Dyno graph analysis

[anonymous-user]

Hi folks,

After having my little project Suzuki Cappuccino on the dyno I'm keen to have some of you dyno wizards out there analyse the graph.
For those who dont know, the cappo has a 657cc, 3 cylinder with a tiny little turbo attached to it. I did a CT9 turbo swap from a Toyota Starlet GT (1.3l) a custom exhaust manifold, turbo back 2.5" exhaust, bigger injectors, front mount intercooler and am using a monster sport N2 ecu which has been mapped for a larger turbo and injectors. It makes 75hp from the factory and considering its now making 106hp, I'm really happy with the percentage increase.

So my questions are, considering the turbo is plenty big enough for the CC of the engine and it is making good power, surely it should continue making boost right to the limiter? (with a small amount of boost drop expected) It just looks as though I'm loosing a substantial amount of boost higher up the RPM's.

Also I'd be interested to see if anyone can give some ideas for increasing power, and bringing boost in earlier would be a luxury. Maybe a larger inlet manifold?
According to the Starlet guys, the turbo is at its max at around 1 bar so maybe this is holding me back? The ECU is mapped to run at 1.2 bar ideally so possibly a fully customizable ecu might really get some good gains by perfecting the fueling and timing to match the turbo. The AFR's were checked when this setup was running on a previous car and they were pretty bang on. (From what I've been told that is.)

Happy to share more info on the set up if people are interested.

[anonymous-user]

What type of boost control are you using?

As rpm and hence massflow increases, preturbine EBP increases, which blows open the wastegate, reducing boost pressure for a given actuator capsule pressure. Also, post turbine EBP increases, resulting in falling turbine efficiency and hence less compressor work.

[anonymous-user]

Max_Torque said:

What type of boost control are you using?

As rpm and hence massflow increases, preturbine EBP increases, which blows open the wastegate, reducing boost pressure for a given actuator capsule pressure. Also, post turbine EBP increases, resulting in falling turbine efficiency and hence less compressor work.

I should of mentioned, i'm using a fairly basic manual boost controller. It's good as far as manual controllers go as its a spring and ball type as apposed to a bleed valve. No doubt a decent electronic controller would hold and build boost more reliably.

The cams are original still yes. I'll maybe look into aftermarket options from Japan.

The graph is pretty badly labeled I agree! The pink line you can see if boost which is sitting around 1 bar ish...

[anonymous-user]

So i'm going to look into getting some porting work done to open up the head as much as possible. The rev limit does need to be quite high due to gearing although if the boost came on earlier this could be dropped. The car drives amazingly just now and is ideally suited to track use where it will be used quite a lot, I don't want to push it beyond the realms of reliability as its not skipped a beat since the work was done but I would like a little more power if its not going to break the bank....

[anonymous-user]

clemdobain said:

Max_Torque said:

What type of boost control are you using?

As rpm and hence massflow increases, preturbine EBP increases, which blows open the wastegate, reducing boost pressure for a given actuator capsule pressure. Also, post turbine EBP increases, resulting in falling turbine efficiency and hence less compressor work.

I should of mentioned, i'm using a fairly basic manual boost controller. It's good as far as manual controllers go as its a spring and ball type as apposed to a bleed valve.

Well, no wonder boost falls with increasing engine speed then, as the "fixed leak" cannot drop more pressure from the boost capsule as EBP increases.

[anonymous-user]

227bhp said:

Max_Torque said:

clemdobain said:

Max_Torque said:

What type of boost control are you using?

As rpm and hence massflow increases, preturbine EBP increases, which blows open the wastegate, reducing boost pressure for a given actuator capsule pressure. Also, post turbine EBP increases, resulting in falling turbine efficiency and hence less compressor work.

I should of mentioned, i'm using a fairly basic manual boost controller. It's good as far as manual controllers go as its a spring and ball type as apposed to a bleed valve.

Well, no wonder boost falls with increasing engine speed then, as the "fixed leak" cannot drop more pressure from the boost capsule as EBP increases.

What does that mean in understandable everyday English?

Typically a wastegate is a mechanically sprung penny valve. It is held shut by spring pressure and pushed open by both plenum air intake pressure AND preturbine exhaust backpressure. The minimum boost line is set (for any given spring preload) by applying all the plenum air pressure to the air capsule, so the valve is pushed open as early and as much as possible. A "boost controller" works by bleeding off some of that air pressure, so there is less force applied by the air capsule to open the valve. Hence the Max boost line is effectively just the pre-turbine EBP pushing the valve open.

As engine speed increases, and intake massflow increases, then the pre-turbine pressure increases (because more exhaust gas is trying to get out through the turbine). And, if the air capsule pressure is fixed (which it is with a dumb bleed type boost valve) then that rising pressure with engine speed must also act to make boost pressure fall!

[anonymous-user]

227bhp said:

Max_Torque said:

Typically a wastegate is a mechanically sprung penny valve. It is held shut by spring pressure and pushed open by both plenum air intake pressure AND preturbine exhaust backpressure. The minimum boost line is set (for any given spring preload) by applying all the plenum air pressure to the air capsule, so the valve is pushed open as early and as much as possible. A "boost controller" works by bleeding off some of that air pressure, so there is less force applied by the air capsule to open the valve. Hence the Max boost line is effectively just the pre-turbine EBP pushing the valve open.

As engine speed increases, and intake massflow increases, then the pre-turbine pressure increases (because more exhaust gas is trying to get out through the turbine). And, if the air capsule pressure is fixed (which it is with a dumb bleed type boost valve) then that rising pressure with engine speed must also act to make boost pressure fall!

So by 'Air capsule' you mean wastegate actuator (WGA) ?

The WG is held shut by a spring in the WGA, if it is being forced open then it is the WGA which is too weak, not the boost controller, no?
You state that the type of boost controller in question somehow bleeds air off, but I can't see how this is possible as it only has two ports, neither of which is vented to atmos.

You have missed the critical fact: Which is the wastegate is being forced open by TWO things, namely:

1) any positive pressure in the wastegate capsule
2) any positive pressure in the exhaust manifold


With a manual boost "control" system, there is no way of compensating for the increasing exhaust manifold pressure (as engine speed increases) so boost will ALWAYS fall with speed when compared to the boost that can be made at a lower rpm.

[anonymous-user]

Interesting reading! So I assume a electronic or "smart" boost controller would compensate for engine speed and regulate the amount of pressure applied to WGA? Any recommendations for a good controller and most importantly, what differences would I expect to see if the controller did allow boost to be held at higher rpm? Is the engine still at its peak at ~7k rpm or is it not making more power simply because its not able to hold full boost in the higher RPMs?