DMax cams

[Redbone]

Can someone post the stock specs for an LBZ cam? Lift, duration, duration @ .050 (or whatever), and lobe center. Where is the cam timing set on the stock LBZ (Intake CL relative to TDC)?

This is my 3rd DMax, but I'm still a newb to the land of positive pressure. My kneejerk instinct says that aftermarket cam design should be relatively simple for these trucks. Lots of intake lift and duration, make sure V/P clearance is good, minimal overlap, ...

Oversimplified? Trippin or anyone else have any good basic cam info. Thanks from the land of negative manifold pressure!

 

[Tony Burkhard]

I dont think you will find specs from the big cam guys.

 

[McRat]

One thing you need to remember when looking over the Dmax specs, is that it's a 4v engine. The valves are very tiny, so the numbers look like the cams are smaller than they are. .400 lift is alot on a Dmax, IIRC.

No, specs are not published. You pretty much have to go with the experience of the shop.

 

[Redbone]

I understand not publishing aftermarket specs, that's why I was looking for the stock LBZ specs. Just trying to get a feel for valve event timing in these motors.

Right now I'm really intrigued with how cam timing is employed in the turbo diesels vs. how we've historically spec'ed cams for the alcohol engines.

 

[MAXLLY]

Guy has what you are looking for.

 

[malibu795]

stock dmax cam is 176* @.050 390" lift at the vlv

i have seen a comp cam spec close to ~.490 at the vlv cant rememeber the duration

as pat said dmax is a 4 vlv engine. so alittle here and there is alot more then compare to a std 2v engine

 

[maddogg101920]

http://store.summitracing.com/partdetail.asp?part=CCA-132-500-12&autoview=sku
http://store.summitracing.com/partdetail.asp?part=CCA-132-501-12&autoview=sku
heres 2 i found on summit, from comp cams.

 

[malibu795]

they have a third one some were...

Basic Operating RPM Range: 1,500-4,200 197*/202* @ .050, 0.450/0.450 lift
109* LSA
and the
second one
Basic Operating RPM Range: 1,200-3,800 185/188* @.050 .420/.420 lift lsa 108*
both run a lash of .010"

think i dont like about these is the narrow LSA 108 and 109* but that is tipical of the cams that i see form comp narrow LSA are common with them


i would take guys cam over these any day.. narrow LSA is IMO a bad thing for turbo engines

 

[Trippin]

stock dmax cam is 176* @.050 390" lift at the vlv..........

My cam doctor shows it pretty close to the above on a 108 L/C

 

[malibu795]

thanks Guy... didnt know stock was 108*

i still think that they should be at least 110* :rofl:
but im not a cam guy :baby:

 

[Redbone]

Hey, now this is some good stuff! I'm with you 'bu, my gut would never have guessed a 108LSA. I would have thought more than that, but what do I know. This is gonna take some thinkin.

 

[McRat]

Just thinking - Since we have a relatively high drive pressure, leaving the exhaust valve open past TDC probably doesn't do alot. If the exhaust were to be "tuned", I'd think the low pulse should occur fairly early. By the time the piston is slowing down near TDC, the actual gas velocity going out the exh valves should be slow; high drive pressure (backpressure), high temperatures, low chamber volume, low RPM, all push the velocity down.

Opening the intake valve early would create EGR under high back pressure, which occurs mostly as a function of RPM for us. The higher drive pressures can allow exhaust gases to remain in the chamber instead of being flushed out by the intake charge. As RPM goes up, we might actually want LESS overlap, not more.

Now when to open the exhaust valve? Probably early. To get momentum going for the gases for high RPM operation, and to allow for possible exh system pressure wave reversion scavenging, getting an early start would seem to make sense.

For the intake closing? Leaving the intake open quite a bit past BTC, would make more sense the faster you spin. We spin 50% higher than design RPM, allowing intake charge momentum to continue into the compression stroke sounds good. Will make for hard starts though.

I could be wrong, but I'd still want to look at high LSA, high duration cams for high RPM use. Less overlap than even a stock cam.

Problem is, until someone gets an engine dyno for rent that will do Dmaxes, this is very hard and very expensive to learn.

 

[mytmousemalibu]

Hmmm, thats some overlap!

Me too on the LSA! Woulda thought more LSA in there 4 sure!

Wonder how and what way this affects combustion events,egt,drive psi, ETC.

Great thread too!

 

[malibu795]

i think im tracking you pat..

at least on the the LSA part.. making it 110-114* IMO do two things.. increar clean air charge in the cylinder and rais dynanamic pressure..
2 drive pressure would be higher as well.. one waht to thwart that is increar exhasut pipe dia

if that make sense at all..................

 

[Redbone]

Just thinking - ... The higher drive pressures can allow exhaust gases to remain in the chamber instead of being flushed out by the intake charge. As RPM goes up, we might actually want LESS overlap, not more.

Now when to open the exhaust valve? Probably early. To get momentum going for the gases for high RPM operation, and to allow for possible exh system pressure wave reversion scavenging, getting an early start would seem to make sense.

Which is what exactly what I believe makes cam design interesting about these things. Exhaust valve timing in particular, because we are exhausting
to a positive pressure plenum essentially because of the charger drive pressure. The big question becomes at what point in the exhaust stroke does cylinder pressure equal plenum (drive) pressure.

Along those same lines, since we are not exhausting to atmospheric pressure, how effective is pressure pulse management in cam and header design? Cool stuff!

 

[Redbone]

edit

 

[Brayden]

From the looks of the factory exhaust system it isn't very important to them.. But we're way out of factory design intent.

Along those same lines, since we are not exhausting to atmospheric pressure, how effective is pressure pulse management in cam and header design? Cool stuff!