351c vaccuum

[69me 10]

does anyone know how much vacuum a Cleveland should have? im trying to set the idle mixture and im getting about 10 -12lbs on the guage. seems a little low to me but I am not sure. thanks, mike.

[barnett468 418]

.

 

what are your eng specs?

 

how hot does it run?

 

 

your vacuum should be around a minimum of 18 on a stock properly tuned engine that is in good condition . . if it has a high perf cam, it will be less.

 

plug your dist vacuum and leave it plugged until further notice.

 

set your timing to 6 degrees btdc.

set your idle fairly low.

 

advance your distributor 3 degrees . . listen for an increase in rpm and vacuum if you have a gauge.

 

if the rpm goes up and it still runs smoothly, advance it 3 more degrees . . if rpm goes up again and the engine still runs smooth then advance it 3 more degrees.

 

if the rpm goes up much less than in a previous setting retard it 3 degrees.

 

try to restart the engine after 5 minutes and 15 minutes once it is warm . . if it starts more slowly then we might do something tricky, but for the time being, just reduce it 3 degrees if it starts more slowly when it is warm.

 

 

now, rev engine to around 3000 rpm and tell us what the timing is . . if you have a tach, tell us what rpm it reaches total/max timing at.

.

Edited January 4, 2015 by barnett468

[69me 10]

the car has a mild cam. It runs about 190-195.I am currently not using vacuum advance. It has an Edelbrock torker 351 single plane intake (came on car along with cam).also I am using a summit racing brand carb 650cfm, vacuum secondary. do you think I should check for leaks first?

[barnett468 418]

its always a good idea to check for leaks . . i plug all vacuum ports on the carb itself and to the intake, including the pcv but first check you idle rpm then pinch the pcv hose or pull it out and blocjk it . . if your rpm drops more than around 75 rpm it is too big [flows too much air st idle] in which case i would buy an adjustable one.

 

i use flammable brake cleaner with the long nozzle to focus the spray . . spray GENTLY at carb base and intake at heads.

 

what is your compression or are your pistons flat tops and what heads do you have?

[j69302 11]

If it is running rough, first check for leaks. You can spray break cleaner/carb cleaner around the intake manifold gaskets, and base of carb. Be mindful of painted areas, both of these will eat paint. You can also find SEA FOAM in a spray can, which should not hurt any paint, and should work just as good for finding a leak.

 

If you find a leak, you will need to fix it. You can still adjust your timing with a manifold leak, but there is not much point to adjusting the carb until the leak is fixed.

 

It is very important that your ignition is tuned before messing with the carb.

 

First, get your initial timing set up. The above posted directions are a good way to do it. As a general rule of thumb, 12-16* is a good starting point. Make sure the vacuum line is sufficiently plugged when setting timing

 

As the engine RPM increases with the more advance that is run, the vacuum will naturally go up.. to a point.. Once you find the sweet spot, re-set your idle.

 

Once done, hook up the vacuum advance to "PORTED" vacuum. You will get ALL kinds of debate on either PORTED or MANIFOLD vac for your advance, but just start with PORTED for now, as it is supposed to be. You can go back later and fine tune to your liking. You may have to look up your carb instructions. They may not point it out as "ported", it might say something my obvious like vac advance port, and in the case of Holley's, they called it "timed" port. The "ported" port is usually higher up on the carb as it is sourced from ABOVE the throttle plates, unlike manifold vacuum which is below the throttle plates.

 

Vacuum should further increase once the vac advance is hooked up, along with a slight RPM increase. If you do not notice this, then your vacuum advance is not working. If it is not, then just plug the line for now, and you can fix that problem later. At this point, everything is good enough to start messing with the carb.

 

Is it idling rough? If not, then 10-12 may be all you're going to get. If slightly rough, it could just be because of the cam and intake.

 

Do you know exactly what cam is in there? "mild" does not tell us much. We need duration and lift.

 

With single plane intake, you need to make sure that the idle screws were evenly set BEFORE you started to mess with them. To verify, screw in both screws until they bottom out, then unscrew both screws 2 full turns. Then re-adjust idle screws. With a single plane intake, it is VERY important to turn both screws the exact same amount. If not, one side can be over adjusted, and the other side under adjusted. If possible, use 2 screwdrivers and turn them at the same time, the same amount.

 

If all of this checks out, and you don't get much more of an increase, then that just may be where your combination will be running at, mostly cause by the cam and the single plane intake. In this case, you may have a naturally slightly rough idle, and isn't a cause for concern as long as it is not stalling.

[barnett468 418]

yes, as j69302 also mentioned, one should not use dist vac when setting timing . . this is only a concern when using manifold vacuum instead of ported vac which is rarely beneficial and it needs to be determined if an engine can benefit from using it by doing proper testing first.

 

ported vac is primarily only active at steady throttle.

 

while driving, manifold vac is active at steady throttle and closed throttle.

 

when you accelerate, the dist vac becomes inactive because the vac drops below its range of operation.

.

Edited January 4, 2015 by barnett468

[j69302 11]

actually one should not use dist vac when setting timing . . this is only a concern when using manifold vacuum instead of ported vac which is rarely beneficial and it needs to be determined if an engine can benefit from using it by doing proper testing first.

 

Im confused. I said that the vacuum should be plugged..meaning not used for setting timing.

 

Did you mean to say that it should be hooked up to set the timing?

[barnett468 418]

Im confused. I said that the vacuum should be plugged..meaning not used for setting timing.

 

Did you mean to say that it should be hooked up to set the timing?

 

oh sorry, i was only explaining in more detail why it should be plugged . . i will try to make my post more clear.

 

and yes, the last ported vs manifold "debate" here ended up with facts and simple logic prevailing for the use of ported vac [as you so wisely suggested] in most cases but some of the detractors were simply in denial, lol.

 

happy new year.

Edited January 4, 2015 by barnett468

[69me 10]

I was using the manifold vacuum. the instructions that came with the carb say to attach gauge to full manifold vacuum. the car does not idle rough, but it does smell rich. I will look through the box of receipts to find the cam info and post it. I don't think my timing is off (keyword think) by much, it runs well. I think I stumbled onto another problem (vacuum) by trying to fix another. I am going to go through the advised steps after I check for the leaks.

[69me 10]

ok I found the cam info, it is a ford motorsport M-6250-A341 for 351c

int. lift .510 exh. .536

duration 292 302

opens 3? (package torn) 83

closes 78 39

overlap 73

lash hyd hyd

also correction 750 carb not 650

[barnett468 418]

ok holy c__p . . the duration at .050 is 214/224 but there is no lsa, but with 73 overlap it looks to me like you should have around 12 hg of vac on a good day.

 

i hope you have some good gears for that also.

 

the gauge goes to manifold vac . . if you have a vacuum can on your distributor that is what gets plugged for now but will likely end up on ported vac when you are all done.

 

just because it runs ok does not mean that it can run better.

 

plug the dist vac.

 

rev it to around 2500 rpm.

 

advance the distributor around 6 degrees . if your rpm goes up noticeably, you are noticeably down on horse power.

.

.

Edited January 5, 2015 by barnett468

[69me 10]

I will try that when I have an assistant that can watch the tach. hopefully tomorrow

[69me 10]

by the way thanks barnett468 and j69302 for all your input

[69me 10]

I was getting around 10 to 12 on the guage, and I was told it has 410 gears

[barnett468 418]

I was getting around 10 to 12 on the guage, and I was told it has 410 gears

 

yes i saw earlier you had 10 - 12 . . do you like those gears?

[1969_Mach1 333]

With 73 deg overlap you are going to have some rich smelling exhaust fumes. 214-224 deg duration at 0.050 lift isn't bad. That's a pretty old cam grind and is no longer available. I think its in one of my old Ford Motorsports catalogs.

[69me 10]

the gears are ok, I wish they were more highway friendly for going to shows but they pull good through all 4 gears. it is an old cam, summit racing told me it had been discontinued. and I should also change to a duel plane intake. I hope to change intakes once I get some other bills and things sorted out. I do like the sound of the car at idle, it has a nice lope to it. I think it will sound better when I get the exhaust finished and out from under the car. right now the exhaust stops at the mufflers

[barnett468 418]

what intake do you have?

[69me 10]

is there some kind of formula for figuring out vacuum with the cam specs? its starting to sound like I have no real issues with the current set up. I am still going to run through all the motions of timing and idle mixture and leak check, but it doesn't sound like I will get near the 18hg or a noticeable difference in performance. or am I wrong?

[69me 10]

the intake is an edelbrock torker 351 single plane. I've been told its a boat anchor

[barnett468 418]

is there some kind of formula for figuring out vacuum with the cam specs? its starting to sound like I have no real issues with the current set up. I am still going to run through all the motions of timing and idle mixture and leak check, but it doesn't sound like I will get near the 18hg or a noticeable difference in performance. or am I wrong?

 

from post 11

 

it looks to me like you should have around 12 hg of vac on a good day.

[barnett468 418]

the intake is an edelbrock torker 351 single plane. I've been told its a boat anchor

 

its not a boat anchor but its not the best for your app imo . . i would look at a boss 351 intake or a performer with a 1" spacer . . i don't think an air gap will fit with an air cleaner.

 

this one will work . . its only $260.00 and you might get $100.00 for yours on ehay.

 

http://www.ebay.com/itm/Edelbrock-7183-Performer-RPM-E-BOSS-351-Intake-Manifold-/200674163051#ht_1532wt_903

.

Edited January 5, 2015 by barnett468

[LSG 15]

  69me, hope you got your setup figured out. I'm not certain which 'debate' the guys are referring to, but you should run full manifold vacuum to the dizzy. You may need and adjustable can, if you have a larger camshaft. Those who run ported don't understand why ported was created, it is not what you want.  LSG

[Wycked69 20]

Boat anchor ?, Not so. The Torker is actually a decent intake for a "single plane" intake. Single plane intakes are somewhat "unruly" at low RPM's and more so when used with a stock or mild cam on a street motor

[prayers1 153]

Here's what I have:

351 4v closed chamber 63cc heads, SS valves, Scorpion Pedestal roller rockers.
Bullet Custom grind 541/559, 270/283. 50@ 220/231, lsa 110.
Springs #145 @ 1.800 & #350@ 1.200.
Blue Thunder Intake Dual Plane
Carb- Quick Fuel 735 Vac Sec.
Sandersons shorty headers

 

I get about 10 -11 Hg

 

I too tried all sorts of ways to figure why it was so low and I do not have power brakes or AC (other Cleveland experts say that's ok).  I looked all over for leaks and did as Barnett468 has suggested, also I blew smoke in the intake. to trace any. You might want to try it.  I took the carb off, sealed the intake opening and all other vacuum ports. On mine I have a vacuum port on the back off the manifold.  I place a hose on that port and blew smoke in it.  Now your gonna have to use a cigarette or cigar (I don't smoke) inhale then exhale into the hose, then look all over for possible signs of smoke leakage.