Cat Cams vs Schrick?

Dec 14, 2016
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And to explain "why" LSA is important (using that awesome graphic) you have to remember in a boosted environment you are actually cramming your combustion chamber full of air under pressure. If you have overlap (that small section where the two lobes cross over in the graphic, this is actually when both the intake valve and exhaust valve are open at the same time), what you are effectively doing is cramming all that boost right out your exhaust. You don't want overlap in a boosted environment as it is a giant boost leak straight out your combustion chamber into the exhaust right when you are trying to fill that chamber with fresh air.

You want that overlap in a NA environment because you are in a negative pressure state and it creates a scavenging effect which effectively sucks more air into the combustion chamber. At that point the exhaust pulse has gone down the runner of the exhaust manifold or header, and has left a negative pressure zone behind it. That negative pressure zone is under vacuum and effectively sucks air in from the intake manifold during overlap. This is also what gives that lope-y cam sound we are familiar with.

LSA is a massive influence on all engines, it just works differently (and oppositely) when you are in a N/A vs. Boosted environment.

I'm confident you know this, but as a point of clarification overlap does have its place in forced-induction engines. It aids low end responsiveness, the portion of the rev range that the manufacturers are most concerned about. Car buyers don't want turbo lag and will pass on an otherwise fuel efficient engine if its performance feels sluggish. That's why VW/Audi introduced their Variable Valve Timing system to the turbocharged 5v engines in the 1990s. Here is an excerpt from their Self Study Guide explaining the benefits of variable valve timings:


AudiSelfStudy-VVT.jpg




We at FrankenTurbo have been working on the VW/Audi engines for some time now, so naturally we got "Cam Cards" for those engines as well. With that information we can illustrate how that platform's VVT system functions:

VAG-camshaft-curves_VVT-power-torque.jpg



As dyezak pointed out, the VANOS system makes that old VW variable valve timing look pretty obsolete: it not only has control of BOTH cams, it also can specify the exact amount of separation on the fly. Here is a graph of the N54's VANOS system with examples of possible "Torque" and "Power" positions.

N54-camshafts-curves_VANOS-power-torque.jpg



Lastly, since I have it, here are the VAG cam profiles compared to their BMW counterparts.

N54-camshafts-curves_vs_VW-Audi_5v.jpg


When you look at the N54's camshafts versus others, they stack up pretty well. They have more duration and lift. The only profiles in this graph that holds up against the N54 is for an upgraded CatCam intake (in pink) and the European-spec RS4 exhaust.

Thx
 
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V8bait

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Nov 2, 2016
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@V8bait how much benefit can be had in the tuning department if we had increased duration?

A lot, look at the dynos from Tony after he added cams (un tuned nonetheless). Overlap is tunable but longer duration lets us advance the intake opening event which helps in two places specifically- low rpm and ported heads. It all has to do with velocity. Low rpm has low velocity, ported head lower velocity overall. Longer duration lets us move events around more. Tuning these events is ideal though. Leaving them the same like Tony did is ok, you get a little earlier opening event from the longer duration, but it also adds some overlap where you don't want it, which is easily tunable with vanos but it needs a tune to adjust it.
 
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doublespaces

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A lot, look at the dynos from Tony after he added cams (un tuned nonetheless). Overlap is tunable but longer duration lets us advance the intake opening event which helps in two places specifically- low rpm and ported heads. It all has to do with velocity. Low rpm has low velocity, ported head lower velocity overall. Longer duration lets us move events around more. Tuning these events is ideal though. Leaving them the same like Tony did is ok, you get a little earlier opening event from the longer duration, but it also adds some overlap where you don't want it, which is easily tunable with vanos but it needs a tune to adjust it.

So, would the biggest benefits come from better spool?
 

V8bait

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So, would the biggest benefits come from better spool?

From the duration alone? Yeah it can help spool, and can help high RPM power as well especially with headwork. Not to mention the advantages the higher lift has to increase flow in general. I don't see many downsides to cams on VVT cars since you don't really give up as much as cars with static cams. It's more work to tune cams on VVT cars though... well, more work to REALLY get them right. Getting them to work and make more power isn't difficult though, you really only need to change the events over like 4k rpm a little and make sure you're clearing pistons everywhere still. But to really optimize you'll need some dyno time.
 

AD-ENG

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High lift and low duration on a turbo engine is old school thinking, much like the people that still thing turbo cars should be 8:1 compression.

OE keeps the duration (and overlap) low on turbo cars because the turbos are small as fuck. Just about every stock turbo car out there has a emap to map ratio of 2:1 or more when pushed. You don't want your inlet air at 20psi seeing an open exhaust valve with 40psi backpressure behind it.

Fast forward to the ST setups we run (and other platforms) and now we see 1:1... maybe 1.25:1 depending. Now the head starts showing small characteristics of a NA car. We start using big cams to evac, build momentum, and fill the cylinder WITH overlap.

Also remember that lift is time.... a cam of .500" lift on a head that flow plataues at .400" still is beneficial. Why? Because the time is spends at the max flow .400" is greater than a cam with only .400" lift... Even with a greater ramp rate.

Side note for actual vs theory... the cams we run in the drag Hondas are similar specs to the ots NA cams, but we use them at 50psi and make 1300+hp on 2 liters. Food for thought