Vacuum reading at idle 63-327-340 HP

[Richard S.]

I would appreciate knowing the amount of vacuum I should see at nominal idle rpm for my 340 HP 327-4-speed. Car has less than 2000 miles since total engine rebuild. Engine has stock 097 cam with solids.

[G B.]

Re: Vacuum reading at idle 63-327-340 HP

If you're idling at 750 - 800 rpm, and your valve lash is set at .012" and .018", and your idle mixture screws are set to give you about a 13.5 to 1 A/F ratio, and your initial timing is set at 12 degrees BTDC with a ported vacuum connection, and you have stock domed pistons, then you should have a reading of 13 to 14 inches of vacuum on a relatively new vacuum gauge. I don't know what the gauge reading would be if the distributor vacuum advance was hooked to a full time port. I've never tried that set-up.

[Duke W.]

Re: Vacuum reading at idle 63-327-340 HP

The '63 340 HP engine with the OE 3461S carburetor (also used on 300 HP w/MT) is full time vacuum advance, but the OE 201 15 VAC does not meet the Two-Inch Rule, which results in idle instability - loss of idle speed/vacuum and eventual stalling if allowed to idle for more than a few minutes.

I solved this problem in 1965 by installing the '64-'65 365/375 HP 236 16 VAC, which is all in by 8". The modern replacement available under numerous brands including "Delco" is stamped B28. (They are ALL made by Standard Motor Products despite the name on the box.)

With the new setup, which also included the '64-'65 365/375 HP centrifugal weights and springs ( 0 @ 700, 24 @ 2350, OE was 24 @ 4600) it pulled about 12" at about 850 with about +/- 50 RPM lope, but it would idle stabily all day long. Total idle advance was about 32 degrees. It never ran hot and it never detonated with the more aggressive spark advance map, but it had a lot more low end torque, which really helped pull the CR four-speed and 3.08 axle. Highway fuel economy at 70 also improved from 20 to 22 MPG.

All the whys and wherefores are in the following pdf:

DukeWilliamsEngineTuningPerformance&EconomySeminar .pdf (application/pdf Object)

Duke

[Richard M.]

Re: Vacuum reading at idle 63-327-340 HP

Richard, what distributor and what is your manifold vacuum reading? What vacuum advance unit is being used?

Not a 340, but FYI just the other day I reinstalled a original CI intake manifold and restored WCFB on a '63 250HP with it's original Flint powerplant. It had a Edelbrock intake, AFB, and aluminum VC's on it, not a true base engine appearance. My friend, the owner, wanted it back to stock. He was having trouble with the AFB returning to idle and after exhaustive efforts and a off-site rebuild he wanted it out of there. He acquired the car's original intake and Carter carb when he bought the car a year ago. He had the carb restored and on a shelf. I also tossed in new valve seals while I had it all apart, as a puff of occasional blue smoke was happening at startup he said.

Lars restored his original distributor some time ago, which is a work of mechanical and functional art. It included a B26 vac advance. I sanity tested the vac advance on the bench and saw it start at apx 6" and was all-in at around 12"(typo..... 8" in error. misread my notes). Manifold vacuum was around 18-20" on my gauge IIRC.

I put all of the pieces together, set distributor timing on the balancer at 4*, cranked 'er up and all was perfect. Checked timing with a dial back and after a few adjustments to the distributor and carburetor all was good. The engine would idle just fine at normal temperature. After a test drive I let it idle at 750 RPM for about 15 minutes while reading about 178* on the IR gun at the water outlet the entire time. Nice cool runner.

I suspect this engine could idle all night long in a desolate wooded parking lot in northern Michigan while spending special amorous moments with one's sweetheart.

Rich

[Jeff P.]

Re: Vacuum reading at idle 63-327-340 HP

Richard...Quote... It included a B26 vac advance. I sanity tested the vac advance on the bench and saw it start at apx 6" and was all-in at around 8". Manifold vacuum was around 18-20" on my gauge IIRC.
Richard is this B26 VAC meeting the 2" Rule? Would the B22 be a better choice? I'm trying to figure this 2" rule out so I can check my 1968 L-79 with the same spec's. If I have 18-20"manifold Vacuum and the B-26 is 12" that dont meet the 2" rule. This is what came stock on my 327.What am i missing?

[Richard M.]

Re: Vacuum reading at idle 63-327-340 HP

Duke could answer better than me, but I always understood his process to be as long it's.....not less than 2 inches less than idle vacuum....with about 24*-32* total timing at idle.

Lars chose the B26 for this one and knowing it was a base engine so I'd have to say it's correct. Not sure what yours would be until you got actual test results with a dial-back.

Rich

[Duke W.]

Re: Vacuum reading at idle 63-327-340 HP

You guys need to download and READ the pdf in the link I provided. The B22 15" VAC is the best choice to meet the Two-Inch Rule for base engines with manual transmissions that should pull at least 18-19" idling in neutral at 500, B22 for automatics since they don't pull as much vacuum idling in Drive at 450-500.

The best Two-Inch Rule choice for L-79 is the 12" B26 since they typically pull 14-15" at 750. The OE 8" VAC is more aggressive than necessary.

There are only three (read the pdf) currently available single point/TI VACs that are the "best fit" for all pre-emission and emission controlled engines that have been converted to full time vacuum advance, so you have a one-third chance of getting is right by just guessing, but simply taking an idle manifold vacuum reading and properly applying the Two-Inch Rule will get the right answer every time.

It's that simple!

Duke

[Stuart F.]

Re: Vacuum reading at idle 63-327-340 HP

My experience has been that with an AFB on an L-76 340hp, there is not correct return spring tension to provide a consistent idle speed - even with the black generic 64-65 spring (the white spring specified for the 63's by many vendors is wrong). I don't know if it is a mechanical advantage problem or just the nature of the AFB's. At any rate, For driving, I add a small light weight second spring that occupies the second hole on the bracket and the hole in the throttle arm (on some models one may have to drill a hole in the arm if it isn't there). This arrangement works great for me, and you can easily take it off for show.

Another point about AFB's and steady idle problems; they are prone to having worn throttle shaft bores, specially the one on the driver's side primary shaft. When this gets bad, yet not bad enough to leak vacuum, it can still cause an unequal exposure condition of the idle and transition ports in the throttle bores.

I recently had my 3461s primary shaft bores re-sleeved and it not only solved a bad lean surge condition for me, but it helped to give it a smooth 750 RPM idle. My vacuum is a fairly steady 14 to 15" Hg. My valves are set using the Williams-Hinckley method at .008" intake and .016" exhaust (timing degree tape on balancer). I use 10 degree initial mechanical advance timing with 64-65 L-76 weights and blue dot springs, along with a B-28 VAC, a Dyna-Flyte ball bearing plate and the Pertronics II electronic ignition conversion.

I'm away from home now (up here in the frozen northland of Chicago this week and Cleveland next week), otherwise I might post some of my Carburetor mods too.

Stu Fox

[Duke W.]

Re: Vacuum reading at idle 63-327-340 HP

I would appreciate knowing the amount of vacuum I should see at nominal idle rpm for my 340 HP 327-4-speed. Car has less than 2000 miles since total engine rebuild. Engine has stock 097 cam with solids.

So what are your vacuum @ idle speed readings, Richard, and how is your distributor set up?

Duke

[Richard M.]

Re: Vacuum reading at idle 63-327-340 HP

You guys need to download and READ the pdf in the link I provided. The B22 15" VAC is the best choice to meet the Two-Inch Rule for base engines with manual transmissions that should pull at least 18-19" idling in neutral at 500, B22 for automatics since they don't pull as much vacuum idling in Drive at 450-500.

The best Two-Inch Rule choice for L-79 is the 12" B26 since they typically pull 14-15" at 750. The OE 8" VAC is more aggressive than necessary.

There are only three (read the pdf) currently available single point/TI VACs that are the "best fit" for all pre-emission and emission controlled engines that have been converted to full time vacuum advance, so you have a one-third chance of getting is right by just guessing, but simply taking an idle manifold vacuum reading and properly applying the Two-Inch Rule will get the right answer every time.

It's that simple!

Duke

Ouch! That slap in the head hurt, Duke. Telling "you guys" (i.e. me?) to "READ" your stuff? HuH??? My Timing Bible? I've READ and STUDIED your documents many, many times and always use them as a reference in my work. I've probably linked them scores of times in my forum threads and emails to car enthusiasts and friends, worldwide. I info-market your brain everywhere I can. You're one of the many heroes here.

Okay. I'm better now.

So.....back to the facts......I didn't choose the B26, as I said, Lars did.

I sent him a email asking him about it and that you're telling me it should be a B22. I'll pass his response along.

Rich
p.s. I have also asked the OP those questions. I fear not hearing the answers for some time.

[Stuart F.]

Re: Vacuum reading at idle 63-327-340 HP

Richard M.;

Don't take it personally that Duke included you in his "you guy's" exclaimation. Remember, it's not like he's having trouble tolerating our old age loss of brain cells, rather it's like a bunch of us guy's sitting around a circular table, sucking beer, and telling war stories trying to "top" each other - like I would say; "I never met a Fuelie I couldn't beat!"

I love it and I'll buy the next round!

Have a great weekend, guy's.

Stu Fox

[Duke W.]

Re: Vacuum reading at idle 63-327-340 HP

Ouch! That slap in the head hurt, Duke.

Sorry, Richard. That comment was really aimed at Jeff in post #5. I meant no offense to either of you, but Jeff said he didnt understand the Two-Inch Rule, which is explained in the pdf link along with how to set up an optimal spark advance map.

Thanks for spreading the word, but sometimes I get perplexed because guys say they read it, but don't seem to have any more understanding than someone who's clueless.

A 250/300 HP engine with manual transmission should idle at 18-19" at 500 in neutral. The '62-'63 distributors had a 15.5" VAC, which was fine, but maybe not for a Powerglide idling at 450-500 in Drive because that condition pulls less vacuum. How much less I'm not sure because no one has ever provided the data despite my several requests.

The VAC changed in '64 and again in '65, which has been discussed on the TDB. Finally the '67 300 HP got a 12" VAC probably because it worked with Powerglide, but I don't like to see a more aggressive VAC than what it takes to meet the Two-Inch rule. That's why I recommend a 15" B22 for a base type engine, and a 12" for L-79 because it meets the Two-Inch Rule since L-79s typically idle in neutral at 14-15" @ 750, so the OE 8" VAC is more aggressive than necessary.

A more aggressive than necessary VAC can cause part throttle or transient detonation, but has no offseting advantage. So among the three applicable VACs, 8, 12, and 16", always select the least aggressive VAC that meets the Two-Inch Rule for the normal idle configuation, which is in neutral with a manual transmission and Drive for an automatic.

Duke

[Jeff P.]

Re: Vacuum reading at idle 63-327-340 HP

Duke.... Yes i'm picking up what your throwing down! Don't get your feathers all ruffled!! I still want the vacuum lines connected to the carb base if possible. I need to examine this base plate to see if i can drill a passage for this to work. Has anyone done this before?

[John D.]

Re: Vacuum reading at idle 63-327-340 HP

Richard, My '63 360 HP with '097 cam, NOS 201 VA puts out 16" of vacuum at 900 RPM. Same engine as yours except for the FI. John

[Duke W.]

Re: Vacuum reading at idle 63-327-340 HP

Duke.... Yes i'm picking up what your throwing down! Don't get your feathers all ruffled!! I still want the vacuum lines connected to the carb base if possible. I need to examine this base plate to see if i can drill a passage for this to work. Has anyone done this before?

You should start another thread to discuss whatever issues/questions you have with a '68 L-79. This one is about a '63 L-76 even though the OP seems to have gone AWOL. That seems to be happening a lot, lately.

Duke