[Lucifer]

Is there any difference when bumping up CR to 9.5-1 in Shaving the heads and using flat top pistons or just using the 9.5-1 pop up pistons??
A guy is running an EV27 cam and wanted to know which way is better to bump it up if any difference at all. Thanks

[hotroadking]

I have shaved the heads a bit and used thinner head gaskets on my 80 evo

doing this means you don't have to clean up the cyl or bore them 10 over and hone them, change base gaskets etc.

Either way will work

[Art_NJr]

Originally Posted by Lucifer

Is there any difference when bumping up CR to 9.5-1 in Shaving the heads and using flat top pistons or just using the 9.5-1 pop up pistons??
A guy is running an EV27 cam and wanted to know which way is better to bump it up if any difference at all. Thanks

1st thing is that increasing the mechanical compression ratio does not automatically increase power, as is commonly believed. Cylinder pressure makes power & you can increase that several different ways without doing anything to the CR.

2nd thing is if the piston tops & combustion chambers in the heads are not designed to work together, you'll have major problems right off "jump street". So no, you cannot just throw a set of "pop-up" pistons in an otherwise stock engine & expect to gain performance. What you'll probably get is "detonation" - one of the 2 causes of "pinging" (the other is "pre-ignition").

And since there's more power to be found in the heads than anywhere else, you'll get a lot more for your $$$ by having head work done than buying new pistons. And always think "system" rather than individual parts - you can buy the best parts in the world, but if they're not designed to work together, you'll just spend a lot of $$$ for more problems.

[hotroadking]

I'll add to that it depends on your budget but basically doing it bit by bit will not yeild immediate results. that you may want.

JMO if you really want to see significant power increase I'd buy a REvtech 100 or ElBruto from Jireh .com

Other than a little head work and cam the 80 evo is pretty limited on what you'll get power wise without spending a ton of money.

You'd be better off with a complete performance evo as they are pretty cheap relative to the cost of building up an 80 which is limited by it's size.

[Lucifer]

And since there's more power to be found in the heads than anywhere else, you'll get a lot more for your $$$ by having head work done than buying new pistons. And always think "system" rather than individual parts - you can buy the best parts in the world, but if they're not designed to work together, you'll just spend a lot of $$$ for more problems.[/color][/quote]

Yeah, I hear ya, We already talked him out of a bigger carb,told him it will actually hurt performance without headwork because velocity is whats important not volume and you'd need high velocity and a large CFM to need anything other than the CV, also told him porting not polishing the heads would yield the best results. Going fast costs money, how fast do you want to spend. So I'll tell him we're not alone with our thinkin and with the EV27with a free flowing breather, good exhaust and tune the CV he'll have a good streetable bike with some extra punch.Again we'll suggest matching a set of 9.5-1 pistons since he does want CR raised and that mod can be changed back when he wants something else instead of shaving, then thats it.
Thanks for the input fellas,just tryin to keep the guy on earth and not waste a ton of cash.
In the future if he wants more we'll put a package together for him that will work well together, he just gotta know what he wants to do first.