going to post, then i decided i would...

firstly this isnt a stab at the owners of the 'whats the bhp' topics...

so apart from the 'joy' of having a large bhp engine, why do people get hung up on big bhp engines.

Id rather have a car that has greater average torque throughout the usable rev range, this is a better sign of which car will be more tractable, faster, especially off track, or even on track when a car doesnt have narrow power bands and gearing to suit.

More 'under the curve' beats 'max bhp' everytime.

Exactly what I've just done when my cambelt snapped and the opportunity arose to change the characteristics of the engine. I asked Barbz to work the head for better mid-range, rather than peak power. Leighton will be instructed to map it on that basis too.

It now has a genuine 3" downpipe (rather than the actual 2.5" diameter of the "H&S 3" downpipe") and it will have 630 injectors (in place of the 440s that were maxxed out last time it was dyno'd). So - there's a fair chance it will deliver better peak power, but if I was presented with a dyno printout that showed the same 450-ish, but a healthy mid-range increase, I'll be very happy.

Having said that, if the increased mid-range is accompanied by a top-end increase, I won't be heart broken....

Nigel, I keep getting tempted by the shiny 3" down-pipe, but always reject it in my mind as it will loose me torque and increase spool up time. Did you not think about the standard smaller down-pipe as better for driving characteristics?

This is exactly the point I try to get across.
Usually the less Bhp the quicker the car.
For instance a 450 Bhp 2871 will always beat a 500bhp 3076.
More tractable linear power for longer duration with less drama.


However in the pub you couldn't explain this to anyone and frankly they wouldn't care so you need the power figures.
On the road less is quite often more.

The slight loss in torque of a big pipe can be overcome with other measures, such as keeping the exhaust ports in the head small (to increase gas speed)

It's probably correct to say that a standard downpipe will give better low-down power characteristics, but it will absolutely kill the top end. I'm not THAT interested in mid-range that I'm prepared to sacrifice 100+bhp at the top - I just wanted to increase the mid-range, rather than add another 50bhp at the top, with no gain elsewhere

a smaller downpipe will push the torque lower in the powerband. big downpipes / exhaust will reduce bottom end torque.

if you want to be getting big top rpm figures, go big. but big isnt usable until you get into the high rev range... question is - how much time do people spend at 6k rpm?

if you do then your engine wont last too long by comparison to a car that delivers more torque lower down

average torque in the used rev range, that's the key to a quick street car

its all about what is 'under the curve'

There's soooo much more to making a fast car than just making a peak figure on the dyno. Most people understand when you explain to them what makes an actual fast car as opposed to one that just makes pretty dyno graphs (though occasionally some people don't!). People really understand once they've actually driven a genuinely fast car.

But until a person has a bit more understanding of what makes a car fast they'll always be under the mistaken impression that bigger bhp always means faster. Whereas in reality it depends on the situation; sometimes more bhp means faster, sometimes it doesn't - sometimes it means quite the opposite

Rudidudi, it's obvious you have an understanding of what makes a car fast

Having said all that, there's nothing wrong with aiming for the biggest numbers, you just got to know why you're doing it and whether it's best for your particular use.

BTW a smaller downpipe is never a good thing on a turbocharged engine. too small = more back pressure = slower spool = more exhaust gas reversion = less det resistance

Yes, a bigger downpipe will lose a bit of torque at the very bottom end of the revs (I'm talking pulling away slowly from a standstill bottom-end), but that can usually easily be re-gained from good engine component selection (cams, manifolds, etc) and good tuning. I've driven my car with no downpipe at all before and, once you've got moving it there really isn't much appreciable loss in performance off-boost.

There's good reasons for not going bigger than you need though. Mainly cost and ease of fitting. 2.5" will certainly do for anything from 230, to 300 bhp.

It all depends what you want from the car. I built my car so I could spend my time between 5-8k. And what has been said that a 450bhp car will always be quicker than a 500bhp car is nonsense, sorry JBT.

One of my mates has a 400bhp+ setup and I leave him for dead, everytime. There is actually no comparison between the two cars as I took him out in mine and he was stunned at the difference in performance.

power is nothing without control.

Displacement all the way.

Well- clearly it won't be "always", but there are many circumstances when a lower power car will be quicker than the big-power car

A few years ago, Leighton turned up to Curborough with a new 3076 turbo and hardly got full boost all day. Dave Tanner was also there with his near-standard engined 20vt and proceeded to post FTD

There are obviously times when the big power would have triumphed - if our little trackday had been at Silverstone instead of Curborough, I'm sure Leighton's car would have been quickest.

all down to driving style, if you happy to really rev the car then the car with the bigger turbo requiring higher revs will be quicker as it will ultimately produce more power

personally i would rather have the power at more sedate engine speeds allowing me to make quick progress without having to rev the nuts of the car, it's all personal preference though although having a car that didn't start to produce any sort of boost pressure until 4k or so would quickly become tiresome, it's why i don't like type r's, s2000's and the like

I would agree, big bhp is good if you want to go fast in a straight line, the downside being it can get tedious waiting for a big turbo to spool on the road - but you can have it both ways!

I've been playing with a twin turbo setup, which is spooling up quickly making a useable 210lbft@2750rpm. Not sure on top end power but its alot, was having boost control issues going over 5k at the time

I'll post acouple of pics up when I have the chance

Wow, over a week and no one has said anything about a TWIN TURBO setup?

How have you set it up? Large turbo on the manifold and small turbo at the side? Have you got the exit of the large turbo into the top of the small turbo?

I would love to see some more pictures

Wow, missed this one. So is this sequential or parallel turbos?

lol Didn't even notice anybody had posted!

That's some impressive packaging there, Sherlock! Tell us about the pipework!

Wow, that engine bay must get mega hot ....is that the intercooler where the air box normally is ?

SLAP ME IN THE FACE WITH A BRICK!!

we need more info!
this is a coupe first no?

Brilliant work!!

Very interesting! How can I miss this?

Im hoping its a small turbo for quick spool, leading into a bigger turbo for top end power....more info pleeease

Nice! More pics/explaination please.

Agreed, more details required!

Just want to say I really do agree with the original post. Its great running a big turbo if you happen to be in a hurry but as a everyday proposition it spoils the car imo. For example driving in 6th gear at 70 mph putting your foot down and nothing happening is a joke for a car with a 2litre petrol engine





It’s a compound setup – It can and I have been running it sequentially but as it is now its compounding the boost. The small turbo is on the manifold feeding its exhaust into the big turbo’s turbine housing. There’s two 46mm external wastegates one on the manifold the other taken off the back of the small turbo’s turbine housing, they both also feed into the big turbo’s turbine housing. The big turbo feeds compressed air into small turbo’s inlet. That’s it really nothing too complicated, the hardest part is getting everything to fit. Its nothing new in the way its setup but it’s the kind of thing your more liking to find on a diesel engine with it being capable of massive amounts of boost

Phill

This sounds epic....

Good stuff Phill - you've really atarted the boys off now. Mind you, if I'm doing 70mph on the motorway in 6th I drop into 5th and something happens

Yeah, the heat does soak in abit when your stuck in traffic think part of the problem is no heat shield on the manifold. Its running two intercoolers, the one in the pic is the standard one turned upside down

Wooooow any more pics??

Im trying to get my head around how the turbo from the manifold and the exit from the final turbo to downpipe looks.
Or am i not understanding the set up ?

Does it look like this??

http://www.atsdiesel.com/ats2/templates/template_06.asp?p=2029422272&c=36

The thing I can't understand is if the large turbo feeds the small one, surely this will limit top end power??..... Obviously not though!!
Infact I thought it was the exact OPPOSITE to that (small feeding large)..!!
Clever Sh*t.... !!

Nick

One word...

Legend.

Cheers Mate!!

Nick

Thats the one

Thats what the two 46mm wastegates are for, at higher engine speeds there opening up letting the pressure out of the exhaust manifold effectively by-passing the small turbine housing

Very interesting, well done! Which turbos are you using and what wastegate settings have you set? Are you compounding the boost at all?

Phil, correct me if this is wrong, but this is how I think you have your setup at the moment? I also think it will help others get their head around how you have set it up too.



I think I might have the wastegate off the small turbo exhaust housing wrong?

Square pistons Alexis

No, spark plug cover, duh!

HA

I was going to point out that your square pistons are different sizes, which would effect the engines running due to uneven displacement but I thought.... na

New thread required.........

Totally agree, new project build thread required here Sherlock

What do you expect from MSPaint

Love the square piston idea

While we're at it what would happen if you plugged in one of these gizmos from Lenny Henry country

(http://stores.ebay.co.uk/Brierley-Electric-Super-Chargers?_trksid=p2047675.l2563)

as the low boost small turbo

Do those things have ANY effect at all on an engines performance....
If not, How are they ALLOWED to sell these, stateing "more AIR + more FUEL = More Power"!

Nick

The induction part is right, the wastegates feed into the big turbo not into downpipe

Its the standard t28 and a T3/T04b H-Trim, there both set to run 18psi at there respective wastegates , and yeah its compounding. Its a bit difficult to explain how its working, there not running 18psi at the same time. If you feed 18psi into a turbo thats already boosting at 18psi it doesnt add to it the pressure ratios multiply, so as a PR of roughly 2.25:1(18psi) feeding into a turbo already running with a PR of 2.25:1(18psi) would give a final pressure ratio at the manifold of 4.5:1(54psi).
So the small turbo spools to give a manifold pressure of 18psi at 2700rpm, at about 3200rpm the big turbo starts making boost - not alot but enough to get the manifold pressure upto 26psi at around 3600rpm and it's holding 26psi up to 7200rpm as a high boost setting.
Its setup up so as the PR of the big turbo goes up the PR of the small turbo goes right down so I can keep the boost at sensible levels

This is what I understand

Small turbo at 18psi, big turbo at 26psi. When the big turbo starts producing more than 18psi the small turbo is effectively idling with wastegate wide open. It's not compounding the boost (appart from when the big turbo is spooling up). The big turbo just "takes over" from the small turbo once it's going. Both wastegages must be referenced to the manifold pressure hence it's not technically a compound design but a twin sequential series, similar to the twin charger design of the Lancia Delta S4.

Have you measured the pressure inbetween the compressor stages? I suspect in practice the small turbo will still be adding (compounding) some boost because it will still have a lot of exhaust going through the turbine.

Have you got another picture of how that 2nd wastegate is connected? I assume it just bypasses exhaust past the big turbine like the 1st wastegate bypasses exhaust past the 1st turbine.

Couldn't you use the 2nd wastegate off the manifold rather than having to weld something off the exhaust turbine?

So - the first wastegate off the manifold is enough to prevent the turbine housing on the small turbo becoming a restriction?

Are the two turbos in sequence? ie does the already-compressed air feed into the compressor housing of the second turbo, or is it that each turbo feeds the engine directly

Sherlock - what management system are you using??

Refer to my mickey mouse diagram

Air filter -> large turbo compressor -> intercooler -> small turbo compressor -> intercooler -> inlet manifold

In practice, in the configuration you are using, because all the air getting to the engine has to flow through the first turbo's compressor, isn't the potential power output of the engine limited, not by the theoretically possible pressure ratio attainable through compounding, but by the mass flow that the first turbo's compressor can handle? i.e. the limiting factor is the maximum mass flow of the T28.

This is a question - not a criticism of your impressive efforts!

No, not as you are suggesting anyway as the pressure ratio and CFM is very low, well under the limit for the turbo. Adding the big turbo does not change these parameters.

It would be like fitting a turbo to an N/A engine but leaving the wastegate open so it does not make any boost. So there is a minor restriction there but not in the usual sense. And since this turbo is then effectively turbocharged any restriction is easily overcome with boost.

Not sure what you mean, both of those wastegates are working together doing the same thing at the same time. Think of it as one big wastegate controlling the boost of the small turbo

No, I tried it with one wastegate and it didn't work the boost was creeping up under load

The short answer is - I dont know! I guess at some point it may become a restriction but I dont think i'll ever get it to the point where I need to think about changing anything

come on Lancia did this 20 years ago ...... the way forward is supercharged and turbo charged with a bypass .... always the simple ideas is always the best

i have looked into this for my brothers track day car and we are going big turbo as acceleration is not a priority .... keeping the car in the sweet spot is

yeah, did look into supercharger and turbo but I wanted the characteristics of standard car, the only way to do it is with err.. a standard turbo!

out and out low revs power is the super charger route is best been there done that that's why my user is Volumex..... the only way for a turbo charged car is all ... or nothing

So you have 2 wastegates for the original turbo but none on the big turbo?

Impressive..!


Then again, after that they went on to bi-turbo's..
(on 2 manifolds but still)