[1969GPSJ]

Originally Posted by HWYSTR455

Ok, elaborate on the comment ' I put a timing light on it (I have a dial back light, so I can check the timing throughout the range) and it was in spec. '

What's 'in spec'?

What's your initial, total, and timing at 3000 rpm? And how much is the can adding?

When/where does it ping? Rolling of a dead stop, under load at 1800-2800, or above 3000?

If it's not been apart, the pistons are def in the hole, how much is the question.

If you haven't had the heads off, you don't know what the heads CC are.

Rated static CRs are exaggerated.

'sounded like ball bearings in a tin can with just the 93 at 9-10 degrees of timing' . You're obviously talking about initial, which doesn't mean jack.

Definitely need more (accurate) info to make any type of recommendation. If you're willing to change gaskets, you can pull the heads and determine exactly what you deck height is and head volume. Without that basic info, I don't think anyone can give any valid recommendation.

Now, just to say, most shops finish deck and head surfaces to 50 RA or better as SOP, which supports an aluminum head/iron block combo with MLS type gaskets. If it's iron/iron, it's a lot more forgiving, and you could possibly get away with an MLS gasket. Or, you could try 'smoothing' the surface some if you feel brave and lucky.

Another option is you could stack composite gaskets, that too would be if you feel brave or lucky. Neither would be advisable with a performance build, but if you're just trying to 'get away with it' for a short period of time, you could take a shot at it.

This could all be moot if whatever cam in there now is compromised or there are other factors that could be contributing, like heavy carbon build up. You could go through the trouble and try to get 'lucky', but you may end up having it fail and be forced to rebuild.

Can't cheat physics, might be better to just ride it out until you can go through and properly rebuild.



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Thanks for the reply HWYSTR455. I am just looking for some up to date information on something I have not paid a whole lot of attention to in the past few years. I thought that perhaps the thicker head gaskets may be a possible short term solution to get the car on the road until I do more to the engine. I was looking for some solid unemotional, knowledgeable advise about the workability of a thicker head gasket in the short term. The heads have to come off for broken exhaust bolt removal anyway, so I thought I would see what the community has to say about the thicker Cometic head gaskets.

It has been over 15 years since this engine has been run, and even longer since I drove the vehicle it was in on a regular basis. So in spec would mean no more that 30-36 (ish) degrees total timing. It did ping on 93 with the initial set at 9-12 degrees from a start through the operating range. It didn't stop with more throttle, and it still pinged at part and light throttle. Vacuum can attached made it worse, but it did not go away with it disconnected. Because of the ping/knock, this engine spent most of it's time running on 93 octane fuel and seriously retarded timing to avoid the ping/knock. The only time (no pun intended) it did not ping when set at 9-12 initial was when I would run it with (about) a half tank of turbo blue mixed with a half tank of 93 octane unleaded. So in this case the difference in how the engine behaved on 93 octane with 9-12 degrees of initial vs having the initial retarded by 14 degrees does mean "jack".

This isn't my first rodeo, I have had my hands on dozens of '67 through '70 Poncho cylinder heads over the years, and have had about 6 sets of my own on a variety of cars. I used to do some flow bench work and porting 30 years ago. I have cc'd many of the big valve 400 and 428 heads, and most were nominally 72 ccs (give or take a few cc's in the 68-74 cc range).

As far as the engine's current state, I did stick a bore scope in every bore recently to assess cylinder wall, head and piston condition. The pistons had the typical non-428 HO piston dish, intended to yield a 10.5:1 compression ratio with the 16 casting head. There was light, wet carbon build up ("wet" because I have fogged the engine several times over while it was in storage the past 15 years) , typical of a 428 running a little rich, but it was not excessive, and the piston tops and chamber all showed significant areas that were base metal without carbon deposits - so relatively clean. There wasn't any obvious valve, piston or chamber damage, even in # 7 and #8. I didn't take pictures because I was not anticipating any discussion about the condition of the engine. It is fairly apparent that none of the previous owners had done anything internal - I changed some gaskets (intake, valve covers, timing cover and oil pan) and probably replaced the timing gear - but didn't do a cam change and I don't think I even removed the valley pan when I first put this engine in my car about 35 years ago. Darn thing still has the short water pump ( but for not much longer).

Gach suggested that a more aggressive cam may help overall.
The engine will be going back on the road with a Edelbrock Pro Flow IV, so the fuel/air and spark will be managed better than in the past. It looks like a cam change (which was in the works anyway) may be the best solution for addressing the ping/knock issue, but still nobody has really presented a good case about why a thicker head gasket would be a good or bad idea - other than the issues about cylinder head and deck surface quality, which has nothing to do with the thickness of the gasket and what the pros and cons are for a thicker head gasket.

[Gach]

The ticker head gasket, issue (quench) what I’m saying may not be super accurate but it will give you the picture of why its not a good idea. The quench area is or shouldn’t be no more the say .040 to much quench will cause detonation un-burn fuel, so a .080 gasket will incase that. May not solve the problem at all. Especially say your piston are down in the hole say .010 from The factory. Thats why guys go for zero deck, and run say .032 gasket. To allow for piston to head clearance

[Gach]

I say your best bet is to go with a pump gas cam, that will bleed off compression and one that set up more for a 4 speed. Its been a while but I do know automatics like 108-109. Can’t remember but I think 4 speeds like 112. So yeah a .080 gasket and piston.010 in hole well now your at .090 quench.

[Gach]

The other thing the cam thats in your now, was kind of for leaded gas, not gas that has 10% ethanol. In other words when gas was good gas. So from your description you’re having serious detonation. Unless you severely retard the timing. I say pull the heads see what you have a deck height, just to give you and idea, I’m running aluminum rods, so I need .060 piston to head clearance. My compression its 11.1 but its a pump gas cam. And aluminum heads. If I were you I’d go with pump gas cam and no more then .050 head gasket. You have nothing to loose Down road you can go with aluminum heads.

[Gach]

Definitely by the sounds of you mixing gas together getting rid of the detonation your probably around 10-1 10.25. If you end up with zero deck then maybe .060 heads gasket.

[Gach]

Another thing dramatic compression, should be no more the 8. I’ll bet if you run the numbers with your cam your above that. Digimatic compression is whats important. I know I know there’s a whole bunch of theories on that. But all the stuff I’ve done as far as picking cams those are first numbers I run. Though my dramatic compression calculator. More then likely the cam will be on a 112. The chain will stretch and it’ll end up 113-114.

[Gach]

Long story short many running 10.1 compression with iron heads no issue. On pump gas. Just takes right cam.

[Dragncar]

If you need something to get you by until a full rebuild, maybe water injection. Its bolt on, don;t even have to pull the heads.
Modern ones are 500ish $

Designed for boost but they have a controller so they should be able to work without it. Call tech. This one is for a carb or throttle body.
https://www.summitracing.com/parts/sno-20010

Or old school. 90$ on E Bay. I ran one back in the 80s for a bit.
https://www.ebay.com/p/1728425361

Might get you by and better than a quench lilling .080 head gasket.

[242177P]

Originally Posted by 1969GPSJ

The pistons had the typical non-428 HO piston dish ...

428 HOs didn't have special pistons.

[Cliff R]

NEVER for any reason use a thick gasket to lower compression on one of these engines for pump gas. Here I will not for any reason build one of these engines with over .040" quench. These crappy combustion chambers don't like that deal at all and you'll just knock all the balls right out of it and make it want to run hotter, overheat, and ping harder all else being equal.

I've tuned scores of 400', 428's and 455's pre-1971 with higher compression to run fine on this new fuel. Not exactly sure why yours is so octane sensitive? I've ran into a few where I had to shorten up the timing curve and reduce the amount added by the VA, but have always been about to get a good end result IF they were using factory camshafts.

I have ran into a good many that you were NOT going to make happy with any sort of tuning. Most of those were 455's and a few big block Chevy engines.

Having had several 428's in the Ventura over the years I will say that the dished piston versions are finicky due to the added quench area. One of my 428's was only 8.8 to 1 compression and would ping if you tried to run very much total timing on it. It also heated up very quickly and the temps would "creep" up in slow traffic and at stoplights making it rattle even worse till you got moving and cooled it back down some. This was WAY back before I knew about tight quench and selecting the right camshaft. It ended up having a bad crankshaft and had to be removed but I was glad because it was not happy anyhow.

I did some research and talked to the folks at HO Racing and installed the HC-01A camshaft in the next engine. Since I cracked the #96 heads with the overheating previous engine I used 6X-4's instead. That engines was an absolute HOME-RUN and powered the car for nearly 20 years until I built my first 455 for it.

In any case as it pertains to what you are doing here I would NOT lower the compression. Change the cam instead and pick one with a wide LSA and about 15-20 degrees more seat timing than the 067 cam. Moving up to a real 068 would really help, and even on up to the Summit 2802 would fit the bill nicely and still have good idle quality and street manners while lowering dynamic compression at the same time.

I'll add here that static compression is only one "player" in this game, and whoever came up with the proverbial "brick wall" of 9.5 to 1 for pump gas should be banned from posting on the Internet for at least 100 years. That is one of the dumbist statements I've ever heard when it comes to this hobby......FWIW......

[Cliff R]

"428 HOs didn't have special pistons."

The last 428 that I built here was a 390hp version. It had special exhaust manifolds, oil filter adapter, and something different about the harmonic balancer (maybe much wider than the standard variety?) and the big valve heads with screw in studs. It had the same crankshaft, rods and pistons as the 360 and 370hp engines nearly as I can remember. I know for sure they were dished and far as I know that engine had never been apart before I got to it.

I'll add something not well known about 428 engines. They made several different crankshafts for them, early were Arma-Steel, later were "N" cranks. One of the casting numbers is prone to cracking, pretty sure it was the one used on the 1969 360hp engines. I broke one here, and in my search for a replacement (they weren't easy to find 30 years ago) I found several others cracked in exactly the same place. One I obtained looked just fine and when I took it to the machine shop they spun it up and it was wobbling ever so slightly. The machinst hit it with a BFH and it broke into two pieces right in front of us!

He didn't act surprised at all and said he'd ran into a number of them over the years with that issue......FWIW.......

[HWYSTR455]

The last iron head engine I did was in the late 90s, and ran that until mid-2000s or so (I've done many Pontiac engines. Many.). 400, 16 large valve heads, surface clean up, TRW pistons, .030 over. It cam in at 9.97 SCR, and that's at .030 over with a .040 head gasket. I've run many large valve iron heads, and don't think any came in at 72cc, but kind of moot.

I did the timing dance on that engine, have what many here consider a 'large cam', and even sprayed it. I purchased thick cometic head gaskets in an attempt to tame it, but never installed them. You could probably search here and find the listing when I was selling them.

If you look at the engine pics of my 'bird from the 80s, you will see i ran an Edelbrock water injection system, it didn't really help.

Many have opinions on quench, but I can argue that since many other manufacturers had chamber designs that had no or little quench, the hemi is a good example. So I don't put a lot of 'faith' into the idea.

The most you will realistically get from thicker head gaskets is about a half a point of static, and if you're at 10.5-10.75 like mentioned, it ain't gonna help enough.

With that said, really the biggest 'issue' with thick head gaskets is potential to failure, not mentioning the need for longer pushrods, thick intake gaskets, etc.

Try it, I'd like to know how it works out. Like I said, once I was going to try it, but realized even for a short fix, it was far less than optimum, and no guarantee it would control det. so I bailed.


Photo - circa 1981, can see the Edlebrock water injection setup.

CORRECTION: 400 SCR was 9.98, not 9.97, just checked.

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[Jay S]

Pontiac greatly over rated their compressions on all their engines. If I were you, if your interested in switching heads, get the 85cc KRE d ports. The compression would be in the upper 8s then, and you could run what ever gas you wanted, with the engine as it is now.

Guys have came on here with tuning issues with aluminum heads and a small cam with not much over 10:1 compression. Aluminum heads won’t help much. The guys running 11:1 have the induction, cam, and exhaust to move the highest volumetric efficiencies to higher RPMs, spreading the compression out.

The thicker head gaskets make the quench in a range were it will ping worse even though the compression is dropped. That bad range starts around .060” quench, and continues to around .1” quench. After .1” it seems to get better as it increases. But it is no substitute for a good quench. The .060” gaskets generally put the quench in that troublesome range. If your going to drop the compression with head gaskets you have lower it extra, probably about 9:1.

If you switch cams it changes everything. A cam like an 068 with 16s, would likely run on compatible octane to 72cc aluminum heads and the 066.

[Gach]

I’ve tried to water ejection two different applications, don’t waste your money. Or should I say flip a coin.

[HWYSTR455]

Originally Posted by Gach

I’ve tried to water ejection two different applications, don’t waste your money. Or should I say flip a coin.

Yeah, I tried it, didn't do squat. Now meth may work, but dunno, haven't tried it, but know some of the GN guys have had success.

As for cams, you would have to switch to a big enough one that would probably not work well with the setup intended. it would have to be RA IV territory, and still not be enough, depending on what elevation you live at. And with steep gears.

That 9.98 scr engine I had a @ 228/236 .050 cam in it as I recall, and it was still ragged edge. You get a hot day, an 'off' tank of gas, or anything like that, and you had to baby that thing to prevent det. I ran Fel-Pro 1016 head gaskets, before anyone asks, so 'quench' was good.



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[Formulas]

Some of the stock steel shim headgaskets can be found occasionally on ebay i think they are in the .056 range before install
I bought 4 of them last time i looked

something like that could help they are stock so shouldnt be the end of the world to use

[1969GPSJ]

Originally Posted by Dragncar

If you need something to get you by until a full rebuild, maybe water injection. Its bolt on, don;t even have to pull the heads.
Modern ones are 500ish $

Designed for boost but they have a controller so they should be able to work without it. Call tech. This one is for a carb or throttle body.
https://www.summitracing.com/parts/sno-20010

Or old school. 90$ on E Bay. I ran one back in the 80s for a bit.
https://www.ebay.com/p/1728425361

Might get you by and better than a quench lilling .080 head gasket.

I used water injection on another car a number of years ago. Edelbrock actually had a system at that time. Worked really well with 50% distilled water and 50% methanol. I just seemed to run out at the most inconvenient times. If you used tap water the spray nozzel would end up getting hard water deposits and clog.

[1969GPSJ]

Originally Posted by 242177P

428 HOs didn't have special pistons.

I am betting you are right. My gut says so, but I have no experience to confirm.

My battered old '69 shop manual (printed in 1971) implies they did - on Page 6-40 it even shows a picture of all the V8 pistons, with it showing a plain flat top with valve reliefs for the 428 piston top. I think they mixed up the 400 picture (it has the dish in the picture) and the 428. The only 428s I have had apart were the '67 670 headed big valve 4 bolt YH coded 428, the '68 375 HP engine, the '69 360 hp small valve engine (also with a YH stamp on the block), and the '69 370 HP Big valve engine. All of them have the pretty substantial dish in the piston. I just have never disassembled a previously unmolested 428 HO.
Supposedly the 428HO had a quarter point more compression (to 10.75:1) to go with the 068 cam - and those 2 things with the long branch manifolds were apparently what made for the 20 HP difference between the 370 and 390 HP engines.

[Gach]

I put it on my buddy’s 70s judge he calls me, hey this thing is pinging, ok Mamaluke ….did you fill the jug..LOL Greg…oh you have to keep adding water..LOL yes Greg Don’t you remember me telling you keep a gal jug in the trunk.

[Gach]

Originally Posted by 1969GPSJ

I am betting you are right. My gut says so, but I have no experience to confirm.

My battered old '69 shop manual (printed in 1971) implies they did - on Page 6-40 it even shows a picture of all the V8 pistons, with it showing a plain flat top with valve reliefs for the 428 piston top. I think they mixed up the 400 picture (it has the dish in the picture) and the 428. The only 428s I have had apart were the '67 670 headed big valve 4 bolt YH coded 428, the '68 375 HP engine, the '69 360 hp small valve engine (also with a YH stamp on the block), and the '69 370 HP Big valve engine. All of them have the pretty substantial dish in the piston. I just have never disassembled a previously unmolested 428 HO.
Supposedly the 428HO had a quarter point more compression (to 10.75:1) to go with the 068 cam - and those 2 things with the long branch manifolds were apparently what made for the 20 HP difference between the 370 and 390 HP engines.

Ok so spill the beans, whats your plans on moving forward. ?