Use of 110 Octane Leaded in 327

[Clem Z.]

Re: matching the engine components

yes they did that plus they also used a lower dome piston than was used in the 11.25 engines with cast iron heads. since the heads are aluminum you need a composition head gasket not a steel shim type and most composition head gaskets are close to the same thickness.

[Duke W.]

Re: Is no lead regular "greener" than no lead prem

The petroleum industry said they could only produce unleaded gasoline of about 91 RON, given the rapid transition that GM was pushing. I don't know if the fuel industry was dragging their feet, but that was the basic compromise that GM worked out with them. Thus, all engines had to operate on 91 RON, which required all high compression engines to drop about two points from their 1970 levels. Lower CRs also helped reduced NOx emissions, and most OEMs were struggling to meet emission standards in that era.

Beginning in the early seventies, gas stations installed a third pump for the unleaded regular while still selling leaded regular and premium, but EPA had established a schedule to phase lead out of gasoline completely, which was completed in the mid to late eighties. I recall in CA the last leaded premium available was 92 PON from Unocal, but I think the lead content was only 0.1 gram/gallon, By this time unleaded premiums were available at other brand stations rated at 91-93 PON, and the third pump was used for the 89-90 octane midgrade.

Duke

[Clare Carpenter]

Why not a hydraulic cam with lower CR HP engines?

Since GM lowered CR's primarily to help achieve emission standards and not use leaded fuels, why not use a hydrualic grind cam instead of the solid LT-1 in the "LT-1" optioned Camaro's and Corvettes? Chevy had some nice hydraulics already on hand. Obviously it wouldn't have been an LT-1 any longer and perhaps they had a boatload of LT-1 cams to use up. Marketing had something to do with it I'm sure, but wouldn't a hydraulic cam work better with a lower CR and help to lower emissions even further?, or is my thinking all screwed up. I like to understand more how this stuff works.

[Duke W.]

Re: "Charge" Composition

Nitrous oxide (N2O, not NOx) provides extra oxygen, so if additional fuel is added the engine will make more power. An obvious question is: Why not just inject pure oxygen? The answer is that combustion would be too fast and cause the engine to detonate. N2O is stored at high pressure and as it is released into the manifold it cools and cools the incoming mixture, which reduces the tendency to detonate. In the combustion chamber is takes time for the N2O to disassociate and free the oxygen molecule, and this limits the rate of combustion to a level that doesn't create destructive detonation. If pure oxygen is added, combustion speeds up to the point peak temperature and pressure increase too fast and the engine detonates. That's also why hydrogen is not a viable fuel for IC engine combustion. It burns very fast and has poor detonation resistance, so compression has to be kept so low that thermal efficiency is very poor.

Nitrous oxide injection was first widely used by the German aviation industry in WWII to provide extra power for emergencies. The US approach was to increase boost pressure and inject a mixture of water and alcohol to cool the mixture and keep the engine out of detonation. Water/alcohol injection was used for takeoff power on multiengine aircraft, and fighters had a "war emergency power" setting that could be obtained by pushing the throttle through a wire stop. Water/alcohol injection and overboost provide extra power to escape the enemy in a bad situation, but was only good for a few minutes before the engine would overheat and be damaged.

Nitromethane also carries oxygen and burns very quicky. If you dump in enough extra fuel it will provide a tremendous amount of energy, but rapidly overheats the engine. That's why Top Fuel and Funny Cars swap out the pistons after every run, and it's not uncommon for them to burn one or more pistons during a run. The average life of one of those pistons at WOT is no more than about five seconds.

I dont understand you last question. Usually it would be phrased as: How do we maxmimize BMEP across the range with a given fuel octane. The answer at WOT is to keep the timing on the ragged edge of detonation at all time. Modern electronically controlled engines with knock sensors do this, and this is one of their secrets to excellent torque bandwidth and fuel economy. The centrifugal and vacuum controlled ignition maps of our vintage Corvettes are much cruder, and will always require a compromise. For a given engine configuration and fuel aoctane, all you can do is juggle the initial timing with the total centrifugal and then play with the rate of centrifugal to get it all in as soon as possible without detonation.

Duke

[Duke W.]

Re: Why not a hydraulic cam with lower CR HP engin

Emissions were not the primary reason, just part of the overall strategy. The LT-1 probably barely made it. I believe the reason it was originally announced for '69, but didn't show up until '70 was probaby emission compliance related. I'm sure if GM replayed the tape they would not have even bothered with the LT-1. Same for the Cosworth Vega. Both ended up being very expensive money losing products due to the high cost of achieving emission compliance, and the resulting high cost to consumers made them poor sellers.

The LT-1 did disappeared after '72, and emissions was claimed as the culprit. The longer valve timing and overlap on LT-1 made it tough to meet standards. Actually, high overlap cams reduce NOx because they essentially create an internal EGR system due to higher exhaust gas residual at low revs and high manifold vacuum. In fact, this was used in the early seventies as an NOx control strategy on some GM engines, but the LT-1 was high on HC and CO, which is probably what led to it's demise. It was replaced with the Quadrajet-equipped L-82 in '73, which was essentially a lower compression emission controlled version of the '69 L-46. The Quadrajet was designed in the early emission control era, and had specific features to provide tighter air-fuel ratio control in the idle and off idle range where emissions are primarily tested. The Holley architecture did not provide precise enough control to meet emission standards.

Another factor was the cost of emission certification as each engine must be certfied and run through the 50K mile durability tests. By '75 there were only two engines left - base L-48 and L-82, and in some years L-82 was not available in CA due to emissions. It got so bad in 1980 that even L-48 was not available in CA; 1980 CA Corvettes got a common 305 CID engine that was used in several other Chevrolet models. It was the only V-8 that Chevrolet certified to CA emission standards for that model year.

Duke

[Dennis C.]

Re: A couple of questions for Dennis-Thanks

Clare - OK, This may all kind of run together, but, for what it cost: Since I typically plan to drive the car, I do rear end ratios at 3.08 to 3.55. That is because I spend most days cruising @ 60 - 75 mph when going on long outings. I would not suggest these ratios for a Saturday night special, but that is a whole different subject. I have the compression lowered to about 9.5 to 1 static. I won't argue over a point higher or lower. I fill with unleaded premium and head down the road. Close ratio T-10 and 3.08 screw will not light up the tires too easily, but standard ratio T-10 works great. Typically, almost every other item on the engine is OEM - '097 Duntov cam, heads, etc, etc. Next time I will try Duke's cam suggestion. My closing comment on 11.25 compression ratios. I love 'em - however, left a set of piston ring lands in Iowa AND I was adding way too expensive crap into the fuel at that point. Bottom line: If you just want to drive and enjoy the car, lighten up a bit. If you want to fiddle with a match race car, email me... Woops, forgot MPG - as described: 17 +/-

[Dennis C.]

Re: CR vs power

Gee Whiz Dickie - What do you mean by Nitrous Oxide? Sounds like some sort of chemical that should be banned from the planet Earth... Of course, I have no idea what this product would possibly be used for...

[Joe C.]

Re: "Charge" Composition

Duke:

Thanks for the excellent, and as usual, detailed discussion. Also thanks for the N2O clarification, but the N2O molecule is composed of 2 nitrogen atoms, and 1 oxygen atom, so, when it dissociates, it will create O atoms. Oxygen molecules exist in their natural state, as O2, with a double (or possibly single) covalent bond holding the 2 atoms together.

It has been a very long time, but I remember when my thermodynamics prof. (Dr.Carl Wojan, God bless his soul) discussed the effect of spark timing on BMEP (Brake Mean Engine Pressure). He always said, to jack up the timing to the point of detonation, back it off a notch, and leave it there. I have followed that good advice ever since. What with today's knock sensors, the PCM will now automatically optimize the timing.

One experiment, I did with my '85 (L98 with ECM/TPI). Given, the price of hi test vs. regular fuel. Given, that the ECM will adjust the max advance to compensate for fuel octane levels. I found that the increase in fuel economy with hi test did not compensate for the additional cost. The power differential was barely noticeable. In spite of this fact, it still makes me feel better to fill 'er up with Amoco Ultimate (the '85, that is).

[Duke W.]

Re: "Charge" Composition

At the temperature and pressure in the combustion chamber I don't think the oxygen atom that disassociates from the N20 molecule has enough time and/or it is too energetic to combine with another oxygen atom to form an O2 molecule, so it is ready for immediate reaction with any available hydrocarbon radical, and, of course, the O2 molecules from the air must disassociate to oxygen atoms before they can react. The one thing I'm not sure about is whether N2O disassocitaion is endothermic or exothermic. A certain threshold energy is required to initiate disassociation, and I belief there is a net release of energy, but I haven't been able to confirm it - haven't found a reference on N2O formation or disassociation that includes the net energy flow.

Your professor's advice is still valid for pre-knock sensor cars. In modern cars the knock sensor and microprocessor is constantly adjusting the timing in essentially real time to keep the engine operating at the ragged edge of detonation or a programmed maximum advance value for all speeds and loads, which will make the most power for the least fuel.

Several friends, at my suggestion, have begun using regular unleaded fuel in their modern premium fuel cars. I cautioned them to listen for detonation and further warned that the car might not feel as peppy, but none claimed to notice ANY difference in engine performance and no detectable detonation, though none I could consider "aggresive" drivers.

I note in Chevolet's published specifications for the new LS2 that the CR is 10.9:1, and premium fuel is "recommended, but not required."

Duke

[Duke W.]

Re: A couple of questions for Dennis-Thanks

Your points are well taken, Dennis. My philosophy is to push the CR as far as possible, even if I have to make timing map adjustments. Then I still have the option of doping the fuel and bumping the timing for more power, but if you build a SHP engine with a true 9.5:1 CR, you can run a fairly aggressive timing curve and not worry about detonation with pump premium. This allows no hassle drving anywhere.

I, too, like 3.08 gears and that's how I ordered my L-76 SWC. With a 76 MPH first gear at 6500, it's no drag racer, but I love the relaxed 3100 revs at 80 MPH cruising and the 20+ MPG it yields. Plus, back in my "wild and crazy days" I never lost a rolling start street race as long as I had open road in front of me.

Duke

[Joe C.]

Re: "Charge" Composition

Duke:

I don't remember either, whether the reaction is endo/exothermic, but that is far beyond the parameters of this forum. Your explanation, from a themodynamic viewpoint is valid, as far as I can determine.

Practically speaking, re.: the LS2 : I am absolutely sure that Chevrolet Engineering would be delighted if all Corvette owners would fill their tanks with Amoco Ultimate (which will, of course, enable the PCM to maximize spark advance). This will produce a marginal power increase, and maximize fuel economy ( although the vehicle owner may not realize that reguler fuel MIGHT be more economical).

[Dennis C.]

Duke - Agree, Agree, Agree... Best, DC *NM*

[Duke W.]

Re: "Charge" Composition

Several years ago I think it was Car and Driver that did an interesting test using regular in premium fuel cars and premium in regular fuel cars. I recall that they tested fuel ecomonmy and at least made subjective evaluations on perceived performance. The results were conflicting to say the least and there wasn't a common denominator other than some (recommended) premium fuel cars got better fuel economy on regulator.

Though they made no mention of this possibility, I have one oil company document that says that some regular grade blends have a bit more energy content than some premiums, and higher energy content will definitely yield better fuel mileage.

Duke

[Joe C.]

Re: "Charge" Composition

Duke:

I'm sure that test was done with engines equipped with knock sensors, otherwise, the engines specifying premium fuels would (probably) detonate with the regular, effectively killing fuel economy (among other things). Subjective testing will definately be subject to the "placebo effect". After all , a car with loud mufflers at 70MPH is travelling a lot faster than a car with quiet mufflers at 70MPH. Right? So, yeah, once you fill 'er up with the hi test, dag nabbit, that ole motor immediately picks up 50 HP.

I also remember a C/D article on fuel economy written by either Pat Bedard, or the then tech. ed. Don Sherman. This was written in the era of the "gas crisis". It showed how the same car, same day, same route (round trip, to cancel topological effects), same brand fuel, same driver could be driven "normally", and "economically", with dramatic differences in mileage. Best tip that I remember was to accelerate on the downhill, and coast/maintain speed on the uphill. These guys obviously never heard of cruise control

[Ralph Harlan]

Re: Is no lead regular "greener" than no lead prem

Even in the early '60s AMOCO sold "white gas" in a "premium". The octane rating was higher than any other "premium" available at the time, and was the choice gasoline for all the local "hot rods" with super high compression in the Atlanta, Ga. area - other than avgas. SUNOCO premium was second choice to the AMOCO, but was not found in the Atlanta area then.

Same AMOCO "premium" was an alternative to the more expensive "COLEMAN fuel" for our boy scout stoves and lanterns - and actually gummed the generators less than the COLEMAN brand fuel.