Same Boost more flow

[Guest Hotplates]

I was wondering if someone could help me here. I'm trying to achieve more power without increasing boost. I believe my RB30DET flows better than the T3 it has on it, so I think Increasing the Compressor size is the way to go, not increasing boost.

I'm currently producing about 165rwkW, with boost set at 0.8 bar (from 2600-4200rpm) after that it drops of to about 0.5 bar by 5500rpm. Max power is around 5100rpm.

What do you think, I think the RB25 head should flow much better than that with an RB30 bottom end, and should be able to generate more power in the upper revrange without more boost.:burnout:

[Jay95R33]

Yepp,

A better flowing head will give you more upper power. Also look at your dump pipe. They can choke the top end power heaps.

J

[Guest Hotplates]

The head is a VCT type of a SII R33, should flow well enough, and the dump pipe is a 3" custom item.

I know that some of the piping from the turbo to the throttle body could be better (and will be changed soon).

[Warpspeed]

You are definitely on the right track Hotplates.

Power is proportional to airflow. The only reason boost makes more power is it forces more airflow through all the restrictions.

If you can increase airflow by improving the cylinder head, and manifolding you will make more easy power than by just jacking up the boost.

The mistake most people make is fitting a larger compressor and leaving the small turbine in.

Suppose your existing compressor flows X amount of air through the engine at a certain specified boost. Now you do nothing else but fit a huge compressor to your existing turbo. The same airflow is going to flow at the same boost. The only exception might be that the larger compressor may drop the discharge temperature from the turbo a bit. If you run a decent intercooler, there will be no difference in power at all.

On the other hand a larger exhaust turbine a/r will drop the exhaust back pressure and definitely increase power at the same boost level. Unfortunately it will also increase the boost threshold as well. But one size up is worth a try, you can always replace the original exhaust housing if you are not happy.

Thirty years of playing with turbo engines tells me to first put on the DOHC head and see how it goes. Next fit a longer duration exhaust cam (with stock inlet cam). Last thing fit a larger turbo if you can afford to lose a bit of bottom end response.

If you do all of this, you can easily get something like 50% more power AT THE SAME BOOST LEVEL. Then, you can sneak up the boost a bit, and it will absolutely fly,

[Guest Hotplates]

Thanx Warpspeed,

I already have a DOHC on my RB30, but I understand your point. So if I improve the piping/manifolding, and then upgrade to a highflow T3/T4 or GT3040 or so it should work a treat.

The reason I was wondering if to increase the compressor size is because the VL T3 that is on my car has a decent looking Turbing housing, but the compressor looks tiny.

I don't care about loosing a little bottom end, I can basically drive away in 5th gear. Boost starts at 1400rpm, have 0.8 bar at 2500rpm. I'd rather be coming on full boost about 3000-3500rpm (if not higher).

Do you think going for a tubular exhaust manifold would help? If I need to go for a new turbo do I go external Wastegate?

[Guest Hotplates]

To give you some idea, before I put on a 3" mandrel exhaust, it had a 2" and the car produced over 105rwkW at 3000rpm on the dyno, now its making closer to about 110rwkW at the same revs with the exhaust (thats about 500Nm).

[Warpspeed]

I believe the VL T3 turbo uses a 60 series compressor which is the largest T3 size available. Going to a T4 compressor is quite a step up, and may lead to surge problems.

From memory that particular turbo has an 0.63 a/r exhaust housing which you could probably increase to either 0.75 or 0.82 a/r. These housings would bolt straight on and use the same internal wastegate and dump pipe that you already have.

Changing the exhaust a/r is going to make a larger difference than changing the compressor, and is cheap power - if you can find a suitable housing.

If it was me, I would try and beg, borrow, or steal a larger exhaust housing to try. If you can afford one, a GT ball bearing turbo would be far better in every way. Which size yo go for really depends on the low end response, top end power tradeoff.

Whatever you end up doing remember, the biggest gains are going to be found on the exhaust side of the engine.

Fit a pressure gauge to your exhaust manifold. If you have never done this you are in for quite a surprise. Anything you can do to lower the exhaust MANIFOLD pressure is going to make a large improvement. Pressures as high as twice boost pressure are not unusual on stock turbo setups.

This is the key to big horsepower. You may need a monster turbo, or maybe, be a bit clever with choosing optimum exhaust wheel/ar combination will get you there without losing too much response. If it is nearly right, an optimum individual runner exhaust manifold design is important, and will sharpen up the response.

If the exhaust turbine/housing is either miles too big, or miles too small, a good exhaust manifold will not make much difference over a horrible manifold.

[R31 POWER]

Hotplates,your car sounds like it's gonna be a animal once you sort the turbo out,even more so than now.

[Guest Hotplates]

Cheers Guys,

I think that will help me, a lot! It looks like I will be going for something a bit bigger (T3/T4), or perhaps a TD07 or TD08. I gotta fix up all the piping (from the exhaust manifold to the piping from the turbo/intercooler to the throttle body).

I will defenetly have to go buy myself a Electronic Boost Controller soon. I've been meaning to do so for months.

[Cubes]

Those T3 turbo's on the VL's arn't BB either are they?!?!

Do you really need an EBC Hotplates.

When you get the new turbo get the wastegate to suit say 1 bar or more..

Then a cheap bleeder or mod the actuator that will do the trick nicely if you need more boost than 1 bar.

and save you around $1000. 1 less thing for the cops to find defect you for.