Here’s where we act like we know something technical about cars. Feel free to ask us about your technical troubles. Write us ator pbskids c/o Tech Support, 831 S. Douglas St. El Segundo, CA 90245. Feel free to include a picture of your project or tech problem.
Beg To Differ
Q I own a naturally-aspirated ’93 240SX that has a KA24DE with a non-turbo Z32 differential. I’m looking to change the diff ratio to 4.08— my car is daily-driven and driven hard (on occasion) if weather and traffic conditions permit. I spend a significant amount of time on the highway, so I’m looking to reduce my RPMs from 3,800K to about 3K when I’m at 65mph. I don’t know if I should go lower or higher based on the ring and pinion? What do you recommend?
A Calculating gear ratios is easier than many people think. All you’ll need is a tire diameter size, a vehicle speed, a desired RPM and the car’s transmission overdrive ratio. Then search the Internet for a “differential gear ratio calculator” and plug in your numbers to come up with an ideal gear ratio. We’re a little confused. First, the Z32 non-turbo came with a 4.08 gear ratio, so changing to a 4.08 won’t change anything. Second, 3800 RPM at 65 MPH sounds a bit high. You might want to see if you’re running a proper tire diameter before playing with your gearing. As for an inexpensive option for the R200 differential, the 97-01 Infiniti Q45 had a 3.69 ratio, which might work for you.
Q I recently bought an ‘88 Mazda RX-7 (FC) and plan to change the engine—but I’m a bit worried by the choice of the engine. I first planned to swap the non-turbo 13B for a SR20DET, which is a swap that has already been seen. Some have told me that it would be easier to swap a 13B Renesis or 4AGE in. Is the Renesis motor reliable? What about the 4AGE? That’s an AE86 engine, but that just doesn’t seem to make sense. What setup would give my FC the most potential?
Laval, Quebec, Canada
A In terms of the most potential, it’s difficult to beat an LS V8 swap. If you want bang for your buck, the Ford 5.0 is a great alternative. To answer your other questions, the RX-8 Renesis engine has proven to be reliable. The 1.6L 4AG is small for even a Corolla, and would not be a good candidate for the FC. The SR20DET is a great engine, but its front sump oil pan creates issues when swapping it into the RX-7. Bottom line, the FC chassis is a great platform for an engine swap. It has a great suspension design, looks great and is inexpensive to buy. If you want easy, stick to a common engine swap that has an off-the-shelf swap kit available. If you want different, be prepared to either use an undesirable engine or a cool one that doesn’t lend itself to an easy swap. Almost everything else has been done.
Old or Modern?
Q I have a ‘72 240Z project car—everything’s sorted out except for the engine. The L24 is nice but I’m really interested in the RB26DETT or L28ET. What do you think is the better out of the two?
Fort Smith, AR
A Although the term “better” is subjective, from a performance standpoint, the RB26DETT is clearly superior. Straight out the box, you get a dual cam head, twin turbos, individual throttle bodies, an underrated 280HP and an 8K redline. With a few bolt-ons and some added boost, you’ll be pushing 350WHP without even stressing the engine. But, this comes at a baller price as these engines go for a premium. Additionally, a RWD transmission (RB25DET or modified Z32), custom rear sump oil pan, a mount kit, custom wiring, upgraded fuel system and a custom intercooler setup will all be needed. If you want more of an old school look and can appreciate what the L series has to offer, the L28ET is still a good choice. It really boils down to what you like and how much you want to spend.
RB for S13
Q I have an S13-chassis 240SX and I want to swap the RB26DETT in. Which rear end and axles do I need to complete the swap?
A Most people use the RB26DETT engine mated with an RB25DET RWD transmission and the stock 240SX differential and axles. On a street car, the stock 240SX differential and axles hold up fine because the tires spin before the parts start breaking. With purpose built drag cars, the axles are the first to go. The good news is that companies such as driveshaftshop.com offer beefy axles for these types of extreme applications. The stock differential is quite strong; most racers simply replace it with a stock one in the rare event that it fails.
Brake It Down
Q I have an ’06 Nissan Sentra SE-R SpecV without the Brembo brake package. I recently bought the spindles, calipers and discs off an ’05 Altima SE-R and it converts my 4-lug to 5-lug perfectly up front, but I can’t seem to find the right parts to convert the rear. Do you know which parts I’ll need?
Las Vegas, NV
A We’re not Mike Kojima but the last we’ve heard, there isn’t a direct-fit five-lug hub that bolts on to the B15 rear spindle. The next best thing is to purchase a sleeve and spacer kit, which allows the ’90-’99 Maxima rear hubs to bolt on to the existing rear spindles. For detailed information on this conversion, check out the Sentra forums such as b15u.com and sr20forum.com.