gtred

I'm putting together a decent effort at an engine and spare to run approx 12 weekends of scca and conference roadracing sessions this season.
What I have been using is a 250whp oem motor with a garrett 2860; squaretop/exhaust/ms3. Now at midpack. I need to gain about 1 1/2 sec a lap to get to upper midpack and catch up to a few old racer friends. It needs to last for 20-30 minute sessions.

What is a reasonable/reliable method of getting to 275+ rwhp? Higher revs/ mid-boost levels?, or lower revs/higher boost?

Engine 1: 9:1 JE/ Carrillo/ ATI damper. I plan to begin work on the head once I am able to find a compatible cam profile. Square-top. I think most use 1000cc injectors at this point. I think most use a coolant reroute at this point. Unclear if ACT/ street organic clutch will be a benefit to save the drivetrain, or if it will slip? I'm also unclear when the garrett gets innefficient?

Engine 2: oem msm pistons/ china rods/ ATI damper/ oem msm head/cams/ squaretop/ 450cc injectors/ ms3. ACT street clutch.

Help me with your experiences on rpm and boost levels in an extended session. Thank you!

Savington

iTrader: (31)

25whp will not find you 1.5sec. More like 50-75whp. 250 to 325whp is a paradigm shift on track. Totally different engine, drivetrain, cooling requirements.

It will be far cheaper for you to buy that 1.5sec in the form of stickier rubber, diff upgrade, better aero, or better shocks, if you haven't done those already.

Canyonfive

Whats the configuration and class for the car? +1 for what savington said

codrus

+1 on what Savington said, if you're looking for time then the motor is probably not the easiest way to do it.

That said, on the original question, 300 at the wheels is about where a GT2860RS is done. Maybe with heroic measures you'll get it to 325, but going to a GTX would be a lot easier. That's on gasoline -- if you can get E85 and you're not using it already, then that's worth investigating.

My sense is that within reasonable limits, it's easier to make reliable power with more boost than with more revs.

--Ian

aidandj

iTrader: (5)

We don't have e85 around here.

He's running on hoosiers iirc, but I'm not sure about diff/suspension.

Above 300hp you can also start treating transmissions as consumables.

gtred

I'm in a "run what you brung" type of class, so no rules. The car is a little heavy at 2450# with driver. MCS coilovers with standard racing rates. 6-speed/msm diff.
Q: Will a sub-300 hp car stay together for 30 mins sessions?

I'm presently trying to sort out a cam. To do that I need to get a better grasp on rpm and boost levels to pass on to the cam grinder. I think that I could get pretty close to what I need with a 7800 redline and 15# boost. Does this sound about right?

Well, if I can't catch up with my old buddies, then maybe I can at least get in their way a little at T-1...

aidandj

iTrader: (5)

Kinda depends on how much you want to spend. A built motor, oil cooler, good cooling system could hold together quite well.

Also this is PIR, its 2 drag races with a couple corners in between them. Power helps

Some sort of clutch type diff might help too.

You should swing by sometime when I have my setup running and we can talk some more about all the "reliability mods" that people like to run.

Savington

iTrader: (31)

2860 is not going to make it past 300whp without substantial complaining. You need a GTX or an EFR to do that. I would also avoid aftermarket cams at that power level, since anything you gain at 7800rpm will just result in lost power at 4800rpm. Power is power, 300whp at 7000rpm will accelerate you just as hard as 300whp at 7800rpm. The difference is that the 7000rpm motor will make a bunch of torque down low, whereas the cammed 7800rpm motor won't. Cams and revs are for NA cars that don't have any other option.

aidandj

iTrader: (5)

idk, we don't have a ton of data on cams, and most off the shelf cams are for N/A builds. I'd love to see someone work with a manufacturer and find a cam that benefits a turbo build anywhere. Which is what it appears is going on. I'm always in for experimentation

Savington

iTrader: (31)

You can add lift and increase power everywhere. If you want to change the shape of the curve or move it up/down, you have to add duration, which is going to harm low-end power. Stock cams nose over at 6600-6900 depending on the cam. If you want cams to work at 7600-7800rpm, you are going to lose low-end. There's no getting around that, IMO.

aidandj

iTrader: (5)

I'm not necessarily disagreeing. But there is so little data on turbo BPs with cams compared to other platforms.

Craig, maybe also consider a change in gearing? Instead of revving it out maybe find a longer final drive. The 4.1 and 6 speed combo is pretty short for a 250hp motor. It was put in a 180hp setup originally.

Savington

iTrader: (31)

At PIR you are deep into 6th no matter what, so gearing should be run as short as possible to make the 4-5-6-7 work. Unless you are running out of gear as you track out of 7, going taller will not make the car faster.

aidandj

iTrader: (5)

Going taller saved me a shift on the front straight, nothing on the back. Kept me from hitting the rev limiter between 6 and 7. All depends on speed though.

gtred

Yeah, you may be deep in 6th, ...but I'm currentlyonly seeing 5th... but, having to rev to 7400 in 5th to avoid a brief upshift at the chicane entrance and at the end of the backstraight. After 7000rpm I'm just coasting and making noise. It'd be nice to bump the power curve up 500 or so. I'd have to look at datalog, but I don't think that I ever get below 4500 at any of the NW tracks I drive. Ive never make it too far South; Willow Springs or Texas. Is there a reason that lower rpms might be helpful there?

I suppose that things could change if I'm adding more boost (previous engine was stock rods). Maybe I'll be using 6th.

Sav: Tell me more about your tires? I've presently got several sets of your 6uls in 15's; 8's and 9's I think. Not sure what size of slick is used on a miata. In the past experience, moving from hoosier dot's to slicks was worth .5 seconds at my home track.

Aidan: Cat cams just sent me a profile that shows a mild bump in duration from the oem camshaft (I think)?, a slight bump in lift and a good lobe center separation. (M-turbo "cam questions" in engine performance). After seeing what Andrew had to say, I wonder if this "mild cam" might be a good option?

ridethecliche

iTrader: (2)

Just wanted to clarify that Sav=Andrew of TSE and Emilio=949 6UL's.

Regarding this thread, I'm curious how much difference aero would make if not on the car already. I.e. splitters, wing, louvres, etc.

From what I've seen, you're likely going to want a reroute and hood vents to keep things happy!

Signed,
Aidan's Favorite Bench Racer.

codrus

Weight reduction is almost certainly the most effective way to improve the lap time.

The power limit on the turbo comes from the flow rate of the compressor. If you take a look at the GT2860RS compressor map, the rightmost line is around 35 lb/min of air flow. Rule of thumb is around 9-10 hp per lb/min of air, so the 2860's compressor is done at 320-350 crank hp, or about 300 whp. The turbo doesn't know what speed the motor is turning, all it cares about is flow.

The compressor map for the GTX2860R, OTOH, goes to the low 40s, suggesting it'll do 50-75 hp more than the GT. The GTX turbos are basically just a straight upgrade of the GTs with a better-designed compressor, so it should spool similarly and will probably just bolt up in place of the turbo you have now, making this a relatively easy (albeit not cheap) upgrade.

EFR is even better but doesn't bolt up, so you'd probably need other new parts (down pipe at least, possibly manifold as well).

--Ian

gtred

Oops. Sav... but I do have to say that your BBK certainly improved my threshold braking skills. Thanks for producing such a quality product! What do you think of this smallish CAT Cams turbo grind? (engine performance thread). https://www.miataturbo.net/engine-pe...estions-92812/

AFBR: No aero at this point... unless you count the fake MSM rear trunk lid spoof.

ridethecliche

iTrader: (2)

This thread should be pertinent to your interest: https://www.miataturbo.net/race-prep...st3-4-a-92020/