[Healeys] Cams - Was: Re: Vernier timing gears

[Oudesluys]

As you do not have rockers in a twin cam set up you can allow higher RPM 
without the need of stiffer valve springs. It is also easier to play 
around with the valve timing as you can set up inlet and exhaust cam 
separately. You can also create a better shape of the combusting chamber 
and a multivalve set up, i.e. better breathing.
This is shown by many of the racing engines already developped in early 
motor history and also in most powerful modern engines with a high 
specific output.
Kees Oudesluijs.



Op 9-7-2017 om 3:28 schreef John Rowe:
>
> Not sure of the advantages, by my Alfa Romeo GTV is definitely a nicer 
> engine than either of the Healeys or any single cam Japanese car I’ve 
> driven
>
> John Rowe
>
> Qld Australia
>
> *From:*Healeys [mailto:healeys-bounces at autox.team.net] *On Behalf Of 
> *Bob Spidell
> *Sent:* Sunday, 9 July 2017 6:00 AM
> *To:* healeys at autox.team.net
> *Subject:* [Healeys] Cams - Was: Re: Vernier timing gears
>
> I never understood the advantage of 'twin' cams (assuming two cams per 
> bank of cylinders, one for intake and one for exhaust).  Can't the 
> same results come from lobe profiles; i.e. one profile for intake and 
> one for exhaust, on the same cam?  All the twin cam setups I've seen 
> have both cams driven by the same belt, so timing will be the same for 
> both cams. Is this idea just to have less 'load' for each cam?
>
> What does make sense to me is variable cam timing.  My Mustang 
> accelerates smoothly and seamlessly, but on coasting deceleration 
> there is a noticeable 'bump' down in RPM around 1,800-2,000 RPM as the 
> ECU changes--advances?--the cam timing, but it only has one cam per 
> bank.  I know the Honda VTEC engines have a third lobe, that only 
> comes into play at higher speeds (thanks Edd!).
>
> On 7/8/2017 12:43 PM, David Porter wrote:
>
>     I guess my point in generating some "traffic" is best expressed by
>     Mr. Lawrence. With a single cam acting on the valve timing, one
>     can set it close to factory or deviate a couple degrees advanced
>     or retarded for low end torque or high rpm breathing. It is still
>     a trade off versus a twin cam head where both can be affected and
>     gains can be easily (?) obtained for both instances he states. Not
>     too sure we all have easy access to a dyno. These old long stroke
>     6/4's were designed for grunt. That would be the wise choice. They
>     don't like to be spun up much, then the Welch crank would be
>     necessary. $$ dave
>
>     On 7/7/2017 7:16 PM, WILLIAM B LAWRENCE wrote:
>
>         According to Iskendarian You can optimize cam timing either to
>         provide a boost in low end torque by advancing the timing by
>         up to 8 degrees or in high end power by retarding it a similar
>         amount.
>
>         Since I am looking for a low end boost and will rarely exceed
>         3500 on the road I set mine 4 degrees in advance.
>
>         Waiting to see how it works out...
>
>         Bill Lawrence
>
>         BN1 #554
>
>         ------------------------------------------------------------------------
>
>
>
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