[Fot] Six cylinder cams

Sat Oct 31 17:10:25 MDT 2015

P. J. — I’m off away from camshafts here, but how much weight can you pull off the car?  Light wheels and tires can help but might be a ways down some peoples’ list for ways to reduce the weight of the car.  Already got a lightweight flywheel you can use?  Final drive change (or taller/lower profile tires to make an equivalent change) might be worthwhile to check out.  I have a tiny (NSU) race sedan that tops out at 93mph whether I have tall tires or low-sidewall tires (different rpm, obviously), so its speed is drag/power limited, and apparently not limited by having the wrong final drive ratio — however opting for taller tires (or a lower numerical final drive ratio) means I’m not accelerating as quickly, plus the car’s center of gravity sits higher, which doesn’t help the handling.

Duncan

> On Oct 31, 2015, at 5:44 PM, McKearn McKearn <mckearn2 at gmail.com> wrote:
> 
> I can tell you that I already have a GT6 with a good flexible power band and good reliability. It lacks quickness however, due in part to the TR6 engine which is not highly tuned  and I'm sure the gearing could be better (3.27 rearend-Toyota T50 trans.)( Good for the highway.) My old car is pretty much to the point where I don't want to do anything more to it so I want to move on to another project.  This time I want to build a car that snorts . I do however need to put it on and off the trailer and I'm not thrilled about breaking parts with max. RPMs so I can't afford to go all out.  I'm looking for quickness through the gears and good handling. 
>                                                          P.J. 
> 
> On Sat, Oct 31, 2015 at 3:43 PM, Duncan Charlton <duncan.charlton54 at gmail.com <mailto:duncan.charlton54 at gmail.com>> wrote:
> Larry’s comments make me wonder the precise intended purpose of the engine mentioned by the original poster.  “Track days” might mean different things to different people.  Does P. J. want a good flexible power band, or does he need an ultimate dyno horsepower figure?  Does the motor have the gear set to be able to take advantage of an engine with very little low-end torque? How high among his priorities is the ability to be able to drive the car back on the trailer at the end of every track weekend?  Lack of sponsorship and cash prizes mean that I must find the setup that maximizes the fun/cost ratio.
> 
> Duncan
> 
> 
> > On Oct 31, 2015, at 1:34 PM, Larry Young <cartravel at pobox.com <mailto:cartravel at pobox.com>> wrote:
> >
> > That is an interesting article, but only speaks to one side of the issue.  I always say that you want to pick an intake duration for an RPM range that you're willing and able to turn. We all know what happens to a stock TR4 crank which sees >6,000 on a regular basis.  Some guys want a cam good beyond 7,000, but they are just not willing to push it that far. Nowadays I'm more of a street car guy, but still like to have power.  I don't believe the choices should be to do nothing or go all the way to race specs.  From 1968 on Triumphs were severely detuned to pass emissions.  Compression ratio and duration and hence cam overlap at TDC were reduced.  For example, the early TR250/6 had 193 degrees duration (measured at 0.050), while the TR4 was about 215 and the early PI TR5/6 was 226. It seems crazy to rebuild a street car of this era to the original specs.  Bumping the compression ratio by a point and increasing the duration to something like 210-215 will make the engine the way it would have been without emission restrictions.  I would not feel guilty about polluting the planet, since most of these cars see few miles annually and most of the other pollution controls (e.g. ignition retard) probably quit working years ago.
> > - Larry
> >
> > On 10/29/2015 7:25 AM, Duncan Charlton wrote:
> >> Cam specs and static CR are interactive.  This will give you a rundown if you are not already knowledgeable about this subject:
> >>
> >> http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility <http://www.crankshaftcoalition.com/wiki/Cam_and_compression_ratio_compatibility>
> >>
> >> Duncan
> >> (Texas)
> >>
> >>
> >
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