250 l6 potential

[noJeepshere]

My theory behind why the I-6 doesn't get the fuel economy based on size is that cylinders 1 and 6 are much farther away from the carb then cylinders 3 and 4. To compensate for any vacuum problems with the distance, the carb has to be tuned rich to make the end cylinders run correctly. My theory. That's why I'm going to put a vortec efi system from a 4.3l V6 on mine.

 

[dyeager535]

The straight sixes didn't live long into the 80's did they? Emissions standards might have been the cause for that if the runner distance was an issue, although it may have also been the advent of the 4.3. Don't know if the I6 and 4.3 were phased out/introduced roughly at the same time or not.

What's the difference in runner/port length on an I6 furthest cylinder from carb, and cylinders 1, 2, 7, and 8 and the primary sides of a Q-jet on a V-8? That's quite a run as well, although as I recall from a very few pictures, the I6 is quite long.

 

[noJeepshere]

Heck ya the gubbament regulations had something to do with it! And the 4.3 was introduced about the same time. I think maybe with the price of the aluminum head for the six, I'll get a 4.2 I6 from a TrailBlazer, hear one can get those for relatively little dime.

The difference in length on the runners is greater then for a V8, the sixes are really long, and the carb hangs on the side, instead of on top.

 

[mr.smartass]

I'm fascinated with the idea of doing more with less...

*cough* ricer *cough cough*

I was waiting for you to chime in on this thread.

 

[pauly383]

A 292 will make a lot more torque down low than a 305. But I doubt if it will match it in fuel economy. They are known as notorious gas hogs. I had one in and old work truck with a utillity bed. Even with the stock 1 barrel carb it only got 14 MPG if you drove it easy.

I'm lucky to get 13 mpg from 93 six lug K2500 pickup with the injected 350 , and thats with overdrive , 235/80/16's , and 3.73's . Don't matter if its freeway driving either

 

[jonrpick]

So what are the numbers for the 305 and the I6? I'd compare 350 as well because by all accounts, 305's and 350's end up getting the same mileage in these trucks. We already know the 6's don't do as well as you'd expect in mileage based on their displacement, which means they AREN'T efficient. I suspect you'll be pretty surprised at the 305 low end torque. Not sure if all were, I suspect yes, but the truck 305's were all 9.2:1 compression ratio, so if looking at another vehicle 305 just for comparison, make sure compression is the same.

The thing is, nobody has ever been able to say to me what makes an L6 more or less efficient, at least in regards to these trucks.

In and of itself, it's just an engine. It can be built to work in a specific RPM range and tailored to its application. No different than any engine, really.

From what I've seen, the 292 was put in a position to fail, at least in terms of 73-87 trucks. Put it in a 3/4-ton longbed with low gears for working and pulling, and have the thing try to do it all sucking through a 1bbl carb.

Doesn't exactly seem like a recipe for success.

In terms of efficiency, small blocks were (and are) constantly revised, both from the OEM and the aftermarket. L6's did not have much aftermarket support, and the OEM design didn't change much, if at all from the early 60's through the 80's. In stock form a 1986 K20 with a 292 would be a newer truck with a 20-year-older engine. (Combustion chambers and ports being two of the limitations of the original)

I see the mention of the AL head, but looking at Clifford, their rebuilt head is over $1000. You can do a V8 with Vortecs for less than that! On that note, the cylinder heads appear to have the same problem Oldsmobile does...outdated chamber design that doesn't perform as well as modern stuff, and that will ALWAYS be a hindrance to the motor. If whoever is making it is smart, the new head will have updated combustion chamber design, but when Edelbrock made their Oldsmobile stuff, they ignored technology in favor of the cool factor of aluminum.

The new AL head is supposed to be a bolt-on deal that improves performance. It'll be a 12-port design (no siamesed intake ports) and IIRC the ports will be raised some to improve the airflow around the short-radius turn.

Their previous Ford AL heads are being used in both daily-driver and performance applications with better-than-stock results across the board.

In any case, if a rebuilt stock cast iron 6 cylinder head is over $1000, I can't imagine a new, aftermarket AL head is going to be cheaper.

It won't be cheaper. I believe around $1400.

There is something to be said about doing things differently, but unless it's a show truck, being different doesn't mean it makes sense, at least to me. If you could get V8 torque down low (heck, V8 all around power) with mid 20's mileage, I'd be all about it, but that's just not the case.

Again, compare the 292 to a 305. Hell, bore the 292 out to 305ci and match the compression.

What you'd have is two very different engines with the same displacement, utilizing those cubes in two very different ways.

I want to see those two motors doing several dyno pulls with calculations for fuel consumption.

 

[jonrpick]

The straight sixes didn't live long into the 80's did they? Emissions standards might have been the cause for that if the runner distance was an issue, although it may have also been the advent of the 4.3. Don't know if the I6 and 4.3 were phased out/introduced roughly at the same time or not.

The L6 was discontinued for cost reasons. Solving those little issues like fuel distribution were not hard.

The 4-cyl version (181ci) is still in production as a marine engine. Guess what GM did? They redesigned the head, un-siamesed the intake ports, and added MPFI capabilities. It would've been pretty easy to do the same for the 'six'. They didn't because L6's wouldn't fit in the newer generation of passenger cars. V6's would fit. It made more the most financial sense to have only one family of 6-cyl engines.

 

[Thunder]

GM still has an Inline 6 still in production.
But I dont think anyone will say a Trailblazer with a 4.2 is a gas mileage champ. It gets some of the worst MPG of any other SUVs in its class. I think the V8 5.3 gets the same or better mileage. It puts out some impressive HP. but torque is lacking. My Toyota Highlander with a 230 hp 3.3 V6. Puts as much torque as a GM4.2L. It gets 26 MPG highway doing it.
Go ahead and build an inline. it is fun and they are very easy engines to work on.
But from my experience with them , I have built 3 good running performance inlines. Dont expect stellar MPG.
If you build a stock 250-292 with headers, small carb and very mild high torque cam. Yeah 20 MPG highway should be no problem in a totally stock truck. Throw some big tires, HD running gear and extra weight and the MPG will go down fast. So will performance.
If I were building a 6 cyl for MPG and performance I would go with the 4.3. Even stock in a truck they make more power and get better MPG than inline sixes did. Mabe thats why GM discontinued inlines in the 80s and went with the 4.3 V6 for so many years

 

[USSkoval]

The straight sixes didn't live long into the 80's did they? Emissions standards might have been the cause for that if the runner distance was an issue, although it may have also been the advent of the 4.3. Don't know if the I6 and 4.3 were phased out/introduced roughly at the same time or not. .

They actually made it almost through the eighties, through '88 for sure. I think it was only in the 1 tons though and it was a no-cost option over the 350. Pretty silly, but it explains why so few were produced later on.

 

[dyeager535]

The thing is, nobody has ever been able to say to me what makes an L6 more or less efficient, at least in regards to these trucks.

In and of itself, it's just an engine. It can be built to work in a specific RPM range and tailored to its application. No different than any engine, really.

Except that it's limited to what, two bore/stroke combos in the same block? (factory) A small block V8 had how many factory bore/stroke variations for people to play with, let alone cylinder head castings?

The new AL head is supposed to be a bolt-on deal that improves performance. It'll be a 12-port design (no siamesed intake ports) and IIRC the ports will be raised some to improve the airflow around the short-radius turn.

Their previous Ford AL heads are being used in both daily-driver and performance applications with better-than-stock results across the board.

It won't be cheaper. I believe around $1400.

So what did they do about the combustion chambers? Even the aftermarket realizes that the performance benefits of the "fast burn" chamber is a winner hands down, all the way around, don't tell me Edelbrock has a hand in these heads too.

Again, compare the 292 to a 305. Hell, bore the 292 out to 305ci and match the compression.

Better yet, compare apples to oranges, but as closely as possible. What was the best carbureted stock output of either engine? Look solely at torque if we think that is what GM was using the L6's for. There's not much reason to dyno, GM did it for us.

Never thought I'd use my old Chiltons again, but that's about all it was good for, it listed the various HP/TQ figures for all the engines for each year.

 

[3 on the tree]

This one gets 18-20 mpg, with 3.73 gears. In my 70 K5. One of 1229 made. 89K miles, with a Merc Marine head and 3" exhaust.I also added a HEI distributor

 

[jonrpick]

They actually made it almost through the eighties, through '88 for sure. I think it was only in the 1 tons though and it was a no-cost option over the 350. Pretty silly, but it explains why so few were produced later on.

The stuff I read was 3/4 tons only, and through 1987 in light-duty trucks...

 

[jonrpick]

Except that it's limited to what, two bore/stroke combos in the same block? (factory) A small block V8 had how many factory bore/stroke variations for people to play with, let alone cylinder head castings?

So what did they do about the combustion chambers? Even the aftermarket realizes that the performance benefits of the "fast burn" chamber is a winner hands down, all the way around, don't tell me Edelbrock has a hand in these heads too.

Better yet, compare apples to oranges, but as closely as possible. What was the best carbureted stock output of either engine? Look solely at torque if we think that is what GM was using the L6's for. There's not much reason to dyno, GM did it for us.

Never thought I'd use my old Chiltons again, but that's about all it was good for, it listed the various HP/TQ figures for all the engines for each year.

No, this is not an Edelbrock product. I need to get to work, but when I get home I'll dig up the link to the company. It's a smaller company. If Edelbrock were behind it, I'd expect the cost to go down. This company deals primarily (if not solely) with inlines.

 

[dyeager535]

The stuff I read was 3/4 tons only, and through 1987 in light-duty trucks...

1986 last year for 292 in our (US) trucks according to GM, which makes sense, since all motors after that were injected.

Used Dremu's page.

 

[jonrpick]

1986 last year for 292 in our (US) trucks according to GM, which makes sense, since all motors after that were injected.

Used Dremu's page.

Yep...forgot about that being the cutoff year for carbs.

The Brazilian and Mexican 'sixes' got TBI.

 

[dyeager535]

Yeah, TBI wouldn't have helped enough for our emissions more than likely if the runner length was an issue.

Not to mention that was the start of the second "horsepower wars" and GM probably figured the market wasn't great enough to make production profitable.

 

[USSkoval]

1986 last year for 292 in our (US) trucks according to GM, which makes sense, since all motors after that were injected.

Used Dremu's page.

According the the '88 bruchure on this site, it was still available (carbed) in the crew cabs and chassis cabs. I also remember seeing one for sale several years ago. Not all carb motors were gone after '87, there were still the '88 carbed Monte SS's and I once worked on an '89 Accord from Cali that was carbed. I'm sure there were others too.

 

[dyeager535]

I meant all trucks...certain US GM cars were carbed with Q-jets until 1990.

I was wrong though, obviously they had a carbed 454 then too, HD emissions I'd bet.

Interestingly, the L6 is listed as hecho in mexico, that may or may not have been available in the US. Dunno, doesn't make sense either way, since the 1987 GMC brochure doesn't list the L6, makes no sense to disco it for one year and bring it back. And that manual is not directed towards international sales as far as I can tell. I'm confused lol.

 

[original balzer]

Factory horsepower numbers are useless in this discussion. These guys are taking about "building" one, I doubt any of these guys would rebuild it stock.
Another thing to consiter is the years they where used where NOT a good era for HP or efficiancy. I dont have a book handy but I do know my 79 gmc with a 400 small block was only rated at something low like 140HP. My point is they wasnt even trying to make decent power in the 70's and 80's. At least not until the last of the 80's. Not to mention the sales of differnt engines would determine how much R&D a family of engines got. Im sure V8 powered trucks FAR out sold I6 powered trucks.
That brings me to a question about the thinking of the people who packaged trucks. "Why do they offer striped down no frills work trucks with LOWER power engines?"
wouldnt it make more sence to give the "work" trucks more power?

Simply put the market didnt demand improvments to these engines. I think if someone was willing to take the time to do it right the rewards would be just what he or she expected. I personally wouldnt bother with a 250 might as well start with the big boy and build a 292. One built correctly should make exellent torque. Torque would help a vehicle maintain speed, the easier it is for the engine to do that the less fuel it should burn, in theory. Real world results as we all know will tell a differnt story.

Here is how I would build a 292, bore it to a 305, 12:1 pistons a custom ground cam to support LPG, a custom long tube intake with close to equil lenth runners, and I would have to do some research on heads or head work. And finally a good header. I would run this engine on LPG only rather than any sort of dual fuel set up.

 

[3 on the tree]

Personally, I like the 250 better. It will rev, unlike the 92.

In my 70 K5, the 250 goes up a 12K foot pass in high gear, even if its only 35-40 mph.

A pretty good source for mild hop up parts is Mercury Marine. They used the 250 in quite a few inboard applications, and rated them around 165 HP.