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  1. #1
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    Corvette(s)
    1993 Viper Red Coupe

    Default 1993 LT1 Rocker Arms 1.5:1 vs 1.6:1

    Gang, I'm looking for some collective wisdom here. I know old school small block Chevys pretty well but know little about the LT1. My limited research indicates that stock rockers are 1.5:1. Has anybody installed the 1.6:1 aftermarket rocker on a bone stock LT1? What warnings could you offer? Piston interference?

    What benefits in terms of horsepower/torque could one expect. I would like to quantify the horsepower/dollar ratio.

    Given that a set of such rockers with roller tips are available from Jegs for $189 list what can I expect by increasing the lift and some duration by increasing the lift by doing this?

    What are your suggestions? What are your experiences? Difficulty won't be an issue but lack of measurable results will be. Guide me boys if you will!
    I wait to learn at the old Corvette hands knees! (No age shot intended as I am nearing sixty!)

  2. #2
    Member Curious George's Avatar
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    Corvette(s)
    '92 Red Convertible / '99 Red Convertible

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    Hello and welcome...
    I installed 1.6 roller rockers (Summit private label set) on my '92 and did not have any piston to valve clearance issues. The LT1 has "guide" plates, so you do not need self-aligning rockers. The 1.6's gave me a little bit of increased "pep", but not too much. For $189, it was definitely worth the labor if you are going to DIY. To get maximum benefit, you should re-tune your PCM, but that may not be in the budget. On computer controlled vehicles, every modification should be followed by a "tune" to get maximum benefit. Even though most computers can compensate for minor modifications, this increases their overhead... the less the computer has to adjust, the better the car will run. I know this sounds counter-intuitive, but it is true.

    CG

  3. #3
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    Corvette(s)
    1990

    Default

    Quote Originally Posted by Curious George View Post
    The LT1 has "guide" plates, so you do not need self-aligning rockers. The 1.6's gave me a little bit of increased "pep", but not too much.
    I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.

  4. #4
    Member TWISTERUP's Avatar
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    Corvette(s)
    1996 LT1 Coupe

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    I did the 1.6 "self aligning" rockers and LT4 springs. The LT1 springs are not at coil bind w/the 1.6s but I had read they would be "close" and I had over 70K miles at the time, so I replaced the springs also. The cam specs of the later LT1 and the LT4 were very close the main difference was the added valve lift w/the 1.6s on the LT4. It's said you pick up 15-20 hp...I didn't do a before and after "dyno test". I also did a "retune"... as was mentioned above. The rockers are a mod which IMO wake the LT1 up more so at higher revs...I'm glad I did it

  5. #5
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    Corvette(s)
    1993 Viper Red Coupe

    Default

    Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.

  6. #6
    Registered User
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    Corvette(s)
    1995 Bright Red Coupe, 1996 Black LT4 Coupe

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    Quote Originally Posted by vetteoz View Post
    I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.
    I Agree.You need Self Aligning Ones.You'll wear out your push rods & Guide Plates. They both must be Hardened if you use Non-Self Aligning ones.
    15 H.P. Increase is Correct.


  7. #7
    Member TWISTERUP's Avatar
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    Corvette(s)
    1996 LT1 Coupe

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    Quote Originally Posted by Brian Smith View Post
    Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.
    There are many companies that tune/reprogram the ECM/PCM to better use mods that have been made (cam,intake,porting and better exhaust etc.)....the "tune" alone will usually add a few ponies even on a bone stock LT1. Two companies that come to mind are PCMforless and Madtuner.com....there are vendors here on this forum that "tune". Some members will likely chime in with some good and/or bad experiences they have had with different tuners.

  8. #8
    surfer93
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    If your only mod is RR's, I would not think you would need a tune, as your are only going to see any difference at WOT.
    The 92-93 speed density computer do not handle mods very well, but this one is only at WOT.

    One note, if you are going to get the ECM tuned. Then get Datamaster or some other software analyzer first, that way the tuner can better adjust the ECM, because every car has its quirks.

  9. #9
    Member Curious George's Avatar
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    Quote Originally Posted by vetteoz View Post
    I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.
    Thanks for clarifying that point. I try and make sure I post facts and not misinformation. (already too much of that on all the forums)

    CG

  10. #10
    Member Curious George's Avatar
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    Quote Originally Posted by surfer93 View Post
    If your only mod is RR's, I would not think you would need a tune, as your are only going to see any difference at WOT.
    The 92-93 speed density computer do not handle mods very well, but this one is only at WOT.

    One note, if you are going to get the ECM tuned. Then get Datamaster or some other software analyzer first, that way the tuner can better adjust the ECM, because every car has its quirks.
    In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

    If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better.

    CG

  11. #11
    surfer93
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    Quote Originally Posted by Curious George View Post
    In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

    If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better.

    CG
    You are correct, if there is more air flow from idle to WOT, but there is not. The only difference will be seen at WOT and the ECM does not do any adjustments at WOT. Therefore a tune is not needed, it would be helpful no doubt, even a tune on a stock engine will help a little.

    Also, you will see a 8-12hp gain, but it will only be at high RPM's, it will not be across the entire power band.

  12. #12
    Member JAKE's Avatar
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    1996 388 LT1

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    Quote Originally Posted by Brian Smith View Post
    Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.
    No, that's not how it's done.

    The programming in the car's computer needs to be changed; re-programmed to change fuel and timing maps, etc., that are programmed into the computer from the factory. Cost varies, but I paid $175

    Merely disconnecting and re-connecting the battery won't get it done.

    I haven't come across anyone having a piston to valve clearance problem running 1.6 RRs on a totally stock engine. In fact, I'm running 1.7s

    Considering the cost and labor involeved, FULL roller rockers are the only way to go in order to get max benefit from the mod.

    Most recommend changing valve springs too, but some keep their stock springs. However, that's NOT the preferred way. Most of the benefit of moving to 1.6 RRs shows up in the mid-range and up. 1.6s give around .030" more valve lift and 2-3 degree more effective camshaft duration.

    One last point: Even though stock rockers are advertised at 1.5 ratio, when measured they generally check in the 1.4x ratio range.

    Jake

  13. #13
    Member TWISTERUP's Avatar
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    1996 LT1 Coupe

    Default

    [QUOTE=Curious George;985605]In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

    If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better. Quote CG
    Bingo-I agrree 100%-Nail on the head--the 1.6s allow more air in from idle to WOT--i can't think of any internal engine mods that JUST affect WOT----and a WOT switch and nitrous doesn't count as a internal mod LOL

  14. #14
    Member JAKE's Avatar
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    1996 388 LT1

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    My son's stock 1996 LT1 643 heads don't have guide plates of any type. Not even the ones so often referred to as factory installed for assembly purposes. None.

    Jake

    West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
    My son, Ryan M. Cameron, graduated from West Point on 22 May 2010! He was commissioned as a 2nd Lieutenant and I pinned on his first pair of "Butter Bars" PROUDEST DAY OF MY LIFE!!

  15. #15
    Member Curious George's Avatar
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    Quote Originally Posted by JAKE View Post
    My son's stock 1996 LT1 643 heads don't have guide plates of any type. Not even the ones so often referred to as factory installed for assembly purposes. None.

    Jake

    West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
    I have been thinking about this... Can anybody explain why my '92 LT1 would have "assembly guide plates", if this is indeed what they are. And if so, how long did GM use these? As mentioned by "JAKE", his '96 did not have them nor have any other LT1 motors I have seen pictures of on the Internet have them. As far as I can tell, the motor was not modified, in any way, before I bought it. Bone stock from the looks of everything I have found so far.

    When I removed the OE stamped rockers they were self-aligning.

    CG

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