LT-1 Heads

[Romans, Mark]

Hi Carl:  Here's what I found.
http://www.idavette.net/hib/ls1c.html  More below.

Cooling the Traditional Way

Remember 1992, when Chevy raved about the Gen II's reverse-flow cooling?
Well, reverse is, apparently, out. The new engine uses conventional pushrod
V8 cooling. Coolant is pumped into the block, around the cylinders, up into
the heads, then out to the radiator. The reason Gen II went reverse was
that, to make the power Corvette Development wanted; it had to have a higher
compression ratio (LT1, 10.2:1; LT4, 10.8:1). Higher compression made for
detonation. The cooling system was revised to run the cylinder heads cooler
as an antidetonant strategy, and to run the cylinder bores hotter for higher
oil temperature and less friction. Clearly, reverse-flow cooling, the
publicity darling of the Gen II engine, was really nothing more than a fix
that allowed the limited cooling of the old Small-Block head to work with
the higher compression necessary to reach the 300 horsepower level.

Air in the cooling system becomes problematic if it gets into the water
passages surrounding the combustion chambers. This often causes localized
boiling and that, in turn, allows hot spots to develop on chamber walls and
they cause detonation. The problem with reverse flow is that with coolant
flowing downward and air bubbles flowing upward; keeping air out of the Gen
II cooling system was difficult.

Though the LS1 has a lower static compression ratio; its cylinder heads have
improved combustion chamber design and intake ports that breathe better.
Those features allow them to make more power. The clean-sheet-of-paper
approach also allowed design of the cooling passages around the chambers to
be more efficient such that the engine can put out more power than the Gen
II but yet have coolant flow in the conventional direction to eliminate
problems with aeration. With a better combustion chamber and water jacket
design and improved antifriction technology in the block, pistons and rings;
it made sense to go back to the normal-flow cooling system.

Like most engines of the last 20 years or so, the LS1 uses a 195 degree
thermostat. Nominal coolant temperatures are similar to what we see in LT1/4
engines. The new engine will use "Dex-Cool" coolant introduced last year in
many GM vehicles. Dex-Cool has entirely new anticorrosive chemistry that is
longer lasting and more friendly to cooling system parts, especially seals.



----- Original Message -----
From: "Carl Summers" <InTech at writeme.com>
To: <gmecm at diy-efi.org>
Sent: Monday, September 04, 2000 6:50 PM
Subject: RE: LT-1 Heads


> Mark,
>     Are you sure LS-1's are standard flow??? I was just changing a
> thermostat on an LS-1 truck engine and the thermostat was on the block not
> the intake or after the heads(I assume)...you could be right though as I
> noticed only about a 10 degree drop from stock and I verified the
thermostat
> opening at ~160F in a pan of water on the stove(I always do that with an
> unverified product) What gives??? If it is truly a standard flow engine
this
> would explain the lack of temperature drop....engine still runs around
> 185-190F....Anyone else have feedback on this as well????
> -Carl Summers
>
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> -----Original Message-----
> From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
> Of Romans, Mark
> Sent: Monday, September 04, 2000 6:33 PM
> To: gmecm at diy-efi.org
> Subject: Re: LT-1 Heads
>
>
> L98's are standard flow
> LT1's are reverse flow
> LS1's are standard flow.
> L98 and LT1's shares some bottom end components.
> LS1's share no components with prior smalll blocks.
> Mark
> ----- Original Message -----
> From: "Gabe" <gellett at earthlink.net>
> To: <gmecm at diy-efi.org>
> Sent: Monday, September 04, 2000 4:57 PM
> Subject: Re: LT-1 Heads
>
>
> > The LS-1 is a completely new design engine, where the LT-1 still had the
> old
> > small block rotating assembly.  If I remember correctly the LS-1 heads
> have the
> > Ford 4 bolt per cyl setup instead of the 5 like the older heads....
> >
> > Gabe
> >
> > WEG1192 at aol.com wrote:
> >
> > > Ok, what's the difference between the LT-1 and the LS-1? I thought the
> LS-1
> > > was the start of reverse flow cooling? Just trying to educate myself
on
> the
> > > later engines.
> >
>
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