Engine Bogging Under Full Throttle or Something Else? - Cobalt SS Network



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Old 09-12-2017, 05:54 PM   #1
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Engine Bogging Under Full Throttle or Something Else?

Hi all,
I have a very low mile LSJ, just 60.5K on it, it's a 2006 non-lsd.

I have noticed that when in 5th gear, particularly when the car is going uphill when there's higher strain on the engine, that if I floor the gas in 5th at around 2800 RPM (I never would floor it below this) there appears to be a "marbles in the transmission" sound. Is this the engine bogging? Clutch chatter, or some other issue?

If I raise the RPMs to 3200 or so, then floor it in 5th, on the same hill the noise does not appear. It only appears if I floor it below 3K.

Other than this noise I have not noticed any drivetrain issues at all. Transmission and clutch work exactly as expected.

Any experiences with this would be appreciated
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Old 09-12-2017, 06:25 PM   #2
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That's called lugging your engine and you shouldn't do it. Use your RPM range. You do much more harm lugging an engine than you would revving it out. That sound that resembles marbles in a can is most likely your engine pinging/knocking telling you you are running too much timing/boost for the load and rpm.

Nothing is wrong with your engine yet hopefully but driver mod is needed. Next time you feel like flooring it in 5th gear with the rpms below 3,000 rpm, DON'T without downshifting.
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Old 09-12-2017, 11:54 PM   #3
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Originally Posted by jdbaugh1 View Post
That's called lugging your engine and you shouldn't do it. Use your RPM range. You do much more harm lugging an engine than you would revving it out. That sound that resembles marbles in a can is most likely your engine pinging/knocking telling you you are running too much timing/boost for the load and rpm.

Nothing is wrong with your engine yet hopefully but driver mod is needed. Next time you feel like flooring it in 5th gear with the rpms below 3,000 rpm, DON'T without downshifting.
Understood, I wonder why flooring it in second at this RPM doesn't cause issues... Is it due to the fact the revs climb faster in second and I'm not noticing the lugging?

I should have learned this a long time ago. The issue is that the lugging occurs not too often, and I didn't figure out it was below 3000 rpm on hills and below 2800 on the flat roads. Plus it's a bit different for each gear.

But I'm thankful for your advice and welcome the peace of mind.

Cheers!
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Old 09-13-2017, 08:48 AM   #4
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It's all about load. In 5th gear at 2,800 rpm WOT on flat ground you are putting WAY more load on the engine than in 2nd gear at 2,800 rpm on a hill. When you need that extra power, use those gears and don't be afraid to get close to redline.
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Old 09-13-2017, 09:36 AM   #5
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Old 09-13-2017, 09:53 AM   #6
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This should be a sticky in almost every subforum here.
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Old 09-13-2017, 10:27 AM   #7
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Old 09-28-2017, 08:21 PM   #8
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This was all good info that I appreciated. Thank you.

I think I know what caught me out on this, totally newb, but I need confirmation. When I modded my car I chucked on everything pretty much around the same time. The intake went on first, but then I chucked in the 2.8" pulley and the works at once. Not saying I went crazy, but I added quite a bit more boost pretty quickly. BUT I NEVER CONSIDERED CHANGING MY SHIFT POINTS.

I suppose I've been shifting the car at the same RPM and using the same throttle input no matter my mods. I think this was a mistake as the more boost I'm throwing in at lower RPM, the harder it's going to be on the drivetrain...

This being said, is it a "thing" to change the shift-points in a manual car that's been modified to add significant hp? Is this something I didn't realize that everyone naturally adjusts to, but I missed this because I paid too much attention to shifting at certain RPM points?

Hopefully this makes some sense...
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Old 09-29-2017, 07:38 AM   #9
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Originally Posted by boostbalt View Post
This was all good info that I appreciated. Thank you.

I think I know what caught me out on this, totally newb, but I need confirmation. When I modded my car I chucked on everything pretty much around the same time. The intake went on first, but then I chucked in the 2.8" pulley and the works at once. Not saying I went crazy, but I added quite a bit more boost pretty quickly. BUT I NEVER CONSIDERED CHANGING MY SHIFT POINTS.

I suppose I've been shifting the car at the same RPM and using the same throttle input no matter my mods. I think this was a mistake as the more boost I'm throwing in at lower RPM, the harder it's going to be on the drivetrain...

This being said, is it a "thing" to change the shift-points in a manual car that's been modified to add significant hp? Is this something I didn't realize that everyone naturally adjusts to, but I missed this because I paid too much attention to shifting at certain RPM points?

Hopefully this makes some sense...
The more boost and power you make the more careful you have to be about lugging your engine. You really should be using your gears (Just think if you were in an automatic, would it be downshifting?) no matter what your mods are. But the more violent the combustion process the harder it is on your engine when you demand full power at low rpms.
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