Bsp 240z

[reddog]

My first post:

I'm interested in changing autocross classes next year. I've been running an H-Stock Civic for a couple of years but I want to move to something I can modify and that is RWD. BSP has always looked like a lot of fun, and I've always regretted selling my 73. I've got a line on a (relatively) rust free 240Z that is running, so my plan was to start with the suspension. I know I won't be competitive my first year in the car, 2002 will be spent building the car and learning how to drive it. The car will see (very) occasional street duty, but the ride quality is not important.

I'm figuring I'll end up with coilovers in the long run, but to start out I'm thinking springs, Koni's, poly bushings, and adjustable sway bars. What spring rates should I start with? How much can I lower the car without messing up the suspension geometry? How much camber will the car pick up when it is lowered? Are camber plates absolutely necessary, or can I get away with doing them later?

Are there any rear ends that I can ud/bd that have a decent LSD? I know I'll have to put in an aftermarket one eventually, but the budget is pretty tight. Also, what rear end ratios are available? Is there any way to ud/bd 4 wheel discs and is this mod worth doing? I've heard the heads from some years breathe better than others, what years should I look at? I'm guessing that custom FI is the ultimate way to go for power, but since I'm poor what carburator(s) is/are recommended?

What would you recommend for wheels and tires? Will a 13x10 with 225/45/13 Hoosiers (you know, CSP wheels) be enough tire with the stock motor? I'm guessing I'll need to put more rubber down when I start making more power, what wheel/tire combos are the other BSP cars running? If there is an online resource that already has these answers just point me in the right direction. Thanks for any help you can give me.

[John Coffey]

So many questions...

> I'm figuring I'll end up with coilovers in the long run, but to start

> out I'm thinking springs, Koni's, poly bushings, and adjustable

> sway bars.

Replace every suspenstion bushing, steering rack, steering coupler, moustache bar bushing, etc. with poly. When you run coilovers on a 240Z you have to shorten the strut tubes to get back some suspension travel. If you get a set of struts right now you'll have to replace them with shorter ones when you go to coilovers.

> What spring rates should I start with?

For a stock suspension car you'll have to go with whatever springs you can get. You don't have much choice on rates. European Stage 2 springs, Eibachs, or Suspension Techniques are all OK choices. The Euro springs ahve the lowest rate and the Suspension techniques the highest. The Eibahcs (if you cna still get them) at the best choice because they lower the car only about 1".

> How much can I lower the car without messing up the

> suspension geometry?

Any lowering messes up the geometry on the front of a 240Z. The inherent bumpsteer problem is exacerbated and there's no SP legal way to correct it. Without shortening the struts you don't want to lower the car more than an inch.

> How much camber will the car pick up when it is lowered? Are

> camber plates absolutely necessary, or can I get away with

> doing them later?

Probably .5 degrees negative in the front and a little more in the rear. The Z needs about the following alignment settings to get it to work the best in autocross:

Front

Camber - 3 to 3.5 degrees negative

Caster - 6 degrees positive

Toe - 1/4 to 3/8" out

Ackerman - any that you cna get

Ride height - 4.5 to 5"

Rear

Camber - 2.5 to 3 degrees negative

Caster - exactly at factory spec

Toe - 0 to 3/16" in

You need coilovers, camber plates, and offset poly bushings to hit those numbers.

> Are there any rear ends that I can ud/bd that have a decent

> LSD? I know I'll have to put in an aftermarket one eventually,

> but the budget is pretty tight. Also, what rear end ratios are

> available?

No factory LSDs were available in the 240/260/280Z. You have two diff choices, the R180 and the R200. The R180 is the way to go because its lighter and has better halfshaft angles. Its plenty strong for anything up to 300hp. You ahve two ratio choices: 3.36 or 3.54. Go with the 3.54.

A Nissan Comp clutch LSD is $800 new and about $400 used. For autocross you want to run a 70lb preload and you'll have to rebuild it each year. A Quaife is about $1,000. A welded up R180 is about $100 and, with proper suspension tuning, can be very effective.

> Is there any way to ud/bd 4 wheel discs and is this mod worth

> doing?

Not legal in SP and not worth the extra weight at an autocross.

> I've heard the heads from some years breathe better than

> others, what years should I look at?

You'll want to run an L28 using the N42 block and N42 head.

> I'm guessing that custom FI is the ultimate way to go for

> power, but since I'm poor what carburator(s) is/are

> recommended?

The stock 1970 thru 1972 SU carbs are very good.

> What would you recommend for wheels and tires? Will a 13x10

> with 225/45/13 Hoosiers (you know, CSP wheels) be enough

> tire with the stock motor?

> I'm guessing I'll need to put more rubber down when I start

> making more power, what wheel/tire combos are the other BSP

> cars running?

I don't think those rims will clear the front calipers. If so, then they will work but you might have some fender clearance problems. Most folks run either 225/50-15 Kumho or Hoosiers on 15 x 7 or 15 x 8 rims, or 245-265/45-16 Kumho or Hoosier tires on 16 x 8 or 16 x 10 rims.

[24OZ]

Nice one John,

you've answered some of my questions too.

Thanks.

[EricB]

John,

Can I thank you too????

Those are exactly the questions I was just going to pose to the club. And you've answered them all. Cool!

-e

[2ManyZs]

I don't have the autocrossing experience John has nor do any of my cars look as good as his. But I would like to put a penny worth on the table. I would highly recommend spending a little extra money when it come to sway bars and get some decent adjustable bars, especially if you use a welded rear. The added flexibility of being able to adjust the bars according to the course you are running will pay off in the long run.

I ran an ITS 280 with a welded rear and non-adjustable bars. It just had way to much oversteer with the bars I was running and even by swapping out for the stock bar I never could get the car to handle the way I liked, especially when I was racing in the rain. The more adjustability you build into the car the better of you will be when it comes time to run a different course, and that is primarily what autocrossing is, it's not like running around the same race track weekend after weekend. No two autocross courses are ever going to be exactly the same even if it is in the same parking lot.

[John Coffey]

In the context of the original post (basically stock springs, no radical suspension changes) the stock front anti-roll bar and a small (or maybe no) rear anti-roll bar will work best.

You really want to control weight transfer with springs more than with bars. Because an autocross is mostly transitions, stiff bars and soft springs tend to overload the tires so that you get an initial push on corner entry and then snap oversteer as the car falls over on the springs, just when the driver starts turning the other way.

If a person gets serious about building a dedicated BSP car, then there are a number of things that have to be done to get a Z to turn in well and stay planted.

And, no, I'm not going to list those things until I think someone is serious... ;-)

[2ManyZs]

I agree, I guess I was kinda assuming someone was going to get serious about autocrossing. But we all know what the first word is in assume. Most people when they upgrade automatically go out and get the stiffest bars they can thinking it is going to be the best thing they can put on and it isn't always the case. In my case I learned by making that mistake.:mad:

[shock96]

John is the man for autocross.

I would recommend running a 16" wheel if possible. You will get better turn in.

Mike

[Royce]

Just curious, why does a larger diameter(16") wheels give you better turn in?

I was considering smaller diamter(14") to raise final drive ratio (better out of corner acceleration) and lower unsprung weigh on the corners (lighter in corners and brakeing).

I suspect these things may fall into the 'performance tradeoffs', 'personal preferences', or 'what is best for one course may not be best for all courses' catagories.

Thanks!

[shock96]

Regarding the better turn in on the 16" vs 15"...it does seem to be relative.

When I was running my 911 on the road courses, the 15" Fuchs I was running worked very well. When I switched to the 16", I noticed a much smoother transition, especially on decreasing radius turns.

My Trans-Am Mustang with 16" wheels was much better all the way around than with the 15"ers. I used the same tire, just with the increased diameter.

I have been told that by increasing the diameter of the wheel (with in reason) you enlongate the overall contact patch and that helps decrease time to the outside area of the tire.

Mike

[John Coffey]

Or maybe it has something to do with the shorter tire sidewalls giving better response...

[reddog]

OK, so the 240Z I was looking at didn't pan out, but I've got a line on another car. A friend has a (78?) 280Z sale that doesn't run.Since you can update/backdate in BSP, is there any significant advantage to starting with a 240 over a 280? I'm assuming the best way to start would be to ditch the stock FI system and go carbureted. The body and interior are in good condition. He doesn't know how much he wants for the car, he's just looking for a fair deal. I don't want to low-ball him, does $500 sound low, high, or about right? Thanks again for the info!