Vespa intake timing: let's talk numbers

OK, so we all know that cutting the crank to increase intake duration is important for a fast Vespa build, but I never really see people posting specific numbers. It seems like one of the nice things about rotary induction is that you can get usable intake timing numbers just using a degree wheel, without doing a port map and calculating blowdown and all that stuff (which I will admit I am still working to understand.)

vespa-ciao.nl suggests setting the intake to open at 134*BTDC and close at 56*ATDC (http://vespa-ciao.nl/page.php?id=187). Their grind looks relatively mild and I've seen pictures of waaay more aggressive ones, especially with respect to when the port opens. I have to believe that at least some of the people who are doing this aren't just hacking at their crank trial-and-error, and have done some timing calculations and experimentation. What works? What doesn't? How far can you go in either direction without totally killing the low end?

Re: Vespa intake timing: let's talk numbers

I've been waiting for this thread..

Blowdown is degrees of rotation from when the exhaust port opens to when the transfers open, it's still in play.

He is tuning that engine to a specific cylinder (the DR 43mm). When I cut my first crank (standard duration Top, before anticipado ones were available) I cut it to the specs in the cylinder kit (Malossi) instructions. I don't remember the exact numbers it resulted in, mainly just checked they were in the ballpark and that it shut before the transfers opened and vice versa, learning how it worked. Now that I snapped that one I'm going to rebuild using the marzuchelli anticipado. I haven't compared them Yet but hopefully I won't have to make much of an adjustment.

You've probably already seen this, but there's more info and numbers here:

http://vespa-ciao.nl/page.php?id=180

Re: Vespa intake timing: let's talk numbers

Hey Simon-

I've been working on a motor to explore this issue. I forget what my numbers are, but I'll chime in again when I get them in front of me. Anyway, I can share this:

Big Rotary Motor

Re: Vespa intake timing: let's talk numbers

ohHAI! 205 overall, 137 BTDC & 68 after. I based this number on a bunch of maths I did using formulas in the A. Graham Bell book.

Re: Vespa intake timing: let's talk numbers

err... 68 BTDC & 137 after....?

Re: Vespa intake timing: let's talk numbers

I was just checking that post out the other day Josh, eager to see how it works out.

Re: Vespa intake timing: let's talk numbers

Simon Nyi /
snyi OP

It would be 137 before and 68 after, I think. On the down stroke you want to have the intake closed long enough for good case pressure to accumulate and not just spit back out the intake prior to the transfers opening, so it makes sense that it's open much longer BTDC than after, right?

Maciek - what you're saying about blowdown makes sense. If a kit doesn't come with instructions, there's obviously a way to calculate the optimal timing based on your particular cylinder's porting. I'm just trying to get a sense of people's numbers based on their specific setups and how they've performed. That vespa-ciao.nl thread is pretty helpful; I haven't actually calculated my timings yet but it will surely help when I do get around to splitting the cases.

Re: Vespa intake timing: let's talk numbers

yeah woah blast from the past its been many years since i had this math in an accessable region of my short term memory. i did some calculations and i think they are in one of my books currently in storage, but i remember 200 some odd degrees being the deal. i think i was opening much earlier and closing a little bit later but not a lot later. cool how you can do that with roatry.. can't do it with PP or reedz.

Re: Vespa intake timing: let's talk numbers

Simon Nyi /
snyi OP

right, asymmetric port timing is possible with rotary which is rad. the vespa-ciao.nl thread suggests that anything over 200 is gonna give you a pretty narrow power band, but it might be possible to compensate for that with good variator tuning.

i do not think i am going to bother port mapping my cylinder to get it exactly right, honestly. going to take those numbers into consideration in order to get a ballpark figure and err on the conservative side when i get my grind on. (edited)

Re: Vespa intake timing: let's talk numbers

I cut 5mm & 10mm with great results which if i remember right is what molassi says. I cut it so that it had the same shape as it did originally not tapered like this drawing in the link above.

Re: Vespa intake timing: let's talk numbers

Re: Vespa intake timing: let's talk numbers

Thats awesome that yall are doing this right now too! I got some polini speed cases from declan used and modified to have a larger intake duration, so I have a top crank with stock intake duration and a pinasco kit that I want to get optimal intake opening with. Ill be going through the process as well. Just need to print off a good degree wheel and get a port map off this cyl and start working on getting the numbers. Ill update my progress here.

Re: Vespa intake timing: let's talk numbers

Simon Nyi /
snyi OP

FYI/bump from the grave: unmodified stock cases with a mazzy anticipato crank opens at 121* BTDC and closes 45* ATDC, give or take a degree or two. so that's right around 166 degrees of total intake duration. That means the "anticipato" crank yields about 20 more degrees of intake duration over the stock crank, other things constant.

Obviously check your port timing on your specific cylinder if you want to time everything perfectly, but hopefully this is still useful information. Will be getting timings on the speed cases + anticipato soon.

Re: Vespa intake timing: let's talk numbers

Yo josh, care to show your work? As in the maths? I can look it up too, but it would be easier if that info was in this thread as well. Thanks!

Re: Vespa intake timing: let's talk numbers

Simon Nyi /
snyi OP

The Bell book says that the intake port should close no sooner than ten degrees before the transfers open and vice versa. So take a port map, figure out when the transfers open and close, convert mm to degrees of rotation, give ten degrees on either side, and there's your safe maximum. (edited)

Re: Vespa intake timing: let's talk numbers

Nice, thanks simon.

Re: Vespa intake timing: let's talk numbers

Simon Nyi /
snyi OP

just realized that might not be clear. the intake port should close at least ten degrees before the transfers open, no less, and the intake should open no sooner than ten degrees after the transfers close.

Re: Vespa intake timing: let's talk numbers

I'm just getting around to figuring out the basics of porting, and what does what, and why, and through searching, found this thread. I just did some degree wheel fun time and came up with these numbers for a DR kit with a Mazzucelli Anticipato crank in stock cases with a modified intake patch. My numbers seem to be pretty close, which actually shocks me. I'm just seeing if anyone can verify any of this (aside from the intake patch, since it would vary by builder), and also to bump this for more Vespa tech. I'm trying to do what I can with an old kit, setting a goal of 55mph on my Ciao. Top end being more important than low end.

(edited)

1400125790992.jpg

Re: Vespa intake timing: let's talk numbers

Funny, I was just reading this thread the other day, about to have some degree wheel fun of my own to see how the Mazz Anticipato compares to the cut top crank that snapped. In My case it's a Malossi 46.5mm on pretty much maxed out stock cases.

Re: Vespa intake timing: let's talk numbers

Pete Puczasaurus /

I've got a single speed ciao 92mm pulley, proma pipe, 13.13 sha (opening intake patch) 43mm Malossi kit (case matching).

Question: Is cutting the crank a bad plan or would doing so allow me to build up a little more pressure in the case? Or would it kill my bottom end? From what i've read it seems there are more conservative numbers, but it seems like a lot of folks are cutting cranks on variated vespas.

Re: Vespa intake timing: let's talk numbers

Pete Puczasaurus /

Scratch the single speed question...

Re: Vespa intake timing: let's talk numbers

what did You figure out?

Re: Vespa intake timing: let's talk numbers

Pete Puczasaurus /

Well unfortunately I lost my work space and I'm living at my girlfriends place and the moped is in storage. For some reason I don't think she would appreciate metal shavings flying around her kitchen. Ha so I'm mostly scouring the forums and reading the books to figure out as much about port mapping timing cutting and so on.

But rereading some things and deciphering the Dutch language leads me to believe it will be an upgrade regardless.

But as far as crankcase volume, maciek, have you done case work where you have left the bearing oiling holes intact and cut most of the metal out? I saw that purdy one you did. Would it be a big difference in volume with a 43mm kit?

Sorry for the rants and question my moped and wrenching talk is limited to this website. Not many riders up in Montana.

Re: Vespa intake timing: let's talk numbers

Yean, thanks. It does not seem like that much volume at all, I figure it about compares to cases with room for a reed-block. (edited)

Re: Vespa intake timing: let's talk numbers

#CrazyWayne™ rocks. #CrazyWayne /

Adam Blickhahn Wrote:

-------------------------------------------------------

> I'm just getting around to figuring out the basics

> of porting, and what does what, and why, and

> through searching, found this thread. I just did

> some degree wheel fun time and came up with these

> numbers for a DR kit with a Mazzucelli Anticipato

> crank in stock cases with a modified intake patch.

> My numbers seem to be pretty close, which actually

> shocks me. I'm just seeing if anyone can verify

> any of this (aside from the intake patch, since it

> would vary by builder), and also to bump this for

> more Vespa tech. I'm trying to do what I can with

> an old kit, setting a goal of 55mph on my Ciao.

> Top end being more important than low end.

>

Your timing numbers are way wrong did the wheel slip?

Like the ex timing, 90degs ATDC open, 270deg BTDC closing will be 180 or is your crank offset 10mm from the cylinder center line?

Transfers open 140deg close 250deg = 110.

Blowdown 35deg

lol (edited)

Re: Vespa intake timing: let's talk numbers

hmmm... maybe one of those 380 degree flywheels the race guys use to get more duration. that is funny.

Re: Vespa intake timing: let's talk numbers

Finally have My engine out to do the sub-frame (hopped one too many speed-bumps on moped monday I guess), so I took the opportunity to change the crank seal and take the degree wheel to it.

With my very molested intake patch and an unmolested mazzucchelli anticipato; I get the intake opening at 132° BTDC and closing at 57° ATDC, for a total of 189° duration.

Haven't popped the top to check the exhaust and transfers yet, but it seems I have a bit to go, at least on one side. I rigged up a degree wheel externally. I made a spacer to tighten it down out of some tubing, but I suppose the center drive boss from the variator and some washers would have worked just as well. (edited)

Vespa_Degree_wheel.jpg
Intake_Port_Fin.jpg

Re: Vespa intake timing: let's talk numbers

P.S. I can see where he got an extra 20° of exhaust duration, but his transfers seem ok..235ATDC is 125 BTDC, and 125+110+125=360, it's wayne that seemed to be doing the exhaust calculations around 390 degrees; 250 BTDC would be 110 ATDC, and 140 ATDC is 220 BTDC, so that would be a 80° duration or 140+80+140...or 140+110+110 in wayne's magical engine, or maybe 140+110+140 on that 390 degree wheel ;). anyway, i love those late night posts lol.

Re: Vespa intake timing: let's talk numbers

#CrazyWayne™ rocks. #CrazyWayne /

Not my magical anything i know better than to buy a Vespa moped.

Re: Vespa intake timing: let's talk numbers

You got us there, though I'm sure You'd be up for the challenge :).

I took a motivation break and once 'remotivated' got the rest of the numbers:

To recap:

Vespa cases, intake patch close to maxed.

Mazzucchelli Anticipato

Malossi 46.5MM Cylinder and piston.

Intake Opens - 132° BTDC (228°ATDC)

Intake Closes - 57° ATDC

Intake Duration - 189°

Transfers Open - 119° ATDC

Transfers Close - 241° ATDC

Transfer Duration - 122°

Exhaust Opens - 95° ATDC

Exhaust Closes - 265° ATDC

Exhaust Duration - 170°

Blowdown - 24°

Intake-Transfer overlap - 13° (132-119 BTDC / 228-241 ATDC)

I suppose I will find any 3am mistakes in the morning, but at first look the timings look like it should like high RPM..Thoughts?

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