Effect of larger exhaust on afr

[Bigsi15]

Hi guys
So my exhaust isn't long for this world and it seems the right time to go full stainless turbo back. Was thinking 2.5" due to costs but I was wondering will this larger freer exhaust have much effect on air fuel ratios in regard to running richer or leaner? I can't monitor mine so wouldn't want to run lean without realising. Iv done some googling and it's not given much definitively

Car is a 96 850 t5

Thanks guys!

[don kalmar union]

You can find, and order, the Swedish made Ferrita cat back that I stock here on my website: http://kalmar-union.com/parts/volvo-850_s70_v70_c70-exhausts/

The price includes VAT and UK mainland delivery, there is a supplement for some remote Scottish addresses and NI.

The standard software will run the engine properly with this exhaust and there would be a very small increase in outputs. If you were to add the stainless d'pipe with 100cel cat you would need to change the software to avoid check lights etc., you would then have substantial increases in both power and torque.

Don.

[MoleT-5R]

I'd like to help here, but not sure I can fully as I fitted a full 3" system to my 855 t-r a while back along with a few other mods at the same time, but unfortunately bent a rod on the first run out in her after re-assembly, on reflection and listening to advice of others more knowledgeable than me, afr was more than likely to have played a major part in this !! As I was at the time unable to monitor afr's and pushed it too hard at the time (stupid I know), so I'd be careful if you do change it and get it on the rollers afterwards and get it checked, be a lot cheaper than fitting a new engine. I doubt fitting a 2.5 system will make much difference, but better safe than sorry.

[Bigsi15]

Ah mole that's such bad luck sorry buddy :( perhaps it was something else contributing to it not just the exhaust? I have forged Rods so hopefully that will protect me a bit just don't want to run lean and burn a hole in something!

[Harvey]

Just what other jobs were done at the same time ?, I would have thought the ECU would learn quite quickly on a exhaust / cat change.

[MoleT-5R]

Just what other jobs were done at the same time ?, I would have thought the ECU would learn quite quickly on a exhaust / cat change.

Quite a bit was changed at the same time Harvey, an S60R exhaust manifold with the collector ported, polished and knife edged (the other end will be done when the new head gets done), a matching 3" angled flange turbine housing was ported and polished to match and then fitted to the existing 15g, which has also gained an adjustable wastegate actuator. Attached to the turbo is a full cat-less 3" system running right to the rear, so hopefully increasing flow and aiding the previously modified full intake setup. Also an AEM methanol kit was installed but not commissioned at the same time, though should this had been up and running, then possibly the issue may not have happened in the first place. I probably went to harsh on the spring choice to start with in the actuator and also the current set-up runs an MBC which was wound back full off, so in theory just using actuator pressure for setup proposes.

Second gear killed it and a dosy driver, I always thought the rule was do boot it in 3rd, 4th, 5th under 3500 rpm looks like that's a myth I learnt the hard way. The 4.3 ecu couldn't or wouldn't have reacted or learn fast enough as far as I can see and having only been on the road less than 10 minute not really had time to understand the new setup, which it had no control over its own boost conditions. Also as we did fine out when the 4.3's map was disassembled it is not very nice to the car anyway, even though it runs and drives nicely and has helped me to 14.3 on the strip, it turns out that the unknown map just is standard t-5r map with the limits wound though the roof.

Lessons learnt from this are many and a more controlled approach to the next session of testing. I am currently getting everything sorted for the new engine, with a faster 4.4 ecu with new base map that will have hopefully taken into account the various modifications and allow logging of what is happening fuel and knock wise should it occur when and where. As soon as funds allow then I be fitting an AEM failsafe AFR gauge and utilise the low side failsafe output to trigger my newly dreamt up failsafe idea that hopefully will dump boost should conditions good bad fueling wise and in turn instantly improve fuel/air mixture and make me instantly aware of the issue.

[martin_r_smith]

and all that by the next shakey meet?? lol

[MoleT-5R]

and all that by the next shakey meet?? lol

mid may if I'm lucky....:)

[martin_r_smith]

I'm not sure if i can make that one but the one after i will. Hopefully my car will have been to Tim by then too..

[MoleT-5R]

Yep hope to make a run or 2 on 13th or 14th of may and then do 10/11th of June for the weekend

[Harvey]

Reading that long list of jobs , Its fair to say something else other than a new down pipe caused the pain you have now..:grumpy:

[MoleT-5R]

Nope... just a home tuner getting to big for his boots. ..Nothing else..just my own stupidity. ...and I except that but it took 9 years of playing to bend a rod so I ain't that nieve. ..just getting more careful with knowledge. .:)