260s v 264s in a 113 motor

[David Jackson]

Hi Mike; its me again.
There is a set of brand new SE 260s for sale I might be able to get at a pretty good price. As you know the 260 is pretty close to the 264 except .609" lift instead of .635. The duration is actually close; intake timing seems to be advanced in the 260 as opposed to the 264, exhaust also. Duration is within 1 degree for the intake and the 260 has 7 degrees more duration in the exhaust.

The 260 is supposed to be a good cam for the 103" motor, according to the HD catalog. Again, my motor will be 113" with HTCC CNC Ported heads, HD 10.5:1 cr; and I have an HD 51mm CV carb and am using my V&H Pro Pipe (it is maybe not as quiet as I would like but it is paid for.)

On the phone we talked about moving the power curve down a bit, so that the hp would not still be climbing when the motor runs out of revs (I have the HD variable ingnition gadget and can choose up to 7,000 rpm I think; but that is moving some large parts around a bit fast possibly). I have the heavy duty rockers, lifters, support blocks, etc. etc. Whatever was in the race catalog I got.

How does that stack up on your computer model, i.e. the 260 v the 264?

Thanks;

David Jackson

[Mike]

The 260 shows a corrected compression ratio of 8.94 and the 264 shows 8.64 on the modeling. We know from experiance that corrected ratio's of 9.2-9.5 give the best street performance and torque. But this number can be reduced as the motor size goes up simply because of the increase in power that comes with the size. Between 8.8 and 9.2 gives a motor that is easy to start, cooler running and less risk of detonation. These numbers can go up in high altitude areas (Denver) and some engine builders take advantage of this to boost low/mid range torque. Of course, all this is based on intake closing only and totally ignores overlap, lobe centers (LSA) and exhaust timing. In summary, the 260's look better than the 264's on the modeling and from past experiance.
The motor will certainly rev to 7k but piston speeds are fairly high, directly reducing longevity. Unless your racing we do not really want to build something that requires that kind of reving. The hp that is gained at the high rev's would be more usefull if spred out in the lower, more commonly used rev's.
Regards, Mike

[David Jackson]

Thanks Mike;

Based on your computer modelling which SE cam would be the absolute best with my motor? (113", 51mm CV, HTCC CNC Ported heads, V&H Pro Pipe w/either the comp baffle or the street baffle?

Regards;

David Jackson

[Mike]

Technically, the computer likes both the 260 and 258. The 260 gives 8.9 corrected pressure and th 258 gives 9.1. I like the 9.1 number but I also like the higher lift of the 260 (.609 vs 258's .569). The higher lift means the valve is farther off the seat at any point in time and this allows the motor to take a deeper breath, which in turn means a more concentrated charge in the cylinder. A common misconception is that we look at cam lift as a function of max. head flow numbers. Even though a head may stop flowing at .550 lift, the motor may still respond to .650 lift to promote cyl fill. You can go too far and start to loose port velocity not to mention the physical constraints that come with high lift. The latest rage in high lift/short duration cams reflects this philosophy. The duration is kept short because most street heads do not flow enough to to take advantage of long duration or we cannot turn the rpm's required. These cams really promote low/mid range torque, work great with the heads most have and provide great seat of the pants feel.
Stay with the street baffle in the Pro pipe. It will be quiter and actually have a better torque curve (less of a dip between 2-4k vs. the performance baffle).
Regards, Mike

[David Jackson]

HI Mike;

Thanks again, as always, for your expert advice. The tech guy is not well at the local dealer and that is why you don't have my cases yet for the breather.

Regarding the cams; it seems as though it may well be a toss-up between the 258 and the 260 cams. Inasmuch as the 260 uses the same perfect fit pushrods I have now, and inasmuch as I have the highest flowing heads from HD that I know of, then the 260 seems to be the way for me to go.

With the ProPipe; I have used both baffles; I used the standard baffle with the stock displacement and once I got going I did not hear the noise any more. After I went to 103" I used the comp baffle and I always heard the pipe, no matter what the speed.

I can certainly start out with the regular baffle in my 113" motor. Inasmuch as I am not racing anyone I doubt I would notice much difference and the bike might, as you suggest, be more rideable.

I am imagining that for absolute max torque and absolute max hp with 113" I have to go outside HD components and get different cams, different heads, different pistons, and possibly a different carburetor. Maybe next winter ...

If you were building a 113" motor and wanted the maximum performance you could get .... what components would you use? Let's figure 120 mph would be plenty of speed and figure midrange torque would be a desireable goal for a fast, rideable, machine.


Regards;

David Jackson

[Mike]

Well! I would have Baisley perform "Hybrid" head work, Axtell 20 degree pistons to match heads, T-man 650 cam (gear drive) or similar, Zippers 48 Mikuni/air package and D&D boarzilla (loud) exhaust. I would expect 140-145hp/130-135 tq. Starter ring gear and clutch upgrade (TPP lockup) required. $5000-5500 parts plus labor (expect approx. 14 hours, assemble, CC/clay, clearancing).
Costs are just approx for discussion and a complete estimate would be required.
Regards, Mike

[David Jackson]

Wow! Lots of HP, lots of TQ, lots of $$. It cost money to go fast I guess!

Maybe I can make lots of money this summer ...

Regards;

David Jackson

[Mike]

Yep!!!!
Mike