This is my 2nd set of heads on this car. My 1st set came from a vendor on the site and a intake port had a pinhole in it. The cam is a custom grind. I just recently got my 2nd set of heads back and put them on. This cam with the 1st set of heads it made 414rwhp at 6000rpm through my auto. I had a friend come over and use efi live and tune on the car a little add some fuel ect. According to his wideband I was NOT lean. I took the car to the dyno to see what kinda power I was at and I was just dissapointed. Somthing is going on. Their a/f is showing me extremely lean. It looks like its not getting fuel but its got plenty of fuel added into the tune. Another thing im confused about is the tune really hasnt been changed much at all when it made good power. I had my tuner take a little fuel out while I was running the car cam only waiting on my new set of heads. I then had a friend add some more fuel to it when the new heads went on. Why would the car make power then drop drastically then recover? We thought a fuel pump maybe failing. We hooked a fuel pressure guage up and the fuel pressure was about 56psi at wot. I changed the fuel filter as well. Does anyone see any kind of valve float in this graph? Im not to familure with what it would look like on a dyno graph then again why would it somewhat recover. Could anyone identify somthing possibly wrong in the valve train by looking at this graph? When I had a local machine shop install my springs I told them what the install height needed to be. If they messed up the install height could it cause almost a 80rwhp power loss? I've checked my preload several times its 1 1/2 turns at 0 lash. Also if the valve spring install height was wrong, would it mess with your preload any when checking it for pushrod length? I have the correct pushrod length. Im running Patriot double springs. I need some help with what to start looking into next. This damn car should be making more power than it was before



This is the dyno graph with my 1st set of heads stock auto trans slipping badly

 

bump any ideas?

 

well i have to say, neither of those graphs look right, i have never seen a graph that looks like one big wave up and down and up and down. But your most recent graph looks like you most definately have a problem somewhere. wish i had a graph on this computer of mine but it starts low and keeps climbing all the way to the peak of about 6300 with some very small dips on the way up. But i would start with the valve train, it has to be up there if you didn't pull the cam out again and nothing below the heads were touched. It sure as hell aint right though.

 

oh wait, i just figured out your problem, your dyno sheet has a mustang on it, that just fucked the whole thing up!

 

Theres a problem somewhere. Look at the a/f .The original tune that made good power has barely been changed. I had a little fuel taken out when i was running cam only then we added it back for the heads. Their a/f might be jacked up but the car is down on power majorly and its not a # guess you can feel it

 

i know how you feel, i pulled mine apart again cause i didn't run what i should have run at the drag strip. I put down 421 hp and only run a 12.6 and i was convinced something was wrong with it and, tore it down and couldn't find one thing. I now believe i need a driver mod and definately suspension since my car is a 1LE, not exactly made for the drag strip. Good luck with figuring out what it is, i know its frustrating as hell.

 

Well a few things could be culprit:

Where did your friend hook up his wideband?
Where did your tuner hook up his wideband?

When was the wideband last calibrated? (for both)

What were the weather conditions for both days? Similar or vastly different?

Your friend used EFI what did your tuner use (this shouldn't be an issue but still worth factoring in)

 

Get a dial indicator on the rocker and check preload that way.

 

I think 1 1/2 turns is too much preload and may be hangin the valves open when the lifters pump up. This would cause a major loss of power. You should have between .060-.080 preload after zero lash, which is between 1/2-1 turn.

 

bump...

 

all the hydraulic lifter preload #'s I've ever seen are 0.020" - 0.060" of preload and that is usually 1/2 turn to 1.25 turns, but that highly depends on the thread pitch of the rocker stud, and i would also imagine the brand of lifters you use might want more or less preload.
I never really checked actual preload for an LS1, and I have the service manual, but 0.060- 0.080 seems too much to me. And the more preload you try to go, the greater the risk the valve won't fully close.
The best way to do the preload on adjustable rockers is with a dial indicator. I would shoot for 0.030-0.040" depth cold, this is on chevy boat motors they're all the same, but I would doublecheck the amount of preload you should have. Then, remember the number of turns you did on the rocker nut from zero lash with the dial indicator then do all the rest like same number turns.

 

LS motors with stock lifters can accept up to .100 preload with no issues. .060>.080 being a good medium.
Aftermarket depends on brand name.