So I recently visited the only RUF shop in the US, in Southfield, MI. The tech there told me his opinion regarding why he dislikes straight pipes on our cars. He claims that the straight pipes cause "surge" because the small turbos spin too fast and create overboost situations. He says backpressure is actually good for our cars. This goes against everything i've read/heard/been advised by my tuner. Can anyone shed any light on this notion of backpressure being good?

 

I agree, as this is true from real world experiences with 16/16g turbos and straight pipes. I actually lost power when adding them. Now on the other hand, my GT35r turbos love them.

 

But Isn't boost control the duty of wastegates and boost control solenoids?

 

From my own experience they do hurt low end power, I have a set and like my gen 1 no cat fabspeed better, both sound and power. i run 1.4 bar btw

 

Well they are definitely better than stock exhaust for spool times. I assume you are talking about open X-pipes, not just straight pipes from the turbo to the rear of the car.
Anyway, I put an open 3" xpipe on my flashed (1bar) 2002 with stock turbos two weeks ago. The power was instant and I didn't notice any power loss in any RPM range. The problem is they were so loud I had to put my stock exhaust back on. That was two days ago and it definitely takes longer to build boost now and the car feels "choked" at all RPM ranges compared to before.
Just my experience...

 

Psshhh, just turn your stereo up j/k

That aside, I have also heard different things about straight pipes with turbos. Back when I had my BMW 335, there were discussions about straight pipes as well not giving enough backpressure to the turbos and reducing power. The 335 turbos back then in the n54 engine were also small ones meant to spool at about 1800rpm or so. Maybe it is with smaller turbos that backpressure is important whereas larger turbos is less so? Any of the engineers or flow dynamics people have any definite knowledge?

 

Last year I converted to the FVD race pipes (straight from the turbo back) and can say that the car much more responsive to throttle inputs throughout the RPM range. The noise is not fun for street use, but I use it about 90% on the track. Overall boost was only affected slightly, but you get there a lot quicker.

 

it's only bad if the turbos go into a surge condition because of it


turbo cars: less back pressure = better

 

just upgrade the diverter valves while you're at it?

 

Straight pipes increase the exhaust velocity, just like removing a water aerator increases water flow speed. The k16 was designed with a specific flow in mind. Give it too much flow and it can surge, exactly like the RUF mechanic said and put the turbo out of its efficiency range equaling less power.

That being said, a larger turbo can use all the help it can to spool up and is not as likely to surge. I'm sure there can be a workaround with either opening the wastegates earlier or putting bigger wastegates to compensate for the flow, or add bigger turbos to take advantage of the extra flow

 

This is interesting as I was debating on similar (to my K24's) or smaller Turbo's for an upgrade in power. I like straight pipes for the track because the throttle application is smoother so it drives more like an NA car with a lot of torque. For the track I wouldn't have it any other way. I do want a tad quicker spool up though (hence the Turbo upgrade).

 

My engineer friend agrees with you. He also said, "If it is going to surge it'll only do it for a split second before boost control takes over and modulates boost pressure appropriately. The tune is what would drive the turbo out of its efficiency range, not the lack of backpressure". So I am guessing that the personal bias of the RUF tech (older gentleman) as well as shiny expensive exhausts for sale is what drove this misinformation, not the truth. Thanks!

 

^ IF the wastegates are big enough. The closed loop boost control system can be commanding 100% wg duty cycle and due to the nice delta P across the turbine from the straight pipes, still not control boost purely from the physical limitations of the wastegate orifice -particularly during the initial hit and at high rpms. This can be particularly nasty during cold weather.

Other than than, straight pipes FTW if you can handle the noise!

 

That makes sense actually.... hmmm. So what would you suggest? Get an xpipe system? or just upgrade wg's? I don't want to hurt the motor/turbo.
I don't mind the noise really..... I like loud cars.

 

I've got a barely used (less than 200 miles) 3" x-pipe full system from turbo to tip from EBwerks for sale at just over half price if you are interested PM me.