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Last Update 04-21-08

WE MAKE SERIOUS PONTIAC HORSEPOWER

AND WE KNOW MORE ABOUT BUILDING STOCK PONTIAC ENGINES THAN ANYONE.

PUMP GAS COMPRESSION

by Bruce Fulper

With the incredible amount of mechanical ignorance reappearing in both Pontiac magazines

it doesn't surprise me that I'm constantly meeting people whos power and/or heat

problems are directly related to their compression being too high. Do you know anyone like that?

They've tried every "trick" they've heard, and nothing helps. What's the problem?

It's very basic. If you're not meeting the engines octane requirements you will create

unnecessary heat in the combustion chamber. That heat doesn't just go out the exhaust.

It soaks into the piston top and combustion chamber, heating the water more

than normal. It also travels into the top ring where normal heat is

supposed to be transferred into the oil at the top of the cylinder.

If the piston and ring gets too hot the heat will take off the oil

that's supposed to be at the top of the cylinder, setting up at domino effect

of more heat, less oil, the ring scrapes the cylinder wall harder making more

friction - (heat,) now there's less oil for proper cooling - and the top ring turns into a

potato chip. Worse case the top of the piston collaspes, pinches

the top ring and keeps it from expanding against the cylinder wall.

Now oil blows by in larger amounts. You'll see the effect as increased oil

consumption.

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There are no tricks. Water doesn't burn.

Referring to water injection. The dumbest of dumb ideas.

Unfortunately engines like these are still being built every week by shops without

the proper experience. If a shop tells you they "fixed" a potential compression problem,

You need to know specifically how they did it. It's your money - Never be intimidated.

Always feel free to ask me questions - I can explain every bogus "trick."

I'll list every specific problem - it's symptoms - and it's cure.

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BASICS

I'm going to keep this as simple as possible. Those of you who are "super intelligent" and want to

spar with me on this topic - go replace your rod bearings and maybe your crank. J.H.

I have no time for defensive uneducated jerks.

However, I will gladly answer any well meaning questions.

Let me list several typical phone calls to our shop.

"I just had my old high compression original engine rebuilt to stock specs and it's not running as well as I expected. The engine pings and the builder doesn't have any answers why it doesn't run like it should. I'm very disappointed"

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"I've been driving my rebuilt engine for 10,000 miles now and although it never pings it just

doesn't run like I expected. It's sluggish and has no throttle response."

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Add to any lament, "I've installed a new aluminum radiator, used special cooling fluid,

and tried every thermostat on the shelf. Nothing helps."

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"I bought Joe-Bobs cam and he said it would trick the engine into seeing less cylinder pressure."

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Have you noticed at most gas stations there are three different octanes available?

87, 89, and depending on what area of the country you're in, 91 to 94 premium.

You might think - can numbers that close be necessary?

Yes. Engine designs are that sensitive. Most of you know that if you use 87 octane in an engine designed

for premium - it will detonate. There are not enough detontaion resisting chemicals (octane) present

for the cylinder pressure being created. Conversely, what happens if you use premium fuel

in an engine designed for 87 octane? (Most people don't know, so don't feel bad.)

The engine will not detonate - but because the burn rate is wrong the engines efficiency is hindered.

Performance and mileage will suffer. Here's your first tip in diagnosing efficiency -

IF YOU USE TOO HIGH AN OCTANE YOU'LL LOSE POWER AND WASTE MONEY.

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Again, that's too high for what the engine was designed for.

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Most of the 1960's standard Pontiac engines were high compression by todays standards.

Even most of the two barrel engines were 10.5 Cr. That's how they made good power.

At that compression 98 octane or better was needed. You can see the problem now.

Todays octane levels cannot support the older engines demands.

We have learned that no matter what kind of math formula or cam you want to use,

it boils down to this: You are NOT going to have an efficient engine throughout the entire normal operating

on 92 octane if you're over 9.65 static compression and a carburetor. Using cast iron heads the safe zone is 9.5 Cr or less.

BASICS

Cast iron headed engines are mainly prone to this problem.

When using original high compression heads you'll need to select one one of three options in order not to have problems.

#1: Run the correct octane the engine demands.

#2: Change the heads to larger combustion chamber versions.

#3: If you want to keep the high compression heads for looks, you'll

need to use a dished piston - just like the factory used to use.

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While the compression limit with cast iron heads and todays crummy pump gas is best

limited to a safe 9.5 static, an aluminum headed Pontiac engine won't detonate on 92 until you pass 11.5 Cr.

I built an 11.8 Cr four inch stroke engine with aluminum heads and it

experienced detonation on 92. We built another 4 inch stroke and made 661 hp at 11.4 Cr. on 93 octane and using our aluminum heads. I built a 9.65Cr. cast iron head 455 and it was

a loser on 92 octane when the ambient temperature climbed above 65 degrees Fahrenheit.

Be safe - The thought of losing compression frightens guys. I've developed

these low compression combinations for a reason. If you try to push the limits - you run the risk

of losing your engine early.

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Here's one of the saddest salesmen con games going.

"Buy our special cam that bleeds off cylinder pressure. It makes the engine think

it has less compression."

Reeeeeeally? And how does it do that? If you press the salesman for a more precise answer you'll get this:

"The larger duration holds the intake valve open longer bleeding off cylinder pressure."

What you have is HALF a correct answer. But it's a half answer to a situation that does NOT work

under normal operating conditions.

Let me first ask you this - cause I'm a good one at making people think.

Under NORMAL circumstances why does a person buy a larger duration cam?

Answer - to make more power.

Soooooooooo

How does the larger duration cam make more power?

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By filling the cylinder with MORE air and fuel on each filling cycle.

Making MORE cylinder pressure.

Kinda like putting a grenades worth of gunpowder in a .22 shell.

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Of course depending on how much more duration you have - will

directly relate to what RPM it takes for the extra PRESSURE to happen.

So the HALF an answer that is correct from Mr. Dummy is, yes, at idle, or

below 2000 - 2500 rpm the cylinder pressure is lower than a stock cam.

So, as long as you can never put your foot into it, you're fine.

You can never go over 3500 rpm. Is that want you want?

No.

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An engine detonates when cylinder pressure is too high for the detonation

resisting chemicals, (octane) to work. If, you were not meeting the octane

requirement with a stock cam, when you install a bigger duration cam

and build more cylinder pressure, you'll be worse off than before.

You also need to reason - if a bigger duration cam "tricks" an

engine into seeing less cylinder pressure, I guess those

Pro Stock cars have no cylinder pressure at all!

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Anyone that says they have a trick - contact me first.

I'll explain anything anyone tries to lay on you .

There is no magic when it comes to meeting

the octane requirement for any engine.

You simply must!

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How does this effect you?

If you own a 1970 or earlier Pontiac V-8 and are not meeting the octane requirement

of that engine you're probably in trouble. We just took apart a 1967 Firebird 400

that had 3000 miles on it. It was using two quarts of oil every fifty miles.

All of the bearings were showing copper. The pistons were tagging the cylinder walls.

The same thing will happen to you.

We'll post those pictures soon.

Other inaudible detonation pictures also coming.

Don't force your engine to be a martyr for your ignorance.

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I have spent over a decade developing pump gas combinations.

I have been blessed with results that stun everyone.

Whether by owning one, or just by watching one run, you'll be impressed too.

It's time to open your mind - and ask us questions.

No one else does what we do - so it's useless to ask anyone else how we do it.

You won't get a straight answer.

ALUMINUM HEADS VERSUS CAST IRON HEADS

I get this question all of the time. "Why can you run more compression with aluminum

heads over cast iron heads?"

The answer is simple. Aluminum dissipates heat quicker.

Aluminum heads transfer heat into the water passages quicker, thus

they run cooler han cast iron heads.

There's a group of yet-to-learn dudes that argue that cast iron heads

make more power because they retain more heat. If ALL things were the same - that

would be true. But ALL things are not the same.

You cannot port a cast iron D-port head to work as well as our aluminum heads.

Game over.

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If you could run a cast iron head at 100 degrees water temp you

could get away with 10.5 Cr. But that's impractical for most people

to achieve. Boats can do it as they use the lake water to cool the engine.

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That's why I've spent so much time working on practical - pump gas - combinations.

For the everyday (Pontiac) guy to have more power than ever before, and

have it with todays camel whiz. Today - 3/28/03 - we dyno'd two

more King Street 455's. These are 87 octane, (not even 91) street engines.

The smaller cam (245 @ .050) hydraulic roller made 633 lbs. ft at 4200 rpm.

The solid roller cam version made 679 hp at 6200 rpm

I have recently made 603 ft lbs at 3000 rpm with my latest 455 street engine combination.

BMF