Rebuilding a 1340 ci evo engine. As luck would have it I stumbled upon a set of wiseco high compression.pistons. Question is...everything else on the motor is stock. Can I get away with running the high compression pistons or do I have to change cam...carb...heads...etc? As I am just trying to get the bike up and running again and still need to fix the primary before springtime hits...can I get away with these pistons or should I invest in regular pistons. Thanks

 

Welcome to HDF. There are several tuners who are sponsors on here and can give you a definitive reply, but changing only one thing and not others to match doesn't sound like a good idea to me!

The stock cam is nothing to shout about, as Evos were tuned to meet early emission and noise regulations. So changing the cam would be the first significant change most of us would do to a stock motor, not change compression ratio!

So IMHO you have an opportunity here. You could seek further advice and match the other components to your pistons, including cam. But you may find you also need to do some head work.

Browse through recent posts here on tuning Evos (they come along regularly!), while we wait for more answers.

 

P.S. As of right now im not looking to increase horsepower or torque...i just want to make sure the bike will start and not have any issues that cant be adjusted by tweaking the carb or something.

 

For a happy motor, Go with a cam or at least a CV-40 carb.
How many miles are on the motor?
Hatch.

 

If they are 10.0 cr, then a Wood 6 cam is a shoe-in at that ratio.
Great all-around combo.
Scott

 

Scott has given you excellent advice! If you use those pistons and fit that cam you will have a great motor. IMHO it would not be wise to fit the pistons without also fitting a suitable cam.

The alternative is to get stock pistons and leave everything as it is, but if you have to buy them, which will be the most cost effective? New pistons (and reboring the cylinders to match), or using the pistons you have and buy a cam instead, with the bonus of improved performance?

I think you will find most of the regulars here will suggest you follow Scott's advice. He is one those sponsors I mentioned earlier!

 

I think if it needs new pistons, you are better off to go with the higher comp ones. And I'm not so sure I would put the old cam back into a motor i was rebuilding, me I would go with a better than stock cam but I think you should at least check out how much difference in price there is between a stock cam and a better one. Might not make as much power as it would with good, or modified heads but probly b a lot better than stock and u could always upgrade the heads later.

 

I would not go over 10-1 as todays gas isn't what it used to be and I see no improvement in the future. As Scott said 10-1 and a woods W-6 series cam and you will have a smile on your face when you twist the throttle.

 

If you are ok with being stock after your re-build I would just get oem replacement pistons and call it a day. If you choose the wiseco, you should buy at least a cam that is properly matched to that kind of compression ratio. Which is kinda backwards but all works the same in the end. Be prepared to blow the dust off that wallet.