Simple boost reference mod straight from Holley

[ghittner]

Here it is straight from Holley for all that want to do boost reference modification for themselves. Looks simple to me. Like 10 minutes!!!! Download this and keep.

[Wet Dream]

Thats it? Seems simple enough.

[ghittner]

yup, and I don't know why everybody keeps it such a closely held secret I hope people get this picture. I asked and asked for it and no one would help.

[TIMINATOR]

Most double pumpers do not have that setup, with the spark port like that. Just the vacuum secs that no-one uses have it. Thats why I didn't mention that mod. TIMINATOR

[Cheap Thrills]

Here
http://www.***boat.com/image_center/data/500/1127Manifold_Reference_Power_Valve.jpg
C.T. :wink:

[ghittner]

750 dp's exact as the picture. list # 4779-70750 Please let us know the mods for the "other type" double pumpers. Thanks from all of us!

[Warp Factor]

What's the advantage of boost referencing supposed to be?
The prop boats I've seen with it ran rich on the bottom and fouled plugs.

[schiada96]

What's the advantage of boost referencing supposed to be?
The prop boats I've seen with it ran rich on the bottom and fouled plugs.
Think of it as a cheap mans map sensor. Instead of blowing the power valve closed it makes it open at the right time. A blown boat with refrenced valves will run cleaner.You can run the primarys and secondarys a few numbers leaner and it will idle better.

[sgdiv7]

What's the advantage of boost referencing supposed to be?
The prop boats I've seen with it ran rich on the bottom and fouled plugs.
It is for part throttle (crusing) so the engine does not run lean at a higher rpm cruse. I drilled out the power valve restrictor holes a little at a time and droped the jet #'s so when I was at crusing speed which was 2500 rpm & 0 boost for me, the fuel mixture was right. I wound up using a 2.5 power valve for my aplactaion. I have a flatty with 29 gears.
If the boats you saw doing that would play around with power valve sizes alone they could make air fuel ratio much better. I did that first. I wanted the best fuel mileage I could out of a blowen engine crusing and still have the wot fuel mixture.

[Blown 472]

Think of it as a cheap mans map sensor. Instead of blowing the power valve closed it makes it open at the right time. A blown boat with refrenced valves will run cleaner.You can run the primarys and secondarys a few numbers leaner and it will idle better.
What does the idle circut have to do with the power valve and jetting???

[schiada96]

What does the idle circut have to do with the power valve and jetting???
Blown motors change the signals that carbs read.

[ghittner]

Basically a normally aspirated motor at WOT has no vacuum in the venturies and a lot a partial throttle.
A blown motor has full vacuum at WOT making the carb think it is at cruise.
This will lean out the motor and kill it.
This is why blown motors need to refrence vacuum from the intake manifold, not the carb venturies.

[Warp Factor]

I'm still not gettin' it.
My boat never has significant vacuum in the manifold when it's in gear. That means that with boost referencing, even a low rating power valve would be open all the time.
However, there is vacuum at the base of the carb above the blower, and that drops with throttle opening in similar fashion to a naturally aspirated motor, so it seems that leaving the power valve reference at the base of the carb is the best thing.
I can see how it might work on a car, a boat with really small gears, or a jet boat that isn't putting much load on the engine until high rpms, any setup that has significant vacuum at part throttle.
If this mod caused enrichment at 5 lbs. or so, I could see how it would help.
But unless you're pulling manifold vacuum at cruise higher than the power valve rating, the "power enrichement" function will be defeated, and the power valve will be open all the time. This is what was happening on the boats I've seen that were boost referenced, and it just caused them to run rich.

[502 JET]

With a roots supercharger the carb is seeing vaccume even at WOT.That is why people manifold reference the power valve.When the power valve sees boost it will open and add more fuel with it getting its signal from the intake.Vaccume hold the powervalve shut until it drops below the numerical value on the valve then it will open adding more fuel.You can run with out a power valve but I would not reccomend it for part throttle performance.With out a power valve start with jets 8-10 sizes larger and tune from there.

[Warp Factor]

With a roots supercharger the carb is seeing vaccume even at WOT.
I suppose any carb will see some vacuum at WOT, but when I put a vacuum gage at the carb base on mine, it was about 2 inches. 2.5 is the lowest power valve rating, so even that one would be open at full throttle. Depends on carb size, of course.
Why not just measure vacuum at the carb base at, say, 3 psi boost, and put in a power valve of that rating so you have enrichment from that point on?
I think boost referencing would be a great idea if someone came out with power valves that open at a specified boost pressure, instead of when vacuum drops to a certain level. We don't really need enrichment at the same vacuum level as a normally aspirated motor, because generally, our effective compression ratio is much lower at the same vacuum.

[502 JET]

When you are just cruising on the primaries the carbs will see alot of vaccume and hold the valves shut.At this point you may start running lean but be ok at wot.With it reading manifold pressure it would open up and give you the extra fuel that you need.If you have your engine tuned properly and it is running up to your expectations then leave well enough alone.Some guys like power valves some dont some like to manifold reference some dont.It is personal preference on how you run your engine.It is up to you what you can make work for your self or you pay someone to build for you and run as they suggest.
There is some good reading regarding this topic on the website: OFFSHORE ONLY forums.Do a search on power valves, there is alot of info on that topic over there.

[ghittner]

When you are just cruising on the primaries the carbs will see alot of vaccume and hold the valves shut.At this point you may start running lean but be ok at wot.With it reading manifold pressure it would open up and give you the extra fuel that you need.If you have your engine tuned properly and it is running up to your expectations then leave well enough alone.Some guys like power valves some dont some like to manifold reference some dont.It is personal preference on how you run your engine.It is up to you what you can make work for your self or you pay someone to build for you and run as they suggest.
There is some good reading regarding this topic on the website: OFFSHORE ONLY forums.Do a search on power valves, there is alot of info on that topic over there.
What do you prefer?

[502 JET]

What do you prefer?
I prefer to manifold reference the primary power valve.Remove and plug off the secondary powervalves.The power valves will work off engine load vaccume and not false vaccume from the supercharger.You get great part throttle performance set up like this.

[ghittner]

Is it possible to boost reference without an outside vacuum hose?

[502 JET]

Is it possible to boost reference without an outside vacuum hose?
No.You need to connect to the intake under the supercharger.

[novaz]

I am using a single 4150 form Pro -Systems on a stage 2 6-71 and they told me that boost reference was not needed this is on a 350 performer rpm engine (Nova)
The car runs well as it is 10.58@132 :cool: so I dont think I am missing much
Just my limited experience.

[ghittner]

When you are primarily drag racing thats true. However on a boat you idle a lot through marinas and no wake zones with an engine that runs aout 150 deg.. It fattens up real quick without manifold referencing.

[Warp Factor]

When you are primarily drag racing thats true. However on a boat you idle a lot through marinas and no wake zones with an engine that runs aout 150 deg.. It fattens up real quick without manifold referencing.
If anything, manifold referencing is likely to make the engine richer at no wake speed.
Vacuum is higher at the carb base than in the manifold, so the stock setup (not boost referencing) is more likely to hold the power valve closed and keep you from running rich. Yes, I've measured the vacuum.

[ghittner]

If you are not manifold referenced you generally up your jetting subsantially to accomodate for the high RPM leanout and any part throttle and low rpm cruising ie- no wake zones, tends to load up the plugs. Correct?

[schiada96]

I wonder why holley and demon sell boost refrenced carbs?It couldnt be because they don't work.

[Warp Factor]

If you are not manifold referenced you generally up your jetting subsantially to accomodate for the high RPM leanout and any part throttle and low rpm cruising ie- no wake zones, tends to load up the plugs. Correct?
What I've done is remove the power valves on the mechanical secondaries, so any time the secondaries are open I have enrichment as if the power valve was open.
This automatically gives enrichment at higher throttle openings.
With no boost referencing, I've spent more than an hour in no wake zones with no loading up, and very cold plugs.
I have a carb adapter which mounts the carbs with the float bowls at the front and rear though. Side mounted carbs might cause a mixture difference on the two banks with this setup.
Why do holley and demon sell boost refrenced carbs? I haven't asked them, but I'm guessing it's because they work OK on cars.
A car is only using about 20 horsepower to go down the freeway, so the manifold vacuum is high, keeping a boost referenced power valve closed.
Most boats never see power levels and throttle openigs that low.
It also might be a "lesser of two evils" thing on boats. Better to load up at cruise or idle than run lean at the top, with the typical sideways mount carb setup.
I've seen boost referencing work fine on jet boats though. They're more like a car going down the freeway, with higher rpms at lower throttle opening, resulting in higher manifold vacuum.

[ghittner]

What I've done is remove the power valves on the mechanical secondaries, so any time the secondaries are open I have enrichment as if the power valve was open.
This automatically gives enrichment at higher throttle openings.
With no boost referencing, I've spent more than an hour in no wake zones with no loading up, and very cold plugs.
I have a carb adapter which mounts the carbs with the float bowls at the front and rear though. Side mounted carbs might cause a mixture difference on the two banks with this setup.
Why do holley and demon sell boost refrenced carbs? I haven't asked them, but I'm guessing it's because they work OK on cars.
A car is only using about 20 horsepower to go down the freeway, so the manifold vacuum is high, keeping a boost referenced power valve closed.
Most boats never see power levels and throttle openigs that low.
It also might be a "lesser of two evils" thing on boats. Better to load up at cruise or idle than run lean at the top, with the typical sideways mount carb setup.
I've seen boost referencing work fine on jet boats though. They're more like a car going down the freeway, with higher rpms at lower throttle opening, resulting in higher manifold vacuum.
Have you ever loaded up the plugs with this set up? If so, how did it happen?

[steelcomp]

I wonder why holley and demon sell boost refrenced carbs?It couldnt be because they don't work.It could also be that there are more people who "hear" that you "need" boost referenced carbs for blower apps. than actually know what they're doing. Mentality of lemmings. Not saying boost referencing is or ins't the right way to go, just that few manufacturers sell anything just because it works.
502Jet:I prefer to manifold reference the primary power valve.Remove and plug off the secondary powervalves.The power valves will work off engine load vaccume and not false vaccume from the supercharger.You get great part throttle performance set up like this
I'm following this thread and trying to learn here. Isn't vacuum, vacuum? How can it be false? If it has a value, then can't it be used like any other vacuum?
Isn't this what Warp Factor is referring to??

[ghittner]

TOTALLY different. Venturi Vs manifold.

[steelcomp]

TOTALLY different. Venturi Vs manifold.I understand that part, but tell me why one can't be used and the other can? They each have their properties, and they're different, but my question is so what? Why is one real, and one "false"?

[502 JET]

502Jet:
I'm following this thread and trying to learn here. Isn't vacuum, vacuum? How can it be false? If it has a value, then can't it be used like any other vacuum?
Isn't this what Warp Factor is referring to??
In certain situations you will not get a power valve numerically small enough to open because the blower is pulling vaccume (thats why I say false vaccume) greater than the pv rating holding it shut.When in the intake is under boost/positive pressure and it would open the pv if the pv was manifold referenced.
There is no rite way or you must do this way or that way.You tune an engine to suit your needs and how you want it to operate or you pay someone to do it for you and you run it how it was set up.Manifold referencing is just another way of tuning an engine.You can also enlarge the two passages under the pv to get more fuel (can run a smaller jet) so your part throttle is running clean but you get the added fuel when the pv opens.

[Warp Factor]

Have you ever loaded up the plugs with this set up? If so, how did it happen?
Yes, I had to replace 2 plugs that weren't firing (over the last 6 years, aside from normal plug changes). Both times, I had been running in rough water, causing fuel to spill from the float bowl vents into the carb throat.
There is no rite way or you must do this way or that way.You tune an engine to suit your needs and how you want it to operate or you pay someone to do it for you and you run it how it was set up.Manifold referencing is just another way of tuning an engine.
I agree.
If your current setup works OK, why mess with it?
If it's not, it's easy to hook up a vacuum gage to the manifold and see what the vacuum is under various conditions, such as idle and cruise. Check the same thing at the carb base.
If you don't know the rating of your power valves, remove them and look, it should be stamped on the part. A 3.5, for instance, means the power valve opens when vacuum drops below 3.5.
Let's say you show 5" vacuum at the manifold at a slow cruise, and your power valve is a 3.5. The power valve wil be closed, and you should be OK running boost referenced.
Let's say the manifold vacuum is 2" at cruise, and 3" at idle. The power valve will be open under these conditions, and may give problems with plug fouling.
If you reference from the base of the carb, be sure your vacuum drops far enough at high boost to open the power valves.
This is still guesswork though. The real way to know what your A/F is doing is to set it up using a wide-band A/F meter. This can only be done if you're using unleaded gas, and is difficult to do with water injected exhaust.
Second best is probably setting it up on the dyno, where you can actually measure air and fuel going into the motor, but this won't give you load conditions under actual operating conditions when installed in the boat.
I've gotten a little spoiled by modern fuel injection systems on cars. They'll read the A/F ratio, and automatically adjust. Or you can type the amount of fuel you want into a spread sheet, and that's what it will do. Timing can be handled the same way, using the spread sheet or knock sensors. These things can be varied according to coolant temperature and manifold air temperature.
At some point, I'll probably ask "Unchained" to help me set something like this up on my boat, since he's the person I know with the most experience with this, and is using something like this on his twin turbo boat. Prices on components have come down to the point where it wouldn't cost much more than a couple of good carbs. Cold starting, driveability and fuel economy are much better than can be achieved with carbs, not to mention emissions, if that should matter to you. Electronic controls will usually allow more power too.
Maybe he'd do a thread on this if there was sufficient interest.
:rollside:

[502 JET]

As I was typing my last post I was thinking F- it: GO EFI as Warp as mentioned.
If you buy two carbs and pay someone to modify them your pretty close to the efi system.I went to a local well known carb shop to get gaskets and asked them what it would cost for them to do my carbs.They charge $550. for each carb.They look real pretty and in most cases work great but for that much money I would invest in the efi system before I paid them $1100. for carb work.Tuning with an efi must be nice you dont have to get any gas on you like changing jets.