Octane/Detonation Discussion
 

So for discussion I wanted to post something that I read on one of the FB Pontiac groups. I find it interesting because it goes against very common knowledge on this forum & is closer to what most folks think or say when it comes to high compression engines. Note, I am not agreeing or disagreeing with this persons post, I am merely looking to educate myself & have a discussion that hopefully helps others as well. Here is the post in quotations below:

“FYI: Just a notice or reminder to all of you 1970 and ealier 455, 400 engine owners that those engines were made for 98 octane minimum. If you're trying to get away with 91 or 92, even 93, you're looking down the barrel of future problems that most guys will try to blame it on something else. Know this, inaudible detonation can break a crank in two. Seen it. Because the detonation isn't so severe to where you hear a "ping" most guys don't think they're having a problem. All the while they're chasing heat problems or increased oil consumption. I bring this up because there's no education anywhere about this problem. And I want everyone to be enjoying their Pontiacs, not pouring money into them. You do not want to rebuild your engine stock. That's the worst idea. If you're going to run 93 octane or less you must drop the compression to be compatible with that octane. So listen up - the first reply which no doubt is coming will be from some guy trying to defend his high compression engine by saying "I've been running mine for ten years on 92 octane and it runs great!!!" As if that means his combo is safe. Understand that because of the plus and minus allowable factory tolerances I've measured a stock factory rated 10.75Cr. 400 with # 13 heads at 9.75Cr. Still too high for 93 but will last a lot longer before the signs manifest themselves. Here's a pic of inaudible detonation. Good luck everyone and if you have questions“

There are more factors at play as to whether a certain compression number is a go or no go. That post barely even touched the surface.

Not an apples to apples comparison. I don't know when the calculated Octane Rating changed, but in the muscle car heydays, octane was calculated as RON. Our fuels now are calculated by the anti-knock index which is (RON+MON)/2. Fuel octane measured with RON alone will be higher "Octane" than fuel measured as (R+M)/2. Its the same situation we see when talking to the Aussies for instance. Their "98 Octane" fuels are close to our 93 octane fuels. It's just a difference in how the octane rating is calculated.

What IS a known issue is the existence of anti-knock and lubricative agents such as tetra-ethyl lead. Many vintage cars (including but not limited to Pontiac) did not use hardened valve seats. There wasn't as much of a need because the TEL cooled and lubricated the seats and kept them from wearing.

Its not black and white like that.
You can run a 400 with 13s or 62s all day long with the right cam. You can build a 400 that runs PERFECTLY well on 93 with zero detonation.

I agree, it’s not that cut & dry.

Seems like some grand statements from someone that doesn’t have there facts all that correct. That’s likely one of those people that thinks all that era’s 72cc heads are actually 72 cc, which they weren’t. Plus I can’t recall a 400 with 13s ever having 10.75 SCR from the factory. The 9.75 SCR 400 13 head example was probably even high, some 400s with 13s have low 9s compression, the 13 head ran 75-78 cc, cylinder scallops on one side add 1 or 2 cc’s, pistons down about .020”, and on top of that, probably were sporting a .045” to .050” thick head gasket from the factory. Even with a small 067 cam, they would run on 91 octane pretty easy.

Lots of that eras stock grocery getter 400 engines have been rebuilt once are running around with 8VR pistons now too, compression is in the 8s. Not many engines even are configured much like how they were from the factory. Different pistons, surfaces trued up, valve jobs, different cams.

I am trying to remember the last pump gas performance engine I have put together that had less than 9.5 compression. Actual compression, not what the factory soft ball rating. I think I would have to go back into the 1990s.

You have to take it where it is coming from..someone trying to still be current ..

67Lemons do you have a link to fb you could share?

I think his opinion is the same as most folks think when you talk high compression for the street. What I see here is that you all discuss/explain how cam & ignition timing (as well as other factors) come into play for high compression motors not only surviving but performing with the current fuel formula’s we are stuck with.

The author of the FB post is Bruce Fulper

Whoda ever thunk it ?

:pound: :pound: :pound: :pound: :pound:

Bruce was kicked off this forum before I even joined, over 21 years ago so that might tell you something.

This octane/compression subject has been beat to death here multiple times already.

Rock 'N' Roll baby!!

One of the problems I see with race motors today is that many do not take advantage of todays programmable ignition systems, and even the ones that have it do not make full use of it.

At idle many race Cam’ed motors can take and want a lot of advance, even up to 55 degrees (and especially if your trying to get the motor to idle clean and as lean as possible ) but once the throttle gets cracked open that needs to drop back to 30 to 35 degrees .
At about half throttle with a good tune and fast burn chambers that may need to then drop back to 25 degrees.

Once at full throttle then timing needs to advance in the conventional manor.

Your not getting this with springs and weights, although at idle you might come close with vacuum advance.

Fulper, the same guy who said a 400 block could hang with a IA2 in the reliable big power dept.
Whatever you say Flopper.

Why was Bruce chucked off the forum? Over here in UK we have to read and learn because there are no pontiac specialists. I often read his posts on FB and know that he isn't a liked person but, he must still get work. It can't all be wrong surely.

I've known Bruce a long time going back to the first drag race days we had at the firebird nats. So I guess 30 years or so.

I think most peoples issue with Bruce is his arrogance making him hard to talk to for some. Being a body builder and power lifter for most of my youthful life I grew up around arrogant people so that doesn't bother me as much as it bothers others. I tend to find humor in it. So once you get past that you realize he's not a bad guy and has some interesting theories. I don't always agree with him but that doesn't make him a bad guy. Personality aside he's ok. I always did appreciate the effort he put in for the drag races and the give aways were always stellar. Cost him a small fortune to do that every year and he never complained. I never did go back to the nats when they stopped the drags. Bruce had a good thing going there. That should have been continued after his accident but that's a different discussion. Such is life.

Your right, the electronic timing control makes this so much easier.
Ive been able to manipulate mechanical timing control and higher idle timing with vacuum advance on engines like this and have good success that way as you mentioned, but electronic control has the ability for so much more.

Modern water injection will break the octane compression rules.

Otherwise my 472 ran the 1/4 to 12.2s on 89 Octane, no ping, because 9.00:1 CR was too low.

You all are safe to design for 9.5:1 - 10.5:1 depending on details. Then 10.5+ higher compr needs a real plan from real experiences.

Revisit water injection to run super high CR on 93 octane pump gas, for high HP.

Modern water injection will break the octane compression rules.

Otherwise my 472 ran the 1/4 to 12.2s on 89 Octane, no ping, because 9.00:1 CR was too low.

You all are safe to design for 9.5:1 - 10.5:1 depending on details. Then 10.5+ higher compr needs a real plan from real experiences.

Revisit water injection to run super high CR on 93 octane pump gas, for high HP.

"I think most peoples issue with Bruce is his arrogance making him hard to talk to for some."

Most folks had issues with him because he'd take their money for parts, or engine builds, etc.....and NOT deliver.

I've seen this many times over the years but am NOT going to waste any of the valuable time I have left discussing it.......

Bruce Fulper = Tune out.

As has been correctly stated here, detonation is complicated and no single statement will solve it and there is no magic number that will keep it from happening. Just bought my wife a new, "used car". 2018 little Mazda. Static compression 13.2:1 . Regular fuel 87 octane engine. Of course, all the modern electronics and direct injection. I mention this as an example that compression alone does not determine detonation. Internal shapes, piston, chamber, valves, ring pack all play a role. Of course super precise fuel and ignition control as well and variable valve timing. Our old muscle cars are crude and as mentioned, very few are 100% stock anymore. Almost all that are being driven have been rebuilt to some degree. If we want the same, stock look as OE, there is no reason not to use what we have learned over the last 60 years to improve engines ability to run on pump gas available today. Lowering the compression on pre 1971 engines may be part of the formula while raising the compression on post 1971 engines can be done without detonation. Yes, agree it is complicated. Blank statements won't solve this problem.

Some good reading:

http://members.uia.net/pkelley2/DynamicCR.html

https://www.pontiacstreetperformance...mpression.html

https://www.pontiacstreetperformance...pression2.html

https://www.pontiacstreetperformance...pression3.html

Lulz

9.75 is nothing

Quiick note of things people don't consider. when trying to compare the past "numbers"
Static CR Vs Dynamic
"Most" fuel lost LEAD in the early 70's which had a major affect on say a 1970 Ra engine in 1975.
As well stated here, there are many workarounds and mostly REAL numbers now. Solutions abound,
and so does VP fuel !

X2 on Cliffs post Most folks had issues with him because he'd take their money for parts, or engine builds, etc.....and NOT deliver.

I've seen this many times over the years. Living in So Cal I have heard this a lot! People can either accept his personality or not, him talking about something that happened 20-30 years ago stuff that is no longer relevant to him or to me, but the hassle of fighting to either get the parts you paid for or the engine that was promised 8 months ago the phone calls, completion/Timeline promises, the law suites.

for me, its a business decision NOT to do business with him. Every couple of years he comes out of the wood shed and spouts something and this all gets hasted over again. YMMV

I wasnt a victim of any bad business dealings with Bruce. I've heard the stories though. My father and I both have had a couple of his camshafts to try and other small things.
He gave away 2 complete Pontiac engines in raffles we were in. All built with good parts and dynod. I've never known any one else that's done that. I thought that was pretty cool, and he hauled them all the way out to Ohio for the give away.

Not defending the guy, everyone has a good and bad side, I've just never experienced the bad side I guess.

I won Indy!!!!!!

I think Mr. Fulper was a pretty darn good track announcer and a pretty good guitar player. I did it!! I found 2 positive things to say about him.

Whitmore told me a couple of B Fulper stories before he passed. They were friends, at least friendly. Dan made a trip out to CA to see his daughter and stopped by Fulpers shop to say hello.
One time Fulper was in to booth at a big Pontiac drag race in which there was some cars with Dan's engines . He had one of his long rod 400s in a 2nd gen, heavy car. It ran 10s back in the 80s and that was pretty fast back then.
Well, that Bird was coming up to the line and Fulper said over the mic that "it sounded like a Big Block Chevy". After it ripped off a 10 second pass Dan ran up to the booth to let him know it was a Pontiac 400 that he built. Dan took a little offense to it.
Another time there was a group of the Pontiac big dogs back in the day sitting at a table discussing Pontiac engine know how. It was a incredible group of people that I won;t give up the names but the Pontiac world was a smaller one back then.
Bruce was there but had not been invited to the meeting, had not made a name for himself yet. But he hung just outside the door trying to pick up what he could, eavesdropping basically. He used some of that info and claimed it as his own. At least that is what I was told.
My only contact with him was way back when I first started to get serious at the track and called him up for a plug recommendation and he was very rude. By Bruce.
That 64 GTO on the cover of his old green catalog showed up at our track back in the 90s. The owner was on vacation up the coast WITH his car. How cool. I could not believe he was actually at our track. Well, that was before it got resurfaced and he blew the tires off at about the 150 foot mark. Said he would not be back, almost wrecked so the car made power. VERY nice car too.
When I asked about Bruce he said well, nothing good.
He was the guy Bruce ripped on his site for taking apart his engine to find out Bruce's "secretes". It was a "44O" Pontiac with E heads, Flying Toilet and Milodon gear drive.

I have wiped out a 428 due to inaudible detonation. Never heard a thing. Perfect hearing.
5 broken pistons and pounded out bearings.

I ran Edelbrock water injection on my '67 GTO in the late 1980's with the stock 670 heads and 92 octane gas. Didn't help. Had to retard the hell out of the timing. Changed the heads later on to 87cc iron heads.

The most distructive level of detonation that takes place at full throttle you will never hear even with closed exh, but you would have sure as hell seen it on your spark plugs if you knew what to look for , or even first off knew how to determine if you even had the needed heat range of plug in your motor for it to live at full throttle time after time.

If a motor is on the edge with jetting at full throttle and you combine that with a wrong heat range plug your guaranteed to have issues.

Did the 5 pistons break ring lands? Was it a single pattern cam?

Having something like that with no warning will make anyone gun shy on compression.

I attached a screen shot of the compression and photo of one my 91 octane pump gas Pontiac engines. It has headers, other than that it looks like a bone stock smog engine. Modification are on the inside.

I was running a 455 with 62 heads, around 11.5:1 and ran it on 93 no problem.

Cranking psi was 200-205psi across all 8.

That sounds about right. What I seem to find is that when I have an engine that gets up to around 210-215 psi cranking compression it starts to become super sensitive to pump gas.

That's back when I was living in Ohio and had Sunoco 94. Dad had a 455 with #12 heads and flat tops zero decked. I don't remember the compression off hand but it was up there close to 12:1. It was an Ultradyne solid flat tappet cam that was pretty rowdy but I don't remember specs. I just remember on the street and pump gas I had to have the tune really sharp. I used the track to dial in the timing and it seemed to like about 32 degrees total and that was it. That's where it ran best times. Ran that engine for several years like that and it survived fine until he wanted to go faster and the combo changed. Really didn't like the edgy-ness of that engine, it was pushing pump gas limits and it was about that time he went to aluminum heads and more manageable compression.

Out here in Arizona now where we only have 91 octane it's even more tricky. We do daily drive the Z with 11:1 compression and it's original iron hump heads (186's) but the camshaft in those things are fairly rowdy on duration for a little engine (254 @ .050) and the LSA spread out a bit so it's actually very manageable on 91. In fact it makes best power on the dyno with 38 degrees timing and shows no issues with this crappy gas. Been daily driving it for several years and over 60,000 miles. If it were going to pound bearings out (as they say) it would have done that a long time ago. During the build details were paid close attention too though. Custom JE pistons (expensive) with the pin moved to get the piston close to zero deck and things like that, for a true 11:1 compression.

As far as Pontiacs go, my bird with it's RAIII is 10.13:1 with the 068 cam in it and it runs on the same crappy pump gas just fine. Likes 34 degrees of total timing and runs best there. I've been beating on that thing for years like that with more racing than I can count and logged about 50-something thousand miles, it's still got bearings in it. The cam isn't really my first choice but kept the engine legal for PS racing. It works as is. I'd gladly do a bit more compression with more camshaft and be ok with that. I'll save that for a bigger engine at a later date. Maybe one of these days out of curiosity I'll pump it to see what cranking compression is, but I suspect it's not out of this world.

Why throwing soem higher octane race gas is no convertors or 100 octane race/unleaded and see if the motor picks up HP on the dyno or time in the 1/4. My zero deck RAIV 400 picked up 8 HP on the dyno with race gas and no audible detonation-and on dyno we ran mufflers!

There is a point where higher octane and it's slower "burn" can hurt you. Friend with a 66 Acadian(Pontiac Chevy II) and a pump gas SBC ran out of gas at the track and all they had was race gas. Slowed down 0.2 seconds!

Also the variability of the "blend" in pump gas is very wide. You can have a wide band for AFR on your car and see how when you think you have it dialed in that next fill up it is off.

Do you remember which cam you used for that?

From Bruce's website

"Bruce's original Rock 'N' Roll GTO. With it's 9.2 Cr. 400 it ran 10.60's and made people like Pete McCarthy lose their old school mega-egotistical minds. Instead of learning how it was done, Pete wrote letters to magazines and club presidents claiming Bruce's engine was not what it was. All because he couldn't explain how it was done. Poor Pete. Made a fool of himself."

Any of this true?
1) 9.2 Cr. 400 running mid 10's
2) Pete making a fool of himself

Anybody know how Pete is doing? Enjoyed his articles immensely many years ago.

Excellent points, Jay. What many forget is the advertised compression ratios for Pontiac engines and the actual compression ratios were usually .5-.75 a point apart. The 10 to 1 engines were in reality 9.25-9.5 to 1.

No idea. It wasn't something I built, it kinda fell in my lap. It was a hydro flat tappet, .060 over forged pistons with small valve reliefs, block was filled to the water pump, with a single plane intake and a Holley 750DP. Ran like a beast. Still made enough vacuum to run power brakes.

It's now living life in Nevada. Last I heard it's still doing well.

"Any of this true?
1) 9.2 Cr. 400 running mid 10's
2) Pete making a fool of himself"

Not sure but I did hear about it and the "350" build he did that was supposed to run even quicker.

It was "leaked" at some point that the low compression plain old iron headed 350 sported a 4.5" stroker crank and the compression was so high the block was "O" ringed to keep from pushing the head gaskets out of it.

Don't know if the 400 or the little 350 actually existed, or ran any decent numbers in any vehicle at the track, but knowing the source I could care less whether it was fact, rumor, myth, or anything in between.........and even better you can't see any of it from my house!......LOL....