Turbo jet boats: So how do you size a turbo ?
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Turbo jet boats: So how do you size a turbo ?

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    Resident Ford Nut Sleeper CP's Avatar
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    Default Turbo jet boats: So how do you size a turbo ?

    If someone was going to build a turbo'ed +/- 500" engine where do you start?

    Click to enlarge......








    Does it matter what the heads flow or if you have a dual plane intake manifold? I'll assume the engine rpm and cam makes a difference..... or on the cam do you just turn up the boost to make up the differnce?

    If an 82mm turbo is good for 600 hp does that mean two will handle 1,200 hp or will they make more?

    And what the hell is the A/R ratio of a turbo?

    S CP
    Last edited by Sleeper CP; 12-05-2011 at 03:43 PM.

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    Senior Member motormonkey's Avatar
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    Oh man. Dont let GN7 see you posting this. LOL.

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    Senior Member desrtrat256's Avatar
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    Blow through carb or EFI?

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    Hass to the courtesy phone, suprised he hasn't jumped all over this!

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    Senior Member ap67et10's Avatar
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    Its all about airflow. The more air you can put in the more power you will make. Id say to start a build, you need to make goals. If you believe 1500hp is all you want, then spending a ton on engine components doesn't make sense (im not saying just slap a turbo on anything, but it is very easy to make that power with turbos). if 3000hp is what you want.... well, heads, cam, intake, pretty much everything just became a big big deal, because now not only are you trying to put almost 4000 cfm of air into an engine, but you need every bit of the air those turbos flow to make it to the combustion chamber to accomplish what you want, because 4000 cfm is getting towards the top tier of current turbo flow. So you must maximize the engines efficiency in using and transporting that air.

    I have yet to build a turbo boat, but have had my hands on more than a couple turbo cars of all shapes and sizes, both tuning and building. And from the information I heard from the turbo boat guys, I believe the principals don't completely transfer when choosing a turbo for a car compared to choosing a turbo for a boat....primarily because of the load characteristics in a jet boat, which greatly effect exhaust volume at different rpms. I believe turbo lag, is much less of an issue, which also means that turbine A/R is also less of an issue (well too large of an A/R ratio is less of an issue, too small would be a greater issue).

    A/R is Area to Radius ratio. basically in completely simple form, it is the number that tells you how much taper is in the housing (snail portion, whether compressor or turbine). Imagine taking the exhaust housing and unrolling it out on the table so its flat and not in the snail form. you would see a large opening which is the inlet for exhaust from the manifold/header/s, and it would look like a funnel tapering down to a smaller opening. Basically the amount of taper in the housing is what changes with different A/R ratios.

    With a large A/R ratio, such as 1.39 you have much less taper. the inlet is closer in size to the outlet and this cuts down on velocity or speed of the exhaust when the volume is not very great. That means that at a given RPM and load when exhaust volume is low (low load low rpm) the turbine wheel would spin slower than it would if you were using a smaller A/R in the same application, because the exhaust velocity/speed would be less than a housing with more taper (lower A/R). the large A/R housing would result in less power at that RPM when volume is not very high (low rpm low load...cruise...midrange, places like that), because the turbine wheel will spin slower due to having less exhaust velocity to spin it, which slows compressor speed which means less air flow. And since air flow is power, you make less power at that given RPM and load. (in that example we were talking about mid range power) The opposite takes place when an RPM and load is reached when the exhaust volume the engine produces is much greater (high load high rpm). If the turbine A/R is small then it has more taper and the restriction will be greater, along with back pressure when trying to have max flow. If you are looking for peak power you do not want to restrict flow at max load/max rpm levels. A much larger A/R with less taper will create less restriction to flow resulting in more total power potential at that higher load/rpm level.


    Choosing A/R comes down to your goals you made before you started the build. However in a jetboat, because of the instant and significantly high load on an engine, I believe the largest A/R possible is desired in just about every case. if you are building for a car....all bets are off and the end goals need to be looked at before choosing A/R ratio of the turbine housing.



    Andrew

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    Quote Originally Posted by Oldelmn8tr View Post
    Hass to the courtesy phone, suprised he hasn't jumped all over this!

    I thought I'd give the turbo guys something to talk about for a while and some of us might learn something along the ride.

    S CP

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    fast is the other half.
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    Quote Originally Posted by desrtrat256 View Post
    Blow through carb or EFI?

    For the purpose of this discussion lets say blow-thru on E-85:






    S CP

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    " A Government big enough to give you everything you want is big enough to take away everything you have"

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    Highaboosta Unchained's Avatar
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    Andrew explained it pretty good.



    A lower A/R will spool quicker at the expense of maximum flow.
    Just the opposite for the larger A/R.
    The A/R directly relates to the backpressure running the turbine.

    Sizing the turbo's by your HP goal is a common way to go.

    Twin Turbo 1800 HP V-Drive lake boat

    http://s621.photobucket.com/albums/t...t=MAH05771.mp4

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    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

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    Quote Originally Posted by ap67et10 View Post


    Choosing A/R comes down to your goals you made before you started the build. However in a jetboat, because of the instant and significantly high load on an engine, I believe the largest A/R possible is desired in just about every case. if you are building for a car....all bets are off and the end goals need to be looked at before choosing A/R ratio of the turbine housing.



    Andrew
    The sizing of a turbo is interesting when the same turbo covers such a large engine displacement from 120cu. in to 500" and hp levels: A/R .69 on this 108mm turbo
    Last edited by Sleeper CP; 12-05-2011 at 05:52 PM.

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    Senior Member ap67et10's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    The sizing of a turbo is interesting when the same turbo covers such a large engine displacement from 120cu. in to 500" and hp levels: A/R .69 on this 108mm turbo

    the CID of the engines really means almost nothing when choosing the turbo you need. This turbo doesnt care what size engine it is, it only cares about air flow. If a 2.0L makes 500 hp and a 7.4L makes 500 hp they both require about 650-700 cfm of air. The air to make that power is the same, the area of space in which that same volume of air has to occupy is what makes these engines so massively different because it changes how and when that power is made, which is what you consider when choosing A/R .

    You are refering to the A/R of the compressor housing, most all turbos will have just 1 A/R option for the compressor housing....most. It is the exhaust housing which is the main focus when looking at A/R ratio. that is why with this turbo there are 4 different A/R ratios availible.


    Andrew
    Last edited by ap67et10; 12-05-2011 at 06:50 PM.

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    Senior Member ap67et10's Avatar
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    before you decide on A/R ratio you need to figure out if this turbo is the turbo you should be using for what you want to do.



    here is the first place to start:
    1. how much power do you want to make?
    2. how many cubes is your engine going to be?
    3. how much boost are you thinking you would like to run?
    4. What will be your max RPM range on this engine?

    (I should also add that knowing what fuel you will be using is key, because often that is the deciding factor for how much boost you can safely run. you mentioned E85, so you can pretty much run as much boost as you want, you would need to put more thought into whether the engine components you choose can handle the high boost levels.)

    when you know these things we can plug them into a CFM equation to be better suited to choose a turbo, based on a turbo map. Then once you know about what turbo you need, you will then have typically 4-5 choices of A/R for the turbine housing.


    Andrew
    Last edited by ap67et10; 12-05-2011 at 06:14 PM.

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    So on the A/R a big single turbo needs a larger number (a/r) than a TT that is using two smaller turbos? The smaller a/r on them will help them spool quicker?

    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
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    " A Government big enough to give you everything you want is big enough to take away everything you have"

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by Oldelmn8tr View Post
    Hass to the courtesy phone, suprised he hasn't jumped all over this!
    These guys seem to have a handle on it but I will put my 2 cents in also.
    "if we keep doing it the same way we always do..we will always get the same results"
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    Senior Member Hass828's Avatar
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    Most of these turbos that you see available are in small-mid or large frame(or chassis), small being the T3 stuff , mid the T-4 stuff and the large the T-6 stuff. Obviously the T3 stuff is for the smaller rice burners, the T-4 stuff can make some damn stout power even on a bigblock of reasonalble cid but max effort and cid goes to the T-6 large frame stuff as the compressors & turbin housings are just physically larger. I understand that now they have an S500 frame that larger than the T-6 stuff but that would be so far beyond what we would ever need its not worth including in the convo. Andrew explained the A/R perfectly.
    As for picking the perfect turbo for a jet boat app. you "could" go to the books as I've explained in a thread or two before and figure the Cid x intended rpm range x density ratio and convert that to lbs/min and pick a turbo, or just simplify it like most do and figure that for every 10lb/min of flow on the map it makes 100hp, so for 2000hp you would need a set of turbs capable of 100lb/min each or a single large enough for 200lb/min @ the intended pressure ratio(boost).
    That takes care of the compressor side then you need to look at the A/R of the turbin side and figure one that will hit as hard as you desire but not choke at the intended rpm, which in my boat I used the largest available at 1.32 because they offer the least backpressure and the most power potential. Now that being said, a smaller set of housings with a little tad bit more of backpressure would offer more boost contol by making the exhaust move through the wastegates. They would come in a little sooner as well. So it really depends on the caracteristics you'r looking for in the manurisms of the engine.
    When all else fails and you dont like the math then call, Bullseye performance, Paradise Racing, Forced Inductions,Garret turbos, Precision turbos, Turbonetics. Any one of these can help you make the right decision for your application.
    My.02
    Last edited by Hass828; 12-05-2011 at 07:41 PM.
    "if we keep doing it the same way we always do..we will always get the same results"
    H8-2-W8
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