help with 17082224

[bruno]

i will make a new spacer to cover the slot completely. and find the missing numbered drill i need to measure. thx. will post more questions later i’m sure!!

[bruno]

okay, i made a new spacer for under the carb, but the 1/4” gasket above the spacer doesn’t cover the slot in the manifold. the thin gasket under the spacer does, as does the new spacer, but the carb won’t put any pressure on the spacer on that end of the slot. is this an issue? i bought a cheap carb kit for the original carb just to get the thin gasket for under the spacer, and it also has thicker gaskets similar to the 1/4” one i got from you, but none of them cover the slot either. i could use another thin gasket above the spacer, if that would be better. or is there a 1/4” gasket that has the little. kick out on the side to cover the slot? hope that question makes sense.

i also shrunk the LIABs to .068” to see what difference it makes. i’ll let you know that part after i fire it up, hopefully tomorrow.

[bruno]

fired up the car today, here is where it stands: all specs the same as before, except for LIAB are .068”, and idle tubes are .038.

idle is great at 750, no nozzle drip. engine slows down when idle screws are turned in all the way, with both having effect. my idle vacuum at 750(with VA connected to manifold), is 17.5-18”. idle screws don’t seem to change vacuum, until idle starts to fall off. currently set at 3.5 turns from seated. tried all the way to 6 turns out, no noticeable difference in vacuum. it does pick up about 60 rpm when i pull a vacuum line off. no real change if i cover primaries, unless i cover them almost completely, then i wants to die.

timing is set at 8 degrees base, plus 17 from VA, for total of 25 degrees. haven’t checked mechanical yet, but none in at idle. (i lowered idle to 550, no change in timing).

still need tires before i can road test. i’m not familiar with knowing where the timing needs to be, so advice there would help. i think the carb idle is where it needs to be, but i’ll take suggestions there too.
not sure what to do next, until road test.

[bruno]

should add idle doesn’t burn the eyes near as bad now!!

[novadude]

Late to the party, but the cam sounds like a typical generic "RV" grind that has been sold under numerous brands over the years.  I have one in a '69 396 sold by Blue Racer (wolverine gear - used to be owned by crane).  Specs are 204/214 @ 0.050, .476"/.501" lift, 112 LSA.  Allowing for some cam grinding inaccuracies, wear, and measurement error, those published specs almost perfectly match what you've measured.

[Cliff Ruggles]

Sounds like you've made progress.  I'd do some road testing and go back and make adjustments if/as needed.....

[bruno]

that’s my plan, although i’m having some issues with tires and wheels!! can’t seem to get much up here. may have to run a used set for a bit. the ones in there now are 40+ years old!! they will turn to dust if i hit the throttle to hard!

cliff, do you have any suggestions on a timing curve to start with? from reading a ton of posts here, it seems you have a slightly different opinion that the “timing 101” article, so i figure i’d ask for your advice. think i have a bit too much centrifugal currently, and possibly a bit too much Vacuum advance as well.

from what i can gather from reading the internet(i know, don’t believe it), but it seems everyone wants as much initial as possible, 34-40 total, and around 10-15 from the vacuum. i am unsure how to determine the best initial. centrifugal i can figure out by driving the car, same for vacuum. just the best initial is confusing me. thx

[Cliff Ruggles]

For most engine builds, at least those that are well thought out and good choices made for compression and camshaft events they will like around 10-12 degrees initial timing, about 10-11 (20-22 at the crank) from the mechanical advance, and another 10-14 from the vacuum advance.

I try to avoid all the manifold vs ported vacuum advance debates, but for most engines tuned here I do NOT add any additional timing at idle speed and use a ported source to the VA.  Of course saying that on most Forums is a good way to cause a bunch of folks to get their panties all wadded up.  Almost immediately you'll get a link to or copy/paste some LONG lengthy VA article in your face.  It will be followed by stories of how your engine will overheat if you don't use MVA, or it will use more fuel, not make as much power, or even detonate at high RPM's when the ported source applies the VA at WOT.

ALL of those responses are from very poorly informed sources with little to no experience at all doing this sort of thing, but that's the World we live in today and sadly WAY too many folks have opinions about topics based mostly if not all on Internet Google searches instead of actually doing it for a living or at least having a LOT of hands on experience with these things.

I've lost count as to how many of those aftermarket spring/weight "kits" I've removed from distributors over the years, then hooked the VA back up and to it's original ported source on the carb.  I'll go into the distributor and set up the advance curve so no timing is added at idle speed and it advances smooth and steady with increasing RPM's just like the factory set them up.

This "all-in" right off idle NEVER works well and not sure why despite the fact that it's now 2023 and we should be a LOT smarter these days that folks till tune with those JUNK parts.  The fact of the matter is here that the better you do with your choices for the engine build, optimum compression, cam events, tight squish, efficient combustion chambers, etc, the LESS timing and fuel the engine will like, want, need and respond well to once placed in service. 

The super-quick timing curves and "all-in" right off idle plus running initial timing WAY off the scale at idle are in most cases "crutch" fixes for other issues, like WAY too much duration, LSA too tight, compression ratio too low for the cam, or not nearly enough idle fuel available to the mixtures screws for the engine combo.........

[Kenth]

It has to be added that most pre-1968 engines uses full manifold vacuum for the ignition vacuum advance. Are all of these engines poorly thought-out? Of course not. The timing set up is a natural part of the design and due to the principles of the combustion engines. For 1968 the goverment decided to reduce the amonts of certain emissions and to accomplish this the engineers reduced timing at idle speeds using a ported source for the vacuum advance. This heated up the cylinder heads for reduced emissions, but engine effiency suffered, dieseling (run-on) occured and idle-stop solenoids became mandotory, and most cars got a fan shroud. So would you use ported or full vacuum for the vacuumadvance? Use what the engine likes the best, there are really no absolute rules to be obeied, the only difference for the function is at idle speeds, and going from full to ported vacuum requires modifications (enrichening) of the carburetor low speed circuit to have an as complete combustion as possible, and possibly adding an idle solenoid.

And, "if everything else fails, follow the manual."

FWIW

[Cliff Ruggles]

Yep, I forgot about folks reminding me that engines prior to the late 60's used MVA. 

I'd add here that most of if not all of those engines used very low initial timing numbers, then added some additional timing via manifold vacuum advance, but typically not very much.  The early engines also had pretty high static compression, and small cams in them on wide LSA.  They are making a LOT of vacuum without a lot of initial timing.

Those VA cans for the most part didn't add a lot of timing so they were NOT really using much at idle speed and didn't need to. 

This is where the water starts to get muddy with this topic.  Folks make POOR choices for these engine builds, following some stupid proverbial "brick wall" of not being able to run more than 9.5 to 1 compression on pump gas, and installing these "modern" profile whiz-bang short seat timing cams on tight LSA's to try to salvage some seat of the pants power.  Then they find that with "low" compression and all that overlap that the engine REQUIRES a lot of timing at idle speed.  So basically what happens is that they must tune with pretty high initial timing on many of these new builds because they didn't use enough compression, or bought into the BS that tighter LSA and more overlap is somehow going to work better.

Combine that with the resident Forum experts, guru's and "trolls" surfing around on the Internet finding long lengthy articles telling us that we MUST use manifold vacuum advance and butt-loads of initial timing or we're STOOPID.  So the water is muddied pretty quickly.

I've finish with a story, as I have lots of them.  Decades ago before I knew much about all of this I built a 406 SBC for my K-5 Blazer.  I ordered flat top pistons for it not knowing that the compression ratio would be well over 10 to 1 with the heads I was using.  I put a stock 350/300hp cam in it topped with stamped steel 1.6 ratio rocker arms.  That engine didn't like, want, need or respond well to any timing anyplace.  I spent months tuning it, varying the initial timing, total timing, how fast the mechanical curve came in, and varying how much VA was added and went back and forth between ported and manifold vacuum.  It HATED manifold vacuum and INSTANTLY developed a slight skip/miss in the idle note if you hooked it up that way.  I also had to lower the throttle plates some and mixture screws started to be unresponsive/lacking sensitivity (sound familiar).

When it was all said and done I ended up running zero degrees initial, 26 degrees mechanical and 10 degrees from the vacuum advance.  Yep, it ran flawlessly with very little timing added anyplace.  I set up the advance curve with pretty heavy springs so all-in was about 3400rpm's.

That engine made so much power I could ROAST all four tires right off the rims.  It pulled my race car and trailer like it wasn't even back there, and got WAY better fuel economy than the anemic dished piston 400 engine with crappy smog heads it replaced.  You couldn't pour enough timing to the original engine to get it to ping and it didn't make chit for power anyplace, just like all those mid to late 70's Chevy 350 and 400 engines GM put in their trucks and Blazers.

.......continued

[Cliff Ruggles]

It was one of my first experiences with high compression on pump gas and that engine ran flawlessly for well over 100,000 miles before I sold the vehicle.

I did a second high compression pump gas engine shortly after, to power my 1967 Impala SS.  It was the original 327 using flat top pistons .015" in the holes at TDC, .020" steel shim head gaskets, 350/300hp cam and the stock 291 casting 327 heads.  Just like the previous 406 build it ended up at zero degrees initial timing, short timing curve and 10 degrees from the VA (ported source). 

I backed the little 327 with a 4L60 overdrive trans and 3.31 rear gears.  It also made enough power to ROAST the rear tires right off the rims, idled dead smooth with 18" vacuum, and excellent street manners.  It also delivered 18mpg's city and mid 20's highway. 

So come on here and tell me that these engine MUST have all this advance in them, and that you need to run the timing clear off the scale at idle speed, bring ALL the mechanical advance in by 1500rpm's, and put another 20-30 degrees timing in from the VA via manifold vacuum and it's absolutely got to be that way or you are missing out on something someplace......I'm all ears folks....

[Cliff Ruggles]

Before I forget I'll add in here that both of the engines mentioned above, the 406 and 327 never even thought about running hot, overheating or pinging anyplace, and managed currently available pump fuel w/o any issues anyplace.  So there is a lot to be said for tight quench, high compression, well chosen camshafts and turning the heat produced into making power vs putting a butt-load of quench and a lot of overlap into the equation, then dumping all the heat into the cooling system.....FWIW.....

[bruno]

that’s why i wanted to hear!! thanks very much cliff. you have been an amazing help with getting this car running. i will leave the timing where is for now, and see how it goes down the road. just waiting for tires to show up.
I wish i had the time to obtain all your experience, but sadly, very few people around here are into cars, let alone race them. most don’t even run carbs anymore. i love working on them, just don’t have enough experience. but i have learned a ton from you and your book. and even just reading your responses to other questions has answered questions i didn’t even know i had. !!

[Cliff Ruggles]

Thanks. 

One thing is for certain there are a LOT of opinions when it comes to tuning, much like anything else.  I really don't have an "opinion", just facts based on decades of actually doing this for living, running the gauntlet, winning some battles, loosing others and improving my knowledge and skill sets the entire time. 

I was actually asked to write another book a few years ago on custom tuning these engines, but sadly I had to decline.  Just don't have enough time or energy for it.......