4.8 with a big cam. Any hope?

[gmmastertech1]

Hi, I was brought in a 2007 Silverado 4.8 that another tuner messed with and for whatever reason, changed it to SD 2 Bar OS. There was no VE table populated, all 0's. Thanks to Schpenxel, he sent me a VE table to at least start with. I had to really raise the min. airflow and startup airflow. I found a happy medium for timing at around 20 degrees in the lower regions before the pcm started to lower it. It will start and is able to drive now. Barely.

It is very low on power and has almost no power brakes. The map values are too high because the engine lacks vacuum. The cam specs are 275/283. 226/234 @0.50 duration. 525 lift with 109 lobe separation. That puts it a 61 overlap! The engine has a cold air intake and 1218 valve springs nothing else. Look at how jacked up this VE table is! This was after multiple writes and rinses, just to get my fuel trims from -26 to positive 10 for now.

I guess I'm wanting to know, is there anything I can do to make this cam work for him, or is he going to have to change the cam? He admitted it was bought online and it's possible the grind is wrong. I just find this difficult with the map values so high. I'll be honest , I'm fairly new to tuning! I'm a master GM and ASE tech by trade, but just unsure about tuning this. Any hope? Thanks in advance!

Zornes 07 4.8 71643573 base air high, LH spark, Rewrite stock, VE table populated.hpt

Zornes 07 4.8 temp. drive attempt 71643573.hpl

[5FDP]

Are you trying to tune the VE with the MAF still active in the tune?

Because if you are, that is just going to screw you up. You need to fail the MAF to tune the VE correctly.

[gmmastertech1]

Thanks for the reply. No, I had it failed while initially tuning the VE. It was nuts, showed -26 fuel trims still after probably 7 writes. Finally started coming down and swinging the opposite direction. Once I had it close, I re-enabled MAF and LTFT. Driveability is terrible. I'm sure it's a multitude of things on my end, I've never really tuned to compensate for this big of a cam with no other mods to help it. It feels like it needs a 3000 stall

[Paz]

Not sure if it's your issue right now but regarding idle tuning i found this thread to be a huge help- http://www.hptuners.com/forum/showth...ht=idle+tuning

I've got a cam with a fair bit of overlap and it idles fairly well up there in the MAP kpa as yours does.

[schpenxel]

Leave the MAF off

[gmmastertech1]

Well, for kicks I brought my MDI to my home shop and returned the OS back to stock. It did not charge me another license fee! I figured I'd just start from scratch and leave the VVE table alone to see where it was once it started. I guess I'm having trouble wrapping my head around this. A guy puts in a bigger cam and cold air intake:
This truck won't even start without almost flooring it. So, I increased the base running airflow, the idle spark, startup airflow. I went in 10% increments till it finally started and idles without throttle. Very rough idle and if you blip the throttle, it dies. Not sure how to adjust that. Also, if you throttle it fast, it backfires through the throttle body. I don't know if I should scale down the VVE table in the idle regions to lean it out.
I'm not sure what all I'm missing, I know there are people out there with this size cam driving fine, but this thing is terrible. Sorry for the noob questions and assumptions. All help is greatly appreciated.

[5FDP]

Hopefully the timing marks are all right and he degreed the cam, stuff like that can could maybe cause backfires through the intake. Also if the intake tube is bigger or the MAF sensor is in a completely different place in the intake tubing, that is just going to make the starting and idling worse on a non tuned vehicle.

If you have a wideband, then yeah go right ahead with taking fuel out if you think it needs it. I'd just start from scratch again, disable the MAF and start tuning the VVE with either a wibeband error or the LTFT + STFT.

[gmmastertech1]

Well, I turned this vehicle back to the customer. I spent countless hours adjusting tables and nothing I can do will drop this map value down from 71 Kpa at idle! It either has too long pushrods, cam is degreed wrong or ground wrong. I'll update this thread once I find out what it was from him.

[mowton]

Well, I turned this vehicle back to the customer. I spent countless hours adjusting tables and nothing I can do will drop this map value down from 71 Kpa at idle! It either has too long pushrods, cam is degreed wrong or ground wrong. I'll update this thread once I find out what it was from him.

Vacuum just wasn't right.....either cam or some internal vacuum leak

Ed M

[Russ K]

That cam has 12* valve overlap @.050 lifter rise. Wrong cam for a 4.8 in a heavy truck. 71 Kpa idle sounds right.

Russ Kemp

[bloodcamarosexmagic]

Well, I turned this vehicle back to the customer. I spent countless hours adjusting tables and nothing I can do will drop this map value down from 71 Kpa at idle! It either has too long pushrods, cam is degreed wrong or ground wrong. I'll update this thread once I find out what it was from him.

Hello! Did you ever talk to the customer to find out what he did to fix whatever is going on? My little brother just put this same cam (Howards Rattler) in his 4.8 with long tubes, cold air, and 60lb injectors. I got it idling and driving ok in speed density but it just has no ass behind it at higher rpm. It's at about 310 flywheel hp/tq with 28 degrees in it. Maybe I just need a ton more timing but Idk? Thanks!

[5FDP]

It's not a good NA cam on such a small engine. You need more cubes to make such a massive camshaft work.

Read the post above yours, it says the same things.

[kingtal0n]

that cam plus about 20psi of boost should do it

thats probably going to be my next combo style in facts, truthsies 4.8 + 224~/228~ @ .050 under .550 lift 110-112lsa, some 1218's and just over an extra atmosphere, spin it to 7

I am veru excite, most plaze

[Ainttucinaintfu*****]

I?m personally running the Howard?s rattler cam in my 2010 Silverado 4.8 gen 4 and my truck lopes really nice and doesn?t chug like a lot of other peoples do. I don?t have much low end since I did a vvt delete but definitely got good strong pull around 2400+ rpm. My tuner had no problem with my setup but he wanted me to get a BTR like everyone down here runs in trucks but I wanted different and that is what I got and everyone always asks me what cam I?m running so I know that it?s music lopes to peoples ear.