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Old 09-09-2010, 02:11 PM   #1
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fully built to stock specs.. gas saver????

hello im new here and with out a search bar i refuse to waiste time looking for my answer and decided to ask.

it might be obvious but w.e .... IF you fully build a motor with the best all motor parts "at least block wise" and kept it within factory piston size and compression ratio and rod lenth and stroke length but got new lighter parts would it benifit a whole lot? aside from tuning n going dizzy-less n headers and blah blah ... i no its a very expensize route but "when i win the lotto i would do it" ????
also does a very light weight flywheel cause you to rev higher from a stop to go?
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Old 09-09-2010, 05:47 PM   #2
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Re: fully built to stock specs.. gas saver????

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Originally Posted by redfiya View Post
hello im new here and with out a search bar i refuse to waiste time looking for my answer and decided to ask.

it might be obvious but w.e .... IF you fully build a motor with the best all motor parts "at least block wise" and kept it within factory piston size and compression ratio and rod lenth and stroke length but got new lighter parts would it benifit a whole lot? aside from tuning n going dizzy-less n headers and blah blah ... i no its a very expensize route but "when i win the lotto i would do it" ????
also does a very light weight flywheel cause you to rev higher from a stop to go?
IMHO I would think the gains would be around 2%. Reciprocating Mass Loss is a small part of the pie when it comes to today's engines running at the low OEM rpm range. Now as far as racing goes with high reving rpm engines good gains can be made. EDIT For making HP not FE.

The biggest loser when it comes to today's engines is the loss of energy in the form of heat. Not much fuel energy makes its way to the flywheel. Most of it passes through the engines block and head and out the exhaust.
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Old 09-10-2010, 08:10 AM   #3
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Re: fully built to stock specs.. gas saver????

The quickest and cheapest FE mod is a taller ring and pinion. This reduces throttling losses, and reduces engine friction more than adding light weight components.

Leave the engine alone and change the tranny or diff.
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Old 09-10-2010, 10:04 AM   #4
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Re: fully built to stock specs.. gas saver????

What kind of motor are we talking? It sounds like you might be talking about an older V8.

Anyhow, generally speaking the reciprocating mass is usually most important when it comes to higher RPM, higher HP applications. For fuel economy, it doesn't play a major part.

You would be better off looking at a few other things. Camshaft design, for example, is critical. And I picked up about 2-3 MPG by using Rhoades lifters on my big block (although that figure will vary according to several other factors).

If you have the ability to raise your static compression, that will generally help also - however before making that change I would also make sure that you have the ability to control timing. In my personal opinion, most modern engine control systems already rely too much on the knock detector, and if you raise CR any more than you would just be increasing your knock.

At a stoplight, flywheel mass doesn't matter much - the flywheel will have a given rotational inertia, and inertia doesn't require energy (given steady RPM). The time a lightweight flywheel will matter is when you are changing engine speed, since an engine with less inertia (i.e. lighter weight) will change RPM more easily.

One other change that might be beneficial is to get custom pistons with the top ring land higher up. Do this with caution, however, since that will also weaken the land and be more prone to collapse. If you drive your car hard sometimes, or if you don't have your knock under control, you don't want to make this change.

-Bob C.
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Old 09-12-2010, 02:59 PM   #5
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Re: fully built to stock specs.. gas saver????

Ok, cleaned up the thread.

redfiya, it was rude to expect everyone else to spend time when you said your own time was too important. Everyone else, he doesn't need to read any more about it.

Let's have some tech talk in here now.
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Old 09-12-2010, 08:48 PM   #6
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Re: fully built to stock specs.. gas saver????

I prefer a lightweight flywheel for FE because it lets you accelerate a little quicker. To get the most out of it, try shifting at lower rpm. The light flywheel should let you get up to cruising speed without needing to rev it up as high, and high revs will kill FE.
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Old 09-13-2010, 07:02 AM   #7
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Re: fully built to stock specs.. gas saver????

Get your parts teflon impregnated - piston skirts, rings, wrist pins, gears etc will make a big improvement.
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Old 09-13-2010, 12:38 PM   #8
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Re: fully built to stock specs.. gas saver????

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Get your parts teflon impregnated - piston skirts, rings, wrist pins, gears etc will make a big improvement.
My engines pistons tops and piston skirts are treated for this reason. Unfortunately I can't tell you how much of an improvement its made because of all the other mods that were done at the same time.

I think the whole ICE engine needs to be revamped. There are only so many things we can do to this old technology.

I think you could see gains by utilizing light weight engine parts. But you couldn't stop there. You would also need light weight drive-train parts etc. Then ultimately a light weight car. Then you could run with a lower torque engine and save on fuel.

Lower torque engines have some great advantages by utilizing light weight drive-train parts, with less drive-train loss to the wheels.
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Old 09-16-2010, 04:53 PM   #9
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Re: fully built to stock specs.. gas saver????

Depending on the engine I would keep the flywheel the same (or heavier) as a light weight one will allow you to speed up quicker but it will also slow the engine faster when coasting in gear. If you are going through the hassle to replace the pistons ect get it balanced and up the compression.

Most of this is going off of a high TQ low RPM car but over all it depends on the stock characteristics of the motor, transmission, and weight of the vehicle.
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