Dash Rendar

Or even a mediocre job! You could buy a reasonable Supra TT for that kind of money. It does sound like the experience of a lifetime. Go show those lambos who boss!

So Mike, if I'm understanding you right, the wastegate can open regularly at short intervals, to vent off excess boost in pockets? I guess if that sound was essentially being 'amplified' through the screamer pipe, it might explain it. Dunno... Matt, why would you only hear this wastegate noise on lift-off? I thought the wastegate was venting the excess pressure, and that this would happen under full boost? Or is it because the wastegate should only close on lift-off, and that's the only sound you should hear? (This demonstrates my lack of knowledge regarding how a wastegate operates!)

John, I'm not sure I'm in agreement with this argument. (Again, I'm happy to be told I'm being an idiot!) Surely you're talking about chemical kinetics here? I agree that increased pressure need not translate in a proportional manner to power for a number of reasons. You then say: pressure you can get "simply by heating things up". This is certainly true, given the volume is a constant. But saying you get "more boost" but "not many molecules bouncing around" seems like a non sequitur to me. Increased pressure, by definition, means increased collision of molecules. It's the increased number of collisions, and collisions with higher speed (and therefore energy) that causes the physical manifestation of pressure. But, as you say, to get a bigger bang, it's not simply the pressure. Ultimately, it's the reaction between oxygen and gasoline. Increasing the pressure of the air gives us increased concentration of oxygen (since increasing the pressure of a gas amounts to the same thing), which, according to collision theory, will increase the rate of reaction. It's been a while and my chemistry is a bit rusty, but if I recall correctly, the limiting factors will be the steric factor, the diffusion coefficient and the activation energy for the reaction. We can't do much with the steric factor, but increasing the pressure certainly helps with the other two. I would have thought that aside from increasing boost, the only way to mix the molecules more effectively would be to change engine timing, alter injector design, or introduce a catalyst into the mix. But this is where I go quiet, because I don't know a hell of a lot about engines. (But I'm trying to learn!) If only I'd stayed awake in a few more of those chemistry lectures so long, long ago, then I might actually know what I'm talking about... Rather than just pretending to!

I'm chuffed for you Matt. I've only just read about the issues you had with a previous tuner and I was absolutely horrified to see what you've had to put up with. I'm glad everything's back on track. You must have a big wallet!

This has been an interesting thread, and I think I've learned a lot. BTW, Wikipedia has a nice page on turbos which has a surprising amount of detail. I found that useful too, as well as the pages about volumetric efficiency (which I'd never even heard of before). Thanks everyone!

And it sure is tidy.

Apparently, a lot of men have trouble finding the plenum.

It did have an AFR, but I didn't really get any chance to pay attention. So what does a loud wastegate sound like? I thought that would be more like a BOV kind of noise... Only louder. The owner of the car didn't seem too concerned with the noise, but I was just curious. Cheers all.

I guess soundbytes of det are hard to come by!

I'm happy too. Thanks all.

Screws rattling in a tin... maybe. But it was fairly regular and rather loud.

Is it really that simple? So, you're saying that the increased air temperature can actually account for the 20-25% reduction in air density that would be required to give these bhp discrepancies? (And this assumes a linear relationship between boost and FWHP, and since we know machines aren't 100% efficient, this implies that the air density must be dropping by even more than this.) I'm certainly happy to accept this as an explanation, although it means that the smaller tubbies run *much* hotter (compared to big singles) than I had thought. It's the "increased air flow" argument that I just can't buy into. A few minutes ago, I asked if anyone around the office knows anything about fluid dynamics, and it turns out a guy just three desks away has a PhD in fluid dynamics! (What are the chances...) I'm hoping he'll pop in and add his thoughts too. Always lovin' a bit of a debate.

Yes, that was in what the next paragraph was for. (I was endeavouring, and apparently failing, to be systematic.) I can only draw one conclusion from all of this... The question wasn't that stupid afterall! Let's hope some experts on fluid dynamics can come along and give us some PV=nRT action, with solid figures!

Now I'm as puzzled as when I first initiated the thread. I thought the airflow explanation was a good one, and my analogy with the straw seemed to make sense, but only if we assume that the turbo itself and the supporting piping is actually the limiting factor that is generating the pressure. But clearly this is a bad assumption, as I think someone intimated later. The pressure, ultimately, is derived from forcing the air into the engine. Pressure is nothing more than a certain mass of air in a given volume. Since the volume is constant, then the mass of air forced in (per unit time) by hybrids at 1.4 bar, or a single at 1.4 bar, to my mind, should be the same. But from Boyle's Law, we know that a given mass of air exerts more pressure at higher temperature. So, as others have already discussed, a big single will heat the air far less, so an equal amount of pressure (compared to twins) will result in the flow of more air. But can temperature alone account for FWHP differences of nearly 100bhp? Does anyone know the true temperature differences downstream of the turbos, say, between twin tubbies and big singles? I presume someone must have run the equations at some time. Maybe I'm just having a stupid moment. When I was a geeky student, this stuff might have made more sense to me. But working in IT for nearly 10 years has caused my brain to shrivel into a useless lump.

Another good point.

The other day I was fortunate enough to be sat in the passenger seat of a T61 Supra. However, at full (sustained) boost there was a repetetive 'clacking' sound. Imagine hitting steel venetian blinds with a ruler at a rate of about 3 times per second... Only *much* louder. That's what it sounded like. This wasn't apparent until full boost was achieved and sustained. I've been in big-singles before, and only ever heard the mighty 'whoosh' of air. I've never heard a turbo make a sound like this. It was almost as if pockets of air were slamming into something in the system at regular intervals. The owner didn't know what could cause this. I was wondering if anyone has any ideas?

P.S. You'd think I'd know all this already, given that I had a lung collapse on me a couple of months ago.

Thanks guys. Now I realise I was being thick. I started thinking... If I was blowing through a straw, the air pressure would be high, but the air flow would be low. But if I was blowing through a two-inch pipe, the pressure would be low but the air flow would be high. So it's all about pressure and capacity for air flow.

Sorry if these seems an ignorant question, but I'm puzzled. I recently saw a post where a guy has achieved 450FWHP on hybrids at 1.4 bar. But at the same time, there are singles at 1.4 bar that achieve over 450RWHP and around 550 at the fly. If these cars are running the same boost and have sufficient fueling, how can the horse power figures be so very different? Sorry if this is dumb...

I can vouch for that!

You can buy them direct from Blitz UK. "Nur Spec R baffle SUS304 stainless." Only £29 + VAT, which isn't too bad at all.

It's loud and sounds pretty awesome, although I found it a drone on motorway cruising. The silencer/baffle makes a hell of a difference. I would certainly recommend putting it in for long journeys. Afterall, it only takes 3minutes to pop it in. Keep a binliner handy for when you take it out!

Assuming the ring is the correct size and you have a fuel-cut defender, yes. (Without the FCD, the ECU will cut your boost at about 1 bar. It feels like someone slamming on the brakes!) And make sure your fuel pump is up to the job. If it isn't you'll run lean and shorten the lifespan of your engine.

Ater decatting, the problem with the JSpec TT is actually restricting the boost to sensible levels. With a JSpec, you don't need a boost controller. A restrictor ring will do, although you can get more reliable boost control with the EBC. My BPU Supra just had a restrictor ring, which held it at 1.2 bar most of the time. On very cold days, it did slightly overboost. More info in the 'BPU thread', here... http://www.mkivsupra.net/vbb/showthread.php?t=94705

I'm looking forward to maybe having a T61 someday soon....