one for the tech heads???

[taylorstattoo]

im trying to work out the correct size of exhaust bore for my m52,, iv mocked up a standard system with single pipe and cat for the time being to just get it though the mot but this is not good for the engine and is restricting it big time,,
i dont want to cause any damage but due to space ect would like to convert the system permanently to one pipe.

Mass of air that the engine breathes in + mass of fuel = mass of exhaust gases,, To calculate the volume of air the engine takes in, you multiply the displacement of the engine by the engine RPM and then divide by two, i think, then the exhaust system needs to flow 2.2 CFM per engine horsepower. which i think is about 215hp = 473

Pipe Diameter.Pipe Area.Total CFM. Hp s Pipe.HP. d Pipe
1 1/2 1.48 171 78 155
1 5/8 1.77 203 92 185
1 3/4 2.07 239 108 217
2 2.76 318 144 289
2 1/4 3.55 408 185 371
2 1/2 4.43 509 232 463
2 3/4 5.41 622 283 566
3 6.49 747 339 679
3 1/4 7.67 882 401 802
3 1/2 8.95 1029 468 935

im confused ,, lol. think iv worked it out that 2 1/2 inch pipe would be ok!! is this right or what are your suggestions to use for a single pipe system with no cat??

[Rav335uk]

Isn't that right, as most on here use a 50mm twin pipe system.

[taylorstattoo]

50mm is about 2inch so you would think i would need 3 and a half to four inch pipe to run one on its own,,??

[Rav335uk]

Not sure on going to 4" unless it's F/I

[taylorstattoo]

i know ,, it would sound like shit too, lol, but do you know what i mean about getting the same amount of flow out. The chart says 2 and a half but i dont know if iv worked that out right as thats only half an inch bigger, but then the gas is only going though one cat/or none, and one silencer instead of two of everthing..

[leeparkes]

Iirc twin 50mm pipes equate to around 75-80mm for a single pipe.

[leeparkes]

Read Dans post near the bottom in my compact thread.

http://www.e30zone.net/modules.php?name ... &start=175

[Rav335uk]

3" I would say

[taylorstattoo]

have you ever done or had a single pipe? maybe 2 and a half is right then with the loss of one of the cats and a silencer,

[Brianmoooore]

Why are you/have you fitted a cat? Not needed with any E30 M52 install.

[taylorstattoo]

just dont want to lose power by going too big or cause unwanted heating of the engine by going too small

[taylorstattoo]

my mot man said as its an L REG, 94 I think, then it would need one, it had one on as standard and something about only get away with it if the engine was older than 92

[ross_jsy]

As Brian says, scrap the plans for a cat.

Why don't you just fit a twin system? Going to run into clearance issues because of the diameter of the pipe, especially since your car is slammed.

[taylorstattoo]

with a single pipe i can bend and route it alot higher with slimline silencers which got me out of trouble last time, only place it ever scraped was the petrol tank on small humps.. plus was hoping for some bhp gains by keeping the flow smooth, straight though

[jmc330i]

my mot man said as its an L REG, 94 I think, then it would need one, it had one on as standard and something about only get away with it if the engine was older than 92

I got confused by this and possibly so has your MOT man. Brian posted a link in another thread about exactly this. If the car or engine is pre-Aug 92 then a cat isn't needed as we know. Your car doesn't fall into this category, but as there was never a 24v E30 from the factory, the car/engine combo won't be in the MOT database and so the emissions test is carried out with a non-cat test.

[taylorstattoo]

right,, so just make sure all the docs have been sent off to dvla befor the test then?

[nickso]

right,, so just make sure all the docs have been sent off to dvla befor the test then?

Irrelevant I would have thought. MOT bloke has to gather his information from the car in front of him, not what the DVLA have on record. None of my cars have been registered with an engine swap.

[taylorstattoo]

thanks guys, iv made up my mind, ill go 2 and 3 quarters then, that way its in the middle, No cat but a small silencer and rear can, hopefully will give good results.

[jmc330i]

right,, so just make sure all the docs have been sent off to dvla befor the test then?

No. If the tester can't find a match in the MOT handbook/database/regs (whatever they call it), the car is tested with a non-cat test.
I wouldn't bother telling the dvla of the changes IMO.


As for the pipe size, some use a twin 2.5" (63.5mm) and others a twin 2" (50mm). BTB use a twin 50mm system for the S50 converted cars and they seem to make good power!
Personally, I wouldn't go over twin 50mm unless it was FI.

As you want a single pipe system, a 2.83" should be the equivalent of a twin 2" (50mm) system. Obviously, 2.83" isn't a common pipe size, so a single 2.75" (although a little smaller than a twin 2") should do the job nicely. I would think 3" would be too big and just create more noise than performance gains.