Engine modding question

[redpoint5]

Originally Posted by Jorge89

I have a 1994 civic ex 4dr with a d16 engine in it. I was wondering if putting lightweight parts would make a noticeable difference in mileage. I was thinking about a lightweight gear cam and a lightweight flywheel. I've read that lightweight crank pulleys can be bad since they vibrate too much so I don't think I'll change that one.

My guess is you will never have enough fuel savings to recoup the cost of the lighter parts, but some of the value is in the fun of having better performance.

I've heard concerns about vibration damage from lightweight crank pulleys too, but I would think the tension of the belt on the pulley would either dampen the vibration, or the vibration would be negligible to begin with.

I put a lightweight under-drive pulley set on my TSX as an experiment and for fun, with no expectation of recouping the cost. If it gave me better fuel economy, my guess is it's in the 1% range, which is far too low to see amongst normal fluctuations.

You might look into lightweight wheels for your car. If you buy 'em used you should be able to recoup the cost when you go to sell the car. Performance enthusiasts often say that lighter wheels can be the best bang for your buck when it comes to handling and acceleration mods.

[dwarfnebula]

I bet savings of rotating mass are worth more than other weight savings, but if you put too light a flywheel on that thing you may have to bump the idle up to compensate for the lost inertia, which would probably defeat the purpose. Part of the point of a flywheel being heavy is to have some inertia to smooth out the motor at low RPM. The stock one isn't probably very heavy anyhow.

As to the cam gear, since it's spinning 1/2 of engine speed, very small in diameter and the stock one's pretty light to start with I expect any difference would be practically impossible to measure. Don't put one on unless you're sure about it's quality, I'd hate to have it come apart and bend valves for you. I've had some bad experiences and have become very picky about where I source timing components.

You said you like to improve things, in either of these cases I'd say you need to consider what your objective is. Neither a heavier nor lighter flywheel is better, rather a heavier one is better for one set of requirements (idle stability, smoothness, stall resistance) and a lighter one is better for another set (responsiveness, high RPM performance, maximum power) and that's just how it affects how the engine runs. I would bet a lighter flywheel is more prone to overheat and chatter, though I have no data to support my hunch. I know for sure though, there are lots of trade-offs and what's "best" is variable and based on your requirements.

X2 on the lightweight wheels. Cut down rotating mass where it's heavy and big around first, I'm confident that's where you'll see the biggest gains for the least effort.

[California98Civic]

Some time ago, before my transmission swap, I considered wheel swaps for our 1990s Civics. Your stock EX wheels, even if they are alloys are probably at least 16 lbs. Here is my list of adaptable wheels, with their weights:

Possible wheel swaps for gearing and/or weight advantages:
13" Civic VX 8 spoke (higher RPMs but only 9.7 lbs.)
14" Civic HX 8 spoke (approx 11 lbs)
15" Mini Cooper R81 Imola 7-hole (12.1 lbs)
15" Mini Cooper R86 star-spoke (15 lbs)
15" Mini Cooper R96 7-spoke (13.8 lbs)
15" Enkei Classic J-speed (14.1 lbs)
15" Acura Integra GSR (94-95, 16lbs)
Acceptable size ranges: bolt pattern 4x100, offset 35-45, lugs 12x1.5mm, center bore 56.1mm.

You can easily see that there are several options that will probably save you 4 lbs minimum. Multiply that x2 for rotational mass (some say x4) and you could realize a minimum 8lbs per wheel gain, 32lbs on the set, minimum, depending on there you started.