patsmx5

iTrader: (16)

We math'd it in the thread Sean linked that I started, go check it out. The takeaway is heavier flywheel = happier drivetrain, and it can be quantified. You are correct about shock loading, that is exactly what the heavy flywheel minimizes.

I understand what you're trying to say, a heavy flywheel can cause more shock loading between gear changes. Sure, but that's solvable via flat shift, launch control, and driver control. The shock loading via the engines torque pulses is ONLY minimized by damping those pulses, and that is literally why engines have flywheels.

patsmx5

iTrader: (16)

Long time no update. Have been driving and enjoying the car for months. Got another set of 99 NB wheels and had them powdercoated and a set of street tires for them. And put the ID1300's in, and D34 yellow top optima battery. Other than that just oil changes and fuel. Up until a couple weeks ago...

I recently decided I should try turning the front turbo's boost up from 18-20 up to 25 or so to get more midrange power. Well after making about 20 pulls to 8,500, the front turbo had a bearing wear out and developed enough radial play in the front journal bearing to begin contacting the housing. Very minimal damage, easily fixed with a rebuild, but the REASON it failed became obvious, I overspun it.

Honestly I expected the thrust bearing to fail at high boost on a cheap ebay turbo, not a the journal bearing. It has excessive radial play in the front now.

This is the GT2860 plotted on my setup for 15, 20, and 25 PSI.

Kind of obvious why it died after looking at that.

Also I have to say, after driving it with the compound setup for a few thousand miles, there was one thing I've wanted to fix. The current setup, the front turbo was too small. So it would spool up, and not pull all that great until the back turbo finally spooled up. Once the big one comes online it's nuts, but before that it wasn't. The ebay GT28 was only a 49mm inducer on the compressor, where the big turbo is a 69mm inducer. Internet wisdom says you want a small turbo about 10mm smaller than the big one for a compound setup. I was 20 smaller, so way off!

So I've decided to go to a bigger ebay turbo up front. Since I mostly drive this on the street, I want more torque available from the front turbo. It's obvious this GT28 I wasn't happy after 15 PSI. I think something around 20-25 would be a lot better.

After doing some research, and getting some advice from deezums and vlad, I bought another ebay turbo, a GT3076. Specs are:

That's a 57mm compressor, so only 12 smaller than the big one, much closer to the 10mm smaller rule. Also plotted my setup on garrett's map for this turbo

Looks a lot better, and not going off the map after 15 PSI. Should be able to run 20 or 25 reliably on this one I think. I may even try it at 30 (pushing it, but still on the map), and just set the back one to a low pressure to bring it up to whatever final boost I max these injectors out at.

Will be a week before it arrives. I gotta mod my manifold so a T3 will bolt to it (it's a T2 mani) and redo the downpipe. Good news is the new turbo is V-band on the exit of the turbine, so I look forward to not having to deal with bolts on that connection now. Apparently my 88 dollar manifold isn't on ebay any more??? Would just buy a T3 version if they were listed, but my taco taco friend must be out of them right now.

Ted75zcar

iTrader: (2)

Right on man. At 30 psi you must be pushing at least 40lbs through that thing, even if it gets bypassed for the rear at mid rpm. That must be crazy. I really wish I would have put some rods in my proof of concept, it just wants to go and I won't let it. The GTX28 I installed has a clipped turbine (PO) so that is also bumming me a bit, but I don't want to pull it out right now cause it is too much fun to drive, and getting the sequencing in order for my air handling system is taking quite a bit of characterization.

good luck with the upgrade!

patsmx5

iTrader: (16)

Yeah I can't wait. I ran a GT3271 years ago (real garrett though) and it hit 28 PSI at 4,500 RPM on a non-vvt motor. I'm hoping this turbo can spool similarly. Honestly if it will hit 25 PSI or so by 5K from a 2nd or 3rd gear throttle stab at 3-4K, that would be great. Won't know till it's back together but I think this will prove to be better than the previous one, it should be a nice upgrade.

I was never bypassing the front turbo, just shoving boost into it when the big one spooled. Will do the same with this one. Let the 3076 get the party started, and let the GT45 keep it going up top.

Ted75zcar

iTrader: (2)

Oh wow, yeah you totally need a bigger turbo in the front! Do you taper the PR across the smaller compressor via wastegate on the exhaust? I use an external WG to bybass the SC when the turbo is spooled, works pretty well.

Girz0r

iTrader: (1)

patsmx5

iTrader: (16)

No, I keep the front turbo holding a constant pressure relative to the pressure going into it via closed loop electronic boost control. Before it was 20 PSI on the front, and then the back one would add in 18 into it, so the front would output 38 PSI at the motor.

What I would like to do is set the 3076 to 25-28 PSI, and then adjust the big one up until I max out these ID1300's. That way I have good midrange from torque and response, but still have the topend. In this example, if 35 PSI maxed them out, that would be say 25 from the GT3076, and 10 PSI from the GT45.

shuiend

iTrader: (24)

Why not just buy the T3 version of the 1.8 TacoTaco manifold and save yourself some effort modding the other one. They are pretty cheap.

Also what ever happened to you running stock ecu with MS in piggyback and such.

patsmx5

iTrader: (16)

I couldn't find the 1.8 taco mani on ebay any more. If they're still for sale I'll just buy another one for sure. Or if someone here has one.

ECU project has changed a lot, but it's still alive. It's not finished yet.

shuiend

iTrader: (24)

You got a PM. I should have you covered on the t3 tacotaco.

patsmx5

iTrader: (16)

Sweet! I PM'd you back, this will make it easier vs having to mod my T2 manifold. It is an authentic tacotaco T3 mani, right? :P

miata2fast

iTrader: (2)

Just read this entire thread. Can't wait to see the next timeslips.

Have you gotten slicks yet?

patsmx5

iTrader: (16)

I have the mickey thompson drag radials, no slicks yet. But I will be making a BIG change to make the car faster at the track after the turbo is swapped out and working well. Besides the fact that I expect a GT3076 to make more power.

miata2fast

iTrader: (2)

Do you have a size in mind?

aidandj

iTrader: (5)

2 of the big ones.

patsmx5

iTrader: (16)

I'm going to do an auto swap. Once that's done, sorted, and not slipping at full power, I was thinking a 100 shot out of the hole would be nice to get a good launch once the auto is in. But we will see.

aidandj

iTrader: (5)

quicktime bellhousing with a powerglide?

patsmx5

iTrader: (16)

99 auto transmission, built of course. Plan is to swap all the stuff in to do the conversion, drive it at low boost to confirm the swap was a success (it's a pain to do a swap, lot of crap...), then build the transmission and get the boost up to all of it.

aidandj

iTrader: (5)

Why not something proven in the drag racing world to hold real power and shift fast? Easy to control, all you need to do is get a driveshaft and a mount?

patsmx5

iTrader: (16)

It's a street car, a powerglide is a drag car transmission. I can not imagine how slow a miata out of boost would be around town with a powerglide. The only way a powerglide would work in a miata is with a 5K stall so I could launch at full boost, and that would never work for a street car.

I admit I don't know what a built miata auto will take, but I'm about to find out. Good news is these transmissions are dirt cheap to buy, so if I break a couple figuring out what works, it's like 1/4th the cost of a 6 speed.