How To Measure a 2 Stroke Engine - 100 mph Moped Challenge

Today I have a full remeasure of the engine so we have an accurate record of where we are before more modifications.
Patrick Garage's TZR250 project can be found here: / @patricks_projects
Engine Specs:
Bore 54.5 mm
Stroke 41.6 mm
Conrod length 80 mm
Cylinder Volume 97 cc
Conrod length 80 mm
Squish Clearance 0.45 mm
Squish Area Ratio 0.5
Trapped Volume at TDC 7.6 cc
Geometric Comp Ratio 13.8:1
Trapped Comp Ratio 7:1
Exhaust Duration 201.9 Deg
Transfer A Duration 129.6 Deg
Transfer B Duration 126.8 Deg
Transfer C Duration 128.9 Deg
Carb KX 80 PE V502CH06
Bore 28mm
Main Jet 130
Pilot Jet 55
Needle N99A
Exhaust Dimensions mm
Section Dia Section length
30
30 14
33 85
38.5 94
51.5 85
68.5 75
98.5 100
100 80
95 21.6
76.5 43
19.8 108
Ignition Timing
RPM Degrees
2000 15
3000 18
4000 20
5000 22
6000 23
7000 23.5
8000 24
9000 23
10000 22
11000 20
12000 18
13000 11
2 Stroke Stuffing shows how he measures here: E8 - HOW To: Portmaps, Port Durations, And Port Angles. 2STROKE STUFFING
• E8 - HOW TO: Portmaps,...
5:52 measuring squish

[@AutoBeta2T]

Hi all - thanks for tuning in and I have left the engine spec in the description. Cheers Dave

[@remiaubut8354]

Hello, parler vous français

[@AuMechanic]

One instructive thing people should note when watching your videos is that you consistently use precision in measurements and adhere to documented methodology both if which are key to developing 2 strokes, or to put it another way, precision and methodology may not guarantee success but a lack of it will guarantee failure. You can get away with simple trial and error methods with 4 strokes but 2 strokes could take you forever without methodology and precision as there are just too many variables involved most of which influence one another. Just a note on Bells book.too. It is basically a close copy to Gordon Jennings 2 Stroke Tuners hand book with the addition of anecdotal notes from Bell specific to a number of engines. Jennings book is quite dated from the 1970's The expansion chamber equations given by Bell for example is an identical albeit metric version of Jennings imperial based equations which he created as he describes in his book by basically measuring up various works pipes of the era and doing a bit of reverse engineering.

[@AuMechanic]

BTW what was the end MSV for that squish clearance ?

[@AutoBeta2T]

I'll have to work it out. Quite high I recon.

[@AutoBeta2T]

Cheers mate - appreciated. I've even got my red book now for keeping notes of everything I do with dates etc. I tried without but I've got myself lost a few times... There's quite a lot of data to deal with.

[@AuMechanic]

@@AutoBeta2T I plugged the numbers into my MSV calc but wasn't sure of the bowl diameter and the number was about double optimal Using 13k RPM, figured maybe I got the numbers wrong.

[@AutoBeta2T]

Hi mate - I just had a look on EngMod and it has the squish at 48m/s at 11500 rpm.

[@keeneseeley627]

One trick i use when measuring small volumes like that (as it's hard to be precise in interpreting the fine graduations visually): i decided to do it by weight, with painter's scales, measuring the burette/syringe before and after. You can now find affordable 0.01 g scales. Just a thought. Godspeed, keep up the amazing work!

[@miltonulm5102]

A thumb role of squish is 1% of your stroke, so if your stroke is 45mm is 0.45mm a safe squish for performance 2strokes so your 45.5mm squish is totally fine, but you can get up the compression more if your fuel is capable of it 😊

[@AutoBeta2T]

Yes, I've heard of that rule of thumb too. I've been told of another now too so I plan to do a test to see what the engine likes. There is no evidence of the piston touching at 0 .45mm

[@miltonulm5102]

@@AutoBeta2T the lower squish you can have is better because it helps with detonation, by that you have headroom to downjet, add more timing and so on, but test as much as you can but I think you need a higher reaving pipe (14000rpm or more) for more useful power

[@wtm7554]

Hello, for taking this at the exhaust, I use lamp in the duct and watch when light comes. For the transferts, only a 0.10mm gauge.

[@AutoBeta2T]

Hi WTM - I hope you are well? I did try with a 0.10 feeler gauge but I struggled to get consistent results. I did give it a go. The result I got with the 1mm welding wire was very similar to what I got using the light in the duct method.

[@wtm7554]

Yes, with the gauge, the idea is to stop when it's hard to move in it,add little oil for more precision. Your idea work great. 👌

[@AutoBeta2T]

Cheers buddy 🙂

[@james5553]

This is so helpful. I have a simson s51 that I am doing the same thing with. You are helping me understand the text book 😊

[@AutoBeta2T]

Hi James, I'm pleased the videos are helping. What books are you reading?

[@james5553]

Just the 2t tuning guide I got from amazon. It is a bit old school! My simson has an 80cc kit on it and a carb, but I am thinking of going 110. My first bike was a YZ125 with a DT125 motor that someone had registered as the original DT donor bike 🙈🙈. Now I have a vfr750, rsv1000rr and superduke. I still love 2 strokes though - just something about them. @@AutoBeta2T

[@AutoBeta2T]

James, what is the title of the guide? I like to collect books on the subject of 2 stroke tuning :)

[@justanothermotorizedbikech]

I love waking up to watching your videos😝😝

[@AutoBeta2T]

Sweet - i'm pleased they do. Have a great day :)

[@69storky]

The best people to talk to is a gokart motor builder . Get one of your heads and modified so you can put inserts in . What oil are you running rule of thumb in karting in Australia because hot weather gast iron barrel run caster synthetic oil . Chrome barrel full synthetic.

[@AutoBeta2T]

Hi Storky, I have a TS100 head that fits but is meatier than the standard AR head that I was planing to modify to take inserts. The thing is that I have found a load of AR 50 heads on ebay and at £20 - £25 each posted I think they are cheaper than it would cost for the insert material. I've got 5 now so I can try some different head configs with them. Eventually I will probably go to inserts when I get my cnc mill up and running. I run Motul 800 : www.motul.com/gb/en/products/800-2t-factory-line-off-road Me and my racing buddies used to race aircooled 250cc two strokes and used 747 but then switched to the Motul and never suffered another seizure. What oil would you recommend for an iron barrel?

[@69storky]

Depending on how hard you are rev and for how long see full synthetic break down after 14000 rpm with caster oil it done not break down and makes the motor run cooler to but it dirty oil . Just go to local kart shop to what oil they got It hard to say what oil today they change like the weather . I would try both one with full synthetic and then one with synthetic caster in it .

[@Ni9kye]

Hello, couple of things, the book you’re using is as a reference, whilst good for its time is very old, things have moved along a long way since then! Maybe a good place to look for port design would be emulate port design from a motorcross engine. In addition most modern 2 strokes are using special coatings on both the cylinder bore and inside the combustion chamber.

[@AutoBeta2T]

i mate - I only really use the Bell book for reference for the calculations. There is a lot of info on the net that super-seeds that from Frits and Jan in various threads... My ports are quite difficult. The exhaust is a single and there transfers do no sweeping at all... there just is no room to do that. Maybe a new cylinder or fin removal and welding?

[@bananabrooks3836]

​@@AutoBeta2T5:27 Supercede.

[@kevinwootton4006]

Take 4mm off skirt piston will help with power .take 4mm off head then take 4mm off exhaust port top and all the other ports then you are heading in the right direction. now you can say thanks kev.

[@AutoBeta2T]

Cheers Kev - top-tips.

[@Patricks_Projects]

Nice! thanks for the shoutout, i haven´t been able to test my ignitionsettings yet due to a very odd reason. My mothers 'estate' after her death is occupying my garage, and i don´t want to make it smell glorious twostroke =) I measure with a caliper and a 0.10mm feeler gauge lying flat on the dome and into the port. Then measuring from top of cylinder down to piston. Zeroing out the caliper at piston tdc against the deck.

[@Patricks_Projects]

Commenting as i´m watching. 0.45 squish is a little bit tight, in me and my friends project(piaggio twin) i went from 0.45 to 0.75, never dynoed the difference. But we won the 'big race' in Sweden and became Swedish record holders, and only just tenth´s off the world record, managing this with a slight misfire also(the engine never ran this good before) I received the parts i need for this bike(winter overhaul) so look after updates from that one also in my channel =)

[@AutoBeta2T]

@Patricks_Projects cool - that's good to hear. I did think it was a bit tight. I have some more heads (about 4 spare) to machine. I was going to try more comp (back to 7.4:1 corrected) but I'll do another with more squish gap. Cheers

[@AutoBeta2T]

Hi Dave - cheers for the rule of thumb. I think I originally was aiming for .6 but it got a bit closer. I'm going to cut some more heads so I will open up the clearance to 0.7 mm

[@Patricks_Projects]

@@AutoBeta2T In my yamaha i run 0.8mm 51% and 15.5-1 in ratio, but on e85, i´ve got 56mm bore and 49.5mm stroke. 198 degree main exhaust, aux is 192degrees. Transfer is 132/134/134.

[@AutoBeta2T]

Cheers for the info :)

[@darrelltaylor4542]

Another good video Dave ❤

[@AutoBeta2T]

Cheers Darrell :)

[@darrelltaylor4542]

😊

[@postulator890]

It's better to measure squish at front and rear of piston because the head will settle more toward the front opening up the squish on the hot side of cylinder. A way to avoid this problem is to center the head to the cylinder with a tool indexing off the spark plug, then pin the head with a 1/8" dowel. Then squish stays consistent when head removed and replaced.

[@AutoBeta2T]

Cheers for the info Dale. I do have a locating spigot on the barrel that does centralise the head. However, there could be some radial off set as the studs are slack in the head stud holes. I'll double check at 12 and 6 next time too.

[@kennetenglund7808]

The calculator you put your port information in, is that available anywhere?

[@AutoBeta2T]

Hi, it's just a spreadsheet I made from the formulas in Bell's book. If you want a copy email me at: [e-mail]

[@mikemelbrooks]

My understanding was squish gap should be as small as possible without the piston hitting the cylinder head, and that a suggested clearance was only a rule of thumb to allow for play/ expansion. I couldnt see cleary on the video but it looked like a large area where the squish area is blended into the combustion chamber.

[@AutoBeta2T]

That's my understanding too but with a lot of things with two strokes it's a bit more complex than meets the eye. My MSV is quite high with the 0.45 gap.

[@terrypikaart4394]

Why not just put a deg wheel on the crankshaft, so easy and get all open and close times in degrees.

[@AutoBeta2T]

I've always used this method. Never owned a degree wheel. I'll look to get one and see what it is like.

[@henkcox8212]

Can u see the pattern of butterfly on the top of your old piston .

[@sidecarbod1441]

Dave, I think your squish is a little on the tight side, A.G. bells book does not cover squish velocity, I'm sure you are aware of this fact, I would be running at 0.6 to 0.8. The other thing to note is that the squish gap should be at the most parallel or even better it should get larger as you head towards the combustion chamber, you must avoid the 'death triangle'...i.e. when the gap gets smaller heading towards the combustion chamber, this forms a triangle of trapped gas between the piston and the head. Your uncorrected CR is fairly high but the corrected is not, I guess that is because your exhaust duration is quite large. Just a quick question, how come you did not just measure the exhaust duration with the dykes ring fitted to piston?

[@AutoBeta2T]

Hi Pete, agreed it's a bit tight. Possibly why I didn't see a good increase when I raised the compression way back? I think it was 0.55 mm when I measured it before...? I may not have torqued it down previously 🤔 There's no death triangle - I checked and the solder looks parallel. I had previously measured to the top of the dykes ring in the exhaust Dyno tests with the piston just allowing light in from the duct. I did however want something a bit less subjective so I tried the wire method. I've never been happy with any of the ways to measure but I thought I'd better just stick to one... However. Either way I'm at somewhere between 200 and 203 Deg duration.

[@sidecarbod1441]

@@AutoBeta2T I' know that you know a lot about this sort of stuff, so I'm not sure why I've posted this up but I have anyway! My understanding is that if the velocity goes too high it can actually promote detonation, having said that I think you would have heard it and seen evidence of it if you had detonation. But on the flip side maybe the short power runs that you are doing is not allowing enough heat to build up which would then drive the engine into detonation. If you have access to a lathe personally I open up the squish gap a touch and also run a gap of a few degrees.

[@bobawatsit]

If I could just add my 2 bob's worth > As with 4 strokes, I would suggest that the INTAKE side of you engine is the MOST important area to concentrate on. This means that the volume and diameters of the inlet tract before and after the carburetor are very important, the inlet angle has to be as straight to the reeds as possible, which means the inlet tract will be at an angle to the horizontal, which means you need a carb (diaphragm, or FI) that works at an angle. So right from the air entry which needs a bell shaped air corrector thru to the final piston port has to be looked at, Just my years of high performance knowledge .... rob nz

[@AutoBeta2T]

Cheers for the info Bob. The inlet is on my list of things to do. The current set up is pointing the reeds at the inlet ports and I have angled the carb (not sure if I can go further?) But I've not progressed developing it for a while. I was worried about it being too long with my quite complicated adaptor for the larger reed. I have other reeds to try and a larger carb. I'll hopefully get to having another play with the inlet in the new year. Cheers again, Dave 😊

[@henkcox8212]

try gasket 0.3mm under the barrel squish is then 0.75 , transferduration longer . compression-ratio gets more bad, but it could run better

[@AutoBeta2T]

Hi Henk, I did try a gasket during previous tests and I lost power everywhere. But as you say it could have been the drop in the compression ratio. I have some more heads to machine to try same compression but more squish gap.

[@samforsey]

​@AutoBeta2T did you measure the thickness of the cellotape too? Surely it's 0.45+ cellotape thickness

[@AutoBeta2T]

@@samforsey hi Sam, the tape doesn't contact the squish band. It is in the area of the dome of the combustion chamber

[@billshiff2060]

While on measurements, Have you got an estimate of the power that will be required to overcome drag @ 100+? You should include the planned frontal area of the bike/rider that will be used and a rough estimate of the CD too.

[@AutoBeta2T]

Not exactly Bill. I know the original bike got to 94 mph with 21 dynojet horse powers; about 18 on my dyno. I fugured another 2 or 3 on top should do it. I do have a program that does top speed etc that I was going to do a video with but didn't. I'll look to do it at some point soon. I also have John Bradley's book so I'll brush up on Cd too. My program will estimate this but it said that the original bike should have done it. Maybe dynojet hp is a bit over egged? This for me is the best bit about this challenge - physics will be the final arbiter :)

[@portblock]

Im curious, and forgive me if others already suggested, but what about making a new head with 2x spark plugs?

[@AutoBeta2T]

Hi, I think if I had a larger bore then maybe? Something I haven't seen in two strokes too much. Would be interesting to see what would happen?

[@billshiff2060]

Thinking about your squish/quench gap I did some numbers for your engine and see the piston at max pressure where detonation is most likely 11-15deg ATC ATC Piston down bore 11deg .4572mm 15deg .8382mm 25deg 2.336mm If you add the clearance to that it makes me wonder how important it is relatively to get it really close. I remember the GP suzuki 750 back when had no squish bands at all and ran fine with high power for the time. Just food for thought.

[@AutoBeta2T]

A no squish band test - I like the idea of that. Could be interesting!

[@billshiff2060]

@@AutoBeta2T You'd still want the charge concentration in the center that squish bands give but maybe that's a bigger benefit than the squish band itself. There is a small pumping loss from tight squish bands, especially on 4 strokes. There is a trend in cars to relieve the squish pad with an angle opening to the chamber. I remember Kawasaki drag engines (Denco) having double squish bands, which is just relieving the angle with a second one. I wouldn't put too much time in it though, I doubt there is very much in it. Yamaha has an SAE paper on the shapes and effects.

[@kenmoule825]

​@billshiff2060 There is plenty to it. MPS is the number you're looking to hit and back off from there. Having a lower angle and domed piston require much less quench area. Many people cut a piston flat on top so they don’t have to be bothered matching or manipulating angles. Then they keep adding quench area to gain compression 😢

[@billshiff2060]

@@kenmoule825 There is very little power to be had playing with that. Much better off working on other areas.

[@henkcox8212]

At some point the pipe starts sucking ,but cant suck because the transfers still closed. Exhaust opens earlier now after the modification , did you change the transfers also ????

[@AutoBeta2T]

Nope - just the exhaust port. The transfers may need changing, and the pipe, and the compression ratio, and the corrected compression ratio, and the ignition, and the jetting and... and... and.. Bloody two strokes - simple but they aren't

[@dsimila1]

I can't run 2 strings longer than about 30 cm on a 3 hp grass trimmer (engine doesn't reach powerband). How much power is lost to spoked wheels on a fast moped?

[@AutoBeta2T]

Hi buddy TBH i'm not sure. Spoked wheels are often lighter.

[@bierbaum4284]

i'm here from alex👋😊 algorithm works

[@AutoBeta2T]

Brill, that's great to hear that the algorithm is working. I hope you enjoy 🙂

[@bierbaum4284]

@@AutoBeta2T yeah totally! cool project you have

[@AutoBeta2T]

Cheers Bierbaum - fingers crossed we to the 100 mph 😊

[@Scissors69]

A good way to calculate squish clearance, to get a safe ballpark figure, is - 0.015 X Bore Diameter. In your case 0.015 X 54 = 0.81 mm. 54mm bore is a common diameter for a 125 and I know they’re supposed to run at between 0.6 to 0.8. As you’re trying to get to 100mph I might go for closer to 0.6mm

[@AutoBeta2T]

Hi Dave - thanks for the rule of thumb - I will give it a go. I have some ore heads now so I will try different squish gaps... May 0.7mm for a start.

[@oldmanon2wheels]

on my Fantic 80 cc I have 0.7. It has ~19 HP@@AutoBeta2T

[@dutchsailor6620]

I ran 0.65 on YamahaTZ250G cylinders mounted on my TZ750, 54mm stroke, 1mm gasket compressed. Got expensive when a big end gave way.☹

[@AutoBeta2T]

Cool - 0.7 is sounding like a good ball park figure.

[@AutoBeta2T]

Ouch - that does sound expensive. However a TZ720 with TZ250 cylinders sounds very nice! How much power is/was it putting out?

[@daviddjerassi]

May i say i think the wire is to thick would you hammer it flat ? exacting work love the video thanks.

[@AutoBeta2T]

Hi David, I did try with a feeler gauge 0.1mm but didn't get consistent measurements. I may try with some thinner diameter wire?

[@tringuyenngoc7802]

How many tightening torque for the 4 head screws of the Kawasaki AR 50?

[@AutoBeta2T]

16 ft lb from memory, but I need to double-check.

[@tringuyenngoc7802]

@@AutoBeta2T thanks

[@AutoBeta2T]

Double checked and it is 16 ft lb

[@margarita8442]

would add dis turbo,, machina go fast darlinks !!!

[@AutoBeta2T]

What about a super charger? Would that work too?

[@DesignerOnline]

Exhaust = 6.27° cm²/cm³ Transfers = 4.32° cm²/cm³ Blowdown = 0.53° cm²/cm³ Blowdown percentage: 12.08% I estimated your porting using Blair's formulas, which indicate an 18.83 HP output for your engine with the current porting. I would aim to achieve a corrected piston speed of 17.47m/s at 12600 RPM. Is your current output of 17.8 HP achieved at 11900 RPM? Perhaps you could consider shortening your header pipe or lowering the compression ratio (which would further heat the pipe) to reach 12600 RPM. For enhanced performance, raising the transfers (lifting the cylinder, if feasible) would be beneficial. P.S. The correction of the targeted piston speed formula is: 20m/s * sqrt(stroke/bore)"

[@AutoBeta2T]

Hi mate. Thanks for information and sorry for the delay - I had to dig out my copy of Dr Blair's book to refresh my STA knowledge. Can I aske is your power estimate at the crank or wheel? I'm using EngMod2T for the specific time area calculations. The blowdown is: 0.001144 s/m - 27.7hp at the crank at 11500 rpm And the exhaust is: 0.014580 s/m - 23.3 hp at the crank at 11500 rpm. I don't have the STA for the transfers with me and from memory the inlet is lacking a little. I need to recheck but the STA for reedvalves can be a bit lower than what the can achieve. I wanted the keep the rpm as low as possible for longevity of the engine and to prevent it getting too peaky and having trouble in pulling top gear. However, it may be required to get the power I need. I'll re-run the STA figures at a 12600 rpm target and see what it says. The figures you presented at the beginning - are they from the information in the Jennings Angle Area article?

[@DesignerOnline]

Try targeting 10302,83 RPM in EngMod2T. Does your current exhaust and blowdown give a matching hp? What i need to know is transfer STA, Now I based my answer on the blowdown/exhaust ratio (see story below). Maybe we should mail each-other? My ramblings are getting too long :) There's a good reason to only trust Angle*Area Jennings made a few flaws: "One cannot simply substitute angle-area for time-area and ignore the engine speed factor" But Angle*Are at a specific RPM is exactly what the STA is. The RPM "is" the engine speed factor. AA = 6*STA*RPM STA = AA/(6*RPM) blowdown 0.001144 s/m * 6 *11500 = 78.936°mm²/cm³ = 0.78936°cm²/cm³ exhaust 0.014580 s/m * 6 *11500 = 1006,02°mm²/cm³ = 10,0602°cm²/cm³ I wrote my own calculating sheets and that's how I know many tricks from the book. Remember EngMod2T? It actually calculates the AA and you provided the 11500 RPM so it can convert it to STA As you've found out this gives the blowdown 27.7hp and the exhaust 23.3 hp, however there is always a RPM where they should match and give an equal hp. Blair gave us the formula to convert STA to BMEP: Bmep exhaust = 1050 x STA(ex) - 5,975 Bmep blowdown = 8187 x STA(bl) + 1,75 Now I rewrite the formula to match both ports to give equal BMEP: 1050 x STA(ex) - 5,975 = 8187 x STA(bl) + 1,75 then rewrite it to find the STA(ex) providing the STA(bl) gives: STA(ex) = 8187 x STA(bl) + 7.725 /1050 0,016277 s/m = 8187 x 0.001144 s/m + 7.725 /1050 Remember that your actual AA has already been provided and the target STA has been calculated RPM = AA/6*STA 10302 RPM = 1006,02°mm²/cm³ / 6 0,016277 However Blair's formula's are old and Jan Thiel pointed out that you can't trust the historical view of the exhaustport time*area. So that's why I should know transfer STA and you can't use the reedvalve-intake-STA due to inaccuracy..

[@AutoBeta2T]

Hi again - thanks for the reply :) Email would be good - [e-mail] I looked for the convergence rpm and at 9000 rpm the exhaust and the BD STA were about the same (within .2 hp). The transfer STA is 0.008594 s/m at 11500 rpm ( 27.14 hp achievable at 10975 rpm). I have just remembered that I did convert the angle*area for the RSA that Frits Overmars provided to STA. If I remember right Blowdown was near to Blair but transfer was higher - however I cold be completely wrong - I did this about 12 years ago and haven't delved into two stroke technical stuff for maybe 10 years. I probably have my calculations somewhere but I can't find it. Interestingly when I used flow testing equipment it came out with a Flow Time Area (FTA) for my exhaust of: 0.01547 or 25.6 Hp @11500 rpm and a Blow Down FTA of: 0.001092 or 26.65 Hp @11500 rpm. I managed to increase the Flow Time Area by putting some Plasticine in the center of the bottom of the exhaust duct - the noise emitted lowered too and Exh TFA and BD TFA increased to 27.1 Hp and 27.5 Hp respectively.

[@henkcox8212]

Does the boostport aim at the sparkplug ?

[@AutoBeta2T]

Yes

[@henkcox8212]

blowdown 28-30 compression rate corrected 7.4

[@AutoBeta2T]

Is this what I should be aiming for?

[@mariusfridlund55]

🏁👍

[@winnie-the-poohahaha4428]

NeXT version ceramic coatings ?

[@AutoBeta2T]

I wouldn't rule it out!

[@plasma081]

The bore is like almost 54 mm right...? This is the measure of a 125 cc engine if this is 50 cc which is the stroke....? 25 mm of strokes or something similar right...?

[@AutoBeta2T]

Hi - it started as a 50cc but has a big bore kit on it. The stroke is 41.6mm and the current bore is 54.5mm

[@plasma081]

@@AutoBeta2T Ok thanks for the clarification it is like almost 100 cc.... this displacement is better to find real gains in HP

[@kgnico2296]

why you don't use a 360° disc on the crank ? with a 0.1 or 0.05 mm gauge it's very accurate. With your method, if the top of the cylinder isn't exactly level with the piston at TDC all your mesurement are incorrect

[@AutoBeta2T]

Hi, I have never used a degree disk, I have herd they can be inaccurate (parallax error). I have just seen a video with one of the digital angle boxes attached to the crank which looked pretty cool. In my spreadsheet I can adjust for deck height positive or negative so where the piston is at TDC can be allowed for, It just so happens with this one it is at TDC.

[@kgnico2296]

@@AutoBeta2T Tournois racing make these tools in France, he modifies digital angle finder. In France we used to work with degree disk, the first one y had at 15 or 16 is a Compact Disc with a degree wheel printed on top, not the most accurate but good enough at the time,

[@risetvlog1484]

Maybe u must try on road with GPS speedometer

[@AutoBeta2T]

Hi - yes when the weather gets better. I have RaceChrono and a separate GPS receiver. Cheers

[@henkcox8212]

I am afraid that the exhaust -port is more than 203 degrees

[@AutoBeta2T]

Hi Henk - I don't think it is but out of interest what do you think it is?

[@henkcox8212]

You have blowdown from over 36 ?????????????

[@AutoBeta2T]

Is that good?

[@polderfischer8565]

That confuses me too... Is that used in tuned street 2-strokes? I am only used to 18° to 26° in my chainsaws.

[@AutoBeta2T]

Polderfischer - it confuses me too. I have always gone for getting the area required to get blowdown phase done so there is minimal pressure in the cylinder when the transfers open. In my single exhaust port this requires going high but in triple and T port engines it can be achieved at lower timings. In my exhaust test I kept raising the exhaust duration (port height) and the power went up with no loss of power band width. This told me that more area was required to blowdown effectively. I think each engine is different and the dyno or stop watch will tell you when it has what it wants.

[@polderfischer8565]

@@AutoBeta2T Seems to work for you. Perfekt. Maybe saws without a pipe behave different? Also we need no peak power. That may be the point. Thanks for responding! And greetings from cold northern Germany

[@miltonulm5102]

Just looked over your port timings and your transfers should be around 134-136 not 128(128 is good for 10k rpm not more) I think you can find a lot of power there :)

[@miltonulm5102]

Your carburetor is a bit on the smaller side to so test a bigger one like 30-32-34mm I would recommend PWK style carburetors

[@AutoBeta2T]

Hi Miiltonulm, I have epoxied the transfers as I thought I didn't have enough blowdown. They were around 134 anyway. I do plan to grind out the epoxy during a dyno session to see. I have a 30mm carb in reserve,. The 28mm I have seemed to work better when tested a while back but with more power now maybe time for the 30mm?

[@srerccustoms537]

Hi great video sir .I am doing a 50cc with wet nitrous system if you want to see it it’s on sre rc customs on KZbin thanks

[@AutoBeta2T]

Cheers and I'll check you out 😄

[@spacebrowni6761]

1.3% of the stroke for squish gap Some even push it to 1.25%

[@AutoBeta2T]

So about 0.55mm gap?

[@doingitwronggarage9651]

This is the best way I have ever seen anybody do this: kzbin.info/www/bejne/oJS2k2Wwhd-tmqM I think 2-stroke tuning should focus on all port timing from BDC, NOT TDC like a 4-stroke engine. Shop air into the spark plug hole through a modified comp. tester or old modified spark plug will show then the piston closes/ opens the exhaust port for real. :) Then, with no reed valve, closing the exhaust port opening with someting will make it possible to measure true transfer port timing the same way. I will argue that porting the intake port lower until you break through the floor is something worth considering.

[@AutoBeta2T]

Cheers for the link - that's a really cool way as those little boxes seem very accurate. I also like the idea of pressurising the cylinder with air - perhaps with my leakdown tested but attached to a modified spark plug? And then using the angle box to track the crank angle. Cheers - all noted in my red book :)

[@humourless682]

Your method of measuring port height, is not very accurate. Get a Veritas wheel type marking gauge (104388), to establish the port height, and then measure the port height from that using a depth gauge. Squish needs to be measured with solder, at 12 and 6, also 9 and 3, cross pattern, twist together in the middle. Its possible to run .5mm squish on Nikasil motors up to about 70mm, with tight bore clearance, but on something with a wafer thin liner, which is likely to move a fair amount, 1mm would be far safer.

[@AutoBeta2T]

Hi - I've just looked up the Veritas gauge - looks good. I'll get on ordered. Noted on the squish. I have previously only gone 3 to 9 at this is inline with the piston pip and no rock. I'll try with 6 and 12 but always felt that there would be some rock there?

[@henkcox8212]

To find out you have to measure with 360 degree-wheel , now have numbers from the calculator , thats not the same.

[@AutoBeta2T]

Hi Henk - but the number I have gets converted to degrees. I don't really see the difference. On the exhaust 0.1mm is half a degree so fairly accurate. Most degree wheels I have seen have marks for each degree. I would like to try one of the magnetic angle boxes and they have a greater resolution than both of the other methods.

[@robertfield5036]

I’m sure it’s been asked before, but would you get any gains by having a ported piston?

[@AutoBeta2T]

hi Robert - quite possibly! It's one for the things-to-try list.