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Gen 2 to Gen 3 Top-End Swap

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  • Gen 2 to Gen 3 Top-End Swap

    The 3100 and 3400 engines are called Gen 3, because they are the third generation pushrod 60V6 engines. The reason for the swap is simple. Flow and design, both of which the Gen 3 triumphs all previous generations. The iron heads don't have splayed valves, D shaped exhaust ports, or in some cases even the larger valves (1.42/1.72). The Gen 2 Aluminum head engines are the most popular to do this swap, but no matter what you start with, the same steps apply. The Gen 3 parts have D shaped exhaust ports for increased flow, and the 3400 and 2000+ 3100 heads have a 1.76" intake valve which increases intake flow.


    The intakes are also very important. The iron heads had a decent intake manifold setup, but the Gen 2 aluminum intakes are pure BS. Sad but true, you are going to need boost to overcome the design flaws. With larger ports and equal length runners, the Gen 3 intakes are far superior. The 3400 and 3100+ have even larger intakes, which you can check out here. There are some complications with the changes made over the years with the Gen 3 heads and intakes however, so lets address these first.


    Complications, its not always plug and play

    Much of this information comes from Chris Williams (GPXSS), who was the first to do this swap as far as we know. There are some platform specific details that we are hoping the owners will share with us to add at the end. As it sits, this information is based on a swap into a 93 Grand Prix 3.1. Before I get too far ahead of myself though, lets talk about the intake and head changes over the years.


    The 94-95 3100 intakes are easier to use for the swap because the plenum will allow you to use the EGR your computer was programmed and wired for. The downside is that these intakes were the early revision and do not have the larger Gen 3 ports and runners. Increases over stock are still awesome so if you want the easiest swap path, grab these.


    In 96, the EGR changed which means you will have to either disable the EGR in the computer, block the EGR off and pray for a no code situation, or use an adapter plate so your old EGR will work with it. The heads are still stamped steel and not roller rockers unless you are lucky. We believe the W body line may have them though. That applies to the 3100 only, as the minivans started getting the 3400 engines in 96 and these had the larger runners AND roller rocker arms. Sweet deal, so you may as well go for the 3400 if you are going to mess with the EGR. 96-99 are the same for the EGR, and 97 should be the start of the 3100 heads getting the roller rocker arms.


    2000 got another EGR change, so its the same situation as the 96-99. The 3100 now has the same heads as the 3400 (1.76" intake valve) and the 3100 intakes are identical to the 3400 as well (larger ports/runners). There is an issue with the coolant line that goes under the TB into the lower intake however. Instead of a screw in type, they are now pressed in. Create your own threads, or just avoid these lower intakes.


    If you didn't check out the link to the intakes before, now is a good time to check it out because another issue comes from the rocker arm to lower intake manifold clearance. Brad already found this out the hard way so you can learn from his ordeal. Roller rockers really shouldn't have this issue, nor the older rocker arms without the tab over the oiling hole from the pushrod. Basically this was added in the 94-95 engine rocker arms to help direct oil to the pivot ball. If you are getting the heads and intakes from the same engine and using the rocker arms from that setup, this is a non issue.



    Alterations to do the swap

    These are Chris' words on the swap.


    Biggest issues with the swap:


    Power Steering Pump - you'll need to get one that matches the motor. 94-99 for any car with the 3100. It would also help to get the lines since they route differently.


    Front Timing Cover - If you use the 3.1 timing cover, you'll need to modify it to fit the steering pump (shave 1/4" off the back where the PS pump mounts) newer 3100 timing covers have a thinner mount to compensate. You'll also need to make sure you get a 94-99 PS pump pulley.


    Pushrods - The Gen 3 Heads got the 1.6:1 ratio rockers so you will have to get custom length pushrods to match up with them. No big deal, just have to measure for this.


    Throttle cable - This will be a little more difficult for you, there was never a 3100 in a Cavalier so GM didn't make one. You'll probably just have to modify your existing one (they connect to the throttle body differently than with the 3.1)


    Coolant Temp Sensor - 3.1's use a coolant temp sensor screwed into a corner of the rear head.. 3100 heads (at least 96+) dont have the hole for this so you'll need to mount it somewhere else. I'm thinking of putting it in the thermostat housing pipe.


    Rear Manifold To Downpipe Junction - Depending on what year heads and exhaust manifolds you get, you'll need a matching downpipe flange. 3.1 downpipes will not bolt up, plus you'll need the composite donut for the same year.


    Engine Mounts - My Grand Prix uses the dog-bone front mounts, so i ended up grinding quite a bit off one of the head mounts so the thermostat housing pipe would fit.


    Heater Bypass Pipe - 3100's use a different routing method for the metal pipe going across the front of your motor for coolant bypass. I ended up cutting mine off after it comes out of the water pump housing, and meets the 3100 pipe which runs in between the plenum and lower intake, then just used a small length of heater hose to connect the two.


    As far as Sensors, you are going to reuse all of your old wiring since all sensors are retained. You will however need to lengthen the TPS and IAC lines for the throttle body about 5" each. You will need the 3100's vacuum lines. You'll need some misc bracketry to mount thinks like the MAP sensor and purge solenoid.


    I'd suggest mounting the DIS pack in its stock location so you don't have to lengthen the wires.


    • Superdave
      #3
      Superdave commented
      Editing a comment
      NP..

      Also, 5th paragraph:

      In 96, the EGR changed which means you will have to either disable the EGR in the computer, block the EGR off and pray for a no code situation, or use an adapter plate so your old EGR will work with it. The heads are still stamped steel and not roller rockers unless you are lucky. We believe the W body line may have them though. That applies to the 3100 only, as the minivans started getting the 3400 engines in 96 and these had the larger runners AND roller rocker arms. Sweet deal, so you may as well go for the 3400 if you are going to mess with the EGR. 96-99 are the same for the EGR, and 97 should be the start of the 3100 heads getting the roller rocker arms.


      I'd replace "heads" with Rockers.. lol

    • bszopi
      #4
      bszopi commented
      Editing a comment
      What, you haven't seen the stamped steel heads? Must have been a limited production thing...

    • Superdave
      #5
      Superdave commented
      Editing a comment
      lol, those would be awesome paperweights.
    Posting comments is disabled.

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