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Higher RPM - how to get there reliably

This is a discussion on Higher RPM - how to get there reliably within the Internal Engine forums, part of the LSx Technical Help Section category; Hi! I'm working on an Exotic swap project, unusual advice needed... I'm building a Lotus Esprit S1, and adding an ...

  1. #1
    Michael Blue
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    Higher RPM - how to get there reliably

    Hi!

    I'm working on an Exotic swap project, unusual advice needed...

    I'm building a Lotus Esprit S1, and adding an LS1.

    I've been reading up, and know that if I have plans for a lot of HP later, I need a mid-'99+ motor (per Hot Rod's article).

    At first I don't plan on more than 350-400hp MAX.
    I'll be adding ITBs and headers, light flywheel, etc, and the ITBs will requite a stand-alone ECU anyway, so I'll have more control than normal - all good for the next question.

    I would like to make the engine reliably rev beyond the 6K stock redline...Something more in the 7500rpm range.

    Sure, not setting the world on fire, but with the ITBs and headers, etc the added RPM should make the engine sound more the part, being in a Lotus.
    (Yes, I said "sound"...I am just as concerned about the sound and aesthetics of this powerplant as the power.)

    Question is, what is my shopping list for this goal?
    Stronger valve springs, lighter pushrods, sure, but will I need to do anything with the crank or mains? Is there anything else I'm missing?

    Thanks a ton for your help...I am a newbie to the domestic muscle scene, but I'm very impressed by this engine so far!


  2. #2
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    blue
    2000 firehawk

    Exclamation quest for higher rpm

    for high rpm reliability a stock bottom end ls1 should not exceed 7000 rpm;
    a must when running at this rpm or anything above 6000 is upgraded valvetrain work; start with chrome moly pushrods and heavier valve spring
    pressure; new springs, ls6 or better aftermarket valve springs;also lighter spring retainers such as titanium and titanium spring keepers or locks;with all of this in mind choose the roller rockers of your choice and you'll be good to go.

  3. #3
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    blue
    2000 firehawk

    high rpm ls1

    as long as you stay away from power adders the stock bottom end will not be of any concern. if you dont strengthen the entire valvetrain you will be bending pushrods and breaking valvesprings and possibly suck valves.also you
    will want a high rpm intake manifold that will alow the engine to make power up high; reccomend comp. cams for just about everything ven the intake.

    good luck with this project

  4. #4
    Michael Blue
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    LS6 springs,
    Lighter retainers,
    Keepers,
    Stronger, lighter pushrods,
    Roller rockers...

    Check!

    As for the intake, I'm going to be running Individual Throttle Bodies, so that's a non-issue.

    Thanks!

  5. #5
    member since may 2000 nhraformula's Avatar
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    black
    2000 nhra edition formula

    if you spin it that high, forged everything internal.
    i see youre from illinois, call speed inc, see what they think.
    dual springs are way better than ls6 springs.
    2000 nhra edition formula
    a few bolt ons, 379 rwhp
    11.96 @113.25

  6. #6
    Michael Blue
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    Dual springs, check.

    Besides the rods, what isn't forged that needs to be?

    Thanks!

  7. #7
    Junior Member MNR-0's Avatar
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    BLACK
    2004 Monaro

    I have an upgraded valvetrain, crane 1.8RRs with 0.600 lift at the valves and run comp 918s. Titanium retainers only, stock valves. I spin mine upwards of 6800rpm with a redline of 7000RPM and have done so for over a year with no problems. Recently pulled the engine to put in a cam and the bores and pistons were like new - even after 2 years and 33K miles plus 250 QTR miles runs. I even have stock rod bolts.

    It is sacramount to keep your engine well serviced. I change my oil every 6K miles and keep an eye on all fluid levels, letting the car cool down for at least half an hour after each drag run. This allows the diff to cool and de-stress the motor. Hell, I even have the stock unshimmed diff from the factory floor and its a tight as the day I bought it.

    Use good quality oild and lubricants and look after her - she will look after you. Know her limits though and dont flog her time and again without letting her catch her breath. Thats how I treat my car.

  8. #8
    Michael Blue
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    Planning synthetics, extra coolers, etc. before she EVER hits a track.
    No 1/4 mile for me, but AutoX and track days will be common.

    Thanks!

  9. #9
    nc98z
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    better upgrade the rod bolts to arp's there was a problem with the earlier ls1's

  10. #10
    Michael Blue
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    Will probably upgrade all the hardware when it's apart, but I do plan on using a later one.
    What was it...'99.5+ that were the better ones for a build-up?

  11. #11
    I like the way yew tawlk. Ric's Avatar
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    Red
    2000 T/A WS6

    I think from that point up should be the better blocks... basically, they have thicker sleeves, meaning you can hone them a little more, but unless someone else can chime in and correct me, that the only difference in the blocks. I believe 2001-up has the better 241 casting heads, too.

    To go one better, look for a rebuildable LS6 block and heads and put 4340 crank/rods, ARP Wave-Loc rod bolts, lightweight forged pistons, lightweight steel flywheel, and all the aforementioned valvetrain upgrades to it.

    By the way, at those rpms, you may have to deal with having more than 400 hp, 'cuz you'd need a mean cam to spin that high without falling flat on your face.

  12. #12
    Space Cadet RainMan's Avatar
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    Red & Dk Gray
    2002 WS6, '08 G8 GT

    Talking My $.02 worth.

    1st of all you have to remember that the LS1 is still a conventional push-rod engine and by its very nature is RPM limited without serious modifications. This will not be as easy to modify for high rpm operation as say a 4 valve per cylinder dual overhead cammer. These engines have much greater high RPM potential.

    As previously mentioned below, this will require serious upgrades to the valve train, stronger lighter parts capable of sustained operation in the RPM band you seek. 7000+

    To find a Cam that will work well in that RPM range you are probably looking at closer to a 500+ HP power output. It will be critical to match the cam to the valve train components to ensure longevity. Probably in excess of .600 lift with about a 240-250 duration @ .050 lift. This will be a bit radical in the smaller displacement LS1. To get more cubes and still have a high revving engine you may want to consider a larger 4.125" bore block with the short stroke crank of the LS1.

    Standard LS1 uses a 3.90" Bore and a 3.62" stroke, so using the formula bore X bore X stroke X # of cylinders X 0.7845 you end up with the stock 345.95 cubic inches. Using an aftermarket 4.125" bore block with the stock stroke will give you 387 cubic inches. This will lessen the effect of the large cam a little plus give you an engine capable of spinning up faster than a standard LS1.

    Once you've selected a Cam that will operate in the appropriate RPM power band, you need to ensure your intake & heads will support that amount of air flow at the upper RPM range yet still have enough low speed intake port velocity to promote good cylinder swirl for some decent low end torque.

    Although the general consensus is that the stock bottom end will live in these extremes, the question is how long? I feel that to ensure reliability the bottom end will also need some major work. Stronger rods and rod bolts are a must. Consider light weight forged rods and pistons, with a light weight forged steel or even *billet steel crank (*megga $$$$$) . . .ouch! Have the entire reciprocating assembly balanced and blueprinted (Rods, pistons, crank.) Also consider windage in the oil pan. A crank that sheds oil faster will spin up faster.

    One saving grace is the design of the LSX blocks. With the deep skirt and 6 bolt/cross-bolt mains you have a lot of additional strength. Upgrade the oil pump, larger capacity oil pan, and you may also need some custom work to the oil passages to ensure adequate oil flow. Finally, find a reliable tuner, operation at that RPM will require precise calibration of fuel and timing tables in the PCM.

    Then you have to get all that power to the ground, which is whole nuther ball of wax!

    I know it sounds like a lot of expensive work, and I'm sure there will be many contrasting opinions. I've been building small blocks for like 25+ years (stock, street/strip, circle track, etc. . .) and this is just that, my experienced opinion, not the Gospel.

    One other consideration may be to look at a custom built 32 valve Northstar engine. Already a 4 valve per cylinder overhead cammer with high rev capabilities (6700RPM Red Line). Consult an expert with these engines and see what is possible. The 4 valve per cylinder design will make great power with relatively mild camshaft profiles and still be very streetable.
    See: http://www.gm.com/automotive/gmpower...nes/northstar/

    These are just some issues to consider, as always, do your research before making a commitment.

    Later and Good Luck
    Last edited by RainMan; 01-26-2006 at 06:56 PM. Reason: Additional info

  13. #13
    Michael Blue
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    Quote Originally Posted by RainMan
    ...as always, do your research before making a commitment...

    Absolutely!

    I considered the Northstar, breifly. I have never found 2 things for thew N* I require on this kind of project: a suitable manual transmission and proper engine management.

    I'm really not worried if the extra RPMs give buckets of power, but I don't want to back off stock power, or lose reliability. If that means I stick to 7,000rpms max, not a problem. I know the engine will do that without crank work.
    Valvetrain? Yes. Rods and pistons? Maybe, but probably not "necessary"...but I'm planning them anyway.

    Really don't want to mess with the bore or stroke, or the crank itself.
    The plan was to upgrade what I needed to for reliability and a few extra revs without sacrificing any of the OE reliability.

    Thanks for all your help, please keep it coming!

  14. #14
    Tech Junkie hammertime's Avatar
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    Pewter Metallic
    2001 Camaro SS

    Doesn't the LS6 cam spin to 6500+ rpm with just 207/217 duration and a wide 116 lobe separation? I think you could extend your rpm range a bit with something like one of comp's cams in the 214 - 220 range and a tighter lobe sep, and gain some lower midrange torque in the process.

    Sure, 240+ cams are cool, but I don't think that is necessary.
    Hammer - hammertime.us
    2001 Light Pewter Metallic Camaro SS, 6 speed
    K&N, SLP Lid, SLP y-pipe, GMMG cat-back, Lou's Short Stick - more to come!

  15. #15
    Space Cadet RainMan's Avatar
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    Red & Dk Gray
    2002 WS6, '08 G8 GT

    Not trying to insult your intelligence but,

    Actually the Cam will only physically spin at 3250 if the engine RPM is 6500, remember, cams rotate once for every 2 crank revolutions.

    Yes, you are right that the LS6 is rated for 6500 red line. However, RPM Red line and Operating RPM or Power band are two completely different animals.

    Red-Line is the maximum safe RPM that the engine can spin up to as rated by the factory. Operating range (Power band) is the range at where the cam is designed to make the most effective power.

    The LS6 cam may very well be able to survive and physically rotate in a 7000+ RPM engine, but the effective power range may be something more like 2000 - 5800 RPM or 2500 - 6200 RPM as an example. Usually just a couple hundred RPM past where it will make peak power. Anything over that you are not making power and the engine is just making noise.

    According to the 2005 GMPP Catalog
    the LS6 Cam as installed in the 405 HP LS6 crate motor is:
    204/211 @.050 with .525 lift

    Or, in the stand alone cam section it is
    207/217 @.050 with .525 lift for 2001 LS6 & Vortec

    204/218 @.050 with .550 lift for 2002-2004 LS6 (Z06 Cam?)

  16. #16
    Tech Junkie hammertime's Avatar
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    Pewter Metallic
    2001 Camaro SS

    Actually, I do realize the cam is driven at 1/2 the crankshaft speed. When I said it spins to 6500 rpm, I meant the lift & duration characteristics allowed it to spin the motor that high.

    Also, if you look at the dyno graph for the LS6 crate motor in you GMPP catalog, the HP curve on that cam is pretty flat from 5000 - 7000 rpms. If you could shift that cam at 7000, while at the top of its HP curve, the next gear falls more closely to the power curve.

    Example: 2-3 gear in Z06 2.07:1 and 1.43:1 ratios
    Shifted at 7000, the revs drop to 4835 or right at the peak torque.
    Shifted at 6200 as you stated, the recovery point is 4283, below the curve.

  17. #17
    Space Cadet RainMan's Avatar
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    hammertime,

    All very good points. Not saying you are wrong or right, or I'm wrong or right.

    However, this is yet another example of two different schools of thought.

    If you look at the the torque curve for the LS6.
    Draw a vertical intersect line @ 6000 RPM HP peak down. Now at the point* the line intersects the torque curve, draw a horizontal line across the chart. Roughly the 370ftLb line.
    Go back on the torque curve to where the horizontal line intersects the curve @ approx 4000 RPM. This is the second point**
    Plot these two points and you end up with approx 2000 RPM encompassing the torque peak near the 4835 RPM Tq peak you mentioned.

    Now, with the approx 2000 RPM drop during the shift you gave as an example, you want to center these point as close to the same value as possible. In other words, if you shift @ 6000 RPM where the Pk HP is, the torque is approx 370, this is where you want to recover. The same torque value on the rising curve as you shifted on the declining curve. So you shift at 370FTLb and Recover at 370 FTLb, you still accelerate through the torque peak!

    *Plot point 1. Shift
    **Plot point 2. Recovery

    If you shift at 7000RPM as you suggest, you will actually run slower as your shift and recovery are on the same decending side of the torque curve.

    Found a little info that may help with what I'm trying to say.

    http://www.datsuns.com/Tech/whentoshift.htm

    Remember I just used the HP peak reference as an example. You will need to calculate where you vehicle best performs, based on torque curve, gear ratios, etc. . .for each gear, your shift point will be slightly different.

  18. #18
    Junior Member Louie's Avatar
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    Black
    2000 WS6

    Lot's of good info in this thread.

    If you are building the stock cubed engine to rev to 7000, is it optimal to get a decent sized cam (ms3 or so) to make the power up high, bigger heads (225ish) to help it breathe in higher rpms, and a lightweight flywheel to rev a bit faster?

  19. #19
    Michael Blue
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    Probably, but I'm not touching the heads.

    WAY too much $$ for WAY too little gains.

    Cam...Sure. Flywheel...Plan on it.


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