Gridlock Mikey

Over the past few days i've been forced to learn about boost pressures etc and how in a classic scoob, when all the plumbing is in the right place, the ECU actually decides how much boost you can have (Classic scoob, no DAWES or EBC's or owt like that)
It got me thinking, My car is probably running about 230 bhp, decat, filter and white wheels and at present it is only boosting to about 11psi due to an unseen culprit (Restrictor is looking like the villian at the mo, but who knows! ).

Now the JDM cars have got 276 BHP (Ch'yeah right!) so are they running more boost as standard?

You guys with 300+ BHP How much more boost are you running?

That's boost and BHP what about Touque?

Recently I had to drive about with zero boost for about 600 miles, it sucked, then I had to do 600 miles with 5 psi and now i'm back to standard plumbing (But only doing 11 psi )
Obviously with zero boost, it was like driving a heavy old barge. A diesel on at that. It killed me, but even with 5psi iwe were not breaking any records, however it did get to 30 slightly quicker, now normal service has been resumed (ish) Now, has the car gotten faster because the increase in boost pressure has given me more bhp or torque?

There, sort that one out

Bored

vindaloo

It's probably simplistic but think of BHP as "torque x revs".
How boost is managed across the rev. range is a major factor in determining peak torque and BHP. i.e. Not normally any point in having 300lbft of torque at 3K rpm with 15psi boost if the turbo is so small it can only hold 6psi boost at say 6K rpm.

J.

hades

Vindaloo - it's not simplistic at all;BHP = lbft * revs/5252.

The original question is harder to answer. Increased boost does not necessarily equal increased bhp or torque. With a given set up, whilst running within the efficient zone of a gven turbo's capability, more boost (with fuel etc to match) will yield more power. However, take the turbo beyond the good "island" on it's compressor map, you end up putting in hot charge and/or restricting exhaust flow, so adding extra boost will not give you more power.

Similarly, running the same boost on different turbos or even different supporting mods doesn't give the same power, as Volumetric Efficiency can be very different. Things like charge temperature, compressor efficiency, other restrictions, supply of adequate fuel at the right mixture etc. all contribute to power.

jb2000

most classics if you look at rolling road days have high bhp but low torque figures

the easy way to bring the torque up is to change the headers to equal length or modified

BUT some scooby owners will not do this because they like the rumble and a loud exhaust, seems silly to me as I feel torque is just as important.

depending on the intake by this I mean filter tubo intercooler you can get 300 bhp at 1 bar may be less

I believe pat got 283 BHP at 0.4 bar out of an EJ257

hades

Part of the reason a lot of classics have relatively low torque is because they have a relatively small turbo, that can't do high boost or high efficiency in the mid-range. Put on a more efficient turbo and other supporting mods, you can get very healthy torque at 4000rpm, but will have slower spool up - i.e. less torque at say 2500-3000. Most higher tuned turbo cars will have more bhp than torque, as the much bigger turbos required for monster power need a fair few revs to make them really work.

Headers are often a good example of increasing volumetric efficiency, and so achieving better peak torque (and often better peak power) whilst still running the same boost. However, some headers I believe give slower spool up. Again, you'd gain peak torque, but lose torque a bit lower down the rev range

Getting >280bhp out of an EJ257 at low boost is not very surprising. There are normally aspirated 2.5s around giving over 200bhp without even using high revving VTEC trickery etc.