1990 240SX Autocross Build (DSP)

[nissanman04]

edit: *9/20/08 - Project officially on hold for the year - see page 4 for new plans*

Over the last couple years, I've become addicted to competing at autocross events. After debating for a long while about what I want to drive this year, I've decided to keep my 240 and try to build a competitive car in the D Street Prepared class. I believe this car can be competitive in this class because of its relatively lightweight chassis, rear wheel drive, and a torquey engine. The dominant cars at the moment in this class are E36 BMWs (non-m3) and 2.5RS Subaru Imprezas. I am going to prove that these cars can be used for motorsports events other than drifting!

Engine modifications are extremely limited. Cams must remain stock, although intake and exhaust is unrestricted. I do not plan on buying an aftermarket header as I believe money can be better spent on suspension and tires. The rules do allow me to swap my KA24E out in favor of a KA24DE.

Restrictions on the suspension say that suspension bushing type must say the same, so that means no adjustable RUCAs or any of those other cool parts with spherical bearings.

Planned Modifications:

-'91 240SX KA24DE swap-Aftermarket Clutch-Lightweight flywheel-Hockey puck engine mounts (metal mounts are explicitly prohibited)-Short shifter-Trunk-mounted mini battery-Intake relocated to passenger side-OEM replacement Brembo rotors-Hawk HPS pads-Koni single-adjustable sport shocks-Ground Control coilovers w/ 550lb springs front, 450lb springs rear-Front camber plates-14x7 +0 wheels on all corners to reduce unsprung weight and rotational inertia, cheaper tires are a nice plus-Hankook Z214 DOT R-compound tires (225/50R14 to give me shorter gearing for faster acceleration)-Adjustable sway bars (at least front, may leave stock rear due to wheel lift issues)-F/R strut bars-Sparco sprint 5 seat-4-point harness (removable)-Urethane bushings wherever possible-Nismo 1.5-way LSD (already installed last year)-A/C removal-Custom power steering setup using AN fittings

I plan to have the car ready to drive by mid-April. As of now, I've pulled the single-slammer and I'm in the process of removing things from the engine bay so I can prep and paint. I've got a low-milage KA24DE ready to go on an engine stand, just waiting for a clutch and flywheel. I'm really excited about this project, and I think the car will do very well once it's all together and set up.

Here's where I'm at right now, I've barely started...





The front is even higher than it should be since there's an RB20 block sitting in the back, lol...







Modified by nissanman04 at 11:07 PM 2/4/2008

Modified by nissanman04 at 1:52 PM 2/19/2008

Modified by nissanman04 at 12:32 PM 3/28/2008
Modified by nissanman04 at 11:02 AM 9/20/2008

[nismofly]

whats the difference between this DSP and the one that don nimi runs the pdm racing s13 which has way more stuff done to it than what youre talking

[nissanman04]

The Canadian street prepared rules allow more modifications than American SCCA Solo2 street prepared.

[nismofly]

i couldve sworn he came down to the states and ran some events in seattle or something too

im guessing he switched to SM when he was in the states then

[nissanman04]

I think their SP is closer to our Prepared class, so he probably ran in Prepared or SM.

[nismofly]

alright well then

the only thing that catches my eye is are the wheel/tire size rules the same as STX?

[nissanman04]

Nope, wheel/tire size is unlimited. However, if the car was build to STX specs and I wanted to use R-compound tires and run in SP, then I would still need to obey the STX wheel/tire restrictions.

[nismofly]

im not sure i understand

are you saying that a car built to the limit in STX but run on r comps (or a comps in the case of what youre planning on getting) is a car built to the limit of DSP?

auto-x rules confuse the hell out of me...silly scca and their rules that havent changed in 40 years

[nissanman04]

Yeah, it is confusing. What I mean is, an STX-prepped vehicle w/ r-comps is classed in street prepared, even though some STX modifications are not allowed in SP (i.e. brake caliper upgrades and adjustable suspension arms)

[nismofly]

ah i see, so if you run the wheel tire package youre talking about, you could run stuff thats legal in STX but not SP

makes perfect sense...in fact i dont know that id even go as wide as a 245, i was just mentioning it because i knew those were the limits for STX

im not sure how much you auto-x guys take tire OD into consideration but you could run like a 15x7.5 with a 225/45/15, it would be even lighter and the smaller tire would make the car really get up and go, just depends if youre worried about running the effective gearing too tall and having to shift

[nissanman04]

Yeah, that is a good point. I was taking tire OD into consideration. The 245s were the widest tire I could fit with a similar OD (.5" taller). If I went any wider, the tires get over an inch taller than stock, which I don't think would really be advantageous. Finding a 15x7.5 wheel in the right offset may be kind of difficult, but that 225/45R15 tire would reduce the OD by 1.3", which would really help with acceleration. I'm sure I'd end up in 3rd on some courses, though. It would be interesting to try...

I don't think the SSRs will work out, there's a 10-12 week wait

If I wanted to go with a small tire diameter, I could pick up some konig rewinds in 15x7 +0 and run that 225/45R15. The resulting OD would be 23.0" as opposed to the 24.9" that I ran last year. That's quite a significant change...
Modified by nissanman04 at 8:17 PM 2/1/2008

[nissanman04]

Still no pics, the car is covered in snow

I have decided to go with the shorter tire on a 14" wheel for the gearing advantage...plus wheels and tire in that size are nice and cheap, lol.

[simmode1]

I'm curious... you said the cams have to remain stock... But what about the OEM 248/232 or the 248/248 cam setups from other KA24de's? I mean, its all OEM, right? How would they tell anyhow?

[nismofly]

i thought you were trying to keep your z32 brakes though

there isnt a single 14" wheel out there that will clear z brakes

[nissanman04]

Z32 brakes are gone due to a technicality in the rules (I have to choose STX or DSP rules, no mixing the two. STX allows caliper upgrades, but doesn't allow the engine update. DSP allows the engine update, but no caliper upgrades).

14s do clear stock brakes, though.

[x240xdrifter]

why not do J30 brakes then?

[nissanman04]

OK, to clear this up, I can't upgrade my rotors/calipers and to the DOHC swap at the same time. I would only be able to use calipers from another 240sx model, and since all 240sx calipers are essentially the same, there is no point in doing this.

Plus, any brake upgrade would be of very minimal benefit in autocross, as runs usually last only 50 seconds, which is rarely enough time to get much heat into the brakes. Tires are always the limiting factor when it comes to braking. The size of the brakes only comes into the equation once everything gets heated up and brake fade becomes an issue, which doesn't happen very much in autocross.

The smaller rotors have less unsprung weight and rotational inertia, which is way more important than anything a larger brake would be able to give me.

[nismofly]

yeah youll be far better off with stock brakes

for the wheels try to get your 14" wheels to weigh more than a pound less than the comparable 15" wheels would, because the OD will be the same and the 15" tires will weigh around a lb less, so youve got to make the difference more than that in wheel weight

[SR24DET]

Yea, I love auto-X also. I am a drifter first, but i love auto-X. Me and my drift team go auto-X ing and we drift on the track and they allow it. Everyone always tells me," You know, drifting isnt the fastest way around the track." I just go to have fun. I have stripped out the interior of my car so i am put in the R class. I have to race against supercharged Z06's and Porches so as my car stands right now i dont focus on winning until i get my engine done.

[Soravia]

How much have you spent so far?

[nissanman04]

How much have you spent so far?

Too much for a slow car, lol.

[nissanman04]

I'm curious... you said the cams have to remain stock... But what about the OEM 248/232 or the 248/248 cam setups from other KA24de's? I mean, its all OEM, right? How would they tell anyhow?

The engine/drivetrain must be swapped as a unit. If I could swap individual parts, I'd be using SOHC pistons...

for the wheels try to get your 14" wheels to weigh more than a pound less than the comparable 15" wheels would, because the OD will be the same and the 15" tires will weigh around a lb less, so youve got to make the difference more than that in wheel weight

Good point, but the 14" tires are $60 less per set, and the wheels are a little lighter, so it would be close to a wash. I'd rather just save a little money, haha.

[nismofly]

yeah i see, honestly youll maybe see a tenth or two from the weight difference, and that $60 a set will add up quick

[hai1206vn]

damn i can't image how those tiny wheels will look on it. Some more shifting as well i guess, but might be better. i found myself kicking the clutch a lot to bring the rev up in 2nd gear.

stock brakes should be more than enough. I used hawk HP+ last year and they bite a lot better than several z32 setups i've sat in (probably crappy pads). If this car's dedicated, stay away from HPS.

stock 1991 cams are best oem already, so you're good to go

are you gonna strip it out? btw if you need a small battery call me up, i got an odyssey pc680 just sitting there after my crash

[SR24DET]

If he strips it, that will put him in the R class. I know cause it happened to me..........

[nissanman04]

damn i can't image how those tiny wheels will look on it. Some more shifting as well i guess, but might be better. i found myself kicking the clutch a lot to bring the rev up in 2nd gear.

stock brakes should be more than enough. I used hawk HP+ last year and they bite a lot better than several z32 setups i've sat in (probably crappy pads). If this car's dedicated, stay away from HPS.

stock 1991 cams are best oem already, so you're good to go

are you gonna strip it out? btw if you need a small battery call me up, i got an odyssey pc680 just sitting there after my crash

I'm probably going to try a few pad setups this year. Since I have the HPS already I'm going to start with those. I'll probably give you a call about that battery. The engine's still on a stand in my garage, I can't stand this weather around here, haha.

No stripping the interior, that would put me in prepared class...
Modified by nissanman04 at 9:57 AM 2/4/2008

[nissanman04]

Just ordered most of the parts for brakes/suspension.

Tried to order some stuff from JGY customs (flywheel, short shifter, sway bars), but the prices for all those were inaccurate on the website, and the flywheel that is pictured isn't even the one they sell. What a joke. Now I understand why I have heard about so many bad experiences with them.

The Konis are on backorder and should ship in two weeks (I hope).

Ordered the brake parts from SPL. Also ordered the Whiteline sways from there once I heard JGY increased their prices. JGY would have actually been a little cheaper, but I would rather get them from a reputable company like SPL.

I can't wait until this stuff starts arriving so I can get to work...

[frsh13]

Good luck with this build. Where do you autocross? I know auto x season doesnt start for a little while but keep us posted with how you do.

[nissanman04]

Good luck with this build. Where do you autocross? I know auto x season doesnt start for a little while but keep us posted with how you do.

I just autocross locally within my region of the SCCA for the most part. Most sites are within 20-30 minutes of where I live, so it's pretty convenient. I'll do a few events out in Buffalo and a couple down by Seneca lake which is about an hour and a half away. This year I'd like to get to a couple national level events just to see what it's like.

[hai1206vn]

i'm quite curious about those Koni yellows. I'll really wanna hear your impression once they're on

hopefully i can get a 240 before the season, maybe an s14 this time