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.