Shovelhead compression ratio and pinging

[waltcentral]

  My 1980 FLT had problems pinging with 8.0 to one compression. I am going to tear into the engine of my 1983 80" FLH and planning on going to 8.5 to one pistons and and keeping my Dave Mackie DM500 cam and getting heads reworked to allow Evo rockers to match the Velva Touch I am running.
  My question is why was 8-1 compression too much in 1980 and 8.5-1 OK now?  Is gas better?  I know that the additive package in modern fuel hinders carbon build up.

I will be running a Daytona Twin Tex and Voes before next riding season.

[guppymech]

When considering Static CR you need to factor in the camshaft timing and the result is called Dynamic CR.   With a Shovel that has a stock camshaft the MoCo eventually went to 7.4:1 static CR so the engine would run on 87 octane.  The more radical the camshaft the higher the static CR needs to be to have a reasonable dynamic CR. The DM500 cam you're going to use is meant for a Evo, right?  It has a early closing intake valve at 38 deg ABDC and no doubt works good with the stated 8.5-9.5 CR Mackie recommends with the Evo combustion chamber.  IMO the Shovelhead Hemi won't like the same CR as a quicker burning Evo in regards to EVO cam CR recommendations.   

[waltcentral]

To put some things in perspective that cam is in the shovel now but lift is restricted to around .445 with the standard shovel rockers. I just did a  compression test after coming back for a ride and I had 152 Front and 160 rear. never a sign of a ping. I called Mackie and they indicated if run with the correct lift of .500 the cam would work better in the upper and mids.

Mackie's shovel cam is very close to the evo cam as far as numbers go.

Thanks for your input I may seek out a 8.0-1 compression or maybe have Mackie do the heads.

[Ohio HD]

Compression could be due to how they tried to manage EPA requirements in a particular model year, along with jetting, ignition timing, etc. Pinging can be due to lean conditions, timing over advanced, engine heat, carbon buildup from oil, etc.

[JW113]

Opinion mode <ON>

Lift and duration are only somewhat related. You can have short lift and long duration, as well as high lift and short duration. Try to not confuse the two and their relationship to ping aversion. Totally independent of one another.

The problem with Shovelheads, IMO, are the way oversized intake ports in the heads. You will never get good flow with the head design of a stock Shovelhead. Therefore, trying to make it into a fire breathing high RPM monster takes a hell of a lot of time, and especially MONEY. Mid to high RPM power, fahgetaboutit. Go for the low to mid RPM power. That is what the Shovelhead brings to the party.

If you have pinging with 8:1 C/R, then I would first look to the jetting. Shovelheads HATE lean jetting. Hemi head with their slow burn combustion chambers do not mix the air and fuel very well, so to keep the mix that gets into the cylinder from having lean spots, you have to go rich on the jetting. EVOs, TCs, etc, have quench area that induces combustion chamber swirl. Shovelheads do not.

I would not be able to explain why one of your bikes had pinging problems and another did not without knowing a whole lot more about the overall tune of the motor. It matters not. Set it up, then tune it. Electronic ignitions with advance control and VOES go a long way to help tune out detonation. My mostly bone stock Shovelhead, with mechanical advance and points ignition does not ping at all. Can't explain why yours does, other than maybe too lean?

Opinion mode <OFF>

-JW

[waltcentral]

JW,
My 1980 FLT (in 1980) pinged until my harley shop installed base gaskets to lower compression. The only thing I did after that is drill out the plug in the carb so I could adjust air/fuel. I eventuall added a S&S Super E.   This bike I have now I cannot make ping, I just don't want to get there. I intend to add VOES and a Daytona ignition because my bike is noticeably smoother if I add timing but the bike starts to become hard to start hot -- still no ping.

[Burnout]

My 93" Shovel has higher compression pistons and I cut the cylinder bases to bring the pistons all the way to the top of the cylinders.
I did dual plug it though, to speed up the burn, so less spark timing is needed.
However the motor is in a 3 wheeler so it is very heavily loaded.

It doesn't crank hard and it doesn't ping, because I chose a cam with a late intake closing.
The intake closing determines cylinder pressure (dynamic compression).
If the cylinder pressures get too high you have to start applying bandaids like jetting rich and backing off timing.

There are tools available to remove and reset the cam drive gear to alter the cam timing and tweak your setup.

Cams for low compression motors often close the intake as early as high 30's
The cam I chose closes the intake at 50°
This type cam will not work well with low static compression.

So before taking steps to lower CR try retarding the cam a few degrees.
This assumes your spark timing isn't too far advanced and it's not running popcorn fart lean and you have a proper exhaust system.
You can see why I prefer electronic ignitions with a VOES as well. Less ping, easier starting.

Cranking compression pressures is a good clue as to where you are at as well.
High cranking pressures is usually indicative of a cam closing too early for the static compression.
Unless someone has gone crazy with the piston choice or cut a lot off the heads.

[76shuvlinoff]

I know nothing of cam selection and I have no idea of what my actual CR is but on my dual plugged 93" S&S "shovel" mill with an Andrews 7 it shows 185+ psi cyl pressure. If I do my part there is no ping on mid to upper octane pump gas.  No VOES on it.  It used to have the Leineweber L3S but cylinder pressure hit 205-210 and I didn't like that. Neither did my starter.

[Burnout]

I'll check the cranking compression on mine for a data point.

I'm surprised the L3S had more cranking compression or maybe someone has re-timed(advanced) it for use with less compression or trying to lower the RPM it comes on at?
His cams open and close the valves in a SCARY fashion!

I have gotten in the habit of degree-ing cams because taking the marks for granted is a crap shoot.

[waltcentral]

I'll check the cranking compression on mine for a data point.

I'm surprised the L3S had more cranking compression or maybe someone has re-timed(advanced) it for use with less compression or trying to lower the RPM it comes on at?
His cams open and close the valves in a SCARY fashion!

I have gotten in the habit of degree-ing cams because taking the marks for granted is a crap shoot.

As a point of reference, I just checked cranking compression after a ride last week and I got  152 front and 160 rear. Again that is with a Mackie Evo DM500 cam that intake closes at 38 but the lift was restricted by the shovel rockers.  Retarding the cam timing is a seems to be a good idea, along with evo rockers.

[Hillside Motorcycle]

At 150 +/- psi ccp, no way on God's green earth should any spark knock occur.
Very tame.

[waltcentral]

When considering Static CR you need to factor in the camshaft timing and the result is called Dynamic CR.   With a Shovel that has a stock camshaft the MoCo eventually went to 7.4:1 static CR so the engine would run on 87 octane.  The more radical the camshaft the higher the static CR needs to be to have a reasonable dynamic CR. The DM500 cam you're going to use is meant for a Evo, right?  It has a early closing intake valve at 38 deg ABDC and no doubt works good with the stated 8.5-9.5 CR Mackie recommends with the Evo combustion chamber.  IMO the Shovelhead Hemi won't like the same CR as a quicker burning Evo in regards to EVO cam CR recommendations.

guppymech, my particular DM500 is for a EVO, the Shovelhead DM 500 closes the intake at 42 vs mine at 38

At 150 +/- psi ccp, no way on God's green earth should any spark knock occur.
Very tame.

Good point of reference : I was going off the service manual that indicated anything over 100 cranking pressure acceptable

[capn]

A stock 1980 flt will ping on todays gas.As long as its just on high gear roll on nuthin to worry about.Just shift down.

[waltcentral]

  Given the wide variety of cams from Comp Cams can anyone suggest a EVO cam to run with 8.5 to 9.5 to 1 pistons in my 80" Shovel.

[RTMike]

What do you have for a ignition now,if it has a mechanical advance it may be stuck wide open.

[waltcentral]

The problem with posts that get too long is like it becomes a game of 'telephone'.
My bike does not ping. Just do not want to build one that does.

[Hybredhog]

    150psi ccp Or slightly more, good single fire w/ VOES, and proper jetting should make everything happy. Extra tall gearing, gear selection or excess carbon in chamber, could be an issue.

[waltcentral]

What do you have for a ignition now,if it has a mechanical advance it may be stuck wide open.

I have a Dyna S and will be going with Daytona twin Tech 1005

[Burnout]

Be sure to include a VOES to get the full benefit of E/Ignition

[waltcentral]

I have a switch ready to install.

[bobrk1]

When  I  bought  a  shovel  back  in  86, bike  ran sweet  except  when  taking  off from  a stop it would  ping every  time .  Took  off the  heads and  had them  dual  plugged  ran great  after  that  never  pinged  again .

[Reddog74usa]

Just finished a 68 FLH build with a Sifton 440 cam and KB 9.5-1 CR pistons. I have the stock iggy and when I took it for it's first ride had no pinging at all however I am at 4800 feet elevation here in Colorado.

[waltcentral]

   I bought a 2007 Ultra FLH new.  I installed a set of cams that were bottom end torque cams. I believe it was a Crane copy of a Joe Minton  cam that a  real early closing.             My Shovel FLH has 158 and 160    The 96' engine had a 9.2:1 spec and that bike had 150 to 155 cranking compression. That bike of course did not ping.
    A close friend has said from the time he first saw my bike that it doesn't leak, smoke (even when starting) and is  smooth at 65-70 mph. The bike came with two speedometers totaling now around 36,000 miles.
    I find it hard to believe a 37 year old shovelhead with 7.4:1 compression reads higher  than my 2007  twin cam that had a cam that closed the intake 4 degrees earlier.
   Any Thoughts!
   
   

[JW113]

My bike does not ping. Just do not want to build one that does.

One one. Why are you trying to solve a problem that you don't even know you have?

-JW

[waltcentral]

I guess So am just built that way. I gave up on the rebuild for now.
Craig at Black Widow cams building me a Sifton 112  on Evo  geometry.