Hello Guys,

Can't figure this out. Get this:

At idle:
1.) Barometric pressure reads 30.30, I am in Texas and pretty much at sea level.

2.) MAP reads 20.20 hg's.

**All of these numbers are at idle at around 850rpm.**

This means: That (Baro) 30.30 - (Map) 20.20 Hg = 10 HG in total vaccumm.

Is this not to low?????? Car is equipped with all bolt-ons, XE230/236 cam, ported heads. What are you cammed guys reading?

 

14-16HG on the vacuum gauge with mods in sig whats your LSA? 112?

 

The cam is grounded to 112 LSA, 10 inches of vaccumm is too low, or am I calculating this wrong???? Need more opinions.

 

Your calculation is correct.... BAR - MAP = vacuum.

My 230/242 114LSA runs about 14"Hg MAP (=16"Hg vacuum) at idle.

 

So what is wrong with my car????? Vaccumm leak, I do not think I have one....and how will this affect performance?

 

Valve preload set correctly? Too tight=low vacuum.

 

Valve Preload ? ----- Do you mean adjust the valve lash / rockers?

 

Yes

 

Ok, I will do that, anything else that can cause this? It a new engine with probably no more than 300 miles since I did they full rebuild.

 

Fred, 96Z APPEARS to have an oem displacement engine. Is he aware yours is stroked?

 

I just did heads and xe 230/236/112. Here's what I'm getting now:
30.84 - 18.42 = 12.42

It idles okay I guess, but sometimes it gets rough when it's hot out and the A/C is crankin. I think the Closed Throttle Spark Advance table needs to be adjusted. Stock engine idles with 20* of advance. With the cam I think it needs to be raised. Someone suggested 27* but I'm only up to 23*. Supposedly at the right timing you will have the best vacuum, but I've never done this before so I'm takin the slow steady approach.

 

See signature.

 

Why don't you give the engine a little more time to break in and then check the vacuum with an actual vacuum gage? BTW how are your brakes working? If you only had 10"Hg you would have to stand on the brake. When in doubt of computer, Tonto say check with gage.

 

What Arnie wanted me to point out is that you are not going to see the same results in a stock displacement engine that I am seeing in a 381ci stroker. The added displacement makes the cam "look" smaller. You are also not going to see as much vacuum with a 112LSA as I see with a 114LSA. And with actual dyno tuning vs. a mail order, its likely that my timing maps are set up closer to optimum. But to me 20"Hg seems wrong for your setup.

There was another post by a guy who was seeing 24 -27"Hg MAP (!!!!!!!!) at idle, and I think he traced it down to incorrect valve adjustment.

 

Update:

All right guys, I checked engine vaccumm with my gauge and pretty much stays steady at 10 inches of Vacccum, so that proves my MAP sensor is reading correct.

I also checked our 96Z (Hotcam) and registered 15 inches.

Our stock cammed 94TA check out at 19 inches.

By the way, The engine is .30 over 355 cubic in. LT1, with the XE 230/236 112LSA cam shaft. The engine is broken in with maybe 500 miles on the clock.

I will be check valve lash this coming week-end, all I know is that my valve train is rather quiet when compared to the HOTCAM valvetrain of our 96Z. But then again, the 93 T/A has non self alinging rockers, guide plates and such.

What vaccum result should I look for. 13 to 14?