Heads Cam Journey Has Begun

[Sniper]

On the way to get a little rowdy!

52991

[Old School]

Rowdy is a good thing

[Space Truckin]

Who is doing the work?

[Sniper]

JMB Performance

[StrokerAce]

Specs of cam?

[AAA96]

Interested in this thread. Post as much as you can as you go along please!

[Mikey]

I'm jealous

[Sniper]

Spec of cam: it is aggressive
Not much to post as it's getting work on about 4 hours away from me so I will not have anything until I get the car back.

Car has arrived at the shop.

53001

[Fulltilt]

Dumb question but..............I know some companies use completely different heads as part of the heads/cam package. If so, do you keep your oem heads and can the car be turned back to stock?

[Sniper]

The shop is doing this: CNC port, valve job, and surface cylinder heads.
So, they are using my heads.

[bullitt2735]

nice! what are the goals with the car? drag racing, road racing, street?

[Sniper]

Just for street

[StrokerAce]

Spec of cam: it is aggressive
Not much to post as it's getting work on about 4 hours away from me so I will not have anything until I get the car back.

Car has arrived at the shop.



Aggressive is a relative term. Just curious to some general specs. Some guys think a 250/260 duration cam is aggressive and others think it's too tame. I would imagine the cubic inches eats up the larger cam pretty easily making it more streetable.

Your car looks good.

[Aevus]

aggressive is north of 20 deg valve overlap, more or less.

So 250/260 with say 114 LSA : 255-228 = 27 deg.

[Lawineer]

Aggressive is a relative term. Just curious to some general specs. Some guys think a 250/260 duration cam is aggressive and others think it's too tame. I would imagine the cubic inches eats up the larger cam pretty easily making it more streetable.

Your car looks good.

The rough idle is generally attributed to overlap, more than duration. When the intake and exhaust are both open, as you might expect, you're not going to build up much pressure. At low RPM and high intake restriction (closed throttle body) you're barely getting enough air in there to support combustion as it is. Letting a bunch of the air leave through the exhaust stroke makes it worse.


And, ironically, StrokerAce, it's more stroke that eats up cam, but yeah, it's all relative. I never really thought about it, but I'm not really sure why. I can't intuitively think of an explanation for why stroke makes the idles smoother. Obviously has something to do with piston velocity.

[Jack B]

I did the Prefix HC, then, later added the 9L. The idle did not change.

The car will be up for sale this spring.




The rough idle is generally attributed to overlap, more than duration. When the intake and exhaust are both open, as you might expect, you're not going to build up much pressure. At low RPM and high intake restriction (closed throttle body) you're barely getting enough air in there to support combustion as it is. Letting a bunch of the air leave through the exhaust stroke makes it worse.


And, ironically, StrokerAce, it's more stroke that eats up cam, but yeah, it's all relative. I never really thought about it, but I'm not really sure why. I can't intuitively think of an explanation for why stroke makes the idles smoother. Obviously has something to do with piston velocity.

[13COBRA]

Vroom vroom!

[StrokerAce]

aggressive is north of 20 deg valve overlap, more or less.

So 250/260 with say 114 LSA : 255-228 = 27 deg.

Makes sense. My last had only a 14 split and has a good lope but nothing major. I'd say it's relatively tame compared to the other builds I researched. If it wasn't a street car I'd have gone a slightly different route.


The rough idle is generally attributed to overlap, more than duration. When the intake and exhaust are both open, as you might expect, you're not going to build up much pressure. At low RPM and high intake restriction (closed throttle body) you're barely getting enough air in there to support combustion as it is. Letting a bunch of the air leave through the exhaust stroke makes it worse.


And, ironically, StrokerAce, it's more stroke that eats up cam, but yeah, it's all relative. I never really thought about it, but I'm not really sure why. I can't intuitively think of an explanation for why stroke makes the idles smoother. Obviously has something to do with piston velocity.

Agreed on all points but usually you don't see as much overlap on tame cams and goes hand in hand with the cams with more duration, with variation of course.

My experience has been primarily with LS and SBC BBC stuff but I'm not well versed on what these big V10's like and what makes the best power. Of course power at different RPM's need different specs. So for a streetcar like the OP's I wasn't sure how wild the specs would be, if wild at all.

Rarely do you see a long stroke small bore V8 engine built for performance. There are some long stroke LS3 bore engines out there but they have issues with rocking at the bottom. That's why I went larger bore and kept a 4" stroke on my last build.

Do the stock Gen V valvetrain do well with more aggressive camshafts? How far can you go without modifying the heads and intake?

[Aevus]

''Agressive cam'' = there's also the question of the lift, but I don't know any stock or ported Viper heads that benefits from a lift of more than 0.630'' and even that it's pushing it...

Too much lift is counter productive, not to mention the strain of the valvetrain..

[Aevus]

Do the stock Gen V valvetrain do well with more aggressive camshafts? How far can you go without modifying the heads and intake?

Gen 3-4-5 I think all greatly benefits from lighter valvetrain components and conical springs, especially of you want to reach 6,500-ish rpm and more

The best upgrades are:

- 3/8 pushrods (or thicker/bigger)
- Conical springs w/ Ti retainers and locks
- Hollow SS or Ti valves (very difficult to get for the Viper)
- Shaft mount rocker
- Hyd lifters with tru-arc

And of course the camshaft must fit the air flow (in and out) otherwise you're losing time and money

It's either that or you stay in the moderate +/- 10 deg valve overlap zone...

[Aevus]

So for a streetcar like the OP's I wasn't sure how wild the specs would be, if wild at all.

Mine is modified as a track car but will be used 95% on the street and I went with 24 deg overlap (248/256 114LSA) which is pretty much the max I could go anyway while having enough valve clearance and 11:1 compression, with the pistons I wanted to use.

Dyno tune mandatory. At the moment I can't drive the car at all. Truth to be told, I might've been too far...

Bottomline, be careful with ''agressive cam'' on a Dodge Viper. Ain't that easy.

[Sniper]

Aevus, do you have video clip of what it sounds like?

[13COBRA]

Mine sounds like this after JMB Heads/Cam..


https://youtube.com/shorts/JAAVemI95S8?feature=share

[Sniper]

LOL, nice!!!
What spec cam did you get?

[Aevus]

Aevus, do you have video clip of what it sounds like?

yes but not tuned yet

https://www.youtube.com/watch?v=EzaxOlgPFj4


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

[Sniper]

Nice!
Hoping mine comes back sounding half as nice as both these cars!

[Mikey]

yes but not tuned yet

https://www.youtube.com/watch?v=EzaxOlgPFj4


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

I like it

[Mikey]

This is what mine sounds like

https://youtu.be/IRhVVaFuaDs

[Aevus]

correct me if I'm wrong but I think Dan Lesser said that a mild cam can give the rough idle sound, no need to go crazy if the sound is what you're after


edit: ''mild'' is probably something like 230/240 LSA 114 or so, as long as you have few degrees of overlap

[Aevus]

video on youtube that shows a Roe Racing 710r camshaft

https://youtu.be/PGDCbY7N3lE?t=96

which is 14 degrees valve overlap

[Viper Specialty]

correct me if I'm wrong but I think Dan Lesser said that a mild cam can give the rough idle sound, no need to go crazy if the sound is what you're after


edit: ''mild'' is probably something like 230/240 LSA 114 or so, as long as you have few degrees of overlap


Everyone just needs to remember, the "sound" that everyone likes is the sound of an engine inherently running poorly. IE: Dont be stupid on cam specification or you will regret it in the long run. That said, Gen-4/5 are more forgiving in this regard than G1/2/3 do the the MAF hybrid design versus true speed density.

[Mikey]

What's the eta for them to finish?

[Sniper]

You asking about my car?
They said 6-8 weeks but it could be sooner than that…

[Mikey]

You asking about my car?
They said 6-8 weeks but it could be sooner than that…

That's not bad at all!

[Sniper]

Everyone just needs to remember, the "sound" that everyone likes is the sound of an engine inherently running poorly. IE: Dont be stupid on cam specification or you will regret it in the long run. That said, Gen-4/5 are more forgiving in this regard than G1/2/3 do the the MAF hybrid design versus true speed density.

So, all the videos that have been posted are poorly running engines? And also Nth Motos cams are also running poorly?

[RedTanRT/10]

Everyone just needs to remember, the "sound" that everyone likes is the sound of an engine inherently running poorly. IE: Dont be stupid on cam specification or you will regret it in the long run. That said, Gen-4/5 are more forgiving in this regard than G1/2/3 do the the MAF hybrid design versus true speed density.

So true Dan!! In another 10 years when a number of performance cars go electric, they'll be companies selling piped in exhaust sounds that sound like a nasty cam and also can rumble and pop on deceleration!


Sniper, best wishes on your build!!

[Viper Specialty]

So, all the videos that have been posted are poorly running engines? And also Nth Motos cams are also running poorly?


Facepalm. Learn how an ICE & valvetrain works with regard to overlap, charge filling, volumetric efficiency, MAP and its relationship to cylinder air mass and fuel mass when dealing with cam profiles... and then get back to me, because my point flew way over your head.

Pretty sure I have taught numerous V10 calibrators how to calibrate, and have one of the earliest "start dates" of anyone in this market calibrating V10s.

Read more, post less.

[Sniper]

Facepalm. Learn how an ICE & valvetrain works with regard to overlap, charge filling, volumetric efficiency, MAP and its relationship to cylinder air mass and fuel mass when dealing with cam profiles... and then get back to me, because my point flew way over your head.

Pretty sure I have taught numerous V10 calibrators how to calibrate, and have one of the earliest "start dates" of anyone in this market calibrating V10s.

Read more, post less.


LOL your wisdom far surpasses mine. The only dumb question is not asking one.
Trust me, I’ve read enough that I won’t use your service.

[Viper Specialty]

LOL your wisdom far surpasses mine. The only dumb question is not asking one.

It wasn't the question, it was the implication in how you asked it.

The "Sound" or "Lope" that is associated with cammed performance engines is the sound of an engine that is inherently running poorly, yes. The goal of an engine is to maximize volumetric efficiency, however in the case of a cammed engine, efficiency at the high RPM range is favored in lieu of efficiency at lower rpm ranged where it becomes extremely inefficient and poorly running. This can be masked to a point by calibration, but it will never be gone. Temperament, surging, converter damage, EGT issues, trim lock, altitude issues, stalling, and high-idle, are all things that creep into the scene when chasing that "sound". The more extreme the sound, the more likely there will be a pile of nonsense that accompanies it. Once you hit the limit, the engine will become untunable. Make no mistake, WOT dyno tuning is literally 1% of a properly running calibration, and by far the easiest part.

Speed density based systems, while ideal for Forced Induction, are directly at odds with low-vacuum/large overlap engines, as engine load cannot properly be calculated as intended. MAF systems give a little more wiggle room as they are not as reliant on vacuum. However, charge and thus exhaust contamination are still a problem in the long run.

Short version: Donkey-Dick Camshafts make a calibrator like me want to hit you in the head with it and ban you as a customer for life.


PS- Since you edited, and thats fine. I cant keep up with the ones I have!

[Mikey]

Facepalm. Learn how an ICE & valvetrain works with regard to overlap, charge filling, volumetric efficiency, MAP and its relationship to cylinder air mass and fuel mass when dealing with cam profiles... and then get back to me, because my point flew way over your head.

Pretty sure I have taught numerous V10 calibrators how to calibrate, and have one of the earliest "start dates" of anyone in this market calibrating V10s.

Read more, post less.

I don't think he was being disingenuous

[Sniper]

I’m sorry if you took my post wrong. I was genuinely asking about what you stated as I know very little about engines.

[Viper Specialty]

I don't think he was being disingenuous

Anyone can interpret things incorrectly, including me... but when you see "So, ABC are all wrong, and XYZ is wrong too?" type comments, the implication is pretty clear and definitely defensive.

A non-defensive position would have simply been "Can you please explain what you mean?".

[Viper Specialty]

I’m sorry if you took my post wrong. I was genuinely asking about what you stated as I know very little about engines.

If thats legitimately how you meant it, then I apologize for my tone. I read your message as a fairly pointed slight.

[Sniper]

It was not a defensive statement.

[Sniper]

It was not a defensive statement.

And I’m sure I’ve made my shop pretty short as the questions I’ve asked them. LOL

[Mikey]

If thats legitimately how you meant it, then I apologize for my tone. I read your message as a fairly pointed slight.

As a mechanical idiot myself, I'd suspect his thought process was "What is the point of making the engine inefficient, and is this the case with every shop?"

[StrokerAce]

I get what was being explained but maybe it's that the engine is running poorly at idle. Which makes sense from my big block days with .77X lift cam with 300ish duration that didn't like to idle but that's not what it did most of the time anyway. Yeah, you could damn near almost hear each individual slug as the crank turned. Sounded tough and people liked to hear it start up but it didn't like to idle, but again not what it was for. So yes, at idle I agree it wasn't running great but it sure did like to slam 2nd gear in that powerglide at over 8k RPM's.

For a street car I'd rather error on the side of too small of a cam than too large. To VS's point, usually a Donkey D cam is for bragging and dyno results but fail to deliver in most street driving instances.

Just my experiences.

[Aevus]

Well, that escalated quickly!

hahaha


back to the topic:

I think one should have as big of a cam that is needed (strictly for high RPM use, not sound nor HP) but not a tiny bit more, because that's where headaches start.

and even for higher RPM, since the Viper engine is so limited (oiling system, hyd lifters, valvetrain, long stroke, etc..) you probably better stay below 6,500rpm anyways...

and if you're in it for HP, don't bother, just force induce the beast and call it a day


edit: I think Roe Racing (now bankrupted tho) nailed it with their latest cam version 710R with 14 deg overlap: it was most probably the maximum possible without heavy modifications and tuning issues.

[Aevus]

As a mechanical idiot myself, I'd suspect his thought process was "What is the point of making the engine inefficient, and is this the case with every shop?"

Mikey, upgrading the camshaft is just about deciding on a compromise. Anything with some sort of valve overlap simply make the engine somewhat unbalanced, especially at lower RPM.
The benefit of that (besides of the rough choppy idle sound) is the performance at higher RPM... Scavenging effect

https://help.summitracing.com/app/answers/detail/a_id/4794/~/the-scavenging-effect

-----------------

You can visually see it there, on the graphs:

https://www.compcams.com/dyno-graphs

The ''bigger'' the cam, the peakier it is in high RPM, and the more absolute HP you get at the peak (at the cost of lower RPM performance)...

That being said, if you don't care about high-RPM performance... it's an absolute no-go to choose a very big cam. Especially with final gears between 3.07-3.55 and stock-ish valvetrain...

Maybe Dan can confirm, but I'd say anything between 10-12 deg overlap would be more that sufficient to have the sound AND the low-end torque AND something tunable.

More than that, you better have a higher compression, lighter/stiffer valvetrain, ported heads, headers/exhaust, 3.73+ gears, etc... Basically all I had to do for my 22 deg cam.

[Mikey]

Did you figure out what you're going to do for tuning, Sniper?
I THINK prefix just uses the standard race module for heads/cam, and then the custom tuning for the 9L builds

[Sniper]

My builder said they will be able to tune it.

[13COBRA]

Justin can definitely do it.

[Mikey]

What are they using to tune?

[Sniper]

HPTuners

[Dan Cragin]

We have had good luck tuning "bigger" cams as long as the LSA is is around 114-116. The 108-110 LSA cams tend to be dirty down low,
don't like catalyst and altitude changes, they surge at low speeds and are hard to tune, more so on the earlier speed-density models. Plus, you really don't make much more usable power unless its a race car with high compression and race gas.

Later engines that include MAF and have better heads and bigger bores, tune better with cams that have more overlap.

At the end of the day, you can make great great power and even pass emissions with the right combo. I agree with Dan Lesser.

Just my opinion, yours may differ.

[heath1225]

We have had good luck tuning "bigger" cams as long as the LSA is is around 114-116. The 108-110 LSA cams tend to be dirty down low,
don't like catalyst and altitude changes, they surge at low speeds and are hard to tune, more so on the earlier speed-density models. Plus, you really don't make much more usable power unless its a race car with high compression and race gas.

Later engines that include MAF and have better heads and bigger bores, tune better with cams that have more overlap.

At the end of the day, you can make great great power and even pass emissions with the right combo. I agree with Dan Lesser.

Just my opinion, yours may differ.

Two Dans can't be wrong.

[Aevus]

We have had good luck tuning "bigger" cams as long as the LSA is is around 114-116. The 108-110 LSA cams tend to be dirty down low,
don't like catalyst and altitude changes, they surge at low speeds and are hard to tune, more so on the earlier speed-density models. Plus, you really don't make much more usable power unless its a race car with high compression and race gas.

Later engines that include MAF and have better heads and bigger bores, tune better with cams that have more overlap.

At the end of the day, you can make great great power and even pass emissions with the right combo. I agree with Dan Lesser.

Just my opinion, yours may differ.


In my quest to learn more about camshaft (on a Viper) I saw almost exclusively LSA 113 to 115. Probably a reason for that. Probably many trials and errors behind that...

And yes, at some point you have to get higher compression, which is not that simple for many reasons...

Law of diminishing returns kicks in badly at a certain point:

a ''mild'' cam set-up would cost maybe 5,000$ parts/mods and labor, and you'll get choppy idle sound + around 15-20% extra whp compared to stock

while an ''aggressive'' cam set-up, including all the modifications needed to make any sense out of that big cam, it could cost well over 20,000$ total, for maybe an extra 5% whp... (or +/- 10% if you take the risk to spin it over 6800 rpm) and all the headaches that comes with all that.

All numbers are approximate, but it gives an idea. At least, based on my experience so far.

[Aevus]

also just so you know guys:

high compression + long duration cam makes the engine loud. VERY LOUD.

and if you change the exhaust system for something more restrictive, you'll lose power.

[Sniper]

We have had good luck tuning "bigger" cams as long as the LSA is is around 114-116. The 108-110 LSA cams tend to be dirty down low,
don't like catalyst and altitude changes, they surge at low speeds and are hard to tune, more so on the earlier speed-density models. Plus, you really don't make much more usable power unless its a race car with high compression and race gas.

Later engines that include MAF and have better heads and bigger bores, tune better with cams that have more overlap.

At the end of the day, you can make great great power and even pass emissions with the right combo. I agree with Dan Lesser.

Just my opinion, yours may differ.

So, a Gen V Viper would be ok with a 110 LSA cam? Because you said later engines tune better with cams that have more overlap…

[Mikey]

So, a Gen V Viper would be ok with a 110 LSA cam? Because you said later engines tune better with cams that have more overlap…

Stick to whatever your builder recommends

Even though our cars "only" make 650 at peak, you have more power through the rest of the band than cars at similar horsepower

[StrokerAce]

Stick to whatever your builder recommends

Even though our cars "only" make 650 at peak, you have more power through the rest of the band than cars at similar horsepower

Maybe, if you're speaking of NA cars, but how many are NA? Not many. Much of the power under the curve is from the CI of this engine vs say a high strung smaller cubic inch mill.

[Sniper]

Dyno #s before heads/cam on mustang dyno which is lower than dynojet
551hp/552tq

[Mikey]

Dyno #s before heads/cam on mustang dyno which is lower than dynojet
551hp/552tq

Better than I expected

[T/A KID]

Updates on this???

[Sniper]

Still waiting on machine shop to send parts back to shop.

[Sniper]

Shop said hoping to get items back from the Machine shop later this week

[Sniper]

Latest update:
I'd say 2-3 weeks. Machining pushed it back so no parts yet and they didn't have an eta.

Ugh!!!!!