Blow thru vs. EFI turbo
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Blow thru vs. EFI turbo

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    Default Blow thru vs. EFI turbo

    I just spoke with c & s about any potential downside to carb vs. efi in a turbo application.

    Seems to me that if they are able to keep the air fuel ratio consistant through rpm and boost level then there is not a downside.

    The simplicity is attractive to me.

    Why would I want to use EFI? Any advantages to EFI?

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    ya dont wanna go there, it'll take 5pages long and then it comes down to personal preference and abilities to tune it. if ya have any clue how to tune a carb and you're comfy with it, by all means go c&s they're badass and work(if c&s spec builds it for ya, you wont have to tune it, jus set idle mixture and rpm)! if you're comfy wiring and playin with pc a bit, go efi. both will make huge power, the carb route is cheaper and alot more simple imo.
    Last edited by IMPATIENT 1; 11-23-2010 at 10:59 AM.

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    I don't need every last drop of power out of the engine. I always thought that EFI helped with fuel efficiency in the mid range and with precision tuning allowed better protection against detonation when trying to get every last ounce of power....I am hoping someone can comfirm this or set me straight.

    I don't like all of the extra wiring...for me simple is better.

    Any EFI guys care to add to this thread?

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    I've seen engine tunes (with efi obviously) that have radically different AFR, VE, and Ignition Advance numbers around the same load on only a couple hundred RPM change. What I mean by that is (just an example) AFR at 4800rpm at 7lbs of boost made the most power with 11.4:1 while at 5000rpm at 7.5lbs it liked 11.9:1 both being at 28 degrees of timing......then again at 5200 maybe it like 11.2 AFR with 26 degrees of timing but at 5400 it wanted 29 degrees of timing, but 11.3:1 AFR. these are just numbers i made up, but have see tunes that are like this....they look kinda goofy sometimes, but have had a ton of time spent to make every aspect of the engine running happy and efficient.

    There is so much to be had in mid range, low rpm and light or no load areas of the tuning table that preserve engine life, fuel consumption and drivability. And thats just considering a hot engine. you have cold start and everything in between cold and hot that can be controlled and optimized specifically for that moment on that specific engine. not a general setting that gives you 1 AFR all the time. yeah it may be nice to see an AFR that stays locked at 11.2:1 on a boost run, but that doesn't mean its optimal, efficient, or right. it just means it probably won't blow up...which is good i suppose.

    I like efi and the complexity of it....it doesn't take a rocket scientist to tune efi or a carb, but it doesn't take a rocket scientist to see efi is more complex than a carb either. However its complexity is directly proportional to its ability to control an engine at any possible moment of its running life.

    btw, maybe you should call FAST and see what they say about efi vs carb on a turbo setup

    Andrew
    Last edited by ap67et10; 11-23-2010 at 02:23 PM.

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    Quote Originally Posted by dnewps View Post
    I just spoke with c & s about any potential downside to carb vs. efi in a turbo application.

    Seems to me that if they are able to keep the air fuel ratio consistant through rpm and boost level then there is not a downside.
    Well no shit. Ever see what one of these could do IF they had wings







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    no "if's" about it, a c&s carb maintains very nice afr's thruout idle to wot. if i had a way to upload the datalogs off the f.a.s.t system i could show ya but i have no way right now gn cant see past his 2 carbs and roots blower

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    I'm very blow thru inexperienced so take my reasonings below with a grain of salt:

    Drag race I'd entertain blow thru carb.

    Endurance, I'd go multiport EFI.

    Big reason is.........afr to each cylinder. A carburetor needs air flow straight thru the booster/venturi to meter fuel correctly. Until the new hats, this was near impossible. The newer hats (extreme velocity namely) get you pretty close but not close enough for total comfort. Air is still tumbling (ie: going many different directions) from the violent turn it has to make from the ducting into the carb. Thus why you see many raise the elbow and run more straight length tubing straight down in carb. You can only go so high because of packaging.

    Again, endurance vs drag racing.

    BTW: Only endurance motors I've seen do pretty well with a carb is one with a big enclosure (no hat) and some have a screen type flame arrestor inside the box bolted to the carb to help straighten airflow.
    Last edited by cfm; 11-23-2010 at 03:08 PM. Reason: spelling

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    Quote Originally Posted by gn7 View Post
    Well no shit. Ever see what one of these could do IF they had wings



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    Quote Originally Posted by dnewps View Post
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    Quote Originally Posted by cfm View Post
    I'm very blow thru inexperienced so take my reasonings below with a grain of salt:

    Drag race I'd entertain blow thru carb.

    Endurance, I'd go multiport EFI.

    Big reason is.........afr to each cylinder. A carburetor needs air flow straight thru the booster/venturi to meter fuel correctly. Until the new hats, this was near impossible. The newer hats (extreme velocity namely) get you pretty close but not close enough for total comfort. Air is still tumbling (ie: going many different directions) from the violent turn it has to make from the ducting into the carb. Thus why you see many raise the elbow and run more straight length tubing straight down in carb. You can only go so high because of packaging.

    Again, endurance vs drag racing.

    BTW: Only endurance motors I've seen do pretty well with a carb is one with a big enclosure (no hat) and some have a screen type flame arrestor inside the box bolted to the carb to help straighten airflow.
    The intake maniflod is very important on the blow through stuff. If you do any dyno testing with o2 sensors in every pipe you will see a lot of single four barrel manifolds don't distribute very evenly. The blow through we just did had 10 o2 sensors, one in each primary and one in each collector. We got very even readings across the board, within .5 from richest to leanest. The manifold was heavily modified by Wilson manifolds and it was worth the work. On a drag race deal the Blow through is really good if all the other componets are properly matched. We used a CSU dominator and it is absolutely awesome and trouble free.

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    Quote Originally Posted by ap67et10 View Post
    I've seen engine tunes (with efi obviously) that have radically different AFR, VE, and Ignition Advance numbers around the same load on only a couple hundred RPM change. What I mean by that is (just an example) AFR at 4800rpm at 7lbs of boost made the most power with 11.4:1 while at 5000rpm at 7.5lbs it liked 11.9:1 both being at 28 degrees of timing......then again at 5200 maybe it like 11.2 AFR with 26 degrees of timing but at 5400 it wanted 29 degrees of timing, but 11.3:1 AFR. these are just numbers i made up, but have see tunes that are like this....they look kinda goofy sometimes, but have had a ton of time spent to make every aspect of the engine running happy and efficient. There is so much to be had in mid range, low rpm and light or no load areas of the tuning table that preserve engine life, fuel consumption and drivability. And thats just considering a hot engine. you have cold start and everything in between cold and hot that can be controlled and optimized specifically for that moment on that specific engine. not a general setting that gives you 1 AFR all the time. yeah it may be nice to see an AFR that stays locked at 11.2:1 on a boost run, but that doesn't mean its optimal, efficient, or right. it just means it probably won't blow up...which is good i suppose.

    I like efi and the complexity of it....it doesn't take a rocket scientist to tune efi or a carb, but it doesn't take a rocket scientist to see efi is more complex than a carb either. However its complexity is directly proportional to its ability to control an engine at any possible moment of its running life.

    btw, maybe you should call FAST and see what they say about efi vs carb on a turbo setup

    Andrew
    Sorry Andrew but I'm not buyin it. If your engine needs the ignition & fuel to bounce around like that every 200rpms you must have something loose
    I talked in length with a very smart tuner that I know about this while he was tuning a 750hp 4cyl, on his chassis dyno and he showed me how he could add a degree of timing anywere he wanted as well as take a degree away or make it a little richer or leaner without changing anything else so he could flatten out the tq curve and get all there was out of the engine. But his ignition or fuel curve didnt end up with any wild swings that I could tell. It was damn cool to hear that thing make the pony's on the dyno though. You couldnt hear anything but the turbo.
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    I am new at this so work with me. If I understand this correct a carb does not EASILY allow consistency in air fuel mix between all cylinders while an efi set up does. This means that I cannot get all of the potential power. If I am not looking for every ounce of power do I care? Does this hurt the longevity of the engine since some cyl are not dead on or can it just be set up a litter richer and it is fine? do I need to have +1 -1 deg of timing? how much should I care about the torque curve in a boat that I cannot hammer down on out of the hole since I have a bravo based drive? I have to baby it to get on plane then be modest on the throttle getting it to top speed.

    I am thinking 565-598 ci and 1000 hp. My main goals are for the engine to live a long time and not spend a stupid amount of money. I am looking for top speed out of the boat and decent fuel efficiency when cruising at 40mph

    I would like to do all of this with as many off the shelf products as possible
    Last edited by dnewps; 11-23-2010 at 06:20 PM.

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    Quote Originally Posted by dnewps View Post
    I am new at this so work with me. If I understand this correct a carb does not EASILY allow consistency in air fuel mix between all cylinders while an efi set up does. This means that I cannot get all of the potential power. If I am not looking for every ounce of power do I care? Does this hurt the longevity of the engine since some cyl are not dead on or can it just be set up a litter richer and it is fine? do I need to have +1 -1 deg of timing? how much should I care about the torque curve in a boat that I cannot hammer down on out of the hole since I have a bravo based drive? I have to baby it to get on plane then be modest on the throttle getting it to top speed.

    I am thinking 565-598 ci and 1000 hp. My main goals are for the engine to live a long time and not spend a stupid amount of money. I am looking for top speed out of the boat and decent fuel efficiency when cruising at 40mph
    FIRST - either will get the HP you are after. You MIGHT be able to squeeze a handful of HP out of the motor with EFI, but if done properly, BOTH should be very close to each other on HP.

    Look. OBVIOUSLY, efi is more tunable across the entire RPM range. It can control timing to mirror-image the fuel curves so that the two are constantly matched. As mentioned, there are 5 or so pages in another thread about all of the pros and cons of each.

    CARB is much less expensive, but doesn't have all of the bells and whistles that EFI does. IF you boat at several different lakes (altitudes) that would be a primary factor in choosing. EFI will stay in tune regardless of altitude, whereas a carb cannot re-jet itself for more atmosphere or less.

    CARB will NOT warn you and shut the motor down if there are any problems (oil pressure, fuel pressure, LEAN condition). Yes, a carb can run a fuel pressure switch to cut something off when too low, but that's about it.

    The other consideration for you is who else will possibly drive the boat and do you boat all year. EFI will start with only your hand on the key. No throttle, no "babying" until it warms up. No back-pops due to lean (cold) motor where blow-through carbs will have NO CHOKE.

    EFI docking manners can be dialed in specifically if there is a large cam or other "hindering" factors (high drive gears, large props, both).

    EFI idle remains the same when in gear / out of gear. IAC motor compensates whereas a carb can't.
    Last edited by Beer:30; 11-23-2010 at 06:22 PM.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


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    Quote Originally Posted by Hass828 View Post
    Sorry Andrew but I'm not buyin it. If your engine needs the ignition & fuel to bounce around like that every 200rpms you must have something loose
    I talked in length with a very smart tuner that I know about this while he was tuning a 750hp 4cyl, on his chassis dyno and he showed me how he could add a degree of timing anywere he wanted as well as take a degree away or make it a little richer or leaner without changing anything else so he could flatten out the tq curve and get all there was out of the engine. But his ignition or fuel curve didnt end up with any wild swings that I could tell. It was damn cool to hear that thing make the pony's on the dyno though. You couldnt hear anything but the turbo.
    First off, I don't expect you to buy anything I say. Im pretty sure there is absolutely no way at all for you to change your mind about any of this, so Id expect you to say you don't believe it.

    Second, you sure do a great job of not understanding the point of my post at all (i said multiple times i was just making up numbers, which are somewhat exaggerated to help illustrate my point.) and instead, take what I say and twist it as you like. (don't worry, i expect it now, i've learned from the many posts back and forth )

    What I was trying to point out is that I have seen jumps from relatively close rpm spots on AFR and timing tables, not a bunch of jagged lines or "bounces every 200 rpm" like you ridiculously suggested. its not going to go up and down and up and down over and over all across the graph, but rather more of a hickup in a specific curve for a given load.

    From my experience its ignition timing that will often show the most odd ups and downs in what seem like weird places. typically it will look like hickups with timing, and mostly they are isolated to a specific load value, and are characteristics of one load value's curve across the rpm, which don't often transfer to another load value's curve across the rpm. Many times one load value will have a drop or increase over a range of 1000-1500 rpms because you see a torque increase at that load by pulling out or putting in a few degrees. this however may not be the case at a different load value for the same rpm.

    this is how power is fine tuned and gained, especially in the mid range, in ways that carbs and distributors cannot do. I have yet to meet a tuner that charges a bunch of money to program in a bunch of straight lines!

    btw, i do have graphs of FACTORY tunes that very clearly illustrate these characteristics with engines. i would have to modify them so i don't have copyright issues by posting them (not the graph portions), but can probably get something up so you can see it, if you still don't understand what i'm saying. But its not like it would change your mind or anything anyways, so i'm not sure if I should waste my time

    Andrew
    Last edited by ap67et10; 11-24-2010 at 02:49 AM.

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