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