[theoldone]

Originally Posted by Brian Baker

Let us know what the ring lands and rod bearings look like on those 11:1+ CR Pontiacs running on 92 octane after they get some miles on them. Just because you can't hear it pinging, doesn't mean it isn't detonating. The notion that you can fix the problem with a cam swap is misleading as well. This may work fine to bleed off cylinder pressure under part throttle - light load conditions, but what happens when you got to WOT and run it up through the gears?

Two choices...drop the CR below 10:1 or run it on race gas.

VERY GOOD ADVICE ! Once the cam comes in at high rpm- KABOOM !

then it will be big-time pinging

[JSAauto]

MotorDaddy....

"This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch."

Not sure if you're joking about not understanding this or not. The same verbage is posted at the Keith Black website and many others. They are talking about "swept volume" vs. when the intake valve closes effects the cylinder pressure that is developed. If you close the intake valve closer to BDC than later, you're cylinder pressure will be higher (you have more "charge" to compress). If you close the valve later, the cylinder will make less cylinder pressure (you have less "charge" to compress). It's really simple to understand.

They don't mean that the actual stroke of the engine changes, but when the cylinder starts to build pressure based on the intake valve closing, thus making the engine as effective via camming as you would by running a shorter stroke. That's it. So if you wanted to take full advantage of of your stroke, get the intake valve to close as close to BDC as possible.

[JSAauto]

theoldone....
If you were to add another .042 to the deck by adding another head gasket, you're increasing the deck to around .080, maybe even .100 depending on where his "piston to deck" clearance is. Anybody knows that's how you build a dog of a motor, no matter what school of thought you're coming from. You remove the the power gains & effective operation any quench the lousy factory Pontiac chambers had. Ever taken apart a motor that had this problem vs. one that had a good quench/deck. (provided the A/F ratios are correct) The one with excess quench/deck will have a black sooty combustion pattern left on the chamber whereas the one with good quench/deck will have a nice grey pattern left on the chamber.

Putting a larger cam along with the double head gaskets will make this thing run like a real turd.

The RAIII Judge 4 spd I had at age 20 was something like 10.25 or 10.75, I forget. But it was all factory, heads had never been off the engine. I'd have to run race gas to keep the thing from pinging at 34-37 degrees of total timing. I did the exact same thing you just mentioned (double head gaskets) and the car still kept pinging BADLY. The only way I could keep it from pinging was to run the total timing around 20-22 degrees. Put a different cam in, and the problem was GONE!! Took the head gaskets out because a local Ford engine builder had told me the same thing about excess deck and poor quench. Still no ping. The car ran like a striped ape.

Just like 6567gto changed his cam in his 455 and GREATLY reduced his pinging, I eliminated mine altogether. If 65567gto would have installed the correct cam for his application, he could have eliminated the ping completely as I did.

[JSAauto]

Brian writes...
"Cylinder pressure changes throughout an engine's operating rpm range, hence, it is "dynamic". It is my opinion then, that the use of the word "dynamic" to describe the "compression ratio" AFTER the intake valve closes is a blatant misuse of the word."

Funny...... everyone that understands these concepts in the industry seems to have no issue with this. Maybe a call to Duttweiler or Bob Lambeck here in California will clear things up for you?? Or even Butler. I'm sure they will explain it to you, not sure if you'll understand it though.

Actually... I just got off the phone with Chase at Butler performance. He said for anyone to give him a call and he can explain to those of you that disagree with me about installing the right cam will eliminate this guys 455 pinging, plain and simple. (931) 762-4596

The terms Dynamic and Static are fine with us professionals that understand the terms as applied to engines basic theories. The "static" compression ratios are calculated via a formula and actual measurements taken from the engine at hand. Dynamic compression is formulated from those same "specs" or "measurements" but used in a way to understand pumping losses/gains. Thus you end up with a dynamic understanding of the way the engine is developing cylinder pressure, whereas the "static" measurement information does nothing to understand this principal.

Brian writes again.....
"More air and fuel being pulled into the engine at WOT at higher rpm's...being crammed into the same space...and the cylinder pressure doesn't increase?Negative."

Brain... you should stick to whatever you do for a living, because understanding engines basic principals are not your forte'. Play with a compression gauge sometime on an engine that is strapped to a dyno. Take a plug out of one cylinder and see what your cylinder pressure is at idle, 1000, 2000, 3000, 4000, etc. At idle, you'll probably find that the cylinder pressure is around 45-65 psi. There again, because the engine is spinning much faster than "cranking" cylinder pressures. There again... with the throttle open and the engine at cranking speeds, you have more "time" for cylinder filling. At idle, the throttle is held nearly closed, not allowing the same "charge volume" to enter the combustion chamber combined with the engine spinning much faster than at cranking. Snap the throttle with the engine running and you'll see the cylinder pressure go to 150-200 psi (again, depending on the make up of the engine). Load the car and start winging the motor at the different RPMS (1k, 2k, 3k, etc RPMS). After a certain RPM, will start to see that the cylinder pressures start to drop. YES DROP!!!! Because now the motor is starting to go static and atmophereic pressure cannot fill the cylinder fast enough because the cycles are happening way too fast. Now put a positive displacement supercharger on the engine and you've solved the problem until the blower itself goes static. I'm sure Tom Vaught can explain that one to you.

Torqued..... Call Chase or Rodney at Butler performance if you want the truth about what you need to do to solve your problem. I've already told him about you and how you're looking for the easiest fix to your delemma. The Butlers are good people and much more knowledgable than some engine builders out there.

[Skip Fix]

JS one thing you didn't note was he has a 2500 stall convertor. The 284 cam already is fairly big for a flat tappet hydraulic and that convertor. Going bigger is going to KILL the driveability without a bigger stall, which kills more driveablity. I have the Ultradyne comparable cam to the 284 in my new 455 has 12" vacuum, jump to a bigger cam and even less.

Yes the NASCAR guys and other have scienced out running high compression , they also have 9:1 motors in alot of classes. Most of us don't have the time(even doing multiple cam swaps in the same car) or money to do the R&D these guys do.There are LOT of factors that can add to the ping, what's the deck height I tried a .100 down 455 to kill the compression and use small cc head-rattle city without race gas but still made alot of power(UD Cam). My RA IV 400 (same heads as the 455) had no audible ping yet picked up 8 hp on the dyno using race gas-UD hydraulic cam. Going to a bigger UD solid 288/292 it still had 215 psi cranking pressure. This is a 10.25 400 a big UD cam yet still had that much cranking pressure.

Where is the cam degreed, what's the total distributor advance. Rod length affects piston speed and dwell as well as stroke.

Easiest for most normal tuners drop the compression or use race gas.

Recent article the technology gurus have found maybe a plain circular dish is better than a reverse dome dish piston. Food for thought.

[Motor Daddy]

JSA,

Like I posted earlier, Maybe his wording was wrong.

The stroke doesn't change, period.
The swept volume doesn't change, Period.

Those two terms have definitions, maybe you need to see what they actually mean.

It doesn't take a rocket scientist, (or a "professional") to understand that if you compress less air, you have less pressure!

Maybe you need to word it something like:

The intake valve closing point effects the DCR due to the fact that the intake valve remains open for a portion of the compression stroke, effectively reducing maximum cylinder pressure.

The stroke doesn't change, and neither does the swept volume, so don't use those words!

[SlowSpitzer]

So Torqhead...... Now that you know exactly what to do, when are you going to have it finished up?
Good luck in your quest. My old man told me once, don't believe anything you here and only half of what you see.

[WARPed]

I won’t argue that it can’t be done but rather the design/technology we are working with is based on 30+year-old foundation. If one were to redesign a modern combustion chamber one might argue that it could be done, but this is not the case.
Way too many people smarter & wiser have tried and they all end up at the same conclusion, lower cr. GM, Ford & Mopar ALL would have not lowered the cr if there was a better way.

After the proverbial smoke clears and you changed to a larger cam and still have a ping issue will it be because you just haven’t gone big enough? Save your self both time and money, lower the cr to a manageable level and be done with it.

[Motor Daddy]

JSA,

No one is doubting that changing the cam to one that will make the DCR lower will stop pinging.

Lets look at the results of installing a "bigger cam".

The cylinder pressures will be lower
The cam will shift the powerband up, effectively losing a lot of low-midrange power.
Since the uper end of the powerband is higher RPM, you must be able to actually use those upper RPM's.
It the cam RPM rating is say 3000-6500, and your redline is 5500 you just lost use of 5500-6500. Now you usable powerband is 3000-5500.
The car will spend much time below the powerband and when it finally gets there, it's almost done.

All that equates to a DOG!
Big deal, you get rid of detonation, but you can't get out of your own way.

There is much better ways to solve the problem than overcamming!

[JSAauto]

Motor-daddy...
I've built one or two engines in my time, EXACTLY as the combo torqhead has. Because of the compression he is running, it will not be a dog down low. Certainly not as bad as putting in a large cam in a lower compression motor. But the effective/usable torque will be shifted to a higher RPM for sure. This I agree with you on. Others need to read what I've already posted. I've already addressed the stall converter/idle issue with torqued. If he has power brakes, he may have to install a vacuum resevior can. It will definetly have a rough idle, but not as bad as a 400 would with the same size cam. Large cubic inch engines can use more camshaft than a small cubic inch motor and will not have as much problems with idle vs the smaller motor. I asked some questions of torqhead regarding some specifics (i.e. intake lobe centerline installation). Something else may be causing his problems before tearing into the motor.

Motor-daddy writes.....
"The stroke doesn't change, period.
The swept volume doesn't change, Period. Those two terms have definitions, maybe you need to see what they actually mean."

1st of all, please don't patronize me. I know EXACTLY what the terms mean. It is you that is against the majority of qualified engine builders that you are at odds with. Which is EXACTLY why I posted Butler Performances phone number if you care to continue this foolish arguement. Chase or Rodney are there for you to argue with. Let me know where you got with them. I figured you'd respect their words over mine.

You are correct the physical stroke does not change period. I never said it did. But there are two different "swept volumes" that I am talking about that you are not understanding here. The 1st being the "total swept volume" that is "total swept volume capability" of the stroke/bore combination. The 2nd being the total "charge" swept volume which is more dependant on the camshaft profile than anything, and is EXACTLY what the "Dynamic Compression Ratio" refers to. It is a figurative concept which is a "function" of the total swept volume of the cylinder vs. what the camshaft allows to enter the cylinder via a cylinder charge. If you don't understand it after I've exhaustively explained the theory, like I said, Chase is waiting to talk to anyone and explain it to you. I asked if it was OK to use his name and refer people to the Butlers. There you have it.

Skipfix... I totally agree with everything you posted. I found out about Ultradyne over 15 years ago, a great cam company. Actually my favorite. He has lobes that no one else has in the country. An incredibly knowledgable fellow. John Erson, Sig Ersons nephew is someone else I worked closely with over the years. He has ground me some really accurate lobe to lobe cams also.

[Motor Daddy]

JSA, I don't need to call anyone. I understand it fully and I think you have a basic understanding also.

It is a wording problem! Say what you mean, not what you mean to say!

[Hot Rod]

This did not need to get to this point, it's not about who is the English Major
here.... I spoke with Tom Ellison this afternoon and went over what I posted and he said that it was correct from his book. But he also said that was based on the application that was being used. And as I have stated before I respect your opinion whom ever you are.... Motor-Daddy!!!!!

Rodney

[Nickv]

Great thread! I've learned alot here. Now for my lousy two cents on this issue.

In my 67 GTO I'm still running the same shortblock that was rebuilt back in 1992. What you say is the significance of that? Well, It's a 455 +0.30, CC292 cam, it did have #64 iron heads, 3:73 rear and 3000 stall converter. CR was around 10.3-1 I suspect or over. I've never experienced any pinging running on 93 or 94 gasoline and I put over 40 1/4 mile passes on the car myself before changing over to E-heads. The previous owner had the car as a dedicated drag car and had over 50 passes on it with the #64 heads and a CC306S cam.

I now have E-heads on the car. I also spray it, but do put in race gas for that. I might ad also that the car is driven alot on street during the year, expect for Winter of course and has gone on some very long trips with no problems at all.

If the motor was being hurt by detonation because of high CR and iron heads, you would think that after 13 years on the same shortblock it should have gone south awhile back.

[JLMounce]

Great technical thread, great read.

I'm not in the same situation but I can add a bit to the thread. I'm running a 455 block with #62's on it on 91 octane with no notible detonation.

with that said however I've never really driven the car for any length of time. It's been in an ongoing restoration state since I purchased the car in 1999.

I can't however provide any more information on the engine combination. The engine was a fresh build by the previous owner. It doesn't have a wild cam in it (off idle power, smooth idle etc). It's possible the engine has a dished piston but without taking the heads off I would have no way to know that for sure.

[chiphead]

Bore scope! Peek in thru a sparkplug hole with piston at or near TDC, and see what wonders await. LOL

[Nickv]

Originally Posted by chiphead

Bore scope! Peek in thru a sparkplug hole with piston at or near TDC, and see what wonders await. LOL

I have, and when I replaced my iron heads with my E-heads the top of the pistons were perfect and you could even still see the hatch marks on the cylinder walls after 13 years.

[JSAauto]

The original 455 HO in my 64 Grand Prix (was originally an XF code 10.25 comp 455 with 64 heads out of a 70 GP) pinged like an SOB. Totally stock engine that was rebuilt by Fisher racing engines here in the San Fernando Valley way back when. It was a .030 over, flat topped, nothing fancy, stock cam engine. Pinged like mad!! Had to back the timing back to 20 degrees total to run it on Union 76 91 octane!!!

Stuck a RAIV cam in it and it still detonated at light to moderate throttle. Ended up contacting Ultradyne and had him grind a custom cam for it. Had a pretty rough idle till the oil got hot and thin. The Rhodes lifters worked exactly as they said they would. Engine never pinged again. Car had a 800cfm quadrajet, and HEI, a CAST IRON MANIFOLD, some used GTO headers banged to make fit. Car ran a best of 10.92 @ 127 or 29 (I forget now) on two nitrous units (a plate and a hidden custom made fan/port system I built into the manifold). Ran around the 11.70's at Los Angeles Country Raceway at around 117 (3000 ft elevation) on just the plate Had a 3.0 gear, welded spider gears, steel wheels with M&H 9.0X30 slicks, 5000 lbs with me in it, 2 tool trays, spare tires and a floor jack in the trunk. Had to have a custom made driveshaft because the 1st pass at Brotherhood raceway here in Long Beach twisted the stock driveshaft right in half at the line. Chris at Continental made the converter that flashed great at the line and locked up on the big end. I drove this car to the track as I have all my racecars. That is the true "Pontiac way" (starting to sound Indian... LOL!!). Took alot of peoples money at the street races too when people would say, "Ok... I'll race you if you disconnect the nitrous". Then I'd agree with them and say, "Ok... I'll disconnect the 'PLATE' ".... which was all they could see, since the port system was hidden). Loved the look on peoples faces with Twin Turbo 300ZX's on the freeway when a tuna boat 64' GP pulled away from them at 100+ LOL!! Best $2500 bucks I ever spent on a fun/race car. I really miss that car.

[JLMounce]

Originally Posted by Nickv

I have, and when I replaced my iron heads with my E-heads the top of the pistons were perfect and you could even still see the hatch marks on the cylinder walls after 13 years.

It's always nice to see a good conditioned motor when you open it up. A buddy and I just did a heads/cam/intake swap on his 95 GT mustang. With 130K on the clock we were presently surprised with what we saw. NO major carbon buildup on the piston domes, hatch marks clearly visable, head gaskets in great shape and only a very minor amount of wear on the thrust side.

[Half-Inch Stud]

Volumetric Efficiency:

Seems to me the air-in-motion (momentum) causes difficulty to getting High VE during acceleration. Yet VE goes up for sustained engine RPM.

This line of tinking favors spending as much time in 3rd gear., and minimal tim is 1st and 2nd.

Meanwhile, Ignoring the mixture changes during pedal activities. The respective air-charge across RPM (Accel vs steady RPM) will show some engines ping worse while cruising, at peak torque, while also showing indicationd of ping for acceleration.

Finally, Since PING is load sensitive, you all try to consider these words for BTDC and ATDC, to tell ME WHEN ping got manifested, and then WHY ping occurs at BTDC-or-ATDC. his

[amcmike]

Excessive heat can also cause pinging. Have you checked your coolant and oil temperature?