[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]

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

[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. The reason that your engine is detonating at part throttle is probably because the HEI is throwing too much vacuum advance to the engine under high vacuum conditions. That is also probably the reason that you don't have the problem at wide open throttle, because there is no vacuum present under those conditions. GM still sells a vacuum advance with only 12 degrees or so of vacuum advance. Write me a note at my e-mail address and I'll send you the part number. If this doesn't fix the problem, you can richen the fuel mixture in the carburetor a little and if all else fails, you can add 1.65 rocker arms if you can stand the additional valve lift without hitting a piston or causing pushrod or valvespring clearance problems. This would do the same thing as installing a bigger cam. I'm betting that the problem is in the HEI vacuum advance though.

[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.

[Randy Frazier]

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

[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. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

[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]

<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. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

[slowbird]

Thats why i dont run them anymore, more trouble than they are worth. You could put in a bigger cam that would solve the to much vacuum problem

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

[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.

[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. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

[Sun Tuned]

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

[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!

["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.

[Lloyd-TX]

informative article on GM vacuum advance units.

http://www.corvetteforum.com/techtip...=115&TopicID=3

I used information here to pick a vacuum advance for my 10:1 455HO, also running on 93 octane fuel. I'm running 10 degrees intial lead, and my mechanical advance adds 22 degrees of lead - all in at 2700 RPM for a total of 32 degrees lead. The vacuum advance I picked adds 16 crankshaft degrees of lead, all in at 8" of manifold vacuum. I'm sending my distributor to Rocky Rotella for "blueprinting", and he is also going to limit the vacuum advance down to 12 crankshaft degrees to help with some very slight transitional part-throttle spark knock. I do have it running to a manifold source to assist with idle quality. My cam is a Bullet flat-tappet solid grind, with a duration of 232/235 degrees @ .050, and .540"/.567" NET lift using HS 1.72:1 roller rockers (including valve lash).

My setup is a 4.200" bore 455 (467), ported 7F6 heads, 10:1 JE pistons (small dome), 455HO intake, SD Q-Jet, R.A.R.E. 2.45" outlet SD exhaust manifolds, Tom Hand designed and FullBore manufactured prototype single transverse muffler exhaust system with mandrel-bent PYPES X-pipe system to the muffler, GM L88 torque converter (2700 RPM flash), 3.08 gear, etc. The car weighs 3910# with me in it.

Driveability is excellent. Performance to date in my sig below.

Hope this helps some!

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

[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. bill@tigerefi.com

The point to life isn't necessarilly the decimal.

[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

[Kybird]

I used the vac can recommended by Sun Tuned, made a big diff. The stock can was around 22 deg. It cost less than $10!! This was on a 400, TRW's and 16 heads, around 10-1 CR with a RA4 cam. He has other posts that go into much tech detail on various cans and weights for HEI's. May be worth a search!

[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

[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