I have the SE203 cams and it's about as close to a carb "potato potato" sound you can get with an EFI bike. And a lot of my friends are jealous of my sound.

 

can anybody please tell me how to know the overlap value of a cam? I see values like lift or durantion but I supouse the overlap is something diferent.

If I understood correct the more overlap the more similar sound to carb ones?

I was thinking on putting 255 cams in order to get some torque at low rpm but sound is also very important to me.

 

TC-88s (carbed) should idle at 950-1050, not sure if they increased the requirements for the '96.

 

Carbed or EFI have nothing to do with exhaust sound; cam profile, timing and compression are what makes an exhaust note.

Overlap is defined by the time the intake and exhaust valves are both open. If intake opens at 34*BTDC and exhaust closes at 10* ATDC, overlap is 44*. The objective of overlap is for the exhaust gas which is already running down the exhaust pipe, to create an effect like a siphon and pull a fresh mixture into the combustion chamber. Otherwise, a small amount of burned gasses would remain in the combustion chamber and dilute the incoming mixture on the intake stroke. Duration, lift and LSA combine to produce an "overlap triangle". The greater the duration and lift, the more overlap area, LSAs remaining equal. Given the same duration, LSA and overlap are inversely proportional: Increased LSA decreases overlap (and visa versa). More overlap decreases low RPM vacuum and response, but in the midrange, overlap improves the signal provided by the fast moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.

Less overlap increases efficiency by reducing the amount of raw fuel that escapes thru the exhaust, while improving low-end response due to less reversion of the exhaust gasses back up the intake port; the result is better idle, stronger vacuum signal and improved fuel economy. Due to the differences in cylinder head, intake and exhaust configuration, different engine combos are extremely sensitive to the camshafts's overlap region. Not only is the duration and area of the overlap important but also its overall shape. Camshaft overlap duration less than 30 degrees tends to produce good low end power.

When you get it right, overlap helps draw in the intake charge, but excessive amounts actually reduce power by letting intake charge escape out the open exhaust valve. Lots of overlap virtually guarantees a cam won’t work well at low rpm, regardless of how strong it is wide open.

Increased overlap equates to reduced idle quality, vacuum, and harsher running prior to coming up on the cam. Lots of overlap works great at high rpm because more intake charge manages to cram itself into the cylinder. However, lots of overlap will also make the engine run badly at low rpm. Cams with a lot of overlap tend to cause rougher idling because of the lack of vacuum they create in the manifold.

Overlap (lots of duration and tight lobe-separation angles) decreases cylinder pressure, especially at low rpm, which allows an engine to run a higher compression ratio and still work on pump gas. High cylinder pressure, which is caused partly by a high compression ratio, is what makes an engine detonate on pump gas. Decreasing the cylinder pressure by adding duration is just like taking compression out of the engine, but mostly only at low rpm.

Typically, however, small lobe center numbers (more overlap) equates to more midrange power at the expense of top-end power, and big numbers (less overlap) will give more top end, sacrificing midrange.

Looking at camshaft overlap, or top dead center (TDC) lifts can give you an idea of lobe profile. Generally, the larger the TDC lift, the broader the profile. Engines that benefit from higher TDC lifts are stock displacement engines with increased compression & high airflow capacities; also larger displacement engines.

Increasing the degrees of overlap tends to move the powerband up the RPM band. Increasing the overlap can increase peak power, but only if the exhaust system is properly designed to scavenge the cylinder. Decreasing the overlap tends to boost lower rpm performance.

Sorry for the long winded explanation but you did ask about overlap.

 

I wouldn't expect a lope from the 255's, but it should be louder (exhaust) and sound more energetic.

 

Twin cam flywheels don't have the mass to safely run less than 950 rpm. "Stroked" 96's only exacerbate the problem. With all the problems with weak crankshafts, I would never slow down the motor just for a cool sound.( Particularly '07 and '08 cast crankshaft model years.) For the same reason, I'd never run the motor down the road at less than 2200 rpm either.

 

You want the old harley sound I got a 72 Ironhead with Y cams I'll sell you, it likes to mark it's territory and got a nice loping sound.

 

I was after that 800 rpm in mine too.I figured i could get away with it since i have a welded crank and the feuling cam plate and oil pump.It idles with 25 psi on a hot day and charging doesnt concern me because it would only discharge at maybe a red light and would pick up as soon as i started moving.However i found that most fuel controllers like my tts wont let you change the rpm setting trust me i tried OH WELL.

 

..heck...if you want the "mashed-potato-potato"...idle it below 700 for a while....

 

Get a Shovelhead if you want that crunch. Nothing else sounds quite like it.