Um, agreed except for point 5 - as a result of the 3.45:1 diff ratio the
overall gearing is higher on the PI cars than US spec cars.
Acceleration improvement is just down to the increases in power and torque.
But as you say, you pay for it in fuel. Still, its only money..
Cheers,
Neil
> -----Original Message-----
> From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net]On
> Behalf Of Navarrette, Vance
> Sent: Wednesday, January 08, 2003 04:34
> To: 'Don Malling'; 6-Pack
> Subject: RE: PI vs dual ZS vs triple ZS -- dumb questions
>
>
> Don:
>
> The reason PI performed so much better than ZS:
>
> 1. Better mixture balance between cylinders by virtue of
> one injector per intake runner. Carbs are subject to
> the vagaries of mixing and air flow in the plenum.
> 2. PI cars have higher compression (9.5:1) compared to
> a max of 8.5:1 for Carbs (later dropped to 7.75:1).
> 3. The PI cars always had the dual exhaust system, which
> gave better breathing than the single pipe on the
> carb cars. Triumph later added the dual pipe to the
> US spec cars to make up lost performance as emission
> limits were steadily tightened.
> 4. The PI cars had a better cam for most of their life.
> The carb cars had a wimpy cam for most of their run.
> Once again, the cam was upgraded later as emission
> controls took their toll on the carb'ed cars.
> 5. PI cars had lower gears, which gave better acceleration.
> 7. Although it is less certain, the PI cars had a higher
> rocker ratio giving more lift and duration for a
> given cam (1.5:1 vs 1.45:1). This point has been
> disputed.
> 8. The PI cars had cold air induction, the carb'ed cars
> never did. Cold air is denser, which allows more
> fuel to be burned, which makes more power.
>
> So you see, it is much more complicated that just bolting
> n PI and expecting 150HP "because PI is better". No doubt PI is
> better, but it is just part of a whole package that gave better
> performance on the European spec'ed cars. The PI cars
> got TERRIBLE mileage relative to their US counterparts. From
> memory (always dicey with me) it was about 9mpg worse on PI
> cars.
>
> Cheers,
>
> Vance
>
>
> ------------------------------
> 1974 Mimosa Yellow Triumph TR6
> Cogito Ergo Zoom
> (I think, therefore I go fast)
>
>
>
> -----Original Message-----
> From: Don Malling [mailto:dmallin@attglobal.net]
> Sent: Tuesday, January 07, 2003 6:58 PM
> To: 6-Pack
> Subject: PI vs dual ZS vs triple ZS -- dumb questions
>
>
> Some say that dual ZS are sufficient until I run over 5000 rpm for over
> one minute, because that is where I will run into fuel starvation with
> dual ZS. Some say triple ZS will add to performance at any RPM.
>
> What is it about PI that provides a performance increase over
> carburetion?
>
> Is it a case where a theoretically very small carburetor could never
> provide enough fuel air mixture to a theoretically very large engine
> without running too rich -- I assume running too rich means that the
> fuel is not being atomized or vaporized correctly? On the other hand, a
> theoretically very large carburetor could not provide correctly mixed
> fuel/air to a theoretically very small engine because the theoretically
> very small engine can not produce enough air flow to make the
> theoretically very large carburetor work correctly?
>
> Hmmm.... Is that it? There has to be a balance between the "size" of the
> carburetor and the "size" of the engine for things to work correctly?
> And even when working correctly (the best it can work), the carburetor,
> by its nature, still can not generate as much correctly mixed fuel/air
> as can the PI?
>
> If this is the case, then were does triple ZS fall in the scheme of
> things -- on a scale of 1-10, where 1 is dual ZS and 10 is PI? Maybe
> the answer is at low RPM triple ZS is at a 2 and at high RPM triple ZS
> is at 7?
>
> Thanks,
>
> Don Malling
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