Modern Vespa

i'm building a trick motor and comes to a point where i have to choose between disc valve (original) or reed valve. The engine cases are from a sprint, welded up and flowed. Gearbox is PX, primary is 23/65, cosa clutch etc. Longstroke (59mm) flowed crankshaft. Cilinder is a DR177 with Polini timing and a MMW cilinderhead. Carb a Dellorto 28phbh. I know this will run very good with a healthy topspeed and acceleration.
But i'm in doubt. Maybe it's better to put a RD350 reedvalve in. Open up the crankcase. Maybe even a full circle crankshaft ( if i can find one ).
The engine goes in a P150 frame.
Money isn't really a big issue, i do everything myself.
Please make a decision for me.

Thank you
Sara

Sarah both have their merrits, but if you do go with reed intake, don't use the full circle crank... it will only depfeat the purpose of a big intake... block all that flow.. I recommend a bell shape... perfectly balanced.

Send Hot Rod Al your stock crank and have him rebuild it to suit your engine - he does very good work!

http://hotrodscooters.com/

also does a lot of other great mods to heads and everything else !

That's gonna cost her big bucks. Especially when you factor in shipping. Plus she said she was gonna do the work herself

1st - Al can rebuild a stock crank many times as the metal is higher quality.
It wont break nearly as easily . its not that much more expensive if you figure in the durability and the fact that it can be tailor made to YOUR engine setup.
She mentioned buying a crank as well , and it seems to me she also said she WASN'T worried about cash - i think the implied ntion is she is going to build motor herself ... correct me if i'm wrong Sarah.

cheers and good luck however you decide.

believe it or not there are people all around the world who can cut n flow cranks not just hot rod al

I think the comment was made because Sara is from Belgium and postage would be silly, not because it wasn't fair advice.

Reed valves allow crazy intake timings as the reed automatically controls the flow. They do however act as a huge restriction to flow.

Crank intakes can be very efficient and function well, the limit for a Vespa is what you have to work with from Piaggio.

My preference, run the crank intake until something blows up and then go thru the expense of getting the reed valve, etc.

Is it impractical to combine both? The disc could have fairly wild timing and the reed would prevent the power band becoming too narrow. I would have thought that minimizing the crankcase volume would be essential to get maximum benefit from this.

Thanks everybody for the advice. Vader, the full circle crankshaft is in the bin . No, i won't tell you wich.
For the sprint engine there is no bell crank
, so i guess i will have to make my own, as always .
To bad that the crank that i have is already flowed and balanced.
O well, they predict a long winter anyway.
Anyone has a plan of a bell crank? With dimensions?

Thanks
Sara

[quote="Ginch"] Yeah it was more the shipping from Belgium to the states that I thought would be pricey. I have heard hra does very good work at very reasonable pricing

Well that's not completely true, there is one that will fit (as long as your case has the needle roller bearing on the flywheel side). You only need to use a 5mm packer under the cylinder.


http://www.sip-scootershop.com/en/products/bellshaped+crankshaft+mazzu_45041000

Have a read of this to see another reason this is a good idea -
http://www.scootercentral.net/forums/viewtopic.php?f=15&t=15818[/img]

Sara Alexandra,
with a low cost DR and your sealing pad still in a good shape keep your standard system. Find a new crank (or a good second hand one), flow it and choose a timing that fits your DR.
La messe est dite!

If the work that has been done so far was done well and the original valve is still OK, I'd leave that setup and build it up based on that. I personally prefer the disk timing options as you can tweak the opening and the closing of the intake port, which if done properly would give nice results. Reed valves are "clean" but the timing is limited on when it closes.. you can't change that, which has its merits as well ironically because of that same limitation..

Maybe post some pics of the work done so we can help evaluate

The DR177 is a pretty mildly ported kit. I'm thinking stay with rotary for that. Also, no reason to ruin perfectly good rotary cases. I like what was said previously about don't go reed unless you have to.

I ran a P-221cc with a 28mm mikuni on rotary. It was wicked fast and didn't have to be revved up to make power.

Found some engine cases for px 125. After some welding and grinding they will do just fine.
The DR porting will be adapted to the Polini one.

Even the Polini port timings are a little bit conservative. I measured one the other day and without a base gasket the exhaust duration was 165.

Please keep us updated!

sorry i didn't notice before that u were in Belgium.
any way good luck with your project - and let us know how it turns out!

cheers ~

Yea, the Belgium at the bottom of her avatar does look a little like Sheboygan.

I guess you mean my dog?
She's actually a border collie and a certified working dog. Got more diploma's then me

No

Im makin fun at Falcon cause he said he didn't know you were out of country and I said......."Belgium is at the bottom of her avatar, it does look like Sheboygan"!!!

See, you're in Belgium.....I and everybody else knew that cept for Falcon.

And the Sheboygan is a Jerry Lewis joke(you have to be American).

And the whole thing is lost in translation cause im terrible at summarizing.




Side note...........................I want to marry you so I don't have to work on scooters anymore and just ride your work.



The dog can come live with me too.

I have a 2mm base gasket ( 1mm for the longer stroke and 1mm for the transfers and exhoust port)
But i will need another crankshaft anyway for the px cases and that widens my choice. SIP has one, a flowed longstroke that fits my budget (we have a budget?!)
Keep you updated.
Sara

I have a 2mm base gasket ( 1mm for the longer stroke and 1mm for the transfers and exhoust port)
But i will need another crankshaft anyway for the px cases and that widens my choice. SIP has one, a flowed longstroke that fits my budget (we have a budget?!)
Keep you updated.
Sara

Do you have a 2mm base gasket?

keep in mind that "flowed crankshafts" are usually retarded (and not anticiped) to get a longer inlet timing. Is that what you really want? 65 to 70° after TDC before inlet shuts... less torque at bottom end and barely more power past 7000... If you choose a standard crank you can still do what you want... If you keep in mind that your DR won't rev beyond 7500, you'll probably get more torque and power all along the revband opting for a "real"homemade anticiped crank.

^^^^^^

Fastfrog knows his stuff love

classic confusion: "fastfrog knows his love stuff"!

What port timings are you aiming for?

Iv heard about you Frenchmen....

i married six months ago

Your dog?

No, with my wife. We have been together for 25 years, and after this long tryout, we decided it's was time for a wedding. After all, you can't be to sure .

Congratulation to you and yours.

Nothing to extreme. It have to be torquey and rev to about 8000rpm.
I also opened the ports on the base of the DR, just like the Polini.
They where designed to fit on the standard cases and where restricted.
For the moment i would like to try it with the DR, just to see how far i can get, tuning-wise that is.
And my colleague has also a PX, with a lot of money in the engine, a Polini racing cilinder, flowed crankshaft and cases, disc valve, Dellorto 30mm carb, etc....
And he just paid over 600 euro's to get the engine tuned. 15.5 hp.
I want to beat him for a fraction of the money.

Luckily i know how to put my hands and mind at work.
So when spring comes, i will be ready.

DR is a 2 face baby with its exhaust boosters:

Nice work Fastfrog. So what do you mean "boosters"? Good on you Sara, congratulations.

the 2 boost ports...

Ok, so they're boost ports... the words "exhaust boosters" made me think you had found some way to add extra exhaust ports!

never had a dr?