my NA Project 800 hp 7000 rpm roadster

[Aevus]

after a wait of one year and a half (!) finally got my first proper drive with my new ''race'' engine...

Long story short:
it's the biggest cam I could order, while clearing the valves with 11:1 compression and high duration (248/256 @ 0.050'') and while having something that (should) is tunable, with 24 degrees valve overlap... Forged internals, ported heads, 3.5'' exhaust, heat-wrapped headers, lightweight valvetrain, Ferrea valves, Prefix lifters, 69# injectors, Fidenza lightweight flywheel, 4.10 gears, oversized oil pump rotor, etc... All what is needed to make this motor spin north of 6,800 rpm, with the limiter probably around 7,100 rpm.

I've been warned about one billion times to NOT do that, since I'll lost tons of low-end torque and make the car not fun to drive on the street. That's why I installed the 4.10 gears. Which I tested with my stock motor, just before the swap.

I'm very happy with the results. Even not properly tuned (probably doing 5 miles per gal. at the moment lol) the car pulls great. Slightly less torque than stock up to about 2,500-3,000 rpm, maybe 10-20% less, will see on the dyno. But the 4.10 gears works perfectly along with the new engine, as planned. There is a slight lazyness from idle to about 1,500rpm but it's most probably tune-related. Nothing that would make the car undriveable on the street.

So that's good news. I was a little worried about it, to be honest.

Now, I'm on break-in period still so I didnt push it, but it sure look happy at higher RPM. It looks like a very nice powerband that starts to show some serious muscles from 4,500 rpm... I absolutely love the sound from it at mid-high RPM, can't wait to hear it above 6,000 rpm...

Speaking of sound, it's extremely LOUD. We're talking about 10-15 decibels difference over the stock engine (same headers/exhaust comparison). That's huge, wasnt prepared for that.
If there is one point that make the car not streetable, it's the noise it makes. Next week I'll change the mufflers for something quieter, hopefully without being too restrictive... But I'm sure ready to lose few HPs in order to have something quieter.

Bottomline, still some work to do: mufflers and dyno-tune for sure, maybe shaft-mount rockers and titanium valves later, but overall I can't think of any other modifications I could wish for, on that car. Feels lightyears from the stock gen 3 Viper I bought few years ago.

Now, will it make 800 crank horses @ 7,000rpm, more or less? At that point it's only dyno numbers. Car feels nice and racy and sounds awesome, so if it makes 135 mph trap speed 1/4 mile, I'll be very happy.

:-)

[Aevus]

To give you an idea, mid-high RPM sound I was refering to is a mix between that Calvo destroked 7.6L gen 2 and that 9L stroker:


https://youtu.be/M2v7QMKF898?t=41

and

https://youtu.be/pQ-Wavuw-0E?t=50


Very, very happy about it.

Racy, brutal, raw.
And a very choppy idle.

Lightweight flywheel + 4.10 gears sure helps revving faster too, it's 1000% pure fun.

[JGK95]

That's an awesome build!

[Siciliano15]

stock cars ran 125-130mph in the quarter so if you have 800hp you should be close to 145

[Steve M]

stock cars ran 125-130mph in the quarter so if you have 800hp you should be close to 145

Stock Gen 4s, yes, but it takes a good driver and nearly impossible to find weather conditions to hit the upper end of that range.

140 is probably more realistic, and it will be entirely dependent on how well the driver can shift. High RPM shifting can also be quite difficult, especially with an older T-56.

[Aevus]

stock cars ran 125-130mph in the quarter so if you have 800hp you should be close to 145

yeah, 670whp and 3,600lbs including me should make 140mph according to them

https://robrobinette.com/et.htm

but if it's finally heavier and my cam's, exhaust, final gears and overall engine design is not that good it could put me around 135mph (3,700lbs + 620whp) not to mention that I've never drive a car on a strip in my life! haha

[Old School]

not to mention that I've never drive a car on a strip in my life! haha

Taking your car to the strip is almost always a humbling experience.

[Aevus]

Taking your car to the strip is almost always a humbling experience.

I sure believe you!

my first few (dozens?) ET will probably be horrible, so I'll focus on the trap speed because at the end of the day it's probably be the only reliable ''dyno'' I'll ever have

[Aevus]

biggest challenge for now will be the upcoming dyno tuning, I'm a bit anxious about it, and it has nothing to do with how much HP it will do...
Also I have to change the mufflers because it's loud as hell, and that could make me lose some HPs...

Other than that, I just need to wait and see about the valve float.
If I can't spin the thing north of 6,500 rpm (with peak HPs to justify it of course), I will consider my project as a failure. In fact, anything less than 6,700rpm means I will need lighter valves and/or shaft mount rockers. Wouldnt be able to blame anything else really...

[Aevus]

stock cars ran 125-130mph in the quarter so if you have 800hp you should be close to 145

also forgot to mention something important: my 4.10 gears.

Probably not gonna want to shift passed 4th on the drag strip... as Steve mention my TR-56 is not exactly friendly... so, in theory, I'm limited to 139 mph with my Kumho ACR's 27.5'' @ 7,000 rpm


gears410_calculation.png

https://xse.com/gearcalculator?


The absolute highest rev limiter I could think of with my build is 7,200 rpm (assuming I have no valve float before 7krpm) and that's good for 143.6 mph...

... and worst case scenario: if I have valve float around 6,400 rpm with a rev limiter at 6,600 I'm good for only 131.7 mph.

[heath1225]

biggest challenge for now will be the upcoming dyno tuning, I'm a bit anxious about it, and it has nothing to do with how much HP it will do...
Also I have to change the mufflers because it's loud as hell, and that could make me lose some HPs...

Other than that, I just need to wait and see about the valve float.
If I can't spin the thing north of 6,500 rpm (with peak HPs to justify it of course), I will consider my project as a failure. In fact, anything less than 6,700rpm means I will need lighter valves and/or shaft mount rockers. Wouldnt be able to blame anything else really...

I'm on stock Gen 4 rockers, REV stainless intake valves, stock exhaust valves, and some heavy conical springs and have had no issues with valve float at 7000 rpm. I think you will be fine as well.

[Aevus]

Another thing that may interest you guys... Episode 32 Engine Masters

https://youtu.be/Hz0ebc6XkFE?t=686

''Too much oil can kill 20 horsepower''

I'll have to find the sweet spot on my Gen 3 oil system... I may blow the engine OR get hydraulic lifters problems at high RPM

[Aevus]

I'm on stock Gen 4 rockers, REV stainless intake valves, stock exhaust valves, and some heavy conical springs and have had no issues with valve float at 7000 rpm. I think you will be fine as well.

good to know, heath1225
but is there such things as ''heavy conical springs'' ?? usually it's the opposite, they're lightweight no?

[heath1225]

good to know, heath1225
but is there such things as ''heavy conical springs'' ?? usually it's the opposite, they're lightweight no?

I meant heavy as in spring pressure. Comp Cams 7230 - 520 lbs.

[Aevus]

I meant heavy as in spring pressure. Comp Cams 7230 - 520 lbs.

ok got it

You actually have the big brother of my Comp cams 7228. Both are the best options for our Viper's engine

You're good for 0.665'' lift while mine are good for 0.615'', but since I couldnt flow much passed that from my gen 3's ported heads, I figured I'd be better off with less strain on the valvetrain + lightweight springs...

but yeah, actually I'm not surprised at all that you don't get any valve float with those springs, even with heavy stainless valves. That being said, I personally wouldnt blindly trust your stock rockers with that set-up @ 7,000rpm, i'm talking longevity

last summer I saw a gen 4 ACR with mods similar as yours (heavy behive springs) and the rockers failed... If I remember correctly, the rev limiter was set @ 6,500rpm, not even 7,000rpm as you mention.

[Aevus]

and have had no issues with valve float at 7000 rpm. I think you will be fine as well.

good news for the hydraulic lifters potential limitation though. Have anything special regarding the lifters?

[Aevus]

speaking of Engine Masters, you probably all know that already, but here is a short video about valve float and what happens:

https://www.youtube.com/watch?v=Ga-iloeel4Y

Spring pressure is the key, but it's more complicated than that of course. Lightweight valves + shaft mount rockers seems to be the most effective ways of controlling the valvetrain (along with good springs) but unfortunately it's very difficult to get lightweight valves for our Viper engine... When you're shopping you really understand you're not dealing with an LS motor!


another fun video about high RPM project, even tho it's solid not hyd

https://www.youtube.com/watch?v=Qw6h3kt2r6A

[heath1225]

good news for the hydraulic lifters potential limitation though. Have anything special regarding the lifters?

Johnson short travel race lifters.

[Aevus]

Johnson short travel race lifters.

many versions for the gen 4 available on their site

do you have the short travel or the race one?

https://johnsonlifters.com/Products/...T2319V10R.aspx

[Aevus]

I think you have a better valvetrain than mine for high-rpm

got my lifters from Prefix (not sure who makes them) similar to these

https://store.prefix.com/products/ge...nce-lifter-set

but with tru-arc clips, which is better :

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

[Aevus]

Piston speed is also a concern, even though forged internals helps, I'm not sure if longevity of the engine will be his biggest feature... Not going to last 100,000 miles for sure.



https://www.youtube.com/watch?v=Vy2r3p-SOag



Gen 3 = 3.96'' stroke : 4,620 fpm @ 7,000 rpm

Gen 4 = 4.00'' stroke : 4,667 fpm @ 7,000 rpm


not sure but I think Calvo's destroked motor we see on youtube is around 3.6'' stroke, which makes 4,200 fpm @ 7,000 rpm (and they spin it up to 8krpm)

[heath1225]

Mine is on a Gen 2 bottom end. So I used Gen 2 lifters. I can't remember which specific model number of lifter it was. I was also concerned with piston speed, being a stock bottom end, but it's run for nearly 7 years. I've made hundreds of highway pulls and dozens of prepped and no paper track passes.

[Aevus]

that's impressive, congrats you have a very good reliable build

[heath1225]

that's impressive, congrats you have a very good reliable build

Thanks. I might have a little luck too! I hope my next build does a well!

[Old School]

Piston speed calculator that includes rod length as a variable

https://lmengines.com/pages/piston-velocity-calculator