CAMARO6 - View Single Post

PRAY · 08-07-2018, 11:04 AM

Some more thoughts.

When we talk about moving the power band around with cam specs that assumes we have and intake manifold that will comply with our wishes. For us, unless you cut a hole in the hood or go with a short runner sheet metal we are stuck with stock or the MSD. The stock IM has 2 runners that are around 7.5" and the rest are around 11". So peak power pretty much happens at 5,700 no matter what you do. Then there is the MSD. It has 7.5" runners which means we are pretty much limited to peak power in the 6,400-6,600 range. We also then run into total airflow available.

My heads on my bench flow about 350cfm@5" depression@.600" lift. At 28"@.600" lift they flow around 380cfm. But we will have to use my numbers for this information. The stock unported IM/TB combo flows around 270cfm attached to the head. The ported stock IM/TB combo flows around 307cfm. I see significant gains up top ported vs unported even on FBO cars. I have only flow tested the MSD/TB combo ported and it goes around 335cfm. But those flow numbers limit how much power the motor can make N/A regardless of what we throw at it or in it. The motor will only ever see 335cfm. Now with the addition of the ported 95mm TB I am going to guess that those numbers bump into the 340cfm range judging by the gains I saw on the dyno. And the runner length dictates where we make peak power.

So now we have two limiting factors to deal with. The actual max airflow available to make power and the runner length dictating where peak power will be. So we have to design our cam shafts within those limitations. Anything that needs more air or a higher peak power point will only cost us "power". By power I mean both HP/TQ under and over their respective peaks. That is the exact problem I ran into with the NBK cam. I can't get enough air to it or extend it's peak power points with the current manifold/TB set up. There were a bunch of other mitigating factors at play as well but I won't get into those. I am going to see what the NBK cam does on a fresh stock short block and heads and go from there. The next step will be to cut an inch out of the MSD runners and reshape the insides. I am also working on some more things with the heads now that I have a TB that may be able to feed the necessary demand.

I would like to see a legit 355cfm available with the modified MSD and NW 103mm TB. I will also have to flow test the RF dry filter to see if that will be come the restriction. The goal with the NBK cam is 600rw@7,500 rpm through the A8. Then match the rest of the car to it. Till then, I will stick with the baby cams I have been using that make great power under the curve till 6,500 or so.

The next point is about DCR, VVT and locked out cams. I believe I mentioned earlier that we can't seem to control this cam phaser like the LS3 version. So for the most part, trying to use it to your advantage doesn't work. For all of my cams now I use a 0* phaser limiter.

The stock cam retards 10* by roughly 6K. It's fully advanced IVC is around 29* and the fully retarded IVC is around 39*. So that puts the stock DCR in the advanced position at 9.81 if I am remembering correctly and the fully retarded DCR at 9.1ish. The LS cars ran best at 8.8 DCR or so on pump gas. Remember that DCR+TQ. So the stock cam and car is kicking butt just driving around with a small advanced cam and a ton of DCR. That DCR would not be sustainable as rpm climbs with cylinder pressure or we would get detonation. And we would be severely short on power up top if we didn't retard the cam to change the valve events to later in the Otto cycle. So we get best of both world. We retard the cam up top the make it act bigger making more power and bleeding off the DCR.

Now, when we decide to put a cam in the car most people go with a 113-116 lobe sep with not a lot of advance putting our IVC somewhere in the mid 40* range if not later. Essentially killing the low end by reducing DCR up to two full points under most normal driving conditions. So now we have a car that is sluggish until we go WOT and get above 4,500-5K. This is especially detrimental to an A8 car with a stock converter. The only real way to combat that is to try to stay small and early with your cam and advance it. If this cam phaser was better we could really do a lot. But the other way since we can't rely on the cam phaser is to stay small with a tight lobe sep and advance the cam as far as we can in the grind to maintain PTV and then use OL to make up the top end.

08-07-2018, 11:04 AM	#42
PRAY Drives: 2016 2SS Join Date: Jul 2016 Location: Sanford NC Posts: 2,766	Some more thoughts. When we talk about moving the power band around with cam specs that assumes we have and intake manifold that will comply with our wishes. For us, unless you cut a hole in the hood or go with a short runner sheet metal we are stuck with stock or the MSD. The stock IM has 2 runners that are around 7.5" and the rest are around 11". So peak power pretty much happens at 5,700 no matter what you do. Then there is the MSD. It has 7.5" runners which means we are pretty much limited to peak power in the 6,400-6,600 range. We also then run into total airflow available. My heads on my bench flow about 350cfm@5" depression@.600" lift. At 28"@.600" lift they flow around 380cfm. But we will have to use my numbers for this information. The stock unported IM/TB combo flows around 270cfm attached to the head. The ported stock IM/TB combo flows around 307cfm. I see significant gains up top ported vs unported even on FBO cars. I have only flow tested the MSD/TB combo ported and it goes around 335cfm. But those flow numbers limit how much power the motor can make N/A regardless of what we throw at it or in it. The motor will only ever see 335cfm. Now with the addition of the ported 95mm TB I am going to guess that those numbers bump into the 340cfm range judging by the gains I saw on the dyno. And the runner length dictates where we make peak power. So now we have two limiting factors to deal with. The actual max airflow available to make power and the runner length dictating where peak power will be. So we have to design our cam shafts within those limitations. Anything that needs more air or a higher peak power point will only cost us "power". By power I mean both HP/TQ under and over their respective peaks. That is the exact problem I ran into with the NBK cam. I can't get enough air to it or extend it's peak power points with the current manifold/TB set up. There were a bunch of other mitigating factors at play as well but I won't get into those. I am going to see what the NBK cam does on a fresh stock short block and heads and go from there. The next step will be to cut an inch out of the MSD runners and reshape the insides. I am also working on some more things with the heads now that I have a TB that may be able to feed the necessary demand. I would like to see a legit 355cfm available with the modified MSD and NW 103mm TB. I will also have to flow test the RF dry filter to see if that will be come the restriction. The goal with the NBK cam is 600rw@7,500 rpm through the A8. Then match the rest of the car to it. Till then, I will stick with the baby cams I have been using that make great power under the curve till 6,500 or so. The next point is about DCR, VVT and locked out cams. I believe I mentioned earlier that we can't seem to control this cam phaser like the LS3 version. So for the most part, trying to use it to your advantage doesn't work. For all of my cams now I use a 0* phaser limiter. The stock cam retards 10* by roughly 6K. It's fully advanced IVC is around 29* and the fully retarded IVC is around 39. So that puts the stock DCR in the advanced position at 9.81 if I am remembering correctly and the fully retarded DCR at 9.1ish. The LS cars ran best at 8.8 DCR or so on pump gas. Remember that DCR+TQ. So the stock cam and car is kicking butt just driving around with a small advanced cam and a ton of DCR. That DCR would not be sustainable as rpm climbs with cylinder pressure or we would get detonation. And we would be severely short on power up top if we didn't retard the cam to change the valve events to later in the Otto cycle. So we get best of both world. We retard the cam up top the make it act bigger making more power and bleeding off the DCR. Now, when we decide to put a cam in the car most people go with a 113-116 lobe sep with not a lot of advance putting our IVC somewhere in the mid 40 range if not later. Essentially killing the low end by reducing DCR up to two full points under most normal driving conditions. So now we have a car that is sluggish until we go WOT and get above 4,500-5K. This is especially detrimental to an A8 car with a stock converter. The only real way to combat that is to try to stay small and early with your cam and advance it. If this cam phaser was better we could really do a lot. But the other way since we can't rely on the cam phaser is to stay small with a tight lobe sep and advance the cam as far as we can in the grind to maintain PTV and then use OL to make up the top end.