What really limits our engines to rev higher

[Aevus]

... the dyno will tell if that ''reasonnable'' high-rev Gen 3 engine can spin to only 6,400 or as high as 6,800... And then only time will tell if durability is part of the recipe

[usmcfieldmp]

I'm curious as to what needs to be machined for fitment and why the intake manifold is "custom".

[J TNT]

I have a set of Gen 5 heads if you’re looking to upgrade.
Feel free to send me a pm with your cell number if you want more information.
Jay.

[TKO MOTORSPORTS TEAM]

... the dyno will tell if that ''reasonnable'' high-rev Gen 3 engine can spin to only 6,400 or as high as 6,800... And then only time will tell if durability is part of the recipe

Your on a budget with hard earned money why roll the dice on durability????. Motor will stop making power probably around 5200-5500rpm why run it to 6800rpm??

[Aevus]

Your on a budget with hard earned money why roll the dice on durability????. Motor will stop making power probably around 5200-5500rpm why run it to 6800rpm??

With all the mods i'm doing, if it stops making power at 5,500rpm there's a dead squirrel stucked in the headers.

;-)

Viper Speciality with their VS-X700 kit dynoed 613.5 HP at 5950 RPM and Peak Torque at 5100 RPM. That's with a ''torque'' camshaft and non-ported gen 4 head.

I will have a ported gen 3 head with similar flow numbers + a high duration camshaft + 11:1 compression w/94oct dyno tune + 3.5'' straight through exhaust... I'm not too worried that will make some decent peak power north of 6,000rpm, the real challenge is the oil system and especially the valvetrain.

But yeah, obviously, if it doesnt show real power delivery at 6,000rpm I won't push it to 6,800... Would be totally pointless.

[Aevus]

I need to point out that I'm running a tune for nearly a year now with a 6,250rpm rev limit. Stock engine.

Going from 6,250 to 6,800 is not exactly fantastic.

[Aevus]

FYI

Stock Gen 4 Head numbers: Intake 327 CFM / Exhaust 242 CFM (0.600'' lift)

Ported Gen 3 Head numbers: Intake 320 CFM / Exhaust 235 CFM (0.600'' lift)*

* Ported numbers can vary of course, but it gives an idea.



(stock gen 3 head = 265/215 CFM, maxed out much more easily)

[TKO MOTORSPORTS TEAM]

FYI

Stock Gen 4 Head numbers: Intake 327 CFM / Exhaust 242 CFM (0.600'' lift)

Ported Gen 3 Head numbers: Intake 320 CFM / Exhaust 235 CFM (0.600'' lift)*

* Ported numbers can vary of course, but it gives an idea.



(stock gen 3 head = 265/215 CFM, maxed out much more easily)

Factory manifold is where the motor falls on its face for N/A cars, options to fix it aren't real budget friendly. Manifold kinda kills the head work or should say doesnt let you take full advantage of your head work or exhaust. But your running lower RPM so maybe manifold wont impact to much

[Aevus]

Very interesting MT article (yeah I know it's a LS7 engine not Viper's, but still)

https://www.motortrend.com/how-to/18...m-road-racing/

Very decent 400lbs torque from 3,500rpm while having 8,000rpm capability. Pretty impressive. That thing is probably streetable. But it was clearly designed for road course, sustained high rpm...

[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.

[Aevus]

facts_schematic.png

Essentially, the whole idea that all the experts and race gurus are saying for high-rpm:

Make the pushrod's side of the rocker as stiff as possible and make the valve's side of the rocker as lightweight as possible.

That's what I did.

[Aevus]

Few other things that I've learned the past months with this project:

- Stock gen 3 crank is good up to roughly 7,000rpm, especially if properfly balanced and with lightweight forged internals that reduces stress on it. I don't plan to put turbos or SC, so I decided to go with 4032 alloy pistons, which were a bit lighter than 2618 alloy ones.

- Hydraulic lifter is one of the most limitative thing here, but high-rpm still doable on hyd (some even did 7,500rpm+ on other engines) and you keep all the obvious benefits of hyd... Use only lifters with Truarc-type retaining rings, adjusted 1/8 (race setting, becomes a solid lifter more or less..) and 1/4 (street) turn down from zero lash.

- Titanium valvetrain components are great but wears faster than steel so don't expect doing 50,000 miles without replacing valves/retainers (and springs while at it). If you take the steel route it will last longer and cost less but you will most likely lose 200-300rpm (minimum) capability.

- Resonance is a big issue in the valvetrain at high-rpm. Big stiff pushrods and conical (or behive) valve springs, close to coil bind (0.050-0.060'') seems the best methods to reduce resonance, along with shaft mount rocker arm.

- According to everything I've read, it WOULD be possible to make that 8.3 liters engine rev higher than 7,000rpm WITHOUT a destroke, but that would probably require to do very expensive things for a very small benefit: aftermarket crank and/or titanium rods, even bigger cam and maybe higher compression to go along (and E85? adios pump gas), even stiffer valve springs and bigger/stiffer pushrods, maybe ported gen 4 heads if ported gen 3's maxed out... and then of course oiling problems (dry sump), fuel, ignition, computer, transmission, etc... All that for, MAYBE, 7,200 to 7,400rpm peak 700-750whp and weaker avg power and torque curve...

Doable, yeah. Probably a bit crazy though. ;-) At some point destroke or FI makes much more sense.

[TKO MOTORSPORTS TEAM]

De-stroked , solid with good internals and valve train, dry sump .....you will be very happy with the results. If you want to go a bit further add individual throttle bodies

[Aevus]

De-stroked , solid with good internals and valve train, dry sump .....you will be very happy with the results.

Yes but we're talking tens of thousands for such project, just for the destroke and drysump alone... Doesnt make any sense on a vert gen 3, IMO. At some point I have to draw a line. Anything above 7,000 peak power seems to be a worm can.

I'm comfortable with the 6,600-6,800 peak power target, and if for some reasons I'm lucky with the build and it pushes in the 6,900-7,000 zone, i'll just have to tweak the oil system (Accusump or else) on top of my already installed compe coupe pan and Prefix oil pump rotor. OR I'll just don't go there and rev limit the wannabe screamer.. lol

I'm not worried with the crank and even less the valvetrain, but at some point a lot of issues would pop up.

[SRT_BluByU]

if 6600-6800 is your goal why not jsut get a crate Gen V?

[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+

[Aevus]

if 6600-6800 is your goal why not jsut get a crate Gen V?

did they fix the DBW so it's as fun as my TC ?

;-)

also, still no dry sump.

[USAFPILOT]

https://www.youtube.com/watch?v=_uta6RWwx7s

I know this a Viper Forum, but when wondering how to get Revs up higher, this new engine is certainly relevant. Pretty cool. Just illustrating TKO's point above, the Viper V10 is a hydraulic, cross plane, long stroked lazy beast. It can be made to rev higher though. Have a look over at Nelson Racing engines and the work they do. I know other shops also build some great high revving pushrod motors. But will there be any reliability in those builds?

[TKO MOTORSPORTS TEAM]

Yes but we're talking tens of thousands for such project, just for the destroke and drysump alone... Doesnt make any sense on a vert gen 3, IMO. At some point I have to draw a line. Anything above 7,000 peak power seems to be a worm can.

I'm comfortable with the 6,600-6,800 peak power target, and if for some reasons I'm lucky with the build and it pushes in the 6,900-7,000 zone, i'll just have to tweak the oil system (Accusump or else) on top of my already installed compe coupe pan and Prefix oil pump rotor. OR I'll just don't go there and rev limit the wannabe screamer.. lol

I'm not worried with the crank and even less the valvetrain, but at some point a lot of issues would pop up.

Get where your coming just hate to see spending money and not trying to get the most out of every dollar spent. Better option then accusump is exotic engines external oil pump set up.

[Aevus]

Get where your coming just hate to see spending money and not trying to get the most out of every dollar spent. Better option then accusump is exotic engines external oil pump set up.

I don't plan to track the car, though. That changes everything.

I'm doing that project mainly for the fun of doing it and pushing the limits. That will most likely be the last ''true'' sports car I will ever own (RWD, manual, naturally aspirated) so I might as well enjoy it as a constant work-in-progress project that gets modified and driven/tested as much as possible. In other words, the polar opposite of a garage queen.

I've been very luck so far: every dollar spent on mods are highly appreciated, including TKO's parts :-)

[Aevus]

https://www.youtube.com/watch?v=_uta6RWwx7s

I know this a Viper Forum, but when wondering how to get Revs up higher, this new engine is certainly relevant. Pretty cool.

Yeah, exactly, that new Z06's engine is pure porn. That video/demonstration leaves no doubt about it! Wow, triple-check so no service/valve adjust would be needed ''ever''... (from 3:00 in the video) even though it's not hydraulic.

But that's the thing though. Manufacturers need to deal with reliability, noise and emissions issues. That's another world entirely.

Also, while that engine looks amazing, I'm not overly impressed by the 670bhp @ 8,400rpm and especially 460lbs torque @ 6,300rpm. Would be curious to see the torque curve....

[Aevus]

Just illustrating TKO's point above, the Viper V10 is a hydraulic, cross plane, long stroked lazy beast. It can be made to rev higher though.

6,600-7,000rpm maximum
... or higher with destroked+solid and with few more modifications that goes with that kind of project.

And honestly, a destroked 7.6 liters (Calvo) screaming at 8,000rpm like that:

https://www.youtube.com/watch?v=M2v7QMKF898

...is not THAT tempting for my ears. Great engine for sure, but it doesnt sound as a Viper anymore.

[TKO MOTORSPORTS TEAM]

I don't plan to track the car, though. That changes everything.

I'm doing that project mainly for the fun of doing it and pushing the limits. That will most likely be the last ''true'' sports car I will ever own (RWD, manual, naturally aspirated) so I might as well enjoy it as a constant work-in-progress project that gets modified and driven/tested as much as possible. In other words, the polar opposite of a garage queen.

I've been very luck so far: every dollar spent on mods are highly appreciated, including TKO's parts :-)

"Work in progress", " modified and driven/tested as much as possible". VERY COOL......Its what being a gearhead is all about. Since your a TKO customer if you ever need help, info or questions answered we are always ready to support our customers.

[Aevus]

Very interesting article on Motortrend about valvetrain weight factor in general and valves specifically. Tests were made on a LS7, which is a great comparison basis with our engine.

it clearly shows about the possible bottlenecks of a bad combination, that can force you to rev limit as low as 6,300rpm ... or go as high as 7,800rpm if done properly with the right package.


LS7-high-rpm-valve-test.jpg

Katech notes: Nearly twice the bounce by simply changing the valve. This combination is fine for a street car, if the rev limiter is set at 7,000 rpm. In road-racing conditions, we prefer to see a 500-800-rpm safety margin, which would mean a 6,300-6,600-rpm rev limit.

Talk about instability! The severe bounce displayed at comparatively low rpm made it unwise to continue testing up to 7,500 rpm. We flat-out don't recommend this setup.

Minimal bounce at 7,900 rpm! This is an excellent combination all the way to 7,800 rpm—as long as the prep work has been done to the valve stems and bronze guides are used in the head.

The test measured the performance of the stock LS7 valve (74 grams), a REV stainless valve (98 grams) and a titanium valve (66 grams). The heavier stainless valve doesn’t have the separation issue that has occurred with some factory sodium-filled units, but with about a 33 percent increase in weight, it is less stable at high rpm.

It doesnt seem like very much weight, but it adds up very quickly.

Behive and Conical springs seems like the best solutions and since the Viper heads don't benefit more than 0.675'' lift (even 0.625'' or so actually), I would say the conical solution is the best.
Then, titanium or tool steel retainers/locks to go along with the conical's. And finally the valves, either stainless steel hollow stem or titanium or a mix of both, intake/exhaust.

Everything put together, including the shaft mount rocker arm and super stiff pushrods, it should relieve some stress on the hydraulic lifters so they can reach 7,000rpm and even beyond...

The next bottleneck, after that 7,000-ish mark, will then be the oil system... and after that, the crankshaft. Which could benefit from an overbalance, aftermarket swap and/or lighter internals. Just to put a price on things, as of november 2021 of course:

- Titanium valves = more or less 160$ each x 20 = 3,200$
- Aftermarket forged crankshaft = 4,000-8,000$
- Titanium rods = 5,000-7,000$

Not including labor of course.

As for the oiling system, I have no idea about the cost for a gen 3/4. Drysump or less extreme solution but it would be costly for sure.

[Aevus]

... and also, I think Katech's advice for a 500-800rpm safety margin for the racetrack is VERY SMART.

Totally agree with that.

In fact I plan to have a dual tune, one to have fun on the street that would be the most permissive and another one more restrictive for the racetrack (if I ever want to tracktest my car).