Help me understand cam timing (LNF)

[Baldturbofreak.com]

Advancing the exhaust cam would take high(er) cyl pressure and provide more impulse for the turbine to use.
To prevent a negative impact on power one would wand to delay the intake opening until the piston is on it;s way down. Preventing high TIP/end gas in the chamber from forcing intake runner reversion.

Id like to see Turbine inlet pressure on your setup.
Buy an Autozone oil pressure guage with large coil of copper tubing. drill & tap your elbow pre-turbine.

[Baldturbofreak.com]

Buy engine analizer pro and do lots of iterations.

[boostking]

so your saying I should only advance the exhaust cam on the top end?
you recom retarding the intake cam?

the sooner you open the intake the longer it has to fill the cylinder. so how do I know whats to much or not enough.

I was told the sooner you open the exhaust the sooner you can spool the turbo.

should cam timing be the first step in tuning? I have done the air load table to match the way the turbo spools so it doesn't set an under boost code but it does nothing as far as power output on an aftermarket turbo.

my car with fuel and timing is doing 410whp. but if there is way to get more i want too.

BTF if you have some timing I would love to talk with you in a pm about my tune and what you think it will take. all credit for your help will not go unknown.

[boostking]

Wow two additional degrees was enough to throw a code - why have +/- 25* adjustment if it's going to throw codes? What was the maximum value in the table? I understand if you don't want to post up a tune file, but it would be helpful.

As far as spool up, i know hotter exhaust (and hence faster moving) is going to get you a quicker spool. Maybe you could retard timing in small amounts around your boost threshold (keeping in mind that we have main spark tables referenced to cam position). and see what it does for spool up?

I read a lot of your post on CSS.net. It's good you came here becuase there is less BS - and a lot less people trying to convince you that they know all about tuning.

here is a tune file let me know what you guys are thinking.

[oldskool]

How does it do for knock retard? You've added a LOT of timing up top, more than i've ever seen with this system.

As far as your main cam tables (warm), what is the reasoning behind changing the lower load columns say 40% and below? You don't have boost there right? I'm just curious.

[shabby]

You doubled the timing? Heh come on...

[Baldturbofreak.com]

No Im saying that you should advance the exhaust cam when in low rpm/around 100-120% loading where you arnt making boost. Then quickly ramp it back tward near stock timing as pressure (loading) rises.
At the same instance retard intake cam timing to prevent runner reversion.

At the very same load cells play with ignition timing to achieve the highest cyl pressure. That also means the greatest blowdown pressure and best spoolup.

Start by going back to stock on the cam timing. everywhere. Then I will send you specific regions to alter and log for me.

also reset the desired airload table back to stock.
you prevent the underboost code using the max air torque table, we'll tune our intial boost curve there.
Also igintion timing shoud be returned to stock.
This will give me some level ground to work with.

Just as an FYI, beyond 12-13deg @ 240-260% load although it wont cause KR, it also wont make any more power. 13 deg is about the sweet spot for ignition lead on this head/piston combo.

[shabby]

also reset the desired airload table back to stock.
you prevent the underboost code using the max air torque table, we'll tune our intial boost curve there.

Thats a much better way, getting the desired airload table just right with a big turbo will drive everyone nuts.

[boostking]

No Im saying that you should advance the exhaust cam when in low rpm/around 100-120% loading where you arnt making boost. Then quickly ramp it back tward near stock timing as pressure (loading) rises.
At the same instance retard intake cam timing to prevent runner reversion.

At the very same load cells play with ignition timing to achieve the highest cyl pressure. That also means the greatest blowdown pressure and best spoolup.

Start by going back to stock on the cam timing. everywhere. Then I will send you specific regions to alter and log for me.

also reset the desired airload table back to stock.
you prevent the underboost code using the max air torque table, we'll tune our intial boost curve there.
Also igintion timing shoud be returned to stock.
This will give me some level ground to work with.

Just as an FYI, beyond 12-13deg @ 240-260% load although it wont cause KR, it also wont make any more power. 13 deg is about the sweet spot for ignition lead on this head/piston combo.

thank you very much!
I will set cam timing back to stock and the air load table. I didn't know the max air torque table is what stopped the underboost.

the car loves the timing. every 2 degrees was almost 10whp. i have no knock to speak of.

also that tune was not intended for anyone to use. so please dont as there are many things within that tune that are diff. on my veh. anyway thanks BTF and I hope to here from you soon.

[boostking]

How does it do for knock retard? You've added a LOT of timing up top, more than i've ever seen with this system.

As far as your main cam tables (warm), what is the reasoning behind changing the lower load columns say 40% and below? You don't have boost there right? I'm just curious.

trying to get the turbo to spool sooner. just doing testing. the cam timing is new to me...

[SSpdDmon]

This was my input:

http://www.hptuners.com/forum/showth...120#post155120

Are we talking the same thing here?

[oldskool]

I read your post there and it was informative. But some things still did not make sense, like the magnitude and direction of the numbers in the tables, and the numbers you get in a log file.

[SSpdDmon]

I read your post there and it was informative. But some things still did not make sense, like the magnitude and direction of the numbers in the tables, and the numbers you get in a log file.

Make sure you have the right visualization in your head. Exhaust valve events happen just before intake valve events. Don't think intake first. In between them, the piston hits the top of it's travel. So, as the piston is traveling up, it's pushing the last cycle's biproduct out of the exhaust valves. As it nears the top, the valves close. On the down stroke the intake valves open and fresh air is drawn in.

Simply put - as RPM's increase at WOT, the idea is to advance the intake cam timing....or make the valve events happen sooner. Inversely, the same goes for the exhaust cam timing. As RPM's increase, the idea is to retard the timing....or make the valve events happen later. That's what the GM engineers did if you look in the last column of those tables. Down low, the valve events are further apart from each other to maintain low-end torque and throttle response. But as RPM's rise, they come closer together as this helps to generate more power on the top end.

[cobaltssoverbooster]

uh no turbo cams are a little different, turbos dont like a shitload of overlap thats y all the overlap is down low where there isnt any turbo gain and the motor makes all motor and only motor power, when you get turbo gain they back the over lap off some so boost pressure can be made and obtained. you are backwards its ok. think of this in overlap both valves are open thus air flows in and out, but if the intake valve is open too long in overlap then the intake valve isnt closed long enough to allow for pressure to build up. turbo cams will fuck with you after you come from all motor cams lol had me for a bit too.

[SSpdDmon]

uh no turbo cams are a little different, turbos dont like a shitload of overlap thats y all the overlap is down low where there isnt any turbo gain and the motor makes all motor and only motor power, when you get turbo gain they back the over lap off some so boost pressure can be made and obtained. you are backwards its ok. think of this in overlap both valves are open thus air flows in and out, but if the intake valve is open too long in overlap then the intake valve isnt closed long enough to allow for pressure to build up. turbo cams will fuck with you after you come from all motor cams lol had me for a bit too.

I was thinking about this a little further and I still don't understand what I'm missing. The main reason I'm confused is you say more overlap down low is better when the turbo isn't working. At that point, I'd argue that down low (i.e. below 2500rpm), the engine doesn't like overlap either.

At least, my cam experience with LS1's would suggest that overlap is a major PITA at lower speeds. That's why those cars drive so much smoother down low with the stock cam vs. the bigger ones seen on the aftermarket, which have more overlap. So, to say that more overlap down low is better is quite confusing.

[shabby]

I think in one of the lnf engine spec sheets it said that at low rpm a certain percentage of air slips through the valves on purpose to help spool the turbo.

[cobaltssoverbooster]

sure it doesnt like it cause it has plenty in it already and yes you are right on they dont idle with large overlap cams the events become rough down low. but the overlap the stock cams have designed in them down low is enough already, but up to it flows too much air causing failure spool times which is y its backed out and the numbers change showing they are moving the overlap out to help spool times. it takes overlap down low to move lots of air to get the turbo to spin but once it gets goin it needs to be reduce so pressure can start being made then we adjust how much overlap we have in it to maintain maximum flow we can get from our turbo while maintaining pressure at the same time. thus advancing the intake 3 deg up top 5-6k is to help with flow but also above 3k rpm that gets the air flow up and helps with spool time. i do understand overlap is bad for idle to 2500 but im calling down low 3k since pulls and runs are always higher than that. none of that rpm needs adjusting just 3k and above.

[GTPprix]

Hrmm I started my pulls at 2000 RPM

[ChevyHighPerformance]

Ok, could someone look at the attached spreadsheet, mainly the section in red text. Does this make sense, and is it theoretically correct if you assume the vaules in the HPT cam tables are one tenth of a cam degree?

I want to be able to quantify the overlap in any given cell to make adjustments that mean something to me.

Thanks to the pro's here for your help/advice.

I think the overlap that you are calculating is the change in overlap about the base cam. The other parameter is the effective amount the cams are advanced or retarded.

[cobaltssoverbooster]

i cant start at 2k my clutch is f'd coming up on rivets soon i bet. spec on the way soon though.