The thing you have to remember is the higher lift of the cam increases the load on the starter even without an increase in compression which, depending on the timing of the cam, can increase static compression even without any other mods.

 

Had not thought of the higher lift cams causing additional load on the starter ... makes sense ... the additional force of overcoming the valve springs at the marginal spring rate beyond stock .473/.474 ... (does not seem like it would be that much) ....

However, I do not see why cams alone would increase the "static compression ratio" ... the def is the combustion chamber volume divided by the swept volume of the cylinders plus the combustion chamber volume ... nothing in that equation is changed by higher lift cams ...

If anything, my understanding is that the dynamic compression ratio could be decreased a little due to increase in overlap of Int/Exh of the replacement cams ....

What am I missing ...?

 

You're not missing anything, I mistakenly wrote static when I should have written dynamic.

I haven't checked what the timing marks are on these cams, I'm just saying that changing a cam will change the dynamic compression ratio and can make an engine even harder to start than the static compression ratio would indicate.

 

As a general rule no matter what your lift is Longer duration cams will lower compression. Shorter Duration (low end cams) that have less duration than stock will in fact raise compression.

Hence the need for increased compression VIA High Top pistons when using high lift long duration cams. They give back the low end that the extra duration takes away.

Many of the better all around cams will have a very High lift with a very short duration. These provide a good low end torque with good high end RPM power.

 

Okay ... I think I've got it ... my aftermaket cam (mild) Andrews TW37B actually increases duration and has a little more 'overlap' ... thus, lowering dynamic compression ratio ... so, by increasing compression ratio (either by heads with smaller combustion chamber like SE High Compression heads with 72cc combustion chamber or by "decking" my existing heads or thinner head gasket (not much difference) ...) I could get back a little more low end torque ...

But, due to the increased resistance of the cams (attributable to the higher valve lift against the stock springs ... which is at the higher end of the spring rate ...) that will cause additional burden on the stock starter ... (similar to the additional burden on the stock starter from higher compression pistons or heads ...) and thus the S&S "easy start" cams might be a good idea ...?

Well, not sure the actual incremental burden on the starter with an otherwise stock motor would be worth the 'benefits' of the 'easy start' cams ... that would be up to the OP, I suppose ... I don't think I'd go for them vice comparable aftermarket cams (for example Woods or Andrews) ....

R/
'Chop

(p.s. obviously, I chose the TW37B Andrews cams for my application ... never really considered the S&S Easy Start cams at all ....)

 

Talked with Bean today, he suggest getting bigger springs for the heads, the cams will fit with stockers but just. I plan to send the heads to him for street port and springs, will keep teh comp the same at 10. 0 - 1, that the S&S kit is supposed to be at with stock heads and their gasket. He also conformed that thsi is a low to mid cam.

 

In all my years of building engines I have never experienced a situation where adding cams to an otherwise stock engine rendered the oem starter incapable of starting engines reliably.

Surfor you got your mind wrapped correctly around how cams work regarding duration and relative compression.

The easy start cams are really suited to the high comp S&S 97 inch kit. I believe this was what they were designed for,and in that application they needed the compression releases to avoid starter failure due to the high comp pistons.

 

Its not just cams also have the S&S 106 kit which raises compression to 10 - 1, my 107 ate 3 starters in my Ultra in a year and a half and 35k miles. Its the clutches crapping out not the motor.I will be pulling heads this weekend to send to Bean, he will add the springs and do a street port job. Hope to have them back by the time I return from my business travel.

 

congrats masterblaster, after listening to almost everyone on forums i too sent my heads out to and swapping out cams to the 54s

 

I run the 583 easy start cam in my 106" train. Before I had s&s do my heads, I was decreasing in hp after probably 4500 rpm. Now I hit my highest hp at 6200... It picks up like crazy in the higher rpms and the torque pulls hard at all times. Great cam in my opinion. The easy start is nice. Just don't twist your throttle when you start the bike (the lobe will slide over faster and you will know it). No need to do that anyway, just let your computer take care of it. Running a power commander w auto tuner. Putting an s&s 52mm throttle body w s&s injectors, as well as woods lifters. Should run a little harder.