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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: dmerc]
#47667
02/12/08 04:32 PM
02/12/08 04:32 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
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Kalispell Mt.
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Between the Holley carb and big cam I think low 20s will be doing good. Holley carbs are bad on gas but yours is a little small so mabey it will be alright. The cam will make a nice compromise between HP and MPG. It has almost 30 degrees more duration than mine and that will knock off some of the super low rpm efficency.  I am guesing the tranny is a 833 od, that should help. .70 X 408 = 285 so not bad on the cruise prm VS displacement. Are you running a 2.76 or similar gear? Headers?
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: JD340]
#47670
02/12/08 09:35 PM
02/12/08 09:35 PM
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Joined: Jan 2003
Posts: 14,610
Not2farfromNashville, TN
Rug_Trucker
I Live Here
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I Live Here
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Posts: 14,610
Not2farfromNashville, TN
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I thought MARTA here checked at 2500rpm and idle.
"The only thing to do for triumph of evil is for good men to do nothing"
"NUNQUAM NON PARATUS!"
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: JD340]
#47673
02/13/08 03:36 AM
02/13/08 03:36 AM
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Joined: Jan 2003
Posts: 8,089
Sorrento, BC, Canada
4speeds4me
master
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master
Joined: Jan 2003
Posts: 8,089
Sorrento, BC, Canada
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Quote:
Didn't CC build a 69 Camaro or something that sniffed as clean as a comparable late 80's model? Probably got it somewhere here in the archives!
It was about 94 that article came out. It was carbed, ran 11's, IIRC, and sniffed to mid 80's V6 Buick standards. I talk about that one often, saying something like "It's not that it can't be done. It's that most of us are too lazy to try!"
2 Demons...no, not my kids! 
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: Clair_Davis]
#47674
02/13/08 04:35 AM
02/13/08 04:35 AM
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Joined: Mar 2005
Posts: 1,545
Seattle, WA
375inStroke
Special needs person
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Special needs person
Joined: Mar 2005
Posts: 1,545
Seattle, WA
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Quote:
But what's the BSFC for an engine at part throttle? I still haven't seen a good explanation of this aspect of engine/drivetrain design. My gut tells me it's not reasonable to say that because my 340 has it's peak torque at 4000, I should set my highway cruise at 4000rpm for best mileage. Somehow a 400hp Corvette can pull mid-high 20's on the highway while turning maybe 1500rpm. Torque peak on a Z06 sure isn't below 2Krpm. Until I can sort out how VE relates to a throttled situation, I'll stick to thinking that best economy is going to come at the lowest possible engine speed that you have good fuel control.
Clair
Lower RPM flows less fuel, yes, but if the engine happened to be at it's peak torque at the speed you were driving at, it would get better gas mileage. Lets say two similar cars were driving at 60 MPH and at the same RPM. One car was at it's torque peak and the other was under it. The one at it's torque peak would get better mileage. Now they both accelerate to 90 MPH. One car is above it's torque peak, and the other is at it's torque peak. The one at it's torque peak is now getting better mileage than the other car. We have much more to consider in reality than just BSFC and torque peak, but it is one of the many factors.
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: 375inStroke]
#47675
02/13/08 10:14 AM
02/13/08 10:14 AM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
OP
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Quote:
Quote:
But what's the BSFC for an engine at part throttle? I still haven't seen a good explanation of this aspect of engine/drivetrain design. My gut tells me it's not reasonable to say that because my 340 has it's peak torque at 4000, I should set my highway cruise at 4000rpm for best mileage. Somehow a 400hp Corvette can pull mid-high 20's on the highway while turning maybe 1500rpm. Torque peak on a Z06 sure isn't below 2Krpm. Until I can sort out how VE relates to a throttled situation, I'll stick to thinking that best economy is going to come at the lowest possible engine speed that you have good fuel control.
Clair
Lower RPM flows less fuel, yes, but if the engine happened to be at it's peak torque at the speed you were driving at, it would get better gas mileage. Lets say two similar cars were driving at 60 MPH and at the same RPM. One car was at it's torque peak and the other was under it. The one at it's torque peak would get better mileage. Now they both accelerate to 90 MPH. One car is above it's torque peak, and the other is at it's torque peak. The one at it's torque peak is now getting better mileage than the other car. We have much more to consider in reality than just BSFC and torque peak, but it is one of the many factors.
I sort of agree, if it was at the tq peak of whatever throttle angle you were running. Like was mentioned earlier in the thread, How was full throttle tq peak have anything to do with part throttle cruise  If you were to dyno the engine at 1/2 throttle and find a tq peak I think you would be a lot closer to the "ideal" cruis RPM.
Also for the guy with the 3.5 300m. That car is a lot heavier than mine for one. For two it has to meet emisions standards, noise standards, ease of mass production, bean counters. The 300m could get a ton better miledge if they put any effort in it, look at the LS powered camaros, I rode with a guy and even with goofin off a little it got 29 mpg on the highway at 75.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: HotRodDave]
#47678
02/13/08 11:08 AM
02/13/08 11:08 AM
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Joined: Feb 2003
Posts: 4,204
Fort Worth, TX
Clair_Davis
master
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master
Joined: Feb 2003
Posts: 4,204
Fort Worth, TX
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Bingo. If peak torque at WOT was the only thing that mattered - and that's almost always the only throttle position it's measured at - just dropping down a gear or two should improve mileage, right? We could all be driving PowerFlite 2-speeds or manual 3-speeds with 2.93 cogs. Again, I don't have any documents to back me up, but I think a lot more fuel is used with every turn of the crank than there is by changing the BSFC some small percentage. With all else being equal, an engine will use 50% more fuel at 4500rpm than it will at 3000rpm. I think one thing that's killing mileage on many new cars is that they're big, fat, heavy, pigs chock-full-o creature comforts that Average Joe thinks he needs because some corporate marketing wonk told him he did. Take out some of the cruddy worthless "features" of new cars and they'd get a lot lighter. Reducing unsprung weight, like giant, heavy  bLiNg rImZ , will make any vehicle perform better instantly in almost every respect, including mileage. Another thing that hurts new cars is that they pretty much HAVE to stick to 14.7:1 AFR to keep the catalytic converters happy for a long time. Steady-state highway cruising really can tolerate much leaner mixtures, but converters don't work well there, and I think it's NOX emissions that go up when it's lean. If you can tune your carb to pull 16-17:1 at high-vacuum cruise, you can really bump mileage up. GM did this in the late-80's & early-90's EFI systems, but had to disable the code for emissions reasons. The code is still in the GM computers, so I'm planning on enabling that feature when I get my tune better. Going from 14.7 to a conservative 16:1 is an 8.8% improvement right there. If you're getting 15mpg, now you're at 16.3mpg. If you're getting 25, now you're getting 27.2. That's a noticible improvement. Going to 17:1 is a 15.6% improvement... Oh, and before I forget, that's dang good mileage for that little car so far. I can't wait to see how it does once the carb and ignition are better sorted out.   Clair
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: HotRodDave]
#47683
02/14/08 10:03 PM
02/14/08 10:03 PM
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Joined: Jul 2003
Posts: 6,167
Maryland
GO_Fish
master
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Posts: 6,167
Maryland
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Quote:
Also for the guy with the 3.5 300m. That car is a lot heavier than mine for one. For two it has to meet emisions standards, noise standards, ease of mass production, bean counters. The 300m could get a ton better miledge if they put any effort in it, look at the LS powered camaros, I rode with a guy and even with goofin off a little it got 29 mpg on the highway at 75.
Dave, I wasn't refering to your build, I was referring to DMERC's 408 stroker.
However, the 3.5 in my 300m has 10:1 compression (just throwing that out there), and it's curb weight is 3577 lbs. The curb weight for the Avenger R/T with the 3.5 is 3355 lbs. And both average 24 mpg highway. They can get more or less at any given moment depending on the situation. How much does your car weigh in at?
Per the Moparts archives, 67-71 A engined A bodies weigh 3000- 3200 lbs. Do you feel that weight saves that much more gas than aerodynamics?
Last edited by GO_Fish; 02/14/08 10:08 PM.
Scott B.
"I'm a self-made man... I started with nothing, and I still have most of it!"
68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph
69 340 GTS stock 14.18@ 95.60 mph
01 5.9L Ram 1500 Quad Cab 4x4
01 3.5L 300M 16.23@ 86.97 mph
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: GO_Fish]
#47684
02/14/08 11:35 PM
02/14/08 11:35 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
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OP
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Asumeing he builds a 408 stroker with a .70 overdrive. That motor if built to the same compression A/F ratio cam ect... It could potentially use less fuel than my motor is useing right now. It will only be makeing %70 of the strokes as mine at cruise. .70 X 408 = 285.6 cubic inches displaced every drive shaft rotation where mine displaces 323 cubic inches every driveshaft revolution. The only thing is he is going to build compromises into his combo that are different from mine for the sake of performance. His heads are bigger and will flow at a lower velocity than mine are flowing now. His cam will be more duration and overlap that will hurt efficency, he is also going to a lower gear ratio. I don't think his combo will get as good as mine is getting but if he keeps from  he may not do to bad like low 20s. As for the weight thing I think it makes more differance in town. My car the day I bought it we weighed it with a full tank of fuel and it weighed 3060. Since then I have added a 8.75 rear but removed weight via aluminum intake lighter Neon buckets and a mini starter from the front as well as lightening up the rotateing assy a few pounds. I think it is probably around 3100 pounds with a full tank now. It is also sitting a little lower to the ground now. I do think areo is part of the reason for the big drop from 65 to 75 mph. but not all of it. The 300M can not run as lean as my motor because a lean mix will over heat the cat and make the NOX emmisions go up. I set my carb up with the smallest jets and biggest rods I could find and lowered the metering tree till it started to lean miss and then brought it back up a hair so I know it is cruising on the ragged edge of lean right now. It is funny that the problems I expected to have are not being problems at all. No burnt valves no pinging it still makes good hp whenever I want it  Just some stupid periphrial junk 
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Super duper gas miledge 273/318 experiment !!! UPD
[Re: dmerc]
#47686
02/15/08 03:04 PM
02/15/08 03:04 PM
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Joined: Jan 2003
Posts: 5,393
Pikes Peak Country
TC@HP2
master
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master
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Posts: 5,393
Pikes Peak Country
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Quote:
How does that compare with your cam?
Yes, what are the specs on that 273 cam?
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