Divided Intake and Swirl Flap Installation on a 1HD-FT

[VADUS]

another photos

 

[VADUS]

Now for the electrics. We installed a ready‑made solution for RPM control – the BK08 onboard computer. For this, we had to remove the alternator and bring out its W terminal. While at it, we fitted new brushes and belts. For controlling the flaps, we plan to use a large vacuum valve – it's normally closed. Accordingly, we'll need to use a normally closed relay to control this valve in our setup. This automation hasn't been implemented yet – we still need to buy the appropriate relay and hoses.

 

[VADUS]

And now the most interesting part: road tests……

With flap automation not yet configured, I went out last evening with the flaps open on an empty highway to evaluate the pure effect of the split manifold. To my surprise, the effect was VERY significant and noticeable: the car responds much more sharply to the pedal at any speed, acceleration is more dynamic, the engine sound became quieter, and the timbre lowered. So all my expectations were met, and the theory works… The twin‑scroll now has a logical complement; the cylinder groups have become almost completely decoupled, and the engine breathes much more cheerfully. There's clearly more torque.

This morning I drove around town with the flaps closed. The effect is also present – the very bottom end up to 1400 rpm is definitely and noticeably better, at 1600‑1800 it's also better than without flaps. However, from 1800 to 2000 there's a trade‑off: if you drive with light throttle, the flaps are better than without, but if you go full throttle, they are worse. So I'll set the flap switching point somewhere in this range – 1800‑2000 rpm. It's no coincidence that Serega's Mercedes manual mentioned 1850 rpm – it seems very plausible. What's most pleasing is that accelerating to 2000 with the flaps engaged requires much less pedal input compared to the open position, yet the car accelerates more quickly. So fuel economy should be noticeable. As I suspected earlier, for automatic transmission owners the flaps may be rather useless, but the split manifold itself will work very well, especially with a twin‑scroll turbo.

Now a small curiosity in the Toyota technical manual. The employees (apparently marketers) who were responsible for the final document got the photos of the cylinder head orientation mixed up. What they label as "front" is actually the rear. Therefore, the curved swirl port remains open, while the straight port is closed. Below is the incorrect picture – it's reversed.

 

[VADUS]

In the end, our suspicions about the large valve were confirmed. Den took his own identical valve home for testing. It is a regulator that opens at just 3V, which explains the large coil size, and when running on continuous 12V it overheats and starts to malfunction. So we fitted a standard EGR valve instead – it works perfectly and doesn't overheat. By the way, it is also normally closed. Logically, a normally open valve would be preferable, but then there would be an issue with venting the vacuum from the actuator to atmosphere when the ignition is switched off – this cannot be done with an open valve, and you would have to add an extra bleed valve. That's why all these Toyota valves are normally closed.

Yesterday I drove all day without the flaps and felt the real difference in contrast, because the previous two days I had been driving with them. Without the flaps, low‑end pull is much worse, especially in hot weather with the A/C on. Now the system is complete. Just in case, I have four more identical valves in stock. The project can be considered finished, thanks to Den. The result is greater than I was expecting. Divided manifolds work across the entire rpm range, especially noticeable in the mid and high rpm ranges. Swirl flaps work great from the low end to 1800–1900 rpm.

 

[SNLC]

Man you have talked about how the FTE is unreliable yet you are cutting intake manifolds in half and booger welding them back together. Sorry but those welds look like total ass.

All this for very small gains using FTE parts?

I have tossed several intake swirl flap assemblies in the trash. Along with liquid cooled EGR systems, soft shut down valves and so forth. We never build an FTE or FT with any of those parts.

I don’t get why a person would do any of this other than for the fun of playing with the diesel. Back in the day people used to do this kind of thing because you couldn’t buy good aftermarket parts. Now days you just buy the correct combo of parts and you can make as much power as you want.

Cheers

 

[VADUS]

Dude, if you're blind and can't even see that nobody welded the manifolds back together, then it's no surprise you won't be able to understand the rest — even though the whole theory was explained in plain terms in the first post of the thread. As for the weld quality — it's solid, done properly with TIG in argon. In any case, it's much more reliable than that snotty electronic FTE injection pump with its spill valve and a thousand sensors. When welding parts of different aluminum alloys and different thicknesses in a garage, you're not going to win a beauty prize. But I don't care about aesthetics, just like I don't care about the flaps and intercoolers you threw out, or your negative stream of boogers....
Don't worry so much.)

 

[SNLC]

Again I don’t see the point except for fun.

I also strongly disagree that the FTE is an unreliable engine.

Cheers

 

[VADUS]

Exactly — you bring a lot of fun into this thread.
Anyway, thanks for the bump.

 

[VADUS]

I can already make some preliminary conclusions about fuel consumption in city driving with the split manifold and the flaps engaged. The effect is not just noticeable — it's very significant: after filling the tank to the brim, I reach the first quarter mark on the factory fuel gauge with about 235‑250 km on the odometer. That works out to roughly 22.4-23.5 MPG (10‑10.5 liters per 100 km) in city driving with moderate traffic jams (summer) and Moscow traffic lights. I barely used the A/C because it was cool outside. Previously, city driving gave me around 19.5-20.5 MPG (11.5‑12 liters/100km, never less than 11 even in the most gentle mode). Now the driving style is quite dynamic, because throttle response is much sharper — especially if I press the pedal out of habit like I used to. So the bottom line is: the car accelerates noticeably quicker up to 2000 rpm while consuming noticeably less fuel, with a net gain of about 3 MPG. This is the best possible outcome for city driving.

Exact fuel figures will come after the next full fill‑up. But it's already clear — the swirl flaps really work, leaving only the swirl port in the cylinder head active at low rpm. I hope to start highway testing soon — I expect EGT to drop, fuel consumption to decrease, and of course performance to improve, which I've already experienced.

 

[Dougal]

Does this mean a hot Vee V6 layout is superior to I6 due to it's naturally split intake and exhaust?

 

[VADUS]

Not necessarily the Hot Vee, but it is the best example. Traditional V6 engines also have configurations with independent intake manifolds — like the Nissan GT-R VR38DETT. Unfortunately, inexpensive mainstream V6 models don't have a split intake, and the exhaust is also often merged into one common pipe after the split manifolds. For example, if you take a look at the 1FZ-FE exhaust manifold, you will see two separated manifolds 123-456, combined further inside a common exhaust pipe. But in expensive V-models (like the Hot Vee, especially from V8 to V12), the split setup is implemented the right way: two completely separated exhaust systems plus a twin-turbo setup with independent intake manifolds ultimately produce two independent 3-cyl. blocks (with a 240-degree firing interval in V6), like in a Ferrari 296 GTS. Nothing would prevent implementing the same split setup for an I6 — as seen in BMW's S54B32 and S55B30 engines.

 

[VADUS]

As for the split intake in this particular project — it produces an interesting result, especially for those who have already implemented a twin-scroll setup. Given that both the exhaust and intake manifolds are split according to the firing order, and both are divided into identical groups (123-456), we end up with two groups of cylinders that are almost completely acoustically decoupled — just like in expensive V and I configurations, mentioned above. In other words, each group of cylinders works as an independent bank with its own manifolds. The only things that distinguish this setup from a more expensive fully split configuration (with separate turbos and exhaust tracts) are the common twin-scroll turbo, intercooler, and exhaust pipe. But the wave interference downstream of the twin-scroll scrolls is negligible. Similarly, the mutual influence on the intake side, split via a Y-pipe, is also negligibly small.

As a result, we get two separate resonant systems — each with three cylinders and a 240° firing interval. This makes the wave pulses during cylinder ventilation sharper and cleaner — both on the intake and exhaust sides — which further benefits the twin-scroll turbo and improves scavenging, ultimately delivering more air into the cylinders.

To put it simply — the intake-splitting project is the logical completion of the twin-scroll conversion. It maximizes the pulse effect, improve cylinder filling, and enhance the efficiency of the twin-scroll turbo. Those who have already fitted a twin-scroll to a 1HD‑T or 1HZ already got a head start — because the stock manifolds on those engines are already partially split (though not fully, as the divider ends right at the collector inlet).