Cam duration bias and L/Cs for MVA heads on a mild 120 - MVAs in general

[1FSTRK]

1FSTRK,

I can't disagree with any of the theory/academics above. It's just that these odd machines sometimes defy all logic.

Dave it is not that I disagree with the theory, there is a place for it and it is valuable. It is when it is misapplied or misinterpreted that it becomes irrelevant. Too many will memorize Speedtalk and David Vizard's books and then recite them rather than understand and apply the principles to an actual engine design. Just because they do not see the exact text book example they state the principle can not apply or they do the opposite and apply it to all engines equally regardless of their individual design needs.

One statement made over and over is that you can not tune the intake on a Harley. In it's literal definition that may be true. You do not have individual runner intakes or evenly spaced pulses in a shared single plenum. That said anyone that has raced or spent time on a dyno knows that you can use larger and smaller volume manifolds, spacer blocks, and different length and diameter velocity stacks to increase peak power or torque as well as move the the peak points around in the rpm band and that is tuning the intake. Your exhaust example is the same and if enough time is spent you can see where one system will help or hurt the other. Is it a tuned exhaust like the finely formulated exhaust on 2 strokes that do a large percentage of the work to fill the cylinders, no but is it tuned to give an advantage to a specific Harley engine compared to an off the shelf pipe well yes.

I will not pursue this further here taking your thread father off coarse. I do think that with your specific engine and cylinder head you have a good topic and by defining them from the start you removing them as a variable so your cam timing questions should easier to find answers to.

[Admiral Akbar]

My 117 with TW9Bs did not like a propipe at all. Big peak torque, but huge dip in the middle, peak horse not impressive. Tried various baffles to no avail. KW 2" stock dyna looking 2 into 2s, big fat curve, but like a light switch, stand off 12" out of the carb at 5750. Swapped in higher flowing baffles and cut 1" off of the tapered ends. Next day, no stand-off to 6400. Gained 3 horse, lost 3 lbs, still lovely fat curve. It also liked a boarzilla. Less peak horse  than the KWs, but more T. Kept it.

Dave

Great post Dave, it is a great example of how these HD's work as apposed to how the "academics" think they will work. You can read and write all day on the internet about engine design and particularly other engines and how their info applies to the  HD's design but most of it means very little when you go into the dyno cell with a running HD engine. There is nothing like the puzzled look of a automotive or 2 stroke expert when their super high performance designed HD prototype comes up short on the dyno.

Why do you spout out this ridiculous crap?

Speak of the devil and he appears.
How ya been?

I do not think Dave's post was crap and I agree with his post of actual findings over a lot of the theoretical posting above it.

So you think I'm an academic just cuz I understand physics?  Funny.. I've been doing good.  Nope your post was crap. As a mater of fact I swapped stuff for Dave's AR100s. Still have them..     

[dave brode]

I had forgotten that those 2 into 2s went to you. I just looked, they don't make those dyna pipes any more! Good that you still have them.

[HD/Wrench]

Well if you look in the dyno section I have posted up a few 120 ST builds as well a 120ST with the GMR 600 cam in it . I tune for a few local HD dealers and a while back the ST was a hot ticket item and I was staying busy on the dyno with them .

Reason I bring this is up is the 259 cam , and then head volume I was doing a CCP test on each one of them as some ran very well and others not so much . Being I was only tuning and not working on them a CCP test was just for my own info.

I would see more CCP in the better running ones then in the less than engines ..

The 259 cam does work ok with a boost in comp ratio with those heads ,

With other testing I feel you have to pay attention to the EX open point with that head , and CL .. I can look to see if I still have the sheets  if you need or want to look them over  ,...had a computer go south as well the back drive got re formatted by mistake so I lost a fair amount of it

[dave brode]

GMR,

Thanks for the input. The 259E opening is 7 off from your 600s, which seems significant to me. Have you done a back to back between them with no other changes?  I saw the dyno from the failed crank  oval cylinder 120ST. Pretty stout!

Of course, exhaust differences can make all the difference. I read a thread of yours in which you stated your preference of the fatcat "vortex" baffles over the perf baffle. The "vortex" is louvered, and the perf is smooth core punched holes? My little fatcat has the louvered baffle.

Did you check cam timing on the several 120ST engines? I must admit to never having checked cam timing on the cams that I've installed, but I plan to on this engine. I wonder if that may make one a runner over another one that's a dog.

I'd enjoy seeing the sheets if you can find them.
Best Regards,
Dave
[p.s. I like to look of your 600s]

[Timinator]

Still waiting on back to back exhaust duration bias posts with MVA heads. Getting ready to run some myself when time permits.
Still playing with intake tract length and the resultant gains(?) in relation to intake tract length "tuning" issues. No theories yet.
TIMINATOR