Specifically.... valve size and what makes the size ideal.
The back story (ready for abc soup?) is that there are two different "KLZEs" Mazda 2.5 V6 quad cam.
Variant 1 has 10.0:1 compression, hotter cams, "straight neck" intake manifold, and 28mm intake, 28mm exhaust valves.
Variant 2 has 9.5:1 compression, not-so-hot cams, curved neck intake manifold, and was thought to have the same valves.
Both made 200hp, variant 2 made it lower in the RPM range, and was in the Jdm y0 Millenia attached to an auto.
APPARENTLY, variant 2 actually has 32mm intake valves. I imagine this is part of why variant 2 still makes 200hp?
Assuming all other aspects of the head itself are equal... what could i expect if i attempted to use variant 2 heads, with variant 1 cams and bottom end? Any gains? Is this info good for anything at all?
I have a feeling that this is going to go deep in a rabbit hole, and i'm fine with that. I need to learn n/a, since my previous experience at making power consisted of turning a boost knob. 
92CelicaHalfTrac wrote:
Assuming all other aspects of the head itself are equal... what could i expect if i attempted to use variant 2 heads, with variant 1 cams and bottom end? Any gains? Is this info good for anything at all?
More power in the mid to upper RPM's, but your factory cams will probably not allow you to take full advantage. Typically, exhaust flow is or should be in the range of about 75% of intake flow.. It's somewhat unusual to have both valves the same size.
Intakes are almost always bigger.
Zomby woof wrote:
92CelicaHalfTrac wrote:
Assuming all other aspects of the head itself are equal... what could i expect if i attempted to use variant 2 heads, with variant 1 cams and bottom end? Any gains? Is this info good for anything at all?
More power in the mid to upper RPM's, but your factory cams will probably not allow you to take full advantage. Typically, exhaust flow is or should be in the range of about 75% of intake flow.. It's somewhat unusual to have both valves the same size.
Intakes are almost always bigger.
You're not the first person to say that about it being unusual that they're the same size... I will verify on my "Variant 1" this weekend, but i'm 99.9% sure that they're 28/28 on Variant 1.
The factory cams aren't BAD... power starts tapering off around 7000rpms. If i was going to go through all this work, though, i doubt the factory cams would stick around. But even if they did... i'd settle for a gain in midrange.
So far, does this sound worth pursuing? "Variant 2" heads go for peanuts because they all want the "Variant 1s" for the cams. The biggest cost seems like it would be time.
Has no one thought to dyno these things after swapping parts around so you have a 10:1 motor with the bigger valves and hottest cams, etc etc? Any trickery going on in the ECM to limit power somewhere somehow?
Weren't these "miller-cycle" engines? That might explain the odd valve sizes.
pres589 wrote:
Has no one thought to dyno these things after swapping parts around so you have a 10:1 motor with the bigger valves and hottest cams, etc etc? Any trickery going on in the ECM to limit power somewhere somehow?
It would seem that nobody really realized that the "Variant 2" had bigger intake valves until this week. The entire community has been brainwashed into "Variant 1 or nothing!!!!!" for years.
Relatively good gains come from chipping these ECUs, and people have gone far enough to compare stock ecu, MX3 ecu, and "KL36" ecu on variant 1 to see what's the best. MX3 ecu actually seems to yield the most power, but at the expense of some torque.
HappyAndy wrote:
Weren't these "miller-cycle" engines? That might explain the odd valve sizes.
Nah, these are the n/a 2.5 V6s. Miller cycle was more powerful, supercharged, and a 2.3 i think.
The miller cycle is interesting... but far too much work, weight, and physical size to even make it feasible in my case. This motor is going in an Escort.
Based on a single data point (a friend buying one), do not touch the Miller cycle engine, they are a headache and most service departments don't seem to understand them.
That said, if you could get one for very cheap and start mixing in with the 2.5 NA motors, there could be something exciting come out of it perhaps.
What gives the two different variants a different compression ratio? The pistons or the heads? I'd personally cc the heads to make sure they have the same volume. If they do, I'd go for it. If they don't, I'd mill it until they do and go for it!
16vCorey wrote:
What gives the two different variants a different compression ratio? The pistons or the heads? I'd personally cc the heads to make sure they have the same volume. If they do, I'd go for it. If they don't, I'd mill it until they do and go for it!
It's the pistons. The "Variant 2" pistons have a slight dish, the "Variant 1s" are flat top.
However... it may seem that this individual was confused and that both variants have the same valve size, so there goes that. They're all 32mm intake, 28mm exhaust.
But since we're on the subject, as i may be building up an n/a motor for next season.... (Still trying to decide between supercharging or n/a) Learn me what makes a head do it's thing way better than in stock form.
I know the standard formula is cams, oversized valves, port and polish. (And in this case, convert over to solid lifters with lash adjusters in place of the HLAs)
Are there any "rules of thumb" that i should be knowing?
I think a rule of thumb is to get a flow bench and be prepared to "ruin" a few castings in the process.
pres589 wrote:
I think a rule of thumb is to get a flow bench and be prepared to "ruin" a few castings in the process.
Ah... i may have mislead, here. Not a challenge car, so i'm not doing this myself.
Looking more for stuff like "Yeah, if you go with bigger valves, you get more flow, but lose velocity, and that's bad for n/a." (Probably not true, just an example.)
