Softening The Power Of A 270

[mikee]

I

[gazer]

put in 3 head gasketts , it will make a big differance

[Andy]

2 smarta*** replies deleted. Please - if you can't add to this topic by helping the OP with his request, just keep scthum!

[02-apr]

I see the reply about trading in for a smaller motor has been deleted but I could see the logic behind it whether it was meant genuinely or not.

There may be good reasons why you have a 270 even if you knew before buying that it was likely to be more than you required. Now that you have it you need to do something affordable. I know that at least one dealer keeps a stock of reconditioned barrels to offer as an exchange service come replating time. It may be that you could just swap the top end that way (but I don't know what complications might arise with matching the head to a 250 bore, probably someone on here can advise).

[mikee]

Thanks for that Andy

Edited March 3, 2008 by MIKEE

[husky]

The early 270 rev 3 is sharper at the bottom than the later ones,i think its in the porting .Try retarding the ignition about 5mm at the stator plate.i don't think they have a head gasket,its an o ring,but putting an extra base gasket in will calm it down a bit.Repacking the silencer softens the power as well.You;ll never get it as nice as a recent one,but you can make it a lot nicer.Hope this helps

[tucker]

Sorry mikee and i apologise to andy but my reply was sent with a genuine intention after all the talk of rebuilds,new exhaust,changing this and swopping that it would still surely be an option or put up with it?

[Guest majestyman340]

I

[mikee]

Thanks husky,,, thats the type of information I was looking for. I

[subanator]

put in 3 head gaskets , it will make a big difference

This what is done to my bike before I bought it, and what a difference. Smoother and more controllable at low revs, enough pull when opened up.

Mod suits club rider or intermediate skill. My timing and all else is all stock, except jetting.

I was originally after a 200 or 250, at the time this bike came up and was skeptical after ridden other 270's. It goes like a torquey 250 or 200 really.

Good thing its easy to revert back. Dont really understand what happens to the port timing, but the compression is lowered.

I have had this bike for 3 years and haven't felt the need to change anything back.

[mikee]

Thanks for the replies.

I

[subanator]

This what is done to my bike before I bought it, and what a difference. Smoother and more controllable at low revs, enough pull when opened up.

Mod suits club rider or intermediate skill. My timing and all else is all stock, except jetting.

I was originally after a 200 or 250, at the time this bike came up and was skeptical after ridden other 270's. It goes like a torquey 250 or 200 really.

Good thing its easy to revert back. Dont really understand what happens to the port timing, but the compression is lowered.

I have had this bike for 3 years and haven't felt the need to change anything back.

WHOA, just picked up on a miss quote here I replied too. Sorry to mislead you Mikee, but I have 2x extra BASE gaskets + the original = 3 base gaskets, not Head gaskets.

But the effect of one extra base one would be noticeable, as another bike I know of had done it this way and the owner was happy with the change.

With extra head gaskets, I am not sure of the sealing arrangement and how that relates, but certainly lowers the compression. Sorry cant advice on Torque or sealing.

I will watch for your reply to see how you went.

My bike is due for a set of rings and once pulled down I will look at the option of removing a base gasket and adding a head gasket.

Edited March 11, 2008 by subanator

[elmetal]

Typically when you raise the ports you shift the power higher into the rpm band, when you drop them you increase torque. This is very simplified but you get the idea. You definitely want to use the base gasket technique rather than the head gasket for two reasons: head gasket is under much more pressure so fit up is crucial, stacking gaskets (many use an o-ring anyhow) could allow for a leak; secondly by changing the head volume this way you'll change the squish band characteristics which have a huge amount to do with how the bike idles and builds power off idle. I think jetting would turn into a nightmare if you tried this route.

Other thing I forgot to mention is the added base gaskets increase the crankcase volume which decreases the 1st compression stage. This also will slow down the power hit off idle and reduce max power due to the decrease in mix amount.

[subanator]

Typically when you raise the ports you shift the power higher into the rpm band, when you drop them you increase torque. This is very simplified but you get the idea. You definitely want to use the base gasket technique rather than the head gasket for two reasons: head gasket is under much more pressure so fit up is crucial, stacking gaskets (many use an o-ring anyhow) could allow for a leak; secondly by changing the head volume this way you'll change the squish band characteristics which have a huge amount to do with how the bike idles and builds power off idle. I think jetting would turn into a nightmare if you tried this route.

Other thing I forgot to mention is the added base gaskets increase the crankcase volume which decreases the 1st compression stage. This also will slow down the power hit off idle and reduce max power due to the decrease in mix amount.

I have always thought about the theory behind this.

But a couple of things confuse me and I see it as:

The stroke and piston sweep is the same, adding base gaskets raises the exhaust port, as the gaskets lift the barrel and the exhaust port would be found earlier to the piston TDC to degree of port window - peakier?

(I am not sure what happens to the intake and transfer ports timing by doing this apart from being raised too)

The squish area volume when the piston at TDC would increase, as the piston is effectively lower in barrel - less compression.

I don't see how the crankcase volume would change as the swept area is only as much charge as the piston can deliver and the negative intake pressure would change in timing as the ports are higher.

Sorry theory can be blinding and I could have this all wrong, correct me if I am, I am interested about how this works, its so effective.

[elmetal]

The stroke and piston sweep is the same, adding base gaskets raises the exhaust port, as the gaskets lift the barrel and the exhaust port would be found earlier to the piston TDC to degree of port window - peakier?

Yes. The higher exhaust port allows the burned mix out sooner. This means the piston holds onto the explosion force for less time which equals less torque. However it allows the burned mix out earlier meaning the motor can rev higher and still breath, this means more horse power. HP is a function of RPM and Torque, if RPM's go up so does HP (am I allowed to use these shortened words here Andy?). HP is harder to control in my opnion but definitely has its uses.

The squish area volume when the piston at TDC would increase, as the piston is effectively lower in barrel - less compression.

Yes. In the case of this in tandem with the exhaust port raise the less compression and earlier opening make the low end much softer. Keep in mind the whole trick to porting a 2T motor is moving these various aspects around individually. Grind the roof of the transfers and exhaust a little higher while using a thinner base gasket. Machine the head shape and squish to work with these changes. It gets very complicated quickly and you need to know what yo want before hand.

I don't see how the crankcase volume would change as the swept area is only as much charge as the piston can deliver and the negative intake pressure would change in timing as the ports are higher.

The lower case volume is everything from the backsides of the reeds to bottom of the rings. Think of the extra gasket as a spacer below the reed block....In a high power motor you reduce the gasket to the smallest you can get and fill as many voids in the case as possible to increase the pressure (balance holes in the crank, extra space around reed block, etc.).