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Do this or something less extreme. Its not just Harley specific but Harley did relieve the 80" decks from the factory but not the 74". Of course it will affect your compression ratio. Another reason to know what you have right now before you go killing the ratio to get flow.
In a street use machine we have found back in the 70s when yea hot rod stuff was the norm porting was a play to make more cash for the shop and the shop had at that time a motorcycle mahogany deck chassis dyno with a 24 inch torque clock - with a adding machine and loose leaf paper and a couple pencils you could determine the HP - it was next to the garage door because it used a water brake and expelled the extra onto the floor - no one else we ever met had one at the track and those days it was all shop owners from everyplace
never found that flatheads or knuckles street use engines benefited from porting on the other hand we found the slag helped carb jetting and low end performance as it broke up the hard drops into manageable mist that could be counted on to do the same thing all weather - no S&S NO jap carbs - English car SU or the linkers - points was the norm - stock coils - we did re do the 62 - 62 - 64 dual point dist and convert it to a single fife in 1970 by using the two points and grinding off the rear cylinder lobe off to hit the rear coil and to set the timing we had to use the point gap at .050 - but it never mattered as it was only the hit we were looking for and we used 2coils so the back charge had plenty of time to re boot for the next plug hit rear cylinder
Do this or something less extreme. Its not just Harley specific but Harley did relieve the 80" decks from the factory but not the 74". Of course it will affect your compression ratio. Another reason to know what you have right now before you go killing the ratio to get flow.
Originally Posted by hellonewman
Here's my stock 80 barrel thats relieved from the factory.
Paul, thats good info and the pictures really help, Ill be out in the shop later farting around and Im going to CC the heads so I can calculate C/R.
I know a lot of the things Im asking about and doing may be unnecessary on these old flatheads, but to me the journey of the build is as important as the end result.
John, that is super interesting, you should write a book or do a YouTube channel.
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