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Then the specific question is are the differences between the two heads (assuming no cam regrinding or parts swapping, but including some light grinding on the alum) pointing to a clear winner - i.e. will the grind of the VVT head prevent the sort of power a longer duration MSM cam can give you.
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while you're chasing down cams and unique heads, I'll just give it a couple more pounds of positive manifold pressure.
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Not chasing anything - I have them sitting on my workbench.
And, less boost = less backpressure, less lag, less heat, more timing, all around more performance and effeciency. THEN I can run more boost. |
Some Cam Specs - profiles
From Integral's site:
http://www.integralcams.com/miata.htm 1.8 Mechanical Lifter Cam Profiles, 1999-2001 engines Seat Duration Cam Lift Stock (intake/exhaust) 248°/251° .326"/.350" (8.28 mm/8.89 mm) Stage 1L 252°/256° .329"/.353" (8.36 mm/8.97 mm) Stage 1 251° .360" (9.14 mm) Stage 2 257° .370" (9.40 mm) Stage 3 263° .385" (9.78 mm) Stage 4 274° .395" (10.03 mm) Stage 5 288° .425" (10.79 mm) Stage 6 292° .440" (11.18mm) 1.8 Mechanical Lifter Cam Profiles for Turbocharged Engines Seat Duration Cam Lift Mazdaspeed stock factory turbo (intake/exhaust) 242°/244° .370"/.350" (9.40 mm/8.89 mm) Stage 2 turbo (intake/exhaust) 257°/256° .370"/.353" (9.40 mm/8.97 mm) 1.8 Mechanical Lifter Cam Profiles, 2002-2005 engines with variable intake valve timing Seat Duration Cam Lift Stock (intake/exhaust) 242°/244° .370"/.350" (9.40 mm/8.89 mm) Stage 1 (intake/exhaust) 252°/254° .373"/.365" (9.47 mm/9.27 mm) Out of all this I get: VVT: Stock (intake/exhaust) 242°/244° .370"/.350" (9.40 mm/8.89 mm) MSM: Stock (intake/exhaust) 242°/244° .370"/.350" (9.40 mm/8.89 mm) '99: Stock (intake/exhaust) 248°/251° .326"/.350" (8.28 mm/8.89 mm) '94: Stock (intake/exhaust) 233°/254° .318"/.339" (8.08 mm/8.61 mm) '90: Stock (intake/exhaust) 236°/248° .310"/.310" (7.87 mm/7.87 mm) Also, I learned that the mazdaspeed site is filled with morons and maybe three guys who aren't morons but they don't know anything. :-) The interesting thing from this info is the exhaust cams are NOT the same, according to these guys. "seat duration" is a few degrees longer on the '99 cams, though lift is the same. The lift is higher for the '01 and up intake cams across the board. For that matter, the MSM and VVT cams have the same exact specs?! Good lord! I wouldn't have thought that... If I had to guess, I'd have said the specs for the VVT and the '99-'00 cams were swapped on their page. I guess I'll just go home and measure it. :-) Anyway, if all this is true, then there's no reason to run the MSM head, if the cams are THE SAME, then the only thing I'm losing out on are the MSM valve springs - since a few folks have said the valves themselves are the same. |
Good lord! The GUDE site says very little, but....
Camshaft 98 - 05 Mazda Miata MX5 1.8L DOHC PART NO: MCZS04 DESCRIPTION: Strong pull from 4000 to redline. POWER BAND: 3000 R.P.M. to 8000 R.P.M. IDLE: (Good) SPECIFICATIONS: Intake: LIFT – 0.420 DURATION – 231 Exhaust: LIFT – 0.400 DURATION – 228 Wow, that's some lift, isn't it? I've seen people saying 370 was too much. I wonder what they cost? |
you may want to verify that a 420 lift cam will actually rotate in your head without hitting the casting!
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Info from Integral:
Overlap is bad for spool. Overlap is good for power in a NA motor. Overlap is bad for power in a turbo motor because you lose to much of the potential intake charge out the exhaust pipe at overlapping TDC. If you varied the cam timing in a turbo motor, it would be a fairly small band from full lift at 113 ATDC at low rpm to 117 ATDC at high rpm. The gain may not be worth the effort in a street turbo project. Different OEM manufacturers swing the intake cam timing around 26 - 50 degrees in VVT NA motors. We could make stage 3 turbo non-VVT cams that had a intake that was 263 degrees x .385" and an exhaust that was 257 degrees x .370". The new steel cam billets would cost $675 for the pair and it would take about 3 weeks to make them. They would also work with the stock valve springs and stock shim-over-top buckets to 7800 rpm. The VVT actually hurts you in the turbo application. Fixed cam timing works better with turbos because they don't like overlap. The stage 2 turbo cams will work with the stock valve springs to 7800 rpm so you really don't need stiffer springs. We don't have a big selection of VVT cams because the castings we currently have don't have enough material to make bigger profiles on them. We will probably make steel billet VVT cams at some point and then offer a larger range of VVT profiles. |
I'm not sure I understand. Lets say I can adjust my cam to have overlap only when I'm below 100kpa and then not when I'm in boost. Isn't that better than always not having overlap?
And contrary to what Integral says, I tried changing the cam timing at a set boost level and it made it worse to have it retarded at low RPM in boost. A graph will illustrate: The green line is with the VVT set to be advanced 6 deg until 3psi and then retarded to -12.5 above that. It is not switched at any particular RPM (just boost). http://www.y8spec.com/dyno/vvt_boost.jpg note how the green line follows the "advanced" line until it hits 3 psi and then drops down to the "retarded" line? Clearly the overlap is helping there. It probably varies for different turbos since scavenging and backpressure play a role, but for my big turbo, it's good into the 4k range. |
1 Attachment(s)
here is a comparison of the datalogs from that run
run 3 and 6-- 3, bright colors, is the full advance run that spool sooner 6, dimmed, is the switch@3psi run that spools slower |
Originally Posted by AbeFM
(Post 321137)
Info from Integral:
Quote: Overlap is bad for spool. Overlap is good for power in a NA motor. Overlap is bad for power in a turbo motor because you lose to much of the potential intake charge out the exhaust pipe at overlapping TDC. If you varied the cam timing in a turbo motor, it would be a fairly small band from full lift at 113 ATDC at low rpm to 117 ATDC at high rpm. The gain may not be worth the effort in a street turbo project. Different OEM manufacturers swing the intake cam timing around 26 - 50 degrees in VVT NA motors. We could make stage 3 turbo non-VVT cams that had a intake that was 263 degrees x .385" and an exhaust that was 257 degrees x .370". The new steel cam billets would cost $675 for the pair and it would take about 3 weeks to make them. They would also work with the stock valve springs and stock shim-over-top buckets to 7800 rpm. which followed Quote: The VVT actually hurts you in the turbo application. Fixed cam timing works better with turbos because they don't like overlap. The stage 2 turbo cams will work with the stock valve springs to 7800 rpm so you really don't need stiffer springs. We don't have a big selection of VVT cams because the castings we currently have don't have enough material to make bigger profiles on them. We will probably make steel billet VVT cams at some point and then offer a larger range of VVT profiles. Way better than Gude's first letter of "600 hp is do able call bill 951 317 5092". I mean, they have a nice site, maybe they do know what they are doing, but 1) it's not what I asked, and 2) they told me NOTHING. First thing I bolded and underlined- He's mostly wrong. This is one of the benefits of turbocharging vs supercharging. With a really high HP setup, overlap is good to clean up the combustion chambers, ridding them of hot gases and already burned gases so that you get it completely filled with new air/fuel, not 92% new air/fuel. Helps to "cool" the combustion chamber as well so a bit of knock suppression is had. With an SC through you loose some of your intake charge doing this and it results in less HP, through more HP per "measured" pound of boost. But with a turbo, it has no problem maintaining the same "level" of boost. Second thing I boldded he is talking about exhaust cam timing, not intake cam timing. Third fixed cam timing is not good. It's a compromise. |
Ok, I'm sure I'm way off here since you're all smart and seem to know what you're talking about.
Why not just use the MSM head and call it good? It was designed for boost. The VVT head was not designed for boost. I agree that VVT is cool, and has its merits but I don't know as it would really be worth all the extra time and effort if you have the MSM head sitting on a bench. If I'm way off, just tell me so and I'll shut up. |
Originally Posted by skidude108
(Post 321282)
Ok, I'm sure I'm way off here since you're all smart and seem to know what you're talking about.
Why not just use the MSM head and call it good? It was designed for boost. The VVT head was not designed for boost. I agree that VVT is cool, and has its merits but I don't know as it would really be worth all the extra time and effort if you have the MSM head sitting on a bench. If I'm way off, just tell me so and I'll shut up. |
Pat: Thanks for posting my ramblings whilst I'm too lazy to do it myself.
Matt: My thought was just the opposite, more advance down low to get more spool, then back it off to where you get the best power. What are good values? I dunno. :-) Still, it seems unless 5* advanced (to pick an arbitrary number) is the absolute best under all circumstances, you can only do better with VVT - unless your ability to control it is outside the bounds where you're not hurting yourself. I expect to start there, but not to finish there. But so far (haven't been home in a while) I've seen nothing to point to any benefit of the non-VVT head over the VVT, though my toyota COP's might be hard to get on there? So it seems if I'm to put money into cleaning up a head, the VVT one is the way to go. Yes, it would be awesome to have better cams done for it down the line, but I think it's a bridge to cross when I get to it. In the mean time, toss in some valves (?) and pistons and portwork and get it going. |
You'll want to adjust the intake cam mainly to control intake valve closing w/ respect to cylinder position. The engine asks for the same amount of air on every intake stroke no matter what. Piston goes down a bore of the same displacement and creates a negative pressure every time. Problem is, as RPM goes up, the time that the valve is open goes down. As RPM goes to infinity, the open time of the valve goes to zero. Not ideal.
Sure would be cool to build a model that considered all the variables and run it to maximize total air flow and see what kinda curve we would get. It would be complex though. Maybe model a few points or something and build your cam timing curve off of that. |
Originally Posted by AbeFM
(Post 322234)
Matt: My thought was just the opposite, more advance down low to get more spool, then back it off to where you get the best power. What are good values? I dunno. :-)
Still, it seems unless 5* advanced (to pick an arbitrary number) is the absolute best under all circumstances, you can only do better with VVT - unless your ability to control it is outside the bounds where you're not hurting yourself. I expect to start there, but not to finish there. But so far (haven't been home in a while) I've seen nothing to point to any benefit of the non-VVT head over the VVT, though my toyota COP's might be hard to get on there? So it seems if I'm to put money into cleaning up a head, the VVT one is the way to go. Yes, it would be awesome to have better cams done for it down the line, but I think it's a bridge to cross when I get to it. In the mean time, toss in some valves (?) and pistons and portwork and get it going. oh and abe, regarding COPs: http://farm3.static.flickr.com/2251/...84de10.jpg?v=0 1. you have to cut the flanges on the coils themselves (and gaskets) 2. you have to hone the holes in the valve cover a little so the coils fit (or at least I had to.. another part no may fit fine) |
Yeah - I have to admit, I would definitely take measured values long before computed ones! I like theory, but it rarely measures up.
Awesome news on the COPs, I was a bit worried about it, though sure I could make something work - but that's pretty clean. for now, you can just call me "The Open Loop". |
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