Holley 94's on race motor (power valves)?

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old28

Well-known member
Joined
Aug 22, 2009
Messages
681
Location
Camarillo, Ca
I am running two holly 94's on a Clifford 2x4 intake with adapters on my Chevy 194 race motor in my vintage dragster. Currently both carbs run 51 jets and 4.5 power valves. The carbs do not use progressive linkage and both open together.

Plugs and exhaust zoomies are very rich. I have always removed the power valves in my 4bl race carbs and tuned by checking the plugs and adjusting the jets.

Should I remove & plug both power valves and tune with my jets only?

This motor idles at 1200 rpm and runs 5800 - 6200 thou the lights.
 
Picture of the carb setup.
 

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Power valves on the 94's

Often called economy valves....can be had in 3.5 as well as the 4.5....but my thoughts are that if it's rich at 4.5 then a 3.5 probably won't help much.....since you are basically wide open most of the time.....so vacuum signals are even lower than that.....I'm assuming you have checked your float levels and also your fuel pressures and ign timing as well....so given that, try tuning with jets only and see if you can lean it out....just be careful you don't go too lean and hurt something.....of course this is JMHO.....:D
 
sgtpontiac -- Both of the 94 carbs are fresh rebuild, the float level is correct, I have a low pressure regulator & gauge set at 3.25# (94's should be 3.0-3.5#), Timing is 36 deg @ 2200 RPM. Like I said before I have always removed and plugged power valve on race only carbs. This is a race only motor.

Currently 51 jets in both carbs & 4.5 PV, I am thinking I might try 53 or 54 jets with the PV plugged as a starting point, what say?

bobw --Had this over rich problem before the rebuild so I am sure plugging PV and stepping up a few jet sizes will be OK? Maybe I should try just plugging PV first and trying the 51 jets.:confused:

I think you are right that with the cam I have in it there is no vac at the hit. Does that mean that the PV is full open at the hit? If it is that's way to much fuel. I think I can do a basic plug test in the shop getting motor up to race temp (195 deg) and then check the plugs.
 
I'd error on the side of caution...

Go to the rich side on the jetting after closing the power valves and then get some full pulls (in a safe area..lol) and do some checking of the plugs..not sure you'll get a true plug reading without a true full pull......even if you have to step up a heat range or two on the plugs...I'd rather run a bit rich than lean it out and melt a piston or two....jmho....I think without the power valves you'll find that the 51's will run lean.....I'd start with the 53's.... you might even find that you'll need to do some drill sizing to get it where you want .........jmho..... :D
 
sgtpontiac -- I'm with you on this, I am using next to hottest plug heat range right now. I have jet sets for both carbs in 50,51,52,53,54,55.

I will make sure the motor is not to lean, this little Chevy 194 L6 with short zoomies will let you know during worm up if it does not like fuel setting. I think I will try 53 jets the first time with PV plugged.
 
Good luck....

keep us advised.....sounds like you got a cool little ride there....never saw anyone do much with the 194 motors....very cool ......
 
I was able to make 3 street test of about 200-250'. The two 94's have both power valves removed and plugs installed. Both carbs have 53 Holley jets in them and I have the accelerator pumps on the #3 setting (longest stroke with most squirter flow). 3.75# fuel pump pressure.

Made my street test with 3 leaves at 1800-2000 RPM. First one the motor was not up to temp (about 140 deg) and the car coughed through the front carb after about 20', On second try motor was up to 160 deg and it was strong at the hit with no hesitation and pulled strong for the 200'. The third pass temp was at 175 deg and I have never felt it pull from a dead start like it did. Removing the PV and plugging was the correct move. I will not be able to see if the 53 jetting is rich/lean until I get it back on the track, but I like what I see.

I pulled the plugs and they were way more dry than before and it was easer to start the motor and set the idle.
 
Success! Glad you got it figured out, Tom. Now you gotta beat the guy with all the carbs, next season.
 
Well I don't know if I can beat him, but I think the sound 194/PG on his tail may play hell with his shifting, we will see.;):D
 
somehow I missed this one, been off line for a few days, and it sounds like you have a handle on the situation.

A few after thoughts.

Holley 94's are known to have an odd sized PV gasket, and many non Holley gaskets don't seal properly, causing an over rich condition.

while many people have for many years plugged off PV's and raced very successfully, it causes the engine to rely on the main system for part throttle A/F ratio, and because the main jet has been increased to compensate for the plugged PV, you are now driving around at part throttle in an over rich condition with a (usually) colder heat range spark plug which may adversely effect the engine when next asked to go full throttle. I found that by installing a vacuum gauge permanently in the dash, and noting vacuum at idle in gear, at idle at staged rpm, an at full throttle crossing the finish line. with the vacuum readings noted you can determine which PV to use, you want it closed at idle, closed during staging (usually higher than idle but controlled for staging) and open at full throttle. with these tiny carbs there is the chance that you may build vacuum in the manifold as you near the finish line if the demand for air is high enough below the throttle plates and the carbs are a restriction you could see a rise in manifold vacuum high enough to close the power valve, resulting in a lean condition.

So, what does this all mean, I prefer to keep the power valve in play, as driving the car around the pits and staging area is done on a lean and clean secondary circuit, which keeps the plugs all shiny and clean. It takes a bit more tuning up front but once set it will make life tons easier.

the zoomie headers while zoomie looking, detract form the low rpm tuning of this set-up, they would be perfect in a clutch set-up that left the line at 5000 rpm. with a torque limited trans like the PG (its like starting out in second gear in a 3 speed) and no trans brake you need all the low end torque you can muster. a proper length 3 into 2 header would be way superior to the zoomies. UNLESS the zoomies kill enough bottom end torque to make getting off the line with hard 6" street tires easier.

just my 2 cents.
 
BlueNorther -- I like you have been off the thread for a few days and just saw your post. Before I get into it Thanks for all the information, some real good points. I will try to brake it down a bit.

Yea, that gasket was the first thing that came up as the newer Holley 4BL PV plug uses a much bigger gasket & most be replaced. I happen to have some misc gaskets left from my fuel injection units and found some that worked.

I have a vac port on the intake that I can temp use to see what vac I have at in gear idle, stage (2200rpm) idle, but there is no room for a permanent vac gauge. I will test both of the first two as soon as I get the new motor in (hope end next month). I am fairly sure that my cam spec's kill all vac at idle and stage so the PV are some what open from the start. This cam was turned to kill the bottom end torque some what as these cars weigh only 1400 #'s and will fry those 6" tires for 20-30' if you can't help the system out. I will check vac & report back next month.

As for the zoomie headers they are not the way to go. First off they work fine on the bottom end but you need the 3 in 1 in about a 28-34" length to make some power for the top end pull. I have a Sanderson L6 kit that will go on the new motor that should work very well. I forgot to add that I don't drive the dragster to & from the strip (pit cart) as I have a very small radiator so I can get my temp up to (175-185) range in short time as this motor is happy in that range as has no lag.

Bin drag racing BBC FM dragsters/altered for going on 49 years with good suggest and this little 194 L6 has challenged me more than all the others, but I keep learning and it will all be good. Keep the information and ideas coming.
 
BlueNorther -- bobw -- and all that have helped with my race carb problem, I would like to bring this thread back up so I can add some more information to it.

First let me tell you where I am with the 94 carbs that are on my Vintage SDRA dragster. I have removed the power valves, plugged and have 53 jets in both carbs. I was using the idle circuits on both carbs. I have rebuilt the head with bigger SBC 1.85/1.60 valves and milled .060 off the head face. I built a set of 3 into 1 headers for the car and got rid of the zoomies.

Yesterday I made a couple of street tests with the car. The motor felt a little on the fat side and was not crisp at running temp. You can see the test on You Tube -- http://www.youtube.com/watch?v=ItoOfRn661Q

Today I ran some Vac tests and they told me what I had thought that with the race cam I run the Vac is real low at idle. Some of the readings, Idle RPM 1200 w/13" Vac / Stage RPM 2200 w/5" Vac / anything above 3000 RPM have -0- Vac.

I was running 4.5 PV in both carbs and I am sure they were starting to open or open when I was staging the car and it was loading way to much fuel at that time. I really do agree with BlueNorther that it's better to run the PV if you can make them work. As all PV for the 94 carb flow the same amount (just come in at different Vac, I am thinking of going to 2.5 or 3.5 power valves so I am sure they are closed up to 2500 RPM and going back to 50 or 51 jets in both carbs. Also I have screwed in the idle screws on one carb all the way in and idle off the second carb with the screws out 1 1/4 turn each.

Sorry it is so long but we don't need to go over old information. Comments
 
first let's visit the stamped number on the power valve, you are currently using 4.5's, that is the opening point of the PV.
it is closed above 4.5 inches of vacuum and open below 4.5.

depending on how accurate your vacuum gauge is you are very close to optimum, idle vacuum at 13" is good, 5" at stage should be ok, 0 vacuum at 3000 is expected, and as long as it doesn't rise above that at 5-6000 rpm and above you should be good. I think I would go to a 2.5 PV and try a full run and watch that the vac. stays at zero as you approach the finish line. some times an engine with a lot of flow potential will go to zero vacuum down the track and gain a vac. reading above the opening point of the PV at high rpm, causing a lean condition in the last 2-300 ft. of the run.

once you settle on the PV it's a matter of jetting for power at the track. going richer from your base line one or two jet numbers at a time.

keep going richer as long as the e.t. comes down and mph goes up, and watch for the first fall-off of mph, the mph will fall off from too rich just as you are approaching proper richness for E.T.
 
Oops, forgot!

I would run all 4 idle screws at the same turns in-out, as the idle circuit has an effect on the transition from idle to intermediate to main circuit.

it will make for a much smoother transition if they are all equal.
 
BlueNorther -- The power valves are from Vintage Speed, FL and have the proper gaskets to get a good seal. I have checked there operation and clearance and they are fine. I am going to order two 2.5 units and try them with #50 jets in both carbs. They have a straight linkage setup and both carbs are synced with an Edelbrock unit. I have Jet sizes from 48 - 56 for the 94 carbs.

Part of the reason I tried the standing idle at 1200 is when I drop it in gear the RPM drop to 1000 and the motor is real smooth. Today with one carb as the idle circuit & the other closed I was able to get the motor down to 900 RPM and when I dropped it in gear it stayed at 900. After I get the new 2.5 PV I will try it both ways.

I do feel that with the PV plugged and 53 jets the carbs were to rich during the staging time and even though the motor did not bog it was not crisp.

Should have the parts in 5-7 days and be able to test it again in a few weeks.

Thanks for the comments
 
Tom,
I don't have anywhere near the carb knowledge BlueNorther has. But I love to see myself in print. Just kidding. Some carbs (maybe all?) keep the idle circuit in play during cruise and acceleration modes of operation. The idle circuit supplements the main metering circuit. So it's possible you would have a different Air/Fuel ratio on each carb by closing off the idle circuit on one.
I kept all three idle circuits adjusted the same on my dragster.

I love the video, you rebel, you, tearing up that nice quiet neighborhood.
 
BlueNorther & bobw -- Thanks to both of you for the information on my carb setup. I think we are all on the same page on the carb settings and when I get the 2.5 PV I will reset the idle screws so they are the same on each carb.

I can see after all the playing around with the 94's why most people just put a 500 cfm 4bl on and go play, but I am an old school guy and I love the look of multi 2bl carbs on hot rods and vintage dragsters. I am also way to stubborn to let these little 94's win the mine game. With your help I will make this setup work.

Really the people on the block like this car way better than the 502" injected BBC Altered that I had before and the kids love it. I do try to keep the tests to a minimum.

I'll get back on in a few weeks after my next test.
 
BlueNorther -- bobw --- & others -- Well I found some information while I was taking the carbs apart a few days ago that explained a lot of things. The two power valve that were in the 94's when all this started were not (4.5), they were (7.5). At idle 1200 rpm and 14" vac every thing was fine, but as I was moving in to stage at 2000 rpm the power valves were full open and the motor was way rich at final staging and on the leave. At 1800 rpm I have only 4" of vac and -0- vac at 2800 rpm on. It's ruff getting old and you can't remember what you installed.

Had a talk with my race buddy (Frenchtown Flyer) today and he said the reason most racers plug the PV is because with the cam duration we run and the low vac the 2.5 & 3.5 have so little vac holding them closed that they are prone to leaking caused from the harmonics of the 6 cylinder motor.

Bob, for your information the power valve & main jets from Holley will fit the Autolite 2100 (1.02 & 1.08 venturi) carbs.

I will try the 2.5 PV & .050 jetting for my next street test, just firing the motor in the shop it sounds a little crisper. I will try this setup for first on track pass and then I want to try a pass with PV plugged and a set of .053 jets. Also I may pickup a pair of 3.5 & 4.5 power valves for future on track testing.
 

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