Leyland Car Owners - LPG Compression Ratio

Hello Shawn,
: As you know, propane has a much higher octane rating than the best available
: pump gasoline -- nominally 105 octane on the R+M/2 scale. That said, there are
: a number of factors that effect an engine's octane requirements. Each of the
: following can have an influence: camshaft timing and duration (overlap),
: cylinder head design, bore diameter, spark plug location, material of construction
: (aluminum is more tolerant), engine temperature, air temperature and ignition
: timing.

: I have zero experience with the 4.0L/4.6L stroker or the Buick 300 heads but
: I do have experience with the Oldsmobile and Buick versions of the 215 and
: also with propane.

: It is my understanding that the Oldsmobile head is more detonation resistant
: than the Buick head. My reading has also led me to believe that the Buick head
: actually flows a bit better than the Olds, thus providing more top end power.


: Now for my real world, first hand experience. I built a Buick 215 for my
: wife's Chevy Vega. That engine had a mild camshaft, about 8.5 to 1 static
: compression, ran premium grade (91 octane) and never detonated. The second engine was
: an Olds 215 using the small chamber heads along with high domed Arias pistons
: yielding a ratio of 13.5 to 1. The camshaft profile was non-stock but rather
: mild. That engine did not detonate at its home altitude of 4,000 FT but did at
: sea-level -- even using 93-octane fuel. Initial time for both engine was set
: at 10 degrees BTDC but the 13.5 to 1 engine needed to be backed down to 5
: degrees initial to forestall detonation at sea level.

: Now to propane. The Vega and Buick engine were ultimately sold. The Olds
: version of the 215 was rebuilt and sits in my son's Corvair. Here is my logic:
: If that high compression engine could survive on 91 octane gasoline -- it would
: dearly love 105 octane propane.

: Again, I have no experience with the 4 liter or 4.6 liter engines nor do I
: have experience with the Buick 300 heads but my personal experience would say
: that you should have few problems with propane at the compression levels you
: anticipate.

: Some of our British and Australian list members may have different
: experiences based on the use of propane in the Rover products. But I believe that most
: of those applications were duel fuel and not optimized for propane.

: http://www.propanecarbs.com/propane.html Propane Facts & Comparison Charts

: http://www.patooyee.com/propane/propane_1.htm Propane: Page 1


: Darius

Date: Tue, 14 Mar 2006

: Back in the '80s I used to work for Petrolane, the propane gas distriburor, and we did conversions.
: If I remember correctly the max recommended compression ratio was about 10.5:1.
: Even though propane is high octane (110) since it is a dry gas, you don't get and evaporative cooling of the
: charge, making it somewhat susceptible to detonation at high compression ratios.
: I am working from memory here but will try and dig up some info if there is interest.
: P Knowles

Leyland P76 Owners 2004

Technical problem

[215V8] LPG Compression Ratio

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