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cylinder heads for an L48

 
Old 02-08-2019, 05:40 PM
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73n95
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Default cylinder heads for an L48

My 73 is a stock L48 with 100k miles. The valve guide seals are shot. It smokes on startup, but that's it. There is no smoke in the exhaust after startup so the valves are good as are the rings. I seem to have an antifreeze leak into the crankcase so I'm thinking valve gasket. Pull the heads, This would be a good time to do the valve guides. But what about the valves, remember it has 100 k. I'm thinking that perhaps this would be a good time to put a nice set of heads on this stock, high mileage engine. What says the forum? Is heads only a reasonable approach? Its just a summer cruiser/parade car so performance isn't all that important. If new cylinder heads are the way to go, which ones?
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Old 02-08-2019, 05:44 PM
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Dynra Rockets
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There are endless head options. If you are keeping everything else the same then the limiting factor for you is the L48 camshaft at .390/.410 lift. With that little airflow then about the only thing another set of heads could do is increase compression ratio and loose weight.

I have a L48 camshaft in my 69 (ZQ3) so I chose 1986.5 L98 aluminum heads to get the 58cc chambers and loose many pounds of weight. Bolted right on. Nice seat of the pants improvement in torque due to the higher CR.

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Old 02-08-2019, 06:13 PM
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Originally Posted by Dynra Rockets View Post
There are endless head options. If you are keeping everything else the same then the limiting factor for you is the L48 camshaft at .390/.410 lift. With that little airflow then about the only thing another set of heads could do is increase compression ratio and loose weight.

I have a L48 camshaft in my 69 (ZQ3) so I chose 1986.5 L98 aluminum heads to get the 58cc chambers and loose many pounds of weight. Bolted right on. Nice seat of the pants improvement in torque due to the higher CR.


Plus a another cam about 2 steps up. Those L98 heads same as what WAS on ZZ4 crate. Chev/GM no longer offers those heads at all & getting difficult to find in junkyard.
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Old 02-08-2019, 07:21 PM
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True, the L98 heads are tough to find in a junkyard, but go to anyone who sells C4 Corvette parts on Craigslist and he'll likely have a pair. I got mine for $500 and put another $500 into LT1 valve springs and having the heads gone over. It was a very nice bolt on to an L48 and raises the compression (because of the tiny 58cc combustion chambers) at least a point to a point and a half. Combine that with a regular old Edelbrock Manifold, a good carb and a cam that emphasizes torque on the bottom end, and you will have a pretty fun ride. Mine sure turned out that way. With it being a stick shift car, with a 3:50 rear end, it was doing 1/4 times in the low 14's, at nearly 95 mph. Lunati steered me to a mild RV-Marine-4x4 cam, which as mentioned before, had the torque on the bottom of the RPM range, straight off the bat. I flogged on it for five years, on the stock 44 year old bottom end, before I finally lost compression in the number one hole. Lots of burnouts, hard pulls and fun times, in between.
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Old 02-11-2019, 02:32 PM
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My local mechanic, who is also an engine builder says that tightening up the valves on my 100,000 mile 350 will highlight a set of tired bearings and rings. Sort of a domino effect. I'm not burning any oil and the oil pressure is within GM limits at idle. I don't put a lot of miles on it (perhaps a couple thousand a year at most) and don't race at all. I'm inclined to leave the block alone and just rework the heads.
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Old 02-11-2019, 07:35 PM
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Originally Posted by 73n95 View Post
My local mechanic, who is also an engine builder says that tightening up the valves on my 100,000 mile 350 will highlight a set of tired bearings and rings. Sort of a domino effect. I'm not burning any oil and the oil pressure is within GM limits at idle. I don't put a lot of miles on it (perhaps a couple thousand a year at most) and don't race at all. I'm inclined to leave the block alone and just rework the heads.
I assume what you mean by "tightening up the valves" is a valve job. Is so then what the mechanic is saying is that by improving the valve seal you may create some blow-by from worn rings. Sometime happens, sometimes not. I would do a compression check without and with oil to see what condition the rings are in.
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Old 02-11-2019, 11:46 PM
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If you are not particularly looking to add 'performance' to your engine, another option is to remove the heads and take them to a local (compentent and reliable) engine/head rebuilder. If the heads are not damaged (other than normal wear-out of moving parts), they can be rebuilt to like new [or better] condition for a few hundred dollars. New valves, new seals, new guides (if needed), re-seat grinding, freeze plugs...and you're good for another 40 years.
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