Just Like Frank's

[Fins]

I've never run regular (87) in the Cadillac. I always run the 93 octane. That's as high as you can get in pump gas here.

It originally was a 10.5:1 engine and it must be a shade higher now that it's new and the heads and block have been milled just a hair. They were cleaned up that's all.

Nothing wrong to warrant doing anything but a cleanup to them.

[Keeper]

There is a big Horsepower Sales place here,They take those crazy L motors like in the Vette,GTO
and those big Cads.To all kinds of crazy parmeters,and yes even 15-1.
I will say this,When I put 110 in the Cad,ANYONE can tell as it will rip off your face.
In my wifes 6cly,250 1967 Camaro,There was no improvement at all. 87 -110 NO DIFFERERENCE!!

[EXCRUISERGUY]

  I bet if I gave the engine a good top end clean I could get away with it more often.

I run a bottle of Seafoam through it every spring when I get it out of storage.
That could make the difference. I run the A/C all the time. My L99 was actually more sensitive to the fuel I used, but the LT1 doesn't care what's in the tank.

GJ

[trvlr480]

I ran 91 or 92 octane in mine for years until I found out, on this forum I could run the 88.  Now I run the 88 in the winter and swap back and forth between the 91 and 88 in the summer.  I heard some pinging on a tank of 88 so I went back to the 91 and just kind of mix them now.

[guidematic]

The old addage that ýou are wasting your money using higher octane in lower compression engines is true. Like Keeper and his wife's Camaro. An 8.5:1 engine will run no better on 93 octane than it will on 87.

But with the newer electronically controlled engines, that becomes somewhat confusing. Knock sensors detect detonation and can dial back ignition advance until knock is not detected, so you'll never hear detonation. However as in any engine, less advance translates to lower power and fuel economy. When ambient temps are cooler, you may get away with a lower octane, but if temps are high then the higher octane is required to get optimum performance.

Also, driving easy may negate the benefits of higher octane in some cases, but detonation can occur in light throttle applications as well as heavy applications. So that is not an exact science either.

Mike

[trvlr480]

You're right, Guide but I'm running 12 degrees advance and 36 total at 2500 rpm instead of the stock 8 degrees.  I've also got very weak springs on the dizzy's counterweights and installed a smaller bushing in the MSD's dizzy on the mechanical advance plate so it will advance further.  I actually had a broken vacuum advance diaphragm on this car for years and never even noticed it wasn't working.  It runs just as good with the vacuum advance disconnected.  At least I could never feel a difference.  I didn't feel any difference when I replaced the bad vacuum can either.

I still don't get any pinging on 88 except the one time mentioned above and with hypertutectic pistons I'm simply not going to take the chance with detonation over a few bucks per fill.  Hypertutectic pistons are quite strong but they have one weakness, detonation.  They are brittle due to the high silicon content.  They like to explode when exposed to detonation.  At least the earlier ones did.  I don't know about the KB's in mine but I've heard horror stories about the KB's as well.  I've also heard success stories with them but not as many.  The other weakness they have is that if the clearances are really off they will cock in the bore enough to wedge themselves in there and the top gets ripped off as the crank pulles the rod downward.  All of the above problems though, seem to happen in racing applications.

All that rattling you heard in the vid I posted was the result, I think, of not clearancing the hypertutectics properly.  They have very short skirts and tend to rock in the cylinder when the clearance isn't exactly right until they heat up.  It's the same reason so many GM cars in the 80's and 90's have had piston slap problems.  They started using hypertutectics way back in the Vette's in the 70's I believe because, supposedly, they seal better and are better for emissions.  I think the 70-72 LT-1's used them which is why I requested them be put in my engine when it was rebuilt.

Had I known then what I know now I would have just put the standard cast pistons in it.  So far though even with the cold rattling they have held up quite well considering the abuse the engine has had over the last 95,000+ miles.  Some engines last forever with the piston slap and others don't.  I'll keep my fingers crossed.

I just remembered I'm talking to a mechanic so I have probably just been singing to the choir.  Oh well.

[guidematic]

On my '70 I run 10 before with 36 degrees full advance, all in by 2200 RPM. Vacuum advance is hooked directly to manifold vacuum and it gives good part throttle response. Of coarse I also have HEI ignition lifted from a '74 Fleetwood intact, including the weights and springs.

With the compression what it is I have to be wary of detonation, hence the use of 94 octane gas when it's hot and I'm using the AC (which at the time is not working).

To be honest, I have not heard any engine, race engines included, that make that sort of racket. But it seems to be OK since you have driven it so many miles and quite hard. If there was going to be an issue with scuffing pistons I think that would have reared its' head by now.

Some engines are notorious for piston slap. One that comes to mind are the 500's. They have much of their skirt removed to compensate for the increased stroke. If they are not properly fitted, then cold slap will occur. It seems to be common with Chev 350's as well. I have had several over the years, and many of them did this, even the '94 will do it for a few seconds after start-up. Chev 292 sixes did it as well.

Another was the initial 4.9's. I replaced many piston/sleeve assemblies under warranty for this. They would rap pretty good for about 20 seconds, then quiet down. Of all the ones I removed, none showed any damage.

I think the worse were the early 3.1 V-6. The tolerances were so tight to prevent cold slap that they would scuff really bad when they warmed up. I replace many engines under warranty for that. The pistons were severely damaged to the point where they would loose compression and consume oil.

Mike

[trvlr480]

To be honest, I have not heard any engine, race engines included, that make that sort of racket. But it seems to be OK since you have driven it so many miles and quite hard. If there was going to be an issue with scuffing pistons I think that would have reared its' head by now.

I always enjoyed the sound of solid lifter engines.  The ticking and clacking.  I'm really not bothered by it at all.  It goes away once it warms up.  I suppose you're right that if it was going to be a problem it would have happened by now.  Maybe I should send a recording of it to the Guinness Book of World Records for the noisiest hydraulic lifter engine that hasn't blown up yet.

[Tailfin Joe]

 The  Cadillac runs good on 93 , but when I use octane booster you can tell the difference, in the old days 93 octane  was the "regular" Sunnco 260 was a little over 100 octane and it put lead in your pencil, I run regular in a lot of the late model cars over the years that require 93 and saw no difference in mpg , driaveability.

[Fins]

Sunoco 260 used to be 104 octane to compete with the 104 that Amarada Hess put out.

[guidematic]

 Yes, the octane numbers have changed in the last 40 years. I'm not up on the science, but the 93 or 94 we use today could be compared to the old Sunoco 260. The '70 required a 97 octane fuel, in which 93 would be sufficient today.

I like an engine to run as quiet as possible, an as such I don't much care for the racket of a solid lifter engine. Those engines are pretty specialised for all out high RPM performance. Something I have no need for.

Mike

[Fins]

I like an engine to run as quiet as possible, an as such I don't much care for the racket of a solid lifter engine. Those engines are pretty specialised for all out high RPM performance. Something I have no need for.

Mike

I contest this remark. Do I need to go dig up the youtube vid of you in the '70 flat out with the secondaries screaming? You were going so fast that you missed your turn.   

[guidematic]

Well, there are always exceptions, right?

http://www.youtube.com/watch?v=eOuAAIZgur4

Mike

[Fins]

Nothing like the sound of a wide open Q-Jet, or an 8V-71 with 6" straight pipes at 2300 rpm.   

[guidematic]

So true. So true.

Mike