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Old 08-31-2011, 09:10 AM   #81
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Originally Posted by NiklasFalk View Post
I bought the last VVT cam blank from MazdaSpeed through MiataRoadster for $125.

Hopefully there will be a new supplier for the VVT blanks when I want to try another design (or I have to weld on the stock cam, but cast blanks is a much better option).

Finding firms that grind cams is not a problem, knowing what to desire is a bit trickier.
Jesel can make cam blanks (or full cam$$$$). I'm not the guy for official quotes, but it'd be probably about $500 for a tool steel spool. Gotta pay for people like me. Tehehehe.

There's always people who would make one-off's.
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Old 08-31-2011, 12:13 PM   #82
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I will take 100 custom cam sets. But i need help determining if the VVT will be able to handle larger cams. (think s14 sr20det... they cant handle large duration cams because of some sort of wizardry)
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Old 08-31-2011, 12:59 PM   #83
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I will take 100 custom cam sets. But i need help determining if the VVT will be able to handle larger cams. (think s14 sr20det... they cant handle large duration cams because of some sort of wizardry)
Looking at a number of places for fragment of information (not just facts, I try to learn the concepts and pitfalls also) there seem to be a number of different aspects.
The biggest one is that to sell an off the shelf upgrade in the US, some seems to only want to sell "lawyer proof" products.

If you increase the duration of a VVT cam on a interference engine you will need to take care. Either reduce the cam movement or make larger valve pockets in the pistons. Both of these is not that shade-tree applicable.
The Miata VVT have 47 crank degree sweep and is 50 degrees into lift at TDC (stock duration, max advance) and have reached half max lift. Add 1mm lift and you need to deal with it.

The tougher issue comes if the VVT can't handle larger valve-spring pressures (can't reach target advance, flops around under spring control), which means that you cannot user steep ramps and you are left with a pointy cam (not as meaty and "square" as you would use for fixed timing), since you are forced to use soft springs to not screw up the VVT.

I hope that the Miata VVT can be used with a bigger cam/tougher springs and can control the advance (full retard is not terrible as a last resort).
Ti Retainers could be a tip though and the Supertech SUBs seems to be a few grams lighter than the MazdaSpeed ones, this and springs on the lighter side (maybe more preload than rate to improve seating but not ramp up the whole force that much?)

I hope it will work. 8krpm without problems would be nice (even though I'm only looking at 7.5 as limit in our regulation).
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Old 08-31-2011, 03:22 PM   #84
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My Supertech 8.6 pistons turned the non interference miata motor into an interference one.
The valve pockets were shallower than factory.

The good news is that for a high revving (especially turbo) engine one would not be too interested in making intake valve open earlier, but more of making it close later. So if your VVT isn't set to open the valve super early you won't have an issue. You can also set up the timing belt so that the max advanced setting isn't much more advanced than you desired max advance.

re: vvt can't handle greater spring pressure - is this an issue on any other cars? The VVT actuator uses oil pressure to progressively advance the cam - I have some rough calculations as to how much torque the actuator can deliver, in an earlier post. You could probably roughly calculate the torque the springs present to the lobes.
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Old 08-31-2011, 03:32 PM   #85
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Originally Posted by JasonC SBB View Post
re: vvt can't handle greater spring pressure - is this an issue on any other cars? The VVT actuator uses oil pressure to progressively advance the cam - I have some rough calculations as to how much torque the actuator can deliver, in an earlier post. You could probably roughly calculate the torque the springs present to the lobes.
It can be FUD that I read in a HotRod article, but time will tell.
There is a limit to the holding momentum, but there should not be any resonance frequency to worry about (the oil should not compress).

My plan is to aim full retard power peak at 7-7.5 krpm and use the advance to reduce the overlap to gain some power in the 3.5-5 krpm range. So I plan to have the actuator in the stock position (to always have a reasonable working solution with the OCV disconnected).
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Old 08-31-2011, 06:28 PM   #86
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There have been some uk people experimenting with JDM RS-roadsters. They found that the only thing revving higher on JDM VVT engines is the tacho. The rev limit is set at the same RPM.
They also found negligible differences in acceleration when compared to bog stock EUDM NBFLs.
I have one of these NB JDM Roadsters and I can confirm the limiter kicks in before you hit the indicated redline. Pretty annoying on the track!
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