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Restoring power

Discussion in 'E30 (1984-1993)' started by az3579, Dec 23, 2008.

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    az3579

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    As we're all aware, a car's engine loses power over the years. Some engines lose more power than others, but what determines how much power is lost over a specific amount of time, and, what can be done to fully restore all of the horsepower an engine came with from the factory?
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    MGarrison

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    Well... every engine internal subject to friction is going to wear over time, resulting in various power and running efficiency losses.

    Once the cylinder bores and piston rings are worn enough that you have enough compression loss for there to be a noticeable loss of power, just about the only fix for that is a tear-down and rebuild. Valve guides & seals wear, valve seats wear, valves gunk up, fuel injectors gunk up, any loss of fuel pressure is bad, afm and throttle-body valves can get sticky/gunky, rod bearings, piston wrist pins wear, crankshaft bearings... etc, etc! No doubt others will have some salient insight too!
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    az3579

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    Right, those are the "irrepairable" parts, and by that I mean parts that would require a complete overhaul/rebuild as opposed to just swapping out components.

    I'm talking about replaceable parts - what replaceable parts could be... well, replaced, in order to restore power?

    I know that spark plugs might be one of them, but what else?




    I ask because I just watched an episode of Top Gear (Season 12, episode 3) and the segment in reference is where they try to make a Renault Avantime go 'round their track as fast as an Evo X Mitsubishi. Of course this is ambitious but rubbish, but at one point of that film, they put the 6-year-old Avantime on a dyno and found that of the 210 hp it had when new, it had 157 hp, and after a good old fashioned tune-up, it was restored to about 206 hp.

    This worries me, because let's face it: 12x hp isn't a lot to begin with.
    In another episode of TG, they had older Italian supercars, and the amount of power that escaped from those engines over time was simply staggering. I can only imagine how much horsepower has escaped from my engine over its 22-year career. I want to at least get it somewhat near this figure, perhaps within 15 hp or so, so that a rebuild wouldn't be completely necessary. Is this at all possible? If not, at what mileage would an engine start to pass the "never fully restorable" point, the point where it will never be able to have the full amount of power it once had?
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    MGarrison

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    Well... the mileage bit would vary based on usage. 300k miles driven all at once at the same speed would induce different wear than 300k of stop & go driving, 12 miles a day.

    The simple stuff to do I think is probably all the standard maintenance tune-up items layed out in the Bentley manual. Plugs, plug wires, distributor cap, rotor, making sure there's no vacuum leaks, and that everthing else pertinent to power production is up to speed.

    Fuel lines, fuel pressure regulator, injectors, and main and in-tank fuel pumps. (checking fuel pressure would move towards indicating potential issues there)

    Among other things, after you address the powerplant and related systems, don't forget drivetrain and what gets the power to the wheels. Any added friction through the drivetrain would be sucking up power too. Paul probably has some pretty good suggestions on this topic, I would think.

    Devilsown guest

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    I for once was haveing issues with my 93 RX-7 one, granted it is a rotary not a piston engine. But I took it to rotary preformace and the owner of the place started my car and told me I needed new plugs, I told him he was full of ship... how can you tell by starting it... So he put it on the dyno and ran it, then put the new plugs in VOLA~ and I ship you not... 53.4 HP all in 4 plugs... I would have never have guessed...(ahhhh my pain killers finaly kicked in) it. So I do see how a simple tune up can fix "restore" power. I tend to replace things in my cars WAY sooner then the factory tells me to like plugs, I do them about every other year with leads. I also use SEAFOAM that stuff is sweet! I also use the Chevron Techron fuel SYSTEM (not injector) cleaner every 2 fill ups. ALSO a detailed engine helps too by it allows you to see leaks and the engine to cool that much more efficintly... Im not a greasemonkey but these are just little things I do to hopfully keep my cars top notch. Speaking of he devil Im due for an oil change.

    Jeron guest

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    I disagree with the premise that "a car's engine loses power over the years". I like the fresh topic though.

    If that were true then you could chart and predict the decline of HP. Until the engine looses a significant amount of compression the HP should remain constant.

    Sure there are things that get dirty or wear out and can reduce HP like plugs, injectors, intake leaks, vacuum leaks, catalytic converters but those are all serviceable items. The engine itself is capable of producing the same HP as long as the ancillary systems are functioning properly and the compression is good.
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    CRKrieger

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    Absolutely.

    missmelyssa guest

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    Chevron Techron fuel System

    For me this would be every other week, depending on the amount of driving I do of course.
    Now did you start using this product recently, or since the car's infancy?
    Currently my car (2006 325i) has right under 27k miles on it. I put about 2k on it a month.
    I want to keep my car in tip top shape (even thought it's still new).
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    mooseheadm5

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    Keep after your tune up parts, including air and fuel filters. Then, one major wear item is injectors. Often overlooked, often spraying a crappy pattern after years of crappy fuel. This makes for poor efficiency and poor power due to poor fuel atomization. Rather than have yours tested and flow matched, upgrade to better ones.
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    az3579

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    Before I continue, I'm not attacking in any way, just trying to figure out what your logic/reasoning is. :)

    So, what you're saying is that theoretically, my engine could always produce the 121hp it came with from the factory given that all serviceable items are fresh?
    Even with the wear on the engine after 310,000+ miles of use?
    Compression may be good, but the engine could still not have 100% of the compression it came with from the factory, no? As a result, I would assume that it can't have 100% of the power that it came with.

    It would seem logical that the engine would lose power over the years due to wear. What reasoning is there to prove otherwise?





    I've seen injectors with "ratings", usually a number with lbs. written after it. What does the car come with stock (325e) and what is an ideal upgrade? Could you please explain how much of a difference newer/other injectors would make if I was to replace what I have?

    Are there any other items that I should be looking at?



    Thanks for all the replies. I seem to have missed the posts after Marshall's, and I don't know why. But, either way, I am going to have the car dyno'ed to see how much power is actually getting on the road. It's mostly the curiosity that's killing me. :cool:
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    mooseheadm5

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    The rating in lbs is lbs of fuel per hour. Upgrading would mean larger injectors to flow more fuel (a similar trick can be done with higher fuel pressure because it will flow more fuel for the same opening time as set by the ECU.) Upgrading also means injectors that are designed with multiple orifaces that atomize fuel better than the original single pintle injectors.

    And, yes, eventually every motor loses some compression and therefore loses power.
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    az3579

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    Thank you sir.

    Would this be a reason why someone would want to rebuild their engine? Or is it to upgrade to large pistons, or is that just a plus side of rebuilding?
    To determine whether or not an engine needs a rebuild, what kind of tests would you run? Compression test? Leakdown (I'm not familiar with this test, just heard it somewhere :eek:)?
    What numbers would warrant a rebuild?

    Or am I on the wrong track?

    (FYI, I will drop in an M/S50 instead of rebuilding down the line, so I'm just asking for knowledge)
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    mooseheadm5

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    Compression and leakdown tests reveal lots. Next is to look at the bearings. Compression numbers should be within 10% of each other and maybe 150psi? not sure about the eta motor. Leakdown I think you generally want less than 10-15%, but 20% is still a workable motor. The valves being cut and lapped restores some compression, as does fresh rings and pistons. Fresh bores and rings prevent blow by and oil ingestion into the chamber. New bearings restore oil pressure. New valve guide seals restore oil sealing. New guides help the seals live and help the valves seat true for better compression. Rebuilds done right restore the power. Rebuilds done exceptionally well can help increase power through blueprinting, balancing, hiking compression, gasket matching, porting, etc.

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