Stock RS2 Airbox - max hp?

[Ducky]

Wondering if anyone on here knows how much horsepower a stock RS2 airbox can flow?

thx

[Jamo]

1 million bhp

The limit isn't the airbox but the intake hose from airbox to turbo. It's a sh*t design and strangles airflow.

Being serious now the limit is not in terms of bhp, it's whether there's enough air flow to stop it going into vacuum. What you need is a filter vacuum monitor that Repo used to use to show airflow http://www.knfilters.co.uk/filterminder.aspx

[Ross]

It didn't seem to add any restriction when used on my car with 375hp (swapping cone to air box) and a BMC foam filter... still using it now with 400+

Sonic uses one at 430hp but whether it's a restriction at that power level is the real question. His foam filter was getting pulled apart which would suggest it's being sucked pretty hard. Fun times . It would be good to perform a test on the dyno back to back.

[Jamo]

dynos measure bhp that's it, everyone seems to think bhp is a measure for everything. You'd need to check if the engine via the turbo is pulling vacuum which shows it's restricted or if there is enough air flow.

[driftin jo]

dynos measure bhp that's it, everyone seems to think bhp is a measure for everything. You'd need to check if the engine via the turbo is pulling vacuum which shows it's restricted or if there is enough air flow.

Actually they don't measure HP at all, the only measure torque and RPM, HP is then calculated using the following equation.

Horsepower = (Torque x RPM ) / 5252

But yes the rest of what you are saying is correct, its the same for exhausts,
you could push 1000hp through a 2 inch exhaust pipe if you wanted to, the question is
how much more power could you have made with a 4 inch pipe giving much less restriction with the same set up.

[Ross]

Hence me saying compare 'back to back'... if you have the tools you could just measure vacuum on the intake, measuring cause rather than effect (dyno). But either is going to tell you whether it's a restriction on power or not. And dyno days are much more fun than intake vacuum measurement days

[Sonic]

It didn't seem to add any restriction when used on my car with 375hp (swapping cone to air box) and a BMC foam filter... still using it now with 400+

Sonic uses one at 430hp but whether it's a restriction at that power level is the real question. His foam filter was getting pulled apart which would suggest it's being sucked pretty hard. Fun times . It would be good to perform a test on the dyno back to back.

Indeed, the pipercross filter lasted about a year. Now replaced with a K&N.

[Rusty]

I'm sure that, to a certain point, what you may lose by the way of a restriction is made up for by the superior cold air feed compared to many cone filter setups.

There is a thread in the sticky section for the intake and exhaust section, in which I did a lot of work trying to make a cone filter perform as well in everyday duties as the airbox. A cold air feed is essential, as is some serious heat shielding. Jamo's old setup with a custom airbox in the inner wing is the sort of thing you need to be looking at for serious power.

[Ducky]

Mmm, reason I ask is that I need to fix my engine (recent Poorly RS2 thread) and it gives me an option to squeeze some more power from it!

I would like 500hp'ish but keeping the stock engine bay look (currently homefried only), but if that's not possible on the stock airbox, I'm tempted to just fix what I need to for now and run it that way for a bit longer (it doesn't do many miles), rather than chuck a shed load of money at it and not get what I'm after.

Doesn't help with the fact I'm moving house, so money could be used elsewhere at the moment.

Decisions, decisions! lol

[Ross]

If you want my honest advice, fix it and map the best of the RS2 turbo if you want to keep it to OEM. If that is not quite enough then go hybrid Turbo up to 450hp with bigger injectors. Rods if you rebuild and silicone hoses with good clamps if not done already. Mine is in the lower 400s and it is mighty rapid, yet retains stock look and reliable.

Above that tends to need more solid bushes, custom breather, generally breaks things more regularly... Personally I think 400-420hp is the threshold.

[Ducky]

Cheers for that, something to think about.