Ozz1967

iTrader: (4)

Hey guys,

I recently swapped a 350 into my 84 T/A but didn't upgrade the torque converter with it. Now I've got very little braking power at idle due to low vacuum. I see that summit sells these vacuum canisters that supposedly "store" vacuum for cars that have large cams. There is even one that is powered that will help supply more vacuum to the system. Would that be a decent fix until i can afford to get a new torque converter or is this just wishful thinking? Any input would be greatly appreciated. Thanks!

Sonix

iTrader: (1)

If you do have a big cam, then yes, they can help.
I don't know what that has to do with the torque convertor though...? Does the torque convertor tame your cam, and give you more vacuum?

Saigon_Bob

iTrader: (2)

The TQ convertor has nothing to do with the idle vacuum. Either he has a lumpy rumpy cam or a vacuum leak

Sonix

iTrader: (1)

That's kinda what I thought, but I figured he must have brought up that thought for a reason.... I was baiting him to find out why

Ozz1967

iTrader: (4)

I had the car into an exhaust shop to have my 3" exhaust put on and while it was there I had him double check all my settings from when I did the engine swap. He (the mechanic) said that my torque converter was too "small" for my cam and engine build (He suggests something with a 2200-2500 stall) because the engine stumbles at idle and likes to not stay running when shifted into gear. To fix it he bumped the idle up to around 1100. The other problem, which I have since noticed when driving it, is that when the engine speed is low (below 1500rpm), I lose alot of my assist for breaking and when I'm at speed, I've got enough (I did a probably fairly dangerous on-road test at speed to test the theory). From my (admittedly) limited knowledge, that tells me that I don't have enough vacuum at idle to help with the brakes (or perhaps another heretofore unknown problem). So, I'm trying to figure out what to do to fix the issue. I have been told, both by the mechanic, and by reading here on the forums that having a torque converter with more stall will help smooth out the engine a bit at idle and would prossibly help with the vacuum issue at idle.

So, in the mean time, instead of paying the money for a Torque Converter (need to save up for it), I was wondering if a vacuum canister would help out with the brake issues (provided I don't have a major vacuum leak somewhere).

Supervisor42

Well, tell us what cam is in it.
We won't tell nobody, honest...

Ozz1967

iTrader: (4)

LOL sorry.

It's a Lunati Voodoo Cam Summit part number LUN-60121. I'm running World Sportsman II heads, Edelbrock Performer Intake with dished 9.2:1 pistons. Rockers are 1.52 Pro Magnum Rollers. I'm using the factory CC distributer with a new MSD Cap, Coil, rotor and plug wires. I know it's not a huge build, but I wanted something that would have a little more kick to it than normal and still keep it a daily driver.

Other specs, 700R4, recently rebuilt with a B&M Transkit and the factory 3.73 Posi rear.

Here are the cam specs.

Product Line: Lunati Hydraulic Roller Tappet Camshafts
Part Type: Camshafts
Part Number: LUN-60121
Cam Style: Hydraulic roller tappet
Basic Operating RPM Range: 1,800-5,800
Intake Duration at 050 inch Lift: 219
Exhaust Duration at 050 inch Lift: 227
Duration at 050 inch Lift: 219 int./227 exh.
Advertised Intake Duration: 270
Advertised Exhaust Duration: 278
Advertised Duration: 270 int./278 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.515 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.530 in.
Valve Lift with Factory Rocker Arm Ratio: 0.515 int./0.530 exh. lift
Lobe Separation (degrees): 112
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer Controlled Compatible: Yes
Grind Number: VDSC-270
Quantity: Sold individually.

Supervisor42

That setup should definately not need a vacuum reservoir. With a 112° lsa and only 219° intake at 050, it should have near stock vacuum.
If it doesn't idle smooth at 800 in neutral with good-plenty of vacuum, something is way wrong.
Re-adjust valves etc.
Also, a 2200 stall would make it launch quicker than a stock one but it should still be happy with stock.
Did you advance your base timing away from stock?
It's going to be happiest with (I'm guessing here) 12-16° of base timing.
Did anyone check the timing? It has everything to do with idle and vacuum.
Wait a minute. How are you running a CC distributor with a carb?
The dizzy can't advance the timing with out the "CC" (ECM) and the ECM won't work without all of it's gadgets plugged in and operating.
If you're going to run a carb, you're going to need a vacuum advance dizzy.

Ozz1967

iTrader: (4)

84 Firebirds came with a CC Q-jet and distributer. It's primitive but it's got it and I kept all that sock. I had originally set my timing at 9* advanced (I ran it very little and actually towed it to the shop) but the mechanic at my shop said he adjusted it to 12* before plugging the distributer in. when I drove it home the 60 miles from his shop it ran good and strong so the timing, if it's out, isn't out much. At idle it's sitting at 1000-1100 and when I drop it into gear it drops to 800 rpm or so and stumbles. When it stumbles...which is about 70% of the time, I have to feather the throttle or it'll die. Sitting at idle, it idles just fine (sounds pretty good too).

Now, o be honest, I haven't driven it all that much in the past two weeks. I tore a ligament in my knee and couldn't get into the car. Yesterday was the first time since the 5th of the month that I finally was able to get into the car so I will be troubleshooting this hard for the next few days.

Supervisor42

oops.
forgot about those It could be that the ECM doesn't like that cam at all and won't richen the mixture.
Or maybe they gave you a "bigger" cam by mistake.
(It sounds exactly like a 274-282 degree cam to me.)
Will it idle stable at 800 in neutral?

Saigon_Bob

iTrader: (2)

Is the idle really choppy below 1000rpm... that cam specs out pretty tame...

The cam I have now is about 224*/234* at .050 and has power brakes and is fairly smooth idling.

now the lunati cam I had before was like 245*+ duration... i dont remember it was big. and lopey and had no power brakes. Keep an eye on the cam and lifters as well as engine vacuum, My cam and lifters self destructed after a month. And i've witnessed another lunati cam and lifters scrap during break in.


As for the convertor killing the car at idle.. your mechanic is wrong. the reason for a higher stall is to let the convertor flash up to the peak torque curve of your engine.


Short answer for the sake of the thread tho. I think you have another problem other than too large of a cam or to tight of a convertor, but a vacuum canister isnt a rig fix nor short term. Its a viable long term fix if you like a rowdy cam
----------
BTW i just read the rest and if you are running the factory 305 stuff electonically still you really need to look into getting a "dumb" dizzy and a holley... the car will run a million times better

Ozz1967

iTrader: (4)

In neutral it idles 900 or so I'd guess (wasn't really paying attention) but it idles pretty stable. When I drop it in gear is when I start having idle and stuble issues.

Supervisor42

!!!!
I bet the cam is timed up wrong, it's one tooth advanced!!!
I had a reman slant-6 that was one tooth off advanced and it idled like a 292° racing cam.
Took me a while to figure it out. Made good power though.
I bet you money that's what it is.
If you want to check it, all you need is a degree wheel and pull one valve cover.
Here's the SPEC CARD. The intake should begin to open at 3.5° before top dead center. If it's off by a whole tooth it will be very obvious. On second thought, you don't even need a degree wheel... Intake valve should start moving when the TDC mark is on the timing tab.

Saigon_Bob

iTrader: (2)

He said it idles normal around 900 rpm... id say its the ecu stuff getting pissed off

Supervisor42

He'd have plenty of vacuum for his power brakes while driving if that were the case.

Saigon_Bob

iTrader: (2)

I think we are in agreement that the cam needs to be degree'd. Ozz can you stick a vacuum gauge on the car at idle and tell us what you have?

Ozz1967

iTrader: (4)

When I'm driving, I do...until the RPMS drop down near idle like when I'm pulling up to a stop light.

For example, I"ll be driving down the road, see a stop light, begin to push the brakes (good feel to the pedal, all is good), then as I slow down I usually let off the brakes and then reapply when my speed is about 20 to come to a complete stop...this is where I have my problems, the pedal goes all the way to the floor (i mean all the way down) and I really have to mash it in order to stop (Feels like my 67 Camaro with no power brakes and drums at this point...only worse). At speed (30mph+), nary a problem. This is where I started thinking it was a vacuum issue that starts as I lose RPM.

Saigon_Bob

iTrader: (2)

hmmm is the pedal stiff like no power brakes or is it super low and unresponsive.

I actually had the same issue when i had my demon carb and mistakenly put the PVC and PowerBrakes on the same vacuum circuit with a t. Quite Scary....

We definately need to know what the vacuum at idle is.

Ozz1967

iTrader: (4)

It gets hard and stiff.

Ok, I took it out for a long drive today up to Bear lake about a hundred miles from here. The car idles at about 1100rpm (the mechanic said he had to set it high or it would stumble and die). When it's cold, it definitely doesn't like to be put into gear with the brakes applied, it tends to die unless you let it roll itself when you put it in gear. The brakes run off their own feed from the back of the carb...it's a hard line so it's not "T'd" with anything. I've also got new hoses that are under a month old.

When I first got and started it, I did a test today. I put the car in reverse and mashed the brake. It got stiff and hard (get your dirty minds out of the gutter!), was like this two or three pushes in a row. Then I put it in neutral, same problem. Swtiched feet (left on the brake now without taking pressure off of it), and gave it some gas. As soon as the Rpm's reved I Pumped the brake with my left foot and it felt like normal with good play. So, once the rpm's get up, that's when I get good response in my brakes.

Now, I've got a guy I work with who is a brake specialist who's been on vacation, he got back today so I called him up and after relaying the whole thing, he came over and did some basic tests...he says that in addition to what we've been saying here, that it might be the master cylinder going bad. but without getting into it personally he couldn't offer more than a hypothesis.

Lo-tec

I would replace the check valve on the booster and the hose that goes to the carb. If it's not better, buy a vacuum gauge and post the vacuum at idle.

You should have 2 or 3 good firm pumps on the brakes with no vacuum, and then the pedal should be hard as a rock.

Ozz1967

iTrader: (4)

What does the booster look like? The hoses are new and connect to a hard line that comes off the carb.

Supervisor42

The booster:______The check valve:

Supervisor42

This won't affect the fact that the engine has to be idled up to 1100rpm to keep from dying when it's put into gear...

Ozz1967

iTrader: (4)

If it's not idled up to 1100, it would stumble like it does when I put it into gear when in park or neutral...and then completely die when dropped into gear.

Just for kicks, what happens when a torque converter goes bad or starts to go bad...any of these symptoms or something completely different?

Supervisor42

Just for kicks...
The 700R4 converters fail in 4 ways.
1. The most common is the one way clutch in the stator strips and the converter cannot multiply torque. This converter works fine except when you go to take off. The take off will be very very slow. Once you get up to speed there is no difference. A stall speed test will show this problem, as the stall speed will be abnormally low.
2. Torrington bearing failure. Symptoms: a jingling sound that turns into a hissing sound when put in gear. Still drives ok for a long while.
3. Turbine/impeller vane failure. This is where the vanes break loose. This quickly snowballs as the more parts break off, they in turn break off more parts. Symptoms: sounds like the converter is full of quarters (loud) when you put it in gear. Barely will move the car.
4. Lockup clutch siezed. Symptoms: Immediately kills the engine with a screech when put in gear. Like popping the clutch on a manual with it in gear. Car not driveable.

Supervisor42

I think a vacuum test will tell us what the booster is already telling us:
The engine has low vacuum at idle (800 rpm).
The problem will be telling which of these 4 causes is the problem:
1: Idle circuit clogged in carb. (too lean to idle)
2: Large vacuum leak. (too lean to idle)
3. Valve action wrong. (cam mistimed, wrong cam, valves too tight)
4. Timing set way too late. (should affect power also)
All of these fit your symptoms.
If you to eliminate them one by one it only requires simple troubleshooting.

Ozz1967

iTrader: (4)

Ok, none of those are even close to what is happening. So that at least should eliminate that.

Ozz1967

iTrader: (4)

I'll need to get a vacuum gauge tomorrow then to check most of that. The car has mad power and really gets after it so I would like to think that it's not the timing set to late. Valve action wrong, perhaps... The rest of it? Will need a vacuum gauge.

Supervisor42

You can check #1 and #2 by setting the idle as low as it will go, right on the border of stability in neutral and putting your thumb over the pcv valve. If the idle speed increases, there is too much air for the amount of gas coming from the idle circuit.
Kinda like taking the 50/50.

Ozz1967

iTrader: (4)

ok, this did nothing...but I have mad suction on my PCV valve.

Supervisor42

Does the check engine light come on? Is it on constantly or disconnected?
You may have to check the mixture solenoid thingy on the carb. There's a post about checking it's "dwell" somewhere here.
I still say that cam should have no problem idling at 800...

Ozz1967

iTrader: (4)

Nope, no check engine light. It is possible the Tach is off, but according to a sunpro tach that my buddy has and we hooked up, it "looked" just about right as far as being accurate. I do plan on sending my gauges in this winter and have them all calibrated.