Inertia is 1/2MV2 so increasing the V (velocity) of the air column is the best way to increase inertia. Make the exhaust pipe smaller, and jamming the same amount of air through it will require one of two things. Either that air will have to get compressed to fit into the smaller pipe (that's backpressure) or it will have to go faster to all get through in time.
In reality, both things happen. With relatively low exhaust flow at low rpm, the velocity helps scavenge the cylinder. At higher rpm, though, it takes too much energy to make the exhaust go fast enough, and backpressure starts to build.
Generations of hot-rodders have seen the small pipe/big torque phenomenon and wrongly assumed it was the backpressure causing the low-rpm benefit.
The whole air column inertia thing really only applies to the header primaries anyway. As you get farther down the exhaust, the air doesn't really have to stop when the valve closes, so its velocity is irrelevant. Bigger, at that point, is better at any rpm. There is a point where a bigger pipe won't help any more, but you can't boost torque by going smaller.
Lawnmower ManI'm 18 and have recently purchased the car I have wanted since the eighth grade, a Nissan 240SX. Because I've been saving money since the sixth grade, I now have some money to start working on my car. I was planning on buying 57C or 57S Gram Lights for my car. Would you recommend these rims? I don't want to spend too much money, but I want to have a strong rim.
I've been following Project Silvia, and plan on copying everything that seems to perform the best, but I do have a few questions. In the July '05 issue, you mentioned switching coilovers. I thought the JIC FLT-A2 coilovers sounded great but were just too harsh on the bumpy roads. Is that right? I was wondering if you have found a new coilover yet and if it performed just as well. (Something compatible with the EDFC or the TEAS would be cool.) The town I live in has really bad roads, due to frost heave and snowplows, so I'm very interested in a softer setup.
You were also going to get a different front anti-roll bar because it interfered with your oil pan. What bar are you using now?
I also noticed that you are now using 235/40ZR-17 Toyo Proxes RA-1 tires. Were the smaller (225) Falkens not enough tire?
Would you still recommend a 38mm offset with the wider tire?
I plan to start working on my car in the spring because it's in storage. Here in Duluth, Minnesota, it can be pretty difficult to drive a 240 up the steep, snowy hills, even with 100 pounds of sand and two friends in the hatch. Will project Silvia's handling stay the same with the softer coilovers or handle better with the wider tires? Hopefully you will have this sorted out by spring so I can copy you.
I would like to buy coilovers only once, since my main income is from mowing lawns.Ryan BradleyDuluth, MN
I've driven a few cars with Gram Lights, but haven't done anything dumb enough with them to be able to comment on their strength. Rays tends to build strong wheels, so I suspect you'd be fine. Gram Lights are actually not all that light, but any wheel that is both extremely light and cast aluminum is gonna get bent in Minnesota. On a lawn care income like yours, waiting for a sale on Gram Lights might be a good plan.