Hi everyone. I'm Giulio from Italy, I don't speak German so excuse me if I don't write in deutsch.
It seems to me that the 177 MHR isn't getting much love. I think it is a very good cylinder design, but I haven't tried much else so I really can't tell.
I just want to give you my experience regarding MHR 177, maybe it can help someone. I am sorry in advance, this will be a damn long post :)
So at first, I had this setup, which I call STEP 1
-MHR 177, 120-174° (standard timings), squish 1.0, CR around 11 or 11.5:1 I don't really
remember
-57x110 Tameni full circle crank -LML cases with intake heavily opened (in the pictures
you will see Weicon resin
used, but after a while that started to leak air so I just removed it and welded the cases)
-vforce4 with phbh 28
-Pinasco 1,6 kg flywheel on original Ducati ignition, 18°
-22/64, 16-19 cluster, z35 4th gear
-A LOT of exhaust tested, I just list the ones that performed the best with this setup: for the boxes Megadella v5cl3, Megadella XL, Faco Racing; for the expansion exhaust 2L Tech Bazooka, Sip Performance 1.0, Pipedesign Bullet M1X
So this engine was quite good, it was my first experince with reed valves and it was performing nicely. My previous engine was a rotary VMC Stelvio, and this reed MHR was quite better, especially at peak power and overrev.
I will leave here some graphs with the exhausts that performed better with this setup, STEP 1.
Overall the peak power/torque was always around 22hp and 21nm.
I noticed that all the expansion exhaust performed worse than the "similar" box exhaust. Box showed no pre-reso hole, very similar peak power, maybe just a little less power in the overrev, but not so much. Also boxes are way cheaper in price, and way more quiet in sound. So I just tought that with this setup, box were basically overall better, probably because of low timings.
The last exhaust I tried was the PD Bullet M1X, which I bought new and I had GREAT EXPECTATIONS for, and the Megadella XL. So after some months with this MHR step 1, I decided to go for the STEP 2, mostly to give the PD Bullet M1X better timings, closer to the producer recommendations.
So here is the STEP 2:
-MHR 187 (native 57mm) with 60mm stroke Tameni crank, not full circle
but rotary valve type, 60x110 127-190° timings, 1.0mm squish, 13:1 CR
-PWK 32 on vforce4
Rest was exactly the same as STEP 1.
The gain in performance was HUGE! Starting from the 22hp of the step 1, I was hoping to get around 25-26 hp, instead GSF Dyno showed 30 hp! I was shocked, and on the road it felt like a whole different engine. At the bottom end I lost very little, this can be explained by the longer 60mm stroke. At peak and overrev the gain was impressive. It was a damn great engine to run, funny as hell, I loved it!
But but but... here comes the sad stuff.
1) 420€ PD Bullet M1X performing way too similar to 220€ Megadella XL. One had toruqe at lower revs, one at higher revs, but the peak power was around 30hp for both, and that makes no sense for me, either the PD Bullet M1X wasn't good, or the Megadella XL was TOO good for the price. This engine with the step 2 had all it could need to make an expansione exhaust perform better than a box: high timings, reed intake, big passage from the reeds to the 3rd cylinder port in order to pick up the exhaust signal, etc. I just came to a conclusion that even with higher timings and all the other things I just mentioned, box exhausts are overall better than expansions! Maybe the PX engine just doesn't work too well with expansion exhausts and goes really really well with boxes, for some reason.
2) this beast of an engine, only lasted 2 weeks, sadly. The crankshaft got twisted, probably because the 60mm stroke cranks have a smaller 20mm conrod pin, instead of the bigger 22mm of the 57mm cranks. I had to split the cases open again, and remove the 60mm crank.
So at this point, because of a lack of money and time, I was forced to use again my previous crank, 57m stroke full circle. Sadly, since I manually raised the exhaust port in order to reach 190° with the Step 2, now with 57mm stroke I have 120-187° timings.
And so here comes the "step 2.5" which was a total failure. 120-187° just doesn't work, it has too much differential between transfers and exhaust. Peak power was decent but torque curve kicked in soooo late, around 5.5k rpm even with Faco box (99% similar to Polini box, which has plenty of torque early at low revs). This is a comparison between step 1 (120-174°) and step 2.5 (120-187°), as you can see, the powerband became way too narrow, way too late to kick in, and only gained a small amount at peak power.
So yeah, step 2.5 was quite bad. I tought that I just ruined the cylinder by manually raising the exhaust port so much. I just took the MHR off, and I installed the VMC Stelvio that I had from the previous engine. I took the chance to make a comparison with VMC Stelvio and Malossi MHR, both iwth standard timings 115-170° vs 120-174°), on the same engine. Surprisingly enough, the VMC performed better than the MHR with the Megadella XL.
The good low-rpm torque of the VMC, combined with the good overrev of the Megadella XL, gave a nice result I think, 23.5 hp and 23.8 nm, 10k rpm with standard 170° exhaust timing, is quite impressive in my eyes.
But... I just didn't want to give up on the MHR. Also the VMC piston is quite noisy under 3k rpm and I really hate it, even if the cylinder is performing really good.
So after some weeks of hard thinking... I decided I wanted to give the MHR another try. Instead of trying to lower the exhaust to get a smaller differential, I just said fuck it, lets raise it to higher timings, lets make this MHR the way it is supposed to be. The only sad thing is that I still have no money for better parts, so I am forced to put something together with what I have at home right now :) So here it goes!
STEP 3
-MHR 177, 130-195°, squish 1.0mm, RC around 11.5:1
-exhaust width still stock, quite small to be honest, with around 70% width on a bridged exhaust. I will gradually widen it to 75/80/85%, which is the max you can do without breaking on the cylinder studs
-57x110 full circle crank, hope this time the 22mm conrod pin doesn't twist!
-28/32/34mm carbs will be tested, vforce4 reeds
-22/64, cluster 16/19, z35 4th gear; this will probably be a little long but I can't go with a z21 sprocket since I have a 8 springs clutch and z21 doesn't exist for 8 springs clutches
-2,1 kg elestart flywheel on static Ducati ignition 18°
-I sold most of the exhausts, the best I have for this setup is a BGM BBS, which I modified on the interior, looks like I gained 3-4 hp over the whole rpm range, but I have to do another GSF Dyno run to confirm.
So yea... this will be step 3, doesn't look great but if I can get close to the 30 hp of the Step 2, I will be happy enough, and this time I should also have some reliability with the 22mm conrod pin, hopefully not twisting the crank again.
My big ass story ends here for now, wish me luck