[Matt@Tick]

The cam design on these engines comes from the design of the cylinder head. They are much like an LS3/LS7 head in a way, because they have a large intake port, valve, and a much smaller exhaust port, and valve in comparison. The problem with a tighter LSA is the amount of overlap you get into. The more you have the worse it will drive and in turn the harder it will be to tune for driving and low RPM. Tighter LSA doesn't mean that you will have more low end. LSA is about valve event placement. So when you see a giant Nitrous cam or Blower cam they will have large LSA, as much as 120 in some cases.
As everyone knows wider LSA makes for less overlap and in turn that cuts out some of the cam sound that everyone loves. Cam advance is also used for valve event placement. The sooner you can open the intake valve without hitting the piston, the faster that cylinder will start to fill with air. But in the case of no valve relief on the intake side of these engines, you are limited to where the IVO can start. With bigger lobe duration the more this can become an issue for PTV clearance.

So in all its a balancing act lol. You want valve events that will work with the cylinder head design, you want cam sound, and we want it to be tuneable and driveable. Just don't think a wider LSA is going to hurt you in any way. If you are not that worried about how it's going to drive, you can always go custom if you want more overlap.

[NickyRacerBoy]

Originally Posted by Joey@Tick

The cam design on these engines comes from the design of the cylinder head. They are much like an LS3/LS7 head in a way, because they have a large intake port, valve, and a much smaller exhaust port, and valve in comparison. The problem with a tighter LSA is the amount of overlap you get into. The more you have the worse it will drive and in turn the harder it will be to tune for driving and low RPM. Tighter LSA doesn't mean that you will have more low end. LSA is about valve event placement. So when you see a giant Nitrous cam or Blower cam they will have large LSA, as much as 120 in some cases.
As everyone knows wider LSA makes for less overlap and in turn that cuts out some of the cam sound that everyone loves. Cam advance is also used for valve event placement. The sooner you can open the intake valve without hitting the piston, the faster that cylinder will start to fill with air. But in the case of no valve relief on the intake side of these engines, you are limited to where the IVO can start. With bigger lobe duration the more this can become an issue for PTV clearance.

So in all its a balancing act lol. You want valve events that will work with the cylinder head design, you want cam sound, and we want it to be tuneable and driveable. Just don't think a wider LSA is going to hurt you in any way. If you are not that worried about how it's going to drive, you can always go custom if you want more overlap.

Thanks for the reply. I have just a small amount of knowledge on this subject. I leave up to the pros! I like the driving aspect.
Car makes nice torque rolling thru the turns for sure @ 4500 rpm and the power delivery is very linear. My lap times are getting pretty decent @ NJ Motorsports Park. As far as the tune hot and cold start up is excellent quick stopping and starting in tight areas is good too...no oscillation.





last session of the day and tires are beat...10 heat cycles at least. Fun either way!

[DFW1LE]

Originally Posted by Joey@Tick

The cam design on these engines comes from the design of the cylinder head. They are much like an LS3/LS7 head in a way, because they have a large intake port, valve, and a much smaller exhaust port, and valve in comparison. The problem with a tighter LSA is the amount of overlap you get into. The more you have the worse it will drive and in turn the harder it will be to tune for driving and low RPM. Tighter LSA doesn't mean that you will have more low end. LSA is about valve event placement. So when you see a giant Nitrous cam or Blower cam they will have large LSA, as much as 120 in some cases.
As everyone knows wider LSA makes for less overlap and in turn that cuts out some of the cam sound that everyone loves. Cam advance is also used for valve event placement. The sooner you can open the intake valve without hitting the piston, the faster that cylinder will start to fill with air. But in the case of no valve relief on the intake side of these engines, you are limited to where the IVO can start. With bigger lobe duration the more this can become an issue for PTV clearance.

So in all its a balancing act lol. You want valve events that will work with the cylinder head design, you want cam sound, and we want it to be tuneable and driveable. Just don't think a wider LSA is going to hurt you in any way. If you are not that worried about how it's going to drive, you can always go custom if you want more overlap.

Part of what Joey explained is what I tried to convey earlier in this thread. The referenced TSP cam spec was not yet posted or that you were a road course guy, but honestly that TSP cam spec looks more like it was spec'd for straight line performance than road course, but heck, I'm no expert.

[PRAY]

99% of my cams are on a 111* lobe sep. They drive great and seem to make pretty good power. As per conventional wisdom, when I lay the lobe sep back it makes power later.

I would also caution on cams relying on retarding them up top to make power. The cam phaser in the LT's sucks. Aftermarket spring pressures over come the spring in the phaser and it will lose control quickly. That is why the big manufactures are now making 4*, 2*, 0* limiters. I have gone to the, lock it out, mind frame and get your valve events correct.

[oldman]

now that Katech has a new billet plate I may do a weekend project and go full lockout, plus I don't like that over-torqued hollow cam bolt... call me old fashion, but like I tell all the hot women, just call me.

[NickyRacerBoy]

Originally Posted by DFW1LE

Part of what Joey explained is what I tried to convey earlier in this thread. The referenced TSP cam spec was not yet posted or that you were a road course guy, but honestly that TSP cam spec looks more like it was spec'd for straight line performance than road course, but heck, I'm no expert.

It's actually quite torquie. Pulls really nicely thru some of the slower turns
As Brett stated it narrow lsa makes power level off earlier then one wider.

[NickyRacerBoy]

Originally Posted by PRAY

99% of my cams are on a 111* lobe sep. They drive great and seem to make pretty good power. As per conventional wisdom, when I lay the lobe sep back it makes power later.

I would also caution on cams relying on retarding them up top to make power. The cam phaser in the LT's sucks. Aftermarket spring pressures over come the spring in the phaser and it will lose control quickly. That is why the big manufactures are now making 4*, 2*, 0* limiters. I have gone to the, lock it out, mind frame and get your valve events correct.

Brett I tossed rod thru stock engine BTW hence why I never followed thru with you.

[NickyRacerBoy]

Originally Posted by oldman

now that Katech has a new billet plate I may do a weekend project and go full lockout, plus I don't like that over-torqued hollow cam bolt... call me old fashion, but like I tell all the hot women, just call me.

Yeah I was talking with Lingenfelter as they had prototype one too. I COMPLETELY locked it out

[PRAY]

Originally Posted by NickyRacerBoy

Brett I tossed rod thru stock engine BTW hence why I never followed thru with you.

That sucks on both accounts. Sorry to hear.

[DFW1LE]

Originally Posted by NickyRacerBoy

It's actually quite torquie. Pulls really nicely thru some of the slower turns
As Brett stated it narrow lsa makes power level off earlier then one wider.

Right, tighter lsa moves torque to lower RPM, but with big duration, I believe it would shift torque curve in the other direction. Any how if its working well for you on the track that all that matters.

[Matt@Tick]

Originally Posted by DFW1LE

Right, tighter lsa moves torque to lower RPM, but with big duration, I believe it would shift torque curve in the other direction. Any how if its working well for you on the track that all that matters.

So, in reality, a tighter LSA advances the exhaust valve events while leaving the intake events in the same place. Moving the exhaust events to open earlier and close earlier, in turn, will bring the peak torque down the scale. Lots of people think that LSA 115+3 would mean an LSA of 112. But that's not correct. the +X number will tell you exactly what your ICL (intake centerline) is. So if you ever had a cam that said LSA115+0 or had no advance, the ICL will be 115.

Its all a relation of air mass that you are trying to move. The higher rpm all motor engines we build typically have an LSA around 117 and the ICL is around 114-118. The reason is so the exhaust opens later. The goal is to use all of the combustion energy that you can before opening the valve. Blower cars like an even later opening event. Nitrous engines like an early exhaust valve open event. N/A falls in the middle of nitrous and blower. It doesn't have the violent fast flame that nitrous does and it doesn't have the big volume of air and fuel that forced induction has.

[PRAY]

Remember as well that using a wider LSA and not advancing the ICL back will give you a very late IVC which kills DCR. DCR = TQ. Also, the more OL you have the larger the cam will act extending it's usable rpm band. So if I use small lobes, keep it advanced, maximize OL for it's size the more DCR you keep and the wider power band you can get. It will also have more driving tq and more power under the curve. In the end, you have to look at the weight of the vehicle, gearing, converter size for A8 or trans gearing for M6's, flow characteristics of the head with an IM attached, exhaust with headers, intended use of the vehicle and a bunch of other stuff to get it right.

The LT head has much larger runners than the LS3 but has smaller valves. Now valve angle and runner length effect the efficiency of the runner size. So don't get all caught up on cross section and runner size. But what you need to realize is that if you don't flow the head with the IM/TB attached and an exhaust tube then you don't really know the flow percentages to spec a cam with. Just flowing the head makes you think you need a wide duration split. But once you put the IM/EX on there the numbers change greatly. This requires a much tighter duration split. You also have to take the entire lift curve of the intake and exhaust into consideration. C/D comes into this equation also. But I digress.

[PRAY]

Some more thoughts before I spend the rest of the night behind the grinder.

Drivability and what not has been brought up. These LT's are not your Dads LS. The DI motor can take a ton more OL and drive just fine. The fuel is being injected under the valves in conjunction with the timing of the exhaust valve closing. Where the opposite is happening with a port injected car. Simple Injection timing changes help quite a bit. Reversion doesn't have the same effect on these cars.

My cams range from 5*-23* of OL. I have personally daily driven a 5*, 11*, and a 23* cam. All of them drive perfectly fine. There are two other guys on here that daily cams with 19* OL. They say they drive like stock.

The computers are much better in these cars and we can get cam cars pretty dialed in now. The TQ based system is pretty powerful once you know what you are doing with it.

[PRAY]

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.