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2G Compression Ratio Increase

Posted by spyderdrifter, Sep 4, 2019

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  1. spyderdrifter

    spyderdrifter Freelancer

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    Tomorrow, Thursday, I'm putting in my 6 bolt short block. My current 7 bolt developed rod knock so I have to do this to continue using the car since my drive to work is going to be increasing drastically as far as distance. I currently have an FP 68HTA turbo with tubular manifold and full turbo back exhaust. Those are the only real mods worth noting. My 6 bolt has 9.0:1 compression Wiesco pistons and Eagle rods. I don't have ECMLink yet, and won't for a little while longer. Will the engine be safe for daily driving so long as I keep the boost limited to 10ish psi? I've gotten all the wiring installed for my wideband, but still have to have the o2 sensor bung welded on, and hopefully will have that done fairly soon so I can monitor that. I've never bumped up the compression past 8.5:1 and had a this good of a turbo, so I just need to know the possible downside to this if I'm not careful. I know increased detonation is a risk, so how can I watch for that too?
     

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  2. Mech Addict

    Mech Addict Proven Member

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    Jackson, Wyoming
    Run the best premium high octane gas you can find, at least when you’re going to drive it hard. You could also adjust base timing, though that robs back some of the power of the higher boost/compression recipe. Definitely make sure you’re not running lean. Make sure thermostat opens completely. Listen for first sounds of detonation, and get off the boost if it does.
     

    Street Build 235  6

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM
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  3. spyderdrifter

    spyderdrifter Freelancer

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    What exactly does detonation sound like? Little explosive knocks? I'm putting on a boost controller to help me stay off higher boost in the event I forget to be easy on the car.
     

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    1996 Eagle Talon TSi AWD
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  4. silvreclips

    silvreclips Proven Member

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    Greenville, South Carolina
    Keep the car on low boost and you will be fine. The ECU will start pulling timing if it picks up any knock, you won't be able to hear it. You also don't need a boost controller, those are used to up the boost higher then wastegate pressure. You can not lower the boost below your wastegate spring.
     
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  5. Vegas smith

    Vegas smith Proven Member

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    If you're just cruising around town getting groceries then no problem. I can drive around all day without getting into boost on any DSM I've ever owned. Just don't go hard on the car and you'll be fine.
     

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  6. Mech Addict

    Mech Addict Proven Member

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    Jackson, Wyoming
    So silvreclips makes a good point about hearing the detonation. My experience with this was an old dodge truck that was designed to run on leaded, and I could hear that big old 383 when it would get a tank of gas that was not up to snuff and I opened the throttle at medium rpms and high load (like pulling up a grade). Hard to describe the sound, especially in writing. You might check Youtube to see if someone has recorded a similar turbo 4 doing it. I've never heard it myself in my car, or any other modern turbo car, though I assumed it would be audible. Perhaps its not, especially if it's slight. The knock sensor should, as described, inform the computer if that it is happening, and that should adjust timing to try to compensate. I wonder if there is a way to rig a warning light when that is detected, and you could ease up on the throttle to relieve boost. That would be outside my limited knowledge of these cars, though.
     

    Street Build 235  6

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM
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  7. spyderdrifter

    spyderdrifter Freelancer

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    Thanks guys for the info. One last question though, since a warning was mentioned, is there a way to tell if it's detonating with the wideband?
     

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  8. ThunderChild

    ThunderChild Supporting VIP

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    With a wideband, not really. Need to monitor knock. Might be able to with a scan tool, I've used a Bluetooth style one with the Torque app and on most vehicles it gives you pretty good data. Can't recall if knock retard is a value as I've never used it on a DSM yet.
     

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    1990 Plymouth Laser N/T
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  9. DSMPT

    DSMPT Proven Member

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    I am not sure what gas you run but CR 9.0:1 is not that high to concern. If you worry then you can use a thicker head gasket to lower the CR a bit.
    As for hearing knock, it is hard to hear while you are driving because it would be mixed with other sound/noise especially at WOT mechanical noise would be louder than knock sound, so you need a knock monitor with a good headphones to "hear" or record it with a laptop and make it filtered to distinguish. Or just get ECMLink or some ECU that allows you to log.
    But you can hear at low RPM if your car is not noisy. The knock sound is similar to the sound that sands hitting oil pan or inside of fenders. A wideband doesn't directly tell you about knock but it will help you a lot in many situations.
     

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  10. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Even a cheap OBDII scanner such as mine can tell you about knock detection. Kinda hard to watch it while driving, but if you feel it's necessary.
     

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  11. spyderdrifter

    spyderdrifter Freelancer

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    I have a scanner with live data. What would be used for knock detection?
     

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    awd · manual · 2G DSM

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  12. BLACK'98DSM

    BLACK'98DSM Proven Member

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    My scanner tells me if there's knock.
     

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  13. spyderdrifter

    spyderdrifter Freelancer

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    Mine doesn't then :(
     

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  14. chrysler kid

    chrysler kid Proven Member

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    Why the f*** are you daily driving a modified dsm with upped compression with a big turbo that you're driving longer distances for work

    Sell your built 6bolt engine and get a daily driver.

    Seriously, imagine a blown motor and getting fired from work on the same day. Not worth it
     

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  15. spyderdrifter

    spyderdrifter Freelancer

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    I did buy a daily car that I don't have to worry about reliability with. I took the block back to the machine shop for them to "fix" the problem. Not holding my breath on that though. Still waiting for their assessment of what went wrong. I'm already pretty sure the crank and rods are done.
     

    900  2

    1996 Eagle Talon TSi AWD
    awd · manual · 2G DSM

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    1995 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

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