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Post Info TOPIC: 327 Engine - what should my idle vacuum be?


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327 Engine - what should my idle vacuum be?


 

327 .040" over, forged crank and rods

flat tops with small valve reliefs

59-60 cc double humps, 2.02/1.6" 461 heads

.040" quench with .016" in the hole and .024" composite head gasket

10.3 static and 8.0 - 8.1 dynamic compression  

280 comp cam, 230 @ .050". .480" lift 110 lsa

L79 intake and dual snorkel air cleaner, 600 Holley

1 5/8" long tube headers

small body distributor with pertonix module and coil

timing is 16 initial and 38 with centrifigual

Idle is set at 750-800 RPM

Ive got  9.5 to 10" Of vacuum. Just discovered my vacuum can is wrong. Vacuum  advance should be all in at idle. From what ive read I need a can rated 2" below  the below idle vacuum. I have a B1 can rated all in at 16". I need the B28 or Vc1810 which is rated at 8" of vacuum to give 16 degrees of advance. My can isnt giving me nearly enough advance at idle. 

Im sure my vacuum will go up and become more stable once I can source the right canister and add more advance at idle.

Anyone have a source for a VC1810 can?

Does 10" at 750-800 with low vacuum advance(presently) sound right for this engine build?

 

 

 



-- Edited by horder on Saturday 19th of August 2017 02:24:34 PM



-- Edited by horder on Saturday 19th of August 2017 02:28:38 PM

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Poncho Master!

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I asked a guy who really really knows his stuff, he said steady at 14-15 with that setup, he thinks you may be right about the vacuum can.

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63 Pariesienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. Parting out a 63 Parisienne convertible.

Mahone Bay, NS Still not old enough to need an automatic



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DonSSDD wrote:

I asked a guy who really really knows his stuff, he said steady at 14-15 with that setup, he thinks you may be right about the vacuum can.


 Thanks very much...

Spending a bit more time looking onto my PCV system as well. I have the L79 system with the PCV valve in the oil tube and a non vented cap. Road draft tube at back of block connected to the air cleaner base with the correct screen installed in the air filter. My PCV valve is the correct orientation, flow from oil tube towards the carb, but I question its condition. Did these styles PCVs have a spring? The restrictor inside mine just falls back and fourth when i move it upside down and right side up. Does this sound normal to you guyss? Ill slide down to my parts store this afternoon and see if they have anything close to this just t see how it moves. If its not moving correctly and limiting the flow at high vacuum situations like idle, this could be just like a vacuum leak. Im gonna go hook up my gauge again and plug the Pcv and see how much my vacuum goes up. 

The car runs really good....not sure why Im looking at all these things. Haha

Idles quite well with lots of chop at 800, no driveability issues, never stumbles or hesitates, great power.

4 speed, 3.73:1, a small tire, and a 3000 pound car allow that cam without issue I guess.

I will put the timing light to it soon and see what advance Im getting out of the vacuum at idle.



-- Edited by horder on Sunday 20th of August 2017 09:52:08 AM

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Poncho Master!

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What year is your 327? I am familiar with the older stuff, up to when they added a PCV on valve covers and eliminated the oil fill tube in 69 I believe.

On a 63 SBC and 409, the connection from the road draft tube connects to a fitting at the rear base of the carb (sometimes with a splitter for power brakes), with the PCV in line between the carb and the road draft tube fitting. My PCV does rattle if I remember correctly. I think it was this same PCV for many years in all Chevy V8's, likely until they went to them in the valve covers.

A good place to check part numbers is Rockauto, for various years and motor sizes.

The connection aside from the carb was either a connection from the oil fill tube to the base of the breather with a closed oil fill cover, like you have, or no connection at all, just the breather style oil fill cap.

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63 Pariesienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. Parting out a 63 Parisienne convertible.

Mahone Bay, NS Still not old enough to need an automatic



Poncho Master!

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You can see some of the setup on my 63 here.

Sep 07 084.jpg



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63 Pariesienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. Parting out a 63 Parisienne convertible.

Mahone Bay, NS Still not old enough to need an automatic



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Yup, confirmed my suspicions regarding  the vacuum can. Only 4 degrees advance from vacuum at idle. About 16 off idle when the vacuum comes up.

I will have to play with some different cans to get that right...

But...ive some how lost 10 degrees advance from my centrifigul... i timed this last year at apprpx 16 initial and 38 total Last year. Im only getting 28 now... ill have to rip the distributor out and see whats up



-- Edited by horder on Sunday 20th of August 2017 11:10:46 PM

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Poncho Master!

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My expert said:
Don Show Cars carries a vacuum advance that's adjustable for those points style distrubitors that he may be able to find easier than those cannisters that he listed.

US32.95, they are very good to deal with and will ship USPS.

7026.jpg

 

 



-- Edited by DonSSDD on Monday 21st of August 2017 01:55:28 PM

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63 Pariesienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. Parting out a 63 Parisienne convertible.

Mahone Bay, NS Still not old enough to need an automatic



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Thanks so much for the info...

Looks like springs are sacked in distributor. Getting centrifugal advance well below idle thats why i wasnt getting enough centrifigal after idle. Going to buy a kit and see where we are at after that...

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Not a ton of options out there for mechanical advance kits. Bought the one from Mr Gasket. OMG. TOTAL GARBAGE.

Spent hours trying to make their springs work...every imaginable combination and nothing that resembled a performace curve. Even with their heavy springs they are advancing the timing at idle.

The weights are another story!

Ended up taking my springs, putting a bend in the hook to shorten them up and add voila! 15 degress at idle, 36 at 2800 RPM.

Ill check this in a few weeks to make sure it hasnt changed. Then ill start playing around with the vacuum can to see if it can take more advance from idle up...





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Poncho Master!

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Progress.

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63 Pariesienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. Parting out a 63 Parisienne convertible.

Mahone Bay, NS Still not old enough to need an automatic



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Thought Id give a follow up on this...

I could not get the VC-1810 can locally. Ordered one through our sponsor RockAuto. It did take a few weeks to arrive but it was the correct B28 can which is meant for cars with low idle vacuum.

The can did what it it was supposed to. It was all in at idle, adding another 16 degrees (31 with initial), with the vacuum can plugged in.  This was too much, as well as the 52 degrees I was getting at cruise above 2800 RPM. The car was twitching a bit at cruise or "trailer hitchng" as they call it although I heard no pinging.

I made a limiter plate for the vacuum advance using a nylon bushing. With some filing I was able to get this to the spot I wanted, around 8 -9 degrees.

I ended up with 15 initial, a touch over 36 with centrifugal. Idle advance(initial + vacuum) is now 24 btdc. I get 45 btdc at cruise. The car runs better than ever and it always ran good. I get 11" hg at 750-800 RPM. Engine runs a touch cooler at idle and power seems spot on.

I tried to follow the guidelines as laid out by Lars Grimsrud. Wow, what a wealth of knowledge this guy has set out on the internet in regards to Holleys, Quadrajets, timing, vacuum advance etc. I emailed him and he helped me by sending me two fantastic documents.



-- Edited by horder on Tuesday 12th of September 2017 06:12:43 PM

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