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Re: Unleaded Fuel

To: "Walter A. Menke" <wallym@ozemail.com.au>
Subject: Re: Unleaded Fuel
From: Bob Palmer <rpalmer@ames.ucsd.edu>
Date: Sun, 02 Aug 1998 08:26:30 -0700
Wally,

There are some different opinions regarding the effects of using unleaded
fuel in older engines. One school of thought is that the lead was important
to lubricate/cool/protect the exhaust valve seats. It appears that most of
this concern was unfounded and just part of the hysteria that naturally
accompanies any change. On the other hand, using unleaded fuel has some
definite benefits in terms of drastically reducing cylinder head deposits
and corrosion in the exhaust system. I don't think we would be seeing 100k
miles between spark plug changes on leaded gas, for example. So, especially
if you do not plan on driving 100k miles with the engine, you can probably
ignore the unleaded gas issue entirely if you like.

Having said this, in my case I chose to (in 1986) build up a set of 351W
heads and used stainless steel valves and hardened valve seats. It is now
twelve years and one valve job later. I had to rebuild the engine because
some $#**^% numbnut bead blasted my intake manifold and reinstalled it with
lots of glass media still exposed on the internal surfaces. So anyway, I
went ahead and redid the heads although they were still in pretty good
shape; just what you would normally expect after 40k miles. Just a light
grinding on the valves and seats was all that was needed. Valve guides with
phosphor bronze inserts were still tight, etc. So, if you want to spend the
bucks for inserts and know someone that can put them in to stay, it might
be some kind of insurance, especially if you plan to run the motor hard.

The other issue with unleaded fuel is the octane rating. Up topside here,
unleaded premium is usually 92 octane. My engine has TRW pop-up  pistons
(nominal 12:1) which works out with a 0.030" over 289 to 10.9:1
compression. The motor runs fine, no pinging no matter how  hard I try to
lug it down. There are several factors here such as porting and polishing
and using a moderately high overlap cam (70 degrees). It's my guess that
the 289W heads would have a problem with this high a compression, at least
I wouldn't guarantee they would work as well. The chamber design of these
heads is quite different and factors like "squish" and "quench" which
affect combustion characteristics are likewise affected.

Considering what it cost me to do the 351W heads compared with what you can
get a ready to install set of aluminum heads nowadays, I would recommend
the latter. Of course you get hardened seats, stainless valves, valve guide
inserts, etc., all of which cost a lot of bucks extra with 289/351W heads.
And, you save 30 lbs or so to boot. Since aluminum heads run a little
cooler, they can also take (need) more compression as well.

I hope this information and personal experience is helpful and good luck
with your project.

Bob


At 08:54 PM 8/2/98 +1000, you wrote:
>Has anyone built-up there engines to handle unleaded fuel?
>
>I'm tempted to do this as it looks inevitable that leaded fuel will be
>phased out eventually. The other factor is that leaded fuel is priced
>higher downunder by about 7/c gallon. ANy experience out there?
>
>
>Cheers
>Wally Menke
> 

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