To Vvt Or Not To Vvt? - That Is The Question!

[ostmike 35]

Well it's been a little over two years since I did my first aftermarket Gen III Hemi VVT tune. After working for many years with variable cam technology on the imports and achieving huge power gains, I Initially had very high hopes for this tech on the Gen III Hemi's. After tuning about a dozen of these cars that had made the rounds through other shops and spending countless hours on the dyno, other than WOT cam manipulation I found the tech to be less than desirable, at least from a tuning perspective. Driveability with the large CI, high compression engines running the Comp 274 w/limiters was a bear to tune and I never really was satisfied. In the grand scheme of things, as a tuner I really strive for driveability and I just couldn't nail down that portion of the tune on every car. Some were close and most of the customers were satisfied but it just wasn't right.

Fast forward a year or so and the 392 cam swaps started showing up. I was able to pick up some more knowledge and make these cams drivable with relatively no issues. But they still weren't where I thought they should be performance or driveability wise.

They say necessity is the mother of invention and as destiny would have it we ended up with a problematic VVT cam swap in the shop. Without going into all the details we discovered that the cam needed a limiter. This cam had been used in other cars with valve reliefs without issue but in a stock 5.7 - well I guess not. In any event, we tried to locate a Comp limiter/lock kit but no dice. Nothing at Summit, Jegs or even Comp for at least two weeks. So we needed another solution. Fortunately with the car running on the dyno and careful monitoring of the cam position I began spending hours identifying and testing the various tables that manipulate the cam as well as the ignition timing tables that were also impacted/utilized. I was pleasantly surprised how I was eventually able to manipulate the cam position at any RPM, engine temp or boost level.

The results of this tuneup were very impressive to me and ultimately I used this new found knowledge and applied it to a previously tuned 392 cam swap. That customer called the next day and stated that his supercharged RT that he drove daily had never run so well.

Please don't take this as me stating I have a vast understanding of Gen III Hemi VVT tuning - because I don't! What I want to put out here is the fact that there is alot that can be done that I wasn't aware of and now I believe there is an opportunity to really take advantage of this tech.

I do want to state that as with anything truly complicated, the more your learn the less you realize you know and that applies here! The calid's and tables for various models tend to be very different and each one will have to be studied and tested to see what tables actually apply to tuning and which ones are bogus.

I wanted to give a shout out to all those that let me bounce ideas, questions and concerns with this particular situation off of: Erik Storms, Josh Schwartz, Joel Applegate, Andy "I'll ship it on Friday" Underwood and Micah Doban. Each of you took time out of your day to answer questions and speculate on what may or may not happen with the tuning changes I had planned. Thanks!!!!

Ok... so here is the result of the tuneup on Stevo's car with a cam and springs swap. I worked hard to keep the timing identical to his tune that the car showed up here with so we were comparing apples to apples. In my book this was a very mild tune and I even richened up the fueling quite a bit to try to make his #4 piston live as long as possible. Ultimately the power gains could have been much larger.

I could make the torque curve vary at will by simply moving the cam and ended up with what you see here. She is pulling like a freight train out the back. Also, keep in mind I stopped at 100rpm less than his baseline pull (again to keep the #4 piston alive) but with the direction of the curve 100rpm more would have been some more ponies for sure.

Update: The cam used in Steve's car was a PWR custom grind: 219/227 583/583 116+2 (the +2 means 2 degrees adv. ground into the cam)

[Andy@PWR 58]

Very easy and simple 50rwhp gain. Very nice

[Boatman 97]

Good Stuff Mike. Guys like you keep the platform moving in the right direction, thanks for all you do for all of us.

[Renfrick1 83]

Sounds like steveo's on borrowed time

[JDW RT 09 20]

Great discussion topic but i am sure like anything there will be pros and cons either way. Still have not heard anything making me regret dumping my vvt for a 6.1 based stroker.

[Truckzilla46 17]

Wow! VERY impressive! When I hear stories like that it makes me realize how much time and effort really go into tuning and the road to perfecting tunes.

[Hemi31 194]

Woot......can't wait to see what Cory's car does!

[StevoHemi 113]

Well.... it has been an interesting month and learned a few things too! I had been planning a cam swap for well over a year and had originally picked up the $70 (Canadian Dollars ) 392 cam and sat on it for a year while reading cam after cam threads here and on LX. A lot of the swaps were hit n miss. Hmmmm.... I started to talk to Andy and Mike about the 274 comp but Andy convinced me to do a custom grind.

Fast forward to the last week of March. Captalbator and I did the five hours drive and delivered the RT to Micah and Mike. You have all seen the picture of No 4 piston in my other thread. What to do? Drop in pistons? Nah... We decided to carry on. Mike tried to tune her "proper" but it was obvious that a limiter was need. Even if a limiter was installed with a stronger tune.... that No 4 piston was lingering in the back of my head. The car has been there since before CF5 and waiting another 2 weeks for a limiter was out of the question. Micah has other cars waiting and I need to get the car home. So, when Mike and I spoke on Monday, I just told him to give it a conservative to get her home. No race tune required. I cannot afford to damage the engine. So the plan is to start saving for a forged shortblock NOW. Hopefully I will return in November or March of next year and Micah can do the swap and Mike can go "balls to the wall" street and race tune.

I am very happy with Andy's choice of cam. We have not seen the full potential of this cam because of the soft tune/no limiter and the current state of that No 4 piston. Still, 50 hp is a good start. Once the new short block goes in, we will see what this cam will really do. I will track the car at St. Thomas Dragway on June 14th. No hot lapping and nothing over 6000 rpms. That will be it for this year.

The Capt and I will pick her up Sunday. He gets to drive her all the way home. His SRT is in storage and he needs to have some HEMI therapy. The Capt gave up two days of his time for me so it is only fitting that he gets all the smiles on the way home! Besides... I have never seen my car driven on the road (I am always in it). Going to be a nice drive home. I presume he will give a write up on how the car feels/performs later on Sunday night.

Thanks very much to Andy, Micah, Mike and Denis (Captalbator). You guys are awesome.

Now.... gotta start saving and watching our vendors for a shortblock sale. Hmmmm.... what to get? 346? 392 or 410 stroker?

Stevo

[70Barracuda 25]

Nice job, glad you guys keep figuring these things out.

[Andy@PWR 58]

Now.... gotta start saving and watching our vendors for a shortblock sale. Hmmmm.... what to get? 346? 392 or 410 stroker?

Stevo

A 426 using a 5.7 VVT block of course. It can be done easily. Hell the 5.7 in my truck is a 416 and has at least 25,000 miles on it already

[jettech104 27]

Great write up everyone. Its always great to hear how the Hemi community keeps pushing forward despite the " do it with your hands tied behind your back " attitude from Chrysler!!!!

[ostmike 35]

Great discussion topic but i am sure like anything there will be pros and cons either way. Still have not heard anything making me regret dumping my vvt for a 6.1 based stroker.

Without a doubt the non-VVT engines are easier to tune, do not require phase limiters for larger cams and have a larger selection of off the shelf cams available. However, check back in a year and I think that may change. Knowing what I do now the next engine for the Jeep will most likely be VVT based.

Woot......can't wait to see what Cory's car does!

What's cool about Cory's car is the fact that his engine and cam are the exact ones I tuned over two years ago (in a different car) and I am eager to have that build back in my hands. I do know that the previous customer's car with a KB like Cory's loved the cam movement at higher RPM's.

[toofart 148]

Cool stuff!

There's a significant torque gain after about 4900 but before that it's under the previous curve. It also drops sharply at about 6000. Stevo if you don't shift above 6000 where will that put the engine after the shift?

[StevoHemi 113]

I dunno TF. .. I am learning this shit as i am going along.

Remember... This is a conservative tune. We will know more when the bottom end is replaced.

Stevo

[ostmike 35]

Cool stuff!

There's a significant torque gain after about 4900 but before that it's under the previous curve. It also drops sharply at about 6000. Stevo if you don't shift above 6000 where will that put the engine after the shift?

I think you're looking at the wrong curve if you are speaking about the data for the new cam dropping sharply after 6000. In fact the torque curve goes flat (for the new cam) at roughly 6000rpm and is a truly beautiful thing! If calculating HP this is what any engine builder or tuner would love to occur. Remember HP is a calculated number based on torque.

(Torque x RPM)/5252=HP so the longer you can stretch that torque out, especially at the higher RPM's is a sweet thing.

With that being said the loss of torque over the previous cam in the lower RPM range as well as the huge torque increase at the higher RPM's will make this cam ideal for a 7000+rpm shift point with an RPM recovery in the lower 5000 to upper 4000rpm range.

[lakersfan7272 59]

Good stuff. With the current block situation this is obviously the wave of the future. Kudos to Mike for pushing it forward.

[Speedy 247]

Dang, that's some awesome stuff. I have been hoping for some real VVT CAM love to come our way and it's finally starting to happen. I figured with the SRT car went to VVT that was going to get it some real attention and I suspect these things will be the go to platform in the next year or so. Being able to move the cam around and manipulate how the power and torque come in are very good things. 50RWHP gain on a conservative tune with similar timing in the engine, no snake oil, tuning shows where this is going.

Were the cam specs ever shared, or if not, a "rough" idea provided?

[JDW RT 09 20]

ostmike:
Without a doubt the non-VVT engines are easier to tune, do not require phase limiters for larger cams and have a larger selection of off the shelf cams available. However, check back in a year and I think that may change. Knowing what I do now the next engine for the Jeep will most likely be VVT based.

----------------
When the advantages to vvt become clearly defined and standardized and an apples to apples comparison can be shown, I would absolutely consider moving to a vvt engine. The ability to get the most power, torque, and performance at any rpm range would of course be what everyone would want and from what little I have read, that is the advantage of vvt. The ability to make that happen seems to still be in the learning stage at this point and i look forward to the best tuners cracking this nut. Eventually it will happen and if the benefit of vvt outweighs the cost of swapping, vvt will become the new standard for the Gen III hemi performance market.

[ostmike 35]

Eventually it will happen and if the benefit of vvt outweighs the cost of swapping, vvt will become the new standard for the performance market.

Just to clarify variable cam technology is not a new standard for the performance market and has been making huge gains in the import market since the 1980's.

Making it work and becoming a "new" standard in the Gen III Hemi's is what we need to continue to investigate.

Speedy - find a dyno near you and let's see if we can make your cam squeak out a few more ponies. That would be some additional "concrete" evidence

Dang, that's some awesome stuff. I have been hoping for some real VVT CAM love to come our way and it's finally starting to happen. I figured with the SRT car went to VVT that was going to get it some real attention and I suspect these things will be the go to platform in the next year or so. Being able to move the cam around and manipulate how the power and torque come in are very good things. 50RWHP gain on a conservative tune with similar timing in the engine, no snake oil, tuning shows where this is going.

Were the cam specs ever shared, or if not, a "rough" idea provided?

Yes, important info that has been added to the original post.

[Speedy 247]

I'm looking for a dyno. My go to place seems to have closed, will keep checking.

[Andy@PWR 58]

Yes, important info that needs to be added. This was a cam that PWR made for Steve. I believe it was based off a 392 cam and reground. I'll track down the cam card tonight and post up the data - unless Andy can comment now?

Definitely not a reground 392 cam. Brand new core and cam from scratch.

219/227 583/583 116+2

Thats the camshaft

[Andy@PWR 58]

When we are profiling a camshaft, we already know what duration, lift, and lsa we want. The ICL or intake centerline is the part you have to play with to get the right curve at the right point. By advancing the cam, you move the power curve down and by retarding it you move it up. The idea is to advance it till you have the most cranking compression without peaking too soon. If we did two 426's and one was a street car and one a drag car, the drag car with the higher stall converter would be on a 113-116icl assuming its shifting at 7000rpm. The street car would be in the 110-113 range so that the power comes on sooner for a daily driver that doesnt spend much time above 5000rpm. With VVT technology, you can electronically advance the cam at the lower rpms and then retard it up top instead of having to select a specific ICL. This way to get more power down low and up top instead of sacrificing one for the other. Definitely the way to go if you know what your doing in the tuning dept. The tricky part is to not advance it so much that you have piston to valve contact down low or up top. With valve reliefs, we could have advanced the cam even more down low for more up a bump in low rpm power.

[TimeWaitsFNM 16]

Exciting news to see more gains here.

[StevoHemi 113]

Andy, what does the +2 mean?

Stevo

[Andy@PWR 58]

Andy, what does the +2 mean?

Stevo

two degrees of advance ground into the camshaft. That means 116lsa minus 2 = 114 intake centerline. There was no need to advance it anymore with the vvt being able to do it for us.