So I know that if i pick up an OBX downpipe that my car will pee itself and throw a CEL

question for you guys, I know the accessport has a feature to clear codes, now if i get a CEL, clear it, then restart the car, will the light come back on? Would i have to use NCS to code against the O2 sensor?

 

The accessport will remove the cel for your secondary 02. Better off being rmw tuned if you want to make power.

 

The AP can have maps configured to ignore that code so it never comes on.

RMW is no longer licensed to tune AP's. Not trying to start anything just saying your better off going some were that has updated software and support. Pretty much any one that has the current protune software can produce comparable power.

 

 

Has anyone whos gotten the CEL turned off passed emissions?

I know its one thing to not throw a code, but just turning off the post cat o2 sensor may fail "readiness" reading, which is what many states' emissions tests check for.

 

For most emissions testing, you need 3 of the 5 readiness codes working. With all our AccessPORT base maps, you will find all 5 will be ready. This even goes for the OP's question regarding the DP!

 

Didn't believe me huh?

 

posted before asking you smart a___

 

So this brings up a question then. Lets say I unhook from that nice clamp right at the bottom of the downpipe and have a local shop (who do beautiful work) build a 3' system the whole way back.. will it throw a code? And if it does.. with the AP (I've got one) I can clear it easily? I'm betting this has been asked before and I'm beating a dead horse..

Also.. like I mentioned they do beautiful work and predominantly Supras, Rotaries and the occasional boosted european car (no minis yet) What can I get away with in the terms of having a downpipe fabbed? Could I essentially go catless? or is their going to be issues? The most information I can gather before pulling the trigger the better!

They've currently got my '86 GLH-Turbo in for exhaust work and to retune it (microtech standalone ecm) for the watermeth kit I just added I will certainly post some high res pics when all is said and done

 

yes you're beating a dead horse. nothing is monitored after the 2nd o2 sensor, thus anything past it (aka your DP) is not monitored and will not throw a code. you're also pouring more gas on a fire thats been burning out, which is the 3" being too large argument. but i won't get into that. imo its too large and that much flow isn't necessary, especially when your turbo outlet is less than 2.5". catless is much more than enough to be free flowing. its just going to up your costs and drone.
my argument again, three friends have stage 3 b5s4's, two running 11's and one with 525 awhp. All have 2.5" exhausts on their bi turbo RS6 hybrid setups on a 2.7L. if a 1.6 with a tiny k03 needs to flow more than that, then take my engineering degree away lol

 

**golf clap**

 

Catless will throw a code and lose some bottom end power, both can be fixed with your AP though. Your best solution for this would be to tune on a dyno, but if you talk to Alta they probably have some decent base maps available for catless cars that will get you 90% of the way there.

 

+1. 3" exhaust on a 170-220whp car is useless weight.

 

Thanks Gents. My curiosity was more about the CEL issues and what was needed on the tune end of things. Now that I've got that issue cleared up, I'll be having them fab a DP for me too. Maybe then a couple of dyno pulls and send them back to alta and see about a better tune.

You are all correct.. 2.5 is most certainly big enough for a 1.6L. Especially seeing as it's a pretty straight shot the whole way back and lacks any major bends. The 2.5L in the GLH however.. saw an increase at about 4100rpm and upward by the switch from 2.5 to 3in. Albeit at that point its spinning to the tune of 26psi...

 

Yes this is beating a dead horse, it's been talked about a lot on here! Sure a 2.5" exhaust may be "good enough" to power, but a good tuner that works on turbocharged cars knows that less restriction from a 3" exhaust is always better in a turbocharged car. A turbocharger's worst nightmare is backpressure, which restricts the turbo from spooling up and hinders upper end HP. Your engine makes more torque when there's boost. The sooner you get spool, the more torque you will have.

Are you sure your buddy with the B5 isn't running dual 2.5" exhaust? If he put in 3" exhaust on his car, he would make more power. It's common for Euro minded tuners to run 2.5" systems on turbo cars, because they are cheaper and quieter. On Japanese cars, all aftermarket exhausts are 3", if it's for a MR2 all the way to a Supra.

On your point of the turbo outlet, the turbine wheel is only 45mm! Are you saying that if the whole exhaust was 2" that would be enough? Absolutely not!

When it comes to 3" on the Minis, most companies stick with 2.5", because its quieter and cheaper to make. While you can say that 2.5" is "good enough," there is more power to get with a 3" turbo back exhaust. If the ALTA 3" system makes 10 WHP, then the 2.5" must make 5-7 HP. If the sound and price suit your needs, then why not go with the bigger 3" system?

 

lol not even going to bother. do what you choose. There will always be people siding to their beliefs. Otherwise, this world would be perfect. Choose what makes you happy OP.

 

SooperCuperErik was talking about the outlet size, not the compressor wheel diameter, and also, your comment on how the 2.5" inch system "must" make 5-7hp if the 3" system makes 10hp, what is that based on exactly? I know a lot of equations, and have never heard of that one!

But hey, I'm just another stupid engineer. :D

 

If these cars had huge turbos with lots of lag then I would see the validity in running a 3" + exhaust. However they don't and in the case of most people they never will. 2.5" isn't just good enough it's all most will ever need if the system is completely catless. Peak torque can be obtained with in the 2.2-2.5k rpm range rather easily. TBH building torque any faster then that will just cause more problems then it will help.

To Alta's credit their 3" system probably does do better then similarly built 2.5" systems using cats. With the cats removed though the same 2.5" system will most likely flow better then a the 3" with cats. This was the results of the testing I did any way.

The other reason I don't like 3" DP's that much is they tend to fit badly. I've yet to see one utilize the lower heat shield. Even with wrap I've seen people manage to melt the fan because that shield was missing.

 

Mike do you have any stock S DP's lying around?

 

I don't, sorry. I kinda push customers to take and keep them.

 

Chris,

What map options are available for those with catless downpipes?

 

We were referring to the turbine wheel/turbine outlet (not compressor wheel) being 45mm. We hear the argument "that if part of the system is sized 2", why does any other plumbing need to be anything other than 2in"? We were trying to give an example of if the turbine wheel is 45mm, why would anything need to be any bigger than that?

Regarding your HP comment, all I was trying to say was if our 3" system makes 10 WHP, the 2.5" is going to make something less. The question is how much? How much we don't know. We have never seen any dyno runs done back to back on the same day which would be the only fair test. Until that happens, everyone is going to argue about it until the end of time.

Huge turbos have nothing to do with it. We see 3" exhausts on cars beat out 2.5" exhausts on cars with tiny turbos all the time. On these cars, catless downpipes make more power, and spool even quicker. Proving that less backpressure (after the turbo) makes more power and spools quicker. We have a dyno graph, where we have a JCW where we removed one cat (removing backpressure) and it spooled quicker and made more power using our 3" system.

If you have these results, why aren't you showing them? Our 3" downpipe (which starts at 2.5" at the turbo) used all factory turbo heat shields. With our bigger downpipe, we never had any melting problems.

What type of problems are you referring to with torque building? Are you saying too much torque down low hurts the engine?


If the exhaust is catless and at least 2.5", we have used our maps on a few cars and datalogged them and showed boost and ignition to be where they should be. But if you have this setup and are concerned, we would love to see a datalog to double check it for you. The ALTA stage 2 and stage 3 maps were tuned on our 3" exhaust with dual cats (JCW with one cat), so a 2.5 catless turbo back should be OK. The only concern we have is overboost due to not haveing any cats.

The debate between 2.5" vs 3" exhaust is going to go on until someone does a back to back test. We've been doing testing like this for over 10 years now on many cars and it seems like a new group of guys that came from the normally aspirated world bring this up and stir the pot every once in a while. If one test was done, it will settle it forever.

We will always provide dyno results of our parts, to give customers proof of how much power our parts will make. You can use them as you like, and compare them to what other people have shown.

 

Just like how your dyno shows 10whp gain from your intake system... Lol. Why is it everyone else (including myself) do not see this 10whp increase on their dynos?

In fact my back to back run from your "cai" to my stock box yields 2whp more with the stock box. Both new filters....


Side note, ten years testing and you've never tested a 2.5" to 3" back to back just to shut people up if you're right?

 

So Chris, by your logic, a 4" exhaust will make 15whp? Just because 2.5" makes more power than 2", doesn't mean that the 3" will make more than the 2.5". Do you get me?

When people say that 2.5" is "enough", it means that nothing can be gained from going bigger, not that the power delta is enough for people.

 

I'd have to agree with this. There's no way that intake makes more power than stock. Still fits like crap too.

It does sound damn cool though.