StyleLab

Hi,

I have a full stainless 3 inch exhaust with WG tie in, cat bypass and magnaflow muffler. I am currently swapping turbos and noticed the inner diameter of my exhaust tapers off from 3 inches to about 2.5-2.75 inches at the triangular flange where it connects to the bottom of the stock downpipe. Was this exhaust built to work with a stock 2.5 inch downpipe or can I upgrade to a 3 inch downpipe? Do the 3 inch downpipes available also taper down in size at this flange or do they remain true 3 inch inner diameter all the way through? Thanks for your time in advance.

-Nick

Bri Bro

The factory down pipe is smaller in diameter then 3 inches and has a bad history of the inner pipe collapsing causing a major restriction to the exhaust.


From Speed Force Racing site:

SFR 3" Downpipe $349
SFR 3" Downpipe w/V-band $429
This is the infamous SFR true 3" downpipe for your turbo. One of the main reasons we decided to build this particular pipe was due to the size of the turbos people are using. Some larger turbos have up to 2.75" outlets on the hotside and the stock downpipe presented a huge restriction.

The stock pipe can be smaller then 2.25" inside diameter. The SFR downpipe is 2.85" on the inside! We machined grooves into the flanges to except the factory o-rings for sealing purposes. The SFR 3" downpipe require two of these crushrings.

87944turbo

This is from the European Car 951 project.

http://www.europeancarweb.com/projec...tem/index.html

I gave Richards the okay to open up a tapered section of my Lindsey Racing piece since we were going to the 3.0-in. downpipe. The Lindsey piece was designed to fit with the stock downpipe, which is why it was tapered, but now it was the last piece to modify for a true 3.0-in. turbo-back exhaust system. Richards did this by simply placing it on his jig, cutting the tapered section off and TIG welding a 3.0-in. section back on.

HTH.

CarbonRevo

The SFR downpipe is a nice piece and I have heard of about 4whp/7wtq gains from it. It's merely for larger turbos. It does require the True 3" test pipe to install it though. So you can't have one without the other. In other words, you will need a true 3" test pipe (the SFR True 3" unit is a '3 inch' test pipe with the neck cut off and a 3" neck welded on). Call Tim at Speed Force Racing. He can get you set up with whatever you need.

Fabspeed offers a stock replacement down pipe if interested.

StyleLab

ok thanks for the helpful replies guys. I measured the flange again and get 67.5 mm. The SFR pipe seems too big. The downpipe at Fabspeed advertises 70 mm. Considering my flange is 67.5 mm would you guys stick to the stock downpipe or the Fabspeed downpipe?

-Nick

rlm328

The larger pipe is less restricitive but will require modifications to your present setup. As descibed above it really does not buy you a lot of extra oomph. If you were stripping the car down to fighting weight and were trying to get every ounce of HP out of it you could for racing purposes I would say go for it, if it is a modification to a street machine I would suggest that you don't waste your time with it.

fortysixandtwo

Unless you're going to use the SFR 3" Down pipe with their true 3" Test pipe, I would not install it. The abrupt step down in diameter can cause flow turbulence and be more restrictive than the factory diameter with a smooth transition from Down to Test pipes.
Using the fabspeed or standard SFR Test pipe ( the ones that flair out from stock to 3") is fine to use with the stock Down pipe. They're designed to be used this way.
I have a SFR 3" Down pipe sitting on the shelf in my garage, and it will stay there until I either find a used true 3" Test pipe, buy a new one, or make one. This is for an engine that can really benefit from an exhaust upgrade.

Bri Bro

I have a stock unit, but I do inspect it every year, I also want to keep the mounting tab. If you lift up a turbo with the down pipe attached, you start to appreciate the weight involved.

PorscheDoc

The fabspeed downpipe is a nice piece for a stock replacement that gets rid of the dual wall issue when not running a true 3" exhaust.

CarbonRevo

IIRC, the pricing on the fabspeed down pipe isn't too bad. I know if I pulled my turbo and was going to stick with a stock size downpipe, I would go ahead and replace it with a fabspeed unit. Having piece of mind that your inner walls aren't collapsed is a nice feeling.

I however plan on going with the SFR 3" downpipe with V-Band. I'm getting it prepared for future mods to make life easier down the road.

Lorax

The thing not being mentioned her is spoolup. I didn't see any power gains going from a normal dp with 3" exhaust to a full turbo back 3", but I did see a decrease in spool time. I cut off somewhere between 50-100rpms. Not on a stock turbo.

CarbonRevo

To me...shaving 100rpms isn't worth $350 bucks lol

But yes, it should obviously decrease spoolup by at least some. In the end, the 3" downpipe has very small performance gains to it on anything other then big HP cars. Even then, it is really used for the reason SFR stated, the size of some turbo's today need something other then a stock down pipe in terms of size.

Lorax

That's where we differ... to me, $350 for 100rpm's is a steal. Maybe we have different ideas as to what qualifies as a high hp car.. In my mind if you are running a turbo that is larger than stock and upgrading your exhaust, there is no reason not to tack on the 3 dp while you are at it.

CarbonRevo

Well, to clarify...I don't think a 3" would be a necessity for a 26/8 or something along those lines. I plan a Vitesse Stage 3 down the road...so I see a 3" DP as a necessity lol

Most people will skip the down pipe though. It requires them to buy 2 pieces, that can only be installed when the other is. So when you're looking at over a grand for two pieces of exhaust...people start to consider priorities. I just wish you could run the true 3" test pipe with a stock down pipe. I would have had a 3" test pipe installed last year if that was the case.

nick_968

The fabspeed website shows these as 70mm diameter, but the pic looks like it might be a little smaller at the turbo end graduating to 70mm at the exhaust end. Has anyone actually measured both the inlet and outlet sizes?