I have ran 355s with 0 deck height and Chevrolet steel shim gaskets we painted with cheap paint and a solid flat tappet cam without checking anything but valve clearances and it ran like a scalded dog. Old roundy round racing. We ran Sunoco 260 or aviation fuel and 36 to 38° total timing or until it pinged then backed it down just enough to stop the spark knock with cold plugs. We had lead in the gas back then. Good old Ethel. Yep, I am old.

.032 to .034 is real world safe BUT CHECK PISTON TO VALVE CLEARANCE is a must . Good info .

Just some practical info for those that don't live in the US (except California perhaps), that actually have to meet emissions, and run a catalytic converter etc.... A very tight squish will indeed increase TDC turbulence (any increasing amount of squish exit velocity will) and prevent end gas detonation, and thus increase power due to less pumping loss by lower burn time, and at the same time be more knock resistant so MBT timing (or closer to it) can be achieved. Mostly the increase in detonation/"knock" resistance is due to the fact that gasoline mixes don't burn closer to cooled surfaces than ~3 mm or ~1/8", having the quish very tight delays the point of sufficient squish opening at a ignitable distance from cooling faces and exposure to the main combustion event happens after peak pressure, preventing end gas detonation... However (there is ALWAYS a "but") not all fuel/air mix escapes the quench, regardless of how tight it is, this is what would otherwise detonate if exposed to the main combustion at too early of a time (like with a larger gap), but in a very tight squish where it won't be able to detonate, and where the squish opens later it is often a very rich mix, which due to all the cool faces the fuel is not vaporized (air escapes the quench much easier than the fuel) it will burn late and "cold" causing oxygen deprived secondary combustion and some of will also polymerize, causing excessive CO and HC by-products, making it hard to pass emissions. You can still have a bit of both worlds tho, if you have smaller squish areas, but more distributed along the chamber. Which by being shallower allows for faster progression of the flame front at squish open not giving time for end gas detontation to happen, giving opportunity to get heat in early enough (more gradual increase in heat in the qench/squish area) for the end gas mix to contribute in a normal combustion just slightly later on, instead of the trapped gasses being pig-rich, and hard to combust. That's why modern 2v engines has squish on both sides of the chamber, but smaller (unlike the old CI heads in this video, with just one large squish area on one side), or why in general 4v heads are basicly "mainstream" by OEM's these days, which lends itself the benefit of still having good squish induced turbulence, without needing to run the squish so tight that it makes alot of CO and HC, that makes one fail emissions (well, fails emissions in the most of the "developed" world, anyway)

I learned this lesson the hard way a long time ago, had know idea the pistons were rebuilder specials. They had a comp. height of 1.540, causing a quench of about.060 though it was for a basic rebuild it ran and detonated under a load. Cause all kinds of problems such as overheating, burnt exhaust valves and poor performance. It’s important to pay close attention to what your purchasing, a deal that’s to good to be true really is!

9 months later and I get a rec to watch this video from another video and rediscover what I already watched, and it prompts major redesign in my project, for better or worse, we will see :)

I'm running my 383 with the pistons .018 in the hole and a .015 head shim. At 10.75:1 compression, i run on 87 octane in the winter and 89 in the summer with no detonation. 33 degrees total timing. It does work and work well.

The old way of measuring the quench was by using plasticine or blue-tack, this only works if you know beforehand what the measurement should be! Once you have this info, all you have to do is the Math, so as to alter the head gasket thickness. This has always been a tricky subject, but you have explained it well. Thanks for your explanation.

I just installed 440 source heads on my 68 Hp 383 engine. True zero deck engine from factory…piston tops right even with deck. All original bottom end in engine including pistons. I have .039 clearance from head gasket. Engine now runs well on 89 octane gas. Heads made a huge difference over original 906 open chamber heads

Why's that important you might ask. In every video. Great videos. GREAT information.

It's all relative to bore size, I built a Yamaha blaster years ago with extensive porting, peak power at around 8700 rpm, quench was a verified .016" and that was an air cooled single that spent it's entire life being beat like it owed me money. A full hemispherical chamber and the piston crown matched it. I'd have to look at my old notes but squish band was around 35% of the bore, it seemed to break all the rules. But never failed and for a 198cc air cooled twin it would run with piped banshees up to 45-55 mph, in tight trails they couldn't keep up with it. Never ran hot, actually ran cooler than it did when stock. Guys with 383/385 sbc are running 4132 forged slugs around .028 - .035 no problems at all on na street stuff. The tighter piston to bore. Clearance, and small lt1/lt4 chambers and a flat top allow them to get away with it, I'm sure the reverse cooling doesn't hurt either. And they get revved to 6500-6700 rpm. I think .040 is kind of an old general rule of thumb. Have seen turbo LS engines tore down where the owner didn't know better and assembled with .025-.028 quench and never had a problem. Most in the know tend to agree for 4" -4.040 bore stuff .039-.041 is fine and not really any more power or detonation resistant going any tighter.

Thank you. Your art work for a visual explanation was much better than that Steve guy lol

Great video on an important subject. I mentioned you in my presentation at Forsyth College, the video should be out soon. AG

The simple answer is always BOOST 💪🏻

Ive seen some race head shops shave off around 5 k from this quench area,they angle it towards the exhaust valve,it helps to prevent detonation while ruining higher compression

When the piston approaches the head it Squishes the air from the closing gap into the remaining cylinder space.....When the piston approaches the head it can Quench any flame propagating between the two cold surfaces of the Squish Zone....

One oversight I'd like to mention about "piston rock" is that a hyper piston will run "HOTTER" and be more likely to detonate although tighter in the bore and nothing I'd use with any compression ratio over 10.5:1. They are cast pistons with a coating that heats up more that is "budget" friendly. Forged pistons or billet pistons are "sloppier" when cold, and are known for piston slap, but they like aluminum rods expand once up to temp and the "slap" tends to dissipate. Thus, a little expansion is expected, so running a slightly thicker MLS head gasket is a safer bet just as a margin of expansion. And if you are running NOS in a high-compression street motor of, say 11.5:1, you'd never run a hyper piston, and the rings need to be "loose".

Good video, biggest overlooked measurement in engine building

If I remember correctly, David Vizard says you can go down to 0.029” piston to head clearance. I’m running an LS with pistons coming 0.005” out of the hole and an 0.040” head gasket. Not running yet but we’ll see. Turns over fine by hand, anyway!

You still need a minimum of three to six thousands clearance in the quench area to stop the vacuum from the Piston jerking away from the head happening there and pulling the flame away from the spark plug

I made 422 HP with a Holley 500 2 barrel carb on a Vortec headed 355 dirt track engine! The engine made 486 HP with a HP 750 4 barrel Holley.

Gaskets only do so much, which is to say you will select pistons/machine deck to suit gaskets that fit the head and are suitable to both combustion chamber size and the bore size in arriving at desired compression ratio. A gasket diameter 0.020" bigger than the bore is damn close - you don't want to risk fire ring sitting on the chamfer, which is not flat. Often, +0.030" is a minimum margin, but check machine shops work: they must put some in to allow for easy piston install. Last build, I had to go with +0.070" on account of combustion chamber casting dimensions. Perfect? No, but fire ring was properly clamped in place and not going to squish out of place.

Amusing reading the comments. I spend way to much time watching KZfaq, No one even watches my KZfaq 379ci Chevy build, otherwise I'd do more.depending on how I feel, might show my 2bolt main small block Chevy, has stock rods, JEGs cam, shift it @8500rpm yeah, it has cast flat top 4 eye brow pistons. Yes, and Street drivable. Actually it was my daily driver. I'll keep watching, see how you go with your build. 👍

All well and good, but keep in mind, this all being measured cold. Watch what happens when the piston sees heat. Then watch what happens when you hit a certain rpm. It's a lot tighter than you think. Don't forget piston rock. Even with a steel rod and especially with an iron block. Aluminum blocks have that safety factor built in at 0, because the block grows taller giving more distance with heat, unlike iron. You only need enough quench distance to keep the carbon off the tops of the pistons under the quench pad without it actually hitting. Unfortunately, no way of knowing what that is, unless you run the same exact combo and rpm, and creep up on it. Point is tighter the better except in big power adder stuff. You actually need as much as you can get while keeping the desired compression ratio. Many factors are involved, but general rule of thumb in most is .036"- .045" will work on anything with a steel rod. After .049", the ability to help suppress detonation diminishes, and. 060" and over, or no quench distance. Does nothing. This is all provided you have the correct cam profile, compression, desired cylinder pressure, piston design and heads that actually have enough quench pad.

What you're describing is two different concepts wrapped into one. Quench used to be the distance from piston to cylinder head, not just piston to cylinder head surface distance. The term 'quench' means to extinguish flame, so your definition has no relation. Squish was the term for piston to head clearance. What you're describing that creates the lack of pinging is combustion shape as well as atomization created by tighter squish as it creates a far more efficient combustion, lessening the need for to start the combustion sooner. Quench is, or at least used to be, the term used to describe the shape of the ball of air-fuel mixture, not piston to head surface clearance. Making a word mean two nearly opposite principles is improper use of language... It confuses people, even if your concept is correct. Quench can't mean the distance needed to properly design the combustion to eliminate pre-ignition, as it's a very different concept to putting out a fire or eliminating thirst... quench is about the combustion itself.

Check out Alameda racing… he cuts strategic v grooves in the quench area for a more complete burn !!

On all my circle track motors I run as close to .035 deck ht. as I can. Some turn in excess of 8000rpm and when I refresh them they show signs of being very close to the head. The burn on the quench of one of the heads I could read .030 that transferred from the piston, it was written in carbon. I don`t believe the engine would have survived for 1800 laps if it was any tighter. That was 20 some years ago now I leave em .007 in the hole and use the gasket to get .035. In the hole helps with the rocking situation too. Little light shiny valve smiles with no deformation in the pockets are OK

Bro you explain on video like I do ! I know what I want to say but my brain processes other ways to say it . We know what we want to say but our thoughts aren’t in order . I recommend for our selfs to practice what we want to say and say it . I pause a lot and say huh or I repeat words . You don’t repeat words that much but I do . And I say huh a lot or pause and then continue. It’s all good though ! Keep going ! We’ll get better !

Quench is the result of squish. Crevice volume is a trapped area. Singh grooves relieve the areas and produce swirl.

Love all your vids ! Very easy to understand and follow!!!

Again like you said not recommended, I've build several will piston .010 in the hole with a steel shim gasket. They are great performers. Much more throttle response than a unmilled block. The best was a flattop 350 pro top line 200cc runner 49cc chamber heads with a 285b6 comp cam. Shifted at 6700 in a 79 malibu with 4.30 gear ran 11.36 in a quarter

Great video! Good info as always!

We go piston to valve clearance sometimes put cutouts in the pistons for the valves to allow for high lift Camshafts

The less gap you have between your Pistons and head the higher your compression will go . In short the longer the rod the torq will rise . Asking everyone 13-5to 1 compression 512 cui flat top Pistons static is there boost can I run is .?

We ran a 305 sprint car engine at 0.027” piston to head clearance. It survived and ran for two season like that.

huge insight i learn from you, thanks

so this came up the other day and I was talking to my tuner and I asked him where should compression be for a e85 boost engine. tuner said around 10/11 :1 he told me that u should sand the heads after u have them machined or have a machine shop do it if they have a cnc to avoid quenching the pistons and heads. he then showed me his high dollar performance heads and he said it's very little to nothing. if ur having doubts just look at the aftermarket heads they do especially when the chamber is smaller then factory

I like your explanation of Quench, but you do have to understand wet flow of the intake port and why a tight quench makes better power. All factory style cylinder heads have all the wet flow coming around the short turn radius, and then the fuel collects on the quench pad, this is raw fuel in droplet size and not very burnable. Like you explained the tight quench helps force the fuel across the chamber toward the spark plug, and reduce the need for spark timing. But if you study the carbon in the chamber you will see where fuel is and where is is not. So if you look at the area around the intake valve , you will see very little carbon build up there. This is because there is no fuel there to burn. If you remember about 20 years ago AFR was experimenting with golf ball dimples on that portion of the chamber, thinking this was fuel wash. The real fact is that there was no fuel ther to build up any carbon. They did not understand wet flow either.

Very nice job explaining it all

Always bring the piston to TDC and open the valve as far as it can go minus 40 th an inch and you'll know the highest lift cam you can use.

With decking the head, what about intake ports aligning between the heads and intake.

Enjoyed the content!

How much life are you getting out of the speedpro hypereutectic pistons, and how hard are you working them, what sort of scr/dcr and cranking compression?

I wonder how much quench really matters in a Supercharged engine, If it does have dished pistons - which changes quench a lot.

you nailed it excellent vidy question what kind of gains Would you expect to see you from no other changes then tightening up the quench from stock to 35 on a small block Chevy something like a Vortech 350

We delt with all this back in the early 80s

Can you recommend a good valve spring upgrade for stock 062 GM Vortec heads? Lift at valve will be .474. Hydraulic roller.

My theory is that with the compression being higher vac and suction will be higher if boost is equal to that will this work ?

That rocking of the piston and I’m sure you know this is called piston slap Subaru motors are famous for it I had to have two pistons replaced thank God it was under warranty at 90,000 miles I bought the extended warranty sometimes it pays when you buy the extended warranty I only paid 1500 bucks for that warranty they pull the motor out to replace yPistons it would have costed me 4 thousand dollars

The zz4 is a perfect example of to much quench.

Which video is the one to check you deck height ,thanks for videos I'm learning so much this next build from you.

Professional opinion please. Had my SBC done at a local machine shop. 350 bored .040 over. New Eagle bottom end. Cast crank and rods. Block not decked. Rebuilder pistons. Which the machinists wasn’t aware of the lower compression height. So he ordered +6.0 flat 4 valence relief hypereutectic pistons. I measured deck height as best as possible without a bridge. I’m getting around .040-.045 height. With the thinnest .015 head gasket this puts me at a .055-.060 quench. Compression around 9.2:1. Dynamic compression around 8.10:1. I’m running Profiler as cast aluminum 70cc heads. I was hoping for higher compression, especially with aluminum heads. But I wasn’t going to pay him tho tear it down again to deck the block. You thoughts on this compression and quench combo. Cam is a Howard’s Rattler. Thanks!

Fact, composite gaskets blow at high boost vs copper

Who put BBs in my intake?? Thats detonation friend

No wonder hemi heads with the spark plug in the middle run so good. Little to no quench area

Will you make CNC files of your heads specifically the vortec ports

On piston rock. Are you saying the rock would be .009 from the lowest to the highest point when mesuring from the same side or would it be the total rock divided by two, to get the piston height?

Personal experience: wide quench, deep exhaust note Tight quench: crisp/sharper note NA/NOS engine: run as tight as possible Boosted engine: quench is not important matter of fact there is a chamber mode intended to delete the quench pad called "chamber softening" it allows to run additional timing without knocking and it is perfect for a full blown race engine that give no 2F about MPG

Cool video thanks

Would you have some time and ideas for a D16Y7 with a Y8 head that is being massively modified in the port bowls and the quench pads champhered to deshroud the valves for a turbo build?? I'm literally cutting into the cooling chamber and plan to weld the "low flow" bowl to create an even flow between the two intake ports/bowls.

Another AWESOME video! Love to hear some recommendations on a head gasket bore?..... # 683 TBI 4blt roller 350, 0 deck, 908's, stock rotating assembly. Waiting on dial gauge and bridge to arrive, but, assuming average "in the hole" numbers, what gasket bore diameter do you recommend? You and the masses say quench @ .035"-.070", so if i can get close to that i was wondering, hypothetically, why can't i un-shroud a valve to a 4.060 bore gasket, then install a 4.080-4.100...or proportionally larger. Scribe out a 4.080 gasket to grind to, then install a 4.120? Or do you alwaus want to un-shroud to the line/gasket? I hope that made sense. Plenty of gasket thickness selections out there and 3x as many bore sizes. If not, im sorry I wasted your time. 😊✌

my block was 30 over and the cam i use was xe 262 h comp cam

I bought a L31 out of a 99 2500HD Suburban to build and to replace the 2-bolt main L31 in my 96 Silverado std cab Short bed. I noticed that the Rods are different in the 96 L31 vs 99 L31. I assume the 96 still had the forged rods and maybe the 99 4-bolt L31 are using powder metal rods? Wondering if the 99 L31 4-bolt had stronger rods? Also what Flat-Top piston Choice is a good recommendation for the build? I want to go as much compression as possible using High octane 91/93 fuel only @ the pumps. I am going to reuse whichever one of the connecting rods thats best from one of the L31 with ARP bolts, ARP main cap Bolts, mid length headers with 2.5" exhaust, Lt4 Hotcam with 1.6 roller rockers, and upgraded fuelpump and the 36lbs "improved spider injection system I found on eBay and finally a Tune from a reputable tuner for the combination. As for tranny build, its a 4L60E with all the upgrades and heavy duty rebuild kit, maybe a 2500 stall or something around. Rear end is a limited slip posi unit with a 3.73 or 3.90 gear/pinion. What do you think about both connecting rods and which would be best? And what type flat top hyper .30 over piston? And compression? Ive been studying your videos and LOVE ALL YOUR INFO, but trying to figure this out. I trust your recommendations. Keep posting vids! I am hoping my standard cab, short bed truck can run in the 12's after all this, maybe. Lol and of course , removing some weight to lighten up some. Its been a project for some time now.

hey got a question for you i got 1990 blazer 5.7 tbi had engine rebuild about month ago got a few up grades bigger cam so i had to get my computer chip tune to raise fuel and timing on the chip i change pressure regulator and adjust that the cam i have in there is xe 262 h comp cam the block was 30 over.and i still have the factory swirl port heads i should had put some vortec heads on there...but for some reason cant get it to run right just dont have no power and im getting a ping sound from engine and #6 had oil on spark plug threads only the rest of plugs are fine i dont no where im getting the ping sound dont no if the oil on the spark plug have anything to do with it or something with the fuel and timing is not right..........

If not the cops of the head would have no matter, that is why there are different cc heads which in reference to the area where the valves are I beleave

No se exactamente en que te enfocas, pero debes saber qu las formas, materiales,la relación de compresión el tipo de cámaras, combustible calidad de refrigeración,los grados de apertura del termostato,el grado termico de la bujía insideden en la temperatura de la combstion y la posibilidad de detonaciones. Yo personalmente trabajo con medidas de proximidad de las válvulas con el pistón y luego cúbico todo el conjunto para no pasarme de 11 a 1 luego trabajo la culata eliminado puntos calientes y filos agudos y rebajando la superficie y trabaja super .Los octanos los compenso co los grados de avance del distribuidor si lo tiene hasta el punto que no cascabelee con el motor caliente.

Thanks

Good show!

Building a 383 0 deck with the eBay aluminum heads assuming that it’s 68cc I’ll be needing a .06 gasket for 10.1 compression and 10.9 with a .03 , It will be a street engine with pump gas , what do you suggest either port the chamber to get more cc and a thinner gasket or leave the head alone and get a .03 or .04 gasket and run pump gas and 10.5+ compression

this makes a lot of sense. my 360 would start pinging once it gets to temp, i thought it was too much advance. i cant tell you how many times i put the timing light on it and moved the distributor... i used the 4.060 kit from jegs and thought it was good. the CR calculator said it was like 9.4 to 1. Maybe i should get a cooler plug, it has autolight 45 tapered seat. it spends its whole life at 2000 feet elevation and over 100F degrease ambient air temp. would you recommend a better spark plug?

Yea just asking for a leaking head gasket I know it happened to me get the good gaskets

Compression Stroke. Squish. Exhaust Stroke. Quench.

Did you ever do the video about the dome pistons?

With an aluminum rod I'd go 60 th inch clearence of valve to piston clearence

If the piston were to hit the head what would happen? Break the piston? Break the crank? Or would it just stop and quit running? Would it damage the head? I had my heads shaved on an old carbureted 360 bored 40 over and I think that could have happened. My mechanic replaced a piston head but I dont think that really fixed that motor. Also I had it reringed after that and we found what was probably a screw or something laying on the piston head. It was beat up. This experience is what kept me from getting into motor building. I let it get to me too much I guess. 😕. Apparently it runs now but it is in better hands.

Call as you won't but all the area inside the cylender head is a combustion area

I have a 355 with 11.7-1 tips on using pump gas and 91 through 93 octane

I guess you never made the video explaining the humped pistons or dome pistons and what has to be done to use them?

I have a Honda k20 engine. I have 1mm oversized dished valves on the intake and I have stock size flat faced valves on exhaust side. Is this a good set up?

I have a 305 vortec 98 silverado daily driver needs more power hauling trailer for my job would it be better to get new heads with behive springs and cam to match or keep vortec heads and just change rockers for more lift

Quench is temperature Squish is pressure

Is it normal for new piston rings to make a slight scraping noise when turning crank by hand? I just put some in and was surprised to hear anything, but it seems to be the rings riding on the newly deglazed cyclinder wall. I even uninstalled the piston to check the rings and cylinder wall, and it was all good.... Just a bit confused with noise - just hope it is normal... crank turns quite effortlessly. Any wisdom from experience rebuilder would be most welcome!

Great video thanks! I’m using a 4.4” piston with a 15cc dish to get a 9.8:1 compression ratio. I have 0.045 quench height but with the dish the quench pad is only about 1/4 inch wide - is that enough quench? I would have preferred a flat top piston but I’m limited with head choice.

So if you run a dished piston for lower compression, should you only dish the side on the combustion chamber in order to preserve quench? Or should you primarily adjust the combustion chamber size to change compression?

So I am building a engine that I have been trying to learn from you. I'm also a roundy round stock class. Not wanting to blow up my engine in the first round either. 😂 really don't think someone will have that much of an advantage over me to be pushing the limits on the engine next to having a good suspension setup. So are you saying that if I have my block 0'd out and use a regular head gasket I will be in a safe zone? Also if I do that and ran into ever needing to get new pistons, could I run into a problem with it pushing past my zero deck height? Thank u again for your channel.

could quench be measured on an assembled engine? maybe with some solder through the spark plug hole?

Unfortunately I have dished pistons. Im pretty sure I know the answer to this but do you treat dished pustons the same as flat top pistons as far as the ridge all the way around the dish. The top of the outer ridge or ring on top of a dished piston is where you measure quench and that needs to be the same as flat top?

So, are we talking about the possibility of an 11:1 carb or port injection engine on 93 ? or is this more to keep the average 9.6:1 engine from pinging on 87 ?

Building a sbc 383 with vortec heads and using a COMP Cams 12-242-2. Been trying to order an Eagle rotating assembly but all I can find is with flat top pistons with 5cc pistons. From what I read this will give me 10.1 CR. Would the 10-12cc dished pistons be a better choice to achieve 9.5 CR. Or can I get to 9.5 CR with the 5cc pistons with a thicker gasket. What are peoples recommendations here. 🤔

Iam running 2.5 thou in the hole on my Harley m8 street bike

great info thank you

What mild Cam can I put on a 5.7 l out of a 98 suburban without interference ?

Why won’t domed Hyper pistons work with Vortec heads? Only flattops or forged I hear. Any insight?

Quench is only important if it’s perfect. It rarely is. If quench isn’t perfect; Eliminate it. HEMI = ZERO quench

Ford 302, 9.9:1, iron heads, .035 quench, 87 octane, no detonation.

A classic "popup" or domed piston gets in the way of flame travel and airflow with high lift or long overlap cams, but some will use them to get quench in a big chamber. In a perfect "clean sheet build", its best to have as small a chamber as possible and let combustion occur in the dish of the piston. why? because the combustion is creating expansion, and its better to have it working mostly on the piston, rather than working mostly on trying to push on the cylinder head. so have it occur where the "most surface area" is applied. But of course, not every engine is a clean sheet, no budget build--and we work with what we found in the junkyard or in the used classifieds.

hey pat I have a question I just installed 8803 cam AFR vortec heads on a l31 block I have a sniper with timing control and it idles great I went on a test drive and it's popping like the timing is off any advice would be highly appreciated thanks

How much does dynamic compression come into play vs quench? My understanding is dynamic compression shouldn’t be much beyond 8.5:1 on pump gas. I’ve got a 350 block bored 40 over, 64 cc heads, 12cc dished pistons that are about .02 in the hole, and advertised compression of the gasket is .041. My math is showing 9.8:1 static compression, 8.48:1 dynamic compression, and quench of .061. The engine isn’t together yet. It’s going to be a street driven car. Would looking for a thinner gasket really make that much of a difference?

Would the .060 max piston to head clearance apply to a 454 also? I have a 454 short block that the pistons are .045 in the hole and the thinnest gasket I can get for a 4.350 bore is .039 thick.

Im building a 99 ls1 5.7l with stock short block, double cut valves in a set of 862 heads. 61cc combustion chamber i believe. I think 10.7 to 1 compression rn. I want to run a thinner head gasket to get to 11 to 1. I know pistons rock a little in the hole rn. Its still being built. Pistons go .003 out of the hole at tdc. Any advice?

The ford 400 detonated often and I fixed them by adding a second head gasket to reduce volume in the chamber.