wrcturbo

Hi,

Why do people tend to go for big bhp figures with remaps? To my suprise recently I bought an old jtuner mag in which I read that rally cars are limited to 300bhp (which I knew) but they kick out 500 ft lbs of torque? (which I didn't). How is this acheived and has anyone gone done the big torque figure route? If so what have they done to achieve this?

911

I have read the same, and asking the same question to a very respected mapper, he siad it is huge boost levels.
The restrictor (32mm?) in the air intake limits the air volume passing into the engine, but the turbo can make huge ie 4 bar I think pressure.
This is maintained in the engine by anti lagg etc.

I am sure there is a facinating description of all the details but you never see it written down.
Clever engineering.
All on pump fuel too.
Graham

ZEN Performance

They do it because it's the way to be faster. If they didn't have to run such small restrictors and could run with say 450hp, they would.

A 2.5 with small turbo can produce bags of torque and little power, if you go too far it's not nice to drive at all.

Paul

hades

Never forget that power and torque are directly related, bhp = lbft * rpm / 5252

500lbft of torque at 3150 revs would give 300bhp (500lbft at any higher revs it would give higher power). The conclusion is that in the rally cars, peak torque is produced at very low revs, and peak power also at pretty low revs. The combination of the restrictor, and high tuning and high boost to maximise the power output through that restrictor gives a powerband not that unlike a very serious Turbo Diesel (note I say power band not power delivery or power output). The aim for rally cars is pretty much to produce a flat power curve where the car is capable of delivering the macimum of ~300bhp across the entire rev range used in any gear.

Because of the restrictions limiting development in some areas, there are various things which get an awful lot of attention inside a works rally engine that get fairly well overlooked in "normal" tunes road engines. They spend a lot of time and money reducing internal friction and other losses inside the engine on the rally cars for example

You can't just re-map a slightly tweaked STi to produce 500lbft of torque instead of slightly higher power, at least not whilst expecting it to hold together. Generally mappers will try and produce the maximum safe (for engine life)torque as wel as the maximum safe power, they aren't mapping for one at the expense of the other.

As Paul kind of said already; if you take the restrictors out of the rally cars, they'd be capable of mapping to MUCH higher powers than they presently are, and would be faster as a result. If you spent the same amount of money developing an unrestricted engine, you'd get serious powers. They don't do that as they aren't allowed to within the rules.