Why 4 vavle heads questions ? and one cam question?

[itsafatboy]

I just want to understand why HD went from one cam to two cam i always thought it was the pushrod angle , but then why go back to one cam?

2. why 4 valve heads? and if a lot better then can't we just put them on twin cam?

3. what is variable timing thing they are doing,

sorry a lot of questions just want to understand why we went from better geometry back to worse , seems sportster is best for that   

[speedzter]

My simple take on this:


Going back to a single cam simply means a cheaper to produce engine , and also less parts to wear .

4 valve heads flow a lot more than 2 valve heads.
Higher flow can equal more power and efficiency.
If someone made 4valve heads that fit a twin cam, then sure, you could make use of them.

VVT is a method of altering cam timing events on the fly (advance or retard the Cam).
This can improve efficiency and fuel economy and emissions.
And can widen the power band.

[smoserx1]

Another advantage of 4 valves is lower mass for the individual valves which at least in theory could allow for higher RPM as the valves would have less inertia when operating.

[cheech]

If I remember right one of the reasons I read way back for the Twin Cam configuration, was they increased the pinion shaft bearing diameter which raised the single cam setup to high and did result in worse than ideal angles and Wille G didn't like the styling of the situation either.
This is one article that touches on it.

As to back to single cam?
As already said surely to simplify things.

How did they achieve that on the M8 over the Twin Cam?
I'd guess someone would have to compare the case deck heights, cylinder lengths, on and on against the Twin Cam.
Beside the 4 valve heads I'd guess going back to a single cam was maybe a design priority for the M8, so if so they hashed that out in depth and found an ideal solution over the Twin Cam.

[Ohio HD]

Yes, they raised the M8 deck height from the TC 6.000" to now 6.500" for the M8. And for reference the Evo and Shovel are 5.375".   

[itsafatboy]

thanks that answers questions , so i wonder why we dont have 4 valve heads for twincam seems like it wouldnt be that hard, especially now that they have the rockers and stuff from M8 , well i suppose why go backwards 

[Ohio HD]

Feuling made and sold four valve heads for Evo's, they didn't seem to catch on.

Then a guy named Jeff Stark Starke tried to resurrect them for Twin Cams but I don't think there were many made. At leas that's how I understood the Twin Cam head. 

[speedzter]

What ever happened to the Feuling 3 valve head ??

[harpwrench]

I don't think there would be much if any advantage to 4V on a twin cam because of the cubic inch and engine speed limits. It might make sense if we were seeing 140hp 107 m8's and bumping 150hp on 114's but that's not happening.

[kink04fxd]

Single cam to simplify production, 4 valve heads and VVT to complicate production.

[FLSTFIDave]

The 4 valve head has much better air flow in and out of it than the two valve head.

VVT changes cam timing, making a broader torque curve and more efficient engine. My VVT M8 makes more power than my previous M8's and get better mpg.  I'm averaging 49 MPG.

[HogMike]

The 4 valve head has much better air flow in and out of it than the two valve head.

VVT changes cam timing, making a broader torque curve and more efficient engine. My VVT M8 makes more power than my previous M8's and get better mpg.  I'm averaging 49 MPG.

That's awesome mileage for sure!
I'll be interested to see how mine compares to my friends new CVO Streetglide
I DO expect his mileage to be better than mine. My OD transmission may help me at the higher speeds when I can use 6th gear!
A lot depends on the rider of course! LOL

[60Gunner]

The 4 valve head has much better air flow in and out of it than the two valve head.

VVT changes cam timing, making a broader torque curve and more efficient engine. My VVT M8 makes more power than my previous M8's and get better mpg.  I'm averaging 49 MPG.

It should make more power. It's a bigger motor. Any real power upgrades will require doing away with the vvt.
It's more for emissions and mileage in this case...a single cam engine. Still well short of 1hp per cu.in.
Like 105hp for a 121? Not that impressive power wise when a twin cam 103 with pipes can do 80+.
Not much progress in how many years?
It's the end of the road when it comes to power and EPA compliance when it comes to the v-twin.