Mark A. Rogalski

iTrader: (1)

Any idea on what's going on here? The car seems to have steady power now..but less of it after the install of Crane 1.8's, Crane springs, Titanium retainers. Has LT's and true duals, everything else stock.

glennster

iTrader: (1)

Whats the A/F ratio? My car fell off at 5500 and was pig rich.

QuietTahoe

I'd recommend checking your lifter preload. The rockers themselves are not going to cause valve float. I suspect that you don't have enough preload. Those rockers have instructions on preload adjustment that should result in 1 3/4 to 2 turns of lifter preload. Did you buy the entire rocker kit with the 7.250" pushrods? If you try to run the stock 7.400" pushrods, the rocker geometry will be all screwed up and they won't have the proper lift rate. Also, been my experience the LT's necessitate some tuning due to o2 sensor placement! Hope this helps!!

Mark A. Rogalski

iTrader: (1)

Yes sir, bought it all, pushrods included. The shop that did it knows the Vinci guys well. They knew about all those "damn" steps" to adjust them correctly.

Adrenaline_Z

I disagree.

A higher rocker ratio ramps the valve faster making the effective mass of
the valve heavier due to velocity.

Pre-load isn't going to cause float. RPM, valve spring pressures, valve train mass
are more to blame.

Mark A. Rogalski

iTrader: (1)

Could it possibly be "excessive preload'. I noticed for the first time ever some backfiring after throttling it a little inside my garage. It's NEVER done that before.

Adrenaline_Z

Incorrect Pre-load will cause power loss if that's what you mean.

I wouldn't attribute valve float to incorrect pre-load...I would attribute
power loss to incorrect pre-load.

Who installed the camshaft and set the lash/pre-load? DId you change springs,
or shim the current springs to get correct open and seat pressures for the
new 1.8 ratio rockers?

Mark A. Rogalski

iTrader: (1)

I had an OEM rocker arm loose its bearings and decided to just have the top done with all Crane products (rockers, pushrods, dual springs, tit retainers, guides). There is no new camshaft, it is the OEM. www.xmsengineering.com did the work this last week.

Everyone, thanks for you help on this, I really mean that.

Here is the car:
http://www.ls1.com/forums/showthread.php?t=542932

QuietTahoe

1.8's will require less seat pressure due to the larger mechanical advantage, but seat pressure should be at least 110# which is higher than stock ( remember this is a stock cam) In 33 years, with thousands of dyno runs behind me, I have seen improper preload (not enough ) lead to valve float because all pushrods flex and the lifter will pump up (as much as it can to take up the valve train separatin before the plunger hits the snap ring) and now you have an essentially solid valvetrain without clearance ramps. At high speed this will aggravate valve train separation. Too much preload can cause the valves to hang open after operating temp is reached but that shouldn't be a problem with an aluminum block and heads. It is with an iron block and iron heads.

Adrenaline_Z

When the pushrod flexes, it reduces the overall length. THe lifter compensates to take up slack.

This would happen after the lobe peak.

During the ramp up, the slack is taken up by the load of the spring.
Unless there is an oscillation during valve closing, there should be no pump-up
event. That would lead to spring pressure issues again.

If the springs are weak, at fast RPM, the valve jumps off the peak of the
cam lobe. This is normally when the pump-up occurs (weak open pressure).

vettenuts

iTrader: (4)

Do you have a dyno of before the rocker installation? I am curious about your exhaust system. How well do those BMW mufflers flow? Guess I am just wondering if there is more than the rockers that might be an issue.

Mark A. Rogalski

iTrader: (1)

Those mufflers are for a 370HP 12 cyclinder BMW 85o and aredesigned to increase flow over OEM mufflers. Have them on my other car. Basically, you can see right through them.
No Dyno before.

mimic42100

I am by no means an expert..but i'll throw this sudgestion out there.
Fuel pump. MY dyno sheet drops at about 5200 when the pump gives up.
Just throwing out ideas =)

vettenuts

iTrader: (4)

If you know the Crane installation was the cause of this problem, I would opt for a re-adjustment of the rockers. You have the recommended springs, rockers and push rods so this seems like a logical way to proceed unless you have other suspicions on the car. How is the fuel filter?

Dustin Butts

iTrader: (5)

Hey Mark,
Did you ever find out the problem? Please share....

Mark A. Rogalski

iTrader: (1)

I have it going in the shop Friday to change out to a SLP LS6 intake and politely talk the shop into relooking at the valve train adjustments at that time.

Let you all know next thursday when I am back in town and pick up the car.

vettenuts

iTrader: (4)

I am curious as well as the Cranes on high on my mod list and you are the first that I have seen that apparently have some problems with them.

Good luck.

Gman2002Z06

I'm running the Crane 1.79 accelerated lift rockers with my set-up and they work perfectly up through 6800 rpms...So, unless they didn't get the preload set properly, I would not blame the rockers...

I measured each rocker preload as I went through the 8 hour procedure and ended up with approx. 0.090" of preload after completing the procedure...

And, as was mentioned earlier...Are you on the stock tune still...With the LT Headers and the higher lift rockers, your A/F ratio may be way off and that power drop may be a combination of KR, timing and A/F being off for your set-up...

Peace...Gman

mrr23

iTrader: (3)

the rockers aren't wrong for his setup. i have the same vinci/crane dual springs, titanium retainers, pushrods, and 1.8 accelerated lift rockers with the stock cam as well.

here's my before and after dyno. it's not valve float, too much spring pressure, or rockers too heavy. it's just plain stock cam petering out.

and the wife's car made more power before the rockers that his did after he put the rockers, LTs and dual exhaust. at the time the wife's dynos was run, all it had was lid, filter, MAF ends, bassani 1 3/4 optimum length headers, hi flow cats and borla 3" catback and on stock tune. and to boot, her's is an auto with stock converter. so, it should be lower than his. seeing that his is a manual. her car also has about double his miles 60K at that time.

so. i'd say he needs to look elsewhere.