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  #1  
Old 08-19-2002, 10:35 PM
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Default Part 2-Power Valve Tuning

OK the long awaited part two in this continuing saga is finally here:

Power Valve…. What the heck is that?

Let's first of all look at the function of the power valve…when you initially stomp the throttle open the front end of the carb is running 8 jet sizes smaller (right?) so it needs to catch up to the rear…we'll explain this off balance situation in a moment.

If you look at a metering block where the P/V screws in, you'll see two tiny holes, these are called the "Power Valve Channel Restrictors", big name for a couple of little holes. This is where the fuel dumps through the power valve to richen the front half of the carb when you smack the throttle. Remember what I said about the 8 size smaller jets in the front?…well the "Power Valve Channel Restrictors" dump fuel through the valve at a rate equal to a #8 jet which gives you the balance we're looking for…so the big question? Will a Holley power valve work in your BG carb?
I don't know as I don't have a Holley P/V to compare it to or can I find any specs on the efficiency rating of a Holley P/V…but you know I have this gut feeling that they're probably not quite the same. So lets say you don't have the required 8 size split in the front side…..your going to have a lot of problems getting it to transition from the idle circuit to the primary circuits properly resulting in a hesitation or stumble. Having the incorrect jet split will cause the front and rear sides to operate at different A/Fuel ratios especially during the transition.


The correct way to determine the optimum vacuum rating of the power valve is to first hook up your trusty vacuum gauge to the lower or below the throttle plate spud, now fire it off and drop it in gear….. You'll probably see a reading of 6-12 depending on the amount of overlap on your cam for this example we'll use 8. This is of course after you have everything else set correctly in the idle circuits and timing.

The formula is 1.0 to 1.5 below idle in gear vacuum, so we would use a 6.5 power valve in this case. This is the correct method and you should not vary from it.

I want to address some idle questions that have been filling my email box, one of the major problems in getting your performance engine to idle is lack of idle timing a high compression engine with a big cam needs timing to burn the required amount of fuel to make it run. Don't expect your hot small block to idle at 900 with 10 degrees of initial timing in it, it just won't happen. You need about 25 to 30 degrees of initial timing to enable the engine to burn the fuel efficiently and not drip it out the collector. To test this theory if your having problems getting it to idle using my instructions in Part 1 and try advancing the timing at idle up to about 25 and then give it a try, you'll find the idle speed will jump way up…why? You didn't give it any more air or fuel??? Your now burning all the fuel, so now idle down and do your four corner adjustment …you'll now have that crisp snappy throttle response that we we're looking for off idle.

CAUTION!!!!!!!
This is ONLY a TEST you cannot run your engine this way you'll end up with 50 degrees of max timing if your distributor is not curved correctly and catastrophic failure or death may occur.

Ok so now we've got the idle circuits adjusted, the idle timing set correctly, just snap the throttle a bit and you'll see that that hesitation is gone and you'll get the urge to take it for a asphalt ripping test drive…stop! see previous paragraph.

When you go to the distributor shop and tell him you want 25 initial and 38 max at 2200 he's going to look at you funny……he's just used to Holley's and Edelbrock's and there insensitive idle circuit and transition technology.

HOT TIP:
For you drag racers looking for that bottom end tork to annihilate your 60' times, stick a 1"- 4 (FOUR HOLE) spacer under your Demon.

Next chapter we'll talk about nozzle extensions, critical fuel velocity, wet flow Vs. dry flow, accelerator pump cams and maybe more. I'll explain how and why a 750 Mighty Demon 540-2010GC flows at 930CFM on the Holley tester….you won't believe it!

How about a bigger carb that will actually lean your motor down…..

When we're done here you'll all be experts and able to tune your Mopar to the optimum with ease at any altitude………..

This is Cuda66 for Mopar Mystery's…. soon available in paperback….well
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  #2  
Old 08-19-2002, 10:49 PM
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Ed...can you stickey this one to the others?
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Old 08-19-2002, 11:21 PM
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It's stuck.
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Old 08-19-2002, 11:30 PM
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Cool Cuda66273

I would like to thank you for your sharing with all of us. I am saving all of your prints.
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Old 08-20-2002, 12:01 AM
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Hey maybe you'll get it published before me!...LOL

I was at the track last friday and there was a group of young Moparians huddled under the hood of a fine old rusty Dart...they had one fist full of paper and the other full of screwdrivers, feverously thrashing on an nasty looking Edelbrock...I strolled by and asked ..."What are you Guy's doing?"...the owner of the car explained that he had gotten this hot tune up deal off the internet from a Buddy of his...guess what....LOL

I guess they missed the part "If a Big Ole Fat Guy with a dirty old Dodge hat walks up...hand him the screw driver"

I just chuckled and left them to it...they were having way too much fun.

I saw them jabbering in the staging lanes later and giving each other high fives so I guess they got some improvement out of the old beast.

ED:
Thanks for the sticky

Did you have a chance to review the Detonation post?....maybe a sticky?
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  #6  
Old 08-20-2002, 12:31 AM
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73Challenger11@ 73Challenger11@ is offline
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Ok Don I had my dist curved for my MP .509 so I don't know the max setting for the advance is.Now how much can I rely on the vacuum advance in this process?
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Old 08-20-2002, 12:41 AM
Tarrbabe Tarrbabe is offline
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Cool cuda66273

I had missed the post but went back and copied it and saved it. Thanks for the info.
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  #8  
Old 08-20-2002, 01:35 AM
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73 Chall:
I would put my dial light on it and check it through all stages, but your in Wi. and I'm here in Oregon.....try and find a dial light and see where your getting max advance with and without the vacuum advance....Ideally about 2200 for max for racing and 2800 for street, and all you can get at idle..let me know what the numbers come out at.
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Old 08-20-2002, 01:59 AM
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I'll try what you suggest when I fire it up towards the end of the week and I'll let you know what I get.

Lou
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  #10  
Old 08-27-2002, 09:06 PM
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wow

Hey cuda66273, I just went and tried what you said with timing and It idles nice now...picked up another 4 inches hg. I disconnected the vacuum advance and tweaked the idle mixtures. I couldnt resist going out in front of the house though. I pulled out of the driveway and let it rip!!! I had all I could do to keep it on the road!!! The rear was all over the place with tons of tire smoke I almost went in the ditch!! I had to clean my pants after I pulled back in ( don't you just love that feeling?) I just need to get the dist curved now though. 25 initial and what 35 in at 2500? Doesn't that add up to 60? Its a speed demon 850 by the way. One problem, it seems to have more power with the throttle just before full. I hooked up a vucuum guage and ran it. It happens when vacuum gets below 5". It was doing this before the timing adjustment both with and without vac advance connected. Anny suggestions? Its a 440 in a duster.
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Old 09-04-2002, 01:38 AM
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Don,

Let me serve this one to you...

I am seeing the manifold and cam bump that power valve open at 1 to 1.5...

@ 1100 I am pulling about 6 lbs of vacuum... Should need 4.5 front and rear... I put a 4.5 and it keeps bumping open - had to go to a 3.5 - that cleared it up.

I assume this is due to the extreme nature of this engine???

Thoughts?

BTW - this is the first time I have ever seen it stray beyond 1.5,,,

Another question - We usually take the secondary power valve out for street / strip - what about leaving it in???

Do you think that would clear up my rich condition down low??

mkm
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  #12  
Old 09-04-2002, 02:12 AM
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"I put a 4.5 and it keeps bumping open - had to
go to a 3.5 - that cleared it up."

When you get down that low it's almost impossible to keep a steady vacuum pressure and the variance in the P/V's couild cause this bump open problem...look at it as a % of total vacuum.

"Another question - We usually take the secondary power valve out for street / strip - what about leaving it in???"

I wouldn't do it, as soon as your vacuum drops to 3.5 your gonna add even more fuel, exagerating your condition.

Have you tried more initial idle timing to see if it burns the fuel better at lower RPM?

I think your getting overconcerned about that 2500 RPM rich condition...can you send me the Dyno Sheet? I talked to Jerry about your numbers as I could remember and he seemed to think that your real close.
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Old 09-25-2002, 05:34 PM
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Cuda: Don't want to get picky here, and my memory may be failing me. It has been a long time since I played with the Holley. If I remember correctly, the Power Valve Channel Restriction (PVCR) holes are in the metering block of the carb, not in the power valve itself. They are the two holes located on the taper, just above where the power valve screws into the metering block. This is a good thing, as you can drill them to whatever size you want to get the proper WOT mixture. The holes in the power valve itself are set to be bigger than the PVCR, so they don't cause a restriction. The power valves with holes are for small PVCR setups, and the square opening (picture window) power valves are for larger PVCR setups. This is a great setup, as it allows you to tune when and how much enrichment you get.

The only exception to the non-metering of the power valve is the two stage units, which open progressively at two different vacuums. The first stage opens at higher vacuum and has a restriction that is smaller than the PVCR area, so it limits the enrichment. The second stage opens bigger than the PVCR and at a lower vacuum, so the enrichment is handled by the PVCR size. Getting the correct two stage power valve, and PVCR size is very tricky, but can really improve part throttle response.

I hope this makes sense!
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Old 09-26-2002, 08:05 AM
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"If you look at a power valve you'll see two tiny holes in the metal case, these are called the "Power Valve Channel Restrictors", big name for a couple of little holes."

Your right I didn't explain that very well....I meant the metering block when I said the case that it screws into...I'll edit the post..thanks for pointing that out.
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Old 09-26-2002, 08:15 AM
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Turbododge:

Great addition to this post...thanks

Unless you really know what your doing and have some way to measure the fuel delivery and engine requirements I wouldn't suggest that anyone start drilling out their Demons as Turbo explained..

Quote "Getting the correct two stage power valve, and PVCR size is very tricky"
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Old 09-26-2002, 11:57 AM
turbododge turbododge is offline
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Cuda is very wise to advise caution (especially with a drill). I do think that there are some big gains to be made (in a lot of cases), by doing the more sophisticated (and dangerous) tuning changes. The best thing to do is to find yourself someone who really knows their carb tuning (you will be able to tell by driving one they have tuned) and work with them to learn how. The availability of air fuel mixture meters has helped a bunch, but understanding and experience are still the biggest factors.
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Old 09-27-2002, 01:32 AM
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Yes, it's fast and No, you can't drive it...LOL

I had a guy come up to me the staging lanes one morning and offer me $50.00 to make one pass in the Fish.....I almost took it.....but then I took my little blue sanity pill and said no....

I have a nice set of matching metering block paper weights on my desk....slightly altered with a drill bit...I was nice and only charged him $250.00 to fix it and adjust it properly...

He was used to one of those Holley's where the mixture screws are oposite...in richens and out leans talk about screwed up or would that be screwed down.....LOL I think they were made for the Australian market...
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Old 09-29-2002, 09:18 AM
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Quote:
Originally posted by cuda66273
Yes, it's fast and No, you can't drive it...LOL

I had a guy come up to me the staging lanes one morning and offer me $50.00 to make one pass in the Fish.....I almost took it.....but then I took my little blue sanity pill and said no....

I have a nice set of matching metering block paper weights on my desk....slightly altered with a drill bit...I was nice and only charged him $250.00 to fix it and adjust it properly...

He was used to one of those Holley's where the mixture screws are oposite...in richens and out leans talk about screwed up or would that be screwed down.....LOL I think they were made for the Australian market...
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Old 09-29-2002, 09:21 AM
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Sorry about the last nonsical reply..I meant to add "is that why the carbs sent to us down under dont work???"
Keep the good stuff coming, it may even work for us lot..lol
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Old 09-30-2002, 05:47 AM
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Must be....LOL
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Old 10-02-2002, 10:25 AM
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Default Power valve tuning

cuda you have some of the best post i've ever read, very informative[ i think i spelled it right]. I need alittle advice. I have a 72 dart that weights 3270 w me in it, has a 360 10.1 cr with stock edelbrock heads, hughs he 4854 cam 556/.570lift 248/254 I'm using my 1.6 crane roller rocker . Intake is M1 single plane w/ a 1 inch open spacer and a 800 holley d/p w/76 front 84 rear jets. Ignition is a MSd 6al with the mechanical Ditributor set at 16 inital 35 total all in by 2000 rpms 4400 stall Dynamic converter and 3.91 gears. Best time so far is 12.145 at 110.83 60 ft was 1.74. I think theres alot more left . My problem seem to be ihave 1 to 2lbs of vacuum a ideal so i put in a 2.5 power valve it still ideal very rich.But ideals find and is very reponsive,no stumble or bog. i think i might be losing some Hp in this area, any input you have will be very helpful. thanks Beeman
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Old 10-02-2002, 11:36 AM
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Right off the bat I see a few of things...

I presume that your quoting me cam duration at 50?

So based on that ....

Too Much Carb...with the stock Eddy heads and with your compression ratio at 10:1 I would run a 650 Mighty Demon.

If you pull the heads and do some cleanup work, gasket matching etc. and cut them to bump the compression 1 to 1.5 points then you could possibly gain from a 750 but I doubt it. A 650 Mighty wet flows at around 800 CFM but maintains the velocity of a 650 which is what you need.

The open spacer is wrong, you need a four hole spacer and not one of those cheap $20.00 Chinese ones, you need a good one like the BG 110072. The open hole spacer is for top end and causes the fuel to ball up at low velocity and drip into the bottom of the manifold, which could be part of your rich idle condition.

The power valve is way to small but you need to find out why your vacuum doesn't make sense first.

Timing...you'll find that when you get the fuel problems fixed it'll want 18-20 degrees of initial and about 36 of total.

Vacuum....1-2 inches....somethings wrong...you need to find out why....could be a bent or poor sealing valve or a vacuum leak but that's not right...try another gauge. I have more duration and compression that you and I have 7.5 - 8"'s and run a 6.5 power valve.

Do a leak down immediatly, did you check your valve to piston clearence with the 1.6 rockers?

Have you checked the valve geometery to be sure your not pushing the valves sideways in the guide and hanging a intake at low RPM???

I see easy 11's in your future which also means your fuel system needs to be able to deliver 1 gal of fuel in 30 seconds or less...please don't tell me your running a Holley Red or Blue pump.....

That should keep you busy all weekend...and you thought you would just sit around and watch Footsball all weekend....

You could also be way to far open on the throttle plates to allow enough air in to achieve an idle, you need to get the throttle plate nearly closed to correctly measure the vacuum, otherwise you've just got a big hole in the manifold.

Pull the carb and look at the transition slots...about .020 is all that should be showing under the butterfly's.

Are you sure your measuring the vacuum from the manifold port and not the ported vacuum side?

Lemme know, we'll work through this and get that Dart screaming!
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Old 10-02-2002, 05:53 PM
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Default Power valve

Yes the cam mesurement are at 050.I checked the cranking cylinder pressure awhile ago and they all were the same 175 lbs. Before i went to the hughs cam i had the mopar 292 / 508 and still had no vacuum or close to it.the spacer is made by TD performance product, and your right i did'nt like the look of it when it arrived from summit but i still used it. Yes i use the vacuum port at the base of the carb and not the one on the side of the metering block. I tried lowering the ideal but did'nt raise vaccum at all. The ideal adjustment screws ar turned out a 1 turn each, like i said it ideals fine just very rich . I'm Not going to tell you i have a Holley electric pump. Thanks for your time beeman
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Old 10-02-2002, 08:47 PM
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The spacer is probably part of your problem and I personally wouldn't go any further until it was swapped out for a 4 hole.

If you look up my post "AMX Project" you'll see what I found with the same spacer as you have....

Holley Blue pumps pump at 94 GPH, reds at 75 GPH or somewhere near there. There $29.00 regulator that comes with them flows at about 90 GPH....nuff said

BTW did I mention that I still have 2 of the BG 280 pumps and BG 5000 filters on sale for $295.00 for both.
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Old 10-03-2002, 09:34 AM
beeman beeman is offline
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Default Barry gant Spacer

Hey Cuda can you get me a four hole spacer you recommend? Let me know cost and how i pay you. I'll Try this first and see what happens. Also let me know on a reg ulator i have a holley on ther now. thankya thankya very much!
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Old 10-03-2002, 12:18 PM
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I am out of stock on the BG spacers but I do have the Canton 4 hole on the shelf..it's a little cheaper and as near as I can tell Identical..I'm not inferring that they make them for BG I'm just saying that there nearly Identical....

Stock is good on the BG pressure regs.

Email me your order off the board
cuda66273@hotmail.com

or call me at 503-830-1368
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