[yankeeralph]

I need some cam expert help.

I presently have some slight pinging under light acceleration with a Comp Cam High Energy 268H cam. Installed in a 68 YC 400 with stock 15 heads, +.030 on cylinder -- I think compression may be higher than the 9.0 the builder was shooting for since he was not that familiar with pontiac engines. Have timing at 8 BTDC, 24 with vacuum advance and 32 total at 3000. Under hard acceleration I cannot detect any pinging, quite possibly because of all the other noises. Under light acceleration and slight/heavy load (going up incline)I stll hear some pinging, but not excessive like my 92 ford truck.

My problem is that Comp Cams states that if the compression is over 9:1 then the high energy cam will contribute to pinging and that i need a different cam -- like the 270H Magnum -- says it helps because of longer duration? What gives?? Will the 270H help or is there a better choice. This is strickly a street driven daily driver.

Setup: 68 400 block +.030, (CR between 9-10 but unsure), sil-r Lite Pistons (Brand spelling), stock rods and #15 heads, recent rebuild with new Comp dual springs, roller rockers, Edelbrock Intake and carb, 2000 Stall Holeshot with a TH350 transmission, 3.42 posi rear. Running 93 pump gas and want to keep it that way. Hei distributor with AC R43 plugs gapped at .045. 165 deg thermostat with 4-row rad. Cooling is great now that I fixed some leaks.

Car runs good and strong.

Please help! Do I need to back timing down some more and suffer performance, or is the new cam a better choice.

Thanks

[yankeeralph]

Thanks Randy

I have the adjustable vacuum advance unit, can't remember the brand, but it has an adjustment for total advance also. I'll try taking it down several degrees to see what it does for me. Of course this may affect off idle throttle repsonse but I'll give it a try.

[PMDRACER]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Try disconnecting the vacuum advance and see if the pinging goes away. You should not be having a problem unless you are running really low octane gas.
<HR></BLOCKQUOTE>

That's my point. Disconnect the vacuum advance, and all is good. This motor makes enough vacuum that at light throttle the vacuum advance opens, and it pings. Get in it harder to get the vacuum to go away, and it stops pinging.
So the answer is either get a vacuum can that opens with a higher vacuum number, in the order of 12 to 15 inches, or just get on it all the time. Fun, but impractical.
I run 91 octane (at $2.36/gal currently) all the time. 10 degrees static timing (tried it a 8, no help), 32 degrees all in at 3000.

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.

[Cliff R]

Any stock vacuum advance unit can be quickly made into any amount of advance one would like. Here, I simply braze up the slot and refile it to reduce the amount of travel by the arm. For most well prepared street engines with medium compression ratios and a well chosen cam, intake, exhaust, etc, seldom is more than about 8-12 additional degrees of timing needed from the advance. I've seen several other methods used to control the amount of movement of the arm on the advance, including using a small self tapping screw and washer, epoxy and welding/brazing. For distributors prepared here, we reduce the travel to about .100 to .125". This will have the unit add about 8 to 12 degrees. Use a small drillbit as a gauge when modifying the unit.....Cliff

[PMDRACER]

From Geoff -

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> They have a range of about 4" to 17" of vacuum, using the Allen wrench <HR></BLOCKQUOTE>

Are you sure about this? If so, looks like my problem is that the Crane I got is defective. I can only adjust the opening point from 7 to 9 inches of vacuum.

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.

[buwalda]

To PMDracer

Yes, the 4" to 17" range of vacuum is for the Crane adjustable #99600 unit that fits the GM HEI.
As the cam gets bigger in duration, the spring in the stock vacuum advance unit will probably be too stiff to work properly with the lower vacuum of a large cam. This is when the Crane unit works well.

[PMDRACER]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> You could put in a bigger cam that would solve the to much vacuum problem
<HR></BLOCKQUOTE>

A bigger cam? And here I thought mine was plenty:

Intake/Exhaust
@ .006 285/290
@ .050 235/240
Lobe Lift = .338/.331
Gross Lift @ 1.5:1 = .507/.496
Lobe Sep = 106 degrees
Installed @ 102 degrees

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.

[Lloyd-TX]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Randy Frazier:
I have found that most HEI distributors have too much vacuum advance built into the diaphragm. The number of degrees is stamped on the bracket that attaches the unit to the distributor plate so you can check and see what you have.<HR></BLOCKQUOTE>

Hey Randy:

Just a heads up on you comment concerning the stamped number on the vacuum advance bracket. I used to think that was the degrees rating on the unit as well, but as you can see in the article linked in my post above, that number is actually an identifing number stamped by the manufacturer (Dana Coroporation), and has nothing to do with the number of degrees of advance. For instance, the unit I'm using is a Standard Ignition part number VC 177, and is stamped "B28", yet provides a total advance of 8 distributor degrees (or 16 crankshaft degrees). I've verified this with a dial-back timing light when installed on my engine.

Hope this helps.

Later,
"455HO" Lloyd

1972 Formula 455HO; Lucerne Blue; 12.96 @ 104 MPH @ the '03 PSN's; 12.50's or bust this year!
1970 GTO 455HO; Palomino Copper
1972 GTO 455HO; Sundance Orange

[slowbird]

Has anyone done testing on using the vacuum advance compared to not using it? We havent used one in years and we have no problems with over heating and our gas mileage seems to be alright for the setup we have. In fact my dads car has one and he has more heating problems than my 2 without it and his has worse gas mileage.

75bird 7.41 1/8mile at 92mph street car
73Ventura 11.88 at 113 streetcar
69GrandPrix 12.64 at 107 tow car
65GTO 10.14 at 129 tri-power dragcar

[Sun Tuned]

ralph,
try a Delco #1973516 vac adv and see what happens.

[PMDRACER]

I just installed the Crane adjustable vacuum can. What a POS. I can change the point at which the vacuum can starts working from 7 to 9 inches of vacuum. Absolutely no help.

Yes, I can use the limiter tab to lower the total amount introduced from 20 degrees to 10, but if it's coming in too early, who cares? Pinging is pinging.

I bought this unit thinking I could change the opening point to 12 to 15 inches of vacuum, which is freeway cruise.

What I need is a vacuum switch that I could set to come on at somewhere between 12 and 15 inches of vacuum, wire it with my old TCS solenoid so that when I cruise the freeway, the solenoid opens and allows vacuum to the advance can.

Hmmmm....
Me thinks I have an idea....

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.

["Guy]

I'm with the rest of the guys here....stick with your set-up.
Have the distrubutor recurved to your set up.
With that I would say an adjustable vacumm(this will help with lite throttle pining) with a curve of 0 degress before 1000rpm and 24 mechanical advance all in @3000 to 3500rpm. It really depends when it should be all in, with a 3:55 gear if you drive the car on the highway at 60/65mph your going to be at 3000rpm all the time. If that being the case have it all in @3500rpm, if most your crusin is done below 3000rpm have it all in by 3000rpm.
One other thing, cool the car down with a 180 thermostat. It really helps if you put an aluminum radiator in...Rodney Red makes a really nice for the 68/69. Your car should run pefect with this set-up.

[slowbird]

Try disconnecting the vacuum advance and see if the pinging goes away. You should not be having a problem unless you are running really low octane gas.

75bird 7.41 1/8mile at 92mph street car
73Ventura 11.88 at 113 streetcar
69GrandPrix 12.64 at 107 tow car
65GTO 10.14 at 129 tri-power dragcar

[PMDRACER]

Geoff -
Thanks for the reply!
Looks like my problem is my Crane vacuum advance can is defective. Testing with 2 different mityvacs, my Crane only changes it's opening point from 7 to 9 inches of vacuum.

Again, thanks!

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. [email protected]

The point to life isn't necessarilly the decimal.

[Lloyd-TX]

Good info, Cliff - thanks!

Later,
"455HO" Lloyd

1972 Formula 455HO; Lucerne Blue; 12.96 @ 104 MPH @ the '03 PSN's; 12.50's or bust this year!
1970 GTO 455HO; Palomino Copper
1972 GTO 455HO; Sundance Orange

[buwalda]

Ralph,
Stick with it! If your adjustable vacuum adv unit has a notched metal plate to adjust total vacuum advance, it is probably the Crane unit. They are excellent, with good instructions. I have used many of them. They have a range of about 4" to 17" of vacuum, using the Allen wrench; I would try this first, as it is the easiest. Somehow, I think your problem is too much [total] vacuum advance, in which case you need to reduce it with the notched plate. If none of this helps, you could try retarding the cam 2 to 4 degrees. Whatever you do, keep the vacuum advance, as it helps idle, cooling, throttle response & mileage.
Good luck!

[yankeeralph]

I need some cam expert help.

I presently have some slight pinging under light acceleration with a Comp Cam High Energy 268H cam. Installed in a 68 YC 400 with stock 15 heads, +.030 on cylinder -- I think compression may be higher than the 9.0 the builder was shooting for since he was not that familiar with pontiac engines. Have timing at 8 BTDC, 24 with vacuum advance and 32 total at 3000. Under hard acceleration I cannot detect any pinging, quite possibly because of all the other noises. Under light acceleration and slight/heavy load (going up incline)I stll hear some pinging, but not excessive like my 92 ford truck.

My problem is that Comp Cams states that if the compression is over 9:1 then the high energy cam will contribute to pinging and that i need a different cam -- like the 270H Magnum -- says it helps because of longer duration? What gives?? Will the 270H help or is there a better choice. This is strickly a street driven daily driver.

Setup: 68 400 block +.030, (CR between 9-10 but unsure), sil-r Lite Pistons (Brand spelling), stock rods and #15 heads, recent rebuild with new Comp dual springs, roller rockers, Edelbrock Intake and carb, 2000 Stall Holeshot with a TH350 transmission, 3.42 posi rear. Running 93 pump gas and want to keep it that way. Hei distributor with AC R43 plugs gapped at .045. 165 deg thermostat with 4-row rad. Cooling is great now that I fixed some leaks.

Car runs good and strong.

Please help! Do I need to back timing down some more and suffer performance, or is the new cam a better choice.

Thanks

[toddmoll]

I see everyone is after the vacuum advance or total timing. What carburetor are you using? and has it been setup for your engine? Many q-jets had a lean part throttle, this is how mileage was increased. Holleys almost always come out of the box too lean on both ends for a performance engine.


Todd.

[Randy Frazier]

I've never had much luck with the adjustable units. If you can't this one to work, let me know.

[Kenth]

HEI ignition system was required with the hard to ignite lean mixtures during the smog era.
Used on a pre-smog era with fairly rich easily ignited mixtures it will burn off the mixture too fast compared to the point type style ignition system, making the engine ping, with the same timing settings.
It can be made to work well on these engines too, with a fairly amount of tuning.
In my opinion it´s not worth it.
I did some extensive testing on this issue a couple of years ago, but them again, every new generation have to invent the wheel for themselvs, so to speak
Remember that the RAIV and 455SD engines were pretty strong runners with points style ignition.