I need a couple more inches of vacuum inorder for the brakes to work properly.

My set up is an A4 with a 383 with 224/236 lsa 114 cam. I am using the LT1 editor.

Right now I see 10" of vacuum at idle

My idle speed is 900 rpm in gear, and that's about as high as it can go without the car straining at the brakes too much.

I tried advancing the "closed throttle" timing table in the 800 - 1200 rpm range by 3 degrees, but did not notice anything much.

Any thoughts??

In the end I could go with an electric vacuum pump, but it would be nice to be able to finess it ...

thx for any help

LWM

 

here

thats what i use, seems to work good..

 

thx, I'll give that a try

LWM

 

Well, I gave it a try and it did not seem to make a whole lot of difference. I may be a bit on the conservative side when messing with timing.

I went up to 4 degrees advance through out the 400 - 4000 rpm ignition table. MAP readings did not really differ. It did seem a bit smoother with more ignition timing in ...

so ...

the question arises ... which way would likely create more vacuum and thus less MAP and thus better fuel economy using the 224/236 114lsa vs the stock cam??

Any input is appreciated.

LWM

 

did you retard in the idle range? Just seemed you added (advanced) timing from what I gathered from your discussion. Maybe retarding would work better. If you did this already, sorry for the misunderstanding.


Ben

 

Have you verified that you don't have a vacuum leak, or a problem with valve adjustment? My 230/242 114LSA solid roller pulls 15" at 800rpm idle in a 381.

 

I don't think I have a vacuum leak, manifold area is dry, all caps and tubes around manifold area are in place.

Even with my stock engine and computer I only ever saw 16" of vacuum at the stock idle speed of 550 rpm. My MAP readings then were around 35kpa.

Now at an idle speed of 850 rpm I see 10" of vacuum and the MAP reading is near to 51kpa. This 224/236 cam really does "air out the cylinders".

Just a bit of a puzzler because my car has always seemed to be low on vacuum. Must be the 3,500 feet of altitude here in Calgary.

How is your cold start, mine is just miserable untill it gets a little heat into it.

thx for the help


You're correct about my only going in the advance direction, retarding ignition timing is would more than likely have the opposite effect, they used this method to "fast warm" engines in the early 80's (kinda dates me ), the result is a larger throttle opening is required to maintain the idle rpms. The late spark lets the charge heat the cylinder walls rather than push down on the piston.

Thx for the input.

LWM

 

You really don't need to use a vacuum gauge if you have a scanner. Vacuum = barometer (BAR) - MAP. Since you are in Calgary at 3,500-ft, your standard barometer is going to be about 26.3". That means that at 35kPa MAP (~10"Hg) when you were "stock" you will only see 15"Hg when you put a vacuum gauge on it. And that is what you got. You aren't going to see 20-21"Hg at that level on a stock setup. But you would see 20-21"Hg at sea level. You really don't appear to have a problem.

My engine starts and idles normally. But its not running on a stock PCM.