Thread: 20" of vacuum with a 230 - 240 duration

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Long story short I bough a project and the edelbrock EFI is programed for a cam with 230 - 240 duration. Well the engine doesn't idle with any loop and makes 20" of vacuum at 800 rpm. How likely is it to have a cam as described???

http://members.cox.net/stdotjohn/Por...%20007.600.jpg[/IMG]

i dont believe it will loop with a cam thats making that much vac. what valve lift is it? what is your base timing?

dont understand that danny, if he has 20" of vac. he has a good running motor. stopped up exkaust lowers the vac.

yes i think he ment lope. i didnt know how to spell it. i was saying to want or cant lope with 20" of vac. with all that vac. i thought he might have the timing to hi.




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how the hell are you getting 20 inches of vacuum must have a high lobe seperation like 114

he could give you a few " did you spray your carb. again? i dont think he has the cam he thinks he do
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i dont think he wanted to know anything, i think he was just showing his motor.

yea i sprayed it israyed a mst right over top of the carb an it went up just a hair i get better results closing the choke half way , it really revs up bought a intake set plan on installing tomarrow . today took it to a local car show really enjoyed myself not a big show about 30 40 cars but nice cars

hey how do i post pics i think you like this camaro i have pics stored in the computer but im not good with them

Originally posted by S19243H
hey how do i post pics i think you like this camaro i have pics stored in the computer but im not good with them

go to and open new reply or thread, write your message and then where you submit you'll see "browse" click on that, find your pic. click the pic. the file or pic. will go to the browse window. you need to size the pic. to 5x5" or smaller or 500x500 pxl. you cant preview the pic. so dont try.

The reason I asked the question is complicated but I bought the project with a motor and fuel system it came with. It has an edelbrock port injection and the calibration must be matched to the camshaft. The calibration is for a cam in the 230 - 240 duration range, thats the reason It should have that cam. I can't get to run well, meaning it wont idle unless I skew the vacuum to the map sensor. The map at idle must see no more than 14" or it will become to lean to support combustion. There are no vacuum leaks anywhere and the timing is close enough to at least idle. So when I skew the map it will run making a true 20" of vacuum at 800 or so. There is no O2 sensor installed and its been taken out of the map. The engine may not have that cam and if so that is the reason its running lean. My thinking is if the ecm is mapped to a larger cam it will want to see lower vacuum at idle. A higher vacuum given its calibration would indicate a decell event or something. I am just putting thoughts out there at this point.

Originally posted by DennyW
I think you are a little confused on the MAP sensor. Do you understand the job and what it's supposed to do ?

I have spent the last 20 years working as a G.M. dealership tune-up and drive-ability specialist, so yes I know what a map sensor is there for and how it works. That's the reason the engine runs at all. Having to trim off the vacuum is one of the reasons I think the edelbrock EFI program doesn't match the camshaft.
My readings, vacuum and rpm along with the lack of lope in the idle is the reason I suspect the cam may be more stock than one with 230 to 240 duration. Having 20" of vacuum at 800 or so rpm with out a lope just makes me wonder. I am trying to gather information outside the engine to make a decision on my next move. I think the cam just may be different than the one the EFI is calibrated for what do you gents think???

What kind of idle do you have. With 20" of vac. it should idle good. unless you have so much timing jacked into it. When you decrease the vac. its probably decreasing the timing and thats what make it run better, 14" of vac. should make it to rich. what does "dont idle good mean"? at first you said it didnt have a loop or lope and its not gonna with 20" of vac.

20 in. of vac. with a cam that has 230-240 degrees duration.WOW!I would love to buy a cam like this.I will assume that they are talking about advertised duration and not duration at .050 valve lift.The main problem is you can never go by advertised duration because every cam maker is different.