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Discussion Starter · #1 ·
I have a 69 Pontiac Bonneville with a 428 -360 H/P
I think the stock compression ratio is 11/1 and doesn't like anything to drink but Premium fuel , even using the premium fuel that's available today, it still pings
I have been adding some octane booster to the premium fuel, it helps, but really doesn't cure the problem, I did find a additive called "lead substute," that worked really good, but havn't been able to find it in the last few years,,
My Question is,, what would be a good tune-up as far as timing, carb jetting, etc, be , eventually if I keep the car, I will probably either change the rod legnth or go with lower compression pistons, because fuel prices are never going down much ever again, most likely much higher,,
The motor is all original with 38 K actual miles on it, runs perfect, except for the fuel mileage , which I would guess to be maybe 12 -14 mpg if that good, I havn't driven it for over 5 years, because of a restoration.
any ideas Guys?
 

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Discussion Starter · #4 ·
Hey,, Thanks alot guys,, I had a feeling you guys would be the ones to reply on this,
Like I mentioned, the motor doesn't have very many miles on it, but if I am gonna go to the trouble of changing the heads and cam, I might as well take the opportunity to freshen up the rest of it,
:mwink:
I'll start looking for a set of heads,, should be plenty of them around , hopefully,
F-Bird,,, the pinging usually starts when its under some stress, like going up a incline. or a quick passing another car situation,,normal cruzing ,, it isn't really too bad, at least I can't hear it,,, but I'm mostly deaf :D
I'll check the motor # and find out exactly which heads are on it. The carb is a edelbrock 750,, and I know definately the timing needs attention,
like I mentioned,, the car has been setting for at least 5 years,
Thanks again guys.. certainly appreciate the infro,,, :thumbup:
 

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Grumpy Old Goat Herder
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whyholdback said:
Start with the '75-'76 455 heads, then move on to important things like a modest cam and a built 200-4R.
The '75-'76 455 heads had a combustion chamber of about 124cc. That would make a slug out of a 428. The best factory head, IMHO, would be the '73-'74 #46, 350 HO head, with a combustion chamber of about 86cc. The only difference between the HO head and other 350 heads is that the HO head had screw in rocker studs, but screw in studs can be installed in any of them.

http://www.wallaceracing.com/headsearch.htm
 

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No amouint of "tricks" will eliminate detonation. Pontiac engines "enjoy" very unique chamber designs. They are actually TOO efficient (yes, it's possible). This is why Pontiacs don't "like" more than 34 degrees total timing with "stock" heads. Lowering static compression is the only SURE way to eliminate detonation. Enlarging the "dish" in the 428 piston is a fairly simple solution.

Agreed with Bill. 455 heads are NOT the way to go. You need between 88 and 90 CCs for a 428 to have pump-gas "friendy" capability. With the stock pistons, the chamber should be around 80-82. 6X-4s have become popular for the 4" stroke engines, as folks learn they're a bit too "small" for 455-plus engines. The 6Xs respond well to port work, too.

The 46 is a small valve, "medium" chamber head (about 78 CCs). There's another "46" used in '73 and '74 on 350s, including '74 GTO. These are not the same castings as the '69 46s.

We rebuilt Joe Roberts' '69 428 using a larger dish and Comp 265DEH ("Dual Eniergy"). 14 MPG on the first trip (Charleston, WV for POCI meet), '69 Catalina wagon.

FWIW

Jim
 

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Discussion Starter · #7 · (Edited)
I looked at the # on the head (at least tried to ) the heat riser tin piece that is bolted to the center of the exaust Manif,, is still attached to the ext manifold,, but I could see a 4 plainly and the other # looks like a 6 or maybe a 8,, I have the build sheet for the car, it was in pretty sad shape so someone preserved it by applying 2" scotch tape over the whole thing,, and the engine # spot is blank,,but according to the build sheet , the motor code is YH
Are the # for the heads stamped under the valve covers?
 

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WFO
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Bad Rat said:
I have a 69 Pontiac Bonneville with a 428 -360 H/P
I think the stock compression ratio is 11/1 and doesn't like anything to drink but Premium fuel , even using the premium fuel that's available today, it still pings
I have been adding some octane booster to the premium fuel, it helps, but really doesn't cure the problem, I did find a additive called "lead substute," that worked really good, but havn't been able to find it in the last few years,,
My Question is,, what would be a good tune-up as far as timing, carb jetting, etc, be , eventually if I keep the car, I will probably either change the rod legnth or go with lower compression pistons, because fuel prices are never going down much ever again, most likely much higher,,
The motor is all original with 38 K actual miles on it, runs perfect, except for the fuel mileage , which I would guess to be maybe 12 -14 mpg if that good, I havn't driven it for over 5 years, because of a restoration.
any ideas Guys?
Sweet car! One of my all-time favorite Pontiacs was a '61 Bonneville w/a 421 and 4-speed. My Dad had one and we loved that car. Next to that was a '58 Chieftan w/a Tri Power/4-speed, black on black. My brother in law owned it.

Some good ideas so far. I'd like to add my thoughts.

It's a shame the gas has gotten so bad- in 1970 I was hampered by not having enough CR in my 428 to run the cam I wanted to run, and I had 72 cc chambers, too! IIRC the small valve 428 had an advertised CR of 10:1. The chambers and production tolerances generally gave a CR a bit lower than what's advertised. But even so, the CR is still going to be on the high side. Anything over about 9.5:1 is going to be a problem w/pump gas- as you've found out.

That said, I would suggest you first make sure there were absolutely no vacuum leaks, no bad guides or blowby allowing contaminants into the cylinders to dilute the fuel/air charge. Checking the plug condition will help determine this. Also be sure the plug heat range is correct, and that there's not different plug heat ranges mixed in the engine. Depending on the heat range you are now using, a colder plug may help.

It would be good to know how the carb is set up. If there was any work done to the carb in the past in an effort to increase the mileage, there's a chance it's now too lean- especially since the swill we now have for gasoline requires a bit more jet than gasoline of the past.

Another thing you can do is to rid the chambers and piston tops of any built up carbon deposits. If left unchecked, there can be a fairly significant increase in detonation just from this alone. Deposits can also create white hot spots in the combustion chamber that will act as a spark plug that is always firing, this will cause detonation, too. There have been recent threads that talked about ways to rid an engine of built up carbon, a search will give you more info on this rather than me repeating it all here. BTW, this doesn't require taking anything apart.

I'm not a big fan of reducing the timing too much. This just kills power, and at some point won't help detonation if the CR is too high. But you can tailor the ignition curve to be as good as it can be under the circumstances. Depending on the curve that's now in the distributor, one way to do this is to use a very conservative curve that comes in later than usual (may require stronger springs for the mechanical advance), along w/a fairly conservative initial and total timing setting along w/a fairly large amount of vacuum advance that used manifold vacuum. The above suggestions can all be done easily over a weekend, are invisible to onlookers and will cost less than $20. ;) Adding a points replacement module under the stock cap will give you added fire at the plugs, but if the points are in good shape, they'll suffice.

Should removing the deposits and recurving the distributor not work well enough, another possible solution if you wanted to keep the casting number 46 heads on the engine for originality's sake would be to use a set of Keith Black p/n 892 pistons (shown below). They have a D-shaped cup instead of a round dish. The cup is only 10 cc so the deal would be to enlarge the cup to give the dish more volume.

I wouldn't worry about longer rods at this point. Using a thicker head gasket- while lowering the CR- is a less-than-ideal solution because it kills the quench/turbulence that's necessary to promote good flame travel and reduce detonation. But w/o knowing the exact measurements inside the engine, like the piston deck clearance and the thickness of the gasket that's on there now, this can't be entirely ruled out as a possibility. It will require you to disassemble and measure things to know for sure, but you can use a compression tester to get a rough idea of what you're looking at.

As has been said, a set of later model D-port heads like the 6X-4 can also be used, they'd drop the CR and give you bigger valves than you now have. I wouldn't bother adding 1.77" exhaust valves- IMO they're much ado about nothing in the 428 and especially the 455 engines unless they're built stout. The later production heads you'd be looking to use already have hardened exhaust seats and guide plates and screw in studs, With a stud change you'd have an adjustable valve train. Guys have used the bottleneck studs w/lock nuts to get adjustability, but the cost of good straight studs is a minor consideration for the added strength IMHO.

If you were wanting more performance from your 428, I'd have to recommend a set of Edelbrock aluminum Pontiac D-port heads w/87cc chambers. The D-ports allow you to retain the original manifolds and while they're certainly not original they can obviously be painted to look more at home under the hood of an otherwise correct car.

Good luck.

 

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Discussion Starter · #9 ·
Those are some excellent ideas, The motor is dead stock, has never even had the valve covers off. like I mentioned the actual miles is around 38K , never been abused , in any way,, I did change the carb to a 750 edelbrock, because the old Q jet was acting up,, and I happened to have the 750,I do still have the Q jet somewhere, if a rebuild on that would help any,,, its been at least 5 years since the car has been driven, has always ran fine, but pinged some under a pull,, it could be the timing, or any of the things you mentioned, the car isn't a daily driver, just a nice cruiser for nice days,
but I would like to get better gas mileage, and maybe even where I could use unleaded,
I guess to start with,, a good professional tune up, check the things everyone mentioned, and go from there and see what transpires,
but first I need to get it put back together,, its getting there but not as fast as I would like,, its pretty much down to getting the solenoid's for the door openers done, the interior done and glass in the doors installed

Thanks again guys,, its good to have people like you guys with good advice as close as a keyboard,, :thumbup:
 

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WDCreech said:
The '75-'76 455 heads had a combustion chamber of about 124cc. That would make a slug out of a 428. The best factory head, IMHO, would be the '73-'74 #46, 350 HO head, with a combustion chamber of about 86cc. The only difference between the HO head and other 350 heads is that the HO head had screw in rocker studs, but screw in studs can be installed in any of them.

http://www.wallaceracing.com/headsearch.htm
I have a set of those #46 heads from a 73 350, they CCed at 96 CCs. I know for sure as I CCed them myself.I bought a few sets of heads On the based info at hand , none of the heads I bought were close to anything I read, they were all bigger in the chamber.

The good news is that a 428 with a 96 CC head makes 8.51 to 1 if the motor hasnt been decked .
 

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Grumpy Old Goat Herder
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latech said:
I have a set of those #46 heads from a 73 350, they CCed at 96 CCs. I know for sure as I CCed them myself.I bought a few sets of heads On the based info at hand , none of the heads I bought were close to anything I read, they were all bigger in the chamber.
When I say "about", that means that's what the factory says, but any head should be checked to be certain.
 

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Discussion Starter · #12 ·
latech said:
I have a set of those #46 heads from a 73 350, they CCed at 96 CCs. I know for sure as I CCed them myself.I bought a few sets of heads On the based info at hand , none of the heads I bought were close to anything I read, they were all bigger in the chamber.

The good news is that a 428 with a 96 CC head makes 8.51 to 1 if the motor hasnt been decked .
Where would I look to find a set of these heads?
 

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WDCreech said:
When I say "about", that means that's what the factory says, but any head should be checked to be certain.
My apologies bill, I may have sounded like I was correcting you. I am sorry.
I was more or less trying to be emphatic that the chamber sizes I have seen listed are usually not correct, a lot are not even close.
That is why I ended up with 3 sets of heads untill I got a set that would mill to the right chamber size for my build.
So I have a few extr sets now...LOL
 

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I just realized that the 69 428 did use the same number head, even though they are completely different , the numbers on the center exhaust ports would still be a 46 keeping the apperance that the motor was OE ( except for the date code of course) Imagine that.
You can imagine my excitment when I walked up on this 350 with the #46 heads on it.....oh boy a 428, then I saw the EGR valve,awwww :(
 

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Bad Rat,

Timing is NOT the issue. Compression IS. The ONLY way to correct the "pinging" is to increase octane or reduce compression. No "free lunch". This is not my "opinion". This is from educatioin and years of experience.

All Pontiac "d-port" heads (what your 46s are) are pretty much the same except chamber volume and valve size. The large-valve/small chamber heads are considered the better for performance. The small-valve heads are good for "starting" a build, in that the seats can be opened for the large valves and actually flow better than the factory large-valve heads. Chamber volume is the key for your selection. Over 92 CCs wil drop compression under 9:1. 86-90 CCs would be ideal for the 428. As said before, the 6X-4 is a very good head for this application. They can easily be milled to 90 CCs without changing geometry TOO much.

I also must agree, put the Q-Jet back on there. NAPA and others (Borg Warner) sell quality kits and brass floats for the Q-Jet. Q-Jet is FAR superior to the Edelbrlock knock-off of the old Carter.

Jim
 

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Discussion Starter · #17 ·
Mr. P-Body said:
Bad Rat,

Timing is NOT the issue. Compression IS. The ONLY way to correct the "pinging" is to increase octane or reduce compression. No "free lunch". This is not my "opinion". This is from educatioin and years of experience.

All Pontiac "d-port" heads (what your 46s are) are pretty much the same except chamber volume and valve size. The large-valve/small chamber heads are considered the better for performance. The small-valve heads are good for "starting" a build, in that the seats can be opened for the large valves and actually flow better than the factory large-valve heads. Chamber volume is the key for your selection. Over 92 CCs wil drop compression under 9:1. 86-90 CCs would be ideal for the 428. As said before, the 6X-4 is a very good head for this application. They can easily be milled to 90 CCs without changing geometry TOO much.

I also must agree, put the Q-Jet back on there. NAPA and others (Borg Warner) sell quality kits and brass floats for the Q-Jet. Q-Jet is FAR superior to the Edelbrlock knock-off of the old Carter.

Jim
I intend on looking for a set of heads, real soon,, what year and # are these you mentioned?
 

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Discussion Starter · #19 ·
Yeah I definately will have it tuned , ( by a pro,,) :D The guy that built the motor for my Anglia is a good tuner,, :thumbup:
one step at a time,, if it comes to the point of needing different heads, I'll deal with that at that point,, Thanks for all the great advice,, as you guys probably have already figured out,, motors ARE NOT very high on my list of knowledge, :pain:
 

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From reading Bad Rat's initial post, it sounds like he is asking for the most cost effective means of eliminating the pinging. It would be a shame to bust into a stock bottom end with only 39k miles on it to replace pistons. The 068 cam is a great cam, but not for bleeding off compression because of its 114 lobe separation and relatively small duration. I have never liked the idea of trying to band-aid a compression problem with a big cam. That can lead to other problems of drive-ability including bad gas mileage and low RPM response. That leaves the replacement of heads the best choice. When I was up to the GTOAA convention last year I noticed that Oregon does have a little better gas than we do down in SoCal - 92 octane vs 91. Unless Bad Rat is looking for the last ounce of performance before worrying about detonation, a safety margin on the compression is not really that bad of idea. For 91 octane (which might be the highest available at the pump in the future), I've found sticking to 9.3:1 compression is a safe goal. If nothing else, it saves you a few bucks on staying away from the highest grade.

I just had my '67 GTO in a QuickTime electric cutout article in the current April Hot Rod magazine where they dyno'd the car for a before and after performance test. What they failed to mention in the article was the car runs on regular 87 octane gas with a compression ratio of 8.4:1. Not optimum, but I had the pistons so put it together with what was on hand). Uncapped it made 297 horsepower at the rear wheels, and capped up it still made 291 RWH horsepower (it made 298 RWH uncapped on another dyno a year ago - so the numbers should be pretty accurate). This is with the original 400 engine and semi-opened 81cc chambered 670 heads and TRW flat tops milled 24cc dished pistons. It is running the original manifold with an adapter fitting an Edelbrock 800 Thunder series carb. I'm not recommending you follow my build, I'm just showing that it isn't necessary to run the fine line on high compression to obtain decent horsepower.

There are a couple of things you might do now before spending money to see if it helps. First is insure you have fresh gasoline, since any old fuel will deteriorate and be much more prone to detonation. Next is to check the timing and insure that there is an acceptable timing curve. Too far advanced is bad, but too little timing advance will keep heat in the engine and make matters worse. Vacuum advance is a good thing, but a 43 year old vacuum pot could be sticky enough to not drop the timing down quick enough when the throttle is applied. After confirming the above are fixed, and you still have pinging, it's then time to drop the compression. With the stock 428 pistons, 80cc heads would give you exactly 9.3:1 compression. The 6X-4 heads can be milled to obtain the chamber size, as can the 4X-3H, 4X-4H, or the 4X-7H. These all started life advertised as 91cc chambers, so the amount of milling will be dependent on whether the heads have been milled before.

It's too bad Mr. P-Body (Jim) is way over in Virginia because his shop would be an excellent choice for straightening things out for you.
 
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