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Old 01-23-2017, 11:23 PM
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The newest generation of GM truck engines run an 11:1 compression ratio and use regular gasoline, no premium needed. Direct injection makes for an interesting twist in what can be done with compression ratio, cam phasing, etc.

As far as compression ignition. That has never been hard to do....when you don't want to. Remember, the lower the octane the more the fuel wants to explode at high cylinder pressures. Cetane and Octane are inverses of each other. Diesel fuel wants to explode, it is essentially VERY low 'octane'. The speed of the flame propagation is also a lot different between the two.
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Old 01-24-2017, 12:13 AM
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Lessee. Points in order as I remember them:
There were/are model airplane engines that are nearly true diesels. They run on a mix of ether, kerosene, and a lubricant. Highly efficient. I have a boxful of them from the old days. One is a .90 c.i. displacement that produces almost 2 horsepower. They are pure compression ignition, no glow plug, but they use fuel-air mixture, where a true diesel ingests only air, with the fuel injected after the air is compressed.

Converting gasoline engines to diesel is 99% failure. Just for starters, their crankshafts are not stiff enough, so you get nasty torsional vibration. Also the main and rod bearings are not sized to take the load.

Modern gas engines can use higher compression because of the compact combustion chamber shape that the 4-valve configuration allows. Two-valve engines have such a poor shape when combined with high compression piston crowns that a lot of ignition advance is necessary to get the whole charge burned in the requisite time. This leads to detonation problems, since the heat radiation from the initial start next to the sparkplug will light the charge somewhere else unless high octane gas is used. We used to convert 2-valve BMW motorcycle engines to twin sparkplugs to alleviate this, but not many engines will allow that. I still have one. It will run on 80 octane gas, whereas the OEM single-plug engines absolutely demand 94 or higher.

High test gas does not burn any faster or slower than regular grades. It just resists detonation better.

Diesel fuel is anything but "low octane" as judged by gasoline engine thinking. It consists almost exclusively of molecules far longer than octane; the cetane molecule is sixteen carbon atoms, octane molecule only eight. I guess you could say that it's low octane, because there ain't much if any octane in it.

Incidentally, the 4-valve configuration was used as far back as 1912, in an Indian motorcycle racer that won the Isle of Man race. The famous WW1 Liberty aircraft engine was a four-valve, as were the Allison and Merlin engines of WW2.
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Old 01-24-2017, 12:26 AM
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^^ Vespas benefits from a dual plug upgrade too.


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Old 01-24-2017, 12:56 AM
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Not to mention the requirement of looser clearances due to machining technology at the time, When you spun them up, you needed greater clearances ( and requisite thicker oil and higher oil pressure ) to assure that nothing touched.

They build WAY more horsepower today than we drove back then, they spin the bejesus out of then relative to our old hipo stuff, and yet they don't grenade.

That's not only a function of proper engineering, it is a huge testament to the uber precise machining the factories have made commonplace.
You said a mouthful. That was my career from 1993 to 2009. Stiffer blocks, stiffer cranks, multi-valve heads, overhead cams, und-und-und. But a major factor was upgrading their dimensional measurement capabilities so that they could force the machine tool builders to make more accurate parts. Now, for example, GM doesn't have to use several main bearing sizes at assembly to get the proper clearances. By 2006 or 2007 we were getting the blocks machined dead nuts to size. The machine tool guys hated our guts, but we got results. It was an exciting time, but outside the industry nobody has a clue. I might as well be speaking Farsi.
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Old 01-24-2017, 01:00 AM
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^^ Vespas benefits from a dual plug upgrade too.


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And 1970s Suzuki twins with that orange-peel combustion chamber and no squish band. I did it to a T-500 that I raced in Vintage classes in the late '80s. There were squishband heads for them, (sandcastings), but they were rare as hen's teeth.
Old 01-24-2017, 02:42 AM
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And 1970s Suzuki twins with that orange-peel combustion chamber and no squish band. I did it to a T-500 that I raced in Vintage classes in the late '80s. There were squishband heads for them, (sandcastings), but they were rare as hen's teeth.


My 79 iron head sporty liked it too.


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Old 01-25-2017, 09:20 PM
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You said a mouthful. That was my career from 1993 to 2009. Stiffer blocks, stiffer cranks, multi-valve heads, overhead cams, und-und-und. But a major factor was upgrading their dimensional measurement capabilities so that they could force the machine tool builders to make more accurate parts. Now, for example, GM doesn't have to use several main bearing sizes at assembly to get the proper clearances. By 2006 or 2007 we were getting the blocks machined dead nuts to size. The machine tool guys hated our guts, but we got results. It was an exciting time, but outside the industry nobody has a clue. I might as well be speaking Farsi.
I don't know how much you play around on the Internet, but I am starting to dabble in the LS Turbo arena, and one of the early guys playing down and dirty ( and I mean LOW buck, even reusing headgaskets..... ) runs a site called SloppyMechanics. His youtube channel would warm your heart if you see what the results of your work has made possible.

Just this week he threw a set of 210 Lb injectors in his turbo 6.0 Colorado to push it to 1K RWHP on E85.......... He got 992 before it got so lean he thought he lifted a head and took out one of his several times reused headgaskets...... After getting it home and yanked, he found the only damage was he had bent a rod. Tonight, the shortblock is back together with a spare rod from another blown 6.0......... He is going to put anew set of headgaskets on it this time.

Anyway, if you are bored, you might check out his YouTube channel, Sloppy Mechanics.
Old 01-25-2017, 10:18 PM
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http://www.roadandtrack.com/car-cult...wankel-engine/
"says it produces around 1400 hp in its current state of tune, but that number could triple with race gas and turbochargers."

Comment: Call me a dreamer; but I want one!
Old 01-25-2017, 10:22 PM
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I don't know how much you play around on the Internet, but I am starting to dabble in the LS Turbo arena, and one of the early guys playing down and dirty ( and I mean LOW buck, even reusing headgaskets..... ) runs a site called SloppyMechanics. His youtube channel would warm your heart if you see what the results of your work has made possible.

Just this week he threw a set of 210 Lb injectors in his turbo 6.0 Colorado to push it to 1K RWHP on E85.......... He got 992 before it got so lean he thought he lifted a head and took out one of his several times reused headgaskets...... After getting it home and yanked, he found the only damage was he had bent a rod. Tonight, the shortblock is back together with a spare rod from another blown 6.0......... He is going to put anew set of headgaskets on it this time.

Anyway, if you are bored, you might check out his YouTube channel, Sloppy Mechanics.
Yeah, finally. Interchangeable parts that really are interchangeable!

'Fraid my satellite internet hasn't the bandwidth to play happily on U-Toob.

But speaking of headgaskets - you might remember the rash of blown head gaskets in the V-6 they used in the early Ford Winstars. Their machine tools weren't machining the head deck so it was truly flat. The old manual method of gauging it didn't detect the flaw. We did. It was perilous to show these things up, because the corrective actions often cost millions~!
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Old 01-25-2017, 10:28 PM
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So why is premium gas recommended for so many engines still? Does it make much difference to run regular if premium isn't required?

I don't think I've ever seen e85. Is it high octane? Only for flex fuel engines? There was some controversy about going to e15 and I dfdfont think it ever happened.
Old 01-26-2017, 05:37 AM
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If the detonation resistance of premium gas isn't required, buying it is a pure waste of money. It burns with the same BTU output as regular.

The only engines I ever had that actually did produce more power with premium gas were turbocharged engines having a knock sensor as part of the electronic engine management system. My old late '80s Turbo SAABs had this combination. The knock sensor would back the ignition timing off when regular gas was used. That reduces power. I never did find out by how much. I always fed mine premium. A SAAB engineer, (SAAB was owned by GM then), told me that it did bad things for exhaust valve life to run regular in the Turbo SAABs. I suppose this trick could be applied to normally aspirated engines. Whether it has been I don't know.

Alcohol in fuel does raise the detonation resistance. It doesn't light up nearly as easily as gasoline. This is one reason that racing engines were run on straight alcohol for decades before and after WW2.

I remember E85 pumps in Michigan. Around Detroit they seemed to get the latest technology on the roads early, as a kind of beta test program I assume. I even had a couple of vendor salesmen who drove E85 GM cars back before I retired in 2009. Whether there still are any I don't know. (I fled Michigan within months of my retirement.) It's a lousy technology, so my guess is that it hasn't been pursued.
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Old 01-26-2017, 06:54 PM
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Computer controls mean engine timing adjusts for lower octane and there is no knocking. So when car makers recommend premium and you use regular, do you even notice a performance reduction? Do you run a little hotter and need more oil changes or anything?
Are you still doing oil changes at 3,000 miles or stretching that to 5,000?
Old 01-26-2017, 07:13 PM
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Most that call for Premium will run on Regular, albeit at a reduced power level, and yes, you can feel the difference. Doesn't require more frequent oil changes or run hotter, the engine management software just keeps he detonation at bay.

At least here, E85 is relatively available, I wouldn't want to be forced to find it to drive, but within 20 miles I know of at least 3 pumps.

E85, if it is really 85 percent is something like 116???? Octane. Lots of our racers are switching to it due to the cost versus race fuel.

What is really cool is several of the EFI units interface with the stock fuel sensor and you get a real time readout and fuel trim for the actual percentage of Alcohol in the tank, which varies load for load.
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Old 01-26-2017, 07:24 PM
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Computer controls mean engine timing adjusts for lower octane and there is no knocking. So when car makers recommend premium and you use regular, do you even notice a performance reduction?
Some "recommend" and some "insist" on premium. Retarding timing alone cannot always prevent detonation and I suppose that is why some absoutely require it.
Old 01-26-2017, 07:33 PM
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Converting gasoline engines to diesel is 99% failure.
Where does that number come from? There were many mainstream diesels sold in the US that got their start as gas engines. VW, Isuzu, and Nissan are a few. Might even include the Ford/IH 6.9 and IDI 7.3 diesels that was somewhat based on the 7.3 "high torque" gas engine used in school buses. The only one I am aware of that was a total failure was the Oldsmobile series like the 350. That being said, I've heard the 350 diesels make great gas engines when converted back to gas due to the beefed up parts.
Old 01-26-2017, 07:56 PM
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Where does that number come from? There were many mainstream diesels sold in the US that got their start as gas engines. VW, Isuzu, and Nissan are a few. Might even include the Ford/IH 6.9 and IDI 7.3 diesels that was somewhat based on the 7.3 "high torque" gas engine used in school buses. The only one I am aware of that was a total failure was the Oldsmobile series like the 350. That being said, I've heard the 350 diesels make great gas engines when converted back to gas due to the beefed up parts.
Well, I can't speak to foreign engines, except to say that the GM/Isuzu plant in Ohio that I supported for a while was the worst cluster&^%$ that I ever was associated with in my automotive career. That engine was 100% Japanese engineering, not a conversion, as far as we could tell. The documentation was badly translated from Japanese until GM stepped in and made them translate it properly.

Having had Navistar as another client, I'm more than a little sure that the IH/Ford engine you refer to was Navistar/IH all the way; the only similarity being that they were pushrod V8s.

I had a thing for the little diesel Rabbits when they first came out, but soon learned that they weren't notorious for long life, and they were unbridled he11 to start when it got cold. (My brother-in-law had one for a while, when we all lived in eastern Massachusetts.) I never had anything to do with VW, professionally.

Ditto Nissan. The Japanese refused to use our German gauging equipment, despite it being an order of magnitude superior to their own. Even Honda wouldn't buy German until just before I retired.
Old 01-26-2017, 08:06 PM
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And having had Navistar as another client, I'm more than a little sure that the IH/Ford engine you refer to was Navistar/IH all the way; the only similarity being that they were pushrod V8s.
I never said the 7.3 was not based on another IH engine. International Harvester had the MV-446 heavy-duty gas engine often used in school buses in the 70s. When Mopar stopped making the 440 often used in motorhomes, IH stepped in and marketed it as the "high torque 7.3." Same bore and stroke and block profile as the later 7.3 diesel.
Old 01-26-2017, 08:33 PM
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I never said the 7.3 was not based on another IH engine. International Harvester had the MV-446 heavy-duty gas engine often used in school buses in the 70s. When Mopar stopped making the 440 often used in motorhomes, IH stepped in and marketed it as the "high torque 7.3." Same bore and stroke and block profile as the later 7.3 diesel.
Perhaps IH built their gasser on a diesel shortblock? That would be easy-peazy. Bottom end ought to last forever. Would let them jump into a gas-engine market with minimal disruption to their manufacturing systems. (Developing a new block manufacturing process in the '70s took three to five years. If I could avoid that as an IH manager, I sure as heck would if a new market was available for capture.) But you may know those old engines better than I. We were dedicated to bringing a new, almost fully automated "flexible" engine block/head plant on line, and that was mid 2000s. We saw only a little of the older engine parts.
Old 01-26-2017, 09:30 PM
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I think the diesel rabbit only had 2-3 quarts of oil.
Old 01-27-2017, 07:56 AM
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I think the diesel rabbit only had 2-3 quarts of oil.
The 1.5 VW engine holds just short of 4 quarts of oil. It is a converted gas engine and started out as the 1.5 gas engine used in mid-70s VW Dashers.

The diesel uses the same bore and stroke, block, crankshaft, and rods as the gas engine. Less power and higher MPGs. I still have my 1991 1.6 diesel that is near the same engine but with longer stroke and larger head bolts.

1.5 gas engine: 75 HP @ 5800 RPM, 79 lbs. TQ @ 4000 RPM
1.5 diesel engine: 48 HP @ 5000 RPM, 58 lbs. TQ @ 2500 RPM
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