By Zippy (Zippy) (205.188.197.184) on Tuesday, September 18, 2001 - 11:24 am:

Ok, I was hoping someone could explain the whole gear and diff ratio thing to me. I lost the differential in my '94 Isuzu pickup (Tippy 33HS). I am told mine is a 4.10. My year comes in either 4.10 or 4.30. What do these numbers, 4.10, 4.30, 4.93, mean? How do I calculate the differential ratio? The junkyard quoted me $650 for a rear end so I am thinking of putting on a domestic rear end. My speedometer dosen't work anyway, so a small difference in the drive ratio would not bother me. (Todd?)

By the way, I just bought a '01 Sentra SE with the perfomance package. I am in love. The road feel is so good. Acceleration is great. Handling is supreme. I can't keep the revs down. I sort of wish I had waited for the SE-R with the V spec to come out for '02 but I needed a car. I also need a name for this car.

I am taking it to the races soon. I hope one day I can beat it in Zippy. That will be a proud day.

Roger

By Todd (63.50.56.243) on Tuesday, September 18, 2001 - 01:14 pm:

Hey Rog, the differential is basically a reduction for the revs of the driveshaft in your case. For every 4.10 times the shaft spins, the axles rotate once. In the case of our Hondas, for every 4.93 times the mainshaft spins, the diff(which is directly coupled to the axle) spins once.
Math:6000rpm / 3.00(1st gear) / 4.933(final drive) = 405.4 wheel rpm.

Now try 6000/3.00/3.875(lower number = higher gear) = 516.1 wheel rpm.
From this you can see that at the same rpm the two differentials reduce the torque differently. This is why the 4.93 is better for acceleration because you get to 400 rpm quicker than 500 rpm.

By Zippy (Zippy) (205.188.198.164) on Tuesday, October 02, 2001 - 12:21 pm:

So I work with regenerative blowers occasionally and it occurs to me that they would make a good supercharger. I looked around and and found a couple of kits for newer civics for way too much money. So I started thinking about building one myself. I tried to calc how much air a 1200 needs. Say it is modified to 1400 cc then: 1.4 liters, times 7000 rpm, times 0.26 gal/l, times 0.1337 gal/cubic ft, gives roughly 300 cfm. However, I realize that air does not enter the cylinder at atmospheric pressure so you need a bit less air - roughly 50% I'd guess. pv=nrt. Any ideas????

Roger

By ddechon (12.78.180.111) on Tuesday, October 02, 2001 - 12:54 pm:

Hey Roger

Air Density changes with tempurature and pressure. But I don't know how that effects you.

I don't think you want the fan to be constant. The fan should change speeds with the engine...like a blower. So I'm guessing it should belt driven rather than electric.

How much flow do other kits kick out? That might give you an idea of what your car needs. Plus I think they use a different value. I always hear about values in psi. So if you want to sustain positive pressure, your fan flow should be slightly above your engine flow.

There are many conversion calculators online. At work we use a program called "Convert." It might be a free download if you can find it.

Darrell

By Todd (63.50.56.76) on Tuesday, October 02, 2001 - 01:36 pm:

Hey Rog,
I've got a small program I can send you e-mail if you want. It says @ 1.4l, 7000 rpm, 7.5:1 comp ratio will produce a power peak @5800 rpm and require 172 cfm. At 12 psi, it requires 303 cfm, and at 20 psi it uses 389 cfm. (224 hp though). A blower could easily generate 20 psi if it were big enough. Send me info on regenerative blowers.

By ddechon (12.78.180.109) on Tuesday, October 02, 2001 - 02:29 pm:

Here's a site that we sometimes use at work.

http://www.onlineconversion.com/index.htm

When using 1.4L and 7000 RPM I got 346cfm.

Here's a cool site:
http://users.erols.com/srweiss/#jcalc
Check out the blower calculator

Darrell

By Zippy (Zippy) (152.163.206.208) on Wednesday, October 03, 2001 - 06:15 am:

Thanks for the calculator Darrell. Yes Todd please send me that calculator. I searched Yahoo under -honda supercharger centrifugal- and came up with some hits. See carollsupercharging.com and/or vortecheng.com. These things are way too pricey but building one yourself would not be too hard. Lots of people make regenerative blowers. Just take the performance graph to size the pullys, and fabricate a drive shaft and mount and you have power. I saw a leaf blower yesterday that ran 400cfm. That uses a regenerative blower. I'm thinking that a plastic one would be cheap if you could find a supplier. I'm going to keep my eyes open. This is not something I plan to do this week. Check Granger they sell lots of stuff.

By Todd (63.50.56.205) on Wednesday, October 03, 2001 - 07:12 pm:

Hey Rog,
My e-mail has been down for a few days (server problem). They lost most of my addresses including yours. Send me an e-mail and I'll send you the calculator.
ReTodd1200@springmail.com