2 Stroke Head Mods for More POWER | Interesting Results.

[@robertwest3093]

Man you don’t see this homegrown 2 stroke performance stuff very often. I’m loving it 👍🏻

[@AutoBeta2T]

Cheers, Robert, I'm pleased you are enjoying it 😀

[@Sam-ob4of]

If you want more, check out asoftaaja; he's from Finland, but he has english subtitles. So far he's been able to get ~15,5hp and 128 km/h

[@EarthSurferUSA]

@@AutoBeta2T We may be the last generation to do it. :(

[@AutoBeta2T]

Sam, yes, he does some great stuff.

[@AutoBeta2T]

​@EarthSurferUSA probably, everything will be electric or disposable.

[@EarthSurferUSA]

Back around 1990, I modified the squish band on a 1997 KX250 that I rode a lot, (and knew the engine power well). I wanted to break up the droplets of gas into smaller droplets. I ran a pretty tight squish for the 250cc machine (I think about .030"), but I cut "eye droplet" shapes into the squish band with a CNC mill, (like a pool and a nozzle at the squish edge), and I kept the CR the same as a stock head. I was not able to dyno it, but it did feel like stronger power on my favorite trail at the time. I sold the bike with the head on it, and never worked with the design since.

[@AuMechanic]

Good videos as always and thorough. Just note that unless you are at or near to the maximum CR you can run on that fuel before detonation, the MSV is almost irrelevant and that is born out in that research paper too. The only thing optimizing MSV will do is allow you to run the highest CR you can run using the same fuel to avoid detonation. In that case an MSV that is too high can induce detonation, somewhat limiting the maximum CR you can run, whereas an optimal MSV wont and it does that because the higher the MSV the more energy and thus heat you are creating by the more rapid the squish action. So applying that to your observation that a higher MSV compared to a head with the same CR but lower MSV, may yield a slightly higher output but is likely only due to the higher MSV creating more energy / heat, but its not a path worth perusing as the gains will always be minimal. What is well established is higher the CR the higher the power, without exception. In a 4 stroke that is uniform gain throughout the RPM range, in a 2 stroke that is less so at RPM below power band. So in short, forget about MSV as it only matters when you are pushing the CR higher and when you hit the CR where you are getting detonation only then will optimizing MSV elevate that problem allowing you to keep using the highest CR you can to get the best powers without detonation. That said though pushing the CR envelope and increasing power is always going to shorten the life of the engine so you need to keep a close eye on the insides of the engine before they end up flying outside of it.

[@AutoBeta2T]

Cheers, mate. Just out if interest what sort of CR do you recommend on old aircooled engines? I could go higher but I have a feeling that if I go much more the I'll hit problems with det on long runs?

[@AuMechanic]

@@AutoBeta2T Hard to put a figure on it as it has a few variables (could do a whole video on) like the fuel you use for one, also the fact that air cooled engines are quite variable thermally compared to water cooled. Keeping in mind that CR comes down to combustion temperature as it relates to detonation so if you are going to push up CR you would be wise to start using and monitoring a CCT gauge. Another way to look at it is that a properly functioning squish is a bit of insurance against detonation and a too high MSV can compromise that. Being mindful that a few things can raise the CCT in to the detonation zone. Such as you may not get it on a dyno run but on a long run on a given day temps may go into detonation. AF ratios too, ambient temps etc. A fresh bore and ring may run a bit hotter till it beds on. Hence monitoring CCT gauge is a wise choice. On Sprint Karting for example with adjustable AF ratio drivers will monitor EGT to get peak but also CCT as CCT will start cumulatively climbing after many laps when AF is tuned to peak power. For 2 strokes fuel acts as a coolant to some degree which is why best AF for power is ok for short periods but CCT will climb too high after longer periods which is why we stay on the rich side of the curve to avoid that where we have fixed jetting in carbs and running high CR that all relates to the onset of detonation..

[@bobg3034]

Try this? Make your squash band 2 degrees more than you piston dome so the air/fuel mixture will push out easier from the squash band! Work great on big bore 2 strokes!

[@AutoBeta2T]

Cheers, I'll add it to my list of things to try 😀

[@marttimattila9561]

In sixties when I was in Moped age the mynth was that hemisperal fire chamber was ideal. Now we have a new knowledge.

[@impulse_guy_22]

when I used to do this, it was on a 50cc watercooled and you could fit the sparkplug to the head, and then into the lathe using the sparkplug bolt section for the jaws to clamp onto. Not feasible on a finned head, so appreciate you going the extra mile to make a holding tool. Keep at it..please. You'll win!

[@AutoBeta2T]

Cool, I guess there is plenty to grab onto with a sparkplug in a water-cooled head. The tool was fairly easy to make but a bit of a faff to true up. Cheers for the support and hopefully more vids coming soon.

[@madmaxsdog8040]

Just looking at the pics has destroyed the shape I used to use, ie the bad one, having said that I might have been using a wider squish but that might only make a minor difference, goes to show though that just cos something looks right doesn't mean it is right. Also shows how far things have come since my methods way back when.

[@AutoBeta2T]

It's not conclusive. You've just got me thinking: I need to test this shape but with the same squish clearance and SAR to definitely say it is the combustion chamber shape. I have noted that a lot of later combustion shapes are like the 'good' one.

[@madmaxsdog8040]

@@AutoBeta2T I was semi joking Dave, you've got the books from back then which really were only guidelines and no mention of squish velocity in any of them, I'd guess it was an open secret between Jan Thiel and others of his calibre. I'd wondered if it would make any difference but what I was doing "worked" , ie made more power than stock so just kept doing it. Very tight 50% squish gap with a slightly flat top combustion chamber. Or maybe that shape did work best on the engines I modified, mainly RDs and mainly 250/350/400 including LCs with a few Kwaks, Suzis and smaller engines as well

[@HPRaceDevelopment]

lets make you a insertable head

[@AutoBeta2T]

I did think to do this Derek, but there are loads of AR heads on ebay for £20 so I just brought them all... probably cheaper than the ally to machine a insert. That said, I have a mate that has a cnc lathe and a TS100 head that's the same stud pattern as the AR and much meatier... Have you ever tried inserts on air cooled heads? I was told to be worried about heat transfer. I guess thermal paste!?

[@benaco46]

Thermal paste works well on air cooled with inserts

[@AutoBeta2T]

Cool, cheers for that. I guess the stuff used on computer CPU's.

[@benaco46]

@@AutoBeta2T same stuff

[@sidecarbod1441]

@@benaco46 I was going to post up that I doubt you would get good heat transfer to the fins with a head insert, I'm sure that heat conductive paste would help but I doubt it would be as good as the chamber and fins all being part of the same lump of metal. Of course inserts in a liquid cooled head are directly in contact with the cooling system so that's OK, and as we all know, heat is the issue when it comes to 2 strokes. I bet by the time you machine the combustion chamber out of the AR head there would be nothing left of the AR head! I had an old head for my KTM 300EXC that had suffered damage, I machined the whole thing out and made a few inserts for it with various CR's and squish gaps, it looks stock from the outside, so its a 'street sleeper' LOL

[@greenturbo3630]

Great video! Looking forward to the next one. Cheers from Sweden.

[@AutoBeta2T]

Cheers buddy 😄

[@PetefromSouthOz]

Hi Dave, great to see you again. I like the methodical approach you take on your channel. Having the Dyno is a must. I am a bit jealous 😄 It seems there is no rule of thumb set ups, it's all Engine + Pipe + Fuel specific. Keep up the great work, really miss doing this stuff. Cheers Pete

[@AutoBeta2T]

Hi Pete, cheers mate. yeah, the dyno is a great tool to have 😃 The problem is that you always want to try something else!

[@billshiff2060]

What made you suspect less compression might boost power? It seems to like the flatter chamber. Probably because the spark is more centralized in the volume of the chamber. If I wanted to lower the compression I'd leave the plug and squish bands where they are and deepen the chamber around the plug hole only. Yamaha TZ once used a very offset to the rear chamber that I thought had some promise but they stopped using it. In any case I don't think there is a huge amount to be had in the chamber. It is a mass of conflicting requirements.

[@AutoBeta2T]

Hi Bill, less comp from what I read about getting more energy into the pipe... also the original head had much lower compression and wasn't much worse than head A. Head B's shape may be just as good with the same SAR and gap...?

[@billshiff2060]

@@AutoBeta2T Food for thought. Lower compression does put more "energy" into the pipe but in what form? I'm thinking it is primarily heat energy and not pressure/sound energy. If thats what it is then it should behave similar to retarded timing with the extra heat increasing the speed of sound in the pipe, effectively shortening it, causing the power band to move up the rpm range. IF that is the case you might have to lengthen the pipe to take any advantage of it. What method are you using to determine squish velocity?

[@sidecarbod1441]

Yeah I ran a TZ 350 for a while, the offset combustion chamber was a 'thing' back in the day but it was never that great in practice, I had my head welded up and a 'normal' chamber cut into it, much more sensible!

[@mickl8212]

Something I did years ago, I fitted a DT 125 R cylinder head to an early 1986 TZR 125 with working power valve. The combustion chamber pattern on the DTR head was like you ha e here. The TZR one had like a protruding radius cross sectionally on it as standard from Yamaha (difficult to describe). Anyway, the DTR head made the bike run a lot smoother with a bit more power top end. I wonder why Yamaha had this difference between basically two different motors?

[@done-wright_performance]

Ive been waiting for a new video!! I love it!!

[@AutoBeta2T]

Hope you enjoyed it!

[@derranged28]

When you reprofile the chamber, do you add a spacer to the spark plug to get the "right" amount of protrusion?

[@robertblunden7160]

I agree with 100%

[@AutoBeta2T]

Hi, yes I did. I also tried varying this on some tests I did that day but I didn't present in the video. I found no measurable change. Additionally lowering or raising the sparkplug chages the compresion ratio too. 2 strokes!!

[@robertblunden7160]

@AutoBeta2T that true that's changes the compression, but we found 2 stroke engines we use on owl 1/5 scale cars work better the spark plug in the right position works much better, as I do make my own billet heads for 45cc to 71cc motor and pipes

[@TheSteelweasel]

@@AutoBeta2T Ive had deternation on engines and by adding 1 or 2 washers you can eliminate it , it also takes the plug out of the heat a little , and you then have a good idea how much volume you need to add when you pull it off .

[@aurelioquijorna4081]

Gran trabajo, muy interesante tu estudio de las formas de las cámaras de combustión y la velocidad MSV ..GRAN TRABAJO !!! , es un mundo lo de las formas de las cámaras de combustión ..KTM GP tiene cámara como tu cabezal A ... Aprilia GP tiene forma como tu cabezal B ....pero su banda squis es muy grande y por lo tanto su cúpula es muy esférica casi cerrándose , y a 0.7 mm de squis con gasolina 102octanos....al final la conclusión que sacó esque no hay forma de hacer unas directrices universales. Siempre hacer un motor de máxima potencia es un trabajo muy duro y en su ultima fase de desarrollo es un poco ensayo herror Buen trabajo :)

[@TheSteelweasel]

Ensayo e herror es siempre un grand gasto de tiempo , perro mi encantar esto . un embrasso colego

[@owenboyd5674]

Hi Dave, I recently started watching your channel, very interesting and something I was always curious about doing - making exhausts. I used to race RS125 and 250 back in the days at supercups and then road racing m, here in Northern Ireland. I used to experiment with all my bikes, some positive outcomes, and some not so positive lol. I tried countless volumes in my heads and using alternative fuels too. Where would one get some of the silicone or rubber based moulding material? Look forward to watching more interesting content.

[@AutoBeta2T]

Hi Owen, was it a Honda RS 125? The stuff I use for molding is vinamold. If you google it will come up but this was the first result from my google: www.ecfibreglasssupplies.co.uk/vinamold?srsltid=AfmBOooXtMFuHPTg0OBusCHjQrk8hE2RjpHmpAGx7Kb6NCxEgtwT18O6

[@ericschumacher5189]

Have you considered changing the squish band angle (non-parallel) +1-deg, +2-deg, etc….but maintaining the same squish band width??? I know this would reduce MSV, therefore the squish band would need to be wider or smaller squish gap to maintain a similar MSV to the best current head.

[@AutoBeta2T]

Hi, not yet but i have considered it. I want to do some more tesing of combustion chamber shapes in the future... just not ure when.

[@postulator890]

I see you're using O-rings for sealing head to barrel. That's is the way that I ultimately went to eliminate gasket leakage. Originally the RD350's had a 0.040" thick head gasket. That was replaced with a .020" shim type gasket from a RD-400, and ultimately the TZ O-rings. I figured that the TZ used O-rings, so could I. When I went there, I had to reshape my combustion chamber more like the bathtub profile your engine likes. It's interesting that as my engine progressed in stages, the chamber volume went from 18.5 cc's (RD-350) to 23cc's (RD375) as the step was removed from the head and material was removed from top of barrel. Compression went from 150 to 175. This was over the course of several years back in the 80's. Seems like you are progressing down a path I have been before. Love your vids and careful analysis. You might try pinning the head to the barrel especially if the head bolts are a loose fit in the head. That allows the head to slide forward on the bolts opening the squish on the exhaust side of barrel, right where you need the squish the most. I didn't notice what type of piston you're using. I used a DT-175E piston in the RD-375's as they had a keystone type ring which I found to seal so well, that I didn't have to use the second ring and picked up horsepower from reduction in ring friction. Does your engine use a keystone type ring?

[@sidecarbod1441]

RD's and TZ's it sounds like we were brothers separated at birth! (I even ran DT 175 pistons in a 350LC for a while). I raced a TZ350G in an F2 sidecar outfit for a while.

[@AutoBeta2T]

Hi Dale, it's good to hear you had success with o-rings too and the bathtub head. For completeness I would like to try a hemi style head as per head B with the same SAR, gap and MSV as my bathtub head. The barrel has a spigot on it and the head has the corresponding socket to alignment it bob on. I copied this from my X7 race bike that came like that... I do want to try pinning it, however I have never figured it out in my head how to accurately drill the barrel and the head for the pin? The piston for this has a dykes ring. It's interesting to hear you gained more power from ring. This is a test on my list that I want to do some day... I'm pleased you are enjoying the vids and that i'm gong down the right path :) Cheers Dave

[@postulator890]

@@sidecarbod1441 The nice thing about the DT pistons is they are 66mm instead of 64, so the displacement goes up to 375cc

[@sidecarbod1441]

@@postulator890 Yes, that was the reason I used them, it was years ago, from memory the barrels needed machining at the base gasket end as the piston height is less. I had issues with the rings pegs falling out but that's another story.

[@EarthSurferUSA]

@@AutoBeta2T O-rings usually can't handle the heat of a air cooled engine, (about 350 degrees F.). But I found a place called "O-rings west" that had some high temp o-rings (I think about 800 degrees F.). They were expensive, but they worked for a exhaust manifold I used to make in testing.

[@razor1uk610]

​ @AutoBeta2T Hi, 😊 ...the more spherical head design I guesstimate, promotes too much easier continued swirling and increasingly focuses localised refracted fluid harmonic resonances inwards & towards the sparking point pf the sprakplug, 'wetting' the spark, with turbulent flow and or higher pressures being localised much closer to the spark gap, that shrinks the size of the spark and reduces its effective power. Yes the relatively thighter squishband with more angling cpuld likely also directing cylindrical fluidic flowing vortecies from the walls of cylinder into the sparking point region, causing additional turbulences with residual vortecies from the port flow swirlings being compressed by the piston's combustion face/head. Which IMHO together reduces initial spark size and so also the ability of the immediate flamefront propagation upon the fluid's ignition. When at higher RPM's and having less operating time for the harmonic pressure variations & swirling shear forces to stabilise or to become momentarily steady enough for good igniting. Somewhat counter initiative, where as the flatter roof section around the spark point in my dumb 'thunking' refracts some of the harmonics broadly away from & equalising reflecting across off the flatter upper face around the sparking point, rather than condensing the refractions within the spark point, or at least doesn't focus all the vortecies, swirling fluidic currents and harmonic refractions etc into the spark point's zone. Perhaps a shielded or multi pronged sparkplug could work with the more spherical chamber better at higher RPM's ? ..or maybe it's just better operating below certainly rev limited point, with a more domed Combustion Pocket's qith smoother larger radii, so generates lesser turbulent fluidic distortional resonances dulling the spark's power within the longer time around TDC to combust each cycle at reduced max RPM's etc ?! Thinking weirdly further, the domed spherical head's could be partially saved by some golf ball alike shallow (>25% -

[@jritchiejritchie2687]

Great video... what size is the carburettor? It looks huge 😮

[@AutoBeta2T]

Hi its a 28mm carb. Off a kx 80 as I remember

[@TheSteelweasel]

@@AutoBeta2T is it a flat slide ?

[@TheSteelweasel]

interesting results . tight squish makes good power and your bowl on head A is very much like TZ

[@AutoBeta2T]

Great info. What year of TZ?

[@daviddjerassi]

Thank you no stone left unturned loved the video thanks

[@AutoBeta2T]

Cheers David :)

[@markcropper7182]

i had an ar 80 back in the day there where two cdi units the one with the green plug was the full power one i fitted an aurtisa big bore kit micron exhaust it went really well but i could never fix the sliping clutch even with new plates and heavy springs it would easy do 80 mph

[@2strokecarbtuningportingin187]

Great video . Great information thanks 100%

[@AutoBeta2T]

Cheers mate 😃

[@JyveKilla]

have you thought about replicating a late model 85 or 125 head design, or even replicating something aftermarket?

[@Patricks_Projects]

Nice! I said to my self: i bet the one you started with would be the best. This due to quite low ve numbers you probably having. See it like dynamic compression, low ve creates low dynamic compression. This allows for rather high numbers of timing advance. In my tzr im using now 18-1 in compression with methanol as fuel. I needed to shorten the pipes, but as bonus i have reached personal best. =) And! i have normal advance values now, about 10-12 degrees at peak power.

[@AutoBeta2T]

Cool, I did think I'd maybe get more power from less MSV but as pointed out by AUmechanic the MSV doesn't help until you are pushing the CR. I'm doing relatively short runs too. I do need to get out in the real world and test... but maybe after winter. Or ust increase the gearing...

[@Patricks_Projects]

@@AutoBeta2T I´m a bit ashamed,, i dunno what MSV stand for :D However, you might be able to do what i´m doing sometimes to get it to produce on dyno. If having a brake on the roller, push it and let engine work against it at say 10000rpm until you get desired exhausttemp. Brake it down to about 8000rpm and press record, let off the brake. But since i raised compression ratio, i haven´t tested this yet.

[@Patricks_Projects]

Medium squish velocity? If so, i would still figure that if not filling the cylinder efficiant, you get a charge with low density that the piston compresses. And by this you actually get quite low velocity. And lastly, as i often say to my self: Whatever floats your boat =)

[@ferrumignis]

@@Patricks_Projects Maximum squish velocity.

[@Patricks_Projects]

@ferrumignis perfekt, thank you :)

[@dwhxyz]

Another awesome video. I really enjoy your content - its always very informative 👍😎.

[@AutoBeta2T]

Cheers buddy :)

[@miketaylor7487]

Thank you Spark plug could have held the head in the vice.

[@AutoBeta2T]

No probs. I thought about using the spark plug, too, but the fins get in the way. I had that bar kicking about, so I decided to make that tool.

[@EarthSurferUSA]

@@AutoBeta2T I modify little 30cc engines for a living, with only about 2cc of trapped volume. So I measure CR with the spark plug, because it makes a difference in head volume with such small cylinders IMO. For your lathe, and the thread you cut with the hex stock, if you mark what jaw is on what hex wall, and machine it like you did, it will repeat pretty darn good for run out if you index the hex the same way on the 3 jaw chuck. I port my little cylinder with a small CNC mill from "Tormach". I would like to get a CNC lathe to do head work, but my manual lathe works good enough to squelch that desire. I have been living off that Tormach PNC1100 mill (about the size of a bridgeport with 1.5hp), for the last 17.5 years. I may be the first person in the world to port 2-stroke cylinders with a CNC mill, but some my competition was starting to do it too back then. But they have to farm it out. I spent a couple decades becoming a good machinist and getting manufacturing degrees before I started building the little engines about 20 years ago. Doug in Michigan "Earth Surfer Performance"

[@hunter9372]

I love this side of engine tuning, Can you tell me what Dyno hardware along with your software, I have exactly the same Dyno chassis.thanks.

[@AutoBeta2T]

Hi, it's sportdevices SP-1 I'd love to put a retarder on it to do some steady state testing, but that would be quite an upgrade.

[@hu5116]

Great video. Agree with your results. Not sure exactly what you want to do next, but I think you were running squish depth of under half a mm (under 20 mils)? I don’t think you want or can go smaller than that. Car engines run 35-40 mils. Can’t go smaller without risk of thermal expansion crashing your head and cylinder. Maybe you just want to increase quick area? Want clear to me. But increasing compression ratio and quick area should increase power. What is your dynamic compression ratio on these? That would be interesting.

[@AutoBeta2T]

Yeah, it's as tight as I can go and increasing the quench area is the only way to increase MSV now. I haven't measured the psi of the engine properly. I will do it as quite a few people have asked bout this with 160 - 175 psi being good?

[@reyalPRON]

2:32 because of the increased volume in the top on the right side that the left.

[@tonyalto1014]

What is that reusable mold putty? Very cool stuff.

[@AutoBeta2T]

Hi, it's called Vinamold

[@pauloconnor7951]

Very thorough. Well done. Water cooled head perhaps ?.

[@AutoBeta2T]

Cheers :) I have considered a water cooled head but at the min i'd like to get 00 mph fully air (fuel) cooled.

[@88RSI]

Noob question, but if there was no detonation why would you have expected more power from a lower CR and looser squish? I don't know much about 2 strokes, but on 4 strokes the tighter the squish the higher cr we can run without det. And why run flat ignition curves? Usually where the torque starts to drop you and start to load in a lot more timing because its past peak cylinder pressure?

[@AutoBeta2T]

Hi, in theory, the lower compression puts more energy into the pipe, which then works more effectively and raises power. Clearly, in my case, it doesn't 🤣

[@EarthSurferUSA]

@@AutoBeta2T ", in theory, the lower compression puts more energy into the pipe" What does that mean?

[@sidecarbod1441]

20:00 Hey Dave I know that MSV is 'modern-ish' thing, back in the old days is was all just about running the gap as tight as possible, In John Robinson's book he mentions that some people run it so tight that there is evidence of the piston hitting the head at high RPM, Gordon Jennings as an after thought mentions MSV. I must admit that pistons hitting heads sound dodgy to me! Anyway it does appear that with the larger squish gap you just have a classic case of 'wasted' fresh charge, in other words some of the charge is sitting in the squish gap and either not burning at all or burning way after TDC when its too late to do anything useful. GJ also talks about combustion chamber shapes and how they effect the heat going into the piston, mind you I suspect on the dyno you aren't running the engine at WOT for long enough to get heat fade anyway. Measuring the volume and working at the CR is a good thing to do but checking the PSI at cranking speed to worth while process again GJ reckons that with an air cooled engine about 160 PSI is the limit, mines running 160! This seems very low when some people in the Enduro bike circles are running 200+ PSI, the big issue is the cooling method, air cooling is massive limiting factor and there is no denying this! Your CR or around 12:1 is more or less what I'm running, I was running 13.4:1 which I thought was quite reasonable with a decent squish but the detonation I was suffering said otherwise! I'm now running 12.8:1, (7.43:1 corrected) 0.5mm squish. I'm only running 10 degrees advance at high RPM but then again the bore size is only 45mm, yours must be a fair bit bigger. Its interesting that pulling 2 degrees out of the timing is knocking the BHP figures down a fair amount before peak RPM and possibly just giving you a fraction more over rev, I guess because the pipe is getting a bit hotter. It goes to show you that you really need the timing to give you peak cylinder pressure at the right point in the power stroke, yeah you can then adjust it to a small degree to fine tune the rev range but not by much or you just kill the 'area under the curve'. If I was you I'd be using the heads that you have to find one that gives you around 160 PSI then run a head with that volume along with a 0.45mm squish gap, sticking my neck out here but I bet this would be the best head! Yeah on the dyno you might get more by running higher than 160 PSI but remember in the real world the rider is going to have to hold the throttle at WOT for a long time to get to 100 MPH! Anyway, another great video, keep them coming!

[@postulator890]

I used to run the RD-375's at 175 cranking compression, but I had ceramic coated piston crowns too. Much of my information is still out there, just do a web search on "The Art of Squishing Things Till They Give (Power)"

[@sidecarbod1441]

@@postulator890 175 is still 'ball park' 160! I guess the other thing is that the limit of cranking pressure is always going to differ between different bikes anyway, for one thing it will depend on how good the cooling system it and the other thing will be how well the exhaust functions as a tuned pipe. Jennings even states that if you improve the breathing of the engine well enough by changes in the inlet and exhaust system (and I guess the ports too) the stock CR might end up being too high, you might have to run a lower CR than stock, of course this lower CR is offset by the other improvements that have been made. Modern crap fuel does not help much either! Anyway its all interesting stuff, Dave is doing a great job and his methodical methods will pay him back in the end.

[@AutoBeta2T]

I've found the series of articles. The link is below: www.saltmine.org.uk/dale/dale1.htm

[@sidecarbod1441]

@@AutoBeta2T Interesting! I guess this was written before people started to worry about MSV, the article ties up with Gordon Jennings idea of running a very tight clearance. I've used steel pins on my head to locate it.

[@postulator890]

@@sidecarbod1441 It was written back in the early 90's when I retired from racing and wanted to give back all I had learned while racing in the AFM 410/450 Production classes. Using the pins became a requirement after checking squish clearance and find it had disappeared on the rear of cylinder and increased on the front indicating that the head had to be absolutely indexed to barrel.

[@COMA69BAND]

back in the late 80's a friend of a friend raced a TZ 350 powered sidecar, he did his own tuning, and swore buy profiling the head into what he called, a bell shape, no idea if this is of any use at all.

[@AutoBeta2T]

Sounds interesting, I've not heard of that shape before.

[@mikeford5106]

@@AutoBeta2T that "bell shape " was used on LC yams, i'm told it worked well on them, ... sorry , no first hand knowledge personally , Try a 1 degree profile more than the piston angle, ... it is used by a top uk two stroke tuner , [sorry can't give his name]. what octane fuel and percentage of oil are you using ? ... great project. !

[@hunnybunnysheavymetalmusic6542]

In theory, one could re-weld those heads and keep using them for more testing and general use....

[@AutoBeta2T]

Yes, eventually, I probably will. I've found it a bit of a pain eliminating the small pockets formed by all of the contamination in the metal.

[@EarthSurferUSA]

If the welding time and machining time (to make it all straight again), needed is less of a cost than a new head (if you can make what you want from a new head), why not?

[@hunnybunnysheavymetalmusic6542]

@@EarthSurferUSA I have no clue what the prices of any of what you are dealing with are. I have my own machine shop, and the ability to cast anything I want. This may set me apart from others, I do not know, but also, paying much more than scrap weight for aluminum parts is also impractical for me in all cases.

[@hunnybunnysheavymetalmusic6542]

@@EarthSurferUSA Since I have literally never even tried welding aluminum [and would likely do more harm than good] I would likely end up one of those who could not afford to follow my own suggestion. I could re-machine it just fine, but that whole welding part... That would kick my fluffy butt back to the stone age. Therefore, casting with "new" custom alloy metal, even forging to some extent, or even starting with billet, would clearly be my best choice.

[@JS-oy6nn]

This is probably going to sound odd but I’m watching because of my love for ported chainsaws and to see if there’s anything that can I apply for more power.?

[@AutoBeta2T]

Hi, thanks for watching. I'm sure that the will be something here that you can try on chainsaw motors.

[@AutoBeta2T]

kzbin.info/www/bejne/lWW7YYSNl52KmdU Porting the exhaust gave a real big power increase.

[@henkcox8212]

It seems the exhaust restricts the max RPM. I think you need higher RPM //13500 ?? Enginestroke is 41mm??

[@AutoBeta2T]

Hi, I'm about on the limit of STA available. If I raised the rpm anymore, I may lose power due to not enough blowdown STA.

[@ametti000]

It likes 20deg down low and 18 or less degrees up high. Not a flat 20deg

[@AutoBeta2T]

Yeah, I have a proper curve for it that has even more advance lower down. I used a flat curve just to try and reduce variables. Saying that I think it would have been a similar conclusion... it's very difficult to change one thing on these as each change tends to affect several other areas of the engine performance.

[@kingkong81icloud]

I skimmed the top end on one of one of my Yamaha DT125R because I blew it up an I chipped it , got someone to skim it for me , put new piston an rings in an opened power valve out fully, it was fast af was better than a YZ , I have had 4 DT125R s but this one was quite a lot faster than the others

[@AutoBeta2T]

Cool, sounds like that extra CR helped. It probably closed up the squish gap too!

[@SimsComs]

Have you managed to try carb rc odd port yet .. its killer 😮

[@AutoBeta2T]

Hi Buddy, not yet... I've only just got back into it after a busy few months :)

[@SimsComs]

@AutoBeta2T definitely worth try buddy 👍

[@MichaelForrestChnl]

Don't talk about squish as if it works independently of compression, timing, and jetting. All four form a confederacy that can drive us mad.

[@AutoBeta2T]

Noted Michael. Two strokes certainly are difficult :)

[@zacharygillette7810]

Ive tested with dragy and more compression and tighter squish has always went faster until you run into detonation. I run q16 fuel and i run .013in squish 4.8mm band 16.5:1 compression. Ive tried lower compression, looser squish and i lost a ton of low ene grunt off the launch and top end didnt gain anything. I dont have a Dyno so i use dragy ets, im not really worried about how much power it makes im worried about eta.

[@AutoBeta2T]

Cool, great info that tallies with what I have found. I'm going to try more msv and cr. Like you say, it all comes down to the stopwatch and what is fastest is best.

[@madmaxsdog8040]

DT 80 in the live chat, apologies I don't remember your name. I've looked for the notebook with my RD 80 expansion chambers and it seems to be one of the missing ones. Sorry mate.

[@prussien1914]

Why not try a keihin pwk?

[@AutoBeta2T]

I tried a polini copy ages ago and it made less. The carb on it is a keihin off a KX80 - 28mm

[@SimsComs]

16+hp .. you should be around the 30hp mark with all yhe work and effort. Whats home wrong 😮

[@bierbaum4284]

awesome!😊

[@AutoBeta2T]

Cheers 😃

[@grzegorzg7404]

Gary1200 spawana głowicą wsk125

[@fuhkoffandie]

Cool channel. Like and sub 😎

[@AutoBeta2T]

Cheers 😃

[@kamurashev]

Maybe try asymmetrical shape, like a starter cap🧢 ? That’d quite interesting to see if it helps. Another idea is the symmetrical one but with the plug sinked down closer to the piston kinda M shape dome cross section. Hope it’s clear what I meant.

[@AutoBeta2T]

Hi, i have seen these types of designs, but I've never tried. It could be interesting, though, to see how it would work.

[@bananabrooks3836]

2 years ago this project '100mph' etc started. How about a bloody road test?

[@AutoBeta2T]

haha, yeah it would be good but life gets in the way... plus it's nearly winter here and getting cold and wet. Maybe next spring :)

[@bananabrooks3836]

@AutoBeta2T After the new year diet?😁

[@cg7707]

Hi, it is not so complicated. If you raise compression your engine wants less ignition timing. In order to use the squish principle the ignition timing has to be from 17 to 10 degrees. That is where the squish action / powerband occurs. Ideally the timing at max rpm should be 10/11 degrees. MSV should not be too high for high rpm engine, this creates a lot of heat. You should aim for about 15 to 20 m/s, lower msv for more over rev. This is when compression is correct. Good luck!

[@EarthSurferUSA]

I see ignition timing as similar to less or more compression. With advanced ignition time, the spark goes off earlier and generates more cylinder pressure from combustion when compressing. Retarded ignition time creates less cylinder pressure, but puts more heat into the pipe. I port little 30cc engines for a living, and they seem to break some rules. I wonder how your degree numbers would work in the little engines.

[@postulator890]

Dave, is there a way to contact you privately? I can send you my email address on line here if you like.-Dale Alexander

[@AutoBeta2T]

Hi Dale, it's

[@AutoBeta2T]

[e-mail]

[@postulator890]

@@AutoBeta2T Thank you, just sent a reply