Tuning a smallblock
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LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat May 16, 2020 2:10 am quote
Spigot bridge

46FA0495-6669-4BE9-A84D-37CEBCCA96BF.jpeg

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PX 150
Joined: 15 Sep 2006
Posts: 525
Location: Gold Coast, Australia
Sat May 16, 2020 11:34 pm quote
Hey mate, your fairly limited on LML cases. Ive got piaggio cases and im even on the limit with those running an MHR177. Standard cases just dont give you the volume for modern kits these days and thats why im going down the Malossi VRONE case route.
Ive included a pick of the mhr kit and you can see the size of the ports will never be accommodated by stock casings.

20200517_171905.jpg

20200517_171938.jpg

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PX 150
Joined: 15 Sep 2006
Posts: 525
Location: Gold Coast, Australia
Sat May 16, 2020 11:38 pm quote
Mhr177 kit opened ports

20200517_163504.jpg

20200517_163444.jpg

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PX 150
Joined: 15 Sep 2006
Posts: 525
Location: Gold Coast, Australia
Sat May 16, 2020 11:42 pm quote
Dont use JB weld, you'll just set yourself up for disappointment

20200517_171958.jpg

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LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sun May 17, 2020 12:22 am quote
Thanks Jimscoot, those malossi cases look real nice! I love the way the intake flows in front of the crank allowing the use of a fuel circle. But they are just a bit out of my price bracket.
For me itís still about getting the best bang for buck performance but pushing it to the limits. Hence the VMC kit. To be honest I do enjoy the idea of trying to work with as much of the standard motor as possible to see what it will do. I see your point though and especially with those mhr ports!
On the last image captioned donít use JB weld is that related to the image, Iím trying to see whatís gone wrong.
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PX 150
Joined: 15 Sep 2006
Posts: 525
Location: Gold Coast, Australia
Sun May 17, 2020 12:42 am quote
I meant donít use JB weld as Iíve never had a good experience with it.
Ossessionato
76 Sprint V, 63 GL, 62 VBB, 05 Stella
Joined: 16 Jun 2011
Posts: 2852
Location: Nashville
Sun May 17, 2020 7:53 am quote
jimscoot wrote:
I meant donít use JB weld as Iíve never had a good experience with it.
HERESY!

Most of us on here have JBWelded cases at some point. Is it as good as having more aluminum welded on? Of course not, but it's the best option most of us have, and if you prep the surface well, it will work just fine.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Mon May 25, 2020 7:47 am quote
Just an update here. Scooter is back together with new crank and lighter sip flywheel. Iíd definitely say itís going better than before, the flywheel especially has really improved the response and it spins up real quick now.

One thing to note is it seems the flywheel sits further onto the crank than others. At first I couldnít get it to idle it would just die as soon as the revs got below say 2000. Figured after much trial and error that the pickup alignment was probably out. I had to file the back of my stator to get it to also sit further in and now it works great and I can set a nice slow idle.
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LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat Oct 10, 2020 6:21 am quote
Hi guys

Having had the engine running for a period of time now and fully run in Iím Hoping to get some advice on a couple of points

Firstly what sort of compression ratio would you be aiming for on a cast iron, stainless expansion setup.

Iíve been struggling to keep the temps below 160 at wot. Since originally setting the barrel with a 1.2 squish gap, Which gave a psi compression of around 165 Iíve since raised the gap to give me around 130 at 2mm squish. Main jet is at 134 any more and it splutters.

Iíve also dropped my timing down to 15.5 at high rpm. However the temps are still getting over 160 and itís running like a bit of a pig. Which has led me to believe that possibly the head needs some work to bring the squish tighter and in turn opening the bowl out.
What do you guys see as a max temp on your engines? for a while Iíve been led to believe that above 160c is starting to get risky.

The other issue has been that Iím lacking power at higher rpm from 7000rpm and beyond. Itíll get to about 7300 and then itíll very slowly rev out to somewhere slightly below 8000. This is in 4th gear. My port timings are at 180 - 123.5 which I was expecting to give me decent power at higher rpm. Iíve raised the ignition timing and played with the jetting however it still doesnít seem happy at higher rpm.

As a reminder Iím currently using a revolver pipe with a 28phbh reed setup. Gearing Is standard LML 21/68 With p200 4th

Cheers again
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1114
Location: Rochester, Minnesota
Sat Oct 10, 2020 6:51 am quote
Crazyfrog187 wrote:
Hi guys

Having had the engine running for a period of time now and fully run in Iím Hoping to get some advice on a couple of points

Firstly what sort of compression ratio would you be aiming for on a cast iron, stainless expansion setup.

Iíve been struggling to keep the temps below 160 at wot. Since originally setting the barrel with a 1.2 squish gap, Which gave a psi compression of around 165 Iíve since raised the gap to give me around 130 at 2mm squish. Main jet is at 134 any more and it splutters.

Iíve also dropped my timing down to 15.5 at high rpm. However the temps are still getting over 160 and itís running like a bit of a pig. Which has led me to believe that possibly the head needs some work to bring the squish tighter and in turn opening the bowl out.
What do you guys see as a max temp on your engines? for a while Iíve been led to believe that above 160c is starting to get risky.

The other issue has been that Iím lacking power at higher rpm from 7000rpm and beyond. Itíll get to about 7300 and then itíll very slowly rev out to somewhere slightly below 8000. This is in 4th gear. My port timings are at 180 - 123.5 which I was expecting to give me decent power at higher rpm. Iíve raised the ignition timing and played with the jetting however it still doesnít seem happy at higher rpm.

As a reminder Iím currently using a revolver pipe with a 28phbh reed setup. Gearing Is standard LML 21/68 With p200 4th

Cheers again
I usually aim for a 150 psi or so on compression. I think 160 is fine and would have run it also if it were mine. I had a cast iron DR177 in the 150 - 160 psi range when I shaved the head to zero squish to get a 1 mm squish.

As for the 160 Celsius I assume? I had that issue with the cast iron also. Mine liked to start to seize up much warmer than that, had a few close calls, around 170C. I did rebuild the top end with ring gap at a minimum.

What throttle position are you running at and have you tried richening up that area of the throttle range? For instance I usually ran at half throttle riding around, a richer main jet wasnít the answer, since it generally effects 3/4 and up throttle position.

Iím not sure of your gear ratio in fourth, if you over gear a motor it adds stress and can cause heat issues. Not sure what the P200 gear does as far as an over drive setup or under drive setup.

I didnít know this but I was reading some exhaust reviews and a pipe with a larger diameter outlet can cause issues with heat also. It was one of the box exhaust reviews and they were measuring exhaust outlet diameter.

Hopefully something in there might help.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sat Oct 10, 2020 8:43 am quote
Thanks Christopher

Yeah 160celsius, my experience has been similar Iíve had trouble at no too much higher than 160

Good to know you run at similar compression, as mentioned reducing the compression didnít seem to reduce temps much.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Sat Oct 10, 2020 2:36 pm quote
This build certainly got watered down. From 128/190 on a pipedesign to 123/180 on a revolver. How it is performing is about where it should be with these numbers.
Bigger squish can make more heat. Squish clearance should be as tight as you have the bottle for. 0.8mm or less is where it gets interesting.

160C is not hot but about right. With the timing so low and still getting to 160, I suspect the jetting is not so good.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7954
Location: Victoria, Australia
Sat Oct 10, 2020 4:47 pm quote
Christopher_55934 wrote:
I didnít know this but I was reading some exhaust reviews and a pipe with a larger diameter outlet can cause issues with heat also. It was one of the box exhaust reviews and they were measuring exhaust outlet diameter.
I thought it was the other way around? Heat building up and can't get out quickly enough because the outlet is restricted?
Molto Verboso
2007 Stella 150
Joined: 02 Nov 2019
Posts: 1114
Location: Rochester, Minnesota
Sat Oct 10, 2020 4:52 pm quote
Ginch wrote:
Christopher_55934 wrote:
I didnít know this but I was reading some exhaust reviews and a pipe with a larger diameter outlet can cause issues with heat also. It was one of the box exhaust reviews and they were measuring exhaust outlet diameter.
I thought it was the other way around? Heat building up and can't get out quickly enough because the outlet is restricted?
You are most likely correct, I donít understand the why at this point unless itís purely about flow.

https://scooterlab.uk/vespa-big-box-exhaust-shootout-feature-2/
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7954
Location: Victoria, Australia
Sat Oct 10, 2020 5:01 pm quote
Christopher_55934 wrote:
Ginch wrote:
Christopher_55934 wrote:
I didnít know this but I was reading some exhaust reviews and a pipe with a larger diameter outlet can cause issues with heat also. It was one of the box exhaust reviews and they were measuring exhaust outlet diameter.
I thought it was the other way around? Heat building up and can't get out quickly enough because the outlet is restricted?
You are most likely correct, I donít understand the why at this point unless itís purely about flow.

https://scooterlab.uk/vespa-big-box-exhaust-shootout-feature-2/
My italics in the thing below. I don't quite follow though why it should ping more readily with a bigger outlet.
I see the question asked regularly about heat buildup on a FB 2 stroke group I follow. It's usually brought up that too small a stinger diameter will have this effect.
Quote:
Outlet pipe diameter

Outlet pipe diameter is a topic that is frequently overlooked. A small dimension outlet pipe certainly has an advantage when it comes to keeping the noise down, which is nice of course. While there is some discussion whether the size of the outlet pipe actually has positive or negative effects on power and the rev-range, it is common sense that the outlet pipe dimension should increase with the tune of the engine in order to enable it to breathe properly and avoid the build-up of heat.

As a rule of thumb, most expansion pipes aim at a diameter of 25 to 28 mm, whereas the majority of the boxes only have between 16 and 18mm, with the Viper Box, the Resi-Box (both 23mm) and the Malossi (20mm) being the only ones to feature larger diameters. This will not be an issue when using the exhaust for in-town riding or on country roads, however, when riding at high speeds with a lot of throttle for a longer distance, e.g. on a fast motorway trip, you might soon struggle with a pinking engine. This is something we couldnít test on the dyno Ė but it is something to watch depending on what youíre going to use the exhaust for.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sun Oct 11, 2020 12:31 am quote
Jack221 wrote:
This build certainly got watered down. From 128/190 on a pipedesign to 123/180 on a revolver. How it is performing is about where it should be with these numbers.
Bigger squish can make more heat. Squish clearance should be as tight as you have the bottle for. 0.8mm or less is where it gets interesting.

160C is not hot but about right. With the timing so low and still getting to 160, I suspect the jetting is not so good.
The plan is to try the revolver pipe for now as I already have the pipe. Although I suspect Iíll soon want more. The pipe design exhausts donít come cheap and Iím trying to way up if the increase in power will be worth it. For the moment jack what timings would you suggest to best suit the pipe?
Part of the reluctance to go for the pipe design has also been the issue with the barrel having such low timings from factory that to get to the higher timings Iím having to raise the barrel a hell of a lot and the further I go the more the spigot bridges seem to get in the way of transfer flow as highlighted in a previous picture. Iím still not sure how detrimental this would be though if at all?

Made some progress yesterday by bumping the timing back up and reducing the main jet I have been able to get back a good deal of high power to the point that itís now happy to rev easily up towards 8000. But of course this isnít going to help the temperature issue. I think I will have to look at reducing the squish
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Sun Oct 11, 2020 1:12 am quote
At the port timing you have it will not have much top end power. It may rev high but the max power will still be within 500 of 6500rpm.

If you change the base packer to get the transfers up to 126 how big will the squish be? And what will the exhaust duration be?

If you put the ignition timing at 18 degrees and leave it there the rest can be adjusted to it.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sun Oct 11, 2020 1:40 am quote
Jack221 wrote:
At the port timing you have it will not have much top end power. It may rev high but the max power will still be within 500 of 6500rpm.

If you change the base packer to get the transfers up to 126 how big will the squish be? And what will the exhaust duration be?

If you put the ignition timing at 18 degrees and leave it there the rest can be adjusted to it.
At 126, ex duration is 181.75 blowdown 27.9 the exhaust shape on the VMC is very square and already wide which as I understand can allow for a smaller exhaust duration. Do you think this would still pull 4th

Squish will be around 2.2mm I can get the head skimmed to get this to around 1mm so long as the bowl can be opened sufficiently to compensate
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Sun Oct 11, 2020 2:23 am quote
Crazyfrog187 wrote:
At 126, ex duration is 181.75 blowdown 27.9 the exhaust shape on the VMC is very square and already wide which as I understand can allow for a smaller exhaust duration. Do you think this would still pull 4th
I would take it up to 126/185 (at least).
Crazyfrog187 wrote:
Squish will be around 2.2mm I can get the head skimmed to get this to around 1mm so long as the bowl can be opened sufficiently to compensate
Compression is probably on the low side anyway. Skim the head to 1mm squish and forget the bowl. Measure it, if it helps with your conscience.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Sun Oct 11, 2020 12:27 pm quote
For now I think Iíll raise the barrel to get around 125.5 transfer. Iím mindful for the moment of not loosing too much low rpm power, with the revolver pipe I donít think itíll ever get too exciting.

Noticed the piston seems to be getting pretty coloured below the rings. With the previous malossi kit I never had this. does this suggest fuel mix is blowing past the rings?

B518FC63-E08D-47B8-A5FD-512FFA786CCC.jpeg

Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Sun Oct 11, 2020 2:20 pm quote
126/185 will go well with the rest of your set up. For it to go, the exhaust needs to go up too.

Rings look normal. Just not jetted well.
Ossessionato
Joined: 26 Oct 2015
Posts: 2685

Sun Oct 11, 2020 2:40 pm quote
Crazyfrog187 wrote:
For now I think Iíll raise the barrel to get around 125.5 transfer. Iím mindful for the moment of not loosing too much low rpm power, with the revolver pipe I donít think itíll ever get too exciting.

Noticed the piston seems to be getting pretty coloured below the rings. With the previous malossi kit I never had this. does this suggest fuel mix is blowing past the rings?
It must be an optical illusion, but it looks like the upper piston ring locating pin is missing? Also, i'd clean up (or hone) the cylinder if the soft seize transfered any aluminum on to the cylinder walls.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Mon Oct 12, 2020 12:22 am quote
Thanks guys.

Chrome, the locating pin is there it must be the photo. As you can see Ive had a slight soft seize on one corner whilst running in. Iíve cleaned everything up since.

Good to know the piston looks normal.

Having raised the barrel so much, at BDC the piston goes well below both transfers and exhaust. Is it recommended to lower these edges. Having searched the net I havenít been able to find much on lowering the transfer ports especially. The entry ports in the bore are much smaller than where the transfers meet the case. seems like it could be beneficial?
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Mon Oct 12, 2020 6:02 am quote
Jack221 wrote:
126/185 will go well with the rest of your set up. For it to go, the exhaust needs to go up too.

Rings look normal. Just not jetted well.
Jack if I decide to raise the exhaust and possibly widen a touch at the same time. Do you raise/widen the whole of the port down to where the stub exits by the same amount? I understand that itís best to avoid funnelling out at the top
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2443
Location: London UK
Mon Oct 12, 2020 2:21 pm quote
Don't need to take so much out just keep straight to the stub. 185 is still entry level.

Not raising the exhaust will save torque but will cost much more in high rpm power. Widening matters too. 48mm wide and slightly more is possible but be careful with the studs.
Member
LML 187
Joined: 12 May 2020
Posts: 38
Location: England, stoke
Wed Oct 14, 2020 12:05 am quote
Good to know. Iíve realised Iíve measured the exhaust port incorrectly Iím actually only at 60% Iíll take this out towards the 48mm mark as mentioned
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