3" to 2.5" Taper = Power Loss?
 

Finally my Tomei Expreme titanium exhaust arrived today, only had to wait 4 months for it!!!

Its an absolute work of art, and it weighs next to nothing, I was shocked at how little the whole cat back system weighs!

I do have an issue with it though, when I was looking at exhausts, I wanted a full 3" system, not one that tapers to 2.5" as there are plans for 450-500bhp in the near future. I found the Tomei exhaust when searching and all of the pictures I looked at showed a 3" system with no taper. Also no mention of a taper in this particular exhaust specs.

But sadly this system tapers from 2.5" to 3" where it bolts up to the downpipe flange.

So what do I do?

Shall I get a 3" sports cat downpipe that tapers to 2.5" and bolt straight up? If I do this, am I going to notice much power loss with a very short, about 4" of exhaust being 2.5" instead of 3" all the way through?

Or do I get a full 3" sports cat downpipe and find someone I trust to modify the titanium Tomei exhaust to fit so its 3" all the way?

One thing is for sure, one way or another, this exhaust is going on my car!

Cheers :)

You've answered your own question.

Do it once. Do it right :thumb:

Yes, thats my thoughts exactly.

But guess what, nobody near here will touch titanium, they all suck air through their teeth and say "no, we cant work with titanium"!!!!

So, the next question. Anyone in Devon who can be trusted to modify this exhaust?

If not Devon, then I don't mind travelling to visit someone who knows what they are doing.

we need pics :luvlove:

I'd just go for a 3" to 2.5" downpipe like the cobra or prodrive units. They are 3" for the entire length and only narrow to 2.5" at the flange to allow a 2.5" exhaust to bolt on.


Simples.

It might not make any difference....surely the main restriction will always be the cat...sports or not.

Now if you decatted or fitted some fancy bypass pipe, then it maybe a different story.

Have you bought this new? If so why not send it back if it's not what you ordered.

I'll post some pics up later today to clear up the confusion!

I ain't sending it back!!! Waited 4 months for it and I'll be damned if I am waiting another 4 months for a replacement!!

Doubt I could return it anyway as it's a special order item direct from Japan.

I think I will just go with a 3" to 2.5" down pipe for now, then when the 6 speed conversion is done, I'll look at getting it sorted for 3" all the way through.

Can't run anymore power until the conversion is done anyway, currently at 360bhp and I am not comfortable running more than that on the standard 5 speed box!

But surely that will mean yet another full exhaust system change down the road to go 3"? At the price these things are I'd want to make sure it was right first time! eek.

A restriction, is A restriction.

ring steve at davis and snell engineering 01271 813466 he is a genius with a tig welder. converted my downpipe for me to full open mouth , and to be fair it looks oe, tell him paul from brammer said to ring :thumb:

I dont recall mine tapering to 2.5" but if it does (will double check pics) but has not restricted me at 600bhp

OK, so here are some photos, just taken them in the hallway here at work so lighting is not the best!

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In the last few photos you can clearly see where it tapers to meet the downpipe.

Cheers Paul, I'll give him a ring tomorrow :thumb:

That looks awesome.
Bu agree I wouldn't be too happy at that flange, find a titanuim welder and get a 3" flange made

I've been looking at the same exhaust and the matching downpipe from the states but I'm not sure how loud it is so would appreciate some feedback; I'm looking to do track days so don't want it too loud. The other option is a Whifbitz one but they don't have a matching downpipe...;)

Not overly loud sounds great on boost, mine on a recent dyno run all my other videos the screamer dominates so you cant really hear the zorst

I'd be sending that straight back, or getting some sort of price reduction, pointless having a 3" system if it narrows to 2.5".

If you ordered a full 3" then thats what you should receive. I wouldn't let this drop.

Do they sell both turbo back and cat back exhausts?
Maybe the cat back is made to go on existing oem set up, and the turbo back is full 3"?

Such a beautiful exhaust, but I'd be so annoyed with that reduced section like you. How frustrating. As said really, either find a good fabricator to change the flange to full 3" or send it back.

Agreed, wouldn't bother fitting it, pointless its basically a 2.5" system. I don't even know why they bother doing a 3" system if it tampers to 2.5".

Yep, totally pointless. Maybe only so they can build all of their exhausts the same using the same tooling but just change the flange to suit smaller downpipes.


Pointless though, you really want the flange at 3" too.

Ignore this, had issues posting for unknown reasons!

Ignore this, had issues posting for unknown reasons!

So I have been in contact with Tomei in the US. They have advised me that the exhaust that I ordered has three different versions!

Part No: 440005 - GDB A-D(JDM)
Part No: 440006 - WRX / WRX STI 02-07(USDM)
Part No: 440005 - GDB E-G

I ordred the 440005 version.

Tomei have advised me that the one I ordered does indeed have a taper to 2.5" where it meets the downpipe. So I was sent the correct exhaust.

I ordered the JDM version, 440005 as I was, and still am pretty sure that the early JDM applied model A-D GDB exhaust is the same layout and design as any GC8 with a turbo. Same length downpipe, and same length for the rest of the system, there maybe a hanger in the wrong location near the tailpipe, but thats not going to be an issue with an exhaust which weighs so little.

There was no mention of a taper in any specs of the exhaust, and every picture of one that I came across shows a full 3" system. I therefore thought that I was ordering what I saw in the pictures, so my mistake really.

Tomei have told me that the 440006, USDM version of the exhaust is 3" all the way to the downpipe and has a flange that will marry up with a 3" downpipe. The first pipe which meets up with the downpipe will fit all of the versions of the exhaust listed above, they are interchangeable so to speak. They call this pipe Main Pipe A.

I think that if I was to order Main Pipe A 440006, I can then fit a 3" downpipe for a later EUDM/UK GDB as I believe they are the same length as the USDM downpipe.

Can anyone confirm that a USDM downpipe from a later GDB is the same length as a UK GDB?!

It maybe cheaper to get the exhaust changed by a decent fabricator rather than ordering a new Main Pipe A. Considering that I want to change the downpipe to one that has a sports cat as I dont want problems with MOT time and the VOSA roadside checks that are becoming more commonplace these days!

What a nightmare, but I have said it before, and I'll say it again. One way or another, this exhaust is going on this car!

I've had the same thing before with a cobra system and jetex system. Both reduce to 2.5 at the downpipe end. Will be getting the 2.5 section cut out soon. The cobra still got me to 421

Cut and wield looks like the thing to do. Or wouldn't bother fitting.

Swap the pipe. Tomei should pla fair. You won't find a titanium welder ...

It's a point; welding stainless is not something that should be done by someone used to MIG welding mild. Chances are it'll fracture and break off after a few years if the wrong wire and gas is used.

So long as their 3" flange d/p is the same overall length as the one you already have*, then get the vendor to ship it, and you send yours back.**

Even if you have to pay for shipping yours back, the cost will no doubt be similar to having to get a 3" flange welded on anyway. So nothing 'lost' so to speak (but really, if what you say is true, the vendor should pay for everything IMO).

Also, you'll have the proper full system reinstated - with the benefit of its lighter d/p too (should you have otherwise gone down the replacement steel d/p option). So easier to sell on in the future, as well!

It all makes sense.


* I know you're already trying to find confirmation to this question. ;)

** What's a week or two extra, when you waited 16 in the first place. Be patient - you'll be A LOT more happier in the long run. ;)