I had seen a thread on here a while back that recommended picking up a set of 'take-off' TC 96" heads for TC 88" owners seeking a low-budget improvement ....

I was looking for that recommendation and/or data upon which it was based and found what appears to be a fairly well written (a few grammatical mistakes) research paper on the different characteristics and flow rates of the Harley Davidson stock heads .... It focuses predominantly on the '99-'04 heads, points out some improvements made in '05, and compares to '06 and later heads (obviously '06 were 88", but the same heads were subsequently used in the 96" motors) ....

Here is a snapshot of what I found to be the most pertinent data ... at the top is the http web address where I found the paper ....

While the intake valves on the later heads was reduced from 1.850 to 1.805, the exhaust valve size was increased from 1.565 to 1.575 ... also, the valve stem size was necked down to 7mm on the later heads ...

I attribute the slightly lower flow rates at the low opening and increased rates at higher opening to these changes ....

R/
'Chop

 

Call Dwight up and ask him what he thinks the reason is.

 

Great stuff and well done for finding it. Many years ago there was an elderly engine tuner near where I live and when tuning BMW R100RS heads for improved road performance he fitted smaller inlet valves and reduced the port sizes, to increase velocity. Always seemed odd to me, but he had a lot of tuning success behind him that told he knew his stuff. Quite likely the same has been done with those TC heads.

It would be great to hear from some of our engine builders here, if they are happy to share their knowledge!

 

Dwight Barry of Syke Performance ...?

He didn't write the paper ... just provided the data .... The author did not opine on the reasons ... nor did he provide an opinion by Dwight ....

I just thought the data speaks to the recommendation I had seen before with regards to a low-budget 'fix' for TC 88" owners (pre-'06, that is) to get some improved air flow ....

 

Thought maybe you were trying to solicit idea's for the increased flow rates based on the changes made between the different castings.

 

Well ... you know how, on occasion, bad gouge (erroneous information) gets passed on the forum and is then take as gospel ...?

I figured that since I had some data that substantiated this recommendation it might be worth while putting it out ....

BTW ... I like the Road King Classic bags on your Fat Boy ... did you use Cycle Vision bagger tail hardware or come up with your own mounting system ...?

 

The baggertails from cyclevision. Shawn at Dr. V-Twin made me an offer I couldn't refuse.