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How to lower compression on R1 Avanti (?)

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  • How to lower compression on R1 Avanti (?)

    What success have people had trying to lower the compression on R1 engines?

  • #2
    What goal are you trying to achieve by lowering it?
    Pat Dilling
    Olivehurst, CA
    Custom '53 Starlight aka STU COOL

    LS1 Engine Swap Journal:


    • #3
      Eliminate engine "ping" from using too low octaine (sp?) gas.


      • #4
        you could always change the head gaskets to the composition type, that'll give you a little more chamber volume.

        Going an alternate route, you could have your heads cleaned up/ported by someone who really knows what they're doing (maybe check over at racing studebakers) the combination of cleaning up the chambers to eliminate hot spots plus the slight drop in CR due to the material removed will reduce tendency to ping, and if you have them ported and have larger intake valves installed at the same time you might even end up with better performance.

        Finally, there are "semi-dish" pistons available that are in between the stock 289 pistons and the flat-top R-series pistons.

        I like the latter two approaches better as common engine building wisdom says you want to have a nice tight "squish" area between the piston and the flat part of the head for best combustion/performance. Of course, those two approaches are the more expensive ones... (isn't that always the way?)

        55 Commander Starlight


        • #5
          Originally posted by herbpcpa View Post
          What success have people had trying to lower the compression on R1 engines?
          The easiest way would be to trade me your Avanti even up for my 1962 Hawk with standard 289 engine. No modifications needed!
          In the middle of MinneSTUDEa.


          • #6
            Switching to R2/truck heads and the composition gasket would drop you from 10.25 down to below 9:1. That should fix the pinging.

            jack vines


            • #7
              Why did Studebaker choose to give the R2 lower compression than the R1?


              • #8
                One item that you could try is to have the distributor's mechanical spark advance recurved to have the advance come in a bit slower and adjust the vacuum advance to provide a bit less advance too. This will require removal of the distributor and taking or shipping it to someone who still has a distributor machine. It can also be done by trial and error method where you try different stronger springs on the two weights and then go out and road test. I don't recall if the R-1 vacuum advance diaphragm canister is adjustable or not. If it isn't, you will need to replace it with one that is. You just might find that this is all that you need to do to cure the "ping". When done right, the very slight loss in street performance is really not noticeable.



                • #9
                  Originally posted by herbpcpa View Post
                  Why did Studebaker choose to give the R2 lower compression than the R1?
                  When the blower pushes in the air, the dynamic compression raises quickly as well as the temperature of the compressed air, past the 10.25 compression of the R! and the air coming in is hotter, causing preignition. To balance it all, forced induction motors use the lower static compression trick to keep the engines from detonating. Some systems use methanol/water injection to try and slow it ,but as far as I can tell only the direct cylinder injection seems to allow both high static and dynamic compression ,


                  • #10
                    The Prestolite distributors in the Avanti's can be recurved to slow the rate of advance, but that is best done by testing the modifications on a distributor machine. The vacuum advance rate can be slowed by adding extra shims between the spring and the cap on the advance can. If the distributor hasn't been reconditioned in recent history, the centrifugal advance parts could be worn which will cause problems. Also, don't rule out the possibility that there is carbon build up in the cylinders causing a compression increase and hot spots if the engine has high mileage on it. Bud


                    • #11
                      Having these issues and curing them by lowering compression is like fixing the symptoms without addressing the root cause. I'd take a look at my cylinder heads and first make sure I had a carbon-free base to start with, as well as the piston top. But I'd bet that rebuilding the distributor would go a long way towards making the ping go away, as well as checking to be sure you had the correct timing to start with. Try a really well-adjusted stock configuration first, before looking into the mods.
                      '53 Commander
                      Art Morrison chassis
                      LS6 ASA/4L60E


                      • #12
                        When I had my R-1 rebuilt I went to "semi-dished" pistons.
                        The engine rebuilder (a friend of Jack Vine's who does a lot high performance and race engine work) said that should do the trick and hought it was a good idea.

                        I switched for the reason given above. Fuel isn't going to be getting any better...and I won't be pushing the Avanti too hard.
                        It will be interesting to see if it effects performance or HP ratings. Any guesses?
                        Last edited by JBOYLE; 01-22-2011, 05:56 PM.
                        63 Avanti R1 2788
                        1914 Stutz Bearcat
                        (George Barris replica)

                        Washington State


                        • #13
                          I think Nate mentioned earlier that squish much greater than 0.04 inch is not real effective, so thicker gaskets would work as expected if the pistons are already too far down the hole. On the other hand, if thinner gaskets would reduce the squish to an effective value, it is conceivable the octane requirement could be reduced with their slightly higher compression ratio.

                          I think Determining the actual centrifugal and vacuum advance curves is important. It can be done on the car with an "advance" timing light, a tach, and a MityVac vacuum pump. Creative use of "timing tape" (too wide for a Studebaker of the 60s - gotta get the right diamter too) or other means of degreeing the damper would allow a regular timing light to suffice. Pinging while cruising or medium throttle (but not at full throttle) indicates excessive vacuum advance for "conditions". In semi modern cars with EGR a bunch of ignition advance is added when EGR is happening (part throttle) because it is necessary to get the slow burning half dead mixture burned up in time for supper. Even in those low compression engines if the EGR valve should fail to open there will be massive detonation/pinging ( not the same as preignition) due to (now) excessively advanced ignition. We blocked a buddies 78 Volare's EGR off (free fix ) because it wouldn't close and the car idled terrible. Instantly it pinged like crazy at part throttle, just like the troubleshooting guides said it would. The Chrysler lean burn system made all the timing decisions, so we could not easily change the vacuum advance curve, and had to replace the expensive EGR valve.