L48 Valve Job Project - Upgrade Ideas? - NCRS Discussion Boards

L48 Valve Job Project - Upgrade Ideas?

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  • Don L.
    Extremely Frequent Poster
    • August 31, 2005
    • 1005

    L48 Valve Job Project - Upgrade Ideas?

    Good morning all. I've decided to take on the project of removing the cylinder heads from my '72 L48 and doing some needed maintenance on valves, valve guides, springs, guides, etc this winter. This summer, I noticed a loss in power, which led me to find a plug-fouling condition in a few cylinders. A compression check seemed to show good compression in all cylinders. Close examination of the cylinder internals with an endoscope didn't reveal any significant issues other than carbon or burned oil on the top of a few pistons. Scope examination of the valves, guides, seals and springs, however, showed lots of issues. Most significantly, I noticed how the seals seem to have come off the guides and are now not functioning. I see also that at least a couple valve stems are gouged. I have photos of this and can share if/as needed.

    All this has me committed to having the valves, guides, springs, etc replaced and the heads re-ground too. My questions to this group:
    1. Any recommendations on how to best do this work?
    2. Are there any modest modifications I could/should do to the valve train while disassembled to improve performance of the engine?

    I've thought about increasing valve size but don't know enough about the valve train as a whole to know if that change alone would provide benefit. This is a top flight car and I don't want to make any changes that would hurt the car in points scoring.

    Any/all inputs and advice appreciated.

    Thanks.
    Don Lowe
    NCRS #44382
    Carolinas Chapter
  • Dick W.
    Former NCRS Director Region IV
    • June 30, 1985
    • 10483

    #2
    Re: L48 Valve Job Project - Upgrade Ideas?

    Three angle valve job would be a good idea. Cutting the guides for positive seals is a good deal as far as I am concerned. As far as anything else, with a stock cam, intake, and carburetor you would be wasting your time for the minuscule gains you would get

    Years ago I used to install bronze guideliners in all the head work that I did. Some engine builders do this, some don't. It is not hard if you have the proper tools. Maybe ten minutes a guide if you are not used to the work. Manganese bronze valve guides are about $11-$12 each, guideliners are less than a dollar.

    Personally I do not like replacing guides, I have had some bad experiences
    Dick Whittington

    Comment

    • Mark E.
      Extremely Frequent Poster
      • April 1, 1993
      • 4536

      #3
      Re: L48 Valve Job Project - Upgrade Ideas?

      If they need lots of work, consider putting them in the attic for future flight judging and buying new, fully assembled heads. Aluminum perf heads with 2.02/1.60 valves from Dart, Edlebrock, Chevy Perf and others are $600 or so. These flow much better than your L48 heads and have a warranty. Plus your car will be back on the road more quickly.

      You will feel the difference.
      Mark Edmondson
      Dallas, Texas
      Texas Chapter

      1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
      1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

      Comment

      • Don L.
        Extremely Frequent Poster
        • August 31, 2005
        • 1005

        #4
        Re: L48 Valve Job Project - Upgrade Ideas?

        Thanks guys.

        Understanding that a new, high performance aluminum head would improve flow, etc, I just can't go with a non-stock part. I also hope not to have to tear into the lower end of the engine. If when I remove the heads I see problems in the cylinders, my game will change, but it'll still be a stock rework.

        I appreciate the advice on guide liners. I'll talk to whoever I end up using for the machine work about them. BTW, Dart is actually local to me and we've already spoken about the needed work. I'm lucky enough to have connections to them and they are one of the shops that I'm considering.

        Thoughts on installing larger valves as part of the head reconditioning?
        Don Lowe
        NCRS #44382
        Carolinas Chapter

        Comment

        • Joe L.
          Beyond Control Poster
          • February 1, 1988
          • 43219

          #5
          Re: L48 Valve Job Project - Upgrade Ideas?

          Originally posted by Don Lowe (44382)
          Thanks guys.

          Understanding that a new, high performance aluminum head would improve flow, etc, I just can't go with a non-stock part. I also hope not to have to tear into the lower end of the engine. If when I remove the heads I see problems in the cylinders, my game will change, but it'll still be a stock rework.

          I appreciate the advice on guide liners. I'll talk to whoever I end up using for the machine work about them. BTW, Dart is actually local to me and we've already spoken about the needed work. I'm lucky enough to have connections to them and they are one of the shops that I'm considering.

          Thoughts on installing larger valves as part of the head reconditioning?
          Don-----

          You really have nothing to gain by installing larger valves. Your engine, in stock configuration, will perform just as well, if not better, with the valve size you have. Keep in mind that 1962-63 Corvettes with 340 HP and 360 HP used the same valve size as you have.
          In Appreciation of John Hinckley

          Comment

          • Patrick H.
            Beyond Control Poster
            • December 1, 1989
            • 11643

            #6
            Re: L48 Valve Job Project - Upgrade Ideas?

            Originally posted by Don Lowe (44382)
            Close examination of the cylinder internals with an endoscope didn't reveal any significant issues other than carbon or burned oil on the top of a few pistons.

            Any/all inputs and advice appreciated.

            Thanks.
            Don,

            Which cylinders?

            Patrick
            Vice-Chairman (West), Michigan Chapter NCRS
            71 "deer modified" coupe
            72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
            2008 coupe
            Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

            Comment

            • Don L.
              Extremely Frequent Poster
              • August 31, 2005
              • 1005

              #7
              Re: L48 Valve Job Project - Upgrade Ideas?

              Originally posted by Patrick Hulst (16386)
              Don,

              Which cylinders?

              Patrick
              To varying extents, #'s 4, 6 and 8. More importantly, I can see that the seals have come up/off several guides, thereby causing a no-seal condition.
              Don Lowe
              NCRS #44382
              Carolinas Chapter

              Comment

              • Duke W.
                Beyond Control Poster
                • January 1, 1993
                • 15669

                #8
                Re: L48 Valve Job Project - Upgrade Ideas?

                The only thing you can do that will noticeably improve performance is massaging the heads as I explained in the "Tale of Two Camshafts" article, which is an easy Web search and books like "How to Hotrod SB Chevys", which has been around for decades and several books by David Vizard, but if you have an OE single catalyst system, it's a waste because most of the improved top end power at the cylinder level will be consumed in additional exhaust pumping power loss. See Dave McClellan's book to understand why.

                The plain fact of the matter is that trying to get more top end power with that single catalyst system is like pushing on a rope.

                If your spark advance map is OE you can improve performance, especially in the low to mid-range where you spend 99+ percent of your driving time by following my recommendations in the 2012 San Diego National Convention tuning seminar...another easy Web search.

                Larger valves are a waste and even a three angle valve job will have no real effect without the other head massaging operations and a high efficiency exhaust system.

                Once you decide whether or not the valve guides need to be rebuilt you have to decide on what process and seal system to use. There a several, so best to talk to local machine shops and see what they offer and do some Web research.

                Back in the day the dealer method of repairing worn guides was to hand ream the guides with a .003" oversize reamer and install .003" oversize stem valves, which were available through service parts and relatively inexpensive. That meant the heads didn't have to go out to a machine shop, and the job could be done in a day, I'm not sure if GM or the aftermarket currently offer oversize valves, but you should look into it.

                Valve replacement, assuming the guides are rebuilt, is a function of seat condition and stem wear. If stem wear is no more than half-a-thou, I think they're okay to reuse, and exhaust valve stem wear is usually more than on the inlet. If stem wear is not excessive and there is sufficient margin after grinding, they're okay to reuse. It may be a good idea to replace the exhaust valves apriori as they are subject to thermal fatigue.

                Sealed Power OE replacement valves are perfectly adequate, but upgrading the exhausts to 2-21N stainless is not a bad idea. Stainless on the inlet side is a total waste of money and stick with the OE 1.94/1.50" valve sizes. You also need to verify that the stem material or plating is compatible with the valve guide and seal technology.

                Duke
                Last edited by Duke W.; November 19, 2017, 09:58 AM.

                Comment

                • Joe L.
                  Beyond Control Poster
                  • February 1, 1988
                  • 43219

                  #9
                  Re: L48 Valve Job Project - Upgrade Ideas?

                  Originally posted by Duke Williams (22045)
                  The only thing you can do that will noticeably improve performance is massaging the heads as I explained in the "Tale of Two Camshafts" article, which is an easy Web search and books like "How to Hotrod SB Chevys", which has been around for decades and several books by David Vizard, but if you have an OE single catalyst system, it's a waste because most of the improved top end power at the cylinder level will be consumed in additional exhaust pumping power loss. See Dave McClellan's book to understand why.

                  The plain fact of the matter is that trying to get more top end power with that single catalyst system is like pushing on a rope.


                  Duke

                  Duke------


                  This car is a 1972 so no catalytic converter is involved. The first year for catalytic converter for Corvettes was 1975.

                  Valves with oversize stems are the absolute best way to deal with valve guide/valve stem wear problems. As you mentioned, ream the worn guides to proper size and install new valves with oversize stems. Unfortunately, as far as I can determine, the GM valves with oversize stems for the 1972 L-48 application are discontinued. Federal-Mogul/Speed-Pro offers intake valves with oversize stems (V-1926-3 for 0.003 OS and V-1926-15 for 0.015 OS) but they offer no oversize stem valves for the exhausts.
                  Last edited by Joe L.; November 19, 2017, 01:51 PM.
                  In Appreciation of John Hinckley

                  Comment

                  • Dick W.
                    Former NCRS Director Region IV
                    • June 30, 1985
                    • 10483

                    #10
                    Re: L48 Valve Job Project - Upgrade Ideas?

                    Originally posted by Duke Williams (22045)

                    You also need to verify that the stem material or plating is compatible with the valve guide and seal technology.

                    Duke
                    Cast guides are not a good mix with stainless steel valves. Possibility of galling
                    Dick Whittington

                    Comment

                    • Mark E.
                      Extremely Frequent Poster
                      • April 1, 1993
                      • 4536

                      #11
                      Re: L48 Valve Job Project - Upgrade Ideas?

                      Originally posted by Joe Lucia (12484)
                      Don-----

                      You really have nothing to gain by installing larger valves. Your engine, in stock configuration, will perform just as well, if not better, with the valve size you have. Keep in mind that 1962-63 Corvettes with 340 HP and 360 HP used the same valve size as you have.
                      That's interesting. Even the humble L82 uses 2.02/1.6 valves. A bigger cam than L48 may help use them.

                      Don- A fully assembled, all new new cast iron 1.94/1.50 Vortec head from Chevy Perf is only $350. How does this compare to the cost and quality of repairing the existing ones?
                      Mark Edmondson
                      Dallas, Texas
                      Texas Chapter

                      1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                      1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                      Comment

                      • Patrick H.
                        Beyond Control Poster
                        • December 1, 1989
                        • 11643

                        #12
                        Re: L48 Valve Job Project - Upgrade Ideas?

                        Originally posted by Mark Edmondson (22468)
                        That's interesting. Even the humble L82 uses 2.02/1.6 valves. A bigger cam than L48 may help use them.

                        Don- A fully assembled, all new new cast iron 1.94/1.50 Vortec head from Chevy Perf is only $350. How does this compare to the cost and quality of repairing the existing ones?
                        The problem is that you then need a different intake - and Don didn't want to affect judging outcomes.
                        Vice-Chairman (West), Michigan Chapter NCRS
                        71 "deer modified" coupe
                        72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                        2008 coupe
                        Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

                        Comment

                        • Don L.
                          Extremely Frequent Poster
                          • August 31, 2005
                          • 1005

                          #13
                          Re: L48 Valve Job Project - Upgrade Ideas?

                          Thanks to all for your advice and your suggestions. I do want to keep the entire car, including the engine/engine bay 100% stock/original configuration, so I cannot use any aftermarket heads, manifolds, etc.

                          I had heard from one source that larger valves (IE: LT1 sized) alone would give me improved performance. My concern with that was around how just a valve size increase, without all the other LT1 upgrades would improve performance in a L48. It's apparent from this thread that it won't. I'm going to stick with my original heads, re-working the valve guides (inserts), valves, springs, seals, retainers, etc to stock configuration. I'll have the heads smoothed as best I can. Perhaps I'll have the intake smoothed too (?) I'm still undecided as to whether or not hardened seat inserts should be a part of this project.

                          For sure, I'll circle back in the spring with results. Until then, the car will be torn down and re-worked while it hibernates.

                          Thanks again guys! This forum has some great people with incredible knowledge and experience. For that, I'm extremely grateful.
                          Don Lowe
                          NCRS #44382
                          Carolinas Chapter

                          Comment

                          • Duke W.
                            Beyond Control Poster
                            • January 1, 1993
                            • 15669

                            #14
                            Re: L48 Valve Job Project - Upgrade Ideas?

                            The SHP valve sizes will increase top end power, slightly, but you probably wouldn't notice SOTP. The problem is that any heads cut for the larger valve sizes have a more likely tendency to develop a crack between the seats, which is much less common with the standard valve sizes. My recommendation is to always go with the standard valve sizes is that's what they have. The best flowing SB heads in my library of test data have the standard valve sizes.

                            DO NOT HAVE EXHAUST VALVE INSERTS INSTALLED... ABSOLUTELY NOT... NO WAY!!!

                            This has been discussed a zillion times over the years. Valve seat recession with unleaded fuel is only a possible problem on engines that run at continuously high load like commercial trucks and heavy trailer hauling, but the risk is the development of water leaks at the seat and the inserts popping out under operation.

                            If your shop gets adamant about installing valve seat inserts, find another one.

                            Later in the seventies GM did start induction hardening valve seats and installing exhaust valve rotators, but I don't think either applied in 1972.

                            You can increase valve seat longevity (and performance and fuel economy) by modifying the spark advance map, including converting to full time vacuum advance with the same centrifugal curve (a different VAC might also be necessary), but bring the centrifugal in faster - by 3500 as the '76 327/300 non AIR. This modification will reduce EGT and valve and seat operating temperature. The '72 spark advance map was set up to meet emission standards, not performance and fuel economy.

                            Details are in my San Diego tuning seminar, and the modifications are usually undetectable other than maybe a OE replacement VAC.

                            Duke

                            Comment

                            • Joe L.
                              Beyond Control Poster
                              • February 1, 1988
                              • 43219

                              #15
                              Re: L48 Valve Job Project - Upgrade Ideas?

                              Originally posted by Duke Williams (22045)
                              The SHP valve sizes will increase top end power, slightly, but you probably wouldn't notice SOTP. The problem is that any heads cut for the larger valve sizes have a more likely tendency to develop a crack between the seats, which is much less common with the standard valve sizes. My recommendation is to always go with the standard valve sizes is that's what they have. The best flowing SB heads in my library of test data have the standard valve sizes.

                              DO NOT HAVE EXHAUST VALVE INSERTS INSTALLED... ABSOLUTELY NOT... NO WAY!!!

                              This has been discussed a zillion times over the years. Valve seat recession with unleaded fuel is only a possible problem on engines that run at continuously high load like commercial trucks and heavy trailer hauling, but the risk is the development of water leaks at the seat and the inserts popping out under operation.

                              If your shop gets adamant about installing valve seat inserts, find another one.

                              Later in the seventies GM did start induction hardening valve seats and installing exhaust valve rotators, but I don't think either applied in 1972.

                              You can increase valve seat longevity (and performance and fuel economy) by modifying the spark advance map, including converting to full time vacuum advance with the same centrifugal curve (a different VAC might also be necessary), but bring the centrifugal in faster - by 3500 as the '76 327/300 non AIR. This modification will reduce EGT and valve and seat operating temperature. The '72 spark advance map was set up to meet emission standards, not performance and fuel economy.

                              Details are in my San Diego tuning seminar, and the modifications are usually undetectable other than maybe a OE replacement VAC.

                              Duke

                              Duke------


                              I agree; valve seat inserts are completely unnecessary. All 1971-72 Corvette engines were designed to run on unleaded gas and no hardened seats or valve rotators were originally used on these engines. These items were added during the 1973-1975 period but their necessity is dubious.

                              If Don wishes, he could add the exhaust valve rotators by using using rotators GM #14042575 and exhaust valve springs GM #6263796. It's really unnecessary but it won't hurt anything. The GM #6263796 spring is discontinued but a suitable replacement can be obtained under Federal-Mogul/Sealed Power # VS-727.
                              In Appreciation of John Hinckley

                              Comment

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