Pretty sensible IMO. Let him argue with himself as he prattles endlessly to his Audience Of One.

 

Well,ok then but what is Mark going to do?

 

Ill tell you what i am going to do. Like always, ill voice my opinion, post credible information from folks that know more than I do and have reasonable credentials. (like steve pool, posting information seemingly opposite to what Wusz posted . both from careers at 76).
Ill continue to call VR on his voodo, fairydust analysis of reality. (like putting 1 gallon or 10% mix of race gas at 8 bucks a gallon, into his DE stock, M3, so that he feels better about longevity of ths heads, due to a preceived gain in head tempuratures. )
My only comments here were based on Steve poole's text, and things you hear around the paddock. yet, VR Dave Scott, master of all, along with his background singer, Winder (scot) to put me down about something they dont really understand.

So, octane has NOTHNG to do with flame front propagation?
So, octane has NOHING to do with pre-ignition? (that i posted in error, but still it could be debated)
So, race gas vs Av gas should not be used in race cars in any proportion? (even if you know the octane rating equivilance)
There is so much to know here before you can "dis" on somone. there has been comments made from those who know litle or nothing about the subject, yet they are coming across as experts. I only ask the question of why, or post something from someon with a lot more experience than all of us combined, yet I get blasted?

common guys, lets mellow out and discuss this like we were face to face at the track. I know for a fact that at the track, and not on some discussion board where your verbage is thougth to be presevered for generations to come and put downs somehow make you a more valuable person of society, you would act , behave, and speak with a little more politness.

we are discussing race gas and how it contrasts to av gas and can we use it in any form or mixture. Still, out of all this, it seems mixing it might be a safe and cheaper way to go. you still get some of those heavy fuel molecules that burn fast! and using it to mix with pump gas, at 10%, with a fuel that has 10% more octane, thats a 1% change in octane. vaporizaton curves for latent heat rates, probalby are in the same proportions. think that is a wise spend of $8 ???? flame away!

there, off the soap box.

Mark

 

Oh lordy -- do I dare step in to this discussion.......

I'm coming at it form a different view point.

I've got a disassembled 911 RSR engine that I'm told was 12.8:1 CR (who knows)
with domed Ross Pistons.

I'd like to put it all back together as is (assuming everything checks out good)
and then retard the timing so that I can run either AV fuel or 93 Pump gas.

How much performance would I lose?

As I'm probably 1-2 stages above novice driving wise -- I'm not going to miss that
power for quite sometime -- but I do want to have a reliable engine.

thx,

M

 

12.8:1 is way too much for pump gas. especially if you plan on tracking it. i'm not even sure 100LL AVgas is high enough octane for an engine that is almost 13:1 compression (i'd feel more comfortable with 110 octane).

Todd
ReidSpeed

PS some of today's most modern engines can run very high compression ratios right from the factory (11.5 to 12.5:1) but that is because they run DI and run very high fuel pressures, cooling the intake charge and resisting detonation.

 

From article below it looks like you are in the 112 octane range. I would consult a good tuner shop amd find out for sure.

What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the
compression ratio increases the theoretical thermodynamic efficiency of an
engine according to the standard equation

Efficiency = 1 - (1/compression ratio)^gamma-1

where gamma = ratio of specific heats at constant pressure and constant
volume of the working fluid ( for most purposes air is the working fluid,
and is treated as an ideal gas ). There are indications that thermal
efficiency reaches a maximum at a compression ratio of about 17:1 for
gasoline fuels in an SI engine [23].

The efficiency gains are best when the engine is at incipient knock, that's
why knock sensors ( actually vibration sensors ) are used. Low compression
ratio engines are less efficient because they can not deliver as much of the
ideal combustion power to the flywheel. For a typical carburetted engine,
without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels.

http://www.faqs.org/faqs/autos/gasol...section-1.html

 

good info! im still puzzeled with the guys that run pump gas on supercharged stock engines, some as high as 10.5:1 before the blower or turbo. How is this possible? sure the boose levels are very low, but still even at 5-7psi, the tempurature rise alone of the intake charge is pretty warm, even with an intercooler, and these things seem to stay together even at the races, with track temps of 110 degrees!

I know rylan and Kip in their turbo Hondas were running 500 and 700rwhp out of 2.2 and 3.2 liter 4 and 6 bangers. I remember one race at 140F on the track temps, and i figured it would blow if I pushed him hard enough for the 30min race, no cautions. Damn if that little 2.2 liter ran without even a puf of smoke.
pretty amazing. however, im sure at 26lbs of boost, he was running some multicolored fuel of some sort!

 

In case anyone cares:

http://forums.pelicanparts.com/6030768-post2.html

The poster kind of knows something about Porsche engines so his comments on av gas should be given credence.

Scott

 

I dont know if Steve is the best person to give an authoritive comment about Avgas vs race gas. as he said, the octane numbers are different, but you can convert and too much lead. lead doesn heart anything as far as what I have heard.
I'm still puzzled that Steve Poole, and Wusz both have compeletly different takes on the use of avgas vs race gas in race car engines, though working together and for the same company. (76)

mk
Steve from Rennsport also said longevity of an engine relies on 3 things. compression ratio, RPM and build quality. I think load and operational temps would be a 4th.

 

Wouldn't that be fourth and fifth not just forth?

Most folks would not summarily dismiss Steve W as you just did.

 

Kurt,

I would recommend that everyone put Kibort on their Ingore List. Then you would not see his inane comments anymore. Suggesting that and engine builder of Steve's caliber doesn't know what he is talking about shows that Kibort deserves to be completely ignored. What a tool.....

Scott

 

+ ∞ on all the above.

 

Go ahead. beleive everything you read and hear from sourses that migth not be authorities on the subject. Just because you build engines, doesnt mean you are a fuel expert. could be, but probably not. there are specialists in all fields. personally, i would take the advice is safe, but not gospel.

and there you go again, calling names. Dude, get over yourself! YOU re the tool. cant wait to meet you, and believe me, I will see you at the track some time soon, IF you ever go!

 

and spin-boy, you go right on and give folks advice on how to drive. Wow, that is some funny stuff right there!

 

Each and every Redneck here is entitled to their opinions. If you don't care for someone's musings then simply skip over them. Easy as pie...