I need to get a vac reading so that I can install the correct power valves in my Holley 450s. The carbs are on a tunnel ram and there are no vac fittings on the intake. Would it work to take 1" spacers under each carb and tap in fittings for vac readings? This is a last ditch effort before I pull the tunnel ram. The carbs have around 1000 miles on them. Any help with this would be great. Thanks Keith I use an electric vac pump off of a Ford Super Duty truck for my power brake booster. This works GREAT!
I can't answer your question, but I have one for you. What year / model did you get the vacuum pump from? Pickup, or big truck? Is it feeding the booster only, or is it just plugged into the vacuum system from the motor?
I believe the pump was from a 2003. I ran it from the vac pump to a tank I made from 4"pvc. I used a 18" long PVC pipe, capped both ends and used a check valve then ran the vac line to the brake booster. If you want pictures and part numbers PM me and the next time I have it on jack stands I will snap and send some. The tank fits up under the cab.
Don't the carbs have a vacuum port ?? NOT the one up high on the carb..that would be PORTED vacuum... you want one down by the BASE of the carb ...if no ... I'll give ya an educated guess.... been there...(i'm ***uming you have some CAMSHAFT too) ... try a 4.5 ............. ....... jersey Skip
Couldn't you just get a reading off of the intake side at the base of the carbs? I like the spacer idea, and it's reusable...
The one on the carb is for the vac advance and I was told not to use that one. I run an MSD Pro Billet Dist with mechnical advance. Theses are mechnical carbs not vac.
There are no vac ports on the base at all. I just went and looked again just incase I had a brain fart. So I take it I can use 1" spacers with taped fittings? Should I use a Tee and run vac line to one hose for the reading?
Yea.. you can do that ( that'll give you MANIFOLD vacuum--that is what you WANT)...but you SHOULD be using MANIFOLD vacuum to your dizzy anyhow ...NOT ported vacuum... read C9's EXCELLENT post on timing in the tech archives......... ..... jersey skip
you could put a spacer under the carb to measure vacuum, or you could just drill and tap a hole in the manifold if there isn't one already (I would believe that there is not one already). guys, he said he has a mechanical advance dist, no vacuum advance on it.... Do you have some more info about the engine, what problems you may be having with it, etc? I've never run a tunnel ram...so I may not be as helpful as some of the other guys who have....but there may be a way around your problem that doesn't involve taking a vacuum reading, which seems to be a chore on your setup.
and to answer your ORIGINAL question .....check vacuum while engine IDLES ( in gear if automatic) ... and pick a valve about 2-3" lower than your vacuum reading.....you can DO AWAY with the power valve if you like ( plug it and raise jet size about 2 sizes) .....but it DOES help when ya squeeze into the throttle in the real world....so does MANIFOLD VACUUM to the DISTRIBUTOR ... get it right and you'll see a COOLER running engine and MORE MILEAGE TO BOOT ...... Go read c9's post ......... ....... jersey Skip
I run 2 - 450's (vac secondary) on a tunnel ram as well. I had to open up the discharge nozzles from .031" to .036", I also changed over to the REO accelerator pumps as well as changing the vac secondary spring from Brown to the long yellow. One of the big things with a tunnel ram is the pump shot. All that volume of air in there added with all that surface area is alot of room for your "squirt" to condense on - making the stock settings a bit wimpy and often resulting in a pretty big flat spot. Food for thought anyways.
On the subject of flat spot, I understand that the drivetrain has a lot to do with it, and it's critical on a tunnel ram setup...if the engine can build rpm quickly because of gearing or stall speed or clutch operation, it will work better.
Holley says to take a reading and divide by 2 and that would be the correct power valve. I also tried blocking off the power valves and it ran like ****. I have a mechnical dist so the vac ports to the dist are plugged. The engine runs 160 all the time sotemp is not a problem. I also run a 700R4 OD trans with a 2800 stahl and 3.73 10 bolt posi. On the interstate I get 18 MPG. The only problem I am having is a big time stumble from a stop. I believe the plugs are shot and the power valves are also shot. As long as you feather the peddle when you take off it runs ok.
temp might be a problem...try running a 180 or 195 thermostat. A warmer engine has an easier time atomizing fuel. Definitely play with the accelerator pumps. A higher power valve number will give you more fuel at part throttle, which could help cover the lean bog you are experiencing. And the suggestion to add vacuum advance to the ignition sounds like it might help. (relatively) retarded timing contributes to stumbling problems.
After I get a good vac reading I will pull the carbs, change power valve, Install a hotter thermostat and take the dist out and put it on a machine, change weights and springs as needed to get the advance to come in sooner. Anything else besides acc pump settings? Thanks for all of your help, everybody!!
"A higher power valve number will give you more fuel at part throttle, which could help cover the lean bog you are experiencing." HIGHER Power valve numbers DO NOT give more fuel ... the numbers are when they OPEN .......not how much fuel they p***..... for instance--an 8" power valve OPENS when the motor drops BELOW the 8" of vacuum... so if you have an 8" valve and the motor idles at 7" ... the valve is OPEN then .... something you DON'T want ..... choose a valve that is at least 2" BELOW vacuum reading at idle and in gear if automatic.... power valve "tuning" can really wake up throttle response on a motor when ya get it just right .... I drove my 514 " ford with a vacuum gauge taped to the windshield and watched it as I did my daily driving..... I picked a valve that opened right at the "sweet spot" it needed ....major difference in pedal feel .... it turned out to be 2.5" above idle ........ and SHOOTERS are a MAJOR part in tuning for a responsive motor.... different shooter sizes and actuating cams will make it a RESPONSIVE set-up once ya get the right combination ..... trial and error unfortunatly is the best way .......TIMING ( static, total and vacuum) are also players in making for a responsive motor ....... when all things are in concert --- they make MUSIC to your ears ....... And get yourself the "holley book" ..... It explains IT ALL --and then some ....an invaluable purchase for anyone that runs a Holley.... ....... jersey Skip
Skip, I have copy and pasted this so I can work o it this winter. What do you think about thermostats. I have a 160 in now. 180? 195?
I won't disagree with anything you said. But think of the situation with a power valve that has too low a number for the engine it's in....it will stay closed at a throttle position/load situation where the engine could use a bit more fuel, and so going to a higher number will richen it up at that point. I just worded my sentence in a kind of misleading way, I figured when I wrote it that someone would call me on it, and you did
I have to be the biggest pest on here when it comes to picking your brain. believe me when I say that I apperciate the help... Keith
But think of the situation with a power valve that has too low a number for the engine it's in....it will stay closed at a throttle position/load situation where the engine could use a bit more fuel, and so going to a higher number will richen it up at that point. The power valve shouldn't open until you are INTO the throttle under load.....the power valve OPENS BELOW the number on the valve so too high of a number keeps the valve OPEN ( valve number higher than idle vacuum number at idle)--- just as vacuum drops as you get into the pedal ...the valve opens and ENRICHES the circut because by this time the shooters are DONE adding fuel...(vacuum goes AWAY at full throttle) that's why it must be a LOWER number on the valve than what is at idle .......if it is open at idle the motor WILL load up, be almost IMPOSSIBLE to adjust the idle circut,foul plugs and kill any mileage...... been doin' Holleys for a WHILE ......and this is the way to do a power valve tuning ...... again... buy the Holley "bible" ...it explains ANY AND EVERY tuning tip for a holley.... ....... jersey Skip
180 should be fine.. and do your testing with a WARM engine... and listen to what squirrel says too ... he's posted some good stuff here.... just has his power valve numbers backwards this time....and BUY that holley book man !!!! ...... jersey Skip
I don't think I have it backwards....you said: "too lOW of a number keeps the valve OPEN" and I'm saying too HIGH of a number keeps it CLOSED. Having the power valve closed when the engine needs extra fuel might lead to a lean stumble, right?
You say you're having a stumble off idle. This tells me the problem is in your primary accelerator pumps. If you go to larger squirters your pump volume will come on quicker and help eliminate the lean hesitation during normal acceleration from a stop. A change in accelerator pump cam will affect total pump shot volume. Whether or not you have the wrong power valves is irrellevant at the idle to part throttle transition,which is where you say your having trouble. To change the subject for a minute, I recently had a huge bog from a stop when I would floor it. The 600 Holley vacuum secondary carb worked perfectly otherwise. The problem turned out to be a restrictive air cleaner. I pulled off the Hellings style air cleaner and replaced it with a 14"x3 open style I had laying around..... Problem solved. Now I can light up the tires.
Squirrel ... you're right man ..... guess i shouldn't try and write tech with a few Captians in me ... I went back and CORRECTED the ?lower/higher ...take a look ..... geeze ..... alcohol may be good in a motor ,,,but .......duh !!!!!! ....... jeresy Skip
I don't think I have it backwards....you said: "too lOW of a number keeps the valve OPEN" and I'm saying too HIGH of a number keeps it CLOSED. Having the power valve closed when the engine needs extra fuel might lead to a lean stumble, right? __________________ to clarify again ...... the valve OPENS at or BELOW the NUMBER ON THE VALVE ... If you have 10" of vacuum at idle and an 11" ( or higher) valve it will be OPEN at idle ....or any combination of numbers where actual idle vacuum is LOWER than the valve nunber --it will be OPEN .... that's why you need AT LEAST a 2" LOWER number on the valve than what the idle vacuum reading is ..... does that make sense now ??? ( NO Captian this time ...whew !!) ....... jersey Skip
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