Best path to cost effective NA chassis laptimes
 

Feel free to move.

Chassis currently has:

-Build B6 bottom end
-Stock head waiting to go on, gaskets studs etc
-Standalone ecu
-5 speed and HD clutch, light flywheel
-Cage
-Stripped out mostly
-Midrange coilovers
-Bushes are poly
-Hardtop
-2 way diff
-PWR radiator
-catch can


My plans, this is where you tell me my cost per tenth ratio is out of whack.

-AF style tubular, 2560, E85, etc etc, 250 odd HP, responsive high comp build
-15x9 with hoosiers 275's
-Crusher style front bar and wing
-Flat floor
-Diffuser with bumper cut
-As much free weight reduction as possible
-Big ass splitter


Why is any of this not the right answer to cheap speed? Whats better?

Is paying 1000 bucks for a 6 speed and making 300 or more hp cost effective for lap times?

Are the hoosiers cost effective for lap times?

Are lexan windows cost effective for lap times?

Please tell me like im a 5 year old what is right and wrong with this plan for cheap fastness.

Cheers,
Dann

For road courses, sessions of 10 miles to 200 miles.

Higher HP and 6 speed is definitely conducive to lap times and plays to your strengths.

275 tyres on 10's would be better than 9's BUT a little hard to source cheaply down here....pending 6uls. Also require flares.

I am at 250 HP and similar torque....the torsen is not a limiting factor on road circuits yet. It was a limiting factor at Leadfoot hill climb.

Power delivery is another area I am working on...currently my torque is to high in the rev range....dropping this down and improving throttle response will improve my lap times but more importantly for me improve my race results.

Anything you can do to reduce weight has a big influence....way more than I ever appreciated....so lexan windows. Removal of Roof mounting hardware. Headlights and assorted wiring etc. Careful roll cage design limiting material where safe. Removal of under dash heater etc. BIG benefits.

Balance is just as important as outright grip Dann. Make the thing go round corners with the front following the rear.

So... Make sure your sways are matched to the coils and that the spring rates are in the ballpark.

6 speed is your friend at most Aussie tracks, although the torque of the 2560 should help the 5 speed punch above its weight if the tune is good (as I'm sure it will be). I'm doing 1:06-1:07s at WP with 170whp. 250whp will be fine if it is available at the right time and the car handles well. 300whp will not gain much at WP but will be a benefit at SMP GP, North and Brabham circuits as well as PI if it goes south.

Is this "Mr Motel's" car. Why DOTs and not 245 R80s? Surely it's not class related. Yokie A050s in 225 will be as fast or faster than 275 DOTs and will be far more consistent as they cycle through their life.

Otherwise, most of what you said should equate to more speed.

The best path is more seat time to improve the driver...

But beside that obvious bit, weight reduction will help you in braking, cornering, and accelerating. Power increases will mostly just help you in acceleration. So focus on the weight reduction first.

Lexan windows is nice since it pull a good chunk of weight from a higher up area so it lowers your CG and reduces your curb weight. A fiberglass shell hardtop will do the same.

You didn't mention suspension but I'm assuming you have something planned for that. A good corner weight and fine tuning the setup to suit your driving style is essential.

The benefits of your aero mods will vary with track. If you run a lot of high speed tracks the flat bottom and diffuser will help much more than at a slower track. Once again, these devices require fine tuning from track to track to balance the car properly.

with a 1.6l turbo and only 9" wheels you will be faster with 245 hoosiers or even 225. Hoosiers are wide for there specs. 275's work best on 11" wheels. 245's are best on 10" wheels.

@mx5-kiwi
Yeah making the power is easy but the 6 speed is a lot of dollars as a percentage of the build cost.

@zossy1
Its the original Targa Racing (Gough) Na6, its run 1:09's n/a at wakefield before, for the americans, the outright mx5 record at this same track is 1:03's.
In terms of tyres Im weighing up cost vs seconds, A single lock up with R80's is pretty expensive and day ruining, your thoughts?

@cyotani
The car has a hardtop already, my question re lexan I guess is lexan windows, or no windows at all including hardtop window, any suggestions here? The car will be given to a driver with 1000+ laps in a fast mx5 in order to see its fastest laptimes, so thats covered.

@bbundy
I dont have the wheels yet, so lets say we are making somewhere between 250 and 300whp, however with no big torque peak in the midrange, controlled using ecu boost control to help protect the gearbox, what wheels and tyres do you feel are most suitable from a doller per tenth perspective?

Thanks guys.

I don't see how your 5 speed will survive more than a day at those power and grip levels. I would just plan for the six speed and be done with it.

For reference, see the Lazarus thread, the car was thoroughly and relentlessly ridden hard at track days (8-12 sessions were not uncommon) with the 5 speed at 124 whp. Once the turbo engine was put in with 230whp / 230 ftlbs wtq, the transmission died the next track day.

+1 on the weight removal. Any free weight reduction is absolutely worthwhile. Any weight reduction you have to pay for you'll have to make the decision, but lexan front/rear windscreens are probably worthwhile. Everything gets better with less weight.

250 to 300 out of a 1.6l for track use and expecting reliability is ether going to be stupid expensive and require a lot of bleeding edge trial and error or more likely the motor/turbo system will be more unreliable than your 5 speed transmission.

1.6l and reasonably reliable track car is more like 200 maybe a tad more hp if done right. 300 or more reliable track hp is more like built 2.0L stroker territory and $8,000 to $10,000 worth of motor work before applying a turbo kit.

I do not know where the crossover point is where the drag factors of tire width starts costing straightaway speed more so than you are gaining cornering grip, its really going to depend on the track layout and power levels but I do know the sidewall profile of the tire matched to a rim width seems to make a huge difference in the ability to turn consistent fast laps. 275’s on 9” rims feel squirmy vague and snap loose at the limit they feel better on 10”. 245’s on 10” wheels feel like magic. I’ve run 245’s and 275’s back to back on 10” wheels and 245s’ feel better and seem to be about the same lap time on a track with ~325hp. I did not go any faster on 275 A6 than I did on 245 R6. I imagine 245's would feel ok on 9” and potentially could have more grip than a 225 on a 9. But then again 225’s on 9” begin to have that magic sidewall feel again that allows you to drive them at the edge more easily.

Making the power and reliably isnt an issue, Ive built plenty of these, I can do the fab, the building and the tuning, and can supply all of the parts myself. Power plays to my strengths, setup and parts selection for the chassis is what I dont have experience with.

Your tyre advice is invaluable, looks like a 225 on a 9 is going to be the most cost effective combo for me that will suit my requirements.

Thankyou.

Ok with a 2560. Must have a different correction factor for south of the equator or something.

Not familiar with that car myself but 1:09s aspirated suggests it has a solid platform from a handling perspective. Knowing the targa boys, that time would have been on semis so factor in an increase in spring rates if you're moving to a higher grip tyre.

R80s cope surprisingly well with brief lockups but it requires the driver to know how to modulate the pedal. I didn't flatspot a single tyre last year (touch wood) and that's a lot more than I can say for the old Dunlop slicks I used to run. A050s are even more resistant to flat spotting.

Otherwise, an NB8B ABS install is not that hard.

I can do over 250 on the 2560, but I dont have a turbo yet (I have a few 2560's but if buying a T28 of some variety is considered good value for laptimes ill do it)

Zossy, what rates are you using on your n/a na?

Dann

I've tried a variety from 425/300 to 800/500. Running R80s I'm running the stiffer end of that range. Might even go stiffer.

I have run Koni Race and HSD coil overs and both were/are very good with 8-10 KG front and 6 kg rear springs...

If you are going to be really trucking a 9-10 kg front would be my suggestion. 11kg worked well on smooth tracks but anything with bumps (pukekohe) was terrible with more than 10.

Don't buy the whiteline roll bar kit, the rear is way to big. The front is perfect though, i forget the size, maybe 24mm?.....the 14mm or 12 mm oem rear roll bar is the best match..once again if your really pushing probably the 14mm would be best.

I DO have the whiteline kit but have the rear on softest (we figure equiv to 16mm) the front on hardest and 10kg front springs, with 225 nt01's on 9" rims I find the balance superb. Great turn in and front tucks in nicely (oversteer) on throttle.

In regards to tyres, i think if you run NT01 or better (hoosiers, the Yoko's Zoshy recommends etc) 225's on 9's will make you pretty happy. It is an amazing combination at 250hp levels...certainly a more than adequate starting/development point.

I also don't regret going to the 11.75" BBK. However that is in a racing environment...I think in pure lap time chasing (i.e. no passing required) the 11.00" BBK would be adequate ...BUT if buying, go straight to the 11.75 BBK...it is a huge improvement in feel and power over the 11.00"