Blown 540 carb jetting help
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Blown 540 carb jetting help

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    Senior Member Smallblocksperry's Avatar
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    Default Blown 540 carb jetting help

    540 inch 8.2-1 compression
    .650" solid roller .252/.262 @.050
    broddix bb-2 heads
    littlefield 8-71 with intercooler
    8 percent overdriven
    pump gas
    locked out distributor
    Dual Holley 4779 750 carbs, right now they have no power valves and are jetted 82/84, seems like its going to be lean, anybody have any experience with a similar combo, it's going into a 26' cat boat, 100mph long hauls plus being lean is all bad

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    "Need For Speed" Gearhead's Avatar
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    The best suggestion I could offer you would be to have the carburetors modified with "boost referenced" power valves. This properly setup will allow you to have decent cruise fuel economy and the have sufficient fuel enrichment when you step on it.

    Gear

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    Senior Member SHAWN DAVIS's Avatar
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    I did an almost identical 565, even ended up going in a 26 american offshore. But with 850's and no power valves, ran 88's squared
    no boost reference

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    "Need For Speed" Gearhead's Avatar
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    Quote Originally Posted by SHAWN DAVIS View Post
    I did an almost identical 565, even ended up going in a 26 american offshore. But with 850's and no power valves, ran 88's squared
    no boost reference
    Shawn, I am not being confrontational, but you too may consider boost referenced power valves. It is a more normal and superior carburetor operational issue. With 88's in 850's, she probably runs fine, but I bet you load the plugs a bit at low speed and you are evidently not overly concerned with fuel economy. You are leaving a little performance and economy on the table. This modification is fairly simple and adds an additional circuit for use in your carburetor. Holley carburetors are originally produced with power valves for a more efficient fuel system and you would not think of running one on the street without them. Same thing on a HP lake cruiser, but when one uses a roots style blower, then one has to change the power valve vaccuum/pressure referencing. I run pv's on my lake cruiser/racers but also plug the pv's on my race boat, but for a different reason. My race boat never cruises. It idles on the rope for thirty seconds then is decked.

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    Senior Member SHAWN DAVIS's Avatar
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    Yeah I know a lot of people do them, and probably work fine
    I never have used them and like the keep it simple philosophy. I've hurt parts with extra lines coming off, boost retards not retarding and enough crap and gadgets that stops working at the worst possible time.

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    Senior Member Smallblocksperry's Avatar
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    right on, thanks for the info, i like the simple idea of leaving the power valves plugged, but i think im off on the jetting, considering just dropping the cash and dyno'ing it

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    Senior Member jimclauss's Avatar
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    Quote Originally Posted by Smallblocksperry View Post
    right on, thanks for the info, i like the simple idea of leaving the power valves plugged, but i think im off on the jetting, considering just dropping the cash and dyno'ing it
    that would be a smart move

  10. #8
    gn7
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    Quote Originally Posted by Gearhead View Post
    Shawn, I am not being confrontational, but you too may consider boost referenced power valves. It is a more normal and superior carburetor operational issue. With 88's in 850's, she probably runs fine, but I bet you load the plugs a bit at low speed and you are evidently not overly concerned with fuel economy. You are leaving a little performance and economy on the table. This modification is fairly simple and adds an additional circuit for use in your carburetor. Holley carburetors are originally produced with power valves for a more efficient fuel system and you would not think of running one on the street without them. Same thing on a HP lake cruiser, but when one uses a roots style blower, then one has to change the power valve vaccuum/pressure referencing. I run pv's on my lake cruiser/racers but also plug the pv's on my race boat, but for a different reason. My race boat never cruises. It idles on the rope for thirty seconds then is decked.
    Gear, in most cases like the OP's deal the PV is of little use. I agree on a small 18ft flat with some cubes they are a benefit, and on a street car I wouldn't consider not using them. But in something the size of a 26ft AOS with a 8.2 compression 540, its going to be hard to getting it moving without getting the manifold below 4" of vac.

    Chances are if the OP was to even cruise it at 2500, the manifold pressure will be such that the PV would be open anyway. A 540 with 8.2 compression isn't exactly a torque monster without some boost. If he installs a 4.5 or even a 4 PV, the manifold is more than likely going to be under that, if not actually in a slight boost condition.

    I can hardly drive the GN without putting it in boost, and I bet it makes more power than a 8.2 540 when both are out of boost.

    Little confused by the OP's post, because he says "seems like its going to be lean" Based on what?
    My take is it is going to go fat on the top because the carbs are on the small side of borderline if the engine never exceeds 6000. Starved for air is not the same as lean. Undersized carbs = fat top end. It can be dealt with thru air bleeds, but it usually easier to just use the right sized carbs.
    Its also on the borderline for pump gas if it hits 10psi of boost, which will depend on the blower, cam and exhaust.

    Not saying the PVs won't work, but with that much boat, chances are the manifold is going to go under 4" at anything above paning speed.



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    Last edited by gn7; 12-17-2012 at 06:37 PM.

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    Senior Member Smallblocksperry's Avatar
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    Quote Originally Posted by gn7 View Post
    Gear, in most cases like the OP's deal the PV is of little use. I agree on a small 18ft flat with some cubes they are a benefit, and on a street car I wouldn't consider not using them. But in something the size of a 26ft AOS with a 8.2 compression 540, its going to be hard to getting it moving without getting the manifold below 4" of vac.

    Chances are if the OP was to even cruise it at 2500, the manifold pressure will be such that the PV would be open anyway. A 540 with 8.2 compression isn't exactly a torque monster without some boost. If he installs a 4.5 or even a 4 PV, the manifold is more than likely going to be under that, if not actually in a slight boost condition.

    I can hardly drive the GN without putting it in boost, and I bet it makes more power than a 8.2 540 when both are out of boost.

    Little confused by the OP's post, because he says "seems like its going to be lean" Based on what?
    My take is it is going to go fat on the top because the carbs are on the small side of borderline if the engine never exceeds 6000. Starved for air is not the same as lean. Undersized carbs = fat top end. It can be dealt with thru air bleeds, but it usually easier to just use the right sized carbs.
    Its also on the borderline for pump gas if it hits 10psi of boost, which will depend on the blower, cam and exhaust.

    Not saying the PVs won't work, but with that much boat, chances are the manifold is going to go under 4" at anything above paning speed.

    Yea I said lean because of the jetting, not the carb size, I've heard mixed opinions of the carbs being to small, boostpower and Teague say they'll be fine, any v-drive guy says "you need dominators" I just don't like dominators because of the intermediate throttle bores, both sides of both carbs are working with just a crack of the throttle, for a cat that's not what I want, my old man runs dominators on his blown cat, and the back of the boat is black after one run down the river.

    For a 18 foot boat yea dual 1050s for sure, but for me, ill sacrifice a little power for fuel mpg and a clean transom

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    gn7
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    Quote Originally Posted by Smallblocksperry View Post
    Yea I said lean because of the jetting, not the carb size, I've heard mixed opinions of the carbs being to small, boostpower and Teague say they'll be fine, any v-drive guy says "you need dominators" I just don't like dominators because of the intermediate throttle bores, both sides of both carbs are working with just a crack of the throttle, for a cat that's not what I want, my old man runs dominators on his blown cat, and the back of the boat is black after one run down the river.

    For a 18 foot boat yea dual 1050s for sure, but for me, ill sacrifice a little power for fuel mpg and a clean transom


    I NEVER MENTIONED A DOMINATOR DID I? There are 850s, 950s, and 1000 cfm 4150 style carbs before you ever get to a Dominator. Never said they were TOO small, said they were BORDERLINE at anything above 6000.

    If your old mans cat turns the back of his boat black, he needs to learn to tune a carb. It has NOTHING to do with using Dominators.


    I have no idea where you get your info on doms. Doms are available without the intermediate circuit(not bore, what ever that means), and they are also available with progressive linkage that is every bit as progressive as a 4150 crab. Maybe even a little more progressive if you like.


    They will probably be just fine. But if you run it much passed 6000, chances are that you'll be losing a little compared to a set of 850s. I don't see it reving much past 6000 with that cam and boost in a boat that size. And I don't know if you really want rev it passed 6000 with an I/O anyway.



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    Last edited by gn7; 12-17-2012 at 07:33 PM.

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    Quote Originally Posted by gn7 View Post
    Gear, in most cases like the OP's deal the PV is of little use. I agree on a small 18ft flat with some cubes they are a benefit, and on a street car I wouldn't consider not using them. But in something the size of a 26ft AOS with a 8.2 compression 540, its going to be hard to getting it moving without getting the manifold below 4" of vac.

    Chances are if the OP was to even cruise it at 2500, the manifold pressure will be such that the PV would be open anyway. A 540 with 8.2 compression isn't exactly a torque monster without some boost. If he installs a 4.5 or even a 4 PV, the manifold is more than likely going to be under that, if not actually in a slight boost condition.

    I can hardly drive the GN without putting it in boost, and I bet it makes more power than a 8.2 540 when both are out of boost.

    Little confused by the OP's post, because he says "seems like its going to be lean" Based on what?
    My take is it is going to go fat on the top because the carbs are on the small side of borderline if the engine never exceeds 6000. Starved for air is not the same as lean. Undersized carbs = fat top end. It can be dealt with thru air bleeds, but it usually easier to just use the right sized carbs.
    Its also on the borderline for pump gas if it hits 10psi of boost, which will depend on the blower, cam and exhaust.

    Not saying the PVs won't work, but with that much boat, chances are the manifold is going to go under 4" at anything above paning speed.
    Bob,

    Thanks, I had not taken into consideration the weight of that large a hull and the power it takes to get it on plane and cruise. The boats we have been succesful using the boost referenced PV's are in the 550" range and higher than 10 lb boost situations at wot, and are lighter weight hulls such as TX-19's (gullwings) and Daytona's (tunnel) boats that do have vacuum at cruise (2500 to 3500) rpm. We have been able to clean them up well for lake cruise and then put the fuel to them for good power with 15 to 20 lbs boost. I have worked with customers both ways on the dyno... with or without PV's, but the without sometimes seem a bit rich at cruise when jetted good for power.

    Gear
    Last edited by Gearhead; 12-17-2012 at 10:27 PM.

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    Senior Member Smallblocksperry's Avatar
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    thanks for the info, looks like ill stick with no power valves and the 750s since i have no plans on anything over 6000, probable going to dyno it so we can get close on the jetting, and try to install an air/fuel sender and pyrometer sender into my imco powerflow exhaust since i already have the gauges in my dash.

    now fuel pump, i have a single 75 gallon belly tank in it, with -6 line going to a holley black electric pump, to a magnaflow regulator with no return, i think this setup is good for probably 600hp, since im planning on at least 850, i am going to run a mechanical pump off the engine also, anyone have any experience with this, noticed a couple cats running like this, wondering if its a special tee off the mechanical pump or ?

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    Senior Member SHAWN DAVIS's Avatar
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    I'd run a -8 inlet from the tank to the pump
    either a bigger electric pump or a 140 gph mechanical if running only one.
    Or tee kinda like you are saying using the black for a "helper"- ironically wich is the same way I rigged the 26 A.O. with that 565 I built.
    tee the line before the mechanical pump-go to the black then run that up towards the regulator. it also works to prime the system cause the
    fuel will drain back to the belly tank and takes a while to prime without it

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    northern member Canuc's Avatar
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    Quote Originally Posted by Smallblocksperry View Post
    540 inch 8.2-1 compression
    .650" solid roller .252/.262 @.050
    broddix bb-2 heads
    littlefield 8-71 with intercooler
    8 percent overdriven
    pump gas
    locked out distributor
    Dual Holley 4779 750 carbs, right now they have no power valves and are jetted 82/84, seems like its going to be lean, anybody have any experience with a similar combo, it's going into a 26' cat boat, 100mph long hauls plus being lean is all bad
    i can see where you'd be thinkin lean with 82/84 jets even with the small carbs for a 8% over 8-71 . with pump gas i'd go at least 88's square with no p/v on a first run and easy on the timing . any pic's of the redhead bent over the 540
    Quote Originally Posted by gn7 If your ran a cammer your odds of finishing WERE ZERO.

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