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Big Block Vortec Heads

Discussion in 'Tech Discussion' started by Nonstop, Feb 17, 2020.

  1. Nonstop

    Nonstop Full Access Member

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    Guys, as always, you are a wealth of knowledge! Thank you! I have been searching the internet and the information is all across the board! You guys have made it a lot clearer than what I have found! I have rotators on the intakes and exhausts. I will order 2 sets! I am HOPING AND PRAYING this goes as simple as possible!

    Now, from what I have read, there could be some interference issues with the intake side and eliminators. Can I just drill out the eliminators to fit over the guides?

    As always, thank you!
     
  2. bucket

    bucket Super Moderator Staff Member

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    My eliminators (Comp) were made out of some kind of magical tool steel. They laughed at my dremel. I don't remember if I tried a die grinder with various cutting bits.
     
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  3. Catbox

    Catbox Full Access Member

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    Yuppers.
    The interwebs are full of misinformation.
    When I do searches, I try to look at the dates the information comes back with.
    The earlier stuff all seems to be wishy-washy.
     
  4. Nonstop

    Nonstop Full Access Member

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    Just wanted to round this thread out and provide an update. I just finished the install today. I did a low budget install (sort of). I needed the following: rotator eliminators, adapting rocker studs, valve seals, and guide plates. Of course I also needed all gaskets and did an oil change since antifreeze went into the litter valley when I pulled the heads off. The heads had been rebuilt some time ago and looked good, so I just cleaned them up. I transferred over the springs from my old heads (not many miles on them). So, anyway, things started out okay. There was more than I recalled to strip off the front of the engine. Finally I got one of the heads off. Transfer springs over, clean up surfaces and go to put new head on. I torqued it down in steps. On the third and final torque, bolt #12 pulls the threads out of the block. I just put everything inside and walked away before I lost it. The next day, bought a heli coil kit and fixed the hole. Put the head back on (scared shitless as I torque that bolt) and move forward. Made a lot of progress Wednesday. I worked yesterday, but I was back at it today. I was able to button it up today (a lot of small things to bolt on). I have not tuned it yet, and only took it for a short drive, but so far am happy with it.

    My take away: it was worth the effort, but a pain in the ass to do in the truck (4 inch lift) and BB heads are HEAVY! It seems a little peppier and the secondaries seem to open sooner. The idle also does not smell as rich, although that may just be in my head.

    The big lesson I learned was to chase all the threads in the block and on the bolts. I am not sure it would have prevented the bolt hole from stripping, but certainly would not hurt!

    I am looking forward to a drive with it!
     
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  5. Salty Crusty

    Salty Crusty Member

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    Sorry so late to this thread but...
    Dump the Performer intake. It's peanut port and will cause a significant restriction. L29 heads are LARGE OVAL, just like the old 781, 049, etc. and you can easily see this when you line 'em up with a gasket.
    You've already found out that the rocker stud bosses are tapped, but the section that threads into the head is a good bit smaller than conventional. Comp cams has studs that will work.
    The L29's valvetrain is non-adjustable or net-lash as opposed to what we're used to (these are very similar to LS valvetrain setups). Once you get rid of the Gen 6 rockers and replace them with adjustable type, you can set valve lash at zero plus 1/2 or 3/4 turn just like you're used to. I've always had to replace pushrods, OEM are too short.
    All Gen 6 heads will work on Mark IV blocks, just remember to get the gasket that's correct for the BLOCK.
    I've worked on several of these and keep in mind that these were developed for clean emissions, requiring much less timing that conventional open chambered heads, and torque. You should have a noticeable seat-of-the-pants feeling with these installed. If you don't, double check valve lash.
    Glad you learned about chasing threads...more people blame poor block material for pulled threads than their lack of preparation in cleaning the threads.

    There are several threads on these heads at www.teamchevelle.com and you'll find a good bit of info there. One thing for sure. you're probably not going to grind through them when trying to port 'em, they're plenty thick. There is at least one thread at the Chevelles site that has pics of one that's been cut up.

    And OP: next time you have to work on a big block in the truck, use a cherry picker for lifting and lowering the heads. It sounds like overkill but I promise your back and hands will thank you. I use rocker studs to get it at pretty close to the right angle when it's hanging.
     
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  6. QBuff02

    QBuff02 I like Big Blocks and I cannot lie Supporting Member

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    A plain Performer intake can also be for Large Oval heads. But people need to pay close attention when they order, as there are standard versions of these intakes for both small oval and big oval heads. That's where the confusion comes in. People sometimes just order the first "match" they find. But a little massaging will make it fit up to stock Big Oval heads quite readily. On the other hand, The later Performer RPM port size is pretty dead nuts to any big oval felpro gasket you hold up to it. The original performer was designed with the smaller runners to improve low rpm torque and is perfect for an application such as the op's, whereas the Performer RPM was designed for just that, larger volume runners and more power across more rpm range. And although not ideal- Having a small intake runner manifold mated to a large port head isn't a killer. It actually might help your port velocity in a lower rpm application. The big problem is when people go the opposite way and have a large intake port manifold mated to peanut port heads as now basically about half of your intake charge is slamming head first into a brick wall and reverting back up into the plenum.
     
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  7. Salty Crusty

    Salty Crusty Member

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    Every single performer I've seen had peanut ports. You can match them to the port at the entry, but can't get far enough in to do any good.
    The idea is to gradually get smaller from the beginning of the port under the carb all the way to the valve - this speeds up velocity and helps maintain the fuel in the air. When you go from a small runner to a larger runner in the head, the fuel/air mix SLOWS down which can cause fuel fall-out, particularly on the long turn side. Performer RPM on peanut ports does the opposite - larger runner on the intake down to a smaller runner in the head actually increases port velocity which increases cylinder filling and desired swirl.

    Back in the day, it was actually quite common to use a rectangular port intake mated to oval port heads in drag race applications. Larger to smaller increases port velocity and vice versa. It's a huge mismatch but it worked well. Of course, this was back when we all KNEW that the big rectangular port heads were the only ones that would make power. Nowadays, we know that unless an engine is built to take advantage of high rpm capabilities of big ports, oval port combos are the way to go all the way down to about 10 seconds in the quarter mile.

    My old engine guru proved something to me one time - flow is more important than compression. We used a pair of 781's and some 063's, all bone stock. Compression with flat tops on the full open chamber 781's was less than 8:1 and the 063's was almost 9:1. The open chamber, lower compression heads made more power all the way through the dyno pulls in spite of being about a full point of compression lower. And of course, you could use any pump piss you could find for fuel.

    It may all be moot anyway - with a cam designed for lower rpm, port velocity won't be a big factor. Peanut port heads usually out perform ovals to about 4500rpms and since most of us spend most of our time in that range...

    I still think it was worth the swap to the L29's, please keep us posted.
     
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  8. Turbo4whl

    Turbo4whl Full Access Member

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    Yes, just remember a piston engine is nothing more than an air pump. The more air/fuel it pumps through the more power it has.

    Compression number is just that, a number. At higher RPM's the amount of air that has time and speed to move into a natural aspirated compression cylinder may only result in an actual compression of 3:1.

    Salty Crusty states a lot of good points, and I quoted the one that stands out to me most. This is why so many current small displacement engines are factory turbocharged.
     
  9. Nonstop

    Nonstop Full Access Member

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    Thanks for all the responses. I have been tuning it for the past couple of weeks. A couple of observations - I originally put in plugs for peanut port heads, but replaced them with the correct plugs for vortec heads. I gapped them at .055. It felt like it lost power. I was also having some weird idle issues. Pulled out 10 degrees of timing and it still idled the same. I had a spare distributor, which I set up for 22 degrees mechanical advance. As I replaced the distributor, I went to put in a new Summit coil and found my MSD distributor cap which I replaced when I did the heads was cracked under the coil. I replaced the cap and set the timing to 10 degrees. It feels a lot better, but feels like it might need a quicker advance. Still fooling around it.

    My Performer is the peanut port type. What would be a better intake? I have been checking out the Weiand 8123, but is it even worth changing intakes? I am mainly looking for low end torque. I currently have a 4 speed and 4.56 gears on 35’s. I actually forget what the cam is, it is a Comp Xtreme (I think). I built it almost 20 years ago.

    Thank you for any input!
     
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  10. Salty Crusty

    Salty Crusty Member

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    I wish I had a large oval intake laying around to send you to try but I don't.
    Check sleazebay for a Performer RPM. Find one in decent shape for a decent price so that if it doesn't fix the issue, you can resell it and hopefully not lose too much on an experiment.

    You won't feel a real difference with the heads OR intake until you get into higher rpm range, probably 4000- - 4500 and up since that's where the peanut port heads get more restrictive.

    The L29's were designed to make max power with minumum advance...keep that in mind as you set the distributor/timing.
     
  11. TubeTruck

    TubeTruck I like anything fast enough to do something stupid

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    What are you using the truck for? Also what size/kind is your carb?
     
  12. Catbox

    Catbox Full Access Member

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    Might try a 0.045 gap or smaller on the plugs as well.
    I had mine open to .050 on an MSD equip'd engine and gained some when I dialed it back down.

    Simple to do and if it works great, if not no harm.
     

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