Bigger header pipe  By  rd400racer (Read 2,817 times)

If Alleyoop couldn't find one, they MUST be scarce! And, I think a bigger header pipe might be FAR more critical to performance than most of us think... I was going to start a new thread about this, but right here is a good place to get into it.

While my own Xingyue Eagle (same generic 150 Chinese scoot as your Jonway) is apart for brake repairs, I decided to replace the exhaust system as it is pretty much "toast" after 5 seasons. When I pulled the header off, I could barely believe what I saw. The EXHAUST PORT on my engine measures 1" in diameter. The factory header measures a scant 5/8" inside diameter! That means the raw exhaust blasts out of the port right into a header a full 1/4" SMALLER than the port!!!

It's one of the WORST design flaws I've seen in a factory engine. It's like Gentle Ben wearing Winnie the Pooh's undies... It's like feeding Grandpa a cheese pizza when he's been constipated for a week... It's like running a marathon with a clothespin on your nose, and a sock stuffed in your mouth... It's a crime against Pandas... LOL! Anyway, you don't need an engineering degree to see that our engines' exhausts are choked off right at the head. You can gut your muffler, add a free-flowing muffler, run a straight-pipe... No matter what, you're defeated before you begin, RIGHT AT THE HEAD ITSELF.

I have a couple of muffler setups I've acquired over the years, along with the stocker. To determine how "free-flowing" a system is, I figure the average human must have at least 150cc of "displacement" in our lungs... So I blow hard into the exhaust and see how much resistance I feel. Crude, but at least a minor test. I see little difference between the "restrictive" stock muffs, and high-flow units. Of course, new, clean fresh ones taste better...

I found on eBay, a used set of used John Deere generator headers which are a perfect match to my head. They have a "shank" that went into the Deere head which must be cut off, but the flange is a perfect fit to the head/exhaust-port... A full 1" INSIDE DIAMETER, 1 1/8" outside diameter. I also found an exhaust-parts shop on eBay who has 1 1/8" INSIDE DIAMETER aluminized flex-exhaust tubing for use on implements, generators, etc. A piece of THAT will connect my new header "stub" to one of my mufflers.

In order to make the tubing run between the engine, and the frame, I cut a pie-wedge slice in the header, and bent it tight enough to match the factory header and a local muffler shop is welding the cut back up for me as I write this. I'll wrap the new flex-pipe in heat-wrap to keep the heat down where it passes under the engine. It's tempting to just run the new header in a gentle curve UNDER the frame, BUT that makes it the lowest part of the scooter. One hit on a speed-bump and it would likely break the cylinder and head right off the engine block. The center-stand boss protects the factory header from impact, so I think it's wise to emulate the routing of the factory header, even though it requires some fairly precise fitting.

I suspect this phenomenon of the factory header being WAY smaller than the exhaust port causes no end of problems... Many riders have major issues with carb-tuning/air-filter selection, too-rich, too lean... some scoots run very hot... This small header syndrome may be a root cause of MANY of the gripes we have with these Chinese 150's. I'm no expert, but past motorcycle experience has shown me that ANY problem between the air-filter and the muffler, can adversely affect the whole enchalada.

It seems to me that any improved muffler mounted after the teensy head-pipe is pretty much wasted since the obstruction is right at the head, NOT back at the muff.

Probably one of the pricey upgraded exhaust systems does include a full-diameter header, but I'd surely have to see a measurement before I'd spend serious money on one. Making up your own header isn't all THAT hard, and may be the single most effective performance-enhancer available to a stock (or modded) GY6 150. I'm anxious to get mine running and find out!

I simply would never have thought about a factory header on a 150cc scooter being sized about right for a 25cc weed-wacker. Until I saw it for myself!!!

I'll post any results I encounter.

Leo (helping the little scooter breathe) in Texas

Duh... I never thought about buggies, karts, ATV's... OF COURSE! My scooter head exhaust port is 1", so yup... The one-incher is optimal.

I think when we are working on our scooter exhaust systems, we need to check out our 4-wheel GY6 pals, and see what they use and where they get the parts!

THANKS for the heads-up!

Leo

My Echarm header is larger than a GY6 as a muffler for a 250 I had to bore out the adapter . The bonus is it has a bung hole for an o2 sensor if you want to go with EFI