85 Spree, test bed for mods

Diesel Spree · Post by **Diesel Spree** » Sat Sep 20, 2008 8:45 pm

go for the pipe

keithw · Post by **keithw** » Mon Sep 22, 2008 2:12 pm

I bolted on the pipe.

It slowed it down a bit on the bottom end but it is sweet from 20 to 30. The tach runs up to 10,000 rpm with no problem. I still have the shaved head and ported intake manifold. It is a little rich through the mid range so the needle might need lowered a little. It has a 70 main jet in it.

So far this has been what really makes a differance. Next is the ported exhaust. I've got a cylinder ready to go with the exhaust port raised a ring width and the exhaust passage opened up. The plan is to try the ported cylinder with the drilled stock muffler and the tuned pipe.

keithw

Post by **noiseguy** » Mon Sep 22, 2008 8:37 pm

Are you still running the stock pulley setup and belt?

keithw · Post by **keithw** » Mon Sep 22, 2008 11:13 pm

Yep, stock pulley and belt. I'm saving that till I get all I can out of the engine. The plan is to mod the pulley to allow the halves to come closer together and the belt ride higher. I'll make a set of spacers so I can adjust the pulley spacing to vary the ratio.

I just installed the ported cylinder and domed piston. The original piston is dished. So I'll have two things going on, the port mod and higher compression from the domed piston. I'll run it rich and putt around for a while to get the cylinder broken in.

keithw

keithw · Post by **keithw** » Wed Sep 24, 2008 3:35 pm

Reinstalled the stock exhaust and covered the hole to return it to totally stock. Still have the 70 main jet so it is a little rich. I'm not going to do official speed runs untill I get a few miles on it. It pulls strong up to 25mph where I back off. Feels like it has lots more to go. The current mods are ported intake manifold, shaved head, domed piston, raised exhaust port, ported exhaust passage in the cylinder.

I would love to get the peak of the acceleration curve above 3.5mph/sec. I'll feel better about a steaper drive ratio if it doesn't kill the low end acceleration. With it down around 2 it feels like a real dog.

keithw

Post by **noiseguy** » Wed Sep 24, 2008 8:48 pm

What are you using for data acquisition?

Also, you should read up on Express porting on this site. Spree and Express porting is similar:

http://www-staff.lboro.ac.uk/~elvpc/bik ... pics/NC50/

keithw · Post by **keithw** » Thu Sep 25, 2008 8:20 am

Thanks for the site. I'm using my Garmin 76s for data collection. I set the logging interval it 1 per second. After the runs I download the track into my computer. Using the logged times and positions I calculate speed and acceleration. I plot these out in the speed vs acceleration curves I've been posting. I normally do 4 to 6 runs and combine them in one plot. This makes the data denser and smooths things out a bit. I am using the same piece of country road for all the runs early in the morning. It isn't exactly flat so I am only using one direction. It is very slightly down hill so the numbers are a little optimistic but are consistent within the testing.

One of the last things I did before I retired was an engineering study of the 76s for use in testing like this. It is very good and I am comfortable with the results.

keithw

Post by **noiseguy** » Thu Sep 25, 2008 9:51 am

OK: I'm looking over his porting. Bore and stroke from Spree and Express are identical, so we can just talk window heights and have the same port durations. This Express is also a fixed ratio, and so has the same problems that the Spree does with not shifting.

Stock Spree exhaust is 25mm wide (chord) and 9mm tall. Stock Express is 19mm wide (chord) and 9mm tall.

He bumped the exhaust width to 23.5mm and the height to 13.5mm.

A stock late-80's Elite is 11mm tall (from memory) and has a yet wider port... I think if you duplicated this porting it would be a good start. I think that even his more aggressive porting would be fine. Longer exhaust durations should tend to concentrate power up top and might make it "peaky".

He moved up the boost ports as well (he changed the porting by raising the jug and then decking the top to maintain compression. I don't recall what the boost and transfer ports on the older Elite were.

He was running .75mm (0.030in) of piston to head clearance; shaving .020" should put you down around 0.025" clearance.

Exhaust outlet of 25mm, which is larger than the stock exhaust's 19mm outlet. Then, of course, he's running a tuned pipe. Interesting; the belly is 4" in diameter, which is closer to the tuned pipes that I built. He also tuned the whole pipe down to 7500 RPM, whereas mine was designed around 9000.

He also changed the reeds to a larger set; probably close to the stock vs. SB50 set for Spree.

This guy has some other software on his site. It looks like he used MOTO software to develop his portings and run simulations.

keithw · Post by **keithw** » Thu Sep 25, 2008 3:31 pm

It is interesting that he raised the jug 1.25 mm. That is in the ballpark of the ring width that is suggested for raising the exhaust port. So far I haven't messed with the intake ports at all. I raised the exhaust port but did not make it any wider. Too wide and you start eating rings. The cross section area of the exhaust passage is small and the walls of the casting are thin there. I'm not sure how much a wider port would help with the narrow passage.

The exhaust port timing on the Spree is 140 degrees as I recall. The normal used by about everyone is 180 degrees so the Spree is very conservative. I need to do the calculations and see how raising the port changes the timing. Not much point going more than 180.

keithw

keithw · Post by **keithw** » Thu Sep 25, 2008 3:52 pm

Ran through the calculator on the site above. Unless I messed it up it looks like the exhaust port on the Spree needs to be raised 6.5mm or about 1/4" to bring the timing to 180 degrees. That is quite a lot. I'll have to get out my degree wheel next time I have the head off of one.

keithw

Post by **noiseguy** » Thu Sep 25, 2008 6:30 pm

180 degrees is just 1/2 the way up the cylinder wall, right? Should be something like 19mm tall. And that's way too much to start with. 180 deg is race porting, I believe, which wouldn't be good for a scooter that needs broad tuning.

If you run the numbers, you should find that the Spree, at 9mm tall, is something like 110 deg duration, which is really short. It's been a long time since I looked at these numbers, but I remember thinking at the time that the porting stated in the service manual was nowhere close to what was actually on the scoot. In actuality the porting is smaller than what is written.

slaughter83 · Post by **slaughter83** » Thu Sep 25, 2008 9:00 pm

could u post some pics on that exhaust porting. i bet it'd help with the stock muffler with the baffles drilled. thanks

Kenny_McCormic · Post by **Kenny_McCormic** » Thu Sep 25, 2008 9:31 pm

slaughter83 wrote:could u post some pics on that exhaust porting. i bet it'd help with the stock muffler with the baffles drilled. thanks

If you need help with such a mod you shouldn't attempt it.

keithw · Post by **keithw** » Thu Sep 25, 2008 11:53 pm

I could post some pictures but the best thing to do would be to read the "two stroke tuners handbook" by Jennings. It is in the tech documents section. He is better at explaining it than I would be. Everything you need to know is there.

I'm building another tuned pipe based on the Jennings book. Decided to try the outlet on the side of the center section rather than the end. Hope to get out and pick up a lawn mower muffler for it tomorrow. Once I get it together I'll post a picture. The side outlet is supposed to be quieter with no loss in power. It will clear the side panels and the center stand. Something my last one did not do.

keithw

Post by **noiseguy** » Fri Sep 26, 2008 10:06 am

I've seen side outlets on some Goped-type motors and wondered about that. I actually like mine louder.

I never had problems with clearing the side panels, but the center stand was resting on the pipe.