1p39qmb can make how much power on stock crankshaft?

[SirYes]

looking to see if anyone knows how much power the 1p39qmb stock crankshaft can make be for snapping.

just seeing what bolt on I can put on this thing plus cam.

[qwertydude]

Quality is unpredictable in Chinese scooters. With that said unless you're drag racing and have an engine fully kitted out worrying about grenading the engine is not the problem.

The problem is long term reliability. I think I can count on one hand the engines I've seen with a big block that have lasted more than 15,000 miles.

The more power options you put the shorter the engine life is going to be. And the failure point isn't going to be the crankshaft but the bearings and connecting rods if not simply cracking the piston.

So basically if you're just at the point of putting only bolt-ons, snapping the crank simply is not going to happen save a defective crank.

[SirYes]

big bore kit 50mm, 22mm carb exhaust ported head maybe a9 cam but if I can put the a10 in that be cool make it fit right lol.

[SirYes]

well I would like to hit past 10,000 rpm to and I think that crankshaft cant spin that

[qwertydude]

The crankshaft will have no problem spinning that RPM and many more. It's the other components that will beg for mercy long before the crankshaft.

The valves will give out long before then. There's a thing called valve float. You'll make this problem worse with high lift cams. If you know a little about old school muscle car tuning you know that high lift cams actually lower your redline due to increased valve velocity. So you're not gonna reach 10k RPM's AND have high lift cams. Simply not gonna happen.

You also need stiffer valve springs to be able to use high lift cams properly without hitting valve float earlier which means even shorter valve adjust intervals which will happen quite often because of the Chinese pot metal that the valve seats seem to be made of. And go too high on the lift and you can easily hit the piston. You're better off replacing the head with big bore valves than going with higher lift. You'll get more performance that way without shifting the powerband to unpredictable areas due to unblueprinted mystery cams with unknown cam lift, duration and overlap.

Slapping all the bolt on parts you can get your hands on without the necessary tuning expertise is an exercise in futility. Lots of people have gone through bolt-on-itis without realizing much if any gains over a well tuned stock scooter and the downside being they've also reduced reliability.

And who's porting the head? Unless you yourself are an expert in tuning and have access to flow meters and other professional tuning aids you're not going to see any benefits from backyard "porting".

Start with the basics for power. CVT tuning, BBK, then intake and exhaust and carb tuning. After that pretty much everything else bolt on adds minimal if not immeasurable increases in power. The professional tuners in Hawaii and Puerto Rico who know what they're doing put a lot more work than bolt ons to get their incredible outputs. You're talking custom milled and decked heads, forged pistons, 4 valve heads, custom programmed CDI's etc.

Carb tuning is one of the most important skills you should learn too since it's going to be the one skill that makes or breaks your engine literally. Get the tuning right and it'll scream, too rich and your power simply won't be there, too lean and you blow a hole in your piston. And don't bother with the 22mm carb unless you're getting a true 22mm slide carb. A 22mm cv "performance" ebay special carb is nothing but an 18mm carb only partially drilled out so the front measures 22mm and the rear only 18mm. This makes for a difficult to tune carburetor due to abrupt flow changes in the airstream.

[SirYes]

Originally Posted by qwertydude

The crankshaft will have no problem spinning that RPM and many more. It's the other components that will beg for mercy long before the crankshaft.

The valves will give out long before then. There's a thing called valve float. You'll make this problem worse with high lift cams. If you know a little about old school muscle car tuning you know that high lift cams actually lower your redline due to increased valve velocity. So you're not gonna reach 10k RPM's AND have high lift cams. Simply not gonna happen.

You also need stiffer valve springs to be able to use high lift cams properly without hitting valve float earlier which means even shorter valve adjust intervals which will happen quite often because of the Chinese pot metal that the valve seats seem to be made of. And go too high on the lift and you can easily hit the piston. You're better off replacing the head with big bore valves than going with higher lift. You'll get more performance that way without shifting the powerband to unpredictable areas due to unblueprinted mystery cams with unknown cam lift, duration and overlap.

Slapping all the bolt on parts you can get your hands on without the necessary tuning expertise is an exercise in futility. Lots of people have gone through bolt-on-itis without realizing much if any gains over a well tuned stock scooter and the downside being they've also reduced reliability.

And who's porting the head? Unless you yourself are an expert in tuning and have access to flow meters and other professional tuning aids you're not going to see any benefits from backyard "porting".

Start with the basics for power. CVT tuning, BBK, then intake and exhaust and carb tuning. After that pretty much everything else bolt on adds minimal if not immeasurable increases in power. The professional tuners in Hawaii and Puerto Rico who know what they're doing put a lot more work than bolt ons to get their incredible outputs. You're talking custom milled and decked heads, forged pistons, 4 valve heads, custom programmed CDI's etc.

Carb tuning is one of the most important skills you should learn too since it's going to be the one skill that makes or breaks your engine literally. Get the tuning right and it'll scream, too rich and your power simply won't be there, too lean and you blow a hole in your piston. And don't bother with the 22mm carb unless you're getting a true 22mm slide carb. A 22mm cv "performance" ebay special carb is nothing but an 18mm carb only partially drilled out so the front measures 22mm and the rear only 18mm. This makes for a difficult to tune carburetor due to abrupt flow changes in the airstream.

didn't think rod could handle 12hp. titanium valve springs and some more then right.

[buford1488]

the big valve heads that i do for scrappy will give ya alot of bottom end. good for climbing hill's. with other mod's all so. if that is what you are looking for? thanks...................buford..........