What are the advantages/disadvantages with decking the head vs. getting a stroker crank. I would assume they are both used to increase compression only. Not sure though. Thanks.
Decking vs. Stroker
- Thread starter Blastizzle
- Start date
So redesigning the head is basically changing the shape of the dome right? So I'm trying to keep the bike at basically stock bore but not sure what to do first, crank (+3 or +4 don't know) or get the whole P&P with redesigned head.
you will have to get it ported to the crank you get.....so get the crank...get the port...then throw it all together
the +3 crank from vitos is a bolt in crank no other mods needed.
the +4 crank from hotrods is required to get the cases trenched which addes about $75 to the bill.
if you have the cash what i would do is get the +3 stroker then send it out so the head can get redesigned and get the ports lined right up for the stroker so you dont have to use the junk spacer plate..
talk to freek he ran a ported +3 stroker motor im sure he could tell you how much it ripped
the +4 crank from hotrods is required to get the cases trenched which addes about $75 to the bill.
if you have the cash what i would do is get the +3 stroker then send it out so the head can get redesigned and get the ports lined right up for the stroker so you dont have to use the junk spacer plate..
talk to freek he ran a ported +3 stroker motor im sure he could tell you how much it ripped
Decking=smaller combustion chamber=Higher compression.
However, the main benefit of adding a stroker crank is increased DISPLACEMENT. More vertical travel increases the size of the cylinder shaped mass of air that you are compressing. That is why the Vito's kit comes with a spacer plate. It maintains the compression ratio (more or less) while increasing the stroke. The added benefit of more torque is a byproduct of engine geometry, longer stroke engines with make more torque than an equal displacement short stroke motor.
The fact that some engine builders are putting in stroker cranks without the plate is very cool though. Essentially (I'm assuming) they are modifying the head for appropriate clearance (since the piston prob sticks out of the cylinder) and combustion chamber volume, and certainly building in a bit of extra compression at the same time. With a stock compression of only 6:1 the Blaster has a lot of wiggle room for that kind of mod.
The one thing I really can't comment on is what having the spacer or not would do to port timing. Obviously. having it in seeks to maintain stock timing. I'm just not sure what having it out would do. I suppose cylinder porting to compensate would be necessary, at least.
However, the main benefit of adding a stroker crank is increased DISPLACEMENT. More vertical travel increases the size of the cylinder shaped mass of air that you are compressing. That is why the Vito's kit comes with a spacer plate. It maintains the compression ratio (more or less) while increasing the stroke. The added benefit of more torque is a byproduct of engine geometry, longer stroke engines with make more torque than an equal displacement short stroke motor.
The fact that some engine builders are putting in stroker cranks without the plate is very cool though. Essentially (I'm assuming) they are modifying the head for appropriate clearance (since the piston prob sticks out of the cylinder) and combustion chamber volume, and certainly building in a bit of extra compression at the same time. With a stock compression of only 6:1 the Blaster has a lot of wiggle room for that kind of mod.
The one thing I really can't comment on is what having the spacer or not would do to port timing. Obviously. having it in seeks to maintain stock timing. I'm just not sure what having it out would do. I suppose cylinder porting to compensate would be necessary, at least.
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Adding the spacer plate significantly changes the port open period, especially in the transfer ports. The only purpose of the plate is to raise the head enough to clear the piston. I don't use the plates on my builds for two reasons; a) It leaves me with less porting options as the timings may end up taller than I need and b) It is one more gasket area prone to an air leak. One thing I find my customers like is that nobody can tell they have a stroker.
Both the porting and headwork have to be done with the crank decided on. Stroke and connecting rod length will alter port dimensions. A stroker is a very benneficial mod in that it will greatly increase the amount of low to mid torque the engine makes and broaden the power curve. If properly ported you can see very significant gains in peak horsepower and rpm without the curve becoming peaky and un-useable.
Decking the head and/or cylinder is done to add compression and/or correct the horrible wide squish clearance the blaster has from the factory. But, as said above I highly recommend having the head completely re-worked. The blasters stock head design is horrible for making power. Yamaha de-tuned these bikes to make them more freindly for the young/novice rider, they are nowhere near their potential for power output in stock form. The stock head design is one of the ways they accomplished this. I completely re-design the squish band and combustion chamber on them to yeild more power everywhere. The head modification is not optional on a stroker build in our shop, it's manditory to set them up.
-Brandon
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