Better performance out of my 4.5?
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HT4100 4.1, 4.5, 4.9 Discussion, Better performance out of my 4.5? in Cadillac Engine Technical Discussion; Hey everyone, Ive been looking around for performance upgrades for my '89 deville with the 4.5L, i would love to ...
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    highonchai's Avatar
    highonchai is offline Cadillac Owners Fanatic
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    Question Better performance out of my 4.5?

    Hey everyone, Ive been looking around for performance upgrades for my '89 deville with the 4.5L, i would love to keep it as factory as possible, even if it means using other cadillac parts. Somewhere i thought i read that the Allante from '89 with the 4.5L had a different intake manifold, and/or throttle body, giving it a bit more pep, is this true?? What do you think of me finding the allante throttle body and intake and adding it to my 4.5? (if possible) Thanks guys, any other suggestions would be awesome. Thanks, take it easy. oh one more thing, i have a '90 fleetwood hearse that ive wrecked, it has the 4.5PFI in it, and it seemed A LOT faster than my '89 even with all that extra hearse weight, is this simply because of the Port Fuel Injection, or could i have some nifty little parts here? i dont want to do an engine swap or anything even though that PFI engine runs perfectly. Thanks again.

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    Edahall's Avatar
    Edahall is offline Cadillac Owners Enthusiast
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    Re: Better performance out of my 4.5?

    Easiest thing to start off with is advancing the timing around 3 degrees. Factory setting is 10 degrees so set it around 13 degrees. You can advance it more but then premium fuel will be needed to prevent pre-ignition. These cars didn’t have knock sensors so the timing was set conservatively to allow varying qualities of gas to be used.

    Next step would be to replace the rear muffler. A Camaro style muffler such as a Flowmaster 50 series Deltaflow is what I put on my Cadillac. It is very easy to install and hardly louder than stock. I was able to put mine on fittings and clamps I bought at the local automotive store. You can also run the car without any muffler. I ran mine this way for a while and it still made half the noise of lot of rice burners

    As far as putting on an Allante intake, very expensive. Very few of these cars were made and the increase in power was due mainly to increased rpm range. Simply puting on an Allante intake isn't going to do much. It might even decrease torque which is needed to get a heavy car going.

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Better performance out of my 4.5?

    Quote Originally Posted by highonchai
    Hey everyone, Ive been looking around for performance upgrades for my '89 deville with the 4.5L, i would love to keep it as factory as possible, even if it means using other cadillac parts. Somewhere i thought i read that the Allante from '89 with the 4.5L had a different intake manifold, and/or throttle body, giving it a bit more pep, is this true?? What do you think of me finding the allante throttle body and intake and adding it to my 4.5? (if possible) Thanks guys, any other suggestions would be awesome. Thanks, take it easy. oh one more thing, i have a '90 fleetwood hearse that ive wrecked, it has the 4.5PFI in it, and it seemed A LOT faster than my '89 even with all that extra hearse weight, is this simply because of the Port Fuel Injection, or could i have some nifty little parts here? i dont want to do an engine swap or anything even though that PFI engine runs perfectly. Thanks again.
    The best first step would be to get a factory service manual.

    With that, you can ensure that the vehicle is operating properly as a baseline. That likely means a tuneup involving:
    new plugs
    checking (and probably replacing) plug wires
    new cap and rotor
    verifying the fuel pressure
    probably replacing the fuel filter
    changing the oil and filter
    changing the air filter
    cleaning the throttle body of deposits
    Set the timing to factory specs.

    Also wouldn't hurt to change the tranny filter and fluid and put in a new thermostat after draining and refilling the cooling system (and adding the suppplement tabs).

    Other things to check:
    Verify the ISC system is working properly
    Verify the TPS is also working properly
    Run a compression test on all cylinders
    Verify the vacuum is within spec, especially to the modulator on the transaxle, and be certain there are no leaks.
    Adjust the TV cable (controls shifting of the trans)
    (procedures are in the service manual).


    If you're in tune and not generating any codes, that would be the time to consider modifications. The timing change will give you some power, especially if you're willing to run premium. If you listen attentively (for knocking and pinging), you may find some brands allow you to bump the timing up further than others - you'd have to buy them consistently though.

    There aren't all that many things you can do without getting radical. However, you may be pleasantly surprised to find out how well the engine performs when its actually running at 100% (not saying yours isn't, but most aren't, in my limited experience).



    The Allante intake is a pretty sweet piece and, like the Vette and F-body engines of the era, is tuned port injected, but the intake runners are "L" shaped rather than crisscrossing over the manifold - a lot like a 5.0 mustang intake of the same era.

  5. #4
    highonchai's Avatar
    highonchai is offline Cadillac Owners Fanatic
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    Thread Starter

    Lightbulb Re: Better performance out of my 4.5?

    Ok thanks a lot guys. The only reason i asked the question was because i am going to get a full service/ tune-up etc.. so i figure what better time to add a few horses? i did find the 4.5/4.9 w/ allante performance thread just after i posted this one, and i figured it was out of the question anyhow but worth a shot. What do you guys think about using parts from my 4.5PFI engine? would converting it over do anything for performance? Thanks again guys. Youre the Cadillac of Cadillac mechanics!

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