4.9 Individual Throttle Body project
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 Individual Throttle Body project in Cadillac Engine Technical Discussion; This Plus these And runners that I'll need to fabricate. I decided to scrap the 4 tb into 2 project ...
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    Ghost C's Avatar
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    4.9 Individual Throttle Body project

    This


    Plus these


    And runners that I'll need to fabricate. I decided to scrap the 4 tb into 2 project and try and set up ITB's on the 4.9. The CBR600RR throttles are 40mm each, which should flow plenty to feed a 300ci engine that only revs to 5,000rpm. The manifold won't be here until Wednesday

    Issues that I'll need to work out:
    Vacuum log for brakes, FPR and MAP sensor, other stuff would be fine to run off one runner but the FPR, MAP and brakes will need a vacuum log

    Filter setup

    Fuel rail - My manifold isn't coming with the fuel rails from the Allante, however I think the standard 4.9 rail will work? Someone correct me if I'm wrong so I can start looking for one

    EGR - Either will have to be removed, or adapted to work with this manifold somehow. Ideas on this will be appreciated.

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    drewsdeville is offline Cadillac Owners Master
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    Re: 4.9 Individual Throttle Body project

    First of all, I wouldn't expect much gain. The stock throttle body is more than enough to feed the 4.9's small cam and valves. THOSE are what really dictates how an engine breathes. Even with the largest throttle body you could possibly adapt, the engine can only flow as much as the cam and valves allow.

    Would it be a problem that the fuel injection is speed density rather than mass air flow? In theory, a larger, better flowing throttle body will reduce vacuum. That's bad because the PCM's MAP sensor tables are matched to the stock throttle body: for any MAP sensor reading, the PCM knows how much air should be passing the stock throttle body. If you change it, the PCM doesn't know that and still adjusts injector pulse width as if the stock throttle body was still in place. Without a PCM tune, I would expect that you will find a large drop in throttle response and overall worse performance.

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    Re: 4.9 Individual Throttle Body project

    Quote Originally Posted by drewsdeville View Post
    First of all, I wouldn't expect much gain. The stock throttle body is more than enough to feed the 4.9's small cam and valves. THOSE are what really dictates how an engine breathes. Even with the largest throttle body you could possibly adapt, the engine can only flow as much as the cam and valves allow.
    It's not the size of the throttle bodies. One throttle body feeding one runner into one cylinder gives better throttle response and makes more power by being more efficient than a throttle body feeding a plenum feeding runners. It also minimalizes differences in air flow between each cylinder.

    Would it be a problem that the fuel injection is speed density rather than mass air flow? In theory, a larger, better flowing throttle body will reduce vacuum. That's bad because the PCM's MAP sensor tables are matched to the stock throttle body: for any MAP sensor reading, the PCM knows how much air should be passing the stock throttle body. If you change it, the PCM doesn't know that and still adjusts injector pulse width as if the stock throttle body was still in place. Without a PCM tune, I would expect that you will find a large drop in throttle response and overall worse performance.
    I don't think you understand what a MAP sensor does. It has nothing to do with the throttle body and they are not tuned to each individual application. The 1 bar MAP sensor is a common part used on a ton of cars and each PCM is calculated to the engine's specs. MAF would not work any better than MAP. The ideal solution is something called alpha-N tuning, but that's another story for another stage of engine tuning. The problem is, I will need to make a vacuum log for the MAP sensor, and the fuel pressure regulator, and the brake booster. The only issue is figuring out the perfect size to use for this application.

    I forgot to put in my "issues" list that I also need to calculate optimum runner length and diameter for the setup to produce usable power for the 4.9, I think the runners will have to be close to obnoxiously long for a low revving engine.

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    drewsdeville is offline Cadillac Owners Master
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    Re: 4.9 Individual Throttle Body project

    Quote Originally Posted by Ghost C View Post

    I don't think you understand what a MAP sensor does. It has nothing to do with the throttle body and they are not tuned to each individual application. The 1 bar MAP sensor is a common part used on a ton of cars and each PCM is calculated to the engine's specs. MAF would not work any better than MAP. The ideal solution is something called alpha-N tuning, but that's another story for another stage of engine tuning.
    .
    Er...that's exactly what I was trying to get at. I never claimed that the MAP sensor was tuned per application. Rather, how the PCM interprets data is different per engine (not all engines flow the same volume of air at a given BAR). If the throttle bores are larger than stock, which in turn reduces vacuum at the throttle body (where the MAP is connected), the PCM WILL need to be tuned for this to work correctly; the stock fueling tables will no longer be correct. Else, the PCM will assume a larger load than actually exists (due to reduced vacuum), unnecessarily enrichining the mixture.

    Example: At X BAR the PCM assumes that Z cfm flows past stock the throttle blades, and fuels accordingly. Now, you change the throttle body to something with larger bores. X BAR now occurs at a different load/rpm than stock, and Z cfm now occurs at some other BAR. However, the PCM continues to fuel for the predetermined cfm's per BAR for the stock setup.

    A MAF would be more ideal as air measurement occurs AHEAD of the throttle body, and cfm is measured directly rather than assumed through manifold pressure, so any changes made would be, in effect, detected by the PCM.

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    Re: 4.9 Individual Throttle Body project

    The throttle bores being larger than stock has no effect on how much air the engine draws in at idle. The only effect of individual throttle bodies on a MAP sensor is the difference in pulse makes it screwy if you do not use a vacuum log, which is why I'm going to use a vacuum log.

    MAF is less than ideal because I would have to build a plenum on top of the throttle bodies and then pipe air in through a tiny MAF-sized hole, mostly defeating the purpose of an individual runner setup which is immediate throttle response. I'd also have to switch to stand alone engine management, and at that point (and price tag) I would just use alpha-N tuning with stand alone because it is based on rpm, temperature and TPS position - ideal for individual throttle bodies, and it would be easier to tune than a MAF conversion. Which is something I intend to go with... Eventually.

    I know it causes you physical pain any time someone mentions "performance" and "4.9" in the same post, though, so I'll tell you something that you'll like to hear... I've spent less than $220 on this setup so far.

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    Re: 4.9 Individual Throttle Body project

    Quote Originally Posted by Ghost C View Post
    The throttle bores being larger than stock has no effect on how much air the engine draws in at idle.
    Correct, the heads, cam and intake determine that. But what does it do for VACUUM?!?!? Vacuum and air flow are NOT proportional. It sounds like you are assuming that.


    Vacuum is generated by creating a restriction to the air flow. The throttle body is that restriction. As you mentioned, the air flow doesn't change, the engine draws in the same cfm's regardless of throttle body. However, if you change the amount of restriction by increasing or decreasing bore size, you change the amount of vacuum present. Smaller bores will raise vacuum, larger bores will decrease vacuum, air flow will remain the same. This change becomes apparent to ALL vacuum operated devices, including the MAP.

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    Re: 4.9 Individual Throttle Body project

    Quote Originally Posted by drewsdeville View Post
    Correct, the heads, cam and intake determine that. But what does it do for VACUUM?!?!?
    I fail to see how the throttle bodies have any effect on how much air the engine draws or atmospheric pressure. Do you think the PCM needs tuning mid-trip if you drive from New Orleans to Boulder CO? The difference in atmospheric pressure between the two cities would have a far larger effect than switching throttle bodies.

    Quote Originally Posted by Wikipedia MAP sensor page
    Vacuum is the difference between the absolute pressures of the intake manifold and atmosphere. Vacuum is a "gauge" pressure, since gauges by nature measure a pressure difference, not an absolute pressure. The engine fundamentally responds to air mass, not vacuum, and absolute pressure is necessary to calculate mass. The mass of air entering the engine is directly proportional to the air density, which is proportional to the absolute pressure, and inversely proportional to the absolute temperature.
    And so on and so forth.

    Look, you asked for thoughts and I'm giving you them. The fact that this is a 4.9 has nothing to do with my response. It would have been the same for a Chev 350 or a Geo 3 cylinder. Take it or leave it, but don't put down those giving you what you asked for.
    I asked for input on certain areas of the fabrication, not someone telling me it won't work or that it's not worth it to try, which is generally your S.O.P. especially in this particular sub-forum. If you would have chimed in with a tip on how to use the EGR, a calculation for ideal runner length, or knowledge of the differences (if any) between the Allante and 4.9 fuel rails, I would appreciate it. However, you just want to say it can't/shouldn't be done, even going so far as to present incorrect facts in your argument against the project. I don't mean to be a prick, but every topic about performance in this forum has at least one post from you saying something negative, and it gets old.

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    Re: 4.9 Individual Throttle Body project

    I never said it couldn't nor shouldn't be done, I merely pointed out what I think to be a potential obstacle, bud. All I suggested is that a PCM tune may be needed, nothing more.

    If you want my advice on the intake manifold, I'd say build your own to accommodate either fuel rail and scrap the Allante intake. The individual throttle bodies would be great if all runners were straight, clean, and most importantly, equal length. Take a look at the picture you posted above...those runners are anything but that, much of it's design influenced by packaging restrictions under a shallow hood. Anything that you slap on top of that manifold will not change the performance characteristics that your manifold has. You really need to start from scratch and build a custom manifold from the heads to the throttle bodies to get some results.

    Something like this would really take advantage of the idea. Notice all runners are identical in shape and length, running straight into the heads that this manner:



    The problem with fabricating your own is that you have to accommodate for the goofy physical geometry on the top end: the narrow heads, pushrods passing through the intake manifold, valve covers overlapping it all, and accessories that are mounted to the intake, like the power steering pump and alternator. Again, IT COULD BE DONE.

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    Re: 4.9 Individual Throttle Body project



    FWIW, the runners on the Allante manifold are real close to equal length, and I'm 90% sure the fuel rails are interchangeable.

    IMHO, I would look into the throttle bodies combined flow rate as opposed to stock single TB flow rate. If close, I would look into stock runner lengths and diameters for the upper half of the manifold. If not close (I think 40mm throttle bodies are gong to flow A LOT more air), then I would suggest closing the diameters of the fabricated runners a bit to pick up the velocity of the incoming air. Tuned ports.

    Too much flow is/can be a bad thing, especially if the air isn't rushing fast enough. On these short stroked motors you need more velocity than volume.

    My .02...

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    Re: 4.9 Individual Throttle Body project

    Hey ghost i want to see this when you get it done.

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    Re: 4.9 Individual Throttle Body project




    Suspiciously, the diameter of the runners is only 2mm smaller than the throttle bodies. Hm.

    Time for calculations and procrastination.

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    Re: 4.9 Individual Throttle Body project

    look about halfway down http://forum.britishv8.org/read.php?6,13482,page=2 and there is some pics of motorcycle throttle bodies on a tube manifold

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    Re: 4.9 Individual Throttle Body project

    That's basically exactly what my setup will be, except it will work with the ridiculous head setup of the 4.9

    And my runners will be long enough to make power on an engine that only revs to 5k

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    Re: 4.9 Individual Throttle Body project


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    Re: 4.9 Individual Throttle Body project

    Quote Originally Posted by Ghost C View Post
    Suspiciously, the diameter of the runners is only 2mm smaller than the throttle bodies.
    Wow, that's all?!? The combined flow rate should have that motor breathing REAL easy...

    Question though, do you have access to a dyno for a before and after? Just curious for a more black and white approach. I'm looking to put a 4.9 in my Firebird and since I would have to possibly mock-up some exhaust manifolds/headers why not tackle something like this too if the HP gain is good...

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