Originally Posted by k24madness (Post 1062263)

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
Ported 99 head with focus on exhaust flow (Rebello)
Supertech +1mm valves
WebCam grind #264 intake and exhaust, 110LSA, 108in, 112ex.
Skunk2 intake
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 many of motor parts.

Originally Posted by emilio700 (Post 1062758)

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.

Originally Posted by EO2K (Post 1062759)

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 :loser:

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.

Originally Posted by EO2K (Post 1062801)

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

Originally Posted by EO2K (Post 1062801)

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.

Originally Posted by k24madness (Post 1062764)

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.

Originally Posted by emilio700 (Post 1062842)

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.

Originally Posted by emilio700 (Post 1062842)

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.

Originally Posted by k24madness (Post 1062813)

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.

Originally Posted by EO2K (Post 1062860)

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.

Originally Posted by k24madness (Post 1062853)

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.