Charlie Chalk

iTrader: (1)

Why do they make more lbft in rally cars, Or is that not down to the restrictor?

NEEDFORSPEED

this ones gona be interesting, i dont think its down to the restrictor

OvaBoost

High comp i think

Charlie Chalk

iTrader: (1)

I hope so , I wanna know

NEEDFORSPEED

thats all i think its down to high c/r like mine im sure theyll make abit more power with it removed but not alot more.just built for torque

RWD_cossie_wil

iTrader: (9)

Because the restrictor is 34mm, they tune the engines for absoloutly maximum midrange grunt, as obviously at half engine speed ( say 4000 Rpm) the engine is only roughly consuming half / two thirds the amount of air it does at 8000 Rpm, where it would struggle to flow so much air through a 34mm hole. So if you can't have huge bhp you make the engine a stump-puller instead

Thats how I understand it anyway

GARETH T

the whole car is built around that restrictor

so whats it doing! its limits the outright amount of air which the engine can consume!

so we havent got the option of the engine making alot of BHP over a large rev range, because as you know, BHP is a function of torque and revs!
torque is directly related to airflow!

zippyobrien

iTrader: (2)

i thought it was down to the fact they run alot of boost, on small ish turbos aswell?

Spiky

iTrader: (1)

so going by the last comment, an air filter can change your torque?

hoaw about heat soak? well hot air

RWD_cossie_wil

iTrader: (9)

yup

GARETH T

how you mean?

RWD_cossie_wil

iTrader: (9)

a restrictive air filter with a small micron filter and lots of bends such as in an OE airbox can cause restrictions, but equally a cone filter might cause just as many problems as it solves, as you see a lot of tests where the power goes up at the top end, but you loose torque as all the resonance chambers that were in the original airbox set-up are gone, so you loose all the harmonic waves that can be tuned to optimise power/torque at a certain point. Also it may draw warmer ( less dense, less power ) engine bay air in than an OE airbox

Bit like short/ long throttle body bellmouths to put the power where you want it, short for top end power long for torque etc

Spiky

iTrader: (1)

wll you said the torque is related to airflow, so if i had a better filter i'd get better torque???

also

heat soak rom the engine, having a better design, using a box or cold airfeeds, would that be better for torque?

GARETH T

remember you will only flow more if the engine wants to flow more!

your more than likely going to hit the max airflow of the engine before hitting the limit of the filter! does that make sense?

heat soak from the engine? it is better to get the coldest air you can into the engine! buta filter sitting on the front inner wing is normally fine, as at speed the air inside the engine bay is constantly being changed

the hotter the air,, the less dense it is! so the less air per volume

Charlie Chalk

iTrader: (1)

So how do you cap BHP with a restrictor? Like rally cars are capped at 300bhp

cjwood555

The restrictor limits the amount of air that can be drawn into the engine. This is because the airflow will become turbulent rather than laminar beyond a certain flow rate, until the turbulence becomes so great that no greater flow-rate can be achieved.

Power is made by burning fuel in air. To make more power, you need to burn more fuel, which means you need more air. Therefore by limiting the amount of air that can flow into the engine you restrict the achievable power output.

Power is an expression of the torque generated at a certain RPM multiplied by that engine speed (and a constant). Therefore it can be taken that for a lower engine speed, the same torque force equates to less power and less air required. We know this from looking at dyno graphs etc.

The way the rally engines are designed, is to get as much torque as possible from as low an engine speed as possible, and to allow keep making as much torque as possible until the restrictor limits the amount of air that can be drawn in. Once past this point, the car will gradually make less torque and the power output will hit a brick wall.

Chris

Spiky

iTrader: (1)

cheers for the info

Turby2

Similar concept, but current 2 litre N/A F3 engines have a single 26mm restrictor and run approx 210 BHP - rpm power band is approx 4000 to 6500

Chip

iTrader: (3)

Rally cars would run more torque without the restrictor, and a LOT more BHP

89xr2

dont rally cars run alot of boost?

Chip

iTrader: (3)

at low rpm they run a lot of boost, at high rpm they dont, becuase they have a restrictor

the whole engine is built around that restrictor which totally compromises the design away from what it would be without it

Paulo P

The guy at Prodrive told us that the Impreza WRC runs something like 5 bar of boost That doesn't sound right.

GARETH T

i dont think they would run much more BHP (well maybe 400bhp, which i know is 33% )

the compression ratio is right on the limit for the spec of the engine!

Chip

iTrader: (3)

Without the restrictor they wouldnt run that compression ratio or those turbos though in the first place you welsh mong

GARETH T

dont you think i know that! wheres ima when you need him

GARETH T

ive adited it for you

Chip

iTrader: (3)

He's moved on to a higher place where is intelect is apprecaited apparently.

ian sibbert

You'd also not run the

the cams, valve gear, inlet plenum, exhaust manifold, exhaust system, intercooler, injectors and on the list goes.....lol

In fact if you wanted a fast road or track engine, it wouldn't resemble a raly engine at all......

Chip

iTrader: (3)

Indeed and yet still the rally mongs bang on about 10:1 as if it is relevant to anything that isnt running a gay arse restrictor in it

ian sibbert

Ay....careful, they are my brethren.......lol.....

I think most genuine rally people do understand the difference, certainly those who frequent PF do.....

dumped

I dont think that by purely removing the restrictor they would make a LOT more hp but depends how you quantify a LOT. Some properly optimised rally cars run smaller diameter exhaust manifolds to increase gas velocity to produce boost much earlier and increasce torque as they are capped at the top end but the restrictor. This in turn means at the top end they are both strangled by air restrictor and manifold backpressure before you even reach the dinky turbo.

Chip

iTrader: (3)

The standard turbo would be the limiting factor in most cases.
I wasnt talking about JUST removing the restrictor though, was talking about an engine built and specced without having to have one.

foreigneRS

any particular rally mong? perhaps someone that has very recently bought a 'proper rally car'?

Charlie Chalk

iTrader: (1)

Cheers

big_wig_074

as i said earlier rad,dont bother with this,its a racing "restriction",my idea is a better one!!!

Charlie Chalk

iTrader: (1)

Yeah defo