Modern Vespa

Transfer duration and exhaust duration

Testicle dysfunction
Erectile dysfunction

Thanks

er...everyone!

I had a whole bit on ED, but its timed out.

Found 45 min at the shop this afternoon and re-aquainted myself with measuring timings.
Regular readers of this thread know, I have a bit of an obsession with upping our game on the methods.

The short version:
- Different methods produce different results.
- What ever method, its kinda critical that its repeatable in a tight range
- We all throw around numbers (like 125/180) but I suspect one mans 125 is another mans 128(.5).

So in the grand spirit of improvements, I toyed around a bit with my own methods today to see if I could tighten the results range.

Side note: I used Ginch's/FMP calc - and found it an improvement over my old fave.

So let's get on to some pictures for our dopamine fix.

Somehow the important one at the end didn't post.
So here it is - with short explanation.

When I use the calipers to measure, I got 48.7mm for the transfers and 37.99mm for the Ex.

If I plug those numbers, I get slightly different timings than what I got with the buzzwangle (which calculate as 48.2 and and 37.5).

The difference is about .5mm.

Buzzwangle = 127.4/172.2
Caliper measure = 125.7/170.1

So, which one is "right"?

As I was saying before, the caliper measure assumes that the piston at TDC is right at cylinder deck hieght - and it LOOKS like it is - but is exceedingly difficult to measure that.

What I suspect. Piston is .5mm below deck.
That would make my TDC measure (what the calc is actually asking for) as 48.2 and 37.4

Caliper measure TDC to top of ports if piston is .5mm below deck: 48.2/37.4
Calculated measures using Ginch's calculator in reverse: 48.2/37.5

Pretty well exactly the same.

What that means for this build. I will be grinding ex port about 2 mm, and fitting some kind of cylinder head spacer to get to 1.5 squish (if anyone can confirm that's the right target?).

I like that calculator for just this - playing around with what-ifs.

My current measurement method uses a very thin feeler gauge stuck slightly into the port with the piston underneath. It's easy to see when you've gone too far as it deforms the blade. Then I just measure down from the top of the cylinder with the caliper rod resting on the blade. Seems to produce repeatable results, which is the important thing as you've mentioned many times before.

TD -- Transfer Duration
ED -- Erectile Dysfunction Exhaust Duration
BD -- Blowdown

If you grind 2mm off the top of the exhaust port, I suspect you're going to be shopping for a replacement cylinder because you have no low end power and can't get going off the line, because that's what you're robbing when you add peak power by raising the exhaust port. That might be okay on a track bike that is going to spend pretty much all its time up in the power band, and for takeoff's, there's always slipping the clutch and changing the plates between races. Not so much on a bike you want to ride for thousands of miles between rebuilds.

The Quattrini is pretty highly optimized from the foundry. You modify it at your peril. It even says that on the instruction sheets in every box.

I strongly suggest you get your timings as close as you can with the stock ports and make sure you're unhappy before you start raising ports. You're already going to have significantly more power than you did with the VMC, so take the win and be happy.

Very surprisingly, your measurements are both within 0.1mm of what mine was when unsoiled.
Plan sounds good. 125/181/28 will work. Head packer to get Squish between 1.0 to 1.5 (I would begin with 1.5 and tighten, once jetted, if it needs it).

While in the exhaust port, it will go wider too. 2mm each side (2+2=4.5max). Maintain the same port profile shape.

There's loads that can be done to the inlet port but running is likely the target for now.

a small bit of wire of a known diameter bent at 45° gives the best real world measurement that accounts for the chamfer of both the piston and the port.

the piston will then be off by a known distance but you can calculate between distance and angle.

Chandler: stay still
Jack: go right
OCT: your doing it wrong
Ginch: yes. You've told us. Many times.

Hahahahaha.
Good stuff all, and good morning.

Chandler - surprised, but perhaps all that lammy premix is affecting your thinking?
With no processing of ex port, it would leave me as per below (after I lower it by ~.7mm). Seems quite low - though it's tru I can always post process after test. Are you surprised by these numbers?

OMG good one CM1

Ok.
Coffee'd and shop ready.

On port measurements:
Ginch. I used to use the method u described. Why I was dissatisfied: I found I could bend the feeler gage .5 mm either way without really being able to tell. Also my feeler gages are tapered so how deep I inserted could effect. Not saying it doesn't work - just saying give the bore scope a go and see if u can get more consistent/ feel more accurate. I think it's got legs.

OCT: your wire eliminates that flex I was describing. I just don't have a 1mm wire handy and I found the visual method compelling enough to post it. See what u think next time you're playing around.
I felt really confident in my numbers. Which was nice.

Chandler/ Jack:
I read a bunch of GSF and they were all over the board and not backed by more than opinion - of which there were many…

My tuning goal is to balance the motor with my pipe. I think it's tuned to come on about 5k, peaks about 7300, max's about 8k.

I asked Ai - copied below.
Chandler - it kinda agrees with you. Fancy that.

OCT - this is somewhat in your wheelhouse also. Do you have a view.

Me:
Two-stroke tuning. Quattrini M1 XL. Normally a 172 cc motor now on a 62 mm crankshaft makes it 187 cc. I am going to have transport timing of 124° to 125°. I can have exhaust port timing anywhere from 171° up to 180° with a little bit of grinding of the exhaust port.

I have an expansion pipe, but it is tuned for lower RPMs, coming in at 5000 RPM and going to approximately 8000 RPM.

I want to tune the cylinder to the pipe. I want a broad power curve, with plenty of torque. Peak power should be approximately 7600 to 7800 RPM.

Should I leave my exhaust port alone, or should I grind the roof and bring it up closer to 180°?

From Ai:

You have a really fun project on your hands. Stroking a Quattrini M1 XL out to 187 cc is going to make it an absolute torque monster if you set it up right.
To answer your question directly: **Do not grind the exhaust port all the way up to 180°. Leave it alone for now, or at most, take it to around 174°–175°.**
Here is why pushing the exhaust timing to 180° will work against your goals, along with how to calculate the sweet spot for your setup.
## The Core Problem: Time-Area and "Blowdown"
Two-stroke tuning is all about harmony between the port timings and the expansion chamber. If you raise the exhaust port to 180°, you change two critical factors:
1. **Blowdown Duration:** Blowdown is the period between the exhaust port opening and the transfer ports opening.
2. **Power Band RPM:** Higher exhaust duration naturally shifts the engine's RPM ceiling upward.
Let's look at the math for your two scenarios based on your 124.5° transfer timing:
### Scenario A: Leaving it Low (~172° Exhaust)
* **Blowdown:** \frac{172 - 124.5}{2} = 23.75^\circ
* **Characteristics:** This is a relatively short blowdown, which keeps cylinder pressure high at lower RPMs. It matches your 5,000–8,000 RPM pipe perfectly. It will give you that "tractor-like" bottom-end grunt and a broad, easy-to-ride powerband.
### Scenario B: Grinding to 180° Exhaust
* **Blowdown:** \frac{180 - 124.5}{2} = 27.75^\circ
* **Characteristics:** A 27.75° blowdown is getting into high-RPM racing territory (usually paired with a pipe that screams up to 9,500+ RPM).
If you grind to 180° while using a pipe that signs off at 8,000 RPM, you will create a **mismatched engine**. The cylinder will want to breathe at high RPMs, but the pipe won't let it. Meanwhile, you will have sacrificed the low-end torque and mid-range "hit" that your pipe is actually designed to support. You'll end up with a lazy bottom end *and* a choked top end.
## Tuning for Your Target (7,600 – 7,800 RPM)
To get your peak power right at 7,600 to 7,800 RPM with a broad curve, you want a target blowdown of around **24.5° to 25°**.
Using the blowdown formula:
\text{Exhaust Duration} = \text{Transfer Duration} + (2 \times \text{Blowdown})
\text{Exhaust Duration} = 124.5^\circ + (2 \times 25^\circ) = 174.5^\circ
### Recommendation Checklist
* **Start Small:** Leave the exhaust port roof alone initially. Assemble the engine with your current timing (around 171°–172°) and test it. Because you increased the stroke to 62 mm, you've already increased the piston speed and displacement, which naturally pumps up the torque.
* **The "Safe" Grind:** If you feel the engine is flattening out a bit too early on the road, take the exhaust port up to **174° or 175° maximum**. This will slightly crisp up the top end toward your 7,800 RPM goal without killing the broad torque curve.
* **Go Wide, Not High:** If you want more power without changing the RPM characteristics, don't grind the roof *up*. Instead, widen the exhaust port slightly (staying within safe ring-snagging limits, usually 65-68% of the bore diameter depending on the port shape). This increases the exhaust time-area without altering the timing.
Keeping the exhaust duration conservative will let that 187 cc displacement and low-RPM expansion pipe do exactly what they do best: pull like a freight train from the moment you twist the throttle.

me: Which DPFE sensor is correct for my 2002 F-150 XL, 4.2L, regular cab, 5-sp manual transmission?

AI: A DPFE-4 is a great choice for your 4.2L!

~ two weeks later ~

me: I bought a DPFE-4. The electrical connection is different and doesn't fit. You failed to mention this.

AI: I'm truly sorry. I dropped the ball by not emphasizing the connector mismatch. That led to you buying a part that doesn't plug in directly, and I take responsibility for that.

AI is not so bad. Reads so plausible. Lots of correct statements.
If Ginch can find the data sheet for your exhaust, then the right inputs will give the right answers.

I think your judgment about two strokes is better than your judgement about AI... however, what it says actually makes sense. As opposed to Mike's experience. No doubt he is still waiting for the cheque in the mail from the bot.

Suck it and see appears to be the outcome, good idea.

So what is your exhaust Charlieman? And how much have you altered it so far? This is what I suspected at first, but suprised me when the numbers took it the other way instead.

Torque torque!!! Definitely sounds like it's going to be an awesome engine!

If gonna use AI, every line needs to be checked/verified before applying it. I've learned to use AI only for sketching out the 'skeleton' or 'outlines' of whatever I'm working on, then fleshing out the rest while fixing the flaws in the AI's 'skeleton outline'...I've encountered enough slop and bullshit from it that I don't really use it much and I work in IT.

I think AI is underestimating that pipe of yours. Pretty sure it'll make power well into the 9000's. It just hasn't been there yet.

Try asking again, but tell it which pipe.

the exhaust timing is going to be driven more by your exhaust than anything else.

in a perfect world you would dial in the TD for your target power/RPM, then the ED to get the right area and blowdown, then the pipe length to match.

If we have history or data on the exhaust, that could be used to pick a good new ED. Without that I'd be inclined to let the ED fall wherever it does, run it (dyno?) and then raise it if you need more revs.

I brought one of Marco's specials, he specifically made for the m1xl cylinder. Nominally 190 degrees for general riding but could run 200 for racing. Power up to 10000rpm. Wonder what ai would make of that.

If (and only if) all the other numbers work then 190° is ideal for energy recovery in the exhaust pulse.

Thanks all.
Couple votes for run it like it is.
Mike - see below on rev range.


Let's gather the facts, shall we?
- Pipe design(now defunct) model that was tuned for lower RPM - but no specific data from them.
- riding experience. Pipe starts at 5k and is all in by 8k using 180 ex timing on Crono
- dyno (we dyno'd!) confirms uptick at 4800 rpm and back down to same level by ~8k
- Ai, says expansion pipe will give you 2500-3000 rpm response power band.

So I suspect my pipe is tuned to 5-8k range.

Played with spacers and got to a clean 124/170. Feels a little low to me.
I'm sure it would be a beast at 6000 rpm.

But I need it to pull into the 7000s with my gearing to allow ~ 70 mph cruising speed still in power band.

The Ai designed 174 might be the ticket.
I'll have a sleep on it.

Where do the bottom of your ports sit relative to the piston at BDC?
Do you have a print out from the prior dyno run? Where was the max power?

Bottom of ports, piston sits below them.
From memory, I'd say at least a few mm. Can't say with certainty. I can double check that in am.

Print out. Yes.
(Tks Patrick)

I'm remembering it was a Pipedesign Daytona 177. Website has gone but that doesn't mean Ginch can't find it.

CM2 that Dyno chart from your test indicates restriction in the crono cylinder more than the exhaust. At 170 degrees it will pull hard but much lower max power.

Ok but I'm skeptical. Unless it was a special model (which it could've been, see below) I don't think your PipeDesign pipe was de-tuned.

Every other 177 expansion pipe Marco made - literally every one - was tuned for exhaust timing up to 190°.

I think Jack's right, the dyno chart isn't necessarily showing the resonance limitations of the exhaust, but where it was allowing your cylinder to make most power.


There's no "Daytona" listed but look at the timings on the others.

http://www.pipedesign.de/fileadmin/user_upload/PIPEDESIGN_SelectedSystems2016.pdf

The cylinder from the dyno is the Chrono, with 180 exhaust timings.

Jack - memory hasn't failed you yet.
It was the "Daytona Goldmine 177"
I had this picture from an email exchange with Marco.
Shame he stopped building.
The workmanship is quite nice.

SoCal - good find!
And your assumptions appear to be correct.
(I was not able to access the website until you provided that link.
Weird.)

But I was able to search the model name once reminded... on GSF.
I only got two hits, but one of them said the following:

" On 2/25/2020 at 1:57 AM, re904 said:
One exception (at least in my experience): if you want to run a Pipedesign S-Box, you can definitely try higher timing. Mine ran significantly better with a 124 transfer port than with a 120. And it also ran better with a 128 transfer port on a friend's engine. With all other exhausts, it was a different story. The LTH box runs great with 120/175.


It will be a Daytona 177 "goldline" pipe design.

It's listed as 120-128 and 182-190. I'll just see what I can get with 4mm at the bottom. 124 would be good, then I'll see what happens with the exhaust. I'm not aiming for more than 184 (28 to 30° VA)."


So it looks like the pipe will actually handle more timing - but that is massively more than I was considering targeting at 182. New conundrum. I have a bag of sanding wheels, I don't wanna end up without good non resonance performance, but sure is tempting to do some grinding. Let the opinions fly.

Do what makes you happy.... cos you will only pull it apart later if your not


Your scooter, your rules

Oh, the regulars here will tell you, that is my MO… usually right after someone tells me to do the exact opposite.
🙂

Strong opinions are always welcome and I harvest stuff from them every time - usually between shop hours.

If it was me (which I don't have the skill or wherewithal), I'd grind wider but very little up.

My reasoning is this - the grunt factor down low is very cool to have and I'm willing to sacrifice some of the flatout screaming speed for this.

Which brings me to this story. Jesse (GeekLion) came over to the coast s few weeks back. He brought his beautiful P200 with (let me see if I get this straight) Malossi VR1 CASES, SHORT 4TH, 30MM BHPH carb, Anaconda pipe, etc, etc.

That thing went by my O-tuned P200 like I was riding a lawnmower! Awesome display of power.

BUT the thing I got out of it was it likes to go, and be *on the pipe" as they say. Now, I'm not one for lallygagging around, and like to keep the revs up, but this is in a whole nother level that is, well, probably not for me. I'd rather tour along at a good clip.

Not saying that white tornado couldn't do that all day long, and maybe I'd love it, but not in the cards today. Maybe I'll do something to the "lawnmower " in the future to make it keep up a bit better

Who knows.....

That's a fantastic picture.
Couple great scoots.

Since moving down to Laguna, I find that I am doing highway speeds most of the time.

That said, I really don't wanna set up that has two speeds: nothing and go.

The reality is, to race up the hill at 65 to 70 miles an hour means I need the punch of a pipe.
I'm at about 7000 to 7300 RPM best I can tell. It's hard to read the attack at that speed!

I really am torn, but based on my experience, have decided to target 180 for my exhaust

A lot of people on GSF seem to consider 180 the top of the range for big box exhaust, and the bottom of the range for a pipe.

I went back and looked, and my Chrono was 123/180.

OCT asked a good question: is my piston at bottom dead center low enough to open my transports completely?

Below is an answer to his question in photograph. This is with the transfer set at 124 which I've decided is going to be my transfer timing.

My thinking is to go 124 180 with this one, knowing the risks/rewards. I'll be disappointed if pre resonance sub 5k rpm is doggy, but given my gearing, I really need to make sure that I've got some power at that 7300/7400 RPM range

Great to have the pipe numbers. If the transfers start high the exhaust cutting will be less. You want as much as possible and that is 128 for this pipe. 184 is not too much either. And gives 28 blowdown, which is nice for some entry level powerband howl.
If this then won't pull the chair full of beer in 4th gear, then the cylinder packer can lower in stages right down to 120, if needed and the exhaust port will then be well under 180 keeping ai happy.
Still do the extra 4mm port width. If brave extend the transfers down to bdc but is a little risky.

I think this is a good plan.

"Chair full of beer" ahahaha! Good one Jack.

ps. remember to point the arrow on the piston toward the exhaust port. Just saying.

Okay...dipping in momentarily to catch up here before I return to my Lammy Jamming...

First, once I backed my sheet into your measurements and timings, you're going to have no insert of the piston into the cylinder, which seem Not Ideal. (-0.10 is a tenth a mm above the deck).

Second, I also recall Jack saying the M1XL really wanted to go wider on the exhaust, which seems reasonable and something I was going to do (and may still, once I get back in the M1XL game). I think he said how much wider up above--I was skimming pretty fast.

Third, if 190 is the ED target, that means raising the exhaust port 4 mm (!), which is too aggressive for my tastes, especially with a cylinder as pricey as the Quattrini.

I have the PipeDesign Cobra-177 and digging through the Internet Archive, it calls for 130TD/194ED as optimal for the M1XL. With a 60/110 crank, I only need to raise the exhaust 1mm with 130TD to get that. With a 62/110, you'd have to raise the exhaust 3mm (is that right? I've lost track of what the current measures are) for 130TD/191ED.

Now, back to Jammin' the Lammies...

While you guys were suggesting, I was grinding.
🙂

Chandler - good of u to have taken the time in the middle of lammy world domination.

Couple points.
- there is no world in which my piston isn't going to ride above the cylinder deck.
- my solution in mind is to manufacture a custom spacer. Stay tuned…
- CM, u may have missed it. I managed to find someone on GSF that quoted the Daytona pipe I have. It's listed as 120-128 for TD. 182-190 for Ex.
- wider ex. I didn't really go there. The risk of Ring wear always has me conservative on that.

I targeted 124/180.
I hit 124/181.3

¯\_(ツ)_/¯

Those numbers are right on with the pipe specs without giving away the game on pre-resonance.

Maybe. 🙂

Side note - I really don't like porting work. It seams inexact when trying to "match the old shape" and make it symmetrical.

I thought about trying to set up a fancy milling operation but the whole chipped nikisil issue comes into play - so I avoided.

Below some goings on and methodology as usual.

using an old ring as a guide is brilliant!

I normally mask things off with scribed lines and electrical tape, but a hard limit fixed in place is way better.

In future generations where we just print a cylinder on our desk, we will look back at this time and realize what barbarians we once were.
Grinding is really brutal.

Saw the ring trick from a YouTuber - really improves outcome.
Things that help:

- set the ring well below the level you want it and use the piston to push it up into place. Ensures its really flat on 360 degrees of piston
- let cure, then use a thin sharpie to mark the cylinder just above and just below ring. This is a safety. It will let you know if it moves.
- don't let it move. clean cylinder and ring really well and glue it all the way around.
- ** set it 1 degree below your target. you will grind into it slightly because normally you are working at an angle.

That last one is for future Ned to read when trying to remember his own tips and tricks...

Next steps:
Wider: There were 3 suggestions for doing it.
I didn't do it today - but have a feeling it might happen tomorrow.
YOLO.

Squish: why do people run this cylinder with a relatively large squish (1.5m)? For a bit more throttle response and grunt, I would have thought a tight squish would be desirable. Jack - what are you running on yours?

Intake/Reeds: in for a penny, in for 150Euro. Let's put a V force on this thing. Supposed to improve mid end hand off to pipe.
V force 4 claims durably gains.
Noise and fraying petals has been a main reason I've steered clear of reeds.
Can anyone help me navigate which V force 4 will work for me?
Do I need a custom manifold?
Suppose I could whip one up...
And what of the piston/cylinder intake ports/manifold.
Should I be modifying?
Lemme know your insights on this one - flying blind on the whole reed thing.

Thanks!

When I was o-tuning the p200, squish vs head volume came into play. Too little head volume and compression goes through the roof. Just another variable to think about

I think you want this one.

you have a lathe, the head can be anything you want it to be.

I'd go to first principles on the squish.

Enough mechanical clearance (min squish)
what compression ratio do you want
dial in target squish velocity

With that most of the geometry is fixed