4" Exhaust System
22-05-2014, 06:21 PM
#1
4" Exhaust System
I've read a few thread that a 3" exhaust system becomes retrictive at 600bhp.
Soon i'll be fitting a BW 7670 and I could really do with a new exhaust system that goes round the Supra Diff properly, so I was thinking shall I up the exhaust diameter at the same time as maxing out a 7670 is around the 640bhp mark and I don't see myself running anymore than that (600bhp would be fine) would a 3.5" exhaust be more suitable that a 4"?
Hopefully some flow and back pressure experts will be along to explain.
Cheers Rich
Soon i'll be fitting a BW 7670 and I could really do with a new exhaust system that goes round the Supra Diff properly, so I was thinking shall I up the exhaust diameter at the same time as maxing out a 7670 is around the 640bhp mark and I don't see myself running anymore than that (600bhp would be fine) would a 3.5" exhaust be more suitable that a 4"?
Hopefully some flow and back pressure experts will be along to explain.
Cheers Rich
22-05-2014, 06:59 PM
#5
It really nice mate I had all the push fittings replaced with 3" V-Bands and it completely heat wrapped from down pipe to back box.
But if you're in a rush for one mine wont be availble for a few yet.
So it definitley needs at least a 4" down pipe?
Rich
22-05-2014, 07:02 PM
#6
Happily retired
The 201.8mph running 700bhp run was done with a standard 3" exhaust
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22-05-2014, 07:17 PM
#11
cossie fan (unluckerly)
I remember being told it will need a new system made was a good few months ago now I had the chat about bits and pieces
22-05-2014, 08:18 PM
#12
I know Sheady recommends it.
It really nice mate I had all the push fittings replaced with 3" V-Bands and it completely heat wrapped from down pipe to back box.
But if you're in a rush for one mine wont be availble for a few yet.
So it definitley needs at least a 4" down pipe?
Rich
It really nice mate I had all the push fittings replaced with 3" V-Bands and it completely heat wrapped from down pipe to back box.
But if you're in a rush for one mine wont be availble for a few yet.
So it definitley needs at least a 4" down pipe?
Rich
In testing we found a the best downpipe was to get to 4inch as soon after the turo as possible then after that you can taper back to 3.5 or 2x 2.25/2.5.
Mark and rod use a full 3.5 sysstem and get on fine, just individual preferences
22-05-2014, 10:03 PM
#13
10K+ Poster!!
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remember euans (rapid cossie) t4 saph that had a massive exhaust and iirc that made a big difference with dyno plots to show it from ava.
I remember if was fookin quick when I had a go in it when i went to buy it
I remember if was fookin quick when I had a go in it when i went to buy it
23-05-2014, 06:44 PM
#16
24-05-2014, 05:06 AM
#18
I've found that life I needed.. It's HERE!!
18-06-2014, 11:49 AM
#19
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Sorry for the slightly back from the dead reply, but just spotted this.
YES a 3in can do LOTS of power, 600+, but it is massively restrictive.
IIRC even at 500bhp on a YB a 3in system is WELL proven to lose power vs a bigger system. IIRC Stu proved this with Sean Bicknells Grey Reyland Escort years ago.
Not on a YB, but I've personally had very noticable differences, esp in spoolup, by swapping to a much bigger than 3in downpipe on a sub-500bhp engine.
Personally, I'd go at least 3.5in, and if possible start with a 4in downpipe and neck down after that if you lack room.
A big downpipe is the main thing, esp the first few inches after the turbine outlet, as it affects spool a lot. In fact a lot of standard high performance turbo engine have massive turbine outlets these days then necking down to a smaller system.
YES a 3in can do LOTS of power, 600+, but it is massively restrictive.
IIRC even at 500bhp on a YB a 3in system is WELL proven to lose power vs a bigger system. IIRC Stu proved this with Sean Bicknells Grey Reyland Escort years ago.
Not on a YB, but I've personally had very noticable differences, esp in spoolup, by swapping to a much bigger than 3in downpipe on a sub-500bhp engine.
Personally, I'd go at least 3.5in, and if possible start with a 4in downpipe and neck down after that if you lack room.
A big downpipe is the main thing, esp the first few inches after the turbine outlet, as it affects spool a lot. In fact a lot of standard high performance turbo engine have massive turbine outlets these days then necking down to a smaller system.
18-06-2014, 07:40 PM
#24
Could imagine that the 4" system might kill your ears. Even the 3" system gives me headache sometimes.... 
A 4" system means less average temperature for the engine/turbo I guess, cause of the lower exhaust gas back pressure.
Even the 3" system gives me headache sometimes.... A 4" system means less average temperature for the engine/turbo I guess, cause of the lower exhaust gas back pressure.
Last edited by Cossiemainful; 18-06-2014 at 07:43 PM.
19-06-2014, 07:24 AM
#25
You could argue the point of heat loss in a larger exhaust causing a lower gas velocity Due to its density but realistically thats not really going to be relevant so much when your pushing 600bhp down it as its small amount of losses if any are there its next to nothing realistically.
I'm not an expert in exhaust design though just work off what i read and see, so someone could come along and say that's correct but to expect big losses
When Hayward and Scott designed the system for our big power car builds they done it in twin 2.5" pipes to give an overal system area of 3.53 inches I beleive and done it in twin for noise but this system has always worked well with us hence sticking to it and not going any larger
I'm not an expert in exhaust design though just work off what i read and see, so someone could come along and say that's correct but to expect big losses
When Hayward and Scott designed the system for our big power car builds they done it in twin 2.5" pipes to give an overal system area of 3.53 inches I beleive and done it in twin for noise but this system has always worked well with us hence sticking to it and not going any larger
17-07-2014, 11:18 PM
#28
Here's alittle tease of the downpipe, more photos to follow tomorrow.
Got it all bolted up earlier it runs at 98.8dB @ 4000rpm @ 1m-45 degrees very pleased
This one gives you some idea of the size, Karlos very proud of his Tig skills and who can blame him:
Rich
Got it all bolted up earlier it runs at 98.8dB @ 4000rpm @ 1m-45 degrees very pleased
This one gives you some idea of the size, Karlos very proud of his Tig skills and who can blame him:
Rich
24-10-2016, 03:58 PM
#30
Old thread resurrection! Interesting one for me though, very topical given stage of my build today - and keen to hear experiences...
I'll only be running 430bhp ish (2+bar through a T36) but space under the bulkhead and footwells are an issue (ground clearance).
Mark has noticed the old 2.5" system at 414bhp was creating far too much back pressure so has suggested at least 3" system from turbo right back.
Has anyone had two 2" or 2.25" pipes run from downpipe back (can get away with maybe a 3.5" downpipe going to 3" and then split into 2 x 2" or 2 x 2.25") and if so how was it? ie. did it work or did it cause problems?
Thank you
Ben
I'll only be running 430bhp ish (2+bar through a T36) but space under the bulkhead and footwells are an issue (ground clearance).
Mark has noticed the old 2.5" system at 414bhp was creating far too much back pressure so has suggested at least 3" system from turbo right back.
Has anyone had two 2" or 2.25" pipes run from downpipe back (can get away with maybe a 3.5" downpipe going to 3" and then split into 2 x 2" or 2 x 2.25") and if so how was it? ie. did it work or did it cause problems?
Thank you
Ben
24-10-2016, 06:42 PM
#31
Advanced PassionFord User
Cheers Paul
25-10-2016, 09:17 AM
#32
10K+ Poster!!
Isn't it funny that a bit of metal that has been welded can look so nice to us? If I showed that to my wife she would have a very blank look on her face.
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