compression ratio/unleaded fuel tuned 8 valve air cooled

Have an 80's gpz550 engine , what sort of compression ratio could it
be
increasd to for a tuned engine but using unleaded? 10:1 standard but
up to 12:1 on avgas mix for racing.

how effective is octane booster? can someone tell me what a 25% avgas
mix octane rating is, and could this be rating fuel be made of
unleaded/pro boost?

 

Why mix avgas and pump gas when there are so many good racing
gasolines to use? Quality control is much better than you can get
mixing it up yourself.

Compression ratio you can use depends on, apart from octane of the
fuel, cam duration and overlap, and intake and exhaust port flow.

When the NASCAR guys were forced to use restrictor plates under their
carbs, they found that they could use compression ratios as high as 15
to 1, something they could never get away with before.

The short answer to your question is; it depends.

Bill Smith

 

....Building a hot engine for road use and 1/4 mile, that I can run on
pump fuel and octane booster

..... The cams are about 280 degrees duration and probably about 105
/107
lobe centres but .5 mm extra lift. Gas flowed and ported head and 2mm
oversize stainless valves, 28mm smoothbore carbs and tuned 4-1 with
dyna ignition limited at about 11 000 rpm.

What I really want is a direct comparison between unleaded/avgas and
unleaded/octane booster

 

When the NASCAR guys were forced to use restrictor plates under their

Since you sound knowledgeable on this subject do you mind if I ask a
semi-related question?

Is the reason that they can run 15:1 compression ratios is that the
restrictor plate acts like a partially-closed throttle and causes a
partial vacuum during the intake stroke, even at full throttle. Then
the effective compression ratio would be more in the normal range like
12:1. Am I understanding this correctly?

Just trying to increase my understanding of engines a bit...

Doug Eleveld

 

Essentially yes, but you have to avoid expressions like "effective
compression ratio" because it can mislead you. The compression ratio
is always the cylinder volume plus the combustion chamber volume
divided by the combustion chamber volume. But you're right, less fuel
air mixture is getting in there so a smaller space is required to
raise it to the desired pressure.


Bill Smith