Can we have a cam talk 101 discussion?
11-08-2017, 09:03 AM
#1
Can we have a cam talk 101 discussion?
I've been looking over builds here and have seen some cam specs that seem to work for the build being documented. What's left out of the discussion is how that spec was decided on. I'm sure there are some considerations that need to be decided on such as intended use of the car, type of induction, head flow, etc. What I don't understand is how do you use compressor maps, head flow, valve size, compression, etc. to determine the right cam for your build?
Probably a bad example but I'm currently putting together my stock 1.6l with a TDR Rotrex kit (to be upgraded to 1.8 after this motor lets go). I was thinking about swap cams or at the very least changing the timing to reduce overlap. As I kept reading it got me interested in seeing if an aftermarket set is available and what kind of benefit I would see. I don't have the tools however to determine that.
So any pointers? Good articles to read?
Probably a bad example but I'm currently putting together my stock 1.6l with a TDR Rotrex kit (to be upgraded to 1.8 after this motor lets go). I was thinking about swap cams or at the very least changing the timing to reduce overlap. As I kept reading it got me interested in seeing if an aftermarket set is available and what kind of benefit I would see. I don't have the tools however to determine that.
So any pointers? Good articles to read?
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11-08-2017, 04:03 PM
#2
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Join Date: Apr 2011
Location: Oregon
Posts: 301
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Yes, I looked into that earlier this year. I thought that I'd try matching up a ported head with a larger lift and duration cam, while keeping the lobe separation around 115; thinking that this might keep the power going to 7500, instead of tailing off after 7k.
What I found when I looked into it was that most people stick with the OEM cam and then just turn the boost up if they want more power.
Some of the challenges of putting a performance cam into the miata seem to be: 1) There are not many aftermarket cam options for the t-miata. You can go custom, but mazdamotorsports no longer has cam blanks. Web cams can hard weld your OEM cams and then re-grind to your spec. 2) you can't get much lift and still use an OEM base circle, as the nose of the cam interferes with the lifter bore. So, you can have your lifter bores machined for clearance, or go with a smaller base circle cam (perhaps that's why many vendors offer an extended stem on their valves as an option). 3) The hyd lifters are only good to about 7500rpm... and the OEM cam goes to about 7000, so not much gain using a big duration cam if you are using hyd lifters. Solid lifters are available, although at least one thread noted trouble finding adequate shim selection for his SUB retrofit.
As far as turbo sizing goes, that's more of an art. Even when using the OEM cams, I still ran into trouble with using too small of a turbo for the flow capacity of the engine build. The Garret gt2860 would creep to uncontrolled levels when boost exceeded 16#... limiting the potential power output. So, it looks like there is a lot of thought and trial/error involved when designing a complete package. Also, keep in mind that I'm an enthusiast, not a tuner. There seem to be excellent resources on this forum. I'm sure you could get specific recommendations on a well sorted package.
What I found when I looked into it was that most people stick with the OEM cam and then just turn the boost up if they want more power.
Some of the challenges of putting a performance cam into the miata seem to be: 1) There are not many aftermarket cam options for the t-miata. You can go custom, but mazdamotorsports no longer has cam blanks. Web cams can hard weld your OEM cams and then re-grind to your spec. 2) you can't get much lift and still use an OEM base circle, as the nose of the cam interferes with the lifter bore. So, you can have your lifter bores machined for clearance, or go with a smaller base circle cam (perhaps that's why many vendors offer an extended stem on their valves as an option). 3) The hyd lifters are only good to about 7500rpm... and the OEM cam goes to about 7000, so not much gain using a big duration cam if you are using hyd lifters. Solid lifters are available, although at least one thread noted trouble finding adequate shim selection for his SUB retrofit.
As far as turbo sizing goes, that's more of an art. Even when using the OEM cams, I still ran into trouble with using too small of a turbo for the flow capacity of the engine build. The Garret gt2860 would creep to uncontrolled levels when boost exceeded 16#... limiting the potential power output. So, it looks like there is a lot of thought and trial/error involved when designing a complete package. Also, keep in mind that I'm an enthusiast, not a tuner. There seem to be excellent resources on this forum. I'm sure you could get specific recommendations on a well sorted package.
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