low vacuum

[getstroked]

I have a fair size cam in my 383 stroker and am haveing vacuum problems. My brakes suck and i have been told that w/ such bad vacuum that my timeing advance proly isnt work right. Some help would be nice!

[richtazz]

Summit or Jegs should offer some form of vacuum storage canister that will help you out on the brakes. If you have a huge cam, you'd be best going to a mechanical advance distributor, as the vacuum advance cannot run off of a vacuum canister. It has to be able to react to changes in engine vacuum according to throttle input.

[getstroked]

my cam isnt that big i dont think it is a comp cams 12-246-3 (.490in .490ex
230in at .050 236ex at .050 106intake centerline lobe sep at 110) Could a vacuum leak be possible? and wut about a dead spot when i just barly get off of idle in gear(like takeing off nicely)edlbrock performer 750

[richtazz]

It's the 106 intake centerline and 110 lobe separation that's causing your vacuum issue. A stock cam is about 110 centerline and 114 lobe separation. You most likely have a slightly choppy idle, even though your lift/duration specs aren't unstreetably high. Does your car have a stall converter if it's an automatic? The dead spot could be caused by insufficent converter stall.

[getstroked]

No i do not have an aftermarket converter in it yet. I am planning on putting one in soon though. But the next Question Would be is how big of a converter do i need or shoudl have? th350 trans.

[maxwedge]

Originally Posted by getstroked

No i do not have an aftermarket converter in it yet. I am planning on putting one in soon though. But the next Question Would be is how big of a converter do i need or shoudl have? th350 trans.

This another easy place to make a mistake, I would contact any one of the quality performance convertor mfgs, tell them your combo and they will recommend a convertor, btw that cam is fairly aggressive for a daily driver.

[getstroked]

i put a vacuum canister in my car and it helps alot in brakeing aspects but asking about converters everyone says a 2500 stall. it seems a little big for a street car

[richtazz]

The stall speed is calculated at WOT. A stock converter's stall speed is approximately 1800, so 2500 isn't much. Stall speed will depend on weight, gear ratio, carb, intake, etc..., so like Max suggested, contact the converter manufacturer with your combination and they'll tell you what you should run.

[BNaylor]

Mojave has some good info on torque convertors and stall speeds.

http://www.mojave-green.com/stall_speed_


Excerpt:
Why is proper stall speed important?
( Proper selection of stall speed will make for quicker launch, better 60' time, and a better overall ET )

Selection of the right stall speed for your vehicle should be matched to the engines peak torque; engines torque curve, and vehicle weight. In general, the desired stall speed would be 500-700 RPM below the engine RPM at peak torque. The speed allows a margin for application of the torque reserve on takeoff.

When selecting stall speed without having an accurate and precise engine peak torque rating, it is better to conservatively estimate the engine torque than it is to over estimate it. If you over estimate the torque output, the resulting stall speed will be lower than intended and is likely to make the vehicle slow off the line, increasing your ET.


I had a moderately modded Camaro Z28 with LM1/TH350. I had no problems with a B&M Hole Shot convertor with a 2400 rpm stall speed. Worked fine on the street and with my mods.

[getstroked]

will a converter make that much of a difference? so my take offs will be more snappy? How about moveing take offs like at 20-30mph?

[richtazz]

you will be amazed at the difference a proper stall converter will make. It's probably the 3rd most important piece of a proper combination. The Cam is #1 and the Carb is #2 IMO. The first two are the most frequently messed up. Most newbies to performance buy WAY too big a carb and WAY too big a cam for how they will actually drive the car, resulting in an undriveable turd.

[getstroked]

So your saying that the proper converter will literally change how the whole car acts?

[richtazz]

Absolutely, as it puts the engine more in it's powerband before loading it. Think like you're driving a stick shift car. If you let off the clutch without applying a little throttle, the car may go, but not anywhere fast. If you're on the gas, then dump the clutch, you squeal the tires and off you go. Same engine, gear, vehicle weight, etc..., just more RPM at launch. A torque converter works with the same principle, only hydraulically instead of mechanically. At part throttle, unless you have a monster (3,500-4,000) stall converter, you'll barely know it's there. When you get in it, you'll feel a world of difference. The bigger your cam, the bigger the difference you'll feel.

[getstroked]

well i guess that solves that problem thanks