Modern Vespa

Higher/wider transfers give more time for mixture to enter, especially important as rpm increases. Same higher transfers let mixture escape earlier at low rpm. With insufficient blowdown higher transfers cause reversion at high rpm causing flow to reverse for a while which makes less power than lower transfers.

Higher/wider/ flatter exhaust port reduces the pressure quicker at higher rpm. Good for power but at low rpm all the torque disappeared. Opening earlier reduces compression and shortens the power stroke. Closing later lets even more mixture escape at low rpm but at high rpm gives the exhaust longer to ram some of it back in.
The trick is the balance. A few degrees can be a lot. Is all about juggling limits for each application.

For this job on this cylinder 125/181/28 should work well. BGM already has the best of both exhaust port shape, so keep the shape but move it up and down holding the same curve.

Value ^

Can hear the Dremel whining from here.

I thought I mentioned this but now that I'm thinking, I didn't.

Porting transfers are really hard. The angle and size make it really easy screw up a perfect cylinder. If you jack up the angle of the transfer roof the port isn't going to work right. The best thing is when the blow down target is lower than you want which means you can raise or lower the cylinder to your transfer target and just the exhaust through porting.

BT5 - the plan is just that.
All of my calculations that I showed previously show that the transfers reach their target through lifting of the cylinder with a base gasket.
The exhaust port will be the only one that is ground.
Access through the exhaust port stub makes this fairly easy. I've (unsurprisingly) been researching tuning tricks that allow some "best of both worlds magic". I came across this - interesting point on transfer roof angles - the P2 and BGM seemed to have more sedate angles than the Malossi. When cylinder is off - I will try and measure. See his comment on transfer port. No idea if this is effective - but interesting:

From "Marty's Garage"
"Less duration favors low rpm power whereas more duration favors high rpm power. More crankcase compression ratio means there will be more pressure when the transfers open and so the entrance of fuel mixture will be more rapid, needing less degrees to make the complete transfer. The durations in this chart are for around a 1.5:1 ratio. More ratio means more pressure which is advantageous for high rpm power but a disadvantage to low rpm power. Why? At higher pressure the mixture enters the cylinder too fast at lower rpm and loops around to exit partially through the exhaust port before the ascending piston closes it off. Another factor is the angle of the transfer ports roofs. That affects the angle of mixture entry. A steeper angle gets the mixture up to the spark plug faster which is good for high rpm power but bad for low rpm power. A good example is two cylinders I have for the same engine. One had transfers with only 114 degrees and 45 degree roofs. The other had 120 degrees and 15 degree roofs. The one with the lesser duration achieved 8000 rpm, whereas the other only achieved 7500 rpm. But the one with 15 degrees had more power at low and mid range rpm. One way to cheat the system is design for high rpm power (long duration and steep roofs) but allow a bleed off of crank pressure by a narrow boost port that opens much earlier than the main part of the transfers. This does not ruin high rpm power because anything other than the main opening of the transfers is hardly noticed at top rpm. So its like not even there at high rpm, but at low rpm it effectively releases much crankcase pressure before the main part of the transfers open so that the mixture enters at a slower speed to be less likely to loop around and exit the exhaust port."

All true of course. Needful be careful with what you read. Most you will find will be like this. All correct information but incomplete. Leading you to believe you want low ports pointing up steeply with an early boost port. This maybe appropriate for some but depends on what you need and where.

The MHR is more aggressive still. Designed for an expansion but even with the box it will beat the BGM.
This version of BGM will go really well I'm sure. Expecting low 20s and everything better than the Polini. No pressure.

Yeah - what caught my eye was his suggestion on tuning for high end power (high port timing and roof angles) and creating a narrow elevated boost port to siphon off crank case pressure for low RPM riding. Perhaps worth an experiment on one of these cylinders when all said and done.

I'll be interested to see what tools we have to bias the MHR to more "rideable" while garnering its power.
Particularly intrigued to see how it is out of the box tho.

I can also add a riding experience - subjective.
Lots of riding yesterday on the BGM.
Really impressed with its effortlessness.
Terrific "around town" grabbing the groceries CM style.

Got out on the hwy as well.
Mostly saw temps at 284 - but with a bit of lugging saw it reach 300 as well.
But it didn't race there - it climbed and I didn't have the sense - right or wrong - that I was in any danger.
It holds it temp better than the Polini when not being run hard.
With the Polini - when I was grocery getting - it was tough to get over 200 sometimes.
Pipe - as previously discussed - is much happier at 250°
But I didn't want to advance timing more - because it was in upper 200's on the highway - and a 65MPH seize with a side car hanging off the scoot is - lets just say - undesirable...

With the BGM at 55 - 60mph - I am at about 6500 RPM in 4th.
By my calcs - that puts me at about 18° BTDC ignition timing give or take.

You left the burrs out of your stash...


Just out of interest, what sort of distance/speed are you talking about with the high temps?

I saw about 265 with this run.
I'm in 4th, flat out.
Its fairly cool out - 65-67°
7600 RPM.
67/68MPH.

The only time I saw it go up to 300 on yesterday's data in prior post, was on a similar run where I had to slow down for traffic - then got back on the throttle wide open from lower RPM and made it climb back up there.
As dumb luck would have it - it is exactly a 1 mile run.

https://youtu.be/NuRtqGDG8_8

That's a good run for testing. Speed comparable with other comments on bolt on BGM kits. This one is a 187 and low geared but does have a sidecar. 68mph is still a decent speed. Sounds like it's running well. Pickup slow but soild. Easy to ride I guess.

This riding all predictable in the porting. After tuning I would hope it is something like 72mph on the same run and picks up a little quicker.

Ok gents.
Need to confirm our specs on the MHR - while other work goes on behind the scenes here.

The MHR comes in two offerings.
57 and 60mm crank.
Jack - you proposed 57 mm kit previously - but since you tell me I am going to love this and it is going to be my keeper - I'd like to not have a bodge solution in place with all sorts of extra packers and head gaskets.

So can anyone actually identify the specific differences between the two kits (port heights I assume) and sell me on the why's of that idea?
https://www.malossistore.eu/alumin-cyl-kit-63-alum-cvf2-pin-15-mhr-3117163-P

The 60 kit is not a good idea. Can see what you're thinking but no.
It's the same as the 57 but with the 1.5 fixed on the head. Slow. Inflexible. Great if you don't have a clue.

Edit. Can't be fast be without a packer. Like a badge of honour.

More like a bodge of honor for me.

Can u clarify - is the head skimmed 1.5 more on 57?
Have u any idea what the stock timings are with what packer?

I think both kits use the same head.
Problem with the 60 kit is the transfers need to be cut but the 57 will need a head gasket. I know which one bothers me the least.

From SC
57

HubxBore: 57xØ63mm
Capacity: 177,59cm³
Exhaust angle: 178,2°
Overflow angle: 119,2°
Preexhaust angle: 29,5°
Squish edge: 0.7mm (piston is back by 0.2mm at top dead center)
compression: 1:11.25
overflow channels: 7
piston rings: 1
ignition point: 18°v.Ot.

60

HubxBore: 60xØ63mm
Hub capacity: 186,94cm³
Exhaust angle: 178,5°
Overflow angle: 122,5°
Forward exhaust angle: 28°
Squish edge: 0.8mm (piston is back by 0.3mm at top dead center)
compression: 1:11
overflow channels: 7
piston rings: 1
ignition point: 18°v.Ot.

Transfer cuts are a challenge.
Gasket on O ringed head also not ideal.
Comfort level would raise if we were talking numbers here - i.e. timings out of the box and target timings so I can consider the gives & takes.
There are always some...

Lemme ask you this...
Have you pondered what the ideal target timings will be?
I can see what info I can get us so we can scheme a bit on hitting.
Is 125/181/28 the magic number if we could hit?

At least the same as the tuned BGM (is that not done yet?) But I would like to start at 127.

I am preparing another cylinder before I tackle the BGM...
But that news has to wait.
Lemme c what info I can get us on the two kits stock timings.

Ok - found the timings and did the math.
Here is stock if I bolt on with my 60mm crank:

57MM kit with 60mm crank stock and head gasket:
125/180/27.5
-1.3PBT
.8 squish
Have to use head gasket as PBT will be negative.

60mm kit with 60mm crank stock:
122.5/178.5/28
PBT .3mm
.8 squish.

If I want 125/181/28 with the Malossi my options look like this:

57mm kit with 60mm crank:
no change to base gasket.
60mm crank gives -1.3PBT
head gasket required to restore .8mm squish.
about .3mm polished off top of exhaust port.

60MM kit with 60mm crank:
add .5mm to base gasket
basically no grinding (.16mm polish of exhaust port top)
I'm there. but...
Squish is now 1.3mm

So the 57mm kit locks me in to minimum 125 timing.
The 60mm kit looks a lot like my Polini.
The question is - am I going to like the higher timing - or is it going to move me in to the realm of too peaky/ too much transitional bang at 5KRPM.
Could make driving in traffic alota work.

*Edit - decking 60mm cylinder would solve for large squish...

Can still go no gasket on the 57 to get lower. I would start the 57 at 127. Can't do this with the 60. The 60 is as it comes and can't change much. Will be a bolt on with no realistic tuning option.

Stay tuned... so to speak. Wasn't sure I followed this.
60 kit looks to have lower timing out of the box rather than 57 kit?
(See calc detail in pic below).
With 60mm crank:
- 57 kit is at 124.65 with 27.65 blow down.
- 60 kit is at 122.5 with 28 blow down
I know 123 can deliver good torque.
125 - will find out.
127 - sounds high.

I'm not disagreeing the Malossi can produce more power.
Push back is on drivability in traffic/ joy.
127 is going to be a rocket at the high end - but concerned I'll miss the beastiness of 123.

More I ride the BGM stock, more I appreciate its 123 - 25blow down timings.
Does it run out of revs 1000RPM too soon?
Without question.
1500RPM? maybe.
2000RPM - IDK - that would be a crazy rocket - but would it be a beast down low?

What's the rule of thumb for timing and or blow down moving up peak power per 1000 additional RPM?
2° transfer timing inc.
3° blow down
= 1000RPM increase in peak HP output mark.
Reasonable?

That makes 125/181/28 likely to deliver at least 1000 - if not 1500 RPM of HP increase. But that significant gain in blow down is going to also make it peakier too at the edge of grunt deterioration?

127 would be another move up - and would be nothing short of sporty - but we may be playing with the line of too much kick at 5K and too little grunt at 4K?

Side car is weight - but it is also out to the side.
Too big kick at 5K can make it tough to keep the rig straight - there are dividends in power band smoothness.
Locking in too high could limit optimization.
Are you seeing same calcs I am?
60 with lower tr option?

The concept is that this is an experiment and a learning exercise.

The 57 kit has lots of experimenting potential. And the 60 has none.

The 60 is a fine kit, will be very similar to the tuned BGM (not as it is now ie. dull, tug boat). Malossi quote the 60 kit as being 22 bhp. BGM will end up the same.

The only point of the MHR is to be faster than the tuned BGM and still pull the sidecar. It will be faster than you can ride it, I'm sure of that but it will also pull. This will only happen with the 57. The 57 kit tuned as a racer 132/198/33 could be maybe 35 bhp but peaky and hard work. I am expecting your 57 to be about 28bhp and be just like the BGM in pulling but revs at least 1500 more.

Yep, AND drivability for my rig.

Understanding the gives and takes better now - this is how I think we should set up the cylinders to provide the most data.
See charts below.

This will leave me with two very usable cylinders and a good comparison.
One for my every day.
One for smoking the pack on rides.
(The suppliers should be paying me for the cylinder sales to come. How many are going to go home from a group ride and think: WTF - I got passed by a scooter with a f*cking side car and some stupid stuffed dog. I need to upgrade my power.)

That said - I can't process the lack of flexibility you are seeing in the 60 kit.
But let's establish the Malossi timing target so I can double check my calcs.
Im not that opposed to going 57.
Decking is its own hassle.
Clarify for me as well on the 57 - am I putting a head gasket between o ring and cylinder - so one side of gasket must seal on cylinder - other uses the O ring?

Malossi proposed timings?

I used an MHR 57 (210) cylinder with a 60mm crank, rather than the MHR 60 cylinder, to get me to 221cc. The extra flexibility of the 57 meant that I could lift the cylinder by using a base packer to achieve my desired transfer duration. This still left the piston poking out the top of the bore, so I used a head packer (not gasket) between the cylinder and 'o' ringed head. If I had used the MHR 60 kit, raising the transfers with a packer would have left the top of piston well below the deck, giving me too much squish. Machining the head to reduce the squish would have been additional expense.

If the MHR 177 is anything like the 210, you'll likely end up using quite a thick head packer eg. 1.0mm for 127TD. This is no problem with the 'o' ring, but I take your point that a regular thin head gasket (0.2mm) is not recommended with the 'o' ring.

There is no 60 version of the Sport 210, I used the 60 crank with only head packers. The o-ring on one side with just sealant on the other has been a non-issue for me.

Gracious.
Thanks gents.
Some unexpected insights.
I have always thought a "packer" was the same as a gasket.
Can you guys explain difference?
Not sure I am clear.

Thickness.

I guess a gasket is as thin as necessary but a packer is a particular thickness.

SWA - is that what you were suggesting here - or did you mean some other form factor that differentiates packer from gasket other than thickness?

I've got nothing to add, except I kinda already miss the Polini.

Done.
https://modernvespa.com/forum/post2415263#2415263

Now back to the task task at hand.

I have packer to o ring on mine too. No leaks packer to cylinder and no sealer. I would think its only ever the non o ring head that leaks, which is why the o ring works so much better. Head is the part with varying temperature and micro moving against the cylinder.

Without grinding the transfers, there is nothing that can be done with the 60 MHR. Even with high elevation ports 122.5 is only going to make 22bhp without a fat high end expansion. Decking nicasil is a mine field. Might be able to use the BGM head though. Now there's an idea. Would have to check the crown profile but might work.

Yep, as Ginch confirmed, I think of a packer as being a relatively thick slice of alu sheet, as in 0.5mm, 1.0mm, 1.5mm etc. This becomes a kind of extension to the bore and it holds it shape, hence why the 'o' ring just sits on top without any issues. I generally need 2mm of packing for mine:

0.5mm base and 1.5mm head = 126.6 TD and 0.85mm squish (current)
1.0mm base and 1.0mm head = 129 TD and 0.85mm squish (maybe next test)

Jack has suggested I try 128 TD, but that means using a 1.2mm head packer to maintain the same squish, which doesn't exist off the shelf. I'm thinking a 0.25mm paper/fibre gasket from a Polini 210 alu under my 1.0mm packer, so the 'o' ring seals onto something solid.

How I read Jack's last post:

"da da da da da da da.
da da da da da.
da da.
da da da.
Might be able to use the BGM head though. Now there's an idea. Would have to check the crown profile but might work"
Record scratch.
Wait what?!
You had just sold me on the 57kit!
Creative idea tho!

I'm liking the bracketed timing plan for the two cylinders, reposted below.
Fire up your proposal for Malossi timings that fit my bill.
Ignore the devil on your shoulder with a big grin, holding a tach with the needle reading 10K.
Cases can only take so much... smooth power band with grunt is a win.

I'll do some calcs for both cylinder kits - assuming no decking - but throwing the BGM head and gasket on just for fun to see what the numbers would look like.
Will leave me with two tuned cylinders.
Gonna be fun.

Ahh - got it.
Gasket being thin and gaskety.
Packer being a lift of sorts.
And as for O ring - that just sits on the packer - and the packer sits on the cylinder head. Am following with interest - will be good one to see how you like that timing vs current.

The thing with using the BGM head on a 60 is that, it would end up with a packer top and bottom anyway. And thicker than the 57. Won't win anything. Maybe a head with built in CHT if it fits the profile but that's about it.
Get the 57 and this is done.

If you look at my brackets - the assumed lowest timing on the Malossi is for the 57kit...
That's the assumed solution.
So... where is your mind at for the target timings for the Malossi?

Are you doing the BGM yet? Need to know how that pulls before finalising the Malossi tuning plan.

The bolt on 57 Malossi should be set to 127 to start with. Also your kit will not be exactly as spec, so will need to decide from there depending on how it all measures. If 127 can pull the sidecar, we can start the Dremel work from there. Will probably need more than the exhaust done.

Why didn't you just say so?
Tougher to get a commitment on direction from you then my wife - and trust me - that is no low bar.

🙂

Like that plan.
We should have some fresh data off the BGM.
This will give me better sense of how timings feel/perform.
Will also start to get a sense of the changes that come with just lifting the exhaust port relative to the transfers.

Vacation weekend here - which feels a fair amount like the middle of the week on Covid time.
Plan to organize some burgers's and dogs on the grill - but not before I get in a last ride on stock BGM.

In the mean time - here is a riddle for you.
If you look at the Dyno charts - they gave me pretty consistent numbers on ea. of the metering rods - eq29 (richer) and eq31 (leaner).

My butt was telling me the 31 was faster.
Dyno said it was the 29.
But when I looked back - I could see what I was feeling.
The 31 has more power at the 5K rev range - right in the heart of the power band.
The 29 has stronger top end around 7K.

It is tempting to read the chart as if it is a range of throttle - but remember - this is all done with the throttle in single WOT position.

Motor prefers leaner at mid RPMS and richer at high RPMS.
So the question is - what's the cause of this?