Some time ago it was talked about that if your outlet from the turbo was 3" there was no point having a larger exhaust system, i.e 4", as your flow was already restricted by your turbo outlet.
There is a lot more talk about 3.5" or 4" systems these days, so in basic terms, will larger systems net you more hp even if your outlet is 3"?
Just found this, which seems interesting.
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html
Great find
Quote from: davehg;836554Great find
Did you sort your exhaust Dave?
Thats a good read, TBH i dont have a problem beliving you would get a gain by putting a larger bore exhaust on but the question is would the HP gain over a decent 3" be worth the cost of a Custom exhaust being made? Would you still be able to keep a bigger bore quiet whilst keeping the advantage? wouldn\'t a Bigger bore need more to keep it quiet?
The one that confuses me slightly is the downpipes that go from the Turbo to a 4" back to a 3" pipe? because the way i understand it is as soon as the gasses leave the Turbo it starts to cool rapidly / expand, isn\'t letting it fill a larger bore and start to expand then try to force it into a smaller bore the last thing you want? I know you would gain a bit of Turbo responce the Instant you hit the throttle but would it not cause a bottle neck at peak power/flow? Unless i read it wrong shouldn\'t the bore get bigger as the Exhaust gasses cool and expand? (i.e. 3" down pipe slowly getting bigger until it exits the rear?)
I\'m sure i have this wrong and feel free to correct me but it doesn\'t make sence to me.
Quote from: Grizzly;836558Thats a good read, TBH i dont have a problem beliving you would get a gain by putting a larger bore exhaust on but the question is would the HP gain over a decent 3" be worth the cost of a Custom exhaust being made? Would you still be able to keep a bigger bore quiet whilst keeping the advantage? wouldn\'t a Bigger bore need more to keep it quiet?
The one that confuses me slightly is the downpipes that go from the Turbo to a 4" back to a 3" pipe? because the way i understand it is as soon as the gasses leave the Turbo it starts to cool rapidly / expand, isn\'t letting it fill a larger bore and start to expand then try to force it into a smaller bore the last thing you want? I know you would gain a bit of Turbo responce the Instant you hit the throttle but would it not cause a bottle neck at peak power/flow? Unless i read it wrong shouldn\'t the bore get bigger as the Exhaust gasses cool and expand? (i.e. 3" down pipe slowly getting bigger until it exits the rear?)
I\'m sure i have this wrong and feel free to correct me but it doesn\'t make sence to me.
From reading that article, i am not so sure you get a gain from going larger, but you maximise the turbos efficiency, i.e perhaps getting earlier spool up?
I have also "read", how true it is i dont know, a larger system will be quieter, for some technical reason to do with volume and sound!
Not yet I haven\'t, I\'m thinking of getting both silencers re packed to see if that does the trick. I don\'t really want to put a smaller system on if I can help it.
Quote from: davehg;836562Not yet I haven\'t, I\'m thinking of getting both silencers re packed to see if that does the trick. I don\'t really want to put a smaller system on if I can help it.
I repacked my Racing Beat and it made a world of difference, i used Acoustafil, also managed to make the it repackable for the future.
Thanks any pics of your exhaust or how you made it repackable? Where did you get the packing from?
Quote from: davehg;836562Not yet I haven\'t, I\'m thinking of getting both silencers re packed to see if that does the trick. I don\'t really want to put a smaller system on if I can help it.
What size are you using now Dave?
I have 4 inch pipe bore lee from turbo all the way back with a 5 inch tail pipe outlet
Didnt take any pics. I had it cut at one end, then welded a small piece of sheet metal to the cut section so the main exhaust would slide back over it and bolt/rivet in place. Acoustafil is available on ebay :)
Same as mine.
Im debating at the moment the best way to reduce noise by about 5 db so that i have no problems getting on castle coombe next year. Currently db,s are 96 @ idle and 102 @4500 rpm.
I was tempted to take it to bell exhausts in Swindon to get them to repack it etc but I\'m not sure. I thinks it\'s definately worth a try rather than new systems that may not make any difference at all
What noise levels are you at now.
Must admit i\'m tempted to either drop pie size to 3.5" or try and replace my 14" oval midbox with an 18" but not sure if it will make much difference.
I had a custom bellmouth on my FC exhaust system, pretty sure mine was the only one that had ever had it done, meant that the wastegate flapper could actually open as well lol don\'t forget that the larger the pipe the slower the gasses will flow due to the volume, so make sure you match the exhaust size to the engine power/gas flow
i have a custom centre box and hks silent power back box on a 3.5 inch pipe and it didnt make any real noticeable difference.
We run 3 inch systems straight through on 3 race cars and that gets the noise down ok. All cars are running over 500+ hp on full bridgeports.
How much for a centre box and rear silencer with a 5 inch tail Carl
Quote from: m1tch;836577don\'t forget that the larger the pipe the slower the gasses will flow due to the volume, so make sure you match the exhaust size to the engine power/gas flow
So what effects will that have? As it seems that comment completely contradicts the article i found?
Does anyone know where to get oval exhaust piping from? As I been looking under my rx4 today whilst making things for the gear box, and I have no room, none at all:-(
From the various books I have read on turbos and stuff, it seems that once the gases have left the turbo it doesn\'t make too much of a difference.
A larger diameter exhaust on the down pipe should increase spool, good for road cars and track cars or drifting, but how much difference is it going to make for the cost of running a 4" system over a 3"?
As for bigger making a car quieter?? Hmm I would have thought that a larger diameter also the sound wave to expand quicker coming out of the turbo and make a louder crack? I\'m just guessing here BTW. On a 2 stroke when you go from a standard factory exhaust to an expansion chamber the difference is huge.
Quote from: Grant Monkhouse;836593Does anyone know where to get oval exhaust piping from? As I been looking under my rx4 today whilst making things for the gear box, and I have no room, none at all:-(
http://www.stainlesssteel.co.uk/view0c98.html?id=50
How you will bend it though i have no idea :)
Quote from: Grant Monkhouse;836594As for bigger making a car quieter?? Hmm I would have thought that a larger diameter also the sound wave to expand quicker coming out of the turbo and make a louder crack?
There is chat on fduk that 4" systems are quieter, as mentioned i have no idea how or why! :)
Quote from: jetpilot;836598http://www.stainlesssteel.co.uk/view0c98.html?id=50
How you will bend it though i have no idea :)
thanks,the down pipe will be circular but under the car needs to be squashed tubing as i dont want it hitting speed bumps, once i get to the back of the car i can go back to round:)
Quote from: jetpilot;836600There is chat on fduk that 4" systems are quieter, as mentioned i have no idea how or why! :)
yeh ive seen it, but i cant see it being right
Quote from: Grant Monkhouse;836604yeh ive seen it, but i cant see it being right
I think a lot of these things are all hear say rather than legitimately researched, back to back tests are the only real way to find out i guess.
As Carl says with his race cars running 500hp with 3" systems (same with me), but i am now very curious to whether i would get better spool up going to a 4" or even 3.5.
Would love to see some back to back tests on noise and dyno charts, hopefully someone who is buying one of the 4" systems on fduk will provide some evidence.
Yeh but have they got anything from previous? Results to compare?
I think CJR is getting his increased to 4" might be worth getting him to do a before and after??
Quote from: Grant Monkhouse;836609I think CJR is getting his increased to 4" might be worth getting him to do a before and after??
Just put a post up on there asking for some info once they have changed. I presume the car will need a remap too?
I would say so, otherwise you wouldn\'t be getting the full benefits of the earlier spool
Quote from: Grant Monkhouse;836613I would say so, otherwise you wouldn\'t be getting the full benefits of the earlier spool
If its true :Laugh
I really hope someone does, would benefit the maker no end if his systems benefit spool up times and do a good job on noise levels!
Always seems there is a lot of silence within the community when you ask for proven results!
My car was deffo quieter when i went from blitznurspec to 4" system.
I think the reason why it appears quieter is because most people(me included) run huge silencers when they step up to 4" where as before we relied on off the shelf systems so you get what you get IYSWIM
Quote from: lee mills;836615My car was deffo quieter when i went from blitznurspec to 4" system.
I think the reason why it appears quieter is because most people(me included) run huge silencers when they step up to 4" where as before we relied on off the shelf systems so you get what you get IYSWIM
Did you remap Lee?
I did remap but not a fair comparison im afraid as i did a lot of other stuff at the same time.
Quote from: lee mills;836617I did remap but not a fair comparison im afraid as i did a lot of other stuff at the same time.
Its usually the way, people tend to do a bulk of stuff at the same time. So individual items arent tested back to back.
Well there you go, 4" quiter because of bigger silencers. And the restriction caused by these is negligible due to being a larger volume over all
Quote from: jetpilot;836618Its usually the way, people tend to do a bulk of stuff at the same time. So individual items arent tested back to back.
Trouble is unless your doing the mapping yourself its the costs that are involved which hinders testing each individual item.
The only 4" system i\'ve heard first hand had 2 very large boxes fitted and i thought it sounded very Tinny (might just be that one), i know he felt no diffrence in spool but then it had some wild ports.
Quote from: lee mills;836620Trouble is unless your doing the mapping yourself its the costs that are involved which hinders testing each individual item.
P.S If your still looking for a centre box Lee i have just stumbled on these, not a bad price either.
http://www.magnaflowstainlesssteelexhausts.com/mufflers/race-series-mufflers/14153-race-series-mufflers.html
Quote from: jetpilot;836624P.S If your still looking for a centre box Lee i have just stumbled on these, not a bad price either.
http://www.magnaflowstainlesssteelexhausts.com/mufflers/race-series-mufflers/14153-race-series-mufflers.html
Thats what i already have as my centre box with there 24" rear box:D
Quote from: lee mills;836627Thats what i already have as my centre box with there 21" rear box:D
:Laugh So you only want a new one for the packaging :)
Whats the quality like?
Quality is superb.
Only prob is cant really fit a bigger rear box due to clearing the subframe and they dont seem to make a bigger oval mid box although i did find a supplier in the midlands who reckon they can make any size you want so will give them a buzz over winter i think.
Quote from: lee mills;836629Quality is superb.
Only prob is cant really fit a bigger rear box due to clearing the subframe and they dont seem to make a bigger oval mid box although i did find a supplier in the midlands who reckon they can make any size you want so will give them a buzz over winter i think.
So whats wrong with your current system, are you using a round rear box, why do you want to change it?
There are companies who will make up any size, i tried a few recommended from Pistonheads, one company wanted £600 just for a box :Nono!
Nothing wrong with the system and i actually like how it sounds.
The car was initially built to drag race but now decided i\'d prefer to do some track days instead.
With castle coombe being my nearest track (still 100 miles away) and there noise levels being 100db im just above them.
So somehow ive got to reduce noise levels a bit so figured a slightly bigger mid box and a dolphin shaped rear tip should hopefully solve it, but im open to suggestions as the days of being able to throw money at the car have im afraid long gone.
Quote from: lee mills;836632Nothing wrong with the system and i actually like how it sounds.
The car was initially built to drag race but now decided i\'d prefer to do some track days instead.
With castle coombe being my nearest track (still 100 miles away) and there noise levels being 100db im just above them.
So somehow ive got to reduce noise levels a bit so figured a slightly bigger mid box and a dolphin shaped rear tip should hopefully solve it, but im open to suggestions as the days of being able to throw money at the car have im afraid long gone.
Ah, ok, thanks!
Well i did Combe recently and hit 97db first static and then 99 after i got black flagged so around the same ish (3" system).
I would try a repack first with good quality packing, i would imagine the stuff in the magnaflows is pretty rubbish. If you go here http://www.thermalvelocity.co.uk/calc/calculator2.html for acoustafil you can enter your silencer dimensions and it tells you exactly how much to use, very handy! Would be very interesting too see the results, p.s acoutsfil expands with heat so gets better after a few runs!
have you used this stuff yourself with good results?
Ive not tried anything else apart from it, it does get some good reviews and was highly recommended on the threads i read, do a google search and have a read.
Could you confirm your silencer sizes please Lee, from magnaflow i mean. Thanks
I have the one you linked as my midbox and the 24" round one as my rear http://www.magnaflowstainlesssteelexhausts.com/mufflers/polished-universal-mufflers-silencers/14772-polished-mirror-finish-round-stainless-steel-muffler.html
Let me know how you get on if you go the repack route buddy.