Author Topic: Vacuum Measuring Help - Updated 3/10/08  (Read 8014 times)

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Offline Joker (§ir£Ğragon)

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #45 on: January 02, 2008, 01:37:23 PM »
Larry


Offline rkellerjr

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #46 on: January 02, 2008, 01:54:31 PM »
Thanks Larry, I knew I could count on you :)
Rich

Offline Joker (§ir£Ğragon)

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #47 on: January 02, 2008, 01:57:49 PM »
Thanks Larry, I knew I could count on you :)

lol



Except now I'm confused too. Maybe I just did the same to everyone else? :-\
Larry


Offline rkellerjr

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #48 on: January 02, 2008, 03:23:41 PM »
In one of my most recent posts I mentioned that the car did not burn any oil (different from what I've seen).  The only thing I changed (and this has been prompted by the discussion over at TAC above) was that I moved the Vacuum Advance from Ported to Manifold. Would this have an effect on the oil burning issue?  I believe the answer is no but the only dumb question is the one not asked :)
Rich

Offline Rick

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #49 on: January 02, 2008, 03:45:34 PM »
No, Rich, that shouldn't be a factor at all.

BTW -- on the vacuum advance thing...

The factory used different vacuum advance sources according to how they were approaching the emissions control aspect.  Some setups used manifold vacuum for the advance vacuum source, while others used ported vacuum.  The important thing is to MATCH the vacuum source with the vacuum advance canister/weights & springs for your car -- i.e., use the scheme that's appropriate for the way your distributor is set up.  I took great pains to switch mine back to a 1970 setup and swapped out the weights, springs, and vacuum advance cannister for pieces that were equivalent to a 1970 400.  I got some invaluable advice on how to do that from the old HO Racing Specialties back in the day.  They were great to work with, and I got solid performance gains from following their advice.  Bottom line -- either CAN work, but WHICH you should use depends on the ENTIRE distributor setup you decide to go with. ;)

Offline rkellerjr

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #50 on: January 02, 2008, 04:04:39 PM »
It's a good thing that I have no clue what setup I have!   HAHAHAHA!
Rich

Offline Rick

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #51 on: January 02, 2008, 04:56:17 PM »
What I did when I was figuring out how to make my engine run was to go back and reference factory service manuals from earlier years.  My goal was to recreate the performance of the 1970 model year 400s.  In order to do that I had to figure out how my 75 setup worked and then how the 70 setup worked, and make the changes needed to get to that.  In your case you're hampered by not really knowing what you have because of all the changes that were made before you got it.  But I'd think the 1970 model year would be a good baseline to shoot for...in terms of overall performance.  I'd think about getting your hands on the 1970 service manual and doing a little reading -- and then you could go looking through your CDROM from Hitman for the appropriate parts. ;)

Or send the whole shebang off to have it set up for you... :-\ :-\

Offline rkellerjr

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #52 on: January 02, 2008, 06:11:57 PM »
We'll see what we find out when I travel up to Lostsoul's place.  Maybe that will shed some light on various things and I'll go from there.  The car runs much better on Manifold vacuum but I've got a sneaky suspicion my distributor is not set right with weights and such.
Rich

Offline Rocky Rotella

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #53 on: January 02, 2008, 06:57:21 PM »
Vacuum advance will not have any bearing on the oil burning issue.  However, vacuum advance WILL have an effect on the overall feel of the vehicle when it's burning that much oil! 

Oil is not as combustible as fuel, so it slows the combustion burn rate down considerably.  I'd venture to say that your engine would likely continue to run better if you continue to throw abnormal amounts of timing at it.   

Offline Eagle 1

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #54 on: January 02, 2008, 08:29:07 PM »
Quote
I'd venture to say that your engine would likely continue to run better if you continue to throw abnormal amounts of timing at it.   
Or money. ;D
" He done good didnt he Fred?"
"I'm in pursuit of a black Trans Am. He's all mine so stay outta the way."

Offline rkellerjr

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Re: Vacuum Measuring Help - New info added 1/2/07
« Reply #55 on: March 10, 2008, 06:51:27 PM »
By the way, the car is not burning oil like I thought.  Maybe a quart every two tanks.  Still not good but way less than I had thought.  I must have miss remembered when  put oil in it.  I don't know, its not worrisome.

But, that's not the only reason I'm reviving this thread.  The engine is ready pretty good except for two things....

1)  When you floor the car, it sounds like the vacuum advance is not working, i.e. there seems to be a lot of pinging going on under the hood.  At no other time does it do this and it only does it under load.

2)  Only when the engine is running at normal temperature, when I'm sitting at a light or a stop sign, then engine idles at around 750 RPMs.  Nice lope, sounds mean.  But, and it doesn't do this ALL the time, the engine will get slower, and slower, and slower, till its choking at 400 RPMs.  I can hit the gas pedal and she responds instantly but then goes back down to 400 RPMs and almost shuts off.  I put it in neutral, engine revs back up, then falls back down.  After a minute or two... it sometimes comes back up to idle and runs fine.

I am wanting to get these two problems fixed so that I drive the car to the Nationals.  It's driven this way on several 300 hundred mile trips and runs good, except for the idle.  My current though on item one is that my distributor advance is just shot is not doing it's job.  I am leaning towards getting a new distributor but buying one that's pre-advanced is expensive.  The other route is buy one like at Summit and then spend the same money on a Dyno tune.  Anyway, I'm rambling now.  Thanks, in advance, for you help.
« Last Edit: March 10, 2008, 06:54:58 PM by rkellerjr »
Rich

Offline Rick

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Re: Vacuum Measuring Help - Updated 3/10/08
« Reply #56 on: March 10, 2008, 07:41:17 PM »
Rich, problem #1 is from too much timing advance.  Pinging is also called "spark knock" and under load is when it becomes obvious.  Your total advance needs to be backed off until you don't get that.

Now, the problem is...what IS your total timing advance?  The answer is that it is of course that total timeing advance = (initial advance) + (mechanical centrifugal advance) + (vacuum advance).  I'm not sure you know what any of those are except for the initial advance, which you set and check with the timing light.  It's possible to determine the mechanical advance with a tach and the timing light, but I don't think you've done that yet.  And offhand I don't really know of an easy way to determine the vacuum advance.  But in regards to the type of pinging you describe it shouldn't matter that much because under load the vacuum advance is supposed to not be a factor (goes away when the engine gets a load on it).

When I built engine #2, I recurved my own distributor by using a kit from an aftermarket tuner.  I told them what setup I had (heads, cam, carb, vacuum advance type, rear gears, transmission, etc.) and they sent me the proper weights and springs and another vacuum advance motor.  I've never fussed with it beyond setting the initial timing.

Do you have any idea if the distributor's ever been twiddled?  I know the engine is out of a 77 so you may not be able to tell, but it sure would be nice to know what you have... :-\

Offline rkellerjr

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Re: Vacuum Measuring Help - Updated 3/10/08
« Reply #57 on: March 10, 2008, 09:19:28 PM »
All of the parts on the distributor look stock when I took the cap off and removed it last year.  The total setup on the engine follows...

1977 Pontiac 400
Edelbrock Performer intake - 2 year old
Edelbrock 600cfm carb - 2 year old (electric choke)
Heads - 4x
Lunati mild cam w/new lifters - 1 year old
Timing Chain/Gears - 1 year old
Headers

Everything else is stock, to include the fuel pump.
Rich