SMR 511 top end upgrades

[Tom H]

Hi guys, I've got my 511 in for a top end rebuild thanks to a blown head gasket. While the head is off and being inspected to make sure it's not damaged, I'm having the guy look at a port and polish, and also the feasibility of boring it out a little.

Has anybody done this? Is it worth it?

Thanks

 

[Thrasher]

Make it a real 511 !

Zip-ty's done almost everything that can be done.... I think. I'd give them a call. There seems to be a conservative approach with them though. They only recommend thing that work... Someone just like you needs to push the envelope and report back with your bored out, polished 511 (or 550 !). OH YA!!

 

[Tom H]

Haha yeah that would be cool... not sure if it can handle being bored out that much. Im in Aus so I cant really get it out to Zip Ty... otherwise they'd be my first stop!

 

[Tom H]

Has nobody done this before?

 

[DErZ]

Its on my list to do when I take the head off next. HM racing down the road from me can do it and also use their Serdi machine to recut the valve seats.

Take a look at this http://www.supermotoforum.co.uk/bike-builds/77747-husqvarna-tc449-build-off.html he has had his TC449 ported and polished and states he has 60rwhp.

 

[Tinken]

I think the engine can be built up to 500cc, possibly more. I have played with the idea of machining a new cylinder. Not too sure the 6 speed can handle the power though, would have to be a 5 speed.

 

[Tom H]

DErZ, thanks for that. Once it's all done I'll do up a post on it. I'll probably have to run it back on the dyno afterwards anyway. I cut the airbox just like the TC box and fitted it with flyscreen to keep dirt out, but I've had it taped up until I can get some dyno time.

Oh wow, that's a lot of extra size. What do you mean by the 6 speed not handling the power? I've never considered anything like this before so I'm completely in the dark. Do you think it will shorten the life of the engine too? Is that why you haven't done it? I'm keen on more power while the top end is apart but I don't want to kill the poor thing!

Tinken, what is your opinion? Do you think port and polish should be the end of it, or bore it out a little? And if so, how big do you think is a good idea?

 

[Tinken]

Just have your shop axis machine your valve seats, no port/polish.

 

[Tom H]

Why's that? Is there no real gains from the port polish or you think it will make it more fragile? lol I have no idea!

 

[Tinken]

Why's that? Is there no real gains from the port polish or you think it will make it more fragile? lol I have no idea!

I just don't want you to have more hp than me.. :P jk
Choke point is at the valve. Porting/polish might gain 1%.

 

[Tom H]

Oh ok! So do you mean machine the valve seats for bigger valves? And no oversize bore?

 

[Tinken]

No.

 

[Tom H]

No oversize bore - and no larger valves? Then what does machining them do?

 

[Tinken]

It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Larger ports flow more fuel/air at higher RPM's but sacrifice torque at lower RPM's due to lower fuel/air velocity. A mirror finish of the port does not provide the increase that intuition suggests. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%.

The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A 300 - 400 Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports.

The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past, which develops a velocity profile (or gradient) across the duct. For surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this.

I'm actually whooped after a hard day at school so I won't go into wave dynamics, but, in the image below, you can see the short radius turn and then the top and bottom cut is where it needs to be re-machined, no where else.

 

[Tom H]

Wow! That's a lot of info. It makes sense though, so thanks! You're knowledge never ceases to amaze me!

 

[huskylove]

Not sure why this bike has so little power to be honest. It has a huge throttle body/intake tract. Maybe the exhaust valves or single outlet is restricting it?

I know the old 450/510's had dual header ports, maybe that is something to look into.

 

[Tinken]

BMW's motto has always been less about turning the earth on it's axis and more about electrically smooth power. It really doesn't matter how much horsepower these engines develop, its more about when. Let's be real, the only time I am going to use 61bhp@9300rpm is if I'm running from the cops. The 31bhp I make at 3500 rpm is what I really use.

 

[huskylove]

I am getting arm pump from holding my throttle open so long.......on the street! I have not even got to a kart track yet!

I actually think right now my next step is some additional weight reduction.... Try your earth x battery, lightweight forged supermoto wheels, tubeless, run a titanium shock spring (can we get those?). Im out of ideas beyond that.

 

[Tinken]

Earthx is good, change your exhaust.