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Discussion Starter #1
Hi All,

There has been a lot of phone calls and talk lately on all the forums about VVT Cams and what to expect and how they operate,
We worked with Comp Cams right from the beginning to get a true aftermarket solution to market for the modern Hemi and have tested many different profiles to make sure that we could deliver a package that could perform and be tuned, So we decided to post up a FAQ thread with the most common questions.

If you have any questions please reply to the thread.

Thank You.

The MMPG Team.

1. Why Can’t I get that old school Lope?

Old school lope is achieved by overlap. Overlap is the time the intake and exhaust are both open. This can be achieved but not without sacrifice. The larger cams such as the 274 Comp have an aggressive idle but are way too large for a 5.7 displacement engine. Low end throttle response and power will be sacrificed. The smaller cams can get a bit more aggressive idle if lobe separation is tightened to 112 from 114 but will be much harder to tune and still may have some bad driving habits. The VVT style lobes are not a symmetrical design and have a delayed intake opening so they can be advanced in the engine but this reduces overlap.

2. Why do they only make power past 3k Rpms?

We are working on this with some custom lobes at this time but here is the problem. The 5.7 VVT engine as we know has a considerably good head and ports as large as the 6.1. Well with the large port as compared to the old 5.7 head it is hard to increase the low power numbers. Also the factory cams are so small that they inherently make allot of low end power. If we are able to maintain or slightly increase the power below 2800RPM with the larger cam we are doing good.

3. What or Why is the Limiter used for?
Cam phasers in factory engines are used for emissions and fuel economy. They sweep the small factory cam up to 35 degrees to achieve this. When using larger performance cam this must be limited to make sure we do not have piston to valve issues. Even the amount we limit to (about half 17 degree) is too much to move a cam for performance.

4. What can I do to make the most low end torque
The best way to achieve the low end torque is efficiency. I like the best exhaust (long tube header and HF cat) I can find and then make a custom cam to compliment it.

5. Why are some cams losing power in the lower RPMs but show gains in the higher
Refer back to #2. In addition people are choosing cams that are way too big for the 5.7 engines. We have been working on these Hemis since 2005 and although the head has changed (gotten better but larger) what makes people think they can run a 226 or a 222 intake lobe at .050 lift in a 5.7L engine is beyond me. Some of the best running older 5.7s have 214Spartan cams. Also if you look at the cam timing numbers on the larger cams they retard the cams (which hurts low end power) just to make them fit. As previously stated the VVT came profile is non symmetrical and the advertised or @50 number is a bit deceiving. To compare to a normal or more traditional cams you have to add a couple degrees duration.


6. What is the best package to do to get the most out of it. IE Converter, long tubes ect….
It is all about budget and packaging. Ideally long tubes, 3400-3600 converter, 214 or a 218 @50 cam (intake lobe) with correct exh and install timing numbers.

As long as we plan ahead we can pick the right cam or other package parts. If you have to work in stages then you may make some sacrifices till you have time and money to get it all done.

7. Why not just use a 392 OEM Cam? Or your opinion on why not to?
A 392 cam is allot of cam for the money but it is still a factory cam. It is ground on a 121 LSA as opposed to a 114 LSA of a custom cam. It will have an even smoother idle and will give up more TQ below peak torque than a 114LSA cam. The cam install is also later than the custom cam also sacrificing that precious torque we need for these 4000lb cars. Another thing to consider is the install cost, valve spring upgrade, tuning etc. that remains the same no matter what cam you install so why not get the most out of it.
 

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Hi All,

There has been a lot of phone calls and talk lately on all the forums about VVT Cams and what to expect and how they operate,
We worked with Comp Cams right from the beginning to get a true aftermarket solution to market for the modern Hemi and have tested many different profiles to make sure that we could deliver a package that could perform and be tuned, So we decided to post up a FAQ thread with the most common questions.

If you have any questions please reply to the thread.

Thank You.

The MMPG Team.

1. Why Can’t I get that old school Lope?

Old school lope is achieved by overlap. Overlap is the time the intake and exhaust are both open. This can be achieved but not without sacrifice. The larger cams such as the 274 Comp have an aggressive idle but are way too large for a 5.7 displacement engine. Low end throttle response and power will be sacrificed. The smaller cams can get a bit more aggressive idle if lobe separation is tightened to 112 from 114 but will be much harder to tune and still may have some bad driving habits. The VVT style lobes are not a symmetrical design and have a delayed intake opening so they can be advanced in the engine but this reduces overlap.

2. Why do they only make power past 3k Rpms?

We are working on this with some custom lobes at this time but here is the problem. The 5.7 VVT engine as we know has a considerably good head and ports as large as the 6.1. Well with the large port as compared to the old 5.7 head it is hard to increase the low power numbers. Also the factory cams are so small that they inherently make allot of low end power. If we are able to maintain or slightly increase the power below 2800RPM with the larger cam we are doing good.

3. What or Why is the Limiter used for?
Cam phasers in factory engines are used for emissions and fuel economy. They sweep the small factory cam up to 35 degrees to achieve this. When using larger performance cam this must be limited to make sure we do not have piston to valve issues. Even the amount we limit to (about half 17 degree) is too much to move a cam for performance.

4. What can I do to make the most low end torque
The best way to achieve the low end torque is efficiency. I like the best exhaust (long tube header and HF cat) I can find and then make a custom cam to compliment it.

5. Why are some cams losing power in the lower RPMs but show gains in the higher
Refer back to #2. In addition people are choosing cams that are way too big for the 5.7 engines. We have been working on these Hemis since 2005 and although the head has changed (gotten better but larger) what makes people think they can run a 226 or a 222 intake lobe at .050 lift in a 5.7L engine is beyond me. Some of the best running older 5.7s have 214Spartan cams. Also if you look at the cam timing numbers on the larger cams they retard the cams (which hurts low end power) just to make them fit. As previously stated the VVT came profile is non symmetrical and the advertised or @50 number is a bit deceiving. To compare to a normal or more traditional cams you have to add a couple degrees duration.


6. What is the best package to do to get the most out of it. IE Converter, long tubes ect….
It is all about budget and packaging. Ideally long tubes, 3400-3600 converter, 214 or a 218 @50 cam (intake lobe) with correct exh and install timing numbers.

As long as we plan ahead we can pick the right cam or other package parts. If you have to work in stages then you may make some sacrifices till you have time and money to get it all done.

7. Why not just use a 392 OEM Cam? Or your opinion on why not to?
A 392 cam is allot of cam for the money but it is still a factory cam. It is ground on a 121 LSA as opposed to a 114 LSA of a custom cam. It will have an even smoother idle and will give up more TQ below peak torque than a 114LSA cam. The cam install is also later than the custom cam also sacrificing that precious torque we need for these 4000lb cars. Another thing to consider is the install cost, valve spring upgrade, tuning etc. that remains the same no matter what cam you install so why not get the most out of it.
What would be the best way to get lope and still have daily drivability ?
 

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Very good info here!

However i have a quick question. I went ahead and purchased a 6.4 cam for my RT. Reason was it seems like decent gain while still remaining ca carb legal. Are there any aftermarket cams that can do the same for me?

Thanks
 
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