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LS7 why so noisy?

 
Old 10-16-2018, 08:07 PM
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froggy47
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Default LS7 why so noisy?

This is not about the heads problem, just a question I have been curious about since my LT4, LS6, and now LS7. Here are some wiki specs on my 2002 Suburban motor:
LM7[[url=https://en.wikipedia.org/w/index.php?title=LS_based_GM_small-block_engine&action=edit&section=7]edit]
The Vortec 5300 LM7 (VIN code 8th digit "T") was introduced in 1999. It has a cast iron block and aluminum heads, and can be considered the "garden variety" version of the Generation III V8s.

The 1999 LM7 engine produced 270 hp (201 kW) and 315 lbft of torque (427 Nm).

The 2000-2003 engines made 285 hp (213 kW) and 325 lbft (441 Nm).

The 2004-2007 engines made 295 hp and 335 lbft of torque.

The stock cam specs @ .050 lift are: 190/191 duration, .466/.457 lift, 114 LSA, 112/116 Timing

LM7 applications:With 160k miles heads never off it's a very "quiet" v8 compared to my Vettes.

So why are the Vette motors sounding like big sewing machines?
Is it the alum block that magnifies the noise, the compression ration being higher? The heads themselves "thinner" ? I get it why OHC engines sound different, or Subie flat 4's, Porsche, and so on. But what makes these so loud & ticky? My truck's not like that. Theories ARE welcome or if you are a builder who actually knows please share. Is it louder fuel injectors due to need for increased fuel?

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Old 10-16-2018, 09:05 PM
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CorsoZ06
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I am curious to read responses from members much smarter than me when it comes to motors and valvetrains, etc. I think the injectors on the LS7 is a big part of it. I also think the lack of sound deadening material, the carbon fiber fenders and fiberglass hood all do a poor job of masking the sound of an already loud motor, so it makes it seem that it is even louder than it really is, comparatively speaking.

I have the same 5.3L motor in my '00 Silverado that you have in your Suburban. I have owned it since new and with 257K miles, and dino oil every 7-10K miles for probably the last 100K miles, it still sounds smooth and quiet. I currently also have an LS3 in my SS and it is also very quiet. I have had an LS6 and an LS2 in the past...…….well, you get the point.

Interested in hearing theories and/or reasons as to why the LS7 is so noisy.
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Old 10-17-2018, 01:00 AM
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froggy47
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OK good, there ya go, so somebody's not going to tell us we just lucked out with quiet motors on the trucks.


Last edited by froggy47; 10-17-2018 at 01:01 AM.
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Old 10-17-2018, 04:31 AM
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redbird555
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Mainly the block material. I have owned pretty much every na ls made and the aluminum block motors are always much louder than their iron counterparts. Aluminum expands more as well so tolerances will get tossed around more in the alum block as well

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Old 10-17-2018, 09:48 AM
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Block and cam ramp rates with stock lifters & trunnions.

Swap the lifters for high quality units and it quiets down, run che bushings in the rockers and more noise reduction. You could also use the go pedal and wont hear anything 😂
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Old 10-17-2018, 10:09 AM
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Some of it is the car the LS7 was put into - the Z06 was stripped for weight of a lot of sound deafening materials and such. Plus, unlike in your truck, you're also sitting a lot closer to the motor, as well in the Corvette. The LS6 in the C5 Z06 used to drive my Dad nuts even back when it was new, that sewing machine sound common between 1,600 and 2,000 rpm. Same thing for the C5 Z06, it was stripped down for weight of a lot of items that in the other standard Corvettes, remained in the car to improve and reduce road noise.

That said, the combination of my TSP custom cam and lobes designed for LS motors, Johson 2110 SLR lifters adjusted for .039" of pre-load on TSP 7.775" PR's, (much less than OE GM specs on 7.800" PR's and .100" to .120" of preload from the factory,) coupled with the CHE trunnion kit, really went a long ways to reduce that famous sewing machine sound. The Moldstar 90 valve guides probably didn't hurt that equation, either. Don't get me wrong, the sewing machine sound is still there but it's not near as prevalent as it used to be.
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Old 10-17-2018, 11:11 AM
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CabronZ06
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My engine is pretty quiet.. It has 40K on a 2011 Z06 . I can't hear anything outside but I do hear a faint sewing machine tick noise when Im driving.
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Old 10-17-2018, 11:37 AM
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Mine is quiet as well even with the hood open. Some injector noise with the hood open but even that is pretty quiet compared to other cars.... 2008, 22K miles, all stock.
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Old 10-17-2018, 01:42 PM
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z06clif
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I have been told by mechanics ...its the injectors

Clif
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Old 10-17-2018, 03:45 PM
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LS7s are female. A bit whacked in the head(s) and never quiet . . . .



j/k
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Old 10-17-2018, 04:53 PM
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Mine is loud, no idea why. PRC 285's with LS7 lifters.
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Old 10-17-2018, 06:10 PM
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I get why the valvetrain is noisy, being an OHV pushrod motor. This is the first one I've owned too, the Z06 has always been my dream car. But I never expected it to be this loud, that ticking would be a serious worry if I heard it in any of my previous cars. Actually when I first got my Z06 I thought for sure the heads were screwed, since these forums can really make an owner paranoid about the issue. So I got the heads rebuilt and a cam at the same time, and...the noise is even louder.

For those that say it's the injectors, it is most definitely not them.
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Old 10-17-2018, 06:25 PM
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I have a feeling the tap noise may be caused from cyl 1 and 3 being so close together in their valve events and firing all while being directly beside eachother. This has to make a louder noise than the other combos and thus the famous 1800-2000rpm ls engine tap.

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Old 10-17-2018, 11:51 PM
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I don’t know but add a big cam and headers and it sounds really bad under the hood. I would think sometimes something has to be f***** up.
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Old 10-18-2018, 02:16 AM
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I was thinking that too. Injectors.

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Old 10-18-2018, 07:54 AM
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In my experience, the quieter cars I've heard were the ones that actually took the time to check push-rod length accurately, and not just go by some package or forum suggestion. While I am guilty myself of measuring and buying 8 push-rods of the same length because they fit within tolerance, ordering custom length push-rods for each valve is ideal and would greatly quiet the valve-train.
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Old 10-18-2018, 08:13 AM
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Yessir! Its not injectors.
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Old 10-18-2018, 08:21 AM
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My 29K mi 08 H/C/I/E Z06 isn't loud at all... in terms of ticking.. My valvetrain is actually pretty quiet. My 07 TBSS w the LS2 is also nice and quiet even with 103K... Just picked up an 01 Formula Firehawk (LS1) that I can actually hear some intermittent tapping. Typical for the 01-02 4th gens.
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Old 10-18-2018, 11:32 AM
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AzDave47
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Originally Posted by Apocolipse View Post
Block and cam ramp rates with stock lifters & trunnions.

Swap the lifters for high quality units and it quiets down, run che bushings in the rockers and more noise reduction. You could also use the go pedal and wont hear anything 😂
I may be able to comment on this next week when I get my car back from CPR. It is having a forged bottom end done, but also Johnson 2110 lifters and new pushrods. The original stock engine and then with HCI and new OEM lifters/pushrods was still noisy.
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Old 10-18-2018, 11:40 AM
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Apocolipse
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I found johnsons are quieter at the top of their tolerance (0.045") vs bottom (0.025") preload wise.
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