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Post by drawkward on Jan 17, 2011 17:23:17 GMT -5
A few of you have done the 50+ mm cylinder upgrade. Before I buy something, I want to get some advice from the experienced members.
I've got a 42mm crank with 12mm pin. So far I've been browsing around and the best deal I can find is the Autotech 54mm kit. He will ship it to me for $140. This is a basic BBK with no add ons or goodies. $145 w/ 5 extra head gaskets (thanks for the tip guys).
I want to couple that with his "Power Intake + 28mm OKO Carb" kit. Looking at around $300 for all that and jets to tune.
Then I'm thinking customized LV:ZX exhaust to suit... but that's for later.
So in a nutshell: I want the big cylinder power, but I want it with 70cc revs. I know everyone here looks for low end power to get them cruising high speeds at low revs, but I want a big jug screamer. Basically a "Mid Race" setup. Something that I can still somewhat drive on the street, but can still get good results on the drag. Anyone know of a 54mm or similar cylinder that I can match to my 42mm crank that has aggressively tuned ports stock?
I'd also be willing to pay an experienced tuner to port the cylinder and calculate an exhaust to match the port timings for good high RPM power.
PS: This is going in my 1E40QMB-A; no case machining is necessary - though I will do the little trenching from reed inlet to transfer port area that I saw in 190's thread, just for kicks.
If this goes well enough, I might just have to start snatching up all the 1E40QMB-A blocks I can find.
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Post by 90GTVert on Jan 17, 2011 19:37:32 GMT -5
Before going into any other details, I have one big concern. I don't think the stock crankshaft is going to enjoy a "screamer". I know nothing about the FM/QMB-A, but I assume quality is on par with other 50-90cc stock Minarelli engines. It's not that uncommon to see someone turning 12,000RPM with a stock crank and a 70cc kit (2strokd for example). Even with those, a lot of folks say it's a better idea to upgrade the crank if you are planning to go beyond a sport kit. Now consider that a 52-54mm piston is heavy in comparison, so your crank is swinging a lot more weight. So my question is this... Are you willing to sacrifice reasonable longevity/reliability for a bit more power made at high revs?
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Post by drawkward on Jan 17, 2011 20:11:02 GMT -5
I have an unused crank ready to go in (12mm pin, 42mm stroke, 13mm splines) (seems to be of stock quality, likely even the same manufacturer of my stock crank), my cases are split waiting cleaning and tuning, and I've got new bearings and seals on the way. My old crank is trashed (if you guys remember the thread about 9 months ago where I showed you my melted vari fan and stripped crank splines), so this 54mm cylinder is basically the only reasonable option for this motor right now - or at least that is what I keep telling myself  . I understand the risks involved with tuning to higher RPMs and am willing to accept those risks, to a certain degree. I'm very comfortable removing, assembling, and sealing top ends now. I can't count how many times I've done it. The cranks are a bit of a pain in the arse for me; I can manage it, though. I do want to preserve the crank a bit; however, it certainly doesn't have to last forever. I can sacrifice a bit of longevity to achieve my power goals and have a little more fun with the bike. I certainly don't want to push anything over 12k RPM's. I'll save those projects for when I finally go L/C. I'm definitely favoring Carlos' kit, for the following reasons: - Relatively inexpensive - Good quality products - 5 extra head gaskets ($5!) - Can just port map and match to mimic higher end kits - I like Carlos and his unsurpassed level of customer service |
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Post by 90GTVert on Jan 17, 2011 21:20:49 GMT -5
Making one of these cheap 90cc kits rev hard is kinda new to me. I'm working on getting a few more revs out of T2, but I really have no idea how it will turn out. In it's past life, it could make power around 10,000RPM max. You might wanna have a look around T2's build thread... 49ccscoot.proboards.com/index.cgi?board=builds&action=display&thread=436&page=7If you order from Carlos, consider buying some extra base gaskets... unless you just enjoy cutting them. |
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Post by drawkward on Jan 17, 2011 22:46:36 GMT -5
I'll give it another go through tomorrow in between classes - haven't been keeping up with the builds as much lately. I should give them all a good rereading. If you order from Carlos, consider buying some extra base gaskets... unless you just enjoy cutting them. I don't necessarily enjoy doing it, haha. It is cheaper... and they work like a charm. But damn, it is kind of a pain sometimes, and mistakes do happen (I've ripped more than one when doing the finishing cuts). I'll ask him about 5 extra base gaskets. That will save a lot of time and frustration, indeed. Can't beat 5 top end gasket sets for $10. Making one of these cheap 90cc kits rev hard is kinda new to me. I'm working on getting a few more revs out of T2, but I really have no idea how it will turn out. In it's past life, it could make power around 10,000RPM max. We can experiment with this together and compare results. I'm tempted to drive up to your area and get your help with this! |
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Post by 90GTVert on Jan 17, 2011 23:25:46 GMT -5
I have been meaning to go through some threads again and see if I could extract some useful info, but I've been trying to do some other stuff. The link above is where some port/rev info starts showing up.
You better have a long vacation to get this thing together. lol Notice how long my build threads go? lol
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Post by drawkward on Jan 18, 2011 0:18:38 GMT -5
I have been meaning to go through some threads again and see if I could extract some useful info, but I've been trying to do some other stuff. The link above is where some port/rev info starts showing up. Thanks, I'll check it out in the morning. I know if I open it now I'll end up reading the whole thing, and/or getting distracted and opening another thread and reading it. I noticed your article about the QMB-A in the Tech Library. Good work, man. Nicely organized. You better have a long vacation to get this thing together. lol Notice how long my build threads go? lol Yeah! haha. I'm just going to work on it in my free time, so it may take a while. I figure if I don't try to rush it in one night, and just work on it whenever I feel like it, It will ultimately be a better machine. That or I'm just too lazy to do it all at once. |
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Post by 90GTVert on Jan 18, 2011 8:08:23 GMT -5
Thanks, but basically the QMB-A article is yours. So good work on your part. lol
I think they turn out way better when not rushed. If you feel like you have to get it done, especially if you are porting, chamfering, or doing other detail work, it doesn't turn out as well. Or at least that's how it works for me. I'm more likely to pay attention to detail when I feel like working on it.
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Post by 190mech on Jan 19, 2011 20:29:20 GMT -5
I tend to think the RPM limiting factor on 42mm/up engine builds is the short rod length we end up with.Compare how low on the piston the piston pin hole is on our 42+ stroke motors to a modern MX type motor.The short rod causes a lot of side load/piston rock that limits max RPM's they can turn before coming apart,long rod cranks and custom pistons are out of most of our budgets here,so we gotta live with 10,000 rpms and be happy.....
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Post by lshigham on Jan 20, 2011 2:38:11 GMT -5
Pushing 12K on a cast cylinder is inadvisable, and I don't think you can get any alu one's for your stroke.
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Post by 90GTVert on Jan 20, 2011 7:50:44 GMT -5
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