1980 FLT compression ratio.

[autoworker]

Does anyone know what pistons were used from the factory and their compression ratio?I don't believe it came with the lower or lowest compression piston.
Thanks

[Ultrashovel]

Does anyone know what pistons were used from the factory and their compression ratio?I don't believe it came with the lower or lowest compression piston.
Thanks

That's an interesting question. As we all know, the other models in that era were low compresson at 7.4:1. (ed.) This had to do with the hemispherical combustion chamber and the advent of unleaded fuel.

Perhaps someone who knows for sure will tell us.

[panjs]

The owner's manual for my '81 FLT-80 lists the compression ratio as 7.4 to 1.

[Ultrashovel]

The owner's manual for my '81 FLT-80 lists the compression ratio as 7.4 to 1.

That's what I suspected. Harley got caught with the older style hemi combustion chamber in late 1970s when the unleaded fuel came out. Unleaded fuel was really terrible when it first was used and most vehicles weren't ready for it. So, based on your manual, it appears that they had lower compression uniformly throughout the model line.

I know that hemisperical combustion chambers are quite effective on the Dodge vehicles. The difference there is modern computerized ignition and fuel systems. IIRC, the spark plug in in the center of the chamber on those, at least it is in the modern racing Hemis used on drag strips. That would make a tremendous difference.

I know everone seems to like high compression but I have to say, my Shovelhead ran very very well on 7.4:1 compression with a CV carburetor.

[panjs]

The owner's manual for my '81 FLT-80 lists the compression ratio as 7.4 to 1.

That's what I suspected. Harley got caught with the older style hemi combustion chamber in late 1970s when the unleaded fuel came out. Unleaded fuel was really terrible when it first was used and most vehicles weren't ready for it. So, based on your manual, it appears that they had lower compression uniformly throughout the model line.

I know that hemisperical combustion chambers are quite effective on the Dodge vehicles. The difference there is modern computerized ignition and fuel systems. IIRC, the spark plug in in the center of the chamber on those, at least it is in the modern racing Hemis used on drag strips. That would make a tremendous difference.

I know everone seems to like high compression but I have to say, my Shovelhead ran very very well on 7.4:1 compression with a CV carburetor.

I have an '06 Dodge half ton with a Hemi and has 2 plugs per cylinder. The combustion chambers don't have the true round hemispherical shape that worked so well with the gas we used to have.
Years ago I had a Chev 327 with 11.5 to 1 compression and it ran great on leaded premium. Ran like crap with unleaded premium.

[rbonner]

Yeah Compression; just for comparision.  My 78 1/2 manual from just a couple years newer (just happens to be in my desk here) lists the FL compression at 7.25:1.  You'all know what the "H" in FLH stands for right?  High COmpression.  The FLH was 8:1 in that year.  A real hot rod.

Without going too far off topic.

I ran a lot of different HEMI type engines in my life.  The "Continental" brand engines as far as the flat four and six engines used in all sorts of industries, military and especially Airplanes were all Hemi head.  I owned two different aircraft with Continentals, and flew a whole bunch.  Those were all about 8:1 some even turbocharged.

I also owned and raced several Street and Race Hemi cars.  The Race Hemi had such high domes on the pistons and dual plugs that to promote flame propogation we machined two rather large pathes on each side of the valve pocket machined in the piston.  The Street Hemi was about 10.25:1 and the Race Hemi was 12.5:1 with the flame paths.

The Harley motor could run on regular gas, and is the lowest compression motors of all my bikes unless souped.  You start overboring and the CR goes up, stroking too.

I was just talking with Leo my motor guy the other day regarding the long time Harley BUZZ about Unleaded fuel, valve seats and crap like that.  Yes when they originally removed lead from gas they had some issues back in 81 or so with unleaded gas.  The most was in regard to the additives to raise OCTANE in gas after removing tetraethel lead.  I was slightly concerned since my 79 had been sitting through out this period and never converted.


He said, that he doesn't even see any difference anymore and unless the owner is using crap gas with high compression motors and pinging them to death.  So he doesn't bother with seats anymore.

My new motor is 9.5:1 and he just said run good gas.

BOB

[panjs]

Just looked in the old Panhead service manual, for 1948-54 low compression was 6.5, high 7.0.
1955-57 FLH was 8.0 producing 60 HP at 5400 RPM.

[autoworker]

According to some internet information it looks like the 1980 model was 8.0:1 and 1981 was 7.4:1.Still searching some more concrete information though.
Thanks for the replies.