[nicserrentino]

Okay so I’m running into a weird issue with my 18 zl1. Let me first start by saying I had a failed oil pump that was replaced by Chevrolet in the beginning of the year. Also, my car is stock minus rotofab intake.

Okay so my issue: my car made 476/525 on the dyno
I was concerned because after looking online everyone else makes around 530+ as a baseline. The tuner said he thinks it’s just the dyno not being properly calibrated and that the car felt just as powerful as any other ZL1 he’s driven. So that was a bit of reassurance.

Fast forward a few days, they’ve gotten all these parts installed (cam, LTs, exhaust, upper/lower pulley, flex fuel) and the car has been street tuned. Tuner calls me and says the car felt low on power compared to other cars with similar builds so he did a compression test and noticed cylinder #7 was down about 50 psi compared to the others.
They pulled the heads and checked over everything with a scope, made some adjustments and came to the conclusion that lifters were the main culprit for this.
They got in touch with Texas speed, and they’re sending the morels lifters rather than the ls7 lifters.
In my head, even upgrading the lifters, the question still remains: why did it make such low numbers on a stock setup? And that hasn’t been answered yet.
Hoping to get any sort of input from you guys relating to this.
Also, they checked #7 piston from the under side of the motor and noticed no play so they don’t think it’s rings or ring land.

[nighttowl]

if it were a ring most likely the cylinder wall would have been destroyed or glazed over.
It is possible a lifter could have been holding the valve open.
On the dyno - I would see what others have dynoed on the same dyno / dyno operator.

Did the car feel slow to you on the day you dynoed it?

[nicserrentino]

The car never felt slow to me. However I’m not the one who dyno’d it. The tuner mentioned that it didn’t feel slower or down on power at all so he wasn’t concerned.

[nicserrentino]

Bump, no other thoughts on this?

[willzilla]

Can't really compare dyno numbers between different dynos, different dyno day conditions, etc, so, it's probably nothing.

[Spaceme1117]

Lazy tuners not calibrating the dyno. Why would you not take the time to calibrate the main tool you are using to tune a car?

[s346k]

a leakdown test should've been performed prior to disassembly. then there would be no question as to where it's losing compression. 50 lb is a lot and a lifter claimed to be the issue is suspect. bad lifters won't open valves, not the opposite. i'm already leery of this place.

if a lifter was stuck & hanging a valve open you would know it. it would be making engine noise accompanied with misfires & popping.

also have seen -first hand- an engine killed by detonation so bad it literally blew the ring lands off. i have pictures somewhere of rings hanging off the underside of the piston and the cylinder walls looked perfect.

edit: found some of them

[EDFHOBBIES]

Most of the time the lifter will have a hairline crack or be pitted and if nothing is visible it will not move through the bore easily. it will be harder seat or remove So did all that ck out?