[TR] Octane

[Creig Houghtaling]

Terry,

I think Geo has the best answer here.  Try regular and listen for knocking.  No knocking, all is good, don't worry about it.  (That last sentence is strictly my opinion!!! Get information from others who know more to come to your own conclusion.)  Compression is what causes knocking.  But compression ratio of the engine is not the bottom line.  The actual compression you get in the cylinder and when your spark plug fires is the bottom line for knocking.  Modern engines run higher than 9:1 compression ratio and run fine on regular gas.  That's because with modern electronics the ignition can be adjusted on the fly.  With these old engines, the cam also plays a major roll in how much compression you actually have in your cylinder.  If you have 2 engines with the same compression ratio, a mild cam can run well on regular gas and a hotter cam will knock on regular gas.  That is because the mild cam is opening and closing at different positions in the stroke compared to a hotter cam allowing for lower total compression of the gases in the cylinder.  Compared to the hotter cam.

Creig
________________________________
From: Triumphs <triumphs-bounces at autox.team.net> on behalf of Geo Hahn <ahwahneetr at gmail.com>
Sent: Sunday, September 23, 2018 9:51 AM
To: TERRY SMITH
Cc: Triumphs
Subject: Re: [TR] Octane

Terry -

I rather think it was due to compression ratio more than anything else.  But you may just have to experiment a bit to see what works (adjusting advance, listening for ping).

My TR4 uses premium at off-brand stations but seems okay with regular from Shell or Chevron.  My TR3A doesn't seem to care what I put in it, runs fine on almost anything.

Geo

On Sun, Sep 23, 2018 at 6:26 AM, TERRY SMITH <terryrs at comcast.net<mailto:terryrs at comcast.net>> wrote:
Just curious.  Why is Premium gasoline recommended for a TR3 (and I suppose other Triumphs?)while regular is just fine for other vintage cars.  I know it's to prevent knocking, but how and why?  Does it have to do with being a short-stroke engine or something?

Thanks, everyone,
Terry
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