GTS 250 Project Vespa 09/2011

[Micah / AF1 Racing]

GTS 250 Project Vespa.

As anyone who reads this little forum knows I have a little Budget Project Vespa 250 GTS in for a motor job due to a massive overheat.

I decided to take the cylinder head on myself, decking was required at .35mm warpage. Personally I think a new head was in order but for the life of me could not find a working 250-300cc cylinder kit in the USA for sale to me from Piaggio. he SAME head is used on like a dozen or maybe a couple of dozen different models of 125-300cc Piaggio/Vespa/Aprilia motors.

Here is a good place to post some of these pics. Here the bike is seen as it came in, running, but sure as hell not right! 140 pis compression (with a decompressor, hmmm) is very healthy, but coolant shooting out of the exhaust pipe is not good.

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171112&d=1316486326

Wth 30 psi of pressure in the coolant expansion tank, the blown head-gasket was pretty obvious.

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171113&d=1316486347

Here is the piston, crap quality pic, just easy to do in a hurry with the phone.

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171114&stc=1&thumb=1&d=1316486377

So, does this not appear to be a typical Aprilia style removable flywheel weight? Looks almost like a dead ringer for what is on the RSVR/Tuono of recent vintage. Imagine the difference a loss of 2lbs rotating mass would make on a 17bhp scooter engine? This is a case where I can see the lighter flywheel being a really exciting concept.


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171117&d=1316486447


This is a look at the stock combustion chamber and ports to a lesser extent, you can see from the burn marks the massive size of the 72mm piston compared to the 50 or so mm "valve bowl"

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171118&d=1316486471


The micro sized exhaust valves have a large volume of spent gases to deal with quickly, this is not the right porting shape for that, this is the reason that a pipe on a Vespa makes little difference in power, they work, but 1-2 bhp gain are not impressive due to flow limitations of the stock head. This is why the Malossi V4 head makes so much sense!



http://www.apriliaforum.com/forums/attachment.php?attachmentid=171126&d=1316486771


Here are the stock valves compared to the older stock 36mm exhaust valve of a Rotax V990 in the background. The Vespa valves are long and stable, I will give them that. I do like how they did the face area of the intakes with the relieved stems in a critical airflow location.



http://www.apriliaforum.com/forums/attachment.php?attachmentid=171127&d=1316486810



Here is what I decided to do to it...much more detail in my "shop" thread.
http://www.apriliaforum.com/forums/attachment.php?attachmentid=171128&d=1316487443


This is post porting, I figured really, this motor is so starved for air at higher engine speed just simple traditional porting for big "flow" was the way to go, velocity is not a problem in these little ports with a big ass piston pulling real hard on them.

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171129&d=1316487462



Once again, velocity is not a big problem on these ports due to massively being undersized in terms of valve area and valve pocket size.


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171133&d=1316487557


This is the intake, man pictures really show every flaw the naked eye trains your brain to forget!

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171134&d=1316487577

Directions for the future. Thoughts, ideas, scheming...it keep me up at night...

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171148&d=1316488182



Exhaust valves open, I love taking pics this way, need to get some red led flexlights for doing the exhaust ports!
http://www.apriliaforum.com/forums/attachment.php?attachmentid=171145&d=1316487981


Intake valves open at full cam lift, if the piston were not 20mm larger than the area we normally think of as the "combustion chamber" this would look so bitchin:

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171147&d=1316488055


It will be fun to see how this project ends up, stock pipe and all, the bike is only really modded with removal of stock parts in the airbox (works well if you have one of these) so adding a little compression and hopefully the ability to flow and trap more air and fuel! We shall see, it is just as likely a null gain or even a loss, you only learn these things by trying what you feel is right?

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171146&d=1316488028

I figure more to come, maybe a thread for each Vespa getting modded coming though the shop with real go fast goodies, they are amazing well done machines with the ability to learn and adapt to mods pretty well it seems. As power get much above 18 brake on my dyno bigger injector and a fuel programmer will be required!

Please feel free to post and add pics or thoughts of your own, trying to have fun again working on these little machines!

[Micah / AF1 Racing]

Well, in the end all that porting was worth it! The motor is definitely air starved at rpms over half of redline which appears to be just short of 10k rpm. Out storm chasing, well storm waiting, right now so pics and dyno graph are a ways off time wise. At 55mph you see the greatest gain, around 15% bhp gain but even at the highest rpms gains were solid, and this was all with the stock pipe! I out powered my previous best running gts 250 which had a pipe
And airbox mods with the stock pipe, pretty happy about this part. I migh even test out my spare Leo pipe on it for fun, the gains may be more impressive than the same pipe used with the stock porting.

To keep the game totally fair I used the .6mm basegasket and exact same compression ratio piston but in an alloy and nicasil cylinder. This means all gains are from improved cylinder filling and trapping.

Jack, I am now really looking forward to trying out your Malossi head! I see a path to much more scootering fun to be had by all us Vespq queens.

[jrflanne]

I am looking forward for the damn thing to arrive. I do believe this is going to be an interesting project. 15% is a pretty nice number considering the goofy head design.

[Micah / AF1 Racing]

Well, about to call the owner and hand over MY baby to him...dammit! I think I need one of these for myself, and soon! I went ahead and tested with a Leo Pipe to get a 100% accurate view of the porting only gains, to make this bike for this test identical to the last one on the dyno but minus the porting. Definitely my best porting guess to date, but it is a lot easier to squeeze power out of an obviously flawed head than the heads of modern superbikes for sure!


In the end though, even with the stock pipe this is one mean little 250cc bitch, while retaining all the civility of a stock bike. It outpowers the stock GTS 300 from about 7mph to the rev limiter at 81.2 mph with current tranny setup. Nice mods and done for pennies compared to what he would have had to spend on a new head (if you could get one from Piaggio) and other stock stuff.

Will post some more pics once I have time to edit again, had another lightning storm last night so I spent much time outside filling my memory cards up, I might have ended up with only a couple of publishable pics but it was good for the soul to just sit and watch!

[Micah / AF1 Racing]

Lifted from the "What's in the AF1 Shop Thread":



I have been a lurker on ModernVespa for some time and I have learned a lot from that site. I do not contribute over there because the few guys "in the know" are light years ahead of me when it comes to these little engines, until I learn enough to contribute something of value I will just keep trying to make our dedicated Vespa section a little more interesting.

Here are some files and pics from the wrap up on that project. After a few days of gentle riding and heat cycling it was time to go up on the dyno and make sure that the owner's ride home was going to be a success....and of course I needed to quantify the gains or losses...I knew they were gains after even the first ride around the parking lot!

I am going to post all the pics here, sorry, most are from my phone on this round other than the "studio" shots and explain them in the next post for the dyno graphs.

The cylinder kit I ended up getting from Piaggio was the aluminum version, which I wanted but thought to be NLA, the piston however was the same 72mm dished low compression thing from the stock motor. This is actually great news in one way, the compression ratio remaining unchanged allowed a true analysis of the porting ONLY as a change with everything else being constant! When you see these dyno graphs please remember that, the ONLY CHANGE IS THE PORTING.


Here is the Aprilia SportCity cylinder kit I ended up using, same piston and compression as the stock Vespa cylinder but made from aluminum instead of cast iron, a LOT lighter part and should be better able to deal with heat!

http://www.apriliaforum.com/forums/attachment.php?attachmentid=171643&d=1317075805

Notice "dish" in piston to keep compression way down with all that squish area, a perfect forced induction piston if ever I have seen one!


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171645&d=1317075837

One more of the cylinder and piston assembly, nice parts and much lighter weight!


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171644&d=1317075819

All back in one piece and ready to run


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171647&d=1317075876

Here she is on the dyno getting ready for some serious testing of porting mods and a pipe for fun...


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171648&d=1317075892

In this first dyno graph we are comparing a dead stock Vespa 300 Super against the ported 250cc GTS. The 250cc ported motor is the red line in this comparison, I knew it would make more power than the 300cc engine up top, I was surprised that it made more power almost everywhere in the entire usable speed range of the scooter.

In this test both bikes have totally stock exhaust pipes and the only intake mods done to the 250cc motors airbox were removal of the internal silencer tube and opening the intake tube up to full diameter where it feeds into the airbox. This is as fair a test as I could manage against a new 300cc Vespa until the paperwork is finished on what is hopefully about to be MY new 300 Super (in black of course, like my heart...and lungs...)


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171650&d=1317075928


In this graph we have a dead nuts equal on the intake side (same airbox mods) GTS250 BUT, it has a Leo Vince slip on and the test bike at this point in the dyno testing phase was still using the dead stock pipe (you can even see this in my dyno notes to the right side of the screen). The only difference between these two same-size motors is the porting and the Leo Vince pipe on the scooter whose dyno graph is represented in red on this comparison. The ported scooter with the stock pipe is one making TONS more power across the board!


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171649&d=1317075914


For the final dyno test I went ahead and bolted my spare Leo Vince Slip-On pipe onto the ported Vespa making it mod-wise totally comparable to the other test scooter in terms of airbox mods and exhaust mods, both bikes were run with the db killer IN the pipe as it is way too loud for my tastes with the open pipe (db killer removed). The Leo pipe gained only the same amount as if it were bolted onto a stock motor but in this case the porting allows for FAR better cylinder filling as is made obvious by this graph. In this test the red trace is our modded/ported GTS250 and the blue line is an identical bike BUT, with no porting. This is the graph that satisfies me the most!


http://www.apriliaforum.com/forums/attachment.php?attachmentid=171651&d=1317075956


This was quite the fun project and the owner is loving his "new" scoot so far, lets hope it is more reliable even than it was dead stock! Based on EGA traces of exhaust emissions the computer does tend to "learn" a little about the combustion chemistry and apply long term trims over time, so after the ported motor has been run for another thousand miles or so it will go back on the dyno to test and see how much trim the stock ECU is willing to apply to the fuel injector. For MY Vespa a larger injector will be required as will 3-3.5bar fuel pressure, up from the 2.5bar used on the stock efi system. Thank goodness fuel pressure regulators are such generic parts, I have dozens of them that will fit in the Vespa pump assembly in the 3-4bar range from other bikes!

[jrflanne]

A nice padding of upside, eh? Like the look of the curves.

[bunnybash]

any news of the ECU's trimming over time?

[Micah / AF1 Racing]

Scooter has not been back and I think I recently saw it listed for sale on CL San Antonio. I would love to retest on the dyno but this far it has not been an option. Waiting for my ecu and Lockset/keys to come back from the super hacker so I can start a totally new mild to wild 300 Super project, my own scooter this time so as you might guess the finished product may be on the HOT side once tuned.

I did speak with the owner a couple of times after he picked up this scooter, he was pleased as punch but did ask what resale value would be.

[katakilla]

Hi mate. i'm looking at doing something similar with a Aprilia Mojito 125. its the aircooled 2 valve LEADER lump that i'm building up. so far have added a 190cc, variator and gear up kit. Didnt have much impact and when i tried a different pipe, saw that it only made small improvements similar to what you've found here. Ive stripped it down again and looking to get the head ported. will match this up with bigger main jet and Malossi airfilter.

Sounds like need to work on flow and open up the ports but grateful for any tips or recommendations before i start the head work?

thanks rob

[Micah / AF1 Racing]

You really need larger valves to see a difference even with good porting. I know that almost sucks as a suggestion since it is far from easy to replace the seats and do new valves of maximum size...but, they are the "choke point" in the airflow for the LEADER motor. The newest 125-150cc Piaggio air cooled motors are 3 valves per cylinder to accomplish this, the result, more power and better efficiency for Piaggio. Keep us posted, curious to see what gains you can net. The porting is straightforward, smooth transitions and good blending around the valve seats are all you can really expect from a port job, that said, it can make a large gain in power!

[tomd]

can 3 valve head etc go on old motor assy? i doubt as novelty wears thin etc should be alot of these engines around as they get parted sold etc as electrics gain on us the internal combustion waste is about over me thinks Big bro is slowly limiting our mobility everythings within two miles of ya no need to go anywhere plane or train .. to travel Progress that worries me but im almost done here

[Micah / AF1 Racing]

Moving South? Me too one day. I doubt the head will be a straight swap but it is possible. Until I have a pair of motors torn down side by side it will be hard to say with certainty.