage until I can get a cable

10-10-2010, 02:10 AM
what exactly do I need to download from that site cause there is a lot of stuff on there

10-10-2010, 09:31 AM
just go on ebay and buy the ecmspy cable it will come with a disk with the program on it.

your bike will still run ok without it but u will get a lot of back firing on decel and loose alot of low end power

10-10-2010, 11:57 AM
oh ok but no harm done for now right thats all im wondering cause I got a lot of crap to get for it so it will be a couple weeks before I can get one.

10-26-2010, 07:04 AM
Header only can cause damage. Something about fresh air getting to close to the cylinder and causing ignition at wrong times or something. Straight pipes will be fine, but it'll aside from being too loud, it'll run like crap. You'll lose all your torque, the bike will struggle and limp along under ~3k rpms.

Without the ECMSpy tune, you can get away with either a high flow air filter, or high flow exhaust. When you run both on the stock tune, you'll be too lean (more air than fuel) and will misfire a little. Shouldn't cause damage, but I wouldn't risk it.

You'll want a muffler of some kind though. They don't just absorb sound, they tune the powerband in a way.

10-26-2010, 07:41 AM
I'm afraid you are setting yourself up for a poor running bike.
Given that you thought the exhaust had something to do with compression ratio, I don't think now is the time to jump into altering fuel maps. Not trying to be rude. The most important thing is having a bike that is happy that you enjoy riding. If you want to continue on the path to a super loud bike then learn as much as you can prior to taking any action. Not knowing what you are doing can severly shorten the life of the engine. If you've got millions of dollars to spare, then by all means.

But that's just my opinion.

Also be aware that an exhaust that loud will very likely annoy everyone within range and will cause hearing loss to you unless you wear really good earplugs.

10-28-2010, 12:58 AM
I recently put a straight pipe on my 12ss... It has a plate mid bend after it clamps onto the header, and although its louder than anything vie heard before, I don't lose low end torque like most people suspect I would. Is it because of this plate I mentioned within the pipe?

12-09-2010, 03:12 PM
Isnt ther a baffle you can put in the straight pipe that will still give you the sound and preformance