I'm surprised you're not getting bigger harmonic dips in the power curve due to the ITBs. With the Jenvey ITBs you generally see a very big dip at 3600 and a smaller dip at 6000 and peak power around 7800. It looks like you're getting some dips but at around 400 or so less RPM and they aren't quite as severe. What trumpet length are you running?

In Australia we struggle to fit in the larger Jenvey trumpets because of the brake booster / master. Maybe the TWM ITBs would work better.

 

About the same net length (valve seat to plenum/trumpet) as the OEM manifold. 50mm spacers IIRC. I could see how LHD would be difficult. Our filter is right up against the shock and a few other things. Practical limit for us without a custom manifold with a different angle.

Careful VVT table tuning helps smooth the typical ITB torque lumps. It could actually be better but as mentioned, we were running out of time on the dyno.

This motor could use 50mm ITB's.

 

Awesome, thanks for the info and photo. The engine bays of RHD miatas are much more balanced. We end up getting everything crammed in on one side, and nothing on the header side.

One last question from me! We've been debating ceramic coating of headers on an Aus forum. Do you think there is any real performance gains or are you just doing to keep engine bay temps down?

I have exhaust wrap ready to put on, but haven't yet as I don't really have that much of a problem with heat. I was actually thinking of trying to collect some data with no-wrap, wrap and then ceramic coating as a test but it would only be engine bay temp not power. If you already know that ceramic coating makes a difference then I won't bother.

 

Coating is more effective that wrap and lasts pretty much forever. We don't do it for power, although it is worth a few. We coat headers to keep from melting our driving shoes. The coating plus a blanket attache to the underside of the tunnel does the job. More effective to keep the heat off the tub in the first place than letting soak the tub and trying to insulate your foot from it on the inside.

 

You have a lot more clearance for a low-mount turbo though!

--Ian

 

Very true. I did have a good look at the EFR turbos this morning. Not sold on turbos for the events I do though. I have a theory that I can get to 400+ HP with a big Rotrex and not destroy a 6 speed. Just keep a nice smooth linear power band and flat torque curve. I figure its worth a shot once I get bored of N/A.

As Emilio shows a 200whp N/A car can beat turbo'd cars on moderately tight and windy courses. It requires balance across the platform not just power.

 

Cam specs?

 

Two of them, the big ones.

 

Overnighted from Japan

 

I like how you plugged the ITB injector ports and used the injector ports in the head. Its almost as if you, like, know what you're doing and stuff.

 

How do you think this engine would do if you replaced the ITB's with an intake manifold that had 50mm 16 inch runners trumpeted into a 3.5 inch plenum fed by a 65mm TB?

 

Depending on cams you can get into spitback problems with a plenum.
I was completely unable to make sense of mine before the Jenveys.

The more experienced will of course have less problems, but ITBs makes it behave as predicted (somewhat).

 

Dunno. Configured well, I don't think you would lose much power and it would be easier to tune.

 

It's not exactly the specs you requested but about as close as I've seen.

I'm running a Skunk2 Ultra Street which has 9" runners with oval cross sections equivalent to around 44mm ITBs that terminate in 80mm bell mouths into a 1.8 litre plenum. I'm also running a Honda 70mm throttle body.

If you overlay this dyno with Emilio's they are pretty close, even with the dips aligning at similar points. Although the ITBs on the VVT head softens them out a bit.

Ideally I think the runners are a little short as I'm hitting peak power at 8300 whilst HP is still climbing. I think if I was game to rev to 9000 you might see more power up top before it peeks and drops. Longer runners would bring that 6500 upwards power hump harmonic a little lower. I would guess that you really want 11" runners.

The difference between my motor and Emilios is I think mine has much higher duration cams (around 310) with a BP head (so no VVT) and stock bore.

Note: You need to drop 10% or so as this was a hub dyno. If this was on Emilio's engine I think you could add that back again to compare to the VVT head and bigger bore.



As you can see from the dyno, power curve goes a little crazy at lower revs, due map fluctuations caused by the big cam overlap.

I would love to see this manifold tested on a fully developed 949 Racing whammy engine.

 

 

The nonchalant ease of shifting 5-4 and the meatier grunting sound is what I notice compared to my experience.
Extended horns and time behind the wheel... And maybe real dyno time sometime.

What about angled extenders (or angled intake in my case), to bypass the shock "tower" to get a large volume filter on there?

 

The ITG filter was the correct volume, spacing an orientation relative to the horns. Before I started the project, I noticed that every street driven ITB setup I had every seen on a BP had a total horn to valve length too short for the cams being used. To run these without spacers needs some really long duration (290°+) and crazy high lift (12-13mm) cams. I wanted a broad powerband. The filter is critical so we started with the correct one for the engine, shoved it against the tower, measured back from there and had just enough room to get the desired runner length with whatever spacers we ended up using. The cams we're running are modest, 282° 11.5mm. With bigger EP style cams we'd probably cut that spacer length in half to move the power peak above 8k. It's around 7750 now.

Incidentally, this engine is out of the car and for sale, $8500 shipped. ITB's too, $750 shipped.

 

^Booo, I was hoping the Taxi was going to show up for Miatas at Hallett next year.