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Comp QXI Lobes

General engine tech -- Drag Racing to Circle Track

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Orr89rocz
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Re: Comp QXI Lobes

Post by Orr89rocz » Wed Mar 14, 2018 12:33 pm

Imo its the valve motion. Faster lobe faster valve motion

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Re: Comp QXI Lobes

Post by CGT » Wed Mar 14, 2018 12:35 pm

Orr89rocz wrote:
Wed Mar 14, 2018 12:33 pm
Imo its the valve motion. Faster lobe faster valve motion
So, valves hitting seats?
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Re: Comp QXI Lobes

Post by Orr89rocz » Wed Mar 14, 2018 1:55 pm

Its everything. Lifter sliding thru bore faster, valvespring compressing faster, etc it just has a different sound i think. Not sure if the seating velocity is changing, and i hope its not too much or else it could be hammering the seats harder

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Re: Comp QXI Lobes

Post by groberts101 » Wed Mar 14, 2018 2:15 pm

Orr89rocz wrote:
Wed Mar 14, 2018 1:55 pm
Its everything. Lifter sliding thru bore faster, valvespring compressing faster, etc it just has a different sound i think. Not sure if the seating velocity is changing, and i hope its not too much or else it could be hammering the seats harder
I concur. Depending on how aggressive the lobes are to begin with.. when only changing rocker ratio from stock 1.5 to 1.8 ratios can generate a BUNCH more sound.

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Re: Comp QXI Lobes

Post by RevTheory » Sat Aug 31, 2019 2:29 pm

CGT wrote:
Wed Mar 14, 2018 11:44 am
Just curious, In your guy's opinion. What is making the sewing machine noise? Is in the lifter, valves opening, closing? Im always left wondering, if they sound that raunchy...maybe your not even getting "all" of that mean lobe to begin with. I just stay away from those type lobes nowadays.
I'd like to bring this thing back up and see if Mr. Jones has some input. Is it lifters that aren't up to the task? Can it actually be valves coming back on the seat too hard?

CGT brought up an interesting point: if the acceleration is such that you've got lifter noise, are you just screwing yourself by upsetting things and losing the area you were hoping for anyways?

Here's another one: if it's the lifter not being able to keep up, would a larger diameter (more rigid) lifter body and wheel solve the problem?

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Re: Comp QXI Lobes

Post by CamKing » Sun Sep 01, 2019 1:24 pm

The issue is the acceleration/velocity rates on the opening and closing ramps, right off the base circle. To make the cams look better in the catalog, Comp has no "Hydraulic ramps" on either side of the lobe, to gently start moving the lifter to the point the hydr unit goes solid, and starts moving the valve. This gives the profile a real short "Hydraulic Intensity" number, for all the yahoos that think that means something. Problem is, without the ramp, the velocity at which the valve leaves the seat, and is set back down on the seat, is as much as 10 times higher then a standard hydr roller profile.
That's gonna be noisy.
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Re: Comp QXI Lobes

Post by paulzig » Sun Sep 01, 2019 4:59 pm

Can it be improved on by using more seat pressure, and larger diameter pushrods?

You are talking specifically about the 'noisy' lobes like XFI? The other, quiet lobes have a hydraulic ramp surely.?

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Re: Comp QXI Lobes

Post by RevTheory » Mon Sep 02, 2019 9:06 am

Thanks for the feedback, Mike. So to put it in technical terms, they're basically hammering the shit out of the plunger. Assuming that's a leakage issue, would a larger diameter lifter be more rigid and help prevent some of that?

I know the final answer is to buy a hydraulic profile for a hydraulic lifter or go solid but I'm milking this prick out for all it's worth.

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Re: Comp QXI Lobes

Post by CamKing » Mon Sep 02, 2019 10:46 am

paulzig wrote:
Sun Sep 01, 2019 4:59 pm
Can it be improved on by using more seat pressure, and larger diameter pushrods?

You are talking specifically about the 'noisy' lobes like XFI? The other, quiet lobes have a hydraulic ramp surely.?
Force= Mass x Acceleration

Different lifters, springs or Pushrods aren't going to change the force, at which the valve hits the seat.
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Re: Comp QXI Lobes

Post by CamKing » Mon Sep 02, 2019 10:49 am

RevTheory wrote:
Mon Sep 02, 2019 9:06 am
would a larger diameter lifter be more rigid and help prevent some of that?
No.
The force that is hammering the valve open, and slamming it closed, is the issue.
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Re: Comp QXI Lobes

Post by RevTheory » Mon Sep 02, 2019 11:41 am

CamKing wrote:
Mon Sep 02, 2019 10:49 am
RevTheory wrote:
Mon Sep 02, 2019 9:06 am
would a larger diameter lifter be more rigid and help prevent some of that?
No.
The force that is hammering the valve open, and slamming it closed, is the issue.
Well, I think I've addressed the issue from every angle I can think of and the conclusion is that no lightweight valves with boy-howdy springs and unobtanium pushrods and thousand-dollar lifters are going to make a hydraulic roller profile with that acceleration quiet. Is that about the extent of it?

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Re: Comp QXI Lobes

Post by CamKing » Mon Sep 02, 2019 12:20 pm

RevTheory wrote:
Mon Sep 02, 2019 11:41 am

Well, I think I've addressed the issue from every angle I can think of and the conclusion is that no lightweight valves with boy-howdy springs and unobtanium pushrods and thousand-dollar lifters are going to make a hydraulic roller profile with that acceleration quiet. Is that about the extent of it?
Well, since Force is Mass x Acceleration, you can reduce the force, by reducing the mass. Ti valves would help, but that's an expensive bandaid.
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Re: Comp QXI Lobes

Post by Walter R. Malik » Mon Sep 02, 2019 12:35 pm

It's funny but, I have older street rod customers who WANT that sewing machine sound so, they won't use anything except a solid lifter.

That early Chevy F.I.sounding engine is what they are after.

It takes all kinds ... :-k

Just changing valve covers can drastically change the volume of the valve train.
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Re: Comp QXI Lobes

Post by paulzig » Mon Sep 02, 2019 4:54 pm

One reason I go with a HR is less valvetrain noise, so this particular lobe would defeat the purpose...

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Re: Comp QXI Lobes

Post by RevTheory » Tue Sep 03, 2019 9:08 am

paulzig wrote:
Mon Sep 02, 2019 4:54 pm
One reason I go with a HR is less valvetrain noise, so this particular lobe would defeat the purpose...
I tend to agree with you here. Maybe if you were bound by a rule or something but I'm not.

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