Does a downpipe make a difference?

[Lex]

Had a chance to look at the difference a gutted stock DP makes versus a non gutted OEM unit. This is similar to installing a downpipe on the car and wrote a blog post about this since it's a question that comes up often.

Many people on here, once fully bolted, talk about the downpipe not having a huge impact with the stock turbo. They are more or less correct. A large and well flowing intake will have a larger impact on flow but the downpipe will improve response.

Have a read below:

http://stratifiedauto.com/blog/does-...o-mazdaspeed3/

[TRex]

so a 3" intake on a stock turbo (even given the restriction) is a better mod than a dp on a stock turbo? (not saying one or the other, just saying most gains for the mod)


incoming intake price jump

[Lex]

Originally Posted by TRex so a 3" intake on a stock turbo (even given the restriction) is a better mod than a dp on a stock turbo? (not saying one or the other, just saying most gains for the mod) incoming intake price jump

Yes, opening up the compressor side (before and after the compressor) allows for higher mass flow than a downpipe.

[EdgeAutosport.com]

Is this peak hp or area under the curve?

[Lex]

Originally Posted by eric@edgeautosport Is this peak hp or area under the curve?

This is upper RPM flow from about 5-5.5k up where the WG is maxed out (and the comparison can be drawn).

[EdgeAutosport.com]

So its safe to say a true 3'' dp would definitely make more power. I picked up 20+whp on my dp alone but it was 3" all the way through


This is only comparing stock vs stock (one being gutted) correct?

[Lex]

Originally Posted by eric@edgeautosport So its safe to say a true 3'' dp would definitely make more power. I picked up 20+whp on my dp alone but it was 3" all the way through This is only comparing stock vs stock (one being gutted) correct?

Correct - the DP will allow for more power for sure. It's a matter of how much and there are many variables involved including the setup for the rest of the car. The compressor end seems more of a bottleneck than the exhaust end on the stock turbo.

[ckMS3]

I'd like to see what difference a full catless dp would make replacing the 2nd cat as well.

[Lex]

Originally Posted by ckMS3 I'd like to see what difference a full catless dp would make replacing the 2nd cat as well.

Planning on doing that comparison as well but probably going from the OEM DP to a catted (high flow) aftermarket.

IMO the test pipe is worth it from the cost/time perspective as a first exhaust modification. The next focus would be the intake tract including the IC and then finish off with a DP.

[Pseud0logik]

Originally Posted by Lex The next focus would be the intake tract including the IC and then finish off with a DP.

It's funny you drop this tidbit right around the same time that Eric announces a group buy on IC's.

[JacksonMS30]

I had to dig deep for this, but I feel it may be relevant. Here is an old thread from back in the day when @bioevolve was still running around.

Yet again went got another dyno!

NATOR Style DownPipe!!!

The first link is the results of Bioevolve gutting his downpipe and midpipe. The second link is just his how to.

Just thought I'd share his findings...

Last Dyno was: 292whp 299wtq (lost torque using 1.05 map and L/A IC) 66temp 53humidity OTS map 1.05 stage2+sf 93 This one is: 319whp 356wtq 67temp 31humidity OTS map 1.05 stage2+sf 93 Only difference is: I added the Nator Style DP and ITV24's gapped to 26.

[Eric28243]

Originally Posted by JacksonMS30 I had to dig deep for this, but I feel it may be relevant. Here is an old thread from back in the day when @bioevolve was still running around. Yet again went got another dyno! NATOR Style DownPipe!!! The first link is the results of Bioevolve gutting his downpipe and midpipe. The second link is just his how to. Just thought I'd share his findings...

Yeah, but that was when OTS maps sucked too.

[JacksonMS30]

Originally Posted by MuffinSquishies Yeah, but that was when OTS maps sucked too.

Yeah, but its not really about which map he was on because he was on the same map for both the before and the after dyno pull. Its about the gains between the two pulls with nothing different except for the gutted cats and the colder plugs.

[Voltwings]

i will say i have no numbers / vids just tons of racing experience with the downpipes. myself and 2 friends were all bolted (same intakes / testpipes-catbacks) with e85 blends (50/50) and of course had to establish who had the fastest mazda in the group. I have the catted ultimate racing downpipe, my buddy Aaron has the ATP i believe it is catless DP and Jeff had stock.

honestly, we were all so close that 95% of the time it just came down to whoever actually pushed the gas first won, however consistently we saw maybe two things.

Aarons car being catless did tend to have a slightly stronger top end from time to time, typically when it was warmer or more humid and the turbos were being pushed harder, makes sense.

Jeffs car on the stock downpipe could not match Aaron and i on the hit, he would fall behind by maybe a nose / half a car at best and would hold there the continuation of the run.

i would give the downpipe more of a torque gain than horsepower gain after seeing how different cars have responded, but being that we were all on E85 and that gives you such massive torque anyways, it is a bit biased. We were all also tuned by the same guy so the tunes were damn near identical. Just my little tidbit

[Eric28243]

Yeah, you have a point. I think you may be right. And since I'm nearly certain the leaning afr's for highway cruising does not produce any added mileage (tried it a billion times with different tuning approaches and most others feel the same that the gain is negligable unless you're very attentive to your speed/load/temps/windows up or down/air conditioner, etc) the added heat that would destroy stock cats is unnecessary as well. I will truthfully say I do believe a torque advantage exists, as 3rd gear is much easier to spin now that I have no cats. I noticed this as I left the garage where the generous fayetteville folks helped me out. I was already running a very aggressive e85 dyno self-tune that I didn't change after the downpipe. Let's not forget the overwhelming advantage being able to hear the turbines at low RPMs has on one's confidence/self esteem.

[Lex]

27 whp difference from gutting the dp is hard to swallow. It would be nice to know what his boost, timing, etc. were doing in bioevlove's case. Edit: it also looks like bioevolve gutted both cats at the same time. In the scenario above, the car already had a race pipe.

The response and low end torque are of course improved as the turbine can be accelerated at a higher rate without a cat/with an aftermarket DP.

[Dano]

also went from 53% humidity in the 1st run to 31% in the 2nd run...denser air charge makes more power and can probably account for some of the HP gain...if we are talking uncorrected numbers....I didn't follow the link.

air temp can make a difference as well.

[08cosmic3]

Lex, which 3" intake to you recommend?

[Lex]

Originally Posted by 08cosmic3 Lex, which 3" intake to you recommend?

Without bringing specific brands into the discussion:

- Bigger is better in this case but keep in mind you can only fit a 3" down to the turbo without relocating the ECU.
- Air filters make a difference so whatever intake you have on there, a high flowing filter will help out.

You can PM me for more specific details if you like.

[anavrinIV]

Originally Posted by Lex Without bringing specific brands into the discussion: - Bigger is better in this case but keep in mind you can only fit a 3" down to the turbo without relocating the ECU. - Air filters make a difference so whatever intake you have on there, a high flowing filter will help out. You can PM me for more specific details if you like.

In this same line, at what point do we experience diminishing returns on larger intakes? I know that at a certain point the MAF will be too far out of the stream to give an accurate reading, but is there a noticeable difference between 3" and 3.5"?

[Dano]

my 3.5 JBR was super easy to dial in and idles like OE...other parts of my motor are preventing me from quantifying the gains.

[anavrinIV]

Originally Posted by Dano my 3.5 JBR was super easy to dial in and idles like OE...other parts of my motor are preventing me from quantifying the gains.

did you previously have a 3" intake or typical sri? I'm not saying that the JBR one is too big, I'm just wondering if there's any gain from it over a cp-e or sure full 3".

[Lex]

You can probably be fine idling a 4" but it's hard to find and fit on the intake side. You can also run blow through with some customization and just a filter on the turbo inlet ... again if you can fit it.

[Eric28243]

This seems like it should be a really old thread... but there's totally a reason for it and I'm surprised it's not all been addressed at once. Probably would've made a different decision besides COBB for intake products, but I didn't intend to do much more than that... of course. Then one thing led to another... Then again I think there are definitely worse options.

[TRex]

well for the longest time the a DP was considered THE mod to really wake the car up

there were very little options for big intakes on stock turbos (read none) and the BT guys that were using them didnt notice anything because well....BT

im glad it got a revisit....changing an intake is soooo much less of a pain in the ass than the DP

[sidekick]

@Lex; Have you ever tuned someone with a Corksport DP? I like the divorced design, but does it offer anything over a bellmouth design in this application?

[Lex]

Originally Posted by boost_addict @Lex; Have you ever tuned someone with a Corksport DP? I like the divorced design, but does it offer anything over a bellmouth design in this application?

I have tuned this setup and in theory it is better to have a divorced wg and turbine flow. In practice it is difficult to say if there is a difference since the different cars I've tuned have had different setups skewing the results.

[sidekick]

Originally Posted by Lex I have tuned this setup and in theory it is better to have a divorced wg and turbine flow. In practice it is difficult to say if there is a difference since the different cars I've tuned have had different setups skewing the results.

Thanks for the input. Unfortunately theory doesn't always work out in the real world, which is why I asked.

[Voltwings]

Originally Posted by boost_addict @Lex; Have you ever tuned someone with a Corksport DP? I like the divorced design, but does it offer anything over a bellmouth design in this application?

Most that i have seen are VTA on evo's sti's ... and those give similar gains to an EWG because you're basically keeping ALL the WG exhaust out of the stream. The corksport one is still plumbed in and just reduces turbulance right at the turbo outlet, so i imagine you will gain "some" over a regular downpipe, but wouldnt expect anything astronomical.

Actually if i'm not mistaken, the corksport one doesnt even separate the turbine / wastegate because the hotside isnt shaped in a way that makes this possible. Basically you're blending air now through two different pipes... would almost think it would be worse o_O pretty sure its covered in a thread somewhere though before someone takes my speculation for fact.

[boostdmazda3]

with a downpipe and TUNE. I picked up some good ponies....peak hp was a little more but the main thing is power didnt fall off as much after 5500 rpms.

[Lex]

There is a little lip on the flange to separate the 2. I personally prefer a car bellmouth for longevity but very heavy duty steel and solid welds would do as well.