02sierraz71_5.3

iTrader: (2)

I milled my heads .050 which has turned out to be too much and I installed an aggressive cam. Ive had alot of problems with this current setup ie rockers backing out, excessively noisy valve train. And I recieved very little gains 30 rwhp.
heads: milled .050, 2" intake unshrouding, 5 angle job
cam: LPE gt2-5 222/222 .566/.566 I believe the lobes are comps xr

At first I had to short pushrods .735 so switched to .74 stock and alot less noise. I still feel something is off someone commented that my valves might not be closing all the way is there a way to check this? I have no experience with checking valve spring preload, could my preload be so far off that the valves arent closing?

Ive thought about shimming the rockers but dont know how much, but then adjustable or self adjusting rockers would be a better choice?

This is a 5.3 motor na in a truck. I know you guys arent particularly interested in truck engines but I thought Id check with the experts here.

white2001s10

iTrader: (4)

Well it's actually lifter preload you are measuring, and you'd need to put a dial indicator on the backside of a rocker to measure it.
The preload is how deep you are depressing the lifter plunger into the lifter body after all clearance is removed between the pushrod and the rocker arm.

Too much preload can take pressure off the seat and reduce the valve control a bit. The question is what springs you are running with this combo? and did you swap to different lifters too?
Some lifters like very little preload, and I too prefer to run minimum preload.
IMO adjustable valvetrain is superior for custom combos because you have complete control over the preload without swapping pushrods.

Your shorter pushrods would give you that much less preload with your non-adjustable rockers. If your cam is very agressive and you don't like the noise then you should consider upgrading to a performance lifter and adjustable rockers.
That's just what I'd do. Someone else may give you other workable ideas as well.

02sierraz71_5.3

iTrader: (2)

thanks for the input white,

the springs are comp 918's and the lifters are stock. Im seriously thinking of investing in adjustable rocker arms, but I would like to know if they will fix my problem and give me the gains I feel this setup is capeable of.

white2001s10

iTrader: (4)

what exactly is the problem? the noise, or not as much power as expected?
The power difference may not be pushrod/preload related at all.
Jump on a dyno and see if your power drops off suddenly at a certain RPM. That would be a sign of loss of valve control.
I doubt you're losing control of the valves with the 918 springs,
so you may just be looking at a tuning issue.

jd13

iTrader: (3)

I do beleive it is possible to run a thicker gasket to make up for some of the milled difference...

02sierraz71_5.3

iTrader: (2)

I only gained 30 rwhp the thing runs fine now its just Ive milled so much .050 that at 24 degrees i had pinging and had to back off timing. my compression ratio should be 10.4:1 so I cant figure it.
the dyno curves look fine and are what I expected for the rpms range and cam selection the only thing is the gain is minimal I should have alot more timing though. It could be my setup is fine I was thinking the valves werent opening enough but it could be I just cant add enough timing due to pinging because of milling so much. I really wish I could figure this out its driving me nuts and I need to eliminate some of the variables, If I could get race gas that would solve one problem and I could throw more timing at it.

white2001s10

iTrader: (4)

Do you actually hear spark knock? or you just fear what you see on scans from the sensors?
If it's actually knocking, then you just may be running leaner than what your engine wants. What is your wideband readings at WOT?

ssheets

iTrader: (1)

I can't help you as I know enough to follow along, but not to solve the puzzle...I do have a couple quick questins though as my 5.3 truck (Suburban) motor may be my next project.

What's stock CR on a 5.3?

.050" shaved off the heads and an agresse=ive cam...weren't you worried about piston to valve clearence??

I'm putting 5.3 heads onmy LS1 and with an F14 I was told not to take more than .010" off the heads. Now this is with 2.02" intakes and completely different pistons, but I'm still curious. Like I said, I may go for the 5.3 motor in the Suburban next. I figure some shorty headers, bigger valves and a nice cam (and springes of course) ought to wake that little mighty mouse right up.

It amazes me how that 5.3 throws that 6,000lb Surburban around.

white2001s10

iTrader: (4)

Well I've read some from your other posts to get a better idea of what's on your mind.
First, your valves are opening fine and it's not an issue of not enough preload.
Second you probably do not have too much preload making it out of range of what the lifter/spring combo can handle.

Piston to valve problem? I don't know, but you would've heard the valves hitting the pistons after first starting the engine... would've sounded a bit like a solid lifter camshaft. I doubt that happened, because I don't think you would've gained 30 hp after damage like that... though it is barely possible.
Bent valves would show on a leakdown test of cylinder pressure, so do the test to eliminate that possibility.

The shortage of power is pretty easy to see given you are running stock exhaust manifolds. Camshafts with extended duration and overlap definately do NOT like any backpressure in the exhaust. Backpressure will cause the early exhaust opening and the overlap period to work against you, and especially so at the low & midrange RPMs. This is exactly what you're seeing.
Get rid of the backpressure and you'll gain another 30 hp.

The pinging I don't know about for sure. If it actually exists, then I'd go with my first thought of it needing more fuel in the midrange RPM. Your truck is VERY heavy and will load the engine down tremendously (you only have the 5.3 liter) at the shift recovery RPM.

Another possibility with the ping or spark-knock (if it really exists) is a possible mis-match of your bore to your chambers. If you have a sharp steel edge of the bore hanging out, or the steel ring of the headgasket exposed to combustion, then it could be creating a hotspot which would cause detonation (not spark knock). Check your sparkplug insulators for spots.

Mirek

You milled .050 off a 5.3 head and are only at 10.4:1 ? Really?
How thick of a gasket did you use ?
What octane are you running? Does your manifold still fit properly/could it be leaking ?
Does it (ping/knock) do this both when the motor is hot and cold ?
Just trying to help figure this.....
Definatley uncork your exhaust though no matter what.

02sierraz71_5.3

iTrader: (2)

Thats what my machinist said could be wrong though I tryed figuring it myself but couldnt ever find out how much deck height I had with the piston tdc.
Im running 93.
It doesnt ping now but I have timing under 24 degrees.

strokedls1

iTrader: (1)

If you know the chamber cc and gasket bore and thickness you can calculate static compression accurately. I would start by doing a compression and leak down test. This would tell you if you have valves holding open a little. You really need to adjust each rocker individually so that it takes 1-1/2 to 2 turns to get 22 ft/lb preload. I assume these are stock lifters. Have to use the right size push rod with shims for the rockers to set it up properly. My 5.3L heads are milled that much and I had a hell of time with them on my 5.7 motor. I ended up losing a piston and rod from detonation. Compression was in the ball park of 11.8-1 and was supposed to be 11-1. I am still using those heads on my 422ci and it runs great with no leaking issues. If you have those heads milled that much I would think your compression is really much higher.

02sierraz71_5.3

iTrader: (2)

could I run two head gaskets to decrease compression? Or do they make head gaskets that have extra thickness? Id like to decrease the compression.

white2001s10

iTrader: (4)

if your bottom end is stock then just go by the factory spec on the deck height.

Gaskets are made in different thicknesses yes.