Factory exhaust limitations.

[captaudi]

Happy Saturday,

What is the limiting factor on the factory exhaust? My current setup in a Vance and Hines SS2R, Hank Scott jet kit and 5 deg ignition advance. Bike runs absolutely awesome. My plan is the aviationfred formula of factory downpipes, Black Widow collector and Dominator mufflers. His setup will allow me to either mount the Krauser K2 bags that I have or a set of Hepco Becker Juniors. I have a set of factory downpipes and a factory collector coming from eBay. Do I need the Black Widow collector? or is the factory part not a restriction? I saw something about the aftermarket collector being of a questionable grade of stainless. If the factory part is not an issue I may bead blast it and use VHT or similar paint. And yes the header pipes will be polished. The plan for next winter after child support ends is either 1350 or 1380. Whatever I do needs to support that.

Inquiring minds want to know.

[fj1289]

My gut tells me the mufflers are the most restrictive part of the stock exhaust system.  A 4-1 collector is going to perform better up top than the stock collector - but stock collector probably does better down low where you spend most of your time. 

When you go with the big bore engine are you planning to do headwork?  If so - porting only?  Or porting and oversized valves? 

I would recommend you talk with JMR on here about benefits vs costs of head work.   Depends on what you want from the big bore - more torques and power everywhere?  Or a LOT more power up high while retaining stockish levels down low?

You already have a modded two-stroke, so I suspect you might want the bagged sport tourer to be more of the torque monster (that will still put a big grin on your face at higher rpm's too!). 

Long ways to get to: yes, I think your plan for the stock exhaust with aftermarket mufflers will suit your plans just fine!

Another option - see if an exhaust/muffler shop can make you a mid pipe to position your current muffler where you need in to clear the side bags?

[Pat Conlon]

Black Widow collector vs OEM? Fred's the guy for this.

My instincts tell me there would be not much of a difference power wise.
The advantage I see with the Black Widow is lighter weight and less thermal mass.
The weight is not as important as the thermal mass. The oem steel collector box gets hot and things melt down there without insulation.
The Black Widow also gets hot but has less mass to radiate heat. I imagine you could wrap a heat tape around those Black Widow pipes quite effectively (assuming the welds are ok with the trapped heat)
A tube collector with crossover takes up less volume of space than the oem steel box so, in theory, you should get better airflow under there with the Black Widow tubes.

I have a Swain coated (White Lightening) oem collector box and while the Swain coating helps insulate the radiating heat, my ABS chin fairing still has melted spots.
https://swaintech.com/race-coatings/race-coating-descriptions/white-lightning-exhaust-coatings/

I would think a thicker tape wrapped Black Widow collector would be better at keeping heat in the system than my Swain coated oem box.
Just a guess on my part....

All this assumes that the Black Widow is a durable quality part and positions the mufflers where you need them for your luggage.
For durability, it's hard to beat the oem steel box (rust aside) You will have more potential for cracked welds with the Black Widow tubes.

My 1380 is currently not set up for top end. I use stock cams, carbs and oem exhaust with Cobra slip on's.
My engine shines in the 2k-8k rpm range where I enjoy my street riding. The airflow on my stock 36mm Mikunis hold the power back above 8k. No worries for me, it's all about that wonderful 110 ft/lbs of torque instead of a top end horsepower rush. With some cams, 38 or 40mm Mikini TMR's and a 4 into 1 header my top end would wake up, but for me, my current 140hp is enough.

When you do decide to go with the big engine, stay the fuck away from those short skirt Wiseco pistons....don't get me started...

Cheers. Pat

[Millietant]

Which pistons and big bore kit do you recommend Pat ?

I'm thinking of going down a very similar route to you, engine-wise, with a project 1990 FJ that I bought earlier this year.

[Pat Conlon]

The short skirt Wisecos proved unstable, the oil rings did not seal.



The regular skirt Ross pistons are rock stable and better for the street.



The poor oil seal with the Wiseco's wasn't  due to the rings, both Ross and Wiseco used the same XC ring packs. I suspect it was the rocking of the short skirt piston in the long stroke of the FJ that was the culprit

As you see by the kits below, they are 12 : 1 compression...I didn't want that high of compression for an air cooled street engine running on Calif piss water 91 octane gas, ridden in the desert summer heat, so RPM Randy took the Ross pistons and shaved the crowns down to get a more forgivable 10.5 : 1 compression. Turned out to be a Good Move.

https://andrewsmotorsports.mybigcommerce.com/cylinder-kit-yamaha-fj-1412cc-84mm-ross-piston-cylinder-kit/

https://andrewsmotorsports.mybigcommerce.com/cylinder-kit-yamaha-fj-1350cc-ross-piston-yamaha-cylinder-kit-82mm/