tfuith

good morning, where can i find the 2 vac"s you mention above. i have gone to several parts store but they all need a part #. would you have pn# or where to buy them.
tom

aaronz28

go to Napa -
I'd advise you look for the Vacuum Advance Can for either the 64-65 FI Cars, or the 67-8-9 Z28 Camaro with 302 -
both should have the same vacuum can on them - and will pull advance at 10-12" of vacuum

Cheers

tfuith

jerry thanks. i have talked to ken h. and he was kind enough to suggest he make a house call, so he is checking his schedule and will let me know. all the people who responded to to my post have been fantastic and i hope i someday i can return the favor

thanks tom f.

1969RAY

This has been an interesting thread. As the repairs/adjustments are done, pictures would be much appreciated.

SWCDuke

The B28 VACs are out of production by Standard Motor Products, but recently Airtex still offers B28s under their 4V1053 part number.

BTW, L-76 has the same spark advance map as L-84 except L-76 has full time vacuum advance. However the 15" 201 15 VAC does not meet the Two-Inch Rule with the Duntov cam. This caused idle instability and stalling problems.

I fixed it circa 1965 by installing the 365/375 HP centrifugal weights/springs and 8" 236 16 VAC, and the more aggressive centrifugal yielded noticeably better low end torque without causing any detonation.

Of course, those OE parts are long gone, but the B28 VAC has the same specs as the 236 16, and you can buy an aftermarket spring kit like Mr. Gasket 928G and install the lightest springs in the set.

Duke

tfuith

i have ordered the mr gasket spring kit i will let you know.

how accurate do you need to be finding top dead center , i am within 1 hash mark of "0" on the plate on the block

SWCDuke

I'm not sure what you are doing, but if you are verifying TDC with a piston stop or some other method and find the balancer notch one hash mark (which is 2 degrees) from zero on the tab, that's okay considering production and measurement tolerance, but document whether it is advanced or retarded.

With the lightest springs installed, set total WOT advance in the 36-40 range as high as possible without detonation taking into account the error you measured on the timing tab. If you get significant detonation retard in two degree increments until the detonation goes away.

Duke

tfuith

duke, this is what i have as of today with vac connected i get 15 deg at idle 900 rpm, at 2500 rpm i get 42 deg. i havent driven it yet but i will.
is this acceptable or am i missing something i also ordered the springs from mr gasket.

this whole mess started with a surge at a steady speed i any gear i have tried adj the power and economy stops but no help so it has morffed into where were at now, timing. after i drive ill let you know

i have 2017 ZL-1 camaro and i am taking it in for the 500 mile inspection. super car thanks for all your help tom

MelWff

you have to provide those timing figures with the vacuum disconnected and preferably at lower idle speed for the first number.
you have to provide the number of additional degrees you get at idle when the vacuum line is connected to a constant vacuum source.

MikeM

I think you missed Plaidside's post.

You don't need any help setting the timing properly on your car by substituting parts out of an Honest Charlie catalog or a vacuum unit from a later model with and entirely different advance curve and camshaft. Your stock parts should allow you to get what Plaidside says except your mechanical advance will probably come at a higher rpm.

Start over. Unhook the vacuum advance hose and plug it. Set the initial at 12* BTDC. Rev the engine until the distributor quits advancing. You'll probably be around 34*-36* degrees when the distributor plus inital reaches that point. Hook up the vacuum advance and re-run the previous test and note the results of total timing. You should see whatever advance you got the first time plus 12*-14* additional from the vacuum.

If you didn't get these results, you have something wrong and it should be easy to diagnose here instead of just wildly swapping all these non-stock parts in the equation when you don't even have a baseline to start with as yet.

Can I you have verified where TDC is on your balancer reference?

SWCDuke

Does the advance continue to increase above 2500? If you did not test above 2500 to find the point of max centrifugal advance your test is not valid. As stated the VAC must be disconnected and signal line plugged. A golf tee works well.

Start by revving the engine (VAC disconnected/signal line plugged) and observe when the timing mark stops advancing. This is the speed that centrifugal is all in. If the centrifugal advance is OE, maximum is not achieved until 4600.

Total WOT advance, 36-40, should be set a few hundred revs above the speed of maximum centrifugal advance. That means 5000 if your centrifugal is OE, but less with lighter springs.

Then drop revs to idle and below and record the RPM that the advance stops retarding, and the advance you read is intiial timing. It may be 700 or less and it's tough to get a Duntov cam engine to idle stably at this speed for any length of time, but that's not a big deal. The important thing is to get total WOT advance in the right range.

That's why with high overlap cams the Total WOT advance method should be used, because centrifugal might not be fully retarded until such a low speed that the engine will not idle stably long enough to measure and adjust initial timing.

The difference between initial timing and total WOT advance is the amount of centrifugal added with engine speed. OE is 24.

Duke