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Poll: Complete engine rebuild or upgrade heads only?
Just rebuild the heads and add performance upgrades
Rebuild the whole motor. It's worth the effort and expense.
Both choices have pros and cons - it's simply up to you.
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Well, what if I just rebuilt the top end?
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    Post: #1
    Well, what if I just rebuilt the top end?

    As I drove the convertible back home from the store, admiring how smooth the engine sounds (although I would estimate it's horsepower somewhere in the double digits), I thought, "Do I need to tear the whole thing apart just to get some more power?" The motor doesn't smoke a bit or use oil, there are no weird sounds coming from it except a sticky lifter, and the FMX shifts smartly, although very early for my taste.

    So, instead of pullling the motor out and rebuilding it from the bottom up, what if I just pull the heads and check the block and head surfaces to see if they need to be decked. Then maybe a little port and polish, install the new 218/224 cam, accessories, and timing parts, and then bolt on a performance intake, 4 barrel carb, and headers. New Petronix distributor, coil, fuel pump, etc.

    If I find something bad, then I can return to my original plan and tear it apart. Again, what I want is to do some burnouts, take her to some small shows, and run it down the strip once or twice during the summer. Does this sound like a sane approach, or should I simply face the fact that I really should rebuild the whole thing?

    Thanks in advance for any and all opinions!

    Offline 10-23-2010 03:56 PM
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      Post: #2
      RE: Well, what if I just rebuilt the top end?


      While I will participate in the poll, I am also passing on an observation. It sounds to me like you are somewhat happy with the current "setup" as it relates to the car. I think you would do well to make changes in relatively small increments.

      Based on what I have learned/experienced over the last 38 years, this would be my order of "changes:"

      1. The ABSOLUTE best performance upgrade you can make INITIALLY would be going to a set of long tube headers. Believe me, you will feel the difference in the seat of your pants. An added bonus is that change will compliment future changes.

      2. The next "change" would be going to an aluminum 4V intake and a 4V carburetor. This decision will take some thought though as you do not want to get a carburetor that is going to be at odds with any future valve train changes. Based on your apparent plan to use the Comp 242 cam, I would suggest a carburetor around 650.

      3. The next change would be to the rear end, specifically the ring and pinion gear. Based on the cam you are thinking about getting, I would go with a 3.25:1 or a 3.50:1 (if you don't already have it). You may also want to upgrade to a traction lock at the same time.

      4. Next would be the camshaft and ignition changes. Sounds like you already have a "handle" on what you want to do in those areas.

      Each of the above changes (if done in that order) can be done without any adverse impact on the driveability of your car.

      After each change, i would drive the car for a while to get a "feel" for what I have gained (while keeping your fellow board members informed Smile).

      Food for thought?

      Offline 10-23-2010 04:51 PM
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        Post: #3
        RE: Well, what if I just rebuilt the top end?

        I'd say if you're going to all the trouble of pulling the intake, heads, exhaust manifolds, and cam (which includes the timing gear and pretty much the whole front-end of the engine anyway), you might as well yank the whole thing out and have a much easier time of it.

        The top end is the most involved part of the whole process anyway (aside from pulling and dropping back in the engine altogether). You'll be setting everything back to zero when you put it all together - might as well have the rotating mass all squared away at the same time.

        Changing out an intake and carb, rebuilding heads, or swapping to headers are fairly easy things on their own (and by themselves). But if you're going to tackle all of them in one shot along with digging out the lifters and doing pretty much everything EXCEPT mains and rings, you might as well go all-in and take care of the bottom end.

        You're already looking at a new oil pan gasket after you pull the timing cover anyway...

        Not to mention, you can also take this opportunity to freshen up the engine bay without that big ol' chunk of iron in the way.

        Just my thoughts (considering mine is already out of the car...).
        Offline 10-23-2010 06:06 PM
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          Post: #4
          RE: Well, what if I just rebuilt the top end?

          The million dollar question. But in all honesty only you can answer it. Bt's post as always is dead on in my opinion. But on the east end of Tn we are getting ready to have a few months of work time on our hands due to cold weather coming.
          Offline 10-23-2010 06:06 PM
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            Post: #5
            RE: Well, what if I just rebuilt the top end?

            Unfortunately many of these decisions depend on available funding, time, and working space. If you have enough of all three, I'd suggest taking a comprehensive planning approach. Decide what you really want from the car and carefully match all of the components. If funding requires you to work in steps, I'd start with changing the gear ratio and upgrading to a traction-lok (the ratio should be part of the plan). You mentioned burnouts. Peg leg burnouts are not impressive to me. The next step would be to install a relatively conservative shift kit in the transmission. Build the engine third. Unless I was relatively certain that ring seal and bearing condition were good, I'd pull the engine and transmission. If you are going to significantly increase power, that would be the time to have the transmission built to match the engine. Just one opinion.

            Offline 10-24-2010 09:25 AM
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              Post: #6
              RE: Well, what if I just rebuilt the top end?

              My car started out as a completely stock (but newly rebuilt) 4v. It sounds like to me you want out of your car what my car is currently.

              The two best things I ever did to my car was the 4.11 gears and the MSD 6A ignition box...both of these dropped .3 off of my 1/8th mile times each.

              4.11 gears are a bit much though, a 3.50 gear would be much more streetable.

              I have the comp 268H cam, which is very close to what you mentioned, long tube headers, edelbrock performer intake, and a 750 vac. sec. carb. also. It really is a good street setup.

              I strongly, strongly, recommend the MSD box, it can hook up to the stock points distributor or a msd distributor.
              Offline 10-24-2010 11:05 AM
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                Post: #7
                RE: Well, what if I just rebuilt the top end?

                Well you can rebuild the heads and gain a little power if the valves are worn.

                I would see what compression is first, maybe the motor is tired maybe the heads are leaking, maybe the valves need adjustment.

                The stock intake is limited, for bolt on performance, headers will make a difference but that also depends on your current exhaust do you have a duel or single exhaust, converting to headers and a duel exhaust will give you power back. It will also be very noise especially in a convertible.

                Changing the intake and carburetor will give you tuneablity and more power.

                A hotter spark using an MSD box is debatable. An ignitition system in good shape will have as good a spark as any after market ignition. If there is a problem with your stock ignition then you will see a difference. An aftermarket ignition will make maintenance easier. I've seen dyno reports showing a good ignition system up against a hoter coil MSD or petronix showing no hp gains, what you will gain with a hotter spark is more wear and tear on spark plugs and ignition wires. And after market ignition will just make maintaing the ignition system easier not add any real hp gains.

                Basically increasing the amount of fuel and air into and out of an engine will make more power.

                Next up changing the gear ratio will make your 0-60 times decrease. On average for power and cruise people prefer the 3.25 to 3.5 ratios. 2.75 to 3.08 is considered fuel economic gearing because at highway speeds your revs are kepted lower and you use less fuel.

                3.10 to 4.11 is having fun gears.

                Anything under 4.11 is strictly drag racing where your revving passed 6000 rpms in the quarter mile.

                You have gears that low on the street it won't be fun and you will need a 5 speed gear box. Or 4 with overdrive and won't be fun driving on the highway with the engine sounding like it will blow up.

                Changing the gear ratio will have more an effect on the 0-60 then adding maybe 25 hp to the engine. If the engine is warn inside then all these after market bolt ons will just serve to restore some lost power the engine used to have anyway and you won't really be gaining anything above how the car was originally.

                Any transmission loses power through it also. A c6 transmission is known to drop 55 hp from the crank to the wheels, switching to a manual transmission can reduce that power loss to 15 hp.
                This is why lots of people swap autos for manuals.

                How much of a dog are we talking about, how about you time your 0-60 when getting on the highway. My car was making just over 300 at the crank, I'm sure between detuning it and emissions and getting it onto my c6 I'm making In the 200 range my 0-60 was in the 6 second range with a 2.75 rear and matched the acceleration of my 2005 Acura which also claimed 0 to 60 times of 6 seconds, the Acura claimed it was a 300 hp engine as well.

                I have yet to see the effect of changing my end ratio from 2.75 to 3 on my zero to 60 times. I'm sure the change won't be much compared to me throwing a 3.5 In the axle.

                I would really diagnose the engine and see what compression is first make sure the compression. Is even between all 8 and one isn't low before I started to throw money at it.

                Also you mentioned a sticky lifter you can lose a lot of power that way, chances are other valves are not sealing correctly either, that could tell you the heads do need to be serviced.

                Also you mentioned the fmx shifting early, you can also adjust that through the transmission vacuum modulator. Some modulators are adjustable or you can install a new modulator that can be adjusted then you can change the shift points a bit using the vacuum signal from the engine to transmission.

                After that you can get shift kits for the transmission which can also alter shift points.
                Just want to add,

                If you decide to pull the heads and look in the cylinder bores, if the cross hatch hone in the cylinders is not visible you could be looking at a bottom end rebuild or having to rehone them and hope they are still in good enough spec to maintain good compression, with new rings.
                (This post was last modified: 10-24-2010 02:04 PM by 72HCODE.)
                Offline 10-24-2010 01:53 PM
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                  Post: #8
                  RE: Well, what if I just rebuilt the top end?

                  I agree with everything you just said except for the MSD box. I have had the same spark plugs, and the msd, in for about 6 years now, and the car still runs just as good as it always has. Idle quality, low rpm performance, and gas mileage all improved when I installed the box.
                  Offline 10-24-2010 02:12 PM
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                    Post: #9
                    RE: Well, what if I just rebuilt the top end?

                    Like other reponses my biggest concern would be if you only do the top would it put added stress on the block and all the bottom end.
                    Offline 10-24-2010 02:51 PM
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                      Post: #10
                      RE: Well, what if I just rebuilt the top end?


                      I went through the top end of my engine a couple of years ago. I needed to replace the oil pan due to stripped drain plug. With the short block on the engine stand I realized a set of rings and bearings were all I needed to freshen the short block as well. I found 3 rod bearings showing copper (NOT GOOD).

                      IMHO (or maybe not so humble Big Grin) if the engine does not need to be bored freshen the bottom end while you're at it. Find a friend who can help degree the cam. When degreeing the existing cam we found it needed to be retarded 7 degrees to get it to 4 degrees advanced. Advancing a cam will give an engine more low RPM power.

                      Just my nickles worth.
                      Offline 10-24-2010 07:32 PM
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