I have a '97 A4 C5. Installed a Comp Cam 224/224 .567/.567 lifr LSA114. Have Cadillac Racing lifters (suppose to lessen the sewing machine sound), 7.425 push rods, Harland Sharp 1.7 roller rockers, LS6 ported intake.
After these mods were installed the sewing machine sound is louder than the stock valve train.

I used a stethoscope and the valve train sounds fine, the noise is coming from the injectors (30#) and the valve train through the intake runners and top of the LS6 intake. Would installation over the top of the intake quieten this noise?
Another question; is how come some engines with a bigger cam have less of a sewing machine sound? Is it because of the cam maker; isn't all after market cams grind by Comp Cams?
Also; is it true with a lift of less than 550 the sound isn't as loud?
I'm told that this is the sound after a after market cam is installed and just get use to it.
Thanks for any input.
Sleeper

A lot of the noise really comes from the injectors into the intake and why the 2008 LS3 for C6 was redesigned so that it now has a top hat that has foam in it to muffle the sound.

Its hard to say without hearing the noise but alumimum blocks allow more noise to be heard then when steel was used.

Depends on the CAM grind, the LSA and what type of overlap on how the sound is but as long as your sure the correct length push rods and rockers used then assume most noise is natural to the CAM design

Yes the injectors are loud and that is a great idea to have an insulated cover to help with the noise. I was thiking of insulating a cover and put it on the the top of the intake to see if that would help.
As mentioned I'm using 7.425 push rods is what is called for by the base circle measurment and 1.7 Harland Sharp roller rockers.
Long tube headers carries the noise also..
I'll get use to it eventually.

Thanks JR...
Sleeper

I do not use the rail covers the Corvette has because that traps heat under the cover which in turn adds heat to the fuel rail, injectors and the coils.

Without covers then at least some air movement helps pull some heats off those parts.

That is not good and causes more issues when engine is turned off the heat increases which cooks the fuel in the injectors and helps leave deposits so I'd rather have the noise.

After checking for the proper push rod lenght with a push rod checker. I needed 7.500 rather than the 7.450 PR I had installed.
So after installing the correct ones along with Yella Terra roller rockers the sewing machine is about the same level of a stock LS6.
It is clear that the noise is coming from the injectors.

Bottom line is when changing cam and heads, be sure to get to Comp Cam Push Rod Checker to get the correct push rods.

Deno