KPoole9008
New Member
Will a vacuum distributor work well on a sbc with a tunnel ram, two 500 cfm carbs and a 270 cam? Thanks. MAN THIS BOARD IS GREAT!!!!!!!!!!!
Vacuum distributor ?
- Thread starter KPoole9008
- Start date
donsrods
Member
PotvinGuy said:
Why do you say connect to full time vacuum? You want the ported side so the advance comes in gradually as the throttle plate opens past the port. If you connect it to the vacuum side it is all in at idle or slightly off idle.
This is one of those arguments that comes up periodically, but most companies like Edelbrock say to go on the ported side.
Don
Wild Mango
Member
The main side effect of connecting to manifold vacuum is that she won't pop and bang and cackle out the headers on a trailing throttle when you button off.
If you richen the idle mixtures up you can also get flames to go with the sound effects at night.
Another benefit is, it's a self tuning thing inasmuch as it won't take long to blow the guts out of those glasspack mufflers and then Mrs T Bucket will have another 5 minutes warning of your arrival.
LOL!!
If you richen the idle mixtures up you can also get flames to go with the sound effects at night.
Another benefit is, it's a self tuning thing inasmuch as it won't take long to blow the guts out of those glasspack mufflers and then Mrs T Bucket will have another 5 minutes warning of your arrival.
LOL!!
Ported vacuum was an attempt by the automakers to meet federal emission specs in the 60's, along with little or no initial advance. With no advance and no vacuum at idle, some emissions were indeed reduced, but the engine runs hot and rough. At idle, with no load on the engine, you want lots of advance (initial plus all the vacuum) to complete the combustion. As the throttle is opened and the engine loads, the vacuum drops and advance is taken out.
Explain, please, Railroad.
Screaming Metal
Active Member
Well, the guys are giving you solid advice! As you were told...cams have a tendencey to kill your vaccuum signal, also the tunnelram.
What you want to do first is get a Mr. Gasket/ Accel/ or Mallory spring and weight set, put it in, get all your advance coming in early. If your cam is interferring with your vaccuum, you cna always run the varible bleeddown lifters. These can tame down quite a radical cam, if over .575 lift and 275 degrees duration, then when oilpressure and RPM's come up, it goes into full lift.
Anyway, different motors like different timing settings, so play with your system some, if you got the time...but with your small carbs and a really mild cam, should have a winner on your hands.
Mango's right.....the light show is pretty good if done correctly! Ha!
Me personally, I've always loved the look of a Bucket with the fat skins on the rear, the tunnelram, then in the front the wirespoke really skinny wheels....YEA BABY!!!!
ChestersAlive
New Member
In my experience you need the initial retard of the vacuum advance system to provide easy starting. Watch what happens on a timing light when you start a car and you'll see just how much the engine has to advance to idle properly. If you advance the engine this much without using a vacuum advance it'll probably backfire through the carbuerator when you try to start it.(One of my ex-wives got all her hair torched this way!) If you have a wild cam, blower, or tunnel ram, spring the money for a Mallory mechanical advance distributor. It will save you a lot of headaches and maybe a furious wife!
ChestersAlive
ChestersAlive
Screaming Metal
Active Member
Hey dude, do a search for timing, distributor advance, all the guys here and I have hashed this one out on countless occassions, remember when Rooster was having trouble with his dist.?
Anyway, yes, to answer your question, you can run Vaccuum advance. Thats what we ran back in the old days unless we had a really hot setup, then we'd go to the full mechanical dist. advance.
My personal preference is the Electronic dist's with the built in rev limiters...cheap insurance.
Choctaw Bob
New Member
Try it and see. You will know pretty quick if you don't have enough vacuum. Pre emission cars had the vacuum advance directly from the intake. If your distributor is a 60s stock dist, it probably has the diaphragm and spring for full vacuum.
Your engine will run fine with the advance plate screwed down like a drag car and the distributor timing set to full advance. The only problem with this is low speed drive-ability and fuel mileage.
ChestersAlive
New Member
I have a question to someone who runs a daily-driver with a blower. I have a 350 in my Apache project and have installed a Wiand blower from Jegs and plan to run about 5 lbs of pressure. Since I have eliminated the vacuum, is there a way to run a vacuum advance distributor on this daily-driver? Can I get any vacuum from the engine at idle? The power booster is another problem, do I have to get one of the electric vacuum pumps? The cam is one of the solid lifter,1970 Corvette retros from summit. I changed the 202 closed chamber heads for 194 open chamber heads because I have flat topped forged pistons. It runs a 2500 RPM stall converter and 350 Tubo. No bulls--t comments from wanabes here please, this forum is full of experienced racers who can answer me with the truth. This truck will probably never see the track, I just love the sound of a bad-ass engine. My foot will probably be on the brake more than the gas pedal idling around town so I absolutely need that power booster 100%. I have my ideas but would like the advice from a man with a lot of experience with street blowers, not just someone who had one installed for him on his rod.
ChestersAlive (I don't know how,but I am)
ChestersAlive (I don't know how,but I am)
Screaming Metal
Active Member
Yes....you can run vaccuum advance on the blown engine. A blown engine pulls a vaccuum at idle....if you rev a blown engine slowly.....you still got a slight vaccuum....not much, but some....
ellis8500
Member
Here's info posted on T-Bucket Alliance site about vacuum advance.
It's time to talk CONNECTIONS! All carbs which are designed specifically for street use have multiple vacuum line connections available on the baseplate. There will be one large nipple, and up to 3 small nipples. The large nipple is for your PCV connection. And, the others for Transmission modulator, distributor, and an optional timed port(Holley/Ford only). It is very important you connect these properly!
RULE 1: Do not "Tee" any vacuum connections except as a very last resort.
RULE 2: Never "Tee" anything to the PCV connection, I mean NEVER EVER. This line gulps huge amounts of vacuum to extract fumes from your block. Anything else connected here will virtually not function at various throttle positions.
RULE 3: check all vacuum connections with a vacuum gauge to be sure they have a continous vacuum signal, especially the distributor, transmission modulator, and PCV.
RULE 4: Wherever possible, direct connect the PCV and distributor to the intake manifold instead of the carb. The intake manifold is much faster at responding to vacuum signals than the carb.
RULE 5: (Holley Carbs) Never use the vacuum nipple located on the metering block for GM distributors! That port operates BACKWARDS to what your distributor needs. This is reserved for selected OEM Ford distributors ONLY.
RULE 6: Always check your total advance after setting the lowend timing. It is imparative that you do not exceed the limits of your engine/fuel type combination. Failure to check this could result in high speed detonation.
Lee_in_KC
Active Member
Hey Chester, here's some input for you on your blower questions. I have a 6-71 on my T. It's not my daily driver per se, but I do drive it almost daily during the hot rod season here in KC. I set my blower up myself and have been tuning on my motor for coming up on five years. I have a boost/vacuum gauge tapped from the intake manifold (below the blower), and I have a test vacuum gauge that I hook up to the un-ported vacuum tap on the primary carb for tuning purposes. I'm running the blower 1:1, which BDS sez should make 7 lbs. of boost at 5,000 rpm. The most I have ever actually seen on the gauge is 5 lbs. My cam is a Comp hydraulic roller "blower" cam... 224/236 @ .050, .485 lift, 112 LSA.
When I first set this all up, I was surprised at how much vacuum there is under the blower under normal driving conditions. At cruise speed, partial throttle, 2,500 rpm I typically see 8-10" of vacuum under the blower and about 11-12" above the blower. At idle (900 rpm) I see 11-12" under the blower and 17-18" above. What's really interesting is when I let up on the gas to slow down for a stop, the vacuum above the blower pegs at about 30"! I assume this is because the blower is spinning at cruise rpm when I close the throttle, and since a roots blower is positive displacement, the blower is really sucking hard on the closed throttle creating maximum vacuum.
So here's what I would suppose... if you tap the vacuum above the blower you will get a reasonably strong vacuum signal for your distributor and you will pull enough vacuum for your brake booster, since the throttle will be closed when you're applying brakes.
Now, I ran a vacuum distributor for the first two years I had my T on the road. I was having timing troubles so I removed the vacuum advance and just went with mechanical (18 initial, 34 all in by 2800) while I tried to diagnose the timing issues. It turned out the degree tape on my crank hub was off by 20 degrees
uch: so i corrected that and got the timing worked out. But I never re-installed the vacuum advance because I really didn't notice any difference. I'm intentionally running my carburetion rich to stay away from detonation, so fuel economy isn't a concern for me (6 mpg city, 9 hiway :news.
This winter I'm going to put the T on a chassis dyno and put a good tune on it. I'm assuming I'll be jetting down a little once I can see the actual A/F on the dyno, and I may put the vacuum advance back on, as well.
When I first set this all up, I was surprised at how much vacuum there is under the blower under normal driving conditions. At cruise speed, partial throttle, 2,500 rpm I typically see 8-10" of vacuum under the blower and about 11-12" above the blower. At idle (900 rpm) I see 11-12" under the blower and 17-18" above. What's really interesting is when I let up on the gas to slow down for a stop, the vacuum above the blower pegs at about 30"! I assume this is because the blower is spinning at cruise rpm when I close the throttle, and since a roots blower is positive displacement, the blower is really sucking hard on the closed throttle creating maximum vacuum.
So here's what I would suppose... if you tap the vacuum above the blower you will get a reasonably strong vacuum signal for your distributor and you will pull enough vacuum for your brake booster, since the throttle will be closed when you're applying brakes.
Now, I ran a vacuum distributor for the first two years I had my T on the road. I was having timing troubles so I removed the vacuum advance and just went with mechanical (18 initial, 34 all in by 2800) while I tried to diagnose the timing issues. It turned out the degree tape on my crank hub was off by 20 degrees
uch: so i corrected that and got the timing worked out. But I never re-installed the vacuum advance because I really didn't notice any difference. I'm intentionally running my carburetion rich to stay away from detonation, so fuel economy isn't a concern for me (6 mpg city, 9 hiway :news.This winter I'm going to put the T on a chassis dyno and put a good tune on it. I'm assuming I'll be jetting down a little once I can see the actual A/F on the dyno, and I may put the vacuum advance back on, as well.
dustytrails
Member
if you dont have any ported vacume connections and have to T for dist vacume and trans modulator what else can you do
Wild Mango
Member
The reason you don't tee vacuum signals is that the diaphragms on the vacuum devices tend to "modulate" each other because they don't respond to the same vacuum signal. It'll drive you to cheap drink trying to set them up because the same thing never happens twice.
At a pinch you could drill and tap the manifold (1/8"gas hose barb)for a full vacuum signal which would do the trans and plug the distributor into the other one.
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