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I finally got a set of 842 L89 heads. Anybody have any old articles with L89 cars? I'm curious to see what difference in performance the cars had with the aluminum heads vs. the iron. Also what thermostat should I use?

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'69 RS SS 396 375hp L78 Convertible, M22, 3.31 posi, deluxe interior, gauges, rosewood wheel, AM-FM,fold down seat, tilt wheel, Torque Thrust Wheels, console mounted 8 track player, chambered exhaust
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You will likely lose a little power w/the aluminum because they do not hold heat. The upside is typically you can run another point in compression. You might gain slightly with less weight, but on a street car, it's unlikely there will be a difference. Just looks different when you pop the hood at cruise night.
 

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They put bigger exhaust valves in the Alum. heads so HP is about the same. They do run cooler and 80lbs or so off the motor weight doesn't hurt either. The engine will like to run at least 180 deg thermostat.
 

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Discussion Starter #4
Thanks. Got any old road test articles?

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'69 RS SS 396 375hp L78 Convertible, M22, 3.31 posi, deluxe interior, gauges, rosewood wheel, AM-FM,fold down seat, tilt wheel, Torque Thrust Wheels, console mounted 8 track player, chambered exhaust
http://albums.photopoint.com/j/AlbumIndex?u=1169124&a=8603468
 

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Compared to the 3919840 cast iron head, the 3919842 aluminum head had a slightly revised intake port, larger exhaust valve (1.84" diameter vs. 1.72" diameter found on the 840 head), and if I remember correctly, the nominal combustion chamber volume was also a few cc's less. I would expect the 842 head to have a measurable performance improvement over the 840 head despite any heat transfer issues between cast iron and aluminum.

I would also expect that the 72 pounds saved by the aluminum heads would provide a noticeable improvement in handling in a nose heavy big block Camaro. And as was mentioned, there's always the "cool factor" when you pop the hood!


I also agree with the thermostat recommendation - nothing less than 180 degrees for street operation.

As far as period road tests of L-89 equipped cars, the only ones that I'm aware of were done on Corvettes in 1968 and 1969.

Hope this helps.

Regards,

Stan Falenski
 

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The cast iron #840's show the same combustion chamber volume as the AL #842's at 106.8 cc's. The earlier (1967) AL #392's had the smaller 1.72 in ex. valves. I will stick by my original statement that you would never feel a performance improvement w/these heads on a street car. Even the 70lbs saving would amount to under a tenth in the 1/4. The loss of power due to greater heat dissipation of the AL would offset much of the gain due to the weight savings. There have some good discussions about AL vs CI amongst some serious racers on the Chevelle site if you are interested. Bottom line IMO they have the wow factor at cruise night but won't do anything for staight line performance as a bolt-on to an existing street engine.



[This message has been edited by 70 RS/Z-28 (edited 05-17-2001).]
 

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70RS/Z28 where do you get your info. I still have a matched pair of 392 heads they came with 1.84 ex valves {you don't cut stellite seats for bigger valves}These heads were on my 454 bracket 55 Chev. one them pounded a valve guide loose so I put on a fresh set of stock iron big port heads. The car was a tenth and one half and almost 2 mph slower with the iron heads even though the alum had a valve guide bouncing around.
 
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