What really limits our engines to rev higher

[Aevus]

Bytheway, with my 2nd (stock) engine but with all bolt-ons, tune and headers+custom exhaust, I already have 6,050rpm peak power. An extra 600 rpm shouldnt be a problem with that aggressive cam, ported heads and completely upgraded valvetrain, not to mention the forged internals. In fact it's very possible that engine will be 7,000rpm capable, but educated-guesses here of the bottlenecks:

- Oil system = 6,800 rpm max
- Prefix's hydraulic lifters (1/8 turn) = 7,000 rpm max
- Custom cam = 6,900-7,100 rpm max
- Stock crank but machined (oil passage) and balanced = 7,000-7,200 rpm max
- Ported heads = ???
- Fuel system = ???
- All the valvetrain except hyd lifters = 8,000rpm+
- Forged internals = 8,000 rpm+

All educated-guesses because nobody really knows about the real limits of a combination. That makes the engine topic so fascinating!

Take the hydraulic lifters. Nobody in their right mind would dare pushing a hyd above 7krpm, right? WRONG.

and compounded the combination with a set of short-travel hydraulic roller lifters, stud-mounted 1.6:1 ratio roller rockers, titanium retainers, and triple valve springs, and wound the thing up to 7,700 rpm without a hint of valve float.

That wasn't a typo. We revved this thing almost to 8,000 rpm with hydraulic lifters in the block. And it worked.

https://www.motortrend.com/news/rpm-...ic-roller-cam/

So maybe my hyd lifters with 1/8 turn adjust will start to do troubles at 6,800, maybe 7,000 or maybe only 7,500... Almost impossible to know without testing it with all the other parts. Maybe the whole valvetrain will not be the bottleneck at all. Maybe it will be the flow of the heads, or even the camshaft, or the crank, or the oil system (most likely)...

What's kind of crazy is: there is almost always a solution to push the limits even farther. Even though it would seem ''impossible'' at first. Someone somewhere did some tests, trial and errors, and found a solution for a particular problem.

[Aevus]

Made a list of all the potential bottlenecks (for high rev, stock 3.96in stroke) and the crankshaft becomes one of them at a certain point.

Antonio from Calvo Motorsports and Greg Good offered some good advices in that thread:

https://driveviper.com/forums/thread...l=1#post181668

[Aevus]

A little update on my high-rpm gen3 engine project:

Since the heads are not yet ready and the season is over, I decided to order a shaft mount rocker arm, which only makes sense at the point where I am now...

My target is still 6,600-6,800+ rpm peak power, hopefully around 650-670 whp. Forged internals, Fidenza flywheel, either 3.73 or 4.10 gears, oversized oil pump rotor, headers, custom exhaust, etc.. But the most important here is the valvetrain upgrades:

- Compcam Conical springs (440lbs rating)
- Titanium retainers
- 3/8 pushrods w/ 0.135'' wall
- Titanium, lightweight SS valves
- Prefix performance lifters (lash adjusted 1/8 turn so act almost as a solid lifter)
- T&D aluminum shaft mount rocker arm w/ spring oil hole option and 1.75 ratio (if it fits and needed)
- around 11.2-11.5:1 compression ratio

With the custom camshaft and 1.75 ratio, it will be 0.621'' intake lift and 0.613'' exhaust + 238/251 duration @ 0.050 and 1.70 (more at 1.75). + 115 LSA.

I'm still waiting for the benchflow numbers of the ported heads to decide between 1.70 and 1.75 ratio, but basically that's the whole recipe, as I cannot think of anything else to help my case on that project (other than destroke)...
Will have to wait 10-12 weeks for T&D but I can't wait to see the results.

New update FYI

Finally ordered valves from Ferrea Racing.

Lightweight hollow stainless steel stem, custom made for the Viper and my ported heads to allow the very best possible flow with the right angles.

They guarantee 80-85gr weight (exhaust) and 85-90gr. (intake) so roughly 25 grams saving per valve, which is a lot.

Very good option, not too expensive (compared to Titanium) and probably optimal up to 7,500rpm+ Viper engine project.

I'm posting all that info because it's very difficult to get any information regarding valves on Viper. The common solution seems to be Manley race series, but there is Ferrea as well, if you want to get above 6,500 rpm.

[Aevus]

Also, I postponed the shaft mount rocker arm until fall. Will probably have to upgrade the oil system, re-order a more optimal cam or adjust the timing on the actual one for 200-300rpm extra and of course the shaft rocker.

So for now, the target is still 6,600-6,800 rpm. Will see what really happens on the dyno before the next upgrades...

Those upgrades would target the 7,000 rpm mark and up to 7,500rpm if the crankshaft is upgraded as well.

[TKO MOTORSPORTS TEAM]

Also, I postponed the shaft mount rocker arm until fall. Will probably have to upgrade the oil system, re-order a more optimal cam or adjust the timing on the actual one for 200-300rpm extra and of course the shaft rocker.

So for now, the target is still 6,600-6,800 rpm. Will see what really happens on the dyno before the next upgrades...

Those upgrades would target the 7,000 rpm mark and up to 7,500rpm if the crankshaft is upgraded as well.

You will run into block oil galley volume problems running hydraulic lifters when you start edging towards 7000 rpm. Just a heads up

[Aevus]

You will run into block oil galley volume problems running hydraulic lifters when you start edging towards 7000 rpm. Just a heads up

Yes, a lot of problems beyond 7k

[Aevus]

Will have to overbalance my (stock) crankshaft, most probably around 51%.

If you want to read about crank balancing, here is a great article:

https://www.enginebuildermag.com/202...balancing-act/

[Aevus]

You will run into block oil galley volume problems running hydraulic lifters when you start edging towards 7000 rpm. Just a heads up

Upgrades I already have regarding OIL:

- (stock) crankshaft machining to fix the known issues
- oversized oil pump rotor from Prefix
- Competition coupe swing-arm oil pan

Now, I'm not sure if it's the best solution but I was thinking Accusump. I won't track the car, especially not at 6,800-7,000rpm so all I need is some engine protection against short bursts at high-rpm, basically as if it were a strip car.

[TKO MOTORSPORTS TEAM]

Upgrades I already have regarding OIL:

- (stock) crankshaft machining to fix the known issues
- oversized oil pump rotor from Prefix
- Competition coupe swing-arm oil pan

Now, I'm not sure if it's the best solution but I was thinking Accusump. I won't track the car, especially not at 6,800-7,000rpm so all I need is some engine protection against short bursts at high-rpm, basically as if it were a strip car.

If you have a swing pick up oil pan and your not tracking your car on a regular basis you really dont need an accusump. Accusumps are also a little bit of a pain in the ass to work with, take up space in the car and add another layer of complexity. Accusumps are great for classes where dry sump systems are not allowed

[Aevus]

If you have a swing pick up oil pan and your not tracking your car on a regular basis you really dont need an accusump. Accusumps are also a little bit of a pain in the ass to work with, take up space in the car and add another layer of complexity. Accusumps are great for classes where dry sump systems are not allowed

No I'm not planning to track the car and if I do it's gonna be with a tune that is safer.

I'm just a bit worried for issues such as cavitation or anything related to high-RPM, even for street use.

[TKO MOTORSPORTS TEAM]

No I'm not planning to track the car and if I do it's gonna be with a tune that is safer.

I'm just a bit worried for issues such as cavitation or anything related to high-RPM, even for street use.

Your putting together a good combo for street and some track use. Unless your pro driver and really putting the spurs to it you should be fine. There are also plenty of other mods you can do to improve performance and safety that don't involve the motor cost and labor involved are also much less then motor parts.

[Aevus]

Update:

Last piece of the puzzle, the camshaft is ordered:

246/259 @ .050 , lsa 114+4 , .587/.560

Had to reduce the lift on the exhaust side, in order to clear the piston and have min. 0.080'' clearance. My heads are flowing pretty well in the 0.500-0.560'' so it's fine. Also, less stress on the springs and overall valvetrain which is welcome for the high-rpm I'm seeking.

Will have 11.73:1 compression ratio.

I'm hoping (!) for not so much torque below 2,500rpm, because of my 4.10 gears and with 246/259 duration I should be okay....


Can't wait to try that engine

[Dan Cragin]

That cam is hard to tune with the factory speed density system and JTEC. Back in the day we had to go with a TPS/RPM Map, vacuum was so low at
lower rpms Map is hard to calibrate.

[Aevus]

That cam is hard to tune with the factory speed density system and JTEC. Back in the day we had to go with a TPS/RPM Map, vacuum was so low at
lower rpms Map is hard to calibrate.

Even with 114 LSA?

I've been told it will be tuneable.

Dyno-tuned by Torrie from Unleashed.

[LATAMUD]

I wasn't aiming for 7-8k rpm. I still kept it under 6k. I built a Gen3 with forged internals to run around 15 psi through my Paxton. Greg Good posted heads had heavier springs, intake was cut open and ported, Arrow single blade TB. There's an old school mod to convert hydraulic lifters into solid. I used Crower shaft mounted rockers and 3/8 hardened push rods. I modded a Gen4 swing arm oil pickup to use with the Gen4 pan on the Gen3 engine. My block was an 04 but I still used a 05/06 crank to get the beefier snount and crank bolt.
Comp Cams will grind to whatever you desire. I told them solid lifter, 116 LSA for the supercharger. Ended up with a .637/.637 lift. I ran a slightly lower then stock compression I think my pistons were .005 shorter compression height then stock.
I never got any good dyno numbers, I was aiming for 800 on a Mustang dyno. I could never find a reliable tuner and ended up dropping oil pressure so never drove it hard. Car sitting 30 feet away from my house in the street idling, the windows of my house would rattle.
I'm still solid lifter but recently swapped in a Gen4 engine. This setup I'll max the Procharger out at 5700 RPM, I will likely never take the engine past 5500. Again, needs a tune still. It's over built, I don't think I'm going to enjoy this car on the street. Twin disc cluch and billet TOB, only needs about 1" clutch pedal to engage the clutch but it's like 10x heavier pedal than stock. It's so loud, it's louder than the X. On paper, high rev sounds cool but you're gonna miss practical basic Vipering.

Screenshot_20220516-231549_Gmail.jpg

[Aevus]

damn Latamud, you strike me as someone who doesnt like very much his car!

Sorry to hear that


On my side, it's a pretty safe bet: I have another cam on-hand that is less agresssive... and I have another (stock) engine in case something goes really bad.
I spent hours and hours in the last year to study that project and I'm finally close to the results. Still aim 6,800rpm peak power, 7,000-ish rev limit, no track just street but as racy of a feel as possible. Superlightweight valvetrain, tricked out hyd lifters, forged internals, high CR, 3.5'' exhaust, headers, upgraded oil system, ported heads, 69lbs injectors, and a cam to extract the best of all that (crosses fingers).

I have at least as much fun working on the project as driving the car ;-)

[LATAMUD]

Sure, this one I don't like as much as the other ones. I've daily driven 3 of the 5. The ACR-X isn't street legal.

[DEMO MAN]

Sure, this one I don't like as much as the other ones. I've daily driven 3 of the 5. The ACR-X isn't street legal.

Well........ street legal is one of those relative terms, I mean I would guess there are those out there who might drive that X right down I-4

[Aevus]

I wasn't aiming for 7-8k rpm. I still kept it under 6k. I built a Gen3 with forged internals to run around 15 psi through my Paxton. Greg Good posted heads had heavier springs, intake was cut open and ported, Arrow single blade TB. There's an old school mod to convert hydraulic lifters into solid. I used Crower shaft mounted rockers and 3/8 hardened push rods. I modded a Gen4 swing arm oil pickup to use with the Gen4 pan on the Gen3 engine. My block was an 04 but I still used a 05/06 crank to get the beefier snount and crank bolt.
Comp Cams will grind to whatever you desire. I told them solid lifter, 116 LSA for the supercharger. Ended up with a .637/.637 lift. I ran a slightly lower then stock compression I think my pistons were .005 shorter compression height then stock.
I never got any good dyno numbers, I was aiming for 800 on a Mustang dyno. I could never find a reliable tuner and ended up dropping oil pressure so never drove it hard. Car sitting 30 feet away from my house in the street idling, the windows of my house would rattle.
I'm still solid lifter but recently swapped in a Gen4 engine. This setup I'll max the Procharger out at 5700 RPM, I will likely never take the engine past 5500. Again, needs a tune still. It's over built, I don't think I'm going to enjoy this car on the street. Twin disc cluch and billet TOB, only needs about 1" clutch pedal to engage the clutch but it's like 10x heavier pedal than stock. It's so loud, it's louder than the X. On paper, high rev sounds cool but you're gonna miss practical basic Vipering.

I'm not familiar at all with supercharged Viper engine and what type of cam they required, but it seems to me that 0.637'' lift for both in/ex might not be optimal and you're running heavier springs than required (even with ported heads)... Also since your engine runs solid lifter, wouldnt be fun to rev it higher a bit? Say peak power @ 6,200-6,300?

Again: not familiar with SC so I might be wrong and maybe it's the best set-up for your Paxton... My engine project is 100% N/A oriented, there is no way I could put turbos or SC, but then again higher rpm is more important to me than max HP. If I get 750 crank horses @ 6,800 I'll be happy.

[Dan Cragin]

With a 114 LSA the cam it should be tuneable with those numbers. We had issues with the 107-110 LSA cams.
I have found, that unless your heads are really flowing well, the bigger cam does not make more power and
driveabilty suffers.

Gen 4 heads on a Gen 3 motor with the dragpack intake, you can make big power.

[13COBRA]

With a 114 LSA the cam it should be tuneable with those numbers. We had issues with the 107-110 LSA cams.
I have found, that unless your heads are really flowing well, the bigger cam does not make more power and
driveabilty suffers.

Gen 4 heads on a Gen 3 motor with the dragpack intake, you can make big power.

What kind of power??

[Dan Cragin]

The Drag Pack cars made 800hp with unported gen 4 heads.

[13COBRA]

The Drag Pack cars made 800hp with unported gen 4 heads.

Where might one find one of the elusive Drag Pack intakes?

[Dan Cragin]

I think Prefix still has some.

[13COBRA]

I think Prefix still has some.

Emailed, thanks!