safe turbocharging
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  1. #1
    Banned renaulturbo's Avatar
    Join Date
    Oct 2001

    safe turbocharging

    An expert reply to someone writting a letter on a magazine advised that it was safe to turbocharge an 11:1 engine without lowering compression

    Is this guy serious? I thought turbocharging my engine (9.2:1 ratio) was going to require lowering compression needless to ask....maybe i can answer this myself....would it be accurate to say that at 11:1 you wouldnt say more than about 5 or 6 pounds before detonation starts?


  2. #2
    Guru davemcbean's Avatar
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    Apr 2001
    Camden NSW & Selwyn NZ
    would it be accurate to say that at 11:1 you wouldnt say more than about 5 or 6 pounds before detonation starts?
    More like 0.6 or 0.7 psi. An 11:1 engine would be perilously close to pinging in naturally aspirated form, given the fuel available, unless it's a really really good design or has really small bores (like a motorbike engine).

    Generally a suck through carby turbo engine with no intercooler will stand about 7.5psi/0.5bar of boost at 100 octane before pinging sets in. This is a big generallisation though, because combustion chamber shapes, bore sizes and spark plug location have alot to do with it.

    An EFI turbo with intercooler, twin spark plugs, MSD, swirl inducing multi valves and ports and microcontroller controlled water injection could stand quite some boost, but that's a very specific specification which is rare.

    An EFI engine with 9:1 compression running on 98 octane fuel, might get away with 10psi of boost if it has an intercooler and a well designed overall system, but there's alot of factors in it.


    <small>[ 19 December 2002, 05:10 PM: Message edited by: davemcbean ]</small>
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  3. #3
    Fellow Frogger! AlsPug504's Avatar
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    Jul 2002
    Renaltturbo you may wish consider a few points about the compression ratio. The first of which is that if the cam duration or lift are poor then the cylinder pressure wont correspond to 11:1 at full power or if for whatever other reason the ultimate VE is poor then chances are if person knows the cylinder pressure and that it is low enough more than likely he could get away with turbocharging. If he does not? he would be pushing his luck! The other option is it may also be on gas! wether he a tool or or not you will find out in some later artical.

  4. #4
    1000+ Posts CHRI'S16's Avatar
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    Jun 2002
    I've seen several Hi-copm engines force fed, at several dyno places, whilst the highest boost was at a relatively mild 10psi on a 1.8 4cly, the detonation was well controlled with fuel and timming, with bigger/better injectors, pump, and Wolf Computer, they also cheated and used diferent length Plugs, thus just lowering the comp ratio.
    Engine life wasn't a concern as power was at 115Kw at the wheels, (Lancer) and it was intercooled, was all that the owner cared about, hes covered 8000'ks like this and runs it on BP/optimax. The owner admits though, that he wasn't concerned abought the engine as replacements are cheap, for his car.
    I cant see most froggies doing that, for example a replacement engine for my car is 'bout $6000 new or fully re-coed.
    But you can force-feed anything, and get more power than the NA route. However at what cost?? an engine???? ..... not for my frog tx.
    Besides i can't put it to the ground now, wats the point.
    ... ptui!

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