[PONTIAC DUDE]

Originally Posted by mechanic17

P-Dude, I should have said the engine WAS pinging at idle as long as the computer had control of the timing (TBI systems will do that to raise an "unacceptable" idle). Now that I'm on a carb and non-comp HEI, it pings only when it is revved up in park (no load). And, under accelerating load, of course.

The cam is installed correctly--this was rechecked. However, I did not degree this one (in other words, either the chain, cam itself, or a tolerance stack could be contributing to an error.) Another, I suppose, argument for "non-tuners" to go easy on SCR. Engine tolerance for low octane fuel will vary because of these sorts of "built-in" problems. Naturally, the proper degree procedure would have picked up this problem, if it indeed exists.

My personal, current theory is that 9.5 SCR is combining with overefficient valve timing at lower rpms (3k and below) to create too much cylinder pressure. IF that turns out to be the case, (and assuming the factory claim of 9.5 is accurate for this engine) then 9.5 may not be a "safe" number after all, or at least not an "idiot-proof" one. And if it isn't, then we need to work out one that is for people who will insist on being conservative because they don't like to experiment with their cars, time, parts, and money.

Had to do the over 100 post. LOL.

I also subscribe more to the ............ if over 185 cranking compression you might be more susceptible to knocking conditions. But not a general rule either.

[Tim Corcoran]

70 Dream

I suppose by now you have heard enough opinnions to make your head spin. Since the engine has not gone to the machine shop yet I recommend that you do this:

1. Get in touch with one of the Pontiac engine builders and tell him what you expect from your total combo. Then have him recommend a camshaft for you. Then buy the camshaft from the place that made the recommendation. I recommend SD Performance.
2. Then the guy that sold you the cam can recommend a final compression ratio for your combo and your cam.
3. You may want to re-think your machinest as you should be dealing with a machinest that knows Pontiacs well.
4. Also it is very important that you tell your machinest that you want the pistons be set are zero deck, this may require that your pistons be machined with a D-shaped dish to set the proper compression level. This will allow your combustion to be more efficient, prevent detonation and make up for some of the HP lost by the reduction in compression from the factory level. Good luck and have fun with your Pontiac.

[Goin' Topless]

Originally Posted by Cliff R

"Cliff fwiw you seem to have good gas in Ohio. All our trips regardless of vehicle the fillups in Ohio net us our best MPG."

Yep, it must be good.

When my son Matt first got out of the Air Force, he worked here for most of the summer. I sent him to town regularily to fill the fuel cans for the Ventura, as I don't drive it to town that much with the DOT's in place. I specified 89 octane, or 92-93 if they were out of it.

It ran fine, and we even raced it a few times. Right before Norwalk this year, I sent him to town to fill the cans, and reminded him to get 93 octane instead of 89. He said "what?". Yes, 93 octane......then I find out he's been filling them with 87 octane all summer long!

Well, the 11 to 1 compression engine never minded it a bit. The only problem I noticed is that on the very hottest days, when I had the engine really hot, it would try to "run on" for 1-2 seconds, but not every single time.

Never once pinged at any load, rpm, etc.

One comment on the 400 engine with an 067 cam and early small chamber heads. We have customers managing pump fuel with early GTO's and that set-up. Some have minor problems, others none at all.

A few have upgraded to the larger 068 grind, or the Crower 60916 Bruce mentions, and a few on up to the 60243. None of those with the larger cams have reported any issues anyplace, and some of those engines are in excess of 10 to 1 compression with iron heads.....FWIW.....Cliff

X2 to what Cliff said. I run a 462 with 1971 #96 heads and a Crower 60243 cam on 91 octane (highest you can get around here) with no problems. SCR is 9.8:1. When it gets hot & humid in the summer, I add some octane booster for added insurance, but it probably doesn't need it.

You can play it safe somewhat on what parts you buy, but how you tune it will still be important for driveability and staying away from detonation.

[geeteeohguy]

Tim Corcoran, you absolutely nailed it. Perfectly put.

[64woodwheel]

I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane).

[grivera]

Originally Posted by 64woodwheel

I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane).

That's one beautiful engine compartment!

[72LuxuryLeMansLa.]

Originally Posted by JSchmitz

There's no such thing as idiot proof. You can only make things idiot resistant!

Nothing can "resist" my idiocy !

[bobzdar]

Originally Posted by 64woodwheel

I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane).

Any work done to the heads? Any performance numbers?

[64woodwheel]

The heads have hardened valve seats but no porting. Never had it dyno'd but I estimate it's in the 350/400 range.

[Cliff R]

"I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane)."

And it shouldn't have any troubles, as the real RAIV cam has over 80 degrees of overlap and 308/320 seat to seat duration.

With that cam you could easily go another full point on the compression and it would still run fine on pump fuel.

Have you ever performed a cranking compression test? Just curious what the results were?......Cliff

[64woodwheel]

Originally Posted by Cliff R

"I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane)."

And it shouldn't have any troubles, as the real RAIV cam has over 80 degrees of overlap and 308/320 seat to seat duration.

With that cam you could easily go another full point on the compression and it would still run fine on pump fuel.

Have you ever performed a cranking compression test? Just curious what the results were?......Cliff

That's what I've always suspected. I bought the engine already re-built. It has always seemed to lack some firepower. I think a stroker kit and higher CR would wake it up quite a bit. I've never done any serious diagnostics/tuning. Just timing.

[bobzdar]

Originally Posted by 64woodwheel

That's what I've always suspected. I bought the engine already re-built. It has always seemed to lack some firepower. I think a stroker kit and higher CR would wake it up quite a bit. I've never done any serious diagnostics/tuning. Just timing.

Start with tuning before you touch anything else. Another point of compression will gain you about 15hp, but I think the real problem is that unported heads don't have the flow for the raIV cam work properly. If you wanted to wake the engine up, I would port the heads before anything else or swap the cam for a slightly smaller one, but that's my take on it. I'm not a big fan of upping compression for power as the gains are pretty small and much larger gains can be found elsewhere. It's more the last step than the first, imo.

[Skip Fix]

"I have a .040" over 400 with stock #16 heads and ram air IV cam, q-jet w/ iron intake, 9:1 CR. No problems with pump gas (91 octane). " Gorgeous for sure. Even using 75cc for the 16s on Wallace Racing's CR calculator I get 10.2:1, unless it is way down in the deck height.

"The point is that the gasoline we have now is a little lower in octane, but not drastically lower in octane compared to the old days. There's only about 2 octane real difference between 1970's advertised 100 octane Premium(research method) and today's 93 posted octane Premium(r+m/2 method)."


Then why do so many older original setup motors Chevy Pontiac etc detonate like heck on it?

"I was unable to operate my '67GTO in its stock configuration (067 cam and closed chamber 670 heads) on pump gas without pinging. That was the original, never-been -opened engine, and 94 octane at the time." "When I tore it down for an inspection and freshen up, I found that it had four broken pistons, caused by detonation I never heard"

Another reason to why chance it unless you are class racing and need that extra few HP.

[bobzdar]

Originally Posted by Skip Fix

Then why do so many older original setup motors Chevy Pontiac etc detonate like heck on it?

Because a surprising amount of people that own these cars don't even know how to properly check their timing, let alone actually set a timing curve or adjust their carburetor. You can't expect to slap one of these engines together, set the timing by ear and slap a 30 year old unrebuilt carb or box stock edel/holley carb on and have it run properly. This is especially true with those that have a little knowledge and not a lot. So, you read on here that the best carbs to use are late '70's qjets, you can run 10:1 on pump gas as long as you're zero deck and then do those 2 things without really delving into the combo and you have a recipe for disaster. You pick a small cam because you want 'lots of low end torque' and don't rejet the carb which, being late '70's, is extremely lean in stock form and the engine either destroys itself or you have to run 20 degrees total timing and it overheats like crazy. Either way, you're unhappy and you blame 'high compression' for the problems.

I'm not in favor of pushing it on pump gas, particularly if you don't know how to properly tune a car. But, if you've got the tuning portion down and intelligently pick your combination, you can run 10:1 with iron heads and not have problems. If you're putting an engine together from scratch, picking the right compression can be worth 20hp, and it's virtually free or can actually cost you less depending on the parts you have. But, you have to know what you're doing.

The flip side is, if you're gaining more than 20-30hp max by upping your compression, even from 8:1, something was compromised with the original combo. So is it worth the 20hp if you're not confident in your tuning abilities or your combination of parts? No, probably not.

[64woodwheel]

Even using 75cc for the 16s on Wallace Racing's CR calculator I get 10.2:1, unless it is way down in the deck height.

I think the pistons were dished to get the 9:1.

[Cliff R]

"That's what I've always suspected. I bought the engine already re-built. It has always seemed to lack some firepower. I think a stroker kit and higher CR would wake it up quite a bit. I've never done any serious diagnostics/tuning. Just timing."

Install some flat tops with 2 small valve reliefs, zero deck height, shave the heads for closer to 11 to 1 compression, and your RAIV cammed 400 will have an entirely different "attitude as far as power production is concerned.

It simply takes some compression when using a 400 and a cam with that much duration, 113.5 LSA, and over 80 degrees of overlap.

We've worked with quite a few pure stock set-ups using the RAIV cam in the 400 engine, and they make fantastic power, and the vehicles they are installed in run great at the track. They also require plenty of gearing, and a stick shift or high stall converter to effectively use it.

Even with that said, we get more complaints from that CID/cam combination to our shop than any other, simply because they either don't squeeze them hard enough, or use enough gearing/converter behind them........Cliff

[64woodwheel]

Originally Posted by Cliff R

They also require plenty of gearing, and a stick shift or high stall converter to effectively use it.

I am running a 3:73 with a T56 .50 OD. 25.7" tire. One thing I do like is 2000 RPM @ 75 mph and 19 MPG. That's better mileage than my wife's Acadia! And it does have plenty of grunt at 2000.

[bobzdar]

Originally Posted by Cliff R

"That's what I've always suspected. I bought the engine already re-built. It has always seemed to lack some firepower. I think a stroker kit and higher CR would wake it up quite a bit. I've never done any serious diagnostics/tuning. Just timing."

Install some flat tops with 2 small valve reliefs, zero deck height, shave the heads for closer to 11 to 1 compression, and your RAIV cammed 400 will have an entirely different "attitude as far as power production is concerned.

It simply takes some compression when using a 400 and a cam with that much duration, 113.5 LSA, and over 80 degrees of overlap.

We've worked with quite a few pure stock set-ups using the RAIV cam in the 400 engine, and they make fantastic power, and the vehicles they are installed in run great at the track. They also require plenty of gearing, and a stick shift or high stall converter to effectively use it.

Even with that said, we get more complaints from that CID/cam combination to our shop than any other, simply because they either don't squeeze them hard enough, or use enough gearing/converter behind them........Cliff

What power does the raIV make with unported dport heads? I ask because I have a raIV cam and lifters, and if it'd make more power than the 744 with unported heads, I'd do the swap. However, nothing I've seen indicates that's a good move, regardless the compression run. Simulators indicated neutral power at best, with a loss of low end, and anything I've seen posted on that combo indicates it doesn't work that great unless the heads are ported or round ports/alu heads are used. I've driven a 400/raIV combo with unported dport heads in a very similar car to mine ('74 trans am 4 speed, 3.55 rear gears), and it was significantly slower (mine is '78 4 speed with 3.23's), though it wasn't tuned as well. If you have some dyno sheets of a raIV cammed 400 with unported dports, that would interest me.

[Skip Fix]

"I think the pistons were dished to get the 9:1."

I see! again a beautiful motor bet the rest is nice also.

"Because a surprising amount of people that own these cars don't even know how to properly check their timing, let alone actually set a timing curve or adjust their carburetor." But take a late 60s-early 70s 10:1 + motor with fresh rings, bearings, factory replacement cam,factory timing curve in the original distributor, factory jetting(not lean), factory deck -ie tuned as they left the factory -the difference in octane is going to make a significant difference. They will sound like you are running on bird shot especially when lugged and hot weather. They weren't designed to run on our current octane even if they use different rating methods, especially an 11+:1 302,LT1,409,427, and probably some of the higher compression Pontiac motors too.

As I've said before my RAIV 400- 231/239@ 0.050. cam, zero decked had no audible detonation-race gas added 8-10 HP so unless folks are doing a race gas trial on the dyno or track you really do not know if you are OK. If it doesn't need the octane it will sometimes even lose HP.

[Cliff R]

"What power does the raIV make with unported dport heads?"

It will make great power with unported "D" port heads, especially in a 455 engine.

We built and dyno'd one a few years ago with untouched 1973 # 46 heads. We did outfit the with 2.11/1.77 valves, but not sanding roll or grinder ever touched them, not even a port match.

The engine made over 440hp on the dyno and 530tq.

In a 400 engine, you simply need compression to effectively use the RAIV cam, and plenty of gearing and converter.

3.73's would be the absolute minimum gearing I'd want to see with that cam used in a 400, and at least 3000rpms stall speed, or stick shift. 3200-3400 stall would be even better.

It's not really about making more power over a 744 cam, which it will, it's about where in the rpm range it's going to make the power.....Cliff