Expansion Pipe\RPM question

[theo547]

So i have my LV ZXR on my scooter and my Autotech355 70cc kit on my scooter right now, at about 145 psi compression.

Im trying to figure out what i want my RPM range to be at ideally.

Seems like it really likes riding at 8500-9000 rpm's but anything above 9000 seems like its trying way too hard for very little power.

i was reading that the ZXR pipe is tuned for 9500 rpms so doesnt that mean that i should like being around there?

to be honest the most ive seen my scooter hit while under load is 9700 - i have 4.5 gm rollers in it currently.

with my 5gm rollers i was hitting that sweet spot as far as how the engine sounds and uses power, but i was almost 1\3 of an inch off full variator travel with a top speed around 45mph

So i guess my question is: should i be tuning my CVT to jump to 9000 rpm or 8000?!

i love the power im getting from 0-40 but after all the upgrades ive done i really expected more top end. im 6 foot 240lbs

[dude]

I have a ZX-R and a Top Performacnce Trophy stock carb (14mm I think) 12.21 gear ratio ( how many turns the bell turns to 1 turn of the tire) 7grm sliders it turn around 9200 rpm 51mph and I have 15lbs on you.

[reveeen]

The "ideal" thing is, if you were following Brent's build when he did the porting, he posted a chart, as in: degrees of port timing vs. operating rpm.

When you installed your cylinder, you would/should have checked the port timing with a degree wheel. Using that info you target a desired operating range (or you adjust your port timing to suit), then buy/install a pipe that "works" in that rpm vicinity, and you should be good to go.

You may have a pipe that "works" @ 9500rpm, but you likely have a cylinder that runs out of steam @ 8500rpm.

Now, don't get me wrong, 8500rpm is ok, but it requires a re-think. A LV TT, or a V-8 pipe that comes in @ 8500.... and maybe an up-gear.

[theo547]

Thanks for the input guys. i think i finally have this scooter running good - mechanicly good that is....

anyways i think if i go down to 4gm rollers i can hit 9500rpm without over reving.

so let me re-word my thoughts on this.

I have a zxr pipe so i want to be crusing at 9500rpm throughout the power band right?! as long as im not going over 9500rpm im still staying in the power band of the pipe. now my bbk has a max RPM of 10500 so at 9500 im still safe as far as the kit is concerned?!

any of that make sense or am i off base?

[reveeen]

my bbk has a max RPM of 10500

And you know this how? Your terminology is off, if someone says: "maximum rpm of 10500" it means it won't blow up @ 10500, it does not say: a "working" rpm of 10500. Cast iron, 2 ring piston, kits are mildly ported and work at 8500rpm.

[theo547]

this makes alot of sense. thanks raveen.

So i either want to get a new kit or port the one ive got.

or i guess in this order.. try and port it, after i ruin my cylinder buy a new one in the proper power range - figure thats my luck.

Thanks for the help guys i was pretty confused.

[reveeen]

no...... you should, 1st chance you get, check the port duration (timing) of your cylinder (I am not going to suggest you tear down a running motor). As things stand now it DOES run better/faster than stock, so you did get your money's worth, it is just not as good as expected.

You can increase your timing by simply running 2 (or more) base gaskets (and deck the cylinder/head to get your compression back).

See, the difference between a running scooter, and a GREAT running scooter, is in the details...............

[theo547]

Ok did a little digging - im going to buy the 47.6 aluminum kit from autotech and install the iron kit currently on my scooter on my wifes buddy 50. nothing wasted just upgraded.
In the end i think this will be the best route for me to go.

[teddy554]

reveen
What do you mean buy deck the head, i have the same kit and want to do what you are mentioning

[theo547]

By adding base gaskets you would be changing the timing of the engine. But losing some compression on the top end. So taking out the copper gasket would make up for that... Decking

[2strokd]

Decking is basically cutting or shaving some material from the top of the cylinder or the mating surface of the head to get the squish back down to a good number. When you stack base gaskets or add a spacer to get the port duration up, sometimes the piston will not go far enough up the cylinder at TDC. Another way to get the squish is to have a "step" machined into the head

[reveeen]

As 2strokd said: you are lifting the cylinder to increase the port timing, what this does is drop the compression, so the amount you lift the cylinder has to be removed from either the top of the cylinder, or the mating surface of the head, to get your compression back.

The machine shop I go to has a dandy machine for surfacing automotive cylinder heads, it appears to be a belt sander you can load the car head into to give it a quick surface (I do not have a clue what it is called). If you grasp an iron cylinder, holding it square with the surfacing belt, going in a kind of figure 8 motion, you can remove as much, or as little, as you like from the top of a cylinder. They don't charge me for this as long as they aren't using the machine.

If this would fit anything I own I would be all over it:
49ccscoot.proboards.com/index.cgi?board=4sale&action=display&thread=3741

[teddy554]

thanks for the info guys

[2strokd]

Thanks reveeen. I would be all over it too if i had a crank i know would hold up to around allota RPM. I have a BARELY used Airsal T6 A/C kit im thinking of selling as well.?. A lot tamer kit but cheaper and A/C

[reveeen]

All I have here is a vertical mina, and a DIO/NH80/Elite combo I'm working on.

I could use a vertical mina core engine, or a set of cases?