Why aren't miata engines so good for all-motor power?
 

When people build Hondas they make these high revving stroker engines with cams and such, and make ridiculous amounts of n/a power, but usually when people want fast miatas they put a turbo on it, else they do a K swap. What makes Honda engines different? How much power can you make from a miata n/a?
​​​Not sure if this is the right thread. But i was thinking about this lately. Considering buying a Honda just for the experience and fun tuning something different.

Crank support and head design which allows for more air to get to the engine, mostly.

Wut?

I really enjoy messing with my miata and want to work on a K engine. I think it would be fun.

Madjak has a thread in this same subforum in which he makes 220whp out of a BP with all sorts of goodies. I *think* it's a 1.9L. So double the original WHP the car came with. Is that the kind of thing you're talking about?

Now if you just wanna play with a K engine, then go right ahead.

Mostly because you can build a solid low lag turbo miata for less effort than trying to make the same power na. If I wanted NA power I'd not choose a shitty sounding honda engine and put in a light v6/v8 for both require plenty of effort.

This.

Melody,

165whp on E85 is about the limit for cost effective power. N/A BP's don't make serious power without huge cams. Even then a junkyard K24a2 will embarrass it. The funny thing is that N/A power is all cams. You can put a stupid huge set of cams in a bone stock BP4W with nothing more than stiff valve springs and make 185whp on E85..briefly. Madjaks engine is highly developed and just matches the junkyard K24A2 with a header. The difference is the K24 will last like 200hrs.

We have put together maybe a dozen 150-170whp BP track cars in the last 12 years. Only one 8500rpm, 200whp, ITB 2.0L. That car was fun but made no sense in any context.

Then there are turbo BP's. The current record is something like 650whp in a drag motor. But 400whp track builds that have 50+hrs on them are almost commonplace. That full race 400whp BP cost only 2-3k more than a K swapped anything. That the 400whp BP can just about be ordered off a website or two and just bolted together furthers it's position as the preferred option.

There is a reason this forum is named so.

50 hours?

Dammit!

Why do I keep turning up the power if it is shortening the life of my engine so much? This is supposed to be fun and cheap, haha. Maybe I'll stay with 330.

That's not a hard number. That also assumes 50 hours at max power. I think a dry-sump motor with Billet crank and Billet main bearing caps could be built to last longer.

I've always been puzzled by people who, absent any rules-limitations, elect to build insane naturally-aspirated engines.

If you're doing it just for the sake of doing it, then I can respect that. That's Hackaday.com kind of stuff.

But if your goal is to wind up with a car that's daily-driver-friendly yet also insanely fun when you have some open pavement in front of you, and you're working with a 4 cyl chassis, then it just makes no sense to ignore forced induction.

Yeah I know hahaha I looked up MadJaks miata that thing is absolutely wild and probably totally undriveable. Thats why my car is a turbo. I'm not trying to make something like that necessarily, I just think the concept is interesting because miata tuning and Honda tuning are just completely different fields, and I was recently watching some videos on the origins of Spoon, and saw a guy who has like a 700 horsepower n/a k24. I think its just so fascinating and something I want to try when i get more time and money.

Spoon? Their annual tuner and r&d budget is probably more than the cost of a large house.

https://cimg8.ibsrv.net/gimg/www.mia...80547209c8.gif

Ive seen some K series bored and stroked way out so theyre like 2.6L or more, running methanol, making ~500hp. Theyre also drag racing grenades Id imagine.

But to the OP, this tells the whole story:

BP:
https://www.miataturbo.net/attachmen...eadcompare.jpg

B16:
https://www.miataturbo.net/attachmen...e-dsc00704.jpg

K20A flows better stock than a race ported B16 head. This is why they make big power so effortlessly. All you have to do is build it to support the RPM, throw wild cam profiles at it, and you get all the power.

It was an economy engine designed in the 80s.

mindblown.png

I've seen those photos before. Something about them has always bothered me, and I just figured it out.

In the Honda cutaway, the slice has been made right through the middle of the vale-guide bores. This means that the ports have been sectioned at their widest point, presupposing that they are roughly circular and also co-planar with the valve stem.

In the Mazda cutaway, you can't see any of the valve-guide bores. This suggests that the cut is not through the center of the ports.

Or, put visually:

https://cimg2.ibsrv.net/gimg/www.mia...e64f9a0eb0.png


I'm not disagreeing that the port design in the Mazda BP-series heads is sub-optimal, but those photos seem disingenuous to me.

I noticed the same thing. It definitely makes the BP ports look smaller than they are. The shape is very obviously worse though.

The BP just doesnt breathe well and takes too much work to get it to do so in N/A form. 80s technology

The K series engines are modern and breathe very well and they dont mind higher RPM they are designed for it. Modern Technology

OP's next question:
why aren't Miata's so good at transporting a family of 8?
why aren't Miata's so good at being a pickup truck?

stay tuned folks, this is gonna be a real gripper :D

80s tech is even a stretch....

why isn't a t25 as good as an EFR6258?

Why isn't one horse as strong as hundreds of them?

https://cimg0.ibsrv.net/gimg/www.mia...6e36b37694.jpg


Obviously you guys havent tried the tornado on your n/a builds. This was engineered in a wind tunnel! Reap the rewards of whirling air no matter how small your ports.

When I worked at Autozone many moons ago we sold those LMAO.

Why isn't donkey as stronk as ox?

Bad port design and low static compression.

Ehh...

...exactly. The size of the port is not actually of all that much consequence. Bigger ports mean less velocity, which means less low-end torque, even if the flow numbers are the same. The port design is what those photos are showing. The BP's short side radius is laughable. When a pro ports a BP head, they can't even touch the ceiling of the port, because literally all they can do is make it worse. The B16 port looks like a factory race head, just like all of Honda's heads do.

Because every car performs better with an inlet restriction!

What part of vortex dont you understand? Jeez :eek5:

who wants their air STRAIGHT anyway?

Right

GAY air has more fun!

My initial impression after pulling a silicone casting of the intake port was the opposite: leave the floor and work the ceiling.
Have somewhere you can point me to talking more about this?

Port a head and stick it on a Dyno. That's what Andrew, myself and a few others have done for the last decade or so. Bowl blending doesn't mean port shaping in my view. That's just correcting for low cost manufacturing processes. Filling in the short side radius time-tested approach to low port angle heads. In another life, we did that to 2.0L Pinto heads.

it's 2018. We need to let the air choose it's orientation.

Google "short side radius"

Or

mondello.com - Home

unnatural aspirations

I took a casting of a VVT head and then laser scanned the casting. Here it is: https://a360.co/2JKtHkp
Rounding out the flat roof from the injector pocket through to the bowl looks to me like one way to achieve the appropriate change in cross section through the length of the port.

Even with filling the floor as an option I didn't see the shape up top as being good. It doesn't look like it has an appropriate change in cross section through the length of the port.

Just to make some things crystal clear here.. The port roof is where the guide protrudes out of, and the floor is where the short turn radius is.

Id never touch the floor with a carbide cutter because the short turn is so bad

Calling it a short turn is almost an injustice to the term.

It's my intention to do a minimum of blending from the bowl to the port on the floor side.

Also miata valve sizes could be bigger but then you need to cut out and knock in new seats and double check piston to valve clearance... money people dont want to spend

Funny enough, Mazda BP and Honda B VTEC heads have the same valve sizes.

I had the same questions. Our earliest heads (2004) were just cleaned up, bowl blended. Then we started removing material. Several years of failure to improve with several port designs later, I noticed our best area under the curve was with the old cleaned up but basically stock head. Studied more and realized the BP's rod ratio plays a key role in determining intake gas mass hysteresis, peak velocity, avg velocity and ultimately, total flow. Greatly over simplified, high rod ratio (long rod) engines have a sine wave of intake velocity gradients with shallower ramps. The BP is short, sharp. Turns out it's easier to suck the gas and fill the cylinder through a smaller, higher velocity port than a larger, higher peak flow but lower velocity port. I'm not "engine guy" but the white papers and old school knowledge backed up my speculation.
So I asked Keegan to do a head with velocity in the lifts we were using as first priority. Ignore peak CFM. The result kicked ass. It also opened up new flow regimes that lead to further experimentation. That led to the +2 exhaust CNC head that we offer now.

Let us know how your experiment works out. Meaning, post A/B dynos with no other changes.

Long rods are good!

If I get to that, which I doubt, it's going to be a while down the road.
I appreciate you sharing your approach.

What does this actually mean?

Something I made up. I forget what the correct terminology is. The air mass behaves a bit like a slinky. Create a pressure differential at one end (piston dropping) and a pressure wave propagates up the column of gas (atmo + fuel). Takes a while for the other end of that slinky to reach the same velocity as the mass near the piston. Intake manifold, cam and port design help with resonances, mostly 2nd order in production engines. Port wall texture also plays a role in boundary layer friction. Basic HVAC design takes into account boundary layer turbulence as it increasingly occludes flow through a given length of pipe. That occlusion is why small diameter corrugated brake ducts with lots of sharp bends don't do shit.

Hysteresis = slinky. Someone that knows more about it can dig up the correct terminology. The point is short rods need port and cam designs that do not work with long rods. This is again, something I learned by failing a lot by trying to apply tech optimized for longs rods to the BP. Once I went back to square one and got my fundamental understanding more accurately aligned with the platform, we started seeing breakthroughs. My favorite stuff is the tiny mod/big gain experiments. How we get 170whp out of stock cams and intake manifold kind of thing.

You need one of those supertech heavy double slinkies.

--Ian

Valve inclusion angles have also narrowed. The BP has a 50 degree valve inclusion angle, which is rather wide. Narrow inclusion angles create smaller combustion chambers and better squish. They also allow for straighter, taller ports.

i feel personally attacked