3.5 or 4in downpipe on a RHD FC?

[StavFC]

As title really, does anyone have one on their car?
 
 
Im not really happy with running a 3in (despite even some T88 car running one, and no doubt having mega backpressure becuase of it), but there not much room to say the least with the brake master cyl etc in the way. Its an utter ballache removing the 3in one at the moment.
 
Anyone done it? Looks like maybe possible if change a few things, maybe the general direction of the DP.
 
Ta

[m1tch]

Do you really need one that size? If the exhaust is too big it will slow down exhaust gasses, if the outlet of the turbo is 3" then you don\'t need a massive exhaust that is bigger as the exhaust gasses will just leave the turbo and then just empty into a huge space and slow down.

[StavFC]

You might want to look into how turbos and turbo exhausts work before you answer questions like this.
And yes, yes I do need one, actual experience and testing tells me that.
 
Has anyone on here fitted one? Plenty in the USA but LHD makes its easy for them.

[m1tch]

Ok then, fit whatever you want.....

[Brett]

What turbo are you currently running?  As far as I can see the main clearance issue will be caused by attempting to get a decent bend past the bulk head. I\'m pretty certain you should clear the rest.  (unless you have an aftermarket turbo and manifold that has changed the clearances significantly.)

What does the rest of your exhaust system consist of?

[m1tch]

Just convert to LHD like big turbo AE86s do, lots of clearance to fit drainpipes down the right hand side

[StavFC]

Ok then, fit whatever you want.....

So you are saying im wrong and what you said is correct? Havent you got a standard FC T2?
 

What turbo are you currently running? As far as I can see the main clearance issue will be caused by attempting to get a decent bend past the bulk head. I\'m pretty certain you should clear the rest. (unless you have an aftermarket turbo and manifold that has changed the clearances significantly.)
 
What does the rest of your exhaust system consist of?

A stock turbo and manifold would never need more than a 3in really.
Mine is 3in all the way back and seperate screamer, no bends after the DP, and even that is a very smooth shallow bends, but has backpressure still.
Aftermarket turbo and manifold means even the 3in DP is a proper squeeze to clear the brake master cyl etc, bulkhead is no issue, could do 4in all day long if it was only the bulkhead as thats miles away.
 
Only reason im asking is hopeing someone has tried it for sure and can say if it does or not before I go attempting, as its all off at the min, and if it deffo doesnt I got another way around it that will 100% work, just thats lots more work than just bolting it back on.
 

Just convert to LHD like big turbo AE86s do, lots of clearance to fit drainpipes down the right hand side

Thats a rather ridiculous amount of work, way bigger than my other option that would probably make a 5in downpipe fit, so no I wont do that.

[m1tch]

Yeah, standard turbo, custom 3" turbo back exhaust, twin system, will be fitting the T88 next year after I have all the supporting mods, been reaseaching for a while now, exhaust will be custom made at JM garage, he makes exhaust for a living, constantly changing the ones on his 2 rxs to get the best flow, also works with the porche race team, im pretty sure he knows what he is talking about.

At least you will get the flow you want if you want to fit a massive downpipe to be able to clear the rack, less bend etc, it probably is a lot of work, but people do it to be able to fit larger turbos and get the best flow still.

[m1tch]

Yeah, standard turbo, custom 3" turbo back exhaust, twin system, will be fitting the T88 next year after I have all the supporting mods, been reaseaching for a while now, exhaust will be custom made at JM garage, he makes exhaust for a living, constantly changing the ones on his 2 rxs to get the best flow, also works with the porche race team, im pretty sure he knows what he is talking about.

At least you will get the flow you want if you want to fit a massive downpipe to be able to clear the rack, less bend etc, it probably is a lot of work, but people do it to be able to fit larger turbos and get the best flow still.

Im not really going to worry about arguing though, everyones car is different and people want to do different things.

I wish you luck with your car

[StavFC]

Im not really going to worry about arguing though, everyones car is different and people want to do different things.

Nothing to argue about it, its just facts. Saying you can have a "too big" turbo back system, performance wise, regardless of power or engine, is wrong.
 
Simple fact is, regardless of the above, a 3in system is a restriction at my boring engines level, and I know if for a fact. God only how bad it is on a RX with proper power.
 
My question was "has anyone fitted a 3.5in or bigger downpipe to a RHD FC" and you have replied 5 times so far, telling me it will harm performance, to convert to LHD, the spec your car might be in a year, something about some tuner, and some other odd bit I didnt understand.
 
But nothing about the question I asked :3Confused
 
Hopefully someone has done it, but if not, I\'ll just have to wing it like every other bit of tuning I\'ve done to it so far, part of the fun really

[m1tch]

Think this FC is running a 4" as its matched to the turbo

http://www.youtube.com/watch?v=CiwdnETXCRc

[Grant Monkhouse]

I don\'t know about fitting a 4" exhaust to an fc but if you are restricted by the bulk head on the downpipe could you use a tapered centre section to take the diameter to 4"? This would reduce the back pressure more than your current set up? And I do have to agree with stavfc on this one mitch, as an exhaust system is a restriction on a turbo setup from what I have read on turbo systems, as with drag cars running turbos they have as small of an exhaust coming off the turbo to get rid of the exhaust gases faster. However on an n/a engine exhaust systems can be vitally important, on piston engines they have tuned lengths to help scavenge the other cylinders, all to do with sound waves creating a sucking effect to pull the gases out faster. Also on the rotary front I asked racing beat about exhaust design for my 13 b pp engine and they told me to take the exhaust out behind the front wheel! I still have the email and jim mederer said " the less back pressure, the more power "

[StavFC]

The best turbo back exhaust for a turbo car is no exhaust, simple as. The minute you can measure backpressure, and I can, its too small.
 
Its as much the master cyl thats in the way TBH, that combined with my wastegate position really.
 
Its a shame you cant see the bay well in that video, as for all I know he has a pedal box and no master cyl then. Also his turbo sits a tiny bit further forward than mine by the looks of it, and i doubt his WG is in the same place.
 
I can deffo do it, just its debatable if I can without some custom manifold jiggery porkery.

[antnicuk]

i ran a 3.5 inch down pipe and mid section on my FC.  Fitted without problem.  Out of interest,  how do you know you are getting back pressure? i would have thought egt or some kind pressure gauge before the turbo would be the only true way to tell.

I ran 460 hp at 1.2 bar on a GT40 with a 3 inch system,  when i changed to 3.5 all the way to the split by the diff, i had no more power.  This was all measured on the same dyno with the same tuner.

What turbo are you running,  is it still a TO4E?  if so im not sure if you would see any increase in power but then IIRC you run much higher boost levels than most so the bigger exhaust may come into its own above 1.2 bar.

what other tuning have you done with rx7\'s,  anything that worked well thats worth sharing?

[StavFC]

I have a home brewed backpressure gauge post turbo. Wouldve liked to fit one pre but didnt have time before I popped engine.
Got EGT pre turbo, but that dont tell you bugger all about backpressure really as could be varying factors unless you doing back to back exhaust tests.
 
The general concensus in the USA seems to be anything about about 325rwhp and you benefit from a bigger than 3in DP for better spool if nothing else.
On piston engines ive experienced bigger than 3in being better at about 450bhp, but then again had another car that seemed fine at 400bhp at 3in, so its not an exact science, lol.
Bigger is always better if it fits, thas for sure.