Power Needed for Sub-2min Thunderhill Lap?
 

Hello Miata Turbo Forum,

Got my '97 in November of 2010 in Reno, NV, and have enjoyed learning the car over approximately 20 track days. I've installed a pretty good list of chassis, suspension, tire/wheel, and brake mods, but only a Jackson Racing cold air intake, header, and cat-back for the engine. As of today, the car has about 123k miles on it.

I turned a 2:14.xx and pulled 1.49G on 225 NT-01 tires at Thunderhill (bypass) last Saturday and feel I'm getting close to the existing limits. It's time to start looking at power adders and a turbo or supercharger seems like the right choice.

I'll be doing more reading here, before asking the inevitable stupid n00b questions. My only reservations about boost for this specific car is that the engine is starting to make that dry lifter noise on cold start-up. I don't want to hurt the engine or drive train by asking for too much. 8 psi with an intercooler seems a good target.

"How Much Boost" will probably be my first question. That question is probably a common one and I'll read what is on the forum first. The FM 8 psi package seems a strong option at approximately $3,400 for a complete kit with intercooler. I would guess there's about $1k profit in that. Got to see what is available before buying that.

Looking forward to learning from the members here and getting a well-engineered boost system at a reasonable cost. You have all "been-there-done-that and got the t-shirt". So, maybe you can show me how to get to 1:59.99 at Thunderhill? I know...that's a tall order on 8 psi.

Sig to follow...

Hi Builder, enjoy your stay :)

Welcome.

Whats the local SM record there, just for reference? Have you lightened the car? That's free powet right there. Start with MS, there's some weight savings and power to be had with it. Wait for the turbo until you're dyno'd at 130hp and 2000lbs.

Not the answer to your question, but necessary information for building a reliable turbo track car:

https://www.miataturbo.net/showpost....&postcount=123

Track record going over the crows nest/cyclone at turn 5 is 2:06.717. The bypass that the OP drove will be slightly faster.

Hmm, that's quite the track car to be 6 seconds under...but "easily" possible. I wanna say a reliable 250hp, 225 slicks, $2000 grand in suspension and all the supporting mods to go with it. I know my setups around 200hp, I don't think it'd be enough for 6 seconds under SM times, which is where my 250 estimation comes from.

Savington is the one to ask though, I'm sure he's done exactly what your asking and can tell you what power he was running when he did it.

Our Fail Wheel Drive E1 RSX-S with approximately 11:1 Weight/Power ratio in enduro trim is capable of running :59.999 running the bypass.

I assume a well driven, well set-up Miata with a similar power to weight ratio should also be able to run right under 2 minutes. So 200-220 whp?

Emilio and Savington probably have a better idea of what's needed, they have the expertise of running miatas at Thunderhill.

If you have the right suspension/wheels, your car should be capable of SM record times, so 2:07 over the top of 5 and 2:05 using the bypass.

My best lap at Thunderhill using the bypass is a 1:54.5 at 280whp. At 200whp, I was able to do a 2:03.x when the car still had a full interior. With a full-weight street car, you would need at LEAST 250whp, and possibly a little more than that, to get under the 2-minute mark. With a stripped-out race car, you could probably get away with a little less, maybe 210-220whp. Either way, you're going to need to be a hotshoe, and that means finding another 5-7 seconds as your car sits today.

The track was way off prime in this video, but here's Nick's race from last year in Theseus. His best time was a 1:59.1, IIRC. I brought the car back 2 weeks later with a different alignment and got down to a 1:57.8 over the top of 5.

http://vimeo.com/26917442

Thanks, Rick! Lots of great info here.
Thanks! Power-to-weight is definitely a major consideration. This is a street car, but still needs to go on a weight-loss program. I think the best Thunderhill SPEC time is around 2:08.

The car scaled at 2,585# with full fuel and me in it. Guessing power is 100 whp? Stock '97 with 123k miles, cold air, header, and cat-back. That's 25.85 pounds-per-hp. 130 whp and 2,250# (250 for me and fuel) would be 17.31#/hp. That is a ~33% improvement. That's huge! Can you point me to a list of stuff to add to the engine and remove from the car to move in that direction? That would be an amazing increase and great target to shoot for.

Curly, I don't know what MS is?

Thanks, Choke. What a great thread; that list should be a sticky. I will use that as a point of reference moving forward.

Okay, that's lower than I thought.

That's probably a good estimate. I was reading all of the Thunderhill posts in the Lap Times sticky at Miata.net.

Unfortunately 200+ hp is gonna be outside the immediate budget. From what I can tell, a new clutch and 6-speed is needed at >180 whp. I want to see how close I can get with a stock drive train on my next thill visit. Think I can get into the high-13's at this weight. Then, decide on an 8psi package that won't require other extensive upgrades (internals, coils, injectors, etc.). From what I can tell, 7-8psi is a reasonably safe level for a 1.8 with 123k miles on it. Not looking to do a turbo block just yet.

Please stop me now, if that's not correct. At that power level, I should be under 2:10 (somewhat less with significant weigh reduction).

I'm gonna start looking now...anyone have a Miata weight reduction check list? Getting pounds out equals cheap performance upgrade.

Give us an idea of what you suspension setup is. There may be more to gain there for the money if you don't have a good setup.

Thanks, Savington. In what configuration? I think that would be a tall order without equal power/weight and full slicks.

Okay, well...so much for sub-2 with 180hp. I knew that wasn't going to be possible, but I want to see how close I can get at that power level.

New (last Wednesday) Megan EZ Street coil-overs with 8/6 rates, 8x15 6UL with 225/45 NT01. Obvious after one day, I need higher rates. This was my first full day through the bypass; I had done only 3 laps through there before, but was catching air by the end of the day! What a blast!

I turned a 2:15 as is. So when I become a "hot-shoe", I should turn a 2:08 in a naturally aspirated N/A on NT01 tires, which is within three seconds of a SPEC and just 5 seconds slower than a car with twice the power?. Perhaps I misunderstood?

Great video. Looks like the tires are a little hot. Is the throttle (boost) hard to control in that car?

Open to all suggestions. The details are in the sig.

I put over a 1000 track miles on my turbo 1.8 with power varying between 180-230whp and I never had a problem with my 5 speed. The engine let go before the trans ever did. I did baby the trans though, easy shifts, tried not to shock the system ever. YMMV, but don't assume because you have 180whp you automatically need a 6 speed. It's definitely good insurance though.

Im not sure as you havent actually said how much experience you have at the track, or this on in particular, but id say you have a year of track days ahead of you before you are close to the cars limit on that track.

And yes it does take 100rwhp more to drop 3 seconds.

Dann

Welcome, Builder. Check out the Miata Gallery and post up some pics!

Maybe closer to 2:10 through the bypass (bypass is worth ~2.0 seconds). A top SM is about 250lbs lighter and has another 10-15whp, and they will typically set pole at a regional SCCA race in the 2:07-2:08 range going over the top of 5 (so ~2:05-2:06 through the bypass). I would expect the weight loss to find ~2 seconds, and then power to find another 2+ seconds.

Up to around 140whp or so, there are major gains to be had in power, like a second for every 10whp you add. At a certain point, the gains diminish, though - if your car as it sits today (2500+lbs) is capable of a 2:10 through the bypass, a 140whp version might be capable of a 2:06 or a 2:07, but a 200whp version would only get to a 2:04 or so. That's why it would be 250+whp to get down to the 2:00 range.

A little more than normal, yes - it was scorching hot that day, 95*F at least, and Thunderhill does not cope well with heat. Theseus has 350whp, ~300wtq, and a comp weight of under 2200lbs with driver, so it's not a particularly easy car to drive under any circumstance ;)

That's good news. Gonna keep my eyes open for a 6-speed, just in case something happens.

Data point: I remembered to set the trip meter when filling up before going on the track this weekend. I drove all 5 sessions, 6-8 laps per session, put on 110 miles and used a full tank.

MS is MegaSquirt, a standalone ecu (completely replaces stock ecu). You'll need a wide band too, but it can save you some weight in the engine bay, and give you some power if tuned properly.

Your car is heavy. Consider ditching the power steering, air conditioning, charcoal canister, carpet, soft top, spare tire, jack, etc. try searching light weight miata on google, there's a good write up with a list of stuff to take out and how much it weighs.

We'll just have to agree to disagree on the 100hp effect. I would bet heavily that I can get more than 3 seconds by adding 100hp. That's double the existing power. At Thunderhill, 3 seconds is only 0.2 seconds per corner exit.

Yes, I should have put something about my driving history in the OP. I've been instructing for almost 12 years now. Been to Thunderhill every year 6-8 events (Hooked on Driving, TEAM Racing, NCRC). For about the last 7 years, I have been doing between 35 and 50 track days per year as an instructor and driver. Other tracks attended include Buttonwillow a dozen days, Reno-Fernley (Lots!), Sears a dozen days, Laguna a couple of times, and Miller Motorsports Park 6 days. I estimate the total at somewhere around 400 days.

Luckily, I've had some experience instructing in Miatas, but this is the first one I've owned and this is just the start of my second season. I should have reserved the last session for a solo run, but a 16.2 with a passenger is probably a 14.5 without. I'll post that video.

Adding the coil-overs gave me a huge gain. I think what I have to learn to drive is the effect of the new coil-overs on tire grip, which I'm pretty sure will only take me another a day. What an amazing difference! Really hope to see a 13.5 next time. Pretty sure I'll be within a second of max on the current setup, at that point.

I'm in the habit of not threshold-braking, though. I paid for two flat-spotted tires last year...didn't like that!! I'll have to push the braking zone harder to get the last full second.

Thanks, Brain! I will do that.

This is a problem that will definitely affect your lap times. Learn to threshold brake and react quickly if a wheel begins to lock. With experience you can definitely notice a wheel beginning to lock and catch it before it's too late.

That sounds a little more like it. We're still a couple of seconds apart on theory, but, I learned a long time ago that perception isn't always reality and surprise myself.

Yup, that's all logical. Okay, that will probably be third or fourth-year benchmark. It will be fun trying to get there with 180whp!

Sweet! Yeah, hot isn't great for grip or performance. Just out of curiosity, how many hours will you run that engine before freshening?

Yeah, I know...I know. I can concentrate on that next time and weed it out of my driving style pretty quickly, I think...especially now that I have some serious grip available to actually use.

Man, those coil-overs made such a huge difference. Last session, I may have found the true extent of the XP8 pads. No fade, but peddle pressure a lot higher and the tires still held! Speed at the apex of turn-1 in the last session was 5 mph higher compared to the first. Got to love that! Really can't wait til next time to work on braking and entry. I still loose 1 mph turning through 8, even though WOT from 6 to 9.

Oh, yes. I've read a little about MS. That might be a little beyond my capabilities and time available to learn. Do you still have to build those boards and boxes and stuff? Will OBDII still work for smog?

Thanks for the pointer on weight. The Miata will start a diet immediately. Air conditioning? Really? Yeah, that' heavy. Dang, not sure I want to do without that!

100whp in the OP's car would be worth about 7s assuming the car is set up halfway decent.

lbs/hp required is a sliding scale, as gross weight goes up a lower lbs/hp is required for the same lap time. A lighter car stops and turns harder.

A typical lightened HPDE Miata can get down to 2200# with driver and a splash of fuel with spending big bucks. Said 2200# car with an EP style air dam, small duck tail spoiler, 225/45 medium compound tires (R6,NT01,C51 Z214,R888,RA1)
and about 170whp would go under 2:00 in the right weather.

160whp can be had with a stock bottom end, BP5A cam in BP4W or/ VVT head, P&P head, square top, I/H/E and ECU on pump gas. Add 10.5:1 or 11.0:1 pistons and you're above 170whp.

When I pulled the a/c and p/s off of my '97 (with all the block brackets) I weighed it at 36lbs, nearly all of it at the very front of the car.

I also suspect if you're going to get to the lap times you want you might be in for a coilover upgrade as well.

That's more along the lines of what I was thinking. I knew it would be a stretch to get from the current 2:15 to sub-2 with a 180whp kit. But, I figured I could get close. If I get that installed, a good goal will be 2:05.

Having driven probably 75 or 100 different cars on different tracks, from my 4,450# Impala SS to Ariel Atoms, that is exactly how I would state it. Well put, Emilio.

Good stuff. When you say "160whp can be had with a stock bottom end", you don't mean that 160 is all it will hold, though, right? Those numbers are referring only to naturally aspirated?

What are the big-buck items to lower weight? CF parts, A-arms and clutch come to mind immediately.

I don't know what all those initials are for parts and stuff, but will find out.

Thought it might be a few more pounds than that. All adds up and every little bit helps. What does your car weigh?

Coil-over upgrade? Yeah, probably. I just put the Megans in last week, so they will be around for a while. HUGE improvement over the original stuff with 123k miles on them. Maybe 2013. Next step will be top drawer.

Here ya go:
http://www.lightweightmiata.com/beast/
As I said earlier, the biggest stuff is AC, PS, passenger seat, jack/spare, soft top, airbag(momo wheel?), carpet.

Megans isn't really a good track setup.
Not sure why you can't get weight down to 2,400LB. I can do that without trying. Especially without the 100lb cage
145whp, 2270lb and 205 nt01 will get you to 2:02s. So 180whp and 225 will get you to 1:59.99. Adding 200lb add about 2 seconds.

What a great list! Thanks, Curly. Wow, the site owner has way more patience than I for details. Brilliant!

Compared to many coil-overs, probably not. However, they are orders of magnitude better than what I had.

Haven't tried yet, but sounds very doable.

So, slightly more power, slightly more weight, and a slightly wider tire should be right there. You are making me drool for the sub-2 mark.

I read all the Thunderhill lap posts in the "Lap TImes" sticky at Miata.net. It would be great to see if that's possible. Gotta try it!

The ACL bearings have a nickel layer that begins to deposit into the oil when the bearings are worn out, so I do regular UOAs and I'll pull the motor to refresh it when I see the nickel content spike in the oil. I would expect this to happen at around 60hrs of run-time.

Stock bottom end will survive much higher power levels but that's not the point. The point is $$. You will not be required to spend a dime on the bottom end if it is a healthy NB2 (01-05) and your goal is 150-160whp.

Did I miss something or did you state budget constraints? Any questions about setting up a car must have that metric. Vast ocean of prep differences between a $4k and $40k HPDE car.

Ill apologise for this statement, its very vague.

In Australia not many tracks are longer than 1:45.

And my local is 1:10 in my aspirated NA6, top speed 90mph.
So an extra 100rwhp is only worth 3 seconds there, where as on a track thats over 2 mins long, and higher average speed (therefor wind drag) 7 seconds sounds right.

Dann

Ahhh, that's how you save your engine. Didn't know how best to monitor the condition of a race setup. On a refresh, as long as there were no issues, what components do you always replace? Are there parts to machine with every refresh? Can you share a range on cost? Trying to get an idea on budget for a serious build.

By the way, awesome sound track in that video.

LoL, yeah well... Mine is a '97 with 123k miles on it. That's the NB(1) engine? I added a spreadsheet of current costs to the "Details" page in my sig. I've spent $9k, including the car.

Didn't state a budget, but that I'm considering the VooDooII kit for $3,400. I'm budgeting $4k to go up a power level (turbo or supercharger and body changes for cooling, add the Sport Brake brackets to the rear (already have fronts), and keep my eyes open for a 6-speed and/or engine block for future upgrades. I'm spending some car budget on two other vehicles, as well, right now. Got to finish those (new engines) before I can go big on the Miata.

I haven't decided the VD-II is what I want yet, as I suspect there's a good package I can assemble from parts and the knowledge that folks share on this forum. The designed package is an easy and fast way to get everything needed, which has its benefits 'cause I don't know much (anything) about turbo systems. I also want to look at superchargers, as driveability is really important at the edge of control.

All that said, I'm very much in the learning stage on this and open to all options. Maybe it makes more sense to build a $3,400 N/A engine, if it will make a dependable 180whp. I don't have the time budget to do constant rebuilds and I can shift a stock engine all day long at 7k without any concerns.

Now worries, mate! Yeah, Thunderhill is ~3 miles and the front straight allows my Miata to hit 101.xx MPH (10Hz GPS, 105 indicated) with this driver's last turn (15) exit speed.

Edited to say, there are some true race-prep cars that are capable of turning Thunderhill laps at 1:45.

[QUOTE=Builder;836272]Thought it might be a few more pounds than that. All adds up and every little bit helps. What does your car weigh?QUOTE]

My car with my 200lb ass in it was 2522 with half tank of fuel on the corner weight scales... this is a full interior, no lightening done '97 with 15x9 6UL's w/225/45's, Harddog roll bar, FM frame rails, and more stereo gear than stock.

I think since I have a nice Audi for a DD now, it's time to "add lightness".

That's about the same...mine is 2585 with full fuel, spare & jack, 8x15, two UltraShield RallySport seats, etc. No lightness added yet. I do take the spare and jack out at the track.

Gonna be a blast to have more power and lighter weight!

Thunderhill Video
 

The was the best of the afternoon. I had passengers in all three PM sessions. In the second morning session, I turned a 2:14.97 in the damp, but the GPS hadn't arrived yet, so no data overlay on that ( ).

T1
In one video you downshift to what sounds like 3rd. Faster and smoother in 4th.

T2
You sorta late apex but you don't need to. Fastest line there is shortest distance. From extreme right edge coming down hill, angle in towards inside if T2 then brake and brake late. Carry a tiny bit of braking into beginning of turn. You carried very little speed into the turn and released the brakes too soon. If you can release the brakes in T2 that early, you're not carrying enough speed going in.

T3
When you exited T2 you unwound too early and just went straight down the center of the track. You want to keep turning left as you hit the exit kerbing of T2 so you shoot across to the left a little bit. From there you angle back in to the middle of the track and then brake. You were braking while still pointed away from inside of T3 instead of towards it.

Once you begin braking you want to end up on the inside of T3 sooner. You never hit the apex but should be right on top of it for at least half the length of the kerbing. It's way off camber so the less time spent in the turn the better.

T4
You didn't use all the track on exit but you need to. Also you lifted after you made the right left transition. That can upset the car. Better to lift when you first making the steering input to change directions, getting weight on the nose, then back to WOT as you finish the direction change. As you carry more speed off T3 your mis-timed lift will get the rear end to step out in a big way. The other detail is the length of the lift. Make that transition hard, max right to max left abruptly with a very quick lift. That's just time spent coasting :)

T5
Good line but the lift could have been much shorter.

T6-7-8
Good

T9
You brake too much and didn't nearly use all the room on the track out. You should struggle to stay on the track at exit there if you want any speed down the straight. You also don't need to traverse all the way to the left side of the straight. Sticking on the right side save about 50' distance

T10-13
Good

T14
Braking too early and not hard enough. You then hang on the brakes too long and over slow for the turn. Too wide there too. Try just straddling the rumble strips mid turn so the car is loaded harder as you track out of T15.

Other notes:

-Your shifts are kinda slow. Most were a full second, one was over 1s. The slow ones should be 500ms. If you have a light flywheel, you should be able to routinely snap off 300ms shifts.

-You're not braking very hard anywhere. Miatas make a lot of time up under braking. If you are after a sub 2:00 there with just enough hardware to get the job done, you're going to have to learn to threshold brake everywhere. The first time you do T1 right is a bit spooky. You go in deeper and just dab them briefly but very hard. Roll off gradually to set the nose and slip angle then right back to power. It's not a long smooth braking zone.

- You spend a lot of time with your hand camped on the shifter. Stop that. The right hand should only come off the wheel to flick the shifter and reach for a beer.

- I might suggest changing the camera angle to capture the forward view and your hands on the steering wheel. Very helpful to see steering and pedal inputs.

Camera angle I like in my cars http://youtu.be/CXWqcvYBhug

Best guess is that car will go ~2s faster as it sits.

Agreed. With the previous setup, my apex speed was a full 5mph slower and required third. Discovered lat in the day that I have more grip and 4th would be much faster.

Makes sense. I'll give that a try.

Interesting. Never had the grip to get back left on T2 track-out. I'll check it out. Yes, I should have been tighter to T3 and for longer.

Agree I need to go wider on T4 track-out. That worked better earlier in the day. Best result I had was to start the cross-over angle before the drop, then short-shift at the drop, which settles the nose well on the other side. That allows WOT and further turn-in on compression. This was my first day with the bypass and I was trying different things...including not tracking out of 4 and different launch points over the drop. I caught some big air there once and almost weeded left of T5.

Maybe. Looks like I should actually wait another tenth or two after the short shift. I grabbed throttle too early and had to breath throttle before entry. Better to have waited on downhill.

I should go in earlier on 7.

Agreed. I've been taking it really easy on the brakes, but will be using them a lot heavier next time out. Much more grip now and I can go much deeper without worrying about flat-spotting tires. Not hitting my marks well for T9.

Love T10. Could go deeper on all entries, though.

Yup, braking heavier on all corners next time. That was wider than normal. Trying to preserve as much speed as possible onto the front.

Yes, I can easily shift much faster, but am taking it easy on the trans.

Yup, I am pretty safe going into T1, especially with a pax aboard. As stated above, more focus on braking next time.

Haha. You think it's the shifter, but it is actually a beer. I probably won't break that habit until I need more effort to turn. Ain't power steering wonderful?

For some reason, the mount wouldn't stay on the rear glass that day. I think the suction cups were compressed in the box. It's usually pointing over my right shoulder to show shifts and steering input.

Yup, I figured 1.5.

Thanks for the nit-picking, I mean, detailed critique. I appreciate you taking the time to do a thorough dissection. It's great to have this kind of analysis with suggestions that can be put to immediate use. Can't wait to get back there and try some line adjustments, challenge the brakes a little more.