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Cam and compressio ratio?

Discussion in 'The Injection Section' started by HammaK5, Nov 28, 2006.

  1. HammaK5

    HammaK5 Registered Member

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    Alright Ive got a 87 r30 with tbi 454 and a TH400 auto tranny. My question is what compression ratio is safe without complete retuning, also what cam is safe to use? The truck has powerboost brakes and 3.73 gears if that helps. I just dont want to have to deal with custom chips or tuning thanks for the help.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Those are pretty loaded questions actually. :)

    For compression ratio, you can run whatever you want, as long as it doesn't lead to the detonation which the knock sensor will "hear", and reduce performance.

    Cams, a computer safe grind should be ok, any cam manufacturer should be able to recommend one, BUT the caveat is that any changes to the stock setup requires a new tune to get the *best* performance from. Yes, with the right cam you won't have to get a new chip burned, but it will not be *right* as is, regardless of what anyone tries to tell you. Plenty of posts here even (I recall a 454 thread as a matter of fact) where engines were running VERY lean, yet "felt" right. EFI can run great, it's also good at hiding problems that are either potentially very dangerous to the engine, or making you THINK it's operating at peak performance.

    Anyone that has made a change like you are suggesting, and actually looked at what the computer is doing before/after, will tell you that the tune will not be optimal. You will be throwing away power and economy to SOME degree (likely small, but still) without tuning.

    IMO making changes to gain power, then compromising by not retuning and thus preventing more gain, is counter-productive.
     
  3. HammaK5

    HammaK5 Registered Member

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    So you would suggest returning to the stock cam and only increasing compression to prevent needing a custom tune. What is the stock comp ratio on this eng any ideas?
     
  4. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I think that Dorian would agree with me when I say to go for the EFI cam, and set your compression ratio to the max you could still run on 87 octane with a carb without major pinging. I don't know much about big block engines, so I don't know what that ratio would be, its about 9.2:1 on a small block, and back it all up with a custom tune.

    You can greatly improve your engine's power and economy by even just getting a rough tune done on your engine by a dyno tuner, or even by doing so yourself.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    If I was intending to increase compression, I'd be looking at a whole lot more actually. :) Heads, cam, exhaust, all of which, of course, would benefit most with a custom tune.

    Compression increases net SOME power gain, not nearly as much as a matched setup of the above components I mentioned. When talking about those components, the cost of a custom tune would be well worth it, and probably a pretty small expense comparatively.

    Cam alone can create SOME issues, but it really depends on how aggressive it is, etc. If the truck already has an unknown cam in it, and it runs good, I'd leave alone, but still work on seeing how the engine is ACTUALLY running, with winALDL or tunerpro. There is no point guessing how the engine is running when the computer can tell you. :)
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Even on the small blocks it takes a GOOD head (Vortecs or similar if iron) to run 9:1+ on 87, big block should be no different. The "early" heads are junk when talking about technology, which is why the "smog era" 350's were running 8:1 or so, and new engines are well over 9:1 on 87.

    But changing anything that affects combustion affects the timing *NEEDS* of the engine, which can only be "fixed" by a custom tune. EFI is where you truly see that an engine has specific timing requirements where it runs best, and it's not as much as you can run without pinging, which is what a fair number of people still believe.
     
  7. Thunder

    Thunder 3/4 ton status

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    If i were you i would not mess with the compression ratio if you are going to keep the engine stock.
    Just get a GMPP 454SS TBI cam, headers, exhaust, and an adjustable fuel pressure regulator, ect and call it good.
    Unless you get better heads and a higher flow TB. Raising the compression ratio wont do you a whole lot of good and will require either a new chip and/ or an adjustable FPR plus a better (225+GPH) fuel pump.
     
  8. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    454s had 7.8:1 compression up until the vortec came out in 1996. I have installed cams in a lot of TBI 454s and had good results with the stock chip. Honestly though full length headers and a freeflowing (at least dual 3 inch or single 3.5 inch) exhaust gave as good if not better results.
    The problem with the TBI 454s is the crappy cylinder heads and their super small intake ports, putting on some vortec heads or even a set of early oval port heads will help power a lot. The vortec heads have the advantage of small combustion chambers that will raise the compression ratio a full point.
    As far as compression ratio goes I wouldn't recommend going over 9:1 on any big block that will get used for towing, they will just destroy themselves.
    The tune on your stock chip is very conservative, relatively little timing and a fairly rich wide open mixture, so as long as your combination is mild it shouldn't hurt anything but won't be anywhere near optimal and in fact it isn't real great even on a stock engine.
    Please feel free to PM me and I can get more specific on cam recommendations and chip changes as well once I know more specificly what you want to do.
     

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