Recent content by hoffman900

Well, I just ran out of time with this one. The motor is already sold. See Craiglist add for details. https://philadelphia.craigslist.org/...775211090.html Moving to Atlanta for work / life commitments and I just can't bring this with me. I'm highly motivated to get rid of this. Located in...

The large duration is because it includes the lash ramps. Here is the rocker ratio change with the roller rockers throughout the lift curve. This is why cam lobes for these OHC rocker engines are typically asymmetrical. I'll have a stock Yamaha cam and an older Megacycle design measured up...

So three years into this motor build and FINALLY something is happening. I have all the parts I need, dropping the cases and all bearings all to the local machinist on Saturday to have washed and bearings pressed in (need an oven). I also wanted to mock up the cylinder head and checked the...

The profile was measured on a CamDr type equipment and the valvetrain geometry was all accurately measured and drawn in AutoCAD. Then I used Excel to perform analysis. To get 3 axis on the same graph, I just normalized the curves (hence no values a they would be worthless). I had to do some...

"Your lift variance makes me wonder if the angularity of the rocker's arm wasn't accounted for. The effective arm length varies as the cosine of the arm's angle. In the case of the XS650 rocker, swinging thru -6° to +6°, the cosine factor goes from 0.995 to one to 0.995. Yeah, it gets...

Very cool, TwoManyXS1Bs. Here is a little valvetrain project I'm working on myself for the SR/TT500 (they have similar valvetrains to the XS650). I'm interested in observing how the lift curve changes from the lobe to the valve. I currently have two examples of aftermarket camshafts and a...

TwoManyXS1Bs, shoot me a PM with your email. I want to talk more about this with you regarding the SR/TT 500s. Thanks!

If you want to get into the inefficiencies of the 4 cycle Otto engine, watch this excellent presentation by Earnhardt-Childress' Dr. Andy Randolph:

Gary, I only quote in flywheel numbers - maybe where your confusion has arisen earlier. If it's RWHP, I'll let you know. It's an accurate model'ed sim of a real life engine. If you're engines are making power that high with the same CA as a TM-38 offers, then you likely have less CFM per...

Keep in mind this is for my application only and my exhaust design. There are many reasons why the TM-38 on my combination will peak lower than other, but the largest driver is going to be 'Choke flow' and it's a function of CFM vs. the MCSA (in this case 1.77in^2 ) and when the MCSA reaches...

Jack, here is a simulated Mach Index trace of my combination at 7000rpm as taken at the valve throats. Note the mach index on the intake side - right in line with our 7000rpm peak and approaching .55 Mach.

Jack, here is a great post by Larry Meaux (PipeMax creator):

Hey Jack, Good seeing you still around. We're pushing 133cfm/sq-in through the MCSA of the head. Peak flow is 235cfm @ 28" @ .600" lift (230cfm @ .500) through the spigot. With the carburetor and velocity stack bolted on, it goes down to 216.3cfm @ .600 and 208cfm @ .500 A TM-38 will flow...

Gary, No doubt those guys were top of their field during their heyday, but time marches on. We know a lot more about airflow than those guys ever could. Porters working with much higher depressions than Jerry used (looking for flow separation), pitot tubes, etc.Even Branch's Harley stuff...

Gary, Things change a lot - headers for instance, look at a current NASCAR Cup car, 1 7/8" OD tubing off the head and they're making ~850bhp. They were making about 300hp less 35 years ago and were running as big or even bigger primaries. Here is a post from one of the premier header...