80 inch Evo Compression : V-Twin Forum: Harley Davidson Forums

garndavk · 07-09-2009, 01:50 PM

I have a '99 Heritage classic, bought it used a few years ago and it runs well. It has a dyna 2000 single fire ignition, V/H longshots with quiet baffles, Mikuni 42 carb and Hi flow air breather. I checked compression the other day with the throttle wide open with the engine hot and observed 185 PSI front 182 PSI rear cylinders.

I know there is a cam in the bike as it pulls away from my friends evos and all stock 96 inchers quite easily and pulls hard to the 6k rev limiter.

My question is what ratio piston is most likely installed, or can this bump in compression be from the heads milled or early closing from the intake valve. I'll eventually tear into it to see what cam is in it but for now it just runs to good. I really don't know where it stands from a Hp/ Tq standpoint.

Hillside · 07-09-2009, 07:31 PM

It is possible to establish that via re-surfacing the heads, depending on the cam.

Scott

KingofCubes · 07-10-2009, 09:48 AM

We have used a lot of Wiseco pop up pistons and the EV3 cam with similar performance results. Pull a spark plug and look at the top of the piston and see if it's domed or flat top. Back in the Evo days we used to take .060" off the heads with no other changes and get good results but with todays piston options hate to butcher the heads too much.

TheNowhereman · 07-10-2009, 10:49 AM

Quote:

Originally Posted by garndavk

I have a '99 Heritage classic, bought it used a few years ago and it runs well. It has a dyna 2000 single fire ignition, V/H longshots with quiet baffles, Mikuni 42 carb and Hi flow air breather. I checked compression the other day with the throttle wide open with the engine hot and observed 185 PSI front 182 PSI rear cylinders.

I know there is a cam in the bike as it pulls away from my friends evos and all stock 96 inchers quite easily and pulls hard to the 6k rev limiter.

My question is what ratio piston is most likely installed, or can this bump in compression be from the heads milled or early closing from the intake valve. I'll eventually tear into it to see what cam is in it but for now it just runs to good. I really don't know where it stands from a Hp/ Tq standpoint.

Leave it alone and enjoy it.
80 EVOs are almost bullet proof.
Keep changing the oil every 3k and when the compression drops below 12% of your initial reading, do a top end job.
If your on your way over 70k miles, do a bottom end job also.
80 inchers are probably the best motor HD ever came out with.