Just screwing around this weekend relaxing, and I thought I would do this dyno comparison. I know we don’t race dynos and the dyno is only for comparing against itself for before and after, but we’re just having fun. It is comparisons between three 124” builds; hrdtail78, Big_O, and mine. The first two are street/strip while mine was designed for the street. Enjoy:



hrdtail78:
124”
B2 Heads
Tman 662-3 cam – 266/268@0.050 duration
12.75 to 1 compression
93 octane





Big_O
124”
110 heads
Woods TW-68G cam – 268/268@0.050 duration
12.0 to 1 compression
93 octane





TOE_CUTTER
124”
110 heads
Tman 680 PS-1 cam – 248/254@0.050 duration
11.25 to 1 compression
91 octane




Comparing all three torque curves:







It is interesting how good the B2 combo is from the bottom to the top. I have a small cam and exhaust on my bike, and the torque output down low with the B2 is very good. The 12.75 to 1 compression is helping out down with the B2 heads there. I do have to wonder how that compression would do in 100 degree weather though. I do not sit in traffic on days that hot. I’ll be lane splitting or on the shoulder to keep the speed up.

Dave

 

This is just my opinion, with noted Dyno differences the curve is the key not necessarily the numbers.
We all like the big numbers and they are important, where is your power and how do you apply said juice.

Know your curve !!!!

 

Left out a key component in shaping torque curves.

 

Yes, the area under the curve is what we are trying to maximize. The B2 head combo really shows a nice table top curve, and when you can achieve that, especially keeping the torque up at the top end, you’re going to see the “big numbers”.

Dave

 

While there are MANY components that shape the curve, the cam timing and compression define what the maximum optimal potential the curve can achieve. Everything else; cubic inches, air cleaner, TB, heads, cam lift, exhaust, fuel, and tuning either help or hinder the potential.

IMHO,


Dave

 

While I'm sure 60gunner is thinking about the exhaust (very important), there is couple you missed. Different dynos. Also while SAE is an tempt to stabilize readings, the can still be errors in comparisons over different ambient conditions.

 

Yep, exhaust plays a HUGE part in it. Together with cams, they are THEE 2 most important components. Exhaust is the single most misunderstood, under appreciated component there is when it comes to this very thing. Most, or a lot anyway, people choose their exhaust based on looks and sound and are totally oblivious to just how much it affects affects how much and where their power curve is and how it's shaped.
That low end dip in torque is the exhaust and how it's working with the timing and overlap of those cams.
It's the hardest component to "get right" as far as working with the rest of the components and can literally make or break a build.

 

That B2 setup is mine when I had it in my dyna. Custom exhaust played a factor in results. That engine cranked 205ccp hot. I'd bet Jim at Mega-Flo's math is correct and tmans cams aren't exactly what they say they are. It never pinged and never started hard on 93 octane pump gas. Either way that bike ripped and got the hell beat out of it.

 

My curve is 100% because of my pipe. When I had it made he told me straight up there will be a tq dip due to the nature of the muffler. I have a baffle in it now with some tunability that should help it hit lower but wont peak as high.

Comparing different dynos/different days is apples to oranges. I'm happy with my bike, kings happy with his and I'm sure you're happy with yours.

 

That's all that really matters. Dyno numbers don't mean jack.
There is no magic pipe either.
It's always a compromise.
At the end of the day, it's up to you to decide what's tolerable and whether a compromise might be more tolerable.
It usually means losing some top end hp. Nothing that says it has to but usually does.