Way. The OEM BP manifolds are all shaped to be able to get a air ratchet in there. We had to use a very pricey set of Mac open/box wrenches to reach the fasteners. The buttress ribs underneath the runners means you get about 45° swing then flip the wrench over and swing another 45°. Fun!

The OEM lower flange bolts can almost all be reached using a wobble and long extension through the RF wheel well. Tough, but still easier than the Skunk2. No big deal, just a heads up.

SBGarage posted these pics on their Instagram. No word on what it was compared to.

https://www.miataturbo.net/attachmen...1&d=1508954746
https://www.miataturbo.net/attachmen...1&d=1508954746
https://www.miataturbo.net/attachmen...1&d=1508954746

I'd actually rather not post random conjecture or confusing posts in this thread. W/o supporting data, that dynoi plot only serves to muddle. Good info for the other "junk2" thread. Those images have also been floating around for a few weeks.

If it doesn't serve to clarify things, leave it out please.

Do you happen to have a picture, so I can see exactly what you did to make it fit/cut?

Thanks,

~Ryan

Didn't bother. It will be immediately apparent when you attempt to line it up. Not complicated or hard to figure out where to cut it.

Looking forward to this vs square top and how it would correlate on my 6258/Flat top/e85 setup.

I didn't think to access the lower flange bolts via the RF wheel well and from above used an assorted combination of ratchet extenders and flex-joints as well as contorting my arms, wrists, fingers and hands into un-natural positions:
https://s19.postimg.org/xk6xxg0g3/To...ps0e8265d7.jpg
- it's a bitch of a job.

The 99 I have is the second Miata that I have put this squaretop on. It was so aggravating when I put it on my 03 that when I put it on the 99 I did the motor mounts at the same time since they needed changed.
With the mounts out I changed the manifold while the engine was held up with the hoist. I might unbolt the mounts this time to get a little more room.

Thank you for all the heads up.

After reading the install notes, I am really glad that whichever manifold I go with is going onto a newly built engine for me. Emilio, thanks for all the detailed write ups! Can't wait to see your results.

Sorry if this was mentioned before. Gasket material between spacers? And is there some rule of thumb for ideal plenum volume and runner length? Or more directly, is there such thing as too much volume.

​​

Found this on the google machine.

I learned alot when I was on a formula team and we were running a 4cyl street bike engine through a 20mm restrictor so a ton of research goes into plenum designs. As mentioned the ideal(with proper flowing throttle body) is about equal to the displacement. One rule of thumb used for tuning is that the larger the plenum volume the higher the peak power that can be achieved but at the expense of throttle response(TR). I have seen research done going as far as 0.5 to 5x the displacement. The lag of TR comes from the large mass of air having to be moved during the dynamic cycle of air being pulled in to the cylinder.

Runner lengths/diameter, it seems most on here understand, has to do with target rpm for peak power and torque

I think that the added ability to change the plenum volume easily is a great feature. Two of the craziest designs I have seen(FSAE) was one that had an infinitely variable runner length and another similar but variable plenum volume.

I'd also be very curious to see some large plenum testing. I think the impact of a large plenum on throttle response is overstated. We did a lot of testing on our FSAE team with plenum volume, and ended up with a plenum that was constrained by chassis packaging. All I'll say is it was way over 5 times the displacement (which it may need to be larger for peak power with a single cylinder). We didn't see any impact on TR, and even when having other teams drive our car they were expecting poor response but commented that it felt just right. We were making 140 whp/L on a Mustang dyno. I don't think I've seen plenums that large on a larger motor (over 1L), so I think it'd be cool to see the gains.

We plan to test 1 then 2 spacers. If the trend is gains then we'll keep adding spacers until it stops working.

Brief test drive this morning to do a systems check and rough street tune before dynoing.

- Seems like the throttle response is better. Immediately noticeable as I pulled out on to the street and went up through the gears. The better flow path equals higher avg velocity which means better response. No data there, just SOTP.

- It's louder. Peak torque on an NB2 with header usually falls around 4600rpm. With the S2, it turns into a hard edged, Honda-like growl at 6000. Like a mini VTec step. Didn't feel like extra power at that step, just suddenly louder. fun.

bolt on honda mani = surprise vtaks :D

So, just a resonance frequency?

Same 10" runner as OEM so same 2nd order frequency. Not sure why it sounds so different other than that there is less disruption to the air mass and pressure waves moving through the throttle body in both directions.

Think of it this way. Person in room 10' away in direct line of site. Claps loudly. Same person also 10' away but now around corner in hallway with book case in between. One is muted, lower sound energy. The other is higher energy with more audible frequencies.

Vteckiller2000's honda manifold made his car sound like a Honda as well.

You're killing me. I go on these boards to escape thinking about my job, and here you are bringing me right back to it.

Yours truly, a Powertrain NVH engineer.