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  1. #1

    Lightbulb What really limits our engines to rev higher

    Since I'm rebuilding one of my engines, I was looking for ways to get higher RPM limits in order to get both the typical screaming sound of high rev engines and more horsepower (while keeping it N/A)...

    Basically, the pushrod Viper engine is limited by:

    - Valvetrain stability (it's a pushrod)
    - Long stroke
    - Oiling system (especially gen 1-2-3 and no dry sump for gen 4/5)
    - Air flow (2-valves, heads limitations, etc..)


    The ''theorical'' limit for mean piston speed is 25 m/s or 4900 ft per minute, but that's open for debate since some will say 4000 fpm is the maximum ''safe'' limit while others says a race engine can be pushed as far as 5500-6000 fpm. Many factors to consider here...

    But basically a Viper's 3.96'' stroke would be at the 4900fpm limit around 7,400 rpm, which is already a lot. I've seen destroked Viper on youtube going to 8,000rpm and also few others in the 7,xxx range.

    But other than destroking, what is the path to get that huge engine rev higher? Super lightweight and stable valvetrain is probably mandatory, then you need sufficient air flow (ported heads, high duration camshaft, excellent intake/exhaust systems, etc..) and obviously the oiling and cooling systems that will keep that high rev engine from blowing apart...

    But what else?

    Is super lightweight pistons/rods that important, or it's better to focus on parts strenght?
    Same for push rods, is it better to have heavier oversized but very stiff and stable ones?
    Extemely stiff valve springs? at the cost of losing efficiency


    Some interesting stuff here on the subject:

    https://www.motortrend.com/how-to/11...se-engine-rpm/

    ...but probably some tips do not apply for a 7-8000 rev engine.
    Last edited by Aevus; 07-21-2021 at 01:43 PM.

  2. #2
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    I can't really comment due to a lack of knowledge/experience, but two things stuck out to me:

    1. Dailey Engineering makes dry sumps for Gen 2-5 Vipers - you can even retain your A/C for Gen 3-5 (https://www.daileyengineering.com/dodgechrysler/)

    2. In the article linked, this statement immediately stood out:

    In just about every racing class in existence that limits maximum displacement, the quest to turn more rpm than the next guy rules the day.
    For a street/occasional track car without maximum displacement limits, it doesn't make much sense to me. Yeah, high RPMs sound cool, but if you end up having to lose displacement to get there, you are also going to lose torque.

    I don't think you'd even necessarily have to give up displacement. Arizona Vipers spins his 9L up to 7,000 RPMs all the time. That's obviously at the low end of your 7-8,000 RPM range, but still qualifies as high RPMs in my book.

    Maybe I'm just getting too old and need to take a nap...it just sounds like an expensive science project that won't really do much beyond what you already have other than make a lot of noise.
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  3. #3
    Quote Originally Posted by Steve M View Post

    I don't think you'd even necessarily have to give up displacement. Arizona Vipers spins his 9L up to 7,000 RPMs all the time. That's obviously at the low end of your 7-8,000 RPM range, but still qualifies as high RPMs in my book.
    Very impressive to get 7,000rpm from a 9L stroker indeed

  4. #4
    Quote Originally Posted by Steve M View Post
    Maybe I'm just getting too old and need to take a nap...it just sounds like an expensive science project that won't really do much beyond what you already have other than make a lot of noise.
    Just a very different character engine, that's all. Even 7,200rpm would be plenty of fun, best of both world: a relatively high revving engine + large displacement.

    Sure is an expensive science project but far less than a 11,200rpm LS7 engine (!)

  5. #5
    Valvetrain/Oiling/Cooling is more about reliability but can it get there?

    The air flow is the key to just be able to rev high. So I believe anything less than ported gen4 heads won't cut it, for anything north of 7,000rpm

    Here is some flow numbers:

    http://www.speedstore.ca/VP4_flow_sheet.html

    Without going too crazy on the lift, you can get 360 cfm on the intake and 260 on the exhaust, and I heard the porting can be made even better (Greg Good ?) close to 390 cfm, I'm not sure if that's true...

    Then, how big of durations can you push it until it becomes impossible to tune

  6. #6
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    They are hydraulic motors

  7. #7
    Listen to the sound of a high rev gen2, built by Calvo

    https://youtu.be/_0LD6Ty-nxQ?t=85

  8. #8
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    You cant keep the lifter pumped up at high RPM on hyd motor. The lifter passes by oiling hole so quickly at high RPM it wont stay pumped up, then all kinds of problems happen. High RPM motor you just go solid and problem is solved. Then onto factory manifold problem

  9. #9
    That's interesting.

    And what is ''high RPM'', exactly?

    By using the gen 1/2 Mopar slow bleed lifters, what would be the upper limit, 6,500-7,000rpm?


    Found this:

    https://www.motortrend.com/how-to/mo...aulic-lifters/


    At what point can instability with a hydraulic lifter begin to hinder performance? The answer, unfortunately, is combination specific. Valvetrain weight and geometry, pushrod deflection, preload adjustment, spring load, and the cam profile's smoothness and intensity are some of the factors, along with rpm, that can upset a hydraulic lifter's ability to maintain valve control. Even oil viscosity and temperature have been reported to make a difference.

    Though there are too many variables to pinpoint the rpm capability of a hydraulic-lifter camshaft, extensive experience in the use of hydraulic cams can suggest basic guidelines. Depending upon the camshaft/valvetrain/spring combination, standard hydraulic lifters can operate effectively in the 5,500-6,000-rpm range. Typically, anti-pump-up lifters can raise the rpm potential by 500-1,000 rpm more. Certainly, some have far exceeded these numbers, while other combinations experience problems at even more conservative levels.



    The solid cranked 550 hp at 5,800 rpm, and 559 lb-ft of torque at 3,900. Interestingly, the torque levels were quite close at peak, and below at the low-to-middle of the rpm curve. At higher rpm-about 5,200 and above-the solid cam walked away from the hydraulic, pulling cleanly to 6,300 rpm, at which we limited our test. The solid cam's power curve was nicely shaped, exactly what we like to see.

    We had a 30hp gain, with the same "size" camshaft, with the peak horsepower coming in a good 400 rpm higher. There was no part of the curve where the hydraulic showed a clear advantage. Seeing is believing-when it comes to spinning it up, a solid flat-tappet cam does have the edge.
    Last edited by Aevus; 07-21-2021 at 08:32 PM.

  10. #10
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    Quote Originally Posted by Aevus View Post
    By using the gen 1/2 Mopar slow bleed lifters, what would be the upper limit, 6,500-7,000rpm?
    Slow bleed lifters are actually just the normal lifter used in everything from mini-vans to pickup trucks and early Vipers. The fast bleed ones are the weird (and expensive) ones used for emissions reasons.

  11. #11

  12. #12
    https://www.youtube.com/watch?v=GZTdo2-cGCM


    On this episode of Engine Masters, the comparison features 100-percent more hydraulic cam! Last round we compared hydraulic and solid roller lifters on hydraulic and solid cams, respectively. But we have more questions! For instance, can you actually run solid roller lifters on a hydraulic cam? Why would you? And, if you do, will they make more power? How long will they survive?
    Last edited by Aevus; 07-21-2021 at 08:47 PM.

  13. #13
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    Quote Originally Posted by Aevus View Post
    That's interesting.

    And what is ''high RPM'', exactly?

    By using the gen 1/2 Mopar slow bleed lifters, what would be the upper limit, 6,500-7,000rpm?


    Found this:

    https://www.motortrend.com/how-to/mo...aulic-lifters/
    There really is no need to spin any motor past where it makes peak power. 7k on built hydraulic viper motor is very dicey. 6600-6800rpm is a safer bet
    Solid viper motor 7500-8K reliably is not a problem but to take full advantage of 8K RPM you need to improve other aspects of the motor.

  14. #14
    Quote Originally Posted by TKO MOTORSPORTS TEAM View Post
    There really is no need to spin any motor past where it makes peak power. 7k on built hydraulic viper motor is very dicey. 6600-6800rpm is a safer bet
    Solid viper motor 7500-8K reliably is not a problem but to take full advantage of 8K RPM you need to improve other aspects of the motor.
    Ain't easy to find information on solid lifters (and solid cam) for the Viper, probably not a common conversion at all for the snake. Maybe Jesel can make solid lifters for it, but then again will it work with a big hydraulic camshaft or a custom solid roller cam will be needed

  15. #15
    Forget about those lame wives tales about solid lifters always going out of adjustment! That's just not true! We're not in the damn 60's and 70's anymore! The ONLY way the adjustment (lash) can change is if something is either wearing out or going bad, period. If a rocker stud starts pulling out, the lash will increase. If the tip of the valve is getting hammered or mushroomed, the lash will increase. That's what hardened lash caps were made for before we had better material to make valves out of. If the tip, or the cup, of the rocker arm starts to wear out, the lash will increase. If a push rod bends or wears out one (or both) of the tips, the lash will increase. If the lifter is getting cupped or the cam is going flat, the lash will increase. If a valve seat "sinks" or recesses, then the valve is actually lifting or sitting higher, which means the lash will decrease. No matter how you slice it, if a solid lifter cam keeps going out of adjustment, something is seriously wrong or isn't up to par! If nothing is wearing, bending, pulling, mushrooming, backing-off, or getting longer or shorter, then there is zero reason for the valve to go out of adjustment. Guys that say solids will go out of adjustment when using modern components, such as stainless steel valves, screw-in studs, roller rockers with tool steel cups and rollers, hard valve seats, chrome moly push rods, etc, then it's just a wives tale being spread by people who have probably never even ran a solid lifter cam in a real engine before. If you're talking about an era engine with era components in it, well then you just might have to do some adjusting from time to time, but not when you have a modern performance engine, or a 1st generation engine with modernized components in it.

    https://www.badasscars.com/index.cfm...prod/prd67.htm


    I realler wonder why the solid lifter thing is not among the top modifications to be done on the Viper engine if that is so obviously better (no adjustement really needed + a bit noisier but on a noisy car anyway...)

    According to the motortrend dyno test, it delivers same or better torque/HP all the way... and you gain 500-1000rpm potential.

    So, what's the drawback?

  16. #16
    Technology and metallurgy are changing. It use to be that a hydraulic cam wouldn't be very good for a hot street or a mild race engine when in fact, they perform very well. As long as good matching valve springs are used with a set of good quality, light weight lifters, there's no reason a hydraulic cam can't do well on the street, or on the track, and if someone tells you different, have them tell that to the guys running hydraulic cams at well over 7000 RPM in 11 and 12 second street cars.

    Solid lifter cams can be a good choice for a hot street or race engine. They usually have faster ramps (lobes) than hydraulic cams, but not as fast as roller cams. They also need stouter springs than a hydraulic cam, but not nearly as stiff as a roller cam. They're kind of the middle of the road between the hydraulic flat tappet and roller cams.

    So maybe the solution to reach the 7,000rpm mark all hyd is with good springs + lightweight lifters.

  17. #17
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    Quote Originally Posted by Aevus View Post
    So maybe the solution to reach the 7,000rpm mark all hyd is with good springs + lightweight lifters.
    I probably should have clarified "road course" or long duration high rpm use. 11-12 second daily driven drag cars probably ok going hyd since its short runs and motors are pretty mild; and there is no doubt hyd motors are less maintenance and great for more everyday street use. Yes for sure materials have gotten better and machining processes have gotten alot better which has benefited all of us you can see this everyday. But better design, materials and machining processes cant fix the laws of physics and fluid dynamics that we all have to work with or but heads with on a daily basis.

  18. #18
    Quote Originally Posted by TKO MOTORSPORTS TEAM View Post
    But better design, materials and machining processes cant fix the laws of physics and fluid dynamics that we all have to work with or but heads with on a daily basis.
    Agreed.

    After some research, I think the best route to take to play in the 6,900-7,500 is a combination of: shaft mount rockers (Jesel Pro series?) + oversized pushrods 3/8 or even 7/16 + lightweight valves, springs, retainers and finally solid rollers on a big agressive hydraulic cam, the solid rollers would make the hyd cam ''smaller'' by roughly 10 degrees if I understood correctly (because of the lash needed on the solid rollers -which is pretty big because of the aluminum Viper engine-)

    If that all makes sense, the only thing left is to find the most suitable solid rollers that would fit*.

    P.S. and again, if I understood correctly, at high RPM the weight is not as important as avoiding any deflection on the lifter/pushrod side of the rocker. So big pushrod + lifter that will bring stability.
    Last edited by Aevus; 07-24-2021 at 10:04 AM.

  19. #19
    The main answer to the original question is , money. Anything is possible

  20. #20
    Had a discussion with Dale from Prefix, which was very helpful since they have a lot of experience with gen3 and gen4... Well, to sum it up, I'm pretty much back to square 1 because the very limitation is the air flow. While the gen 4's head can flow enough to create enough power up to 7,000rpm and beyond, the gen 3 can't. I mistakenly tought I could avoid that limitation with all the bolts-ons; 67mm TB or single blade + K&N + Headers and also a custom race exhaust + a big camshaft and obviously getting the head ported...but even with a good porting job, the gen 3's head is limited. Will see later on the dyno, but I can expect somewhere around 6,500rpm would be the max useable limit.

    So, what that means exactly is it makes any extreme valvetrain modifications pointless. Including solid lifters, shaft mount rockers, titanium valves, etc... The bottleneck is elsewhere. It just won't rev that high with power to justify it.

    Also, the oiling system is the other limitation. Again, gen 4's system would be needed (swing arm oil pan + machined crank for better oiling alone won't cut it for higher rpm) maybe with Prefix's oversize oil pump rotor but to what extent? For street use it may be okay, but I wouldnt feel comfortable bringing the car to the track, even for just few sessions, which is a shame...

    In conclusion, I will do what I can to get the most from that engine within a ''reasonnable'' budget, and I will post the dyno results as soon as I have them, but yes, as SRT_BlueByU pointing out: with money anything is possible, and it sure takes a LOT of money and work to make a Viper engine run above 7,000rpm.

    No wonder why forced induction is the numero uno solution for big HP.
    Last edited by Aevus; 07-30-2021 at 12:38 PM.

  21. #21
    Quote Originally Posted by TKO MOTORSPORTS TEAM View Post
    There really is no need to spin any motor past where it makes peak power. 7k on built hydraulic viper motor is very dicey. 6600-6800rpm is a safer bet
    From what I understand now, even with all the possible bolts-ons, camshaft and porting, using the gen 3's head would make that 6600-6800rpm very difficult to reach. I hope I'm wrong but if the peak power I finally get is anything north of 6,500rpm I will open a bottle of Champagne.

  22. #22
    Very interesting article:

    https://www.motortrend.com/how-to/ad...e-top-end-rpm/


    Adjusting hydraulic lifters for minimum preload (less turns after hitting the initial "zero" lash setting) can extend maximum engine speed by several hundred rpm.

    Turning the rocker arm adjustment nut a lesser amount after reaching the zero-lash point positions the hydraulic lifter's internal plunger closer to the lifter plunger's snap-ring retainer. At high rpm, this delays hydraulic lifter pump-up because the plunger can't move far enough to interfere with valve closure when hydraulic force overcomes valvespring pressure. In fact, some racers even adjust the nut as close as 1/8 turn or less down from zero lash, which positions the hydraulic lifter plunger practically against the snap ring, effectively causing the hydraulic lifter to act like a mechanical lifter because it can't take up any clearance in the valvetrain. Running tight plunger-to-retainer clearances can be risky if using standard lifters that have a paperclip-type retaining ring because hydraulic pressure may cause the plunger body to pop out of the groove, resulting in catastrophic failure. Lifters with full-contact internal Truarc-style snap rings can better withstand these tight clearances. For long-term street durability with a high-perf cam, adjust lifters with Truarc-type retaining rings 1/4 to 1/2-turn down from zero lash; adjust paperclip retaining-ring lifters 1/2 to 3/4-turn down from zero lash.
    I just received my performance lifters with Truarc-type retaining rings, will adjust somewhere between 1/8 and 1/4 turn down from zero lash.

    Combined with my conical springs, titanium retainers and 3/8'' 0.135'' pushrods I hope the valvetrain will remain stable above 6,400-6,500 rpm...

  23. #23
    Quote Originally Posted by Aevus View Post
    Had a discussion with Dale from Prefix, which was very helpful since they have a lot of experience with gen3 and gen4... Well, to sum it up, I'm pretty much back to square 1 because the very limitation is the air flow. While the gen 4's head can flow enough to create enough power up to 7,000rpm and beyond, the gen 3 can't. I mistakenly tought I could avoid that limitation with all the bolts-ons; 67mm TB or single blade + K&N + Headers and also a custom race exhaust + a big camshaft and obviously getting the head ported...but even with a good porting job, the gen 3's head is limited. Will see later on the dyno, but I can expect somewhere around 6,500rpm would be the max useable limit.

    So, what that means exactly is it makes any extreme valvetrain modifications pointless. Including solid lifters, shaft mount rockers, titanium valves, etc... The bottleneck is elsewhere. It just won't rev that high with power to justify it.

    Also, the oiling system is the other limitation. Again, gen 4's system would be needed (swing arm oil pan + machined crank for better oiling alone won't cut it for higher rpm) maybe with Prefix's oversize oil pump rotor but to what extent? For street use it may be okay, but I wouldnt feel comfortable bringing the car to the track, even for just few sessions, which is a shame...

    In conclusion, I will do what I can to get the most from that engine within a ''reasonnable'' budget, and I will post the dyno results as soon as I have them, but yes, as SRT_BlueByU pointing out: with money anything is possible, and it sure takes a LOT of money and work to make a Viper engine run above 7,000rpm.

    No wonder why forced induction is the numero uno solution for big HP.
    There is always the 9.0L option! yum yum

  24. #24
    Can't the Gen 4 heads be made to work on a Gen 3? I'm pretty sure there's a kit to make them work for Gen 2's ($$$$$). I'm curious as to what all is required; I know the Power Steering is one "concern", but that's an easy fix. Well, having power steering, that is... not sure how easy belt routing is without the PS pump, but I can't imagine it would be that hard to fix.
    1997 Dodge Viper GTS || Matte Bentley Silver | 60k miles ||

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  25. #25
    Quote Originally Posted by usmcfieldmp View Post
    Can't the Gen 4 heads be made to work on a Gen 3?
    Yes of course.

    https://store.prefix.com/products/ge...er-upgrade-kit

    Probably mandatory to get in 7,000rpm territory (enough airflow) but I'm assuming that a decently ported Gen 3 head matched with the proper camshaft will be enough to provide for 6,600-6,800rpm. And that's about the limit of everything, anyway:

    Oiling system (with oversized pump rotor + machined crank) and valvetrain stability (see my post above), not to mention fuel and transmission before you need to upgrade that as well.

    Short story: 6,700rpm is still a reasonnable target. At the limits of pretty much everything but doable.

    7,000-7,200rpm probably is not a ''reasonnable'' target... That may include Gen 4 (ported) head, shaft mount rockers, solid lifters/camshaft, titanium valves, better oiling system and maybe even dry $ump...

    I mean, that extra 300-500rpm seems to be very costly and a lot of troubles to go through. The high rev N/A thing is a lot of fun, no doubt, but passed a certain point SC or Turbo makes more sense if more power is what you want.


 
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