mpg on a 370vs402vs427
05-24-2008, 12:20 PM
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mpg on a 370vs402vs427 trying to build other engine going to be pushing about 14 psi into it. not sure if i should do a higher stress little motor or big one going easy on it. but will be my DD so it will see good amount of miles. gas adds up fast over time. I can get a good deal on a 427. but how much more gas will it use vs a 402 or 370.
AS for how much power am i looking for. answer till i cant get it to the ground. so i will be turning up the boost till its a waste.
AS for how much power am i looking for. answer till i cant get it to the ground. so i will be turning up the boost till its a waste.
05-24-2008, 03:03 PM
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if your worried about mileage i agree u should find something else to commute with , as for mileage my heads and cam m6 3.42 346 gets 17 mpg avg highway and city, it doesnt matter how light footed u are it more takes more fuel to fill more cubes plus boost= more air/displacement=even more fuel
05-24-2008, 04:49 PM
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- Vehicle "X" at some speed on some road (lets say flat land) will ALWAYS require a constant "X" HP output.
- 100HP is 100HP, it does not matter HOW you get it (somewhere I read something about a small car only needs something like 35HP at 65MPH on flat land/no wind).
- So on a highway at constant speed, it really does not matter if you have 289 or 777 CIs, the vehicle will require the same amount of HP (lets say 100HP) to go your intended speed (65). If you supply more HP (101HP), you are ACCELERATING.
- Superchargers and/or heavy rotating assemblies will affect MPG to some point due to increased parasitic drag (Superchargers would be the big one here).
- Just as steady state takes "X" HP, "X" acceleration requires "X" HP. Again 289 or 777 CIs, HP is HP.
- Throttle % is the key. Leaving a stop light, if you always use 50% angle, you WILL be feeding a 777CI engine MUCH more air (and thus fuel) than a 289CI engine. You will also accelerate MUCH faster and thus reach your intended MPH quicker.
Now with all this said, I'm NOT going to try and say you won't loose MPGs with a larger CI engine (I'm not that stupid). I'm just point out that to outright say "don't buy a 427 because the MPGs will suck" is WAY too simple of an answer. My feeling is people blame CIs for heavy feet.
- 100HP is 100HP, it does not matter HOW you get it (somewhere I read something about a small car only needs something like 35HP at 65MPH on flat land/no wind).
- So on a highway at constant speed, it really does not matter if you have 289 or 777 CIs, the vehicle will require the same amount of HP (lets say 100HP) to go your intended speed (65). If you supply more HP (101HP), you are ACCELERATING.
- Superchargers and/or heavy rotating assemblies will affect MPG to some point due to increased parasitic drag (Superchargers would be the big one here).
- Just as steady state takes "X" HP, "X" acceleration requires "X" HP. Again 289 or 777 CIs, HP is HP.
- Throttle % is the key. Leaving a stop light, if you always use 50% angle, you WILL be feeding a 777CI engine MUCH more air (and thus fuel) than a 289CI engine. You will also accelerate MUCH faster and thus reach your intended MPH quicker.
Now with all this said, I'm NOT going to try and say you won't loose MPGs with a larger CI engine (I'm not that stupid). I'm just point out that to outright say "don't buy a 427 because the MPGs will suck" is WAY too simple of an answer. My feeling is people blame CIs for heavy feet.
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05-24-2008, 09:03 PM
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Kind of reminds me of those new Honda commercials where they show some clips of their Honda Indy cars racing around the track and quickly go to their hybrids and civics in the next scene. Could you be sending anymore of a mixed message talking about racing and going green with gas mileage in the same sentace?? haha
05-24-2008, 09:14 PM
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Hmmm ?? My 346 made 490 rwhp 445 rwtq and when I leave it in 6th with the cruise set at 70-80 I see 32-34 mpg. That's highway and mainly due to the 3.42 gearing with the help of a ud pully and Meziere EWP.
Don't ask about my city mileage. Its alright but it just seems my car doesn't become to fuel efficient until I let the computer take over by setting the cruise.
Don't ask about my city mileage. Its alright but it just seems my car doesn't become to fuel efficient until I let the computer take over by setting the cruise.
05-25-2008, 04:43 AM
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Now to the people who say who care about mpg on a V8LS engine. I care, i do alot of long trip driving. To my other house in the moutains. I have to stop one time for fuel at 26mpg. If i have to start carry gas cans some how in my car now its just a pain in the ***. which leaves me with a very nice car thats no fun to drive and deal with.
On the honda part i have a few , but that was not part of my question.
Now any people have info maybe if they went from a 370 to a 402 how much of a change it was.
Last edited by BigRich954RR; 05-25-2008 at 04:57 AM.
05-25-2008, 06:08 AM
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My 408 gets around 10mpg but I still need a tuner to lean it out. it is running way fat right now. but I do have a friend that has a 408 similar setup as mine. and he gets 17mpg, but he isnt in the throttle a lot.
