so my 400 is indeed up and running though not yet at full power...

Now understand...this is my 1st experience actually timing a new engine...had a very experienced mech friend do the final set up on the wheezer build but i didn;t learn much as he just 'got er done while i was the slave..so going this one alone and a bit anxious...and I have to get it running and on the road now. Also 1st time using a timing light..always used vacuum and seat of pants under my tree...glad I'm using the gun as i found that i had initial timing at about 20 to get the best vacuum and i would have known it was too advanced by the serious cranking involved it was good to bring it down to 8* and see that i had 12" vacuum...oops!

only pulling 15" vacuum now at idle...it will idle fine once warm with a bit of a miss...will likely take intake off today and reseal...finding a leak in the back (using starter fluid) and I REALLY want to put goo over the intake/block seam in back and see if I can call it good but know i can't.... The idle is still a little rough but leans up good as soon as it gets a little gas..just a little...no hesitation anywhere. Have it set at 10 initial...not sure where it goes from there...it seems to want more timing and acts a bit retarded at 10...not sure what thats about.

Oh yea...i made my own intake gasket set and used a cut up pan and the rubber ends...never had a prob with the rubber staying in place and it's in place now...i put the rubber in with a bit of goo and let it set up then a tiny bit of goo between the valley pan and surfaces...and goo on the corners...never found much goo inside the intake when torn apart and alsys sealed. I think my intake/head gasket which i made out of thick rubberized material..looked a lot like the cometic(sp?) gasket i used and screwed up with the streetmaster intake i tried. I was concerned about getting the metal gasket to seal with the oz heads given all the problems i had with valve train but i am going with just the turkey pan and goo this time i think. Also I only torqued to 15# which i am comfy with...might go further before i tear it down to make sure but not likely over 20#. Weiand intake.


also the p/s pump went out it seemed but got it back on line...filled it while running to get rid of any air as a test and by god after i cleaned up all the fluid that gushed out when i turned it and shut it off ...i had p/s again... and it just happened to show right at full with clean looking fluid...messiest p/s fuid change in history... i won't quit my day job for sure.

now the tranny is acting up. was ok when i tore it down... now it will go into reverse with a little delay...as it did before....shift into drive but in a higher gear than 1st i think and I can get it into 1st then drive for 2nd...no 3rd...took 5-6 quarts to fill it hot/running in park when i finished...might be a little low yet but not enough to cause this type of issue...

But this thing is a beast... with the roller cam .520 valve lift, aus heads, yada yada it is a force. I have to upgrade the exhaust...it sounded healthy with the 351/400 (not sure-haven't measure it yet) but scares my lab and neighbors with this engine attached.... cherry bombs won't cut it.

so questions:

with 212/218 cam should the idle be any different than a stock build and if it is different...how...as an estimate.

given 9.4:1 cr and the cam with ivc of 36...what pressure reading/range do you think I should have when i do a compression test.

any insight on tranny issue?

anything else/ all input welcome

 

check the line to the vacuum mod on the side the little rubber hose on mine collapsed and did the same thing

 

are you referring to the tranny? must be...will ck it out...thanks

what happens when the vacuum isn't right on a c-6? I thought it was just to down shift type of thingy bobber.

 

that was it with tranny..thnks

torqued intake down and vacuum is now about 12" so will replace valley pan.

 

I would think you would need around 20 degrees or so timing at idle (including vacuum advance if you have it).

 

Not sure if I follow... Did you say you made your own intake manifold gaskets?

Also, many people throw the rubber end seals away, and just use a good bead of RTV front and back of the intakes. Won't blow out as easy.
I would keep the valley pan, too.

 

i was using a cut pan and made gaskets for the ports... it worked but i crushed one of the rubber ends-back-side...which i do use if there is enough clearance without issue or them escaping but...not enough clearance. Used the pan and 'the right stuff' goo this time w/o the rubber ends and will fire it up Sunday. Torqued to 28ftlbs. Still used the weiand but have the performer that came off of it on standby.

I put the intake on w/o gasket and with and it seems to fit well. Measured the home-made gasket that was on it and all contact areas measure .040 so compression was consistent. Hopefully I have it beat..

I'm still trying to understand the timing. Port vacuum vs manifold etc. I'm under the impression that timing is retarded by vacuum and thus when vacuum drops the timing advances... so port vacuum doesn't make much sense.

I had a guy explain it too me but it confused me pretty good. My romac balancer is marked 360* and I had the timing set at 10* (Vacuum disconnected and plugged) when i advanced the distributor
(turning clockwise) it increased indicating that the 10* is btdc or advanced not retarded I moved it from 0-25 or so and found the best vacuum around 20 but it turned over a bit hard. So I assumed i had it timed at adv 10*...right or wrong. Anyway the guy is telling me that I'm 10* retarded and that the stock setting should be about 10* retarded and will idle best at 20* retarded once it's all connected.

so i'm confused....way confused. I've searched and have not found anything on this site to clear up my thinking... still looking though.

 

What does he mean, '20* retarded'??? After top dead center? Cause that ain't gonna fly... lol!
10 degrees BTDC is a good place to start, and that is with the vac advance diaphragm plugged off. Vacuum is often understood by many people. You need vaccum at idle or just off-idle to keep a clean, efficient burn on a street engine, because it advances your timing for an earlier burn to get the most efficiency from the charge (lean mixtures). Just the opposite for rich mixtures (full throttle); The fire time should come a little later to acheive a full burn at combustion. Low vacuum at WOT does that job nicely, almost zero advance. That is why you want advance at idle, to help it run on less fuel.
Here is a little write-up that can explain it better than I can. There are differing opinions. (From hotrodders.com)
TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
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match your timing too your cam card it will give you the best performce cam manufactures spen thousands doing the testing. If you dont have call comp cams w/all your motor info ie cam intake carb ignition pistons and head work and they will tell you exactly where to put it. but I have found the cam cards to be right and offer the best performance.

 

Mark.... that was freaking brilliantly written...thanks....i get it.

Actually i wasn't that far off initially except i didn't realize that the vacuum adv diminished completely and wasn't a part of total timing.

I haven't started the engine since i replaced the parts so I'll be getting it going tomorrow...was a football bum today...how bout them cowboys!

I appreciate you taking the time to explain this and strongly urge fte to add this to the basic info thread.

I spent a lot of time looking for this info and a bit here and there doesn't cut it.

 

I didn't read all of that post but, concerning initial timing. No matter how you run the vacuum advance if you don't see more that 10 degrees at idle (with everything hooked up) it wont idle worth a darn. Especially in a modified engine.

 

it's running ok now... still need to play with it but the intake gasket change was a good thing. I had to retard it more than i would have liked due to full but that will change once i can get to a station.

Now the tranny is giving me fits I think...will post on truck forum.

thanks to all...got the timing down and that feels good.