Static vs dynamic compression - Cam Impact?

[WheelmanSS]

So I was always trying to wrap my head around the static vs dynamic compression differences with changes to my LS1. Now, I'm trying to look at it with my LS3.

Many things obviously impact the DCR such as engine size, heads, deck height, cam, etc., and with the LS3 market being relatively new, I'm wondering which direction we are going with cams, ported heads, valves, etc. Lets start with the Cam, since that is the basis point of many modders with 5th Gen Camaros.

Take for instance, GM's direction from a stock perspective:

The LS3 cam has more characteristics of the LS6 cam. It takes the late-model LS6 exhaust lobe and combines it with the new-model LS6 intake lobe.

Now, a higher static compression ratio is necessary with longer durations and a late closing of the intake valve. Was this stock cam designed to offset the DCR on a new, larger CI motor? Or was this just simply a gas-guzzler consideration by GM? And where do we go from here?

We can assume this relates to the LS3 "cathedral" intake port, but why? Why does it seem there is such a progression in intake? Were the previous LS motors lacking something? If so, what? Exhaust port flow was increased, however the design was not radically different. Interesting.

Thoughts?

[WheelmanSS]

sigh.... bump... Is this forum capable of any discussion besides which "CAI and Catback is best?"?

[jmlozano7]

Originally Posted by WheelmanSS

sigh.... bump... Is this forum capable of any discussion besides which "CAI and Catback is best?"?

I wonder the same but don't know very much. Looking forward to see this thread progress.

[Muscle Master]

Originally Posted by jmlozano7

I wonder the same but don't know very much. Looking forward to see this thread progress.

I been watching this thread all day...

[wbt]

Originally Posted by WheelmanSS

sigh.... bump... Is this forum capable of any discussion besides which "CAI and Catback is best?"?

There are a ton of folks here who are very knowledgeable about this topic.

In short, to answer your question as it relates to any motor:

The item to focus on with cams is overlap. The more overlap, the higher compression ratio needed to off-set. Running N/A, you can only fill a cylinder so much. Your goals are to maintain a high intake port velocity, good cylinder pressure, and good exhaust scavenging. This is the magical formula that not too many are able to achieve.

What is best for a standard LS3? It is best to find a trustworthy shop who has invested enough in R&D to figure this equation out. Several of those are:

Livernois
Vector
Texas Speed
Jannetty

Stock compression ratio running N/A, Vector Motorsports cam running a 114* LSA maintaining high cylinder pressure seems to do the trick.

Almost all the good shops are keeping their cam specs under lock and key as it is considered intellectual property.

[toehead93]

Originally Posted by WheelmanSS

Thoughts?

If you want to increase exhaust and intake flow I'd look at a CAI and catback exhaust. Not only will they really wake the car up but it will sound insane too! No seriously, this is beyond my knowledge. I understnad the concept of duration, compression, and how the impact the cam lobes have but only well enough to explain to my girlfriend who nows nothing about cars. I sound smart to her and like an idiot in here so I'm looking forward to more thoughts

[WheelmanSS]

Originally Posted by wbt

In short, to answer your question as it relates to any motor:

The item to focus on with cams is overlap. The more overlap, the higher compression ratio needed to off-set. Running N/A, you can only fill a cylinder so much. Your goals are to maintain a high intake port velocity, good cylinder pressure, and good exhaust scavenging. This is the magical formula that not too many are able to achieve.

What is best for a standard LS3? It is best to find a trustworthy shop who has invested enough in R&D to figure this equation out. Several of those are:

Livernois
Vector
Texas Speed
Jannetty

Stock compression ratio running N/A, Vector Motorsports cam running a 114* LSA maintaining high cylinder pressure seems to do the trick.

Almost all the good shops are keeping their cam specs under lock and key as it is considered intellectual property.

Ah, enter the days of the secretive specs of "custom" manufacturers. I miss the days when camshaft specs were rattled off like a stock ticker.

I know my question does relate to all motors, but I guess I am interested in the progression with the added CI that GM has been going with. Within the last few years, they have really upped the ante with displacement. I remember when the LS1 first came out, and people were skeptical about the differences from the LT1/LT4 model.... Well, we all know how that turned out lol.

With my LS1, when I built my cam and heads setup, I focused a lot on the cam lift and duration in relation to the head flow and valve size. The 112 LSA had seem to become the "standard", and I was hesitant to vary from that.

With the LS3, preference seems to be higher in the 114+ range. Now, the wider LSA does broaden the power band, and since the LS3 can rev higher than a LS1 (LS3 has stronger crank, rod and rod bolt design), maybe that is the right direction as their is more capability to build power. Plus, the wider range is also needed to offset the power/weight ratio.

I agree with you in that good intake port velocity is a thumbs up.... However, too much can in fact limit top end power. As you mention, the correct formula isn't easy to obtain. I do like your focus on velocity, as more power is made in the heads through port velocity as opposed to the size of the ports.

This is why I wonder about the "cathedral" port design on the LS3. Coupled with the cam, is this formula really the best way to make efficient power?

[wbt]

Originally Posted by WheelmanSS

Ah, enter the days of the secretive specs of "custom" manufacturers. I miss the days when camshaft specs were rattled off like a stock ticker.

I know my question does relate to all motors, but I guess I am interested in the progression with the added CI that GM has been going with. Within the last few years, they have really upped the ante with displacement. I remember when the LS1 first came out, and people were skeptical about the differences from the LT1/LT4 model.... Well, we all know how that turned out lol.

With my LS1, when I built my cam and heads setup, I focused a lot on the cam lift and duration in relation to the head flow and valve size. The 112 LSA had seem to become the "standard", and I was hesitant to vary from that.

With the LS3, preference seems to be higher in the 114+ range. Now, the wider LSA does broaden the power band, and since the LS3 can rev higher than a LS1 (LS3 has stronger crank, rod and rod bolt design), maybe that is the right direction as their is more capability to build power. Plus, the wider range is also needed to offset the power/weight ratio.

I agree with you in that good intake port velocity is a thumbs up.... However, too much can in fact limit top end power. As you mention, the correct formula isn't easy to obtain. I do like your focus on velocity, as more power is made in the heads through port velocity as opposed to the size of the ports.

This is why I wonder about the "cathedral" port design on the LS3. Coupled with the cam, is this formula really the best way to make efficient power?

You will find LSA's all over the board for the LS3. 111 to 114. On a N/A car running stock compression, maintaining correct cylinder pressure is key. Too much overlap and you have a poor running car without increasing the compression. Upping the compression through milling and you start getting into P/V clearance needing to flycut the pistons, replacing pushrods, etc.... This road becomes very expensive and not needed for 90% of us "street/weekend strip" owners.

The LS3 head uses a standard rectangular intake port vs. the cathedral design of the earlier LSx motors: http://www.camarohomepage.com/ls3/page2.htm

The stock LS3 head is a damn good design and will support 600HP. No need to change heads now days to get the performance you want. Keep the stock valve size, CNC porting, and you have a head that will provide all the N/A flow a person will ever need. All key to building that very streetable, 500WHP LS3.

[WheelmanSS]

Originally Posted by wbt

You will find LSA's all over the board for the LS3. 111 to 114. On a N/A car running stock compression, maintaining correct cylinder pressure is key. Too much overlap and you have a poor running car without increasing the compression. Upping the compression through milling and you start getting into P/V clearance needing to flycut the pistons, replacing pushrods, etc.... This road becomes very expensive and not needed for 90% of us "street/weekend strip" owners.

The LS3 head uses a standard rectangular intake port vs. the cathedral design of the earlier LSx motors: http://www.camarohomepage.com/ls3/page2.htm

The stock LS3 head is a damn good design and will support 600HP. No need to change heads now days to get the performance you want. Keep the stock valve size, CNC porting, and you have a head that will provide all the N/A flow a person will ever need. All key to building that very streetable, 500WHP LS3.

Well a wider LSA will give more high end power and less cylinder pressure and the lower RPM, whereas the higher LSA will really raise the cylinder pressure and increase lower end torque. I guess it would be better if we defined "correct" cylinder pressure, as that could, in essence, be a matter of opinion.

The earlier the intake valve closes, the more cylinder pressure you will have. Thus the key is to have the piston as low as possible on the next compression stroke when the intake valve is shut to create the most compression volume. So, would it be safe to say the common application would benefit from a high-lift intake number with a lower duration?

Since we see higher RPM out of the LS3, I don't see why a wider LSA would be a bad thing? Sure, I guess you could suffer a little "driveability" loss, but when you can build power through a wider band, is it now worth it?

Personally, I am a big fan of low end torque over horsepower... but if you have the opportunity to build torque longer... I dunno. I guess it is all relative.