The V8 Owners Forum -

I have a 3.9 RV8 with twin T04B turbos running at about 5psi (think I'll get about 300bhp hopefully), they have external wastegates and I was wondering what I need to do to increase the boost levels? Probably up to 10-15psi. Can I change the wastegates or just the springs? (I'd rather not fit a bleed valve botch thingy).

Reason I ask, is that I am considering a 3.5 turbo build with forged pistons and want to up the boost a fair bit, and I'm trying to figure a) is it worth the expense of a new short block/wastegates etc. and b) what would be the comparable power outputs? (I have stage 3 heads, torque cam, ACT plenum, bigger injectors etc)

And help?

I think on many waste gates you just change the length of the arm linking the spring/ vecuum thingy side to the valve that actually opens to bypass the exhaust (effectivly you change the preload on the spring, not the spring rate).
Mike

Ah sorry forgot to say, these are external wastegates mounted completely separately from the turbos (with screamer pipes) - they have a length of braided hose and attachments which screw into a fixnig on the boost pipes downstream from the compressors on each side.

I was thinking of changing the internal spring, but I have no idea what make they are (Rotomaster??) or who to speak to about them, since they're over 20yrs old. Alternatively (i.e. most expensive route) is to remove them completely and fit some new external wastegates, but that would involve gettting a specialist to remove them (they're stuck in pretty good) and fabrication new screamer pipes and connections to the exhaust/downpipes.

I want to keep it as simple and cheap as possible!

Another alternative is to sell the turbos/wastegates/manifolds and buy a pair of T34s running 14psi with internal wastegates, but again that is waaaay to expensive! (would need £400 just for the manifolds )

Im thinking about going twin turbo with a 3.9L or a 4.6L and I've been wondering what size turbos are best for little lag. Im not after huge power 400bhp is very much and should be considered maximum goal. How do the T04B's respond in low RPM?

well, these are rotomaster T04Bs, and when I drove it last it pulled very well from low revs. The engine has a high torque cam in and only runs 5psi so the turbos spin up quickly. A pair of T34s could see you well into 400bhp on a 4.6 with a standard low comp bottom end.

Anyone any ideas on the wastegates? I've had a look on the 'net but can't find anywhere that sells diaphragms

Just add a bleed valve. Externals arent really any different to internals in how they work.

Plumbed correctly, with a bleed valve, and you can have almost as much boost as you want.


Not sure how you have yours plumbed up.....

Bot normal diagram for an external will have boost applied to both top, and bottom ports of the wastegate.

If you want to raise the boost, you need to bleed pressure off the bottom port.
Either by bleed valve, holes, electronic solenoid, whatever.


Here is an old autospeed article using a pressure relief regulator.
http://autospeed.com/cms/article.html?&A=0670


As for a pair of internally gated turbos. Not a direct fit of course, but throw on a pair of Subaru TD04's. Cheap as chips, very reliable, and will spool fast, and be good for 500+

Hmm... Our old lotus has this wierd wastegate that have a rather large spring inside them. My dad added a spacer under the spring to get more boost from the car. I was rather young at the time so I dont remember how the thing looked like. Maybe you could try the same?

Bleed valves, or simply drilling small holes in a section of pipe to bleed air of is by far the easiest and cheapest way.

Bleed valves being the easiest and cheapest.

Thanks for the info stevie, I know about bleed valves but they're a bit caveman, but I guess I'll have to try though as I can't seem to find parts for my wastegates! That article was pretty good though given me a good start, cheers ;p)

Caveman maybe. But every single boost controller out there works on that principal.


And the simplest of bleed valves, are cheap.

Ollie,

An old but effective trick is if you have a hose that goes to the wastegates you insert a smallpiece of brake tubing which restricts the flow and allows you to run more boost, essential to have a boost guage so you know what your getting and it should be fed from the unrestricted side of the hose to show true boost pressure.

I would have thought 8-10lbs of boost would be adequate to produce 80BHP per litre x 3.95 = 316BHP assuming an intercooler well st up igniton and fuelling.

Kevin.

CastleMGBV8 wrote:Ollie,

An old but effective trick is if you have a hose that goes to the wastegates you insert a smallpiece of brake tubing which restricts the flow and allows you to run more boost, essential to have a boost guage so you know what your getting and it should be fed from the unrestricted side of the hose to show true boost pressure.

I would have thought 8-10lbs of boost would be adequate to produce 80BHP per litre x 3.95 = 316BHP assuming an intercooler well st up igniton and fuelling.

Kevin.

That makes no sense. Unless there is a bleed orifice somewhere, a restrictive pipe will do nothing, apart from create a potential boost spike if it was very restrictive. And even then, chances of that happening are very slim. It would need to be very restrictive, and boost control would be terrible.

Air in the line only gets pressurised, there is no flow as such, until you introduce a leak. So restrictions will do nothing.


A bit like you blowing into a dead ended tube. Squeeze all you like, but its still a dead end, and nothing changes.

The wastegates are mounted directly unde the manifolds (Janspeed), and have a braided hose attached to the top, which then connect to just downstream of the compressor. I think I will T together the two hoses and attach to a bleed valve as suggested above. Been on ebay and there's a fair few cheap in-car bleed valves available, or expensive Apexi etc electronic ones. Not gonna do it for a while, but certainly worth thinking about! Mind you, would have hoped for a bit more than 316bhp at 8psi though with the rest of my engine mods

Stevie,

All you are doing by inserting a short piece of brake pipe into the boost hose is reducing the internal bore and therefore the wastegate will read a lower pressure. It may sound crude but it is very effective, and I know several people who have done it and it costs nothing.

Kevin.