Edelbrock EP4B intake - what's the truth ?.

You can run as high octane rating as you like - even on a low compression engine - it won't hurt. The octane rating ONLY tell you of a particular fuels ability to withstand detonation - hence higher octane than needed will never hurt anything. If detonation is not a problem on a particular engine it won't improve anything either.

This isn't about high octane, it's about high compression. And you don't just randomly mix the shit. You have to maintain that octane, not just throw in a couple gallons each fill up. If he chooses to run high octane he has to run high octane as I stated before. But that's gunna get old real quick at $100/tank.

Fix the damn thing and be done with it.

I made a thread on the PY forum and I'm getting the opposite of what you're saying Chris.

Here are some of the things said over there

"why would higher octane gas hurt your motor? Use what is needed there is no crutch.
too low octane for what it requires can be a expensive problem. that is it will show harm eventually, you may not even notice a problem for a long time. pinging (pre detonation) is relatively harmless, inaudible knocking (detonation) is the silent killer."

"I have a 10.61 compression motor: 68 350 HO in a Firebird for Pure Stock Racing/street use and as long as you do not get on it you could be ok but it takes about 5 gallons of 110 mixed with the rest 93 to make sure it does not ping. I have tried 2 1/2 and that is not enough."

"High octane will not hurt your motor. It will help prevent the destuctive detonation. In your case, you have to worry about too little octane. When running lower octane fuel in a higher compression engine, you need to retard the timing to prevent/reduce the pinging/chances of detonation. However, retarding the ignition robs power and increases the temps. It can be a catch 22, because the higher temps can increase the chances of hot spots and detonation.
I would think the only downside of running more octane than you need is the cost. Higher octane fuel does not contain any more energy per gallon than lower octane fuel. The fuel itself is not more volatile, explosive or generate higher pressures than lower octane fuel.. So if you are concerned about "additional" power of high octane fuel harming the engine, you have nothing to worry about."


"You have heard that the Pontiac Advertise CR was a little higher than actual compression ratio. That is generally true. So you may have started at about 9.8 STATIC compression ratio. A SD 421 was advertised at 10.75 to one You should be below that."

And this is what Pontiac Larry says, he's the guy building my stroker, he's been building Pontiacs for over 20 years.

"I bet that motor is not over 10.0:1 at the most, I was thinking of trying the Torco Accelerator octane booster for getting over the hump so to speak on a situation like this.. but until you drive it....??? Set inital timing at idle , no vacuum advance , at 12 BTDC as baseline and then put light springs in it later and see how it does..hopefully you can run the total mechanical timing up to 36 degrees later or more and drive around with no vacuum advance .. should idle decent.. The part throttle pinging when vacuum advance is hooked up is likely if it used, so just do a quick mechanical advance with as much total you can get by with (38-40) and go drag racing...the small octane boost may fix it if there is a problem at full throttle.
Do you still wanna swap to your ported heads next on that motor after track testing with what you got ? At least you will get to see your pistons and check deck height..

PS: my 400 + .030 over TRW forged flat top '68 400 with '68 #16 heads does not ping on 93 with 38 degrees total , in fact , I have never heard it ping.. factory rated 10.75:1 , actual is about 9.5-9.8 ?"

So the majority, says high octane will work, mixing octanes is fine and I might be fine on even 93 octane.

We'll see how it goes when I get it on the street here pretty soon.

And checking out that hamb forum no one said YOU'LL BLOW YOUR MOTOR UP WITH HIGH OCTANE or that high octane is a no no or mixing octanes is bad. And like they stated, and like I found out on PY, factory compressions are rated higher than they actually are. Plus they're talking about an 11:1 motor.

Also, "What happens is the overlap in the cam bleeds off cranking pressure, resulting in a lower overall actual compression ratio"

So cams do have an affect on compression

SO really, that HAMB forum didn't really have much to back up what you said. Just a handful of guys saying they had problems and a handful of guys saying they didn't have a problem.

Hearing from multiple sources now that factory compression ratios were rated higher than they actually were makes me feel better. Larry seems to think mine is under 10:1 which should be ok on 93 octane. My buick was rated at 10.25:1 and I never had a problem when I ran 87 or 89 octane in it. I didn't know any better back then haha

I had a set of 62 heads ported and polished with a set of 1.94 chevy intake valves installed and after I get my car to the track as is, I'm going to swap heads. That will give me a chance to check the pistons and figure out my compression ratio.

I'm out. I'm not gunna sit here and argue with you. You want to fuck shit up, then fuck shit up. Asking people over at PY!? LMAO! You might as well ask a 5 year old. And read the HAMB article again.

And I NEVER SAID YOU CAN'T RUN HIGH OCTANE. Where did I say you can't run high octane? Sheesh, read before posting MaryAnn. You're just as ignorant as that guy was on HCP. It's the high compression you're running into. And as far as cams changing compression. Cams don't change compression, they change cylinder pressure which are 2 different things. Engines 101 man. Learn it or just sell your damn car and ride a bicycle.

Fuck this shit. You can ban me now cause I'm not gunna buy into your shit.

Hey this isn't HCP. You can cuss, you can do whatever the fuck you want except direct insults at people. This is your warning. I don't care if you like me, or my car or even pontiacs but you're not going to publicly put anyone down. That is pretty much the only rule I have. I don't want this to be like HCP where you and Mike talk shit to everyone and run every one off.

I read the entire hamb article. There were guys saying they run 11:1 with pump gas and other saying they tried and they couldn't. But now it sounds like my motor isn't even 10:1 let alone 11:1 so comparing my motor with an 11:1 motor is like comparing apples to oranges like you said. Every application is different.

PY is the best for old school Pontiac Tech, bottom line. Those guys have been into pontiacs and into racing since the 60s. They're not just bullshitters. These guys know their shit.

High compression won't blow my motor up...unless I run low octane gas. High octane gas is the fix. So no, my motor won't blow up because of the compression...unless I run 87 octane in it.

I'm not going to ban you because we disagree. I'm not that selfish. But you are on your own on this topic. Everyone seems to disagree with you. None of this is my shit. I've never had a high compression motor before. I'm not claiming anything on my experience. Everything I just posted was from experienced pontiac guys. Not just some BS ricer math and guesstimates. These guys have experience with pontiacs

Take it easy Chris, this is just a forum. There is nothing wrong with disagreeing. I have you telling me my motor is going to blow up and I have 15 other guys saying I'll probably be fine. No offense but most of those guys on PY have been building and racing Pontiacs longer that you have been alive. So, I'm going to follow their experience over your less experienced advice.

High compression is only dangerous when you're not running good enough (high enough octane gas). That's a fact

So chill out, if you want to disagree, then disagree. There's no need to get mad about anything. You don't have to buy into "my shit." This isn't HCP, I don't force my opinions on other people.

Read the HAMB article again, they just said high lift and overlap cams will bleed off compression. Just like I was told many times before. It's doesn't change the static compression but it will allow you to bleed off some compression allowing for less octane without problems.

OK, back to the EP4B manifold, that is now sitting here in my living room. As with many other thing i think it's a cool thing in a living room - my wife don't - but that is properbly no surprise .

I checked it against the gaskets that i got from e-bay, that are marked for 55 - 60 pontiac (old aftermarket), and found that the cooling passage (the one that was supposed to be blocked, if i untherstand you correctly). I checked the old shopmanual, and according to the pictures it seems that there are cooling passages from the heads - they have ample size to match up with the ones on the manifold, which are alot smaller. If i check the discription of the cooling system it seems to me that the passage has to be there for return water from the 'gusher' cooling in the heads (or am i getting it wrong ?).

The other thing i wonder about is the blocked passage on the front of the intake, which is connected to the cooling system. What is this for (if anything) . Yau can see it in the pictures that are taken from the buttom, in the middle of the front you can see it standing out (hole with plug is only visible from front..

Oh well, i think it is going to match up one way or another. The manifold is in nice shape by the way.

And by the way, the shop manual also states 10:1 compression ratio for my engine, so my memory was off by .25 . I think maybe the number i remember is from my friends buick 350.

8.6 was apparently only for manual transmission and 420E (economy) engine. I'll post the complete table when i get the time to make a scan...

The passage on the very front of the motor should be where it would connect to the timing cover on the 61-64 motors. This should be plugged.

Also, on your intake if you turn it upside down you can see 2 round holes. The front one on each side should be plugged. The front hole is for the coolant passage on the 61-64 motors. The 55-60 motors use the second passage.

Other than that, the intake should be good to run as is.

Here are some pics I took a few months ago. My Offy intake also fits the 55-60 AND the 61-64.


The gasket is a 61-64 style gasket




See how if you don't block this water port off it will just leak coolant all over your motor. That's a 60 block with 59 heads