Impossible to beat stock derestricted exhaust on low end

[bendover]

Attached is a dyno chart of piaggio AC engine with 70cc polini sport. Stock exhaust in chart is restricted*.

Oftentimes an "aftermarket exhaust" is considered mandatory for tuning, or at least first upgrade. Sometimes even full expansion chamber exhausts. I say stock derestricted exhaust will fit very many, if not most, much better than aftermarket exhausts.






If one would want a stealhy but nice off-the-line accelerating scooter, you would not change your exhaust from stock. Right?

Why?
Even in restricted form, it would be the best choice above all other tested exhausts. Derestricted it would outperform other exhaust even more. Even if you change rollers and clutch springs, you would have to tune variator to be at > 6800 rpm (!) to be able to get more power than the stock exhaust even in restricted form. Derestricted you get 5+ hp at 5500 rpm with stock derestricted, while you need 6800+ rpm for same power with leovince zx. As an added bonus, you can keep your stock variator, stock rollers and stock clutch.

Bottom line:
Below ~6500 rpm you will ALWAYS have more power with stock exhaust - and substantially so if it is derestricted. In other words - to gain power from aftermarket exhaust, you MUST tune variator to > 6500 rpm, and SHOULD tune it to > 8000 rpm depending on exhaust. If you don't, you LOSE power, in addition to reliability, stealth and money. In addition you SHOULD tune clutch to engage a lot later than stock, if you don't, upgrading will make you lose off-the-line acceleration and you will be behind for many seconds, ie. very many meters/yards before catching up. This is a classic problem - "I bought all this stuff, now I take off like a slug.", and after tuning variator and clutch, "Now I take off ok, but rpm and noise is insane!".


This is why derestricted exhaust will fit very many, if not most, much better than aftermarket exhausts.
 

Yes?



* - "Original exhaust" is the stock RESTRICTED according to the source, pedoparts.

[krylon80]

i agree that the derestricted stock exhaust has the best low-end. not looking at any charts or numbers, just speaking from experience.

[spaz12]

If you live in a trailer park full of old people that have their hearing aids turned up so far that they can hear Hank and Mildred doing the horizontal shuffle, then a stock pipe would be great. Heck, you can probably even do wheelies and not piss off the old geezers. Quiet/stealthy would be the only reason imo to keep a stock pipe on a 2 stroke.
Myself, I'll tune the cvt to work within the powerband of the pipe and blow off a stock pipe every day of the week. That's the beauty of the cvt; they are so tune-able.

[190mech]

I agree spaz12!A tuned pipe can be as quiet as stock mufflers,,look at the old Penton/KTM enduro bikes..I spent many miles trying to keep up with them only to hear a woosh of air,then they are gone..They had a full tapered head pipe expansion chamber grafted to a large but compact gas reversion muffler,too bad aftermarket pipe folks forgot about them...

[90GTVert]

A lot of people want speed. If you want speed, you usually need both power and RPM. Tuned pipes win by a landslide there. Some CVT work to make use of the greater output will have the scoot with the tuned pipe leaving the stock piped scoot far behind off the line.

If your goal is not to tune and to have max reliability though, then just leave it all alone. Ride it and maintain it.

Sept 14, 2017 14:35:53 GMT -5 bendover said:

Bottom line:
Below ~6500 rpm you will ALWAYS have more power with stock exhaust - and substantially so if it is derestricted.

I've gotta argue false to the "ALWAYS" part. Maybe the Piggy exhaust is well designed and is hard to beat, but that's not always the case. My old 96cc Minarelli powered Keeway Venus would lift the wheel around 4000-4500RPM with a Phongeer exhaust and pull much harder than with the stock pipe all the way to 9000RPM. No way you'd try both on that scoot and want the stock exhaust unless a few dB were the deciding factor or you didn't like the mount setup. Superior in every way as far as performance, but the fit wasn't as good and it wasn't as quiet at times. Actually, it was 5dB louder at idle, but 3dB quieter WOT.



Quick vid of the Venus. Felt pretty good at low speed to me.

[lostforawhile]

I have a 4t but even I know that a blanket statement that factory over aftermarket isn't true in every situation. People have been tuning 2T stuff for decades, and there is a huge database of information out there, and many good products

[bendover]

90GTVert That is interesting indeed. Maybe some scoots have better matched stock exhausts. I run my 70cc aerox (minarelli horizontal lc) with stock derestricted, I have tried leovince zx-r. Leovince is more power for sure, but bogs for a second at takeoff and is ~92kph instead of ~82kph. So I guess we can conclude that yamaha/mbk put a better matched stock exhaust than keeway, and that "stock exhaust" is not automatically good as I believed. For aerox though, it rips.

**Follow up question**: The piaggio zip I have is a catalyzed version. Anyone have experience derestricting these exhausts? I was told that the exhausts suck even de-restricted because of cat

[ThaiGyro]

There are many good points here...all put together, make a good arguement. Stock exhausts vary from country to country, depending on environmental compliance.

There is no OEM exhaust for any 2T that can cover the entire performance envelope. If you like bottom end...yes! Mid range pipes exist...most "street" or "mild" are sort of that. Top end? most are quite BS...only because they must come as a package.

If you really begin to understand 2 stroke technology...you will know that the engineering design and tuning comes as a synergistic combination. You cannot focus on fuel or ignition or exhaust or compression or whatever by itself...they are all very related! More so than a 4 stroke, by long measures. More power as well.

[repherence2]

YMS v8 black with plastic heat shield works pretty well. Not that loud, but it's got some bottom end power and some power up top. it works on 47mm bores and 54mm bores as well. they look fairly stock as well.

[honda4life]

The peace sounded the best to me.
They should have called it the "disturbing the peace" pipe...
Hahaha!