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Topic Review (Newest First)
03-20-2013 11:12 PM
PontiLac oh okay that helps alot! never knew that im really hoping this fixes my problem and timing aswell ive been super busy for a few days thats why i havent been to active in this feed but im back now @cobalt
03-17-2013 02:39 AM
cobalt327
Quote:
Originally Posted by cobalt327 View Post
If the PV rating is too high, the PV will open at idle, causing idle quality issues.
The above should read "If the PV rating is too LOW, the PV will open at idle, causing idle quality issues."

But I think you understood the gist of it- you want a PV that will open when the engine is under a load, but NOT open at idle or light throttle cruise conditions.

From Holley Performance Products Frequently Asked Questions
Quote:
QUESTION: How do I tell what size power valve I need?

ANSWER: To properly size a power valve, take a vacuum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vacuum reading in gear at idle (w/engine FULLY warmed up) and if the vacuum is below 12" divide that in half for proper size. Example 9" of vacuum in gear at idle will require a 4.5" power valve.There is a video on this procedure on Holley TV.
Holley video explaining it: Holley Carburetor Power Valve | Holley TV
03-16-2013 07:42 AM
Bonneville462 Try 10 initial, 20 mechanical all in by 3000 rpm, disconnect the vacuum advance until you have everything sorted out...

Find 0 degrees top dead center on the damper, measure 2" clockwise from that and make a mark. That will be 30 degrees give or take a few.. You'll see it all come together when you rev the motor with the timing light on the damper...

Did you check the power brake booster, is it leaking? Can it hold vacuum for at least a day or two?
03-15-2013 11:53 PM
PontiLac okay that makes perfect sense, thank you for explaining i really appreciate it. i think once i get the lower rating power valve i wont be leaning out becase how you explain it sounds like what its doing then once the timing is worked out i should be good. what do you think timing wise? 12 inital and 30 total?
03-15-2013 02:35 AM
cobalt327
Quote:
Originally Posted by PontiLac View Post
I just pulled the tranny out today being rebuilt tomorrow it should be back in, i am going to pull all of the plugs, order the kit and diaphragm for the carb/secondaries, also a power valve a higher rating i suppose like someone said on here. then in about a week when i get paid im going to get a new distributor so theres not advancing problems. see how that works out hopefully it fixes the issue.. when i drove it today i payed close attention to when it started to ping, if im rolling or at cruising speed and floor it it will ping in the mid range and stop pining at higher range.. so maybe it is the power valve? because its not giving it the fuel when it needs it
The power valve being old or rated too high could lean it out under load. I recommend getting the timing sorted out, install a power valve in the 55 to 65 range and then see what you have. There's no way to say if the cam is what you want or not at this point.

Regarding the PV- the one you have is supposedly a 35. That means that it will not enrichen the A/F mixture under a load until the manifold vacuum drops all the way to 3.5 in/Hg. Under "normal" circumstances, a PV rated around 65 is recommended- but the exact PV rating is dependent on the engine vacuum in gear at idle. The bigger the cam, the smaller the PV rating (all else being equal). This is because an engine w/a bigger cam idles w/less vacuum than a smaller cam. If the PV rating is too high, the PV will open at idle, causing idle quality issues.

So:
  1. Sort out the timing
  2. Change the PV
  3. Install the secondary diaphragm- if it's torn, there will be a vacuum leak, however the size of the orifices involved will not flow enough air to be a big vacuum leak- but it's a leak, nonetheless
  4. Check the plugs for heat range and color
  5. Check for vacuum leaks

Nothing wrong w/doing a compression test in the meantime. It can give some idea of what the compression is, although it's not anywhere near as accurate as actually measuring things.

As far as the camshaft phasing, this can be looked into further if the above still hasn't rectified things.
03-15-2013 12:45 AM
PontiLac Also do you think the cam needs to be degreed ? is it even large enough?
03-15-2013 12:14 AM
PontiLac I just pulled the tranny out today being rebuilt tomorrow it should be back in, i am going to pull all of the plugs, order the kit and diaphragm for the carb/secondaries, also a power valve a higher rating i suppose like someone said on here. then in about a week when i get paid im going to get a new distributor so theres not advancing problems. see how that works out hopefully it fixes the issue.. when i drove it today i payed close attention to when it started to ping, if im rolling or at cruising speed and floor it it will ping in the mid range and stop pining at higher range.. so maybe it is the power valve? because its not giving it the fuel when it needs it
03-14-2013 01:41 PM
CaptainCaveman something's not adding up... with the little advance on the distributor to the secondaries not opening, are you sure you don't have a nasty vacuum leak somewhere?
03-14-2013 12:30 PM
LATECH 20 degrees initial timing sounds to much.A total of 27 sounds like the dizzy aint working right either.
03-14-2013 04:44 AM
cobalt327
Quote:
Originally Posted by PontiLac View Post
in the 9:1 +. a ball park number is good for me thank you

so im guessing pining is not a detonating issue, 91 octane should be just fine right? its a timing or air to fuel mixture problem?
Could be timing, f/a ratio, or even a hot spot in the chamber(s). Again- be sure there's no vacuum leaks.

Look at the plugs to see if they're the right heat range and at the plug color to see if they look lean.

Get the carb secondaries working. Using the vacuum reading at idle, see if the power valve is correct. Again- if the carb had been used previously then allowed to sit dry, the PV needs replacing.

Map the timing curve and see what the initial and total is, and at what rpm the total is all in by. See how much the vacuum advance is adding. Note whether the vacuum advance is connected to manifold or ported vacuum.

See that the mechanical advance and vacuum advance mechanisms are working freely and not hanging up.

If you don't have a dial back timing light you can make a temporary timing tape (or buy one), in order to use a regular timing light to see where the advance is at various rpm. Post #8 has a link to info on timing.

After you are sure the total timing is not excessive, take it out and see if it's still pinging. If it is, it's time to look closer at the fuel/air delivery. Or the possibility the heads were milled excessively, or that you may have domed pistons.
03-14-2013 12:42 AM
PontiLac in the 9:1 +. a ball park number is good for me thank you

so im guessing pining is not a detonating issue, 91 octane should be just fine right? its a timing or air to fuel mixture problem?
03-14-2013 12:29 AM
cobalt327
Quote:
Originally Posted by PontiLac View Post
where do you think im at compression ratio wise?
Removing 0.020" will reduce the chamber volume by about 4cc or so. But not knowing how far down the piston is at TDC or the head gasket thickness, it's hard to say exactly.

Given an ideal 0.040" quench, the CR is about 9.4:1. But it's likely going to be less than that. How much less depends on the things I mentioned just now, but I suspect it will fall somewhere between 9:1 and 9.4:1. This is w/aftermarket true FT pistons having a 5cc valve relief volume. Stock type pistons have a larger volume than true FT pistons, so using them the CR will be lower.
03-13-2013 08:30 PM
PontiLac So the power valve can cause it to lean out when excessive acceleration ? and a 65 would solve that?
and the cam was just put in straight not degreed. and im not sure what a intake centerline means..

haha thats what im trying to avoid this thing is my baby!

and okay, where do you think im at compression ratio wise?
03-13-2013 08:21 PM
Mr. P-Body Thanks, Bill.

I'm thinking you should have a 65 power valve in there, not a 35. It COULD be leaning out on "tip-in", which can induce detonation. 35 means the valve opens at 3 1/2" of vacuum, 65 = 6.5". Bringing the fuel in "sooner" can help a lot.

Was the cam "degreed"? What is the intake centerline? I've seen some pretty bad detonation with cams when installed too far "advanced". In one case, it was an XE262H and was at 98 (should be 106). It stretch the chain badly, and had two distinct "burn lines" in the cylinders, before it beat the rod bearings out, all in less than 500 miles. The owner wasn't "savvy" and didn't realize the pinging would hurt things. He knows now!

A compression test could be revealing, as well. Cylinder pressure over about 180 lbs. is prone to detonation in Pontiacs, no matter the static ratio. You will undoubtedly hear "success stories" with more, but this is a good "line". A typical 9:1 engine with a mild performance cam will generate around 170 lbs. A stock 400 in '69 would push 210, easy. They were advertised at 10.75:1, but I've found them closer to 10.5:1, and the later "10.5:1" engines were closer to 10:1.


Jim
03-13-2013 08:02 PM
PontiLac okay i found it! i had sanded the entire block and heads lightly and painted it so it kinda got filled in with the paint..
So they are the 8s..

so this is where im at:

Heads - 6x "8" machined ported & polished .20

Cam - .510

Bottom end - Stock

Timing - 20 initial 27 Total advance not working on distributor

Power valve - 3.5 secondaries not working properly

Fuel pressure - 7-8psi

Temp - average 180 degrees

Idle - 600rpm

Gas - 91 octane

is that enough to narrow it down?
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