[Diy_efi] The Hunt effect

Wed Oct 5 18:21:00 UTC 2005

Jim,
  I apologize, I wasn't too clear about the alcohol vs. temp thing.  If you
take a gasoline engine and convert it over to alcohol, it will run cooler,
typically because the engine is not optimized for the alcohol, and therefore
does not see the full benefits of the heat of vaporization differences,
compression ratio allowances, etc.  What determines an engine's cooling
requirement is power production, plain and simple.  If you have a 500 cid V8
gasoline drag motor with a blower making 1300 hp, you have to cool X amount
of heat.  If you have an alcohol variant of the same motor, but for some
reason (usually tuning), it's only making 1200 hp, you have to cool less
than X amount of heat.  However, if that alcohol motor is optimized and is
now making 1500 hp, you will have to cool more than X.

The reason alcohol dragsters (and it's not uncommon is gasoline dragsters
either) don't run a radiator, or run a small one is due to the short
duration that the engine runs.  It doesn't have much time to heat up.  

But on the blowers, yes they can run larger displacement blowers and more
boost because of the knock resistance of the fuel.

FWIW, top fuel dragster engines (500 cid, blown big blocks running nitro),
make approximately 7000 hp at the flywheel.  They must run roughly a 2:1 AFR
to burn the nitro (nitro has so much oxygen inside the molecule that it can
combust on it's own internal oxygen...it needs no outside oxygen to
burn...it just doesn't burn well like that  ;-), but by about half track,
the electrodes of the spark plugs have melted away, and the engines diesel
the rest of the way down the track.  That, combined with the AFR is the
reason most top fuel engine failures occur past half track.  The engine is
relying on dieseling at that point, and if a cylinder fails to ignite, on
the next cycle, it will hydrolock on fuel.

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
Behalf Of Jim Butterfield
Sent: Wednesday, October 05, 2005 12:17 PM
To: diy_efi at diy-efi.org
Subject: RE: RE: [Diy_efi] The Hunt effect

Ohhh John, hence the reason alcohol dragsters dont run
a radiator.... because the run cooler temps.... also
they can run those huge 6-71 12-71 XX-71 blowers on
top of the big blocks... alcohol runs cooler so less
knock to kill pistions...

In our grand prix club, countless guys think just
dropping a pulley sizeto increase boost is ok, not
scanning the car for Knock retard, soon there all
pissed because two of the front three pistions are
chipping from detnoation... them youngn's just dont
get it, they think hp is cheap and easy...

thanks john, your wealth of knowledge is awesome

jim

maybe off line you could explian how too much octane
is a bad thing... guys in the club think 108/113
octane is better for our little 3800 series II engines
and others say 103 is well enough more is a bad
thing???

--- John Gross <jogross3 at hotmail.com> wrote:

> It takes less air to burn an equivalent amount of
> fuel, but since an engine
> is an air pump, it?s typically better to look at it
> from the other
> direction
.you need more fuel to run the engine at
> stoich at a given load
> and given rpm with alcohol.  Methanol has about half
> the AFR of gasoline
> (6.5 stoich compared to 14.7), but half the energy. 
> Where methanol is able
> to make its power over gasoline is 2-fold.  First,
> it has an equivalent
> octane rating of ~113, so you can run a lot of
> compression, boost, whatever.
> Secondly, it absorbs much more heat (almost 4x) than
> gasoline when it
> evaporates, meaning that it greatly reduces intake
> air charge temps, making
> the charge more dense, allowing more mass of air and
> fuel to be inducted.
> If you look at the intake manifold of an alcohol
> dragster on a 100 deg F day
> after it makes a ? mile pass, there?s ice on it. 
> Long story short, alcohol
> engines run cooler, are less prone to knock on an
> equivalent engine compared
> to gasoline, need more fuel to make the same power,
> BUT, could possibly make
> more power on the same engine if correctly
> configured.
> 
>  
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org
> [mailto:diy_efi-bounces at diy-efi.org] On
> Behalf Of Jim Butterfield
> Sent: Tuesday, October 04, 2005 7:32 PM
> To: diy_efi at diy-efi.org
> Subject: RE: RE: [Diy_efi] The Hunt effect
> 
>  
> 
> Hey John ,can I ask the master a question... as you
> said below the alcohol
> AFR is 9:1 so 1)does this mean it takes less air to
> burn... and 2) given
> two engines equal, on setup with proper alcohol
> required fuel delivery, will
> the ahcohol car get more HP if the pcm/ electronics
> were tuned for the
> alcohol????? if so any guess how much HP
> imporvment???? How does the alcohol
> act under a bloan application... heat,
> detnoation-knock etc....
> 
>  
> 
> thx
> 
> jim
> 
> John Gross <jogross3 at hotmail.com> wrote:
> 
> I'd have to look at the ratios, but yes, certain
> additives like ethyl
> alcohol have an effect on octane ratings. HOWEVER,
> keep in mind that ANY
> alcohol will dry out any rubber seals, o-rings, etc
> in a fuel system
> designed for straight gasoline. Also keep in mind
> that ethyl alcohol burns
> at a stoich AFR of 9:1 (it's an oxygenated fuel), so
> if you blend it into
> gasoline, it will change the required pulse width of
> your injectors to
> maintain the correct lambda. Also, it will tear up
> your injectors because
> they're not designed for alcohol either. That's why
> you can't just run E85
> in an everyday car. The fuel pump, fuel lines,
> injectors, o-rings, seals,
> and even fuel tank liner must be designed to work
> with alcohol-based fuels.
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org
> [mailto:diy_efi-bounces at diy-efi.org] On
> Behalf Of dalemahan at charter.net
> Sent: Tuesday, October 04, 2005 4:48 PM
> To: diy_efi at diy-efi.org
> Subject: Re: RE: [Diy_efi] The Hunt effect
> 
> Hi John,
> 
> Ah hah - a chance to ask a real IC engineer about
> fuel questions!
> 
>   _____  
> 
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