MP 528 cam vacuum

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Marcelo Dart BR

Marcelo Dart BR

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Anyone know how much vacuum at idle this cam is making on a 318 with 10/1 compression?

I'm rebuilding my carb and I think the 6.5 power valve is not the right one. I think I will put the 4.5 or 3.5 to see how it goes.
 
Depending on where you installed the cam at, low to non exisitant.
 
You should have good vacuum, actually. It's much smaller than the size indicates. I would leave the 6.5 in it for now. My impression is it will be closer to 10" in gear at idle.
 
I had 10-11" with the mp 528 at 1000rpm, in gear at 800 it was more like 7-8. But I have a 360 and 11:1 comp
 
no

You should have at least stuck it in 110* =2* advance jmo

If you run the cam 4-5* advanced with a single plane ...you;ll get about 9 inches at idle w/4spd
If you run the cam like above but with a dual plane ...you'll get about 12 inches vac at idle w/4spd.

If you run the cam 2* advanced with single plane you'll get about 8 inches vac at idle w/4spd

if you do as above but use a dual plane intake...you'll get about 10 inches at idle w/4spd

all stated manifold vacuum was measured @8-850 rpm with a 4spd trans.

you could not possibly use a power valve less than 6.5-7.5 unless you really have 8.1 compression...


I've run this cam every which way to know.
 
Mine is straight up, and the intake is a dual plane, Edelbrock RPM. Just remember it's a 318.

The only issue is the inconsistent idle. It happens sometimes.
 
What rpm is the inconsistent idle. How bad does it fluctuate.

Sounds like it may be mechanical timing being bled in and out.
 
340 at 800-850.

Too low for a 318 with that cam. Turn it up a bit would be my suggestion. Make sure the initial timing is in the 18-22 range as well, it might need more.
 
850 rpm should be good to idle at. Being it is a 4spd.

I figured what 1W&CG listed as his readings to be what you would get for a high. Unless you installed it oddly, then of course, less. As mentioned,once in gear (As in auto trans equiped cars) idle can drop a bit and with it, vacuum.

I'm glad you have the abilty for power brakes, Often I meet people that claim they can not run them due to low vacuum. (Lord knows what they did)

MRL really hit the head. I was going to mention get a vacuum gauge, but figured from past convo's, you would know that. I'd have to spring for one with performace cams and power Valves. Ya gotta getcha one.

Once you see where the vacuum is at, your power Valve can be adjusted correctly and probably end the weird idle issues your having.
 
Well, 850 sounds high to me but I'll try. I'm running 18-20 initial and 35 total timing. All in at 2000.

Power brakes work good once it's warmed up.

I'll get a gauge as soon as possible, my bad!
 
run as much initial timing as it will still start with fully warmed up.

all of my data is based on 24-26* initial timing and 750 cfm carb, if use a smaller carb it will strengthen the single I would assume.

if you run 12-20* initial timing... theres a chance it's gonna be on the edge of back and forth between the idle circuit and the main system.
 
Ok, now I've tuned the advance. The total is 36 and the initial is unknown but it's obviously a LOT. I have marks on the damper at 15, 20 and 36, and the initial is much closer to 36 than to 20....:yawinkle:
Idle is at 800-850 rpm.

I did a test run on the street and the throttle response is really better. There's no hesitation at all. I think the car never spun the tires so hard at a stoplight. And I didn't even wanted to.:toothy7:


The idle is constant most of the time but I noticed a drop when I stop on a slope. Is it normal?
 
Ok, I will rebuild the carb and change the jets this week because I'm running a bit lean. Then I'll do the proper tuning.

Thanks wild, you helped a lot!
 
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