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Discussion Starter · #1 ·
Hello all,
First post here, this seems like the best place for Supra knowledge online.

I'm considering putting together a TT MkIV Supra to use exclusively for SCCA Solo2 competition in the STU class (rules available here).

I've built a couple winning cars for STU's slower sister class, STS, and have raced lots of different stuff - Honda S2000s, Civics, and ended up 3rd in SM2 last year in a 600hp Vette. I think a Supra would be an absolute blast to run against the M3s, Evos, and STi's in STU. I'm trying to develop a good vision of how the car would end up to see how its chances are.

So, with that said, here's the mods I would do to the car. I'm most curious as to what you guys think the car would end up weighing, and what sort of power it would put out with these mods. Assume each of the parts chosen in modification are top-shelf, and all stock components are in top shape. This is basically everything the rules allow:

6-speed with hardtop (if I can find one)
Suspension:
DA 28-series Konis, adjustable f&r bars, poly/delrin/hard rubber bushings throughout
Widest wheels I can fit under rolled fender lips (10.5" front 12" rear sounds like the limit?)

Engine:
CAI, header (if such a thing exists for stock turbos?), big downpipe, high-flow cat and cat back
lightweight underdrive pullies
100 octane
re-tuned/mapped ECU and/or SAFC-style piggyback device. Have to run stock boost parameters, everything else is free

Misc:
Lightweight race seats
A/C removed
Lightweight battery, moved to rear


Many thanks in advance!! :bowdown:
 

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Hardtop seems like the best way to go for lightest starting weight and chassis rigidity, check this site for what some hardcore lightweights have done, look in the Lightest Supras category http://www.suprahardtopregistry.com/

I didn't read all the rules relating to what you can remove, but it seems you'd be extremely lucky to get below 3100lbs, probably more like 3200 if you're lucky.

I see where you said, and in the rules too, that turbo'd cars must run stock boost levels. Do they literally mean you can't eliminate the OEM fuel cut that limits boost to under 14psi or can you eliminate fuel cut and let the stock turbo system boost to whatever they can? I did see where you must keep stock intercooler, but I don't see a problem with the stock sidemount up to this power level on stock twins.

Power with 14psi would be something like about 370 to the wheels ....others here hopefully will give more accurate power numbers for this level.

Unless you have overfenders or mod the rear fenders a lot, you won't fit wider than 11" on back; I think 10" on front.

For stock turbos even up to 20psi I don't see any point in running a bigger downpipe than the very commonly used 3" with any good lightweight titanium 3" catback.

I only remember hearing bad vibes about underdrive pulleys so I'd say stay away.

100oct is good; can you run 105oct? That would be even better, but I suppose if limited to only under 14psi, 100oct is plenty.

Maybe consider a used gForce main ECU (no longer available new, but somebody else is doing the same ECU mods now) which is an aftermarket moded stock ECU; you get increased rev limit, no fuel cut, no speed cut, tweeked fuel tune, probably use one with stock timing which is pretty aggressive anyway.
 

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FAITH
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You can fit 315 Classics on 11.5 inch rims with moderate negative camber, rolling or cutting the lip, and banging the inner fender. You could fit 12" wide wheels but you would only be able to run 295s..

-Khader
 

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Discussion Starter · #4 ·
Thanks very much for the info thus far guys.

I just remembered the STU-specific ruleset isn't in the rulebook, but it's just like STX, which is. STU grants unlimited width wheels, and a maximum 275mm width tire, which will be what hampers something of the Supra's weight. Ohh, forgot to mention I can go to aftermarket brakes, may be able to save some weight there.

The Yokohama Advan Neova and Bridgestone RE01R are the two hottest tires for the class, and their widest tire I can legally fit specifies up to a 10.5" rim. I know that generally you can go at least .5-1" wider than the mfr recommendation, but 1.5" may be pushing it, so 11.5" out back may be all I can ever use anyway.

That's a good question about the fuel cut, I'm not quite sure of the answer there. That sort of stuff is why the Street Prepared category recently de-regulated boost. In general is the Supra's boost controlled through mechanical means with some sort of overboost protection watchdog, or does the ECU have a boost table?

Fuel has to be DOT approved, Sunoco GT100 is the best stuff you can get of that variety.

Damn, that weight reduction page is great! Low 32xx looks attainable, that's not fantastic, but not bad considering the wheels and power. The M3s have less wheel, less tire, but weight about 400 pounds less. They have about 150 less whp though too... :)

Crossing my fingers I'm not overspending the good will this site issues each newbie, but if anybody could direct me to a source of a dyno with a mod set approximating the one I've described here (or some good seatch terms to try on the site), it would be much appreciated.

Thanks again everyone!
 

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Discussion Starter · #6 ·
Not done yet with the S13, it's just that I'm at the price/performance curve where each extra hp is about 500 bucks, and the car is just about "done". The s13 is just plain slower in a straight line than its rivals - I figure I can make any car handle well, but being at an acceleration disadvantage is just no fun.

If things go well in Kansas this year I'll be looking to move for next season; if they don't, then probably not till '07-'08...
 

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j-rho said:
In general is the Supra's boost controlled through mechanical means with some sort of overboost protection watchdog, or does the ECU have a boost table?
Finding out how far you can go here within the rules will be very significant. There is a LOT of horsepower between factory fuel cut level (under 14psi under most conditions with a free flowing exhaust/downpipe) and running as much as the car can handle in your particular event ...my wild guess is you could crank an additional few psi of boost over fuel cut without any real problems. The OEM method of limiting boost is within the ECU, a pressure sensor tells the ECU you have reached the factory chosen limit and the ECU engages fuel cut, at that point the car feels like you just dropped a 10 ton anchor overboard. The very well accepted work-around is a Greddy BCC (boost cut control) which is just a small "blackbox" the splices into the wiring at the ECU and which limits the signal to the ECU making it think you are near max boost but not over it. With that setup, everything works well and you can crank out as much boost as your application can handle up to the limit of the stock turbos, even up to well over 22psi, say for drag racing, but I don't think the car could handle that high boost on stock turbos for sustained hard driving on a road course.

Seems you are quite serious to me, and I'd love to see anybody who is willing to make a serious effort at campaigning a competitive Supra get all the help we can give them.

There are a few serious roadracers here and hopefully they won't consider you a competitor and help you out with their real life hands-on experiences.
 

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Discussion Starter · #9 ·
BXR SUPRA said:
Where are you in San Diego?
All over, but tomorrow I'll be down at Qualcomm all day with my red S13.

Now that my account is active and I can use the search feature I plan to get much more knowledgeable about the car. At this point I'm inclined to think that if you modify your ECU to not cut fuel at a certain boost level, that is legal, as you are only changing the amount of fuel going into the engine based on certain parameters, you are not asking it to make more boost than originally programmed. The way this mod is implemented matters though, and I'm not sure the piggyback solution is a legal one.

Don't quote me on any of that though, I need to research more...in any case, if it can make mid to low 300's at the wheels, that's probably more than the tires will be able to handle anyway.
 

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Heavy Metal Momentum
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Are you sure about the modified brakes? I haven't added a better setup because I'm staying in an SP class for a while. I'm fairly sure brake upgrades (short of lines, pads or rotor stlye) aren't allowed until SM classes. If not, please let me know, I'd love to have some stopping power.

We've had the boost vs. laws of physics debates locally recently. The rules state for some classes, boost modification is/is not allowed. If a exhaust/intake change is made, freeing up lost pressure is it allowed? I haven't seen a rule stating otherwise. It's almost contradictory, since you'd have to have a boost controller to reduce pressure at that point if even possible since the WG would be controlling the min. pressure. The Subaru/Evo guys have Ecu controlled boost, ours is mechanical. I think taking it word for word by the rules would allow for 'inadvertent' changes in pressure.
Just MHO.
Brian
 

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Discussion Starter · #11 ·
I believe it is probably advantageous in this situation that boost is controlled through mechanical means. Below is the rules wording around engine management modifications. The bolded section is in response to the post above.

E. The engine management system parameters and operation may
be modified only via the methods listed below. Any and all
modifications must meet or exceed the applicable US DOT emissions
standards for the year, make, and model of the car. These
allowances also apply to forced induction cars, except that no
changes to standard boost levels, intercoolers, or boost controls
are permitted. Boost changes indirectly resulting from allowed
modifications are permissible
, but directly altering or modifying
the boost or turbo controls, either mechanically or electronically,
is strictly prohibited.
1. Reprogrammed ECU may be used in the standard housing.
Traction control parameters may not be altered. Altered
engine controllers may not alter boost levels in forced induction
engines.
2. Electronic components may be installed in-line between an
engine’s sensors and ECU. These components may alter the
signal coming from the sensor in order to affect the ECU’s
operation of engine management system. Example: fuel
controllers that modify the signal coming from an airflow
sensor.
3. Fuel pressure regulators may be replaced in lieu of electronic
alterations to the fuel system. It is not permitted to electronically
modify the fuel system AND replace a fuel pressure
regulator.
4. Ignition timing may be set at any point on factory adjustable
distributor ignition systems.
5. VTEC controllers and other devices may be used which alter
the timing of factory standard electronic variable valve timing
systems.
6. All STS vehicles must comply with the Federal 49-state safety
and tailpipe emissions test requirements as a minimum.
 

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Heavy Metal Momentum
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Are those from the STU rules? I must have been reading an old version? Are IC/piping changes allowed in the class? Not sure that I'd be eligible but you'd think a Mk3 would be given it's much worse power/weight ratio.

Thanks for clarifying, how about the brakes, does STU allow modifying?
 

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Nick 95 6sp said:
Seems you are quite serious to me, and I'd love to see anybody who is willing to make a serious effort at campaigning a competitive Supra get all the help we can give them.
Absolutely, I love hearing stories like this! :bigthumb: Drag racing and highway racing aren't the only capabilities of the MKIV. :1poke:

The twins heat up on the road course quickly, but I've known of road racers running about 15-16 psi all day at Road Atlanta with no problems. Too bad there are so many restrictions in this class for the heavy Supra!! With a single turbo you can eliminate any concern of not having enough straight line speed. :D

And regarding over mid 300s HP being too much for the tires, even for 275s it won't be an issue for good performance tires and no concern at all for R compounds. I have excellent road course traction with 480 RWHP with my 295 Kumho MXs.

If you can run the "tunnel ram" front headlight mod, i.e. a cone cut right through the bright light, you will notice a substantial increase in power. I cut out some of the metal below the stock airbox location (my single has a 9" length K&N filter) to allow the air to rush straight to the filter as well. Also, you can remove your stock turn signals and have your parking lights function as turn signals (if you have pre '97 style lights). This increases the airflow to both turn signal cavities. You can see the now open turn signal cavities in this pic:



Keep us posted of your progress! :cool:

Also remember to remove the TRAC control system, it is useless as a performance item and weighs 22 lbs. The stock spare/tool kit are about 50 lbs together. The driver's side adjustable seat alone is 49 lbs!! I've heard racing brake kits w/rotors can be as much as 10-15 lbs lighter per wheel. A lightweight exhaust/no cat could probably save 15-20 lbs as well. A lightweight flywheel can easily save 15 lbs or more and improve road course characteristics.
 

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Discussion Starter · #14 ·
The type of racing I do is Solo2 autocross, which is held at lower speeds, usually in parking lots or burnt-out airfields. Speeds are generally in the 30-60mph range, run entirely in second gear. Torque delivered to the rear wheels is pretty high in second; much higher than the 3rd-4th-5th gear stuff on a road course.

None of the cutting or cooling mods would be legal, but the "laps" are also only about 60 seconds with several minutes of break between, so cooling becomes less of an issue.

Spare/toolkit can come out and seats would be replaced as in the modlist above, which contains pretty much all the stuff I can do. Traction control has to stay in place, but can be disabled.

I can do big brakes in STU, but they have to bolt to the stock hubs without modification. Only other restriction is that they have to at least be as big diameter as the stock pieces.

This project is still several months (if not a year or two) away from beginning, but in the meantime, HERE is a link to the building up my S13 hatch, which has been going pretty well thus far. Would be fun to perform a similar process with a much more capable car.
 

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Heavy Metal Momentum
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Wow, I'm suprised you can upgrade the brakes, the SP classes don't allow that yet have a worse PAX. Here's the portion in STX about brakes:

7. Brake rotors may be replaced with any rotor of equal or
larger diameter made from a ferrous or aluminum alloy.
Calipers are unrestricted, but must mount to the original
attachment points. Drum brakes may be replaced with disk
brakes of a diameter equal to or greater than the inside diameter
of the standard drum part. Brake backing plates (dust
shields) may be modified the minimum amount necessary to
accommodate allowed alternate rotors and calipers.

Maybe I should eventually look into this class and remove my IC (sounds like changes are allowed up to the TB.) They mention battery relocation but can you run a lighter version?
I've got the Braille unit and it's held up well for close to a year but always bring a jump box in case. How are the stock bushings in your mk4, mine were shot in my car and replacing them really gave a better road feel.
 

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Discussion Starter · #16 ·
You can't touch the intercooler or any of its piping.

Yes, you can run a lighter battery:
The make, model number, and size of the battery may be changed
but not its voltage. Relocation of the battery or batteries is
permitted but not into the passenger compartment. If the battery is
relocated and the original battery tray can be removed by simply
unbolting it, the tray may be removed, or relocated with the battery.
Holes may be drilled for mounting or passage of cables. Longer
cables may be substituted to permit relocation. The number of
battery or batteries may not be changed from stock. The area
behind the rearmost seat is not considered to be within the
passenger compartment.
And I don't have a Supra yet, though with any luck, I'll have one by the end of the year.
 

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Forgot to mention the rear folding seatback is around 30 lbs, mine's in the garage..permanently. No adult could ever sit in the back anyway, I left the bottom portion in place because it is feather light and serves as a leather covered storage space, looks nice actually.

Hard to imagine a Supra in a contest where it never leaves 2nd gear! :run: That doesn't really play to its strengths, but at least the torquey stock twins in seq mode will have a nice spread of power for lower speeds.
 

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Heavy Metal Momentum
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There are courses where 3rd is used. It depends on the lot size, course setup, driver and car setup. I try not to overrev so I shift to 3rd @5500 (~55-60 mph) most times, others tach off the rev limiter constantly. I've seen courses where I've been near the top of 3rd (85-90) and I still rather new. The SCCA rules however state 60 mph but other clubs can sometimes run otherwise.

J-rho, I hope you can find a good one. I'd love to find a reasonable priced mk4 that I could use as a BS class car (or maybe it's AS now?). They specifically said nothing after the TB could be changed, I thought maybe the IC piping counted as part of the intake system since it's pre compressor. Keep us posted, I'd like to hear how you do with it.
 

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Discussion Starter · #19 ·
I'd have to keep the rear seat in, there is no allowance to remove it, or any other part I didn't list in the original mod list.

With the rev limit raised to 7200, I calculated a 6spd car on 265/35-18's could reach just over 71mph in 2nd gear at redline, which is plenty fast. It also means I'd be exiting the slow corners down around 3000rpm, but with the free-flowing exhaust and the turbos in stock sequential mode, it sounds like it'll be making good power down that low.

The plumbing I would change:
Air intake up to the turbo inlet, have to keep the stock MAF though. Then I could change the exhaust manifold/header between the cylinder head and the turbos. Not sure how what sort of gains could be had there with the stock twins. Then I'd change the downpipe, but I'd have to have one cat somewhere in there, it'd be a very high-flow unit, within 6" downstream of the furthest aft factory cat. Lightweight and high-flow cat-back from there.

The TT MkIV is an AS car, the non-turbo is an FS car. Some people I know think the NA car could be quite a contender in FS.

A buddy of mine has a car he only occasionally uses as a drift toy, I've already planted the seed in his ear about trading his car for my 2 240's after I get back from Kansas in October. We'll see how it goes...
 

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With a hi-flo cat (one only), TRD catback and stock side mount IC, and NO fuel computer I made 371 RWHP/395 RWTQ at 17 psi. With wimpy stock boost and a hi-flo cat, SAFCII, perhaps you might expect 330+ RWHP/330+ TQ or so with a good tune. But the stock twins give nice, fat, early torque (I had 255 RWTQ at 3000 rpm), so you will still have a nice powerband.
 
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