k24madness

iTrader: (6)

After over revving the crap out of my junk yard motor I opted to build one with some good internals. This was a cheapish build that yielded great results. The secret (I believe) to a great torque curve (for a rotrex) is in the cams. These are WebCam grinds that shorten seat duration by a LOT and increase duration at .050 a bit over stock (think stage 2) and lift the valves .400".

While not impressive by turbo standards this mill should still be a blast on the track. Having 95% of peak torque available from 5,200 to redline will really help get the car moving. Issues with the FPR caused us to run leaner than desired from 7k on up. Once this is resolved the torque should not fall off as much up top.

Supertech 10:1 pistons (11:1 CR after milling block and head)
M tuned rods
Ebay Header
Rebello Ported 99 head with focus on exhaust flow.
Supertech +1mm valves, SUB and heavy dual springs.
WebCam grind #264 intake and exhaust, 110LSA, 108in, 112ex.
Skunk2 intake (TC Design)
ATI Pulley to max 120k blower speed at 8k redline (11-12psi)
E85 fuel
Tuned by Tony at TC Design
Assembled by Rebello Racing.
Trackspeed supplied head parts.

Fireindc

iTrader: (13)

Dat torque curve. LOL, all kidding aside that looks like an excellent track setup. Get some videos of this thing in action.

Leafy

iTrader: (1)

Does this car have an automatic transmission? Torque converter lockup is that only thing I've ever seen make loopdeloops in dyno graphs.

concealer404

iTrader: (3)

Supra dyno chart.

Efini~FC3S

iTrader: (4)

I've seen weird stuff like that on our Dynapack, not sure what all can cause it, but maybe a clutch slip or some other slippage.

Just pretend like the dyno pull started at 4000rpm, seems legit after the curly whirl.

k24madness

iTrader: (6)

Those loops look like gear changes to me. I know he was also having a hard time with the dual 5.5 Tilton clutch. It has no slippage. Light switch on/off. Maybe that's why he opted to start the pull and shift gears.

I spun the stock motor to 7,400. The data logs never dipped below 5k on the track. With the forged internals the new power band will be 5,500k-8,000k. That is where the meat of the power is with this motor.

emilio700

iTrader: (3)

Great work. That's more or less the type of race engine package I wanted to build. Super efficient, instant boost. What are you using for a BOV. I imagine it has to be a monster to not have PTFB, like everywhere.

Duration on the stock BP4W intake cam is 248° seat, 204° @ .050, much shorter than the 264° you have in there BTW.

EO2K

iTrader: (37)

I knew you were local, I just didn't realize how local

Nice to see a Rotrex build where someone is using it where it does the most good (4-5k+) Out of curiosity, do you have a set of IATs logged for the top end of this 120k run? I've really never seen anyone log this, but I also haven't looked very hard

Also, where the hell are you finding E85 in the bay area? I've seen one station listed in Sunnyvale but that's about it.

k24madness

iTrader: (6)

Thanks Emilio. Tial 50mm BOV. It is HUGE.

Here are the cam specs.

..264in............Stock in
243@.010.....248@.010
216@.050.....204@.050
108@.300.....062@.300

..264ex............Stock ex
243@.010.....250@.010
216@.050.....210@.050
108@.300.....080@.300


Forget advertized when looking at cams, .080-.010 is lash spec so .010 is essentially seat time.

Less duration at .010 means more dynamic compression, less overlap.
More duration at .050 means more flow.
More duration at .300 means the valves are fully open when the piston is at maximum acceleration through the 90 degree sweep. This is a critical part of head flow.

18psi

iTrader: (76)

Very nice. Another rotrex to touch 300 like TrackDayHookeys (sp?) and Falcons setups

k24madness

iTrader: (6)

No IAT's logged. When the new ECU goes in I will be able to data log all that stuff easy.

University Ave in Berkley is where I get my E85. Damn tree huggers over there love the stuff.

EO2K

iTrader: (37)

Haha, I wonder if they understand the environmental impact & economic sustainability of the subsidized industrial corn industry

I'm still trying to figure out what I want to do with my C30-74 so I've been trying to follow threads like this around the web. I'm still an ECU away from reinstalling it, or the 80% complete FMII/2560 also taking up space in my garage.

k24madness

iTrader: (6)

Most likely not. Let's keep em in the dark though.

The choice IMHO comes down to street/HPDE car vs dedicated stripped track car. For street/HPDE the turbo is the way to go. I strongly encourage you to run the Tial GT2868 turbo though.

emilio700

iTrader: (3)

Never heard of this grind. Webcams site and catalog only mention one grind for each generation Miata engine. Full lift/ duration specs?
I see they are welded/hardened/ground.

A bit off topic..
The shortest duration cams we could find for the BP6D head moved the torque peak about 900rpm up the rpm band but only made a very slight increase in power. In contrast, the shorter cams we have seen for the BP4W bear more fruit. I think the VVT cams might end up with compromised peak valve acceleration in order to at least match the OEM .370 lift. IOW, I have a suspicion that one could reduce lift by say, .020 in a VVT cam but increase curtain area while keeping peak valve accel low and end up with more power everywhere, and keep the torque peak under 5000rpm.

k24madness

iTrader: (6)

They have a LOT more grinds available than what is listed on the catalog. I worked with Faith over there, she was great! I asked for grinds with around .400 lift and duration between 210-230 @.050, I got 15 options. I opted for the hardwelding but they could have used billet blanks if you have em. I have one exhaust blank (up for grabs if you want it). IMHO the hardwelding is better.

Based on port flow data from ported heads I have seen I would not decrease lift. That is what will help your torque. I played with this a bunch on another NA motor project. For the most part more lift = more torque assuming the head supports it. No real downside other than controlling the valve. Just because the factory cam hammers the valves at .370 lift does not mean that the lift is the problem. Don't shy away from lift because of that.

IVC is what affects torque peak the most. All things being equal +10 duration at .050 = 500rpm higher torque peak.

All of those cams I looked at would work on the VVT. I have a great grind in mind for a NA car that should work well with VVT. The bigger cams @ .050 help offset lift ramps. You will end up using less of the VVT adjustment though. I would not hesitate running the same #264 grind that I did. With VVT adjustment you will carry peak torque to redline and have better power below 5,200 than stock.

I would be happy to help guide you through cam selection if you like.

EO2K

iTrader: (37)

To be honest, that's pretty much the direction I've been moving in.

2868? I've got an Nissan T25 and a brand new GT2560R sitting in the garage. If I buy another turbo chances are it will be a used 2860RS potato. I have no aspirations for 300hp.

k24madness

iTrader: (6)

The 2868 is a GT28 frame with a Tial 68mm compressor. It spools much faster than the 2860 and the 2871. I have played with all 3. The 2868 is the best all around. Spools 500 RPM's sooner than the 2860 and has equal top end to the 2871. It's design is from the new extended tip technologhy that Borg Warner pioneered. I believe this is what the GTX turbos are based on too.

emilio700

iTrader: (3)

Just got off the phone with Faith, then saw your post. Thanks for sharing the info. Yah, we used less and less VVT max cam advance with the longer or greater curtain area cams.

We're in the process of making our own SuperMiata branded chill cast blanks to support up to about .475 lift with the BP6D, BP4W intake/exhaust cams. Probably Q1/14 before we have those here though. Until then, it's weld/grind.

EO2K

iTrader: (37)

Not to derail this any further, but a very quick google search does not produce a compressor map for the 2868. No map no care. Forced Performance will do the 2868 "upgrade" to the (68mm HTA billet compressor wheel) customer supplied RS for a whopping $700. I found a bunch of Audi guys saying this is 48lb/min, up from the stock 35lb/min potato wheel. While this sounds super awesome, it's probably too much turbo for my 225-250hp goal and way too much money.

If I'm doing the math correctly, the potato puts me right in the fat part of the efficiency curve in the middle of the compressor map. The 2560 will meet my goals with some room to spare and the 2860RS will do the same with better efficiency and even more headroom. The T25/28RS footprint is fine, and parts are cheap and plentiful. If I wanted to spend that kind of money FOR A THIRD TIME I'd buy the TSE EFR 6258 kit and be done with it.

But yeah, turbo. You interested at all in buying a spare C30-74 head unit?

k24madness

iTrader: (6)

Does anyone think the Ebay header is leaving power on the table? I recently came across some posts that thought the ebay header was junk.

The one I have looks like a RB 4-2-1 copy. It's not the real deal cause the flange looks different than the Racing Beat pics.