4 inch Dump and 4 inch Straight Pipe
- Thread starter Brule
- Start date
Cheers
Ive done precision S housings 6266, 6466, H housing 7675 and next is g42 Sportsman 7675. Not perfect but work and make some power.
Fair few making 7-800hp through a single 3 inch downpipe and twin stock exhausts but they would need more boost due to back pressure to get to X hp compared to 3.5 or 4 inch downpipe/exhaust. Not sure how much more boost but less restriction is always better on turbo engines.
Yep I tried my best knowing the basics shown there but theres always room for improvement when you do it a 2nd or 3rd time.
3inch will make 800hp but 3.5 or 4 will make 800hp at less boost and back pressure.
Most n54 pop at 600-700 so not many direct or any direct comparisons on an n54 showing X turbo at X boost 3 inch vs 3.5 inch vs 4 inch. For example 6266 28psi = 700hp on 3 inch but might gain 10hp with a 3.5 and another 5hp again with a 4 inch.
I could of made the start of the downpipe smoother but the way the cut is its over 4.5 inches at the 1st sharp bend.
I could of made the exhaust bends mellower at the crossover under the drive shaft but that's the bends I had and I was sick of pie cutting with a 5 inch grinder by then.
I will sell this downpipe with the 6466 gen2. The 4 inch downpipe should allow the 6466 to perform pretty well.
For the 7675 I will smooth out the top section of the downpipe.
For 6266 and 6466 I would not make a 4inch again as its pretty hard and most likely small gains over a 3 inch under 30psi of boost.
I could of made the exhaust bends mellower at the crossover under the drive shaft but that's the bends I had and I was sick of pie cutting with a 5 inch grinder by then.
I will sell this downpipe with the 6466 gen2. The 4 inch downpipe should allow the 6466 to perform pretty well.
For the 7675 I will smooth out the top section of the downpipe.
For 6266 and 6466 I would not make a 4inch again as its pretty hard and most likely small gains over a 3 inch under 30psi of boost.
Exactly what did I say that was incorrect?
If you think that is funny you must not get out much.
Been running a 4inch dump and straight through 4inch exhaust for a long time now, since bottom mount turbo V2.
Butterfly valve at the back to shut things up to route through a modded HMS.
When running straight through we see another 4psi instantly.
5 1/2in cat and vibrant resonator keeps the car stock levels of quiet.
Version 3 point something of turbo kit has had us change the lobster cut dump to the smoothest bends we could squeeze in.
Air intake side has been smoothed with bends as has the intercooler in / out and path to TB.
Waste gate has also been optimised for flow too as I had a better setup on the Motiv based kit previously.
This should all work a treat on my fully monty engine build.
I expect to see significant improvement with the changes with gas and air flow.
Lot of work but worth the time and effort.
Everything is incremental with the n54 once you are up there with the HP.
Keep at it Brule.
Butterfly valve at the back to shut things up to route through a modded HMS.
When running straight through we see another 4psi instantly.
5 1/2in cat and vibrant resonator keeps the car stock levels of quiet.
Version 3 point something of turbo kit has had us change the lobster cut dump to the smoothest bends we could squeeze in.
Air intake side has been smoothed with bends as has the intercooler in / out and path to TB.
Waste gate has also been optimised for flow too as I had a better setup on the Motiv based kit previously.
This should all work a treat on my fully monty engine build.
I expect to see significant improvement with the changes with gas and air flow.
Lot of work but worth the time and effort.
Everything is incremental with the n54 once you are up there with the HP.
Keep at it Brule.
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What I stated was that a smooth transition smaller diameter pipe like a 3.5" will be better and make more power everywhere in the power band than a large 4"
pipe that has sharp bends and no proper transitions when you haven't got the room for it to be done properly, your actually hurting performance.
If you have the room to do a proper 4" or 4.5" than that is different but that's not what was suggested if one was to read back through the comments.
if your going to run a smaller turbo I would do a 4 inch dump transitioning to a 3.5" towards the bottom.
A little backpressure is good for turbos too especially pre spool as it helps to build power a bit quicker.
Yes you see another 4 psi up top but when its closed it actually makes more power down low and half way through the boost climb, that's why I wanted
you to run a boost operated solenoid and not a vacuum one and having the supply to the solenoid run straight of the manifold so when the boost climbs the exhaust valve opens to make it a straight through exhaust only under boost.
Turn the valve off and the exhaust flap is always closed keeping it quiet.
If you dp a ceramic coating and wrap the downpipe you should be in good shape
That's nice and clean and a good example of how it should be done, this will maximise your hp output.
I was going to say I am surprised no one makes larger DPs for the various ST kits on the market. While not needed for most I think enough people would buy them for it to make sense as a product to offer. You only have to make up a jig and build as ordered. DR makes a titanium DP but who needs that?
The DR DP is still bendy(4), it's because of their exhaust runner design:
Compared to 1 gentle bend:
Going down there is a limitation on size as you can only fit so large a pipe. At some point if you are shooting for those high numbers and need a freer flowing exhaust a hood or fender exit(dme relocated) will be easier, more practical, and less expensive. Don't get me wrong I 100% understand the desire to run 4'' from turbo to rear bumper. If someone made one that fit I would buy it. The stock exhaust flows pretty well up to a point. The DP design and bends is determined a lot by the manifold design and where the turbo sits and what turbo. Not all can have a very smooth straight DP like the ACF kit as above and some have to have bends like @Brule. Again if it could have be nice and straight he would have, everyone would have straight and simple downpipes without bends and welds etc. Sometimes it is just not possible.
Also, at some point the charge piping has to get larger as well. 3'' can move a lot but on many platforms larger than 3'' piping is common enough when you are making high hp. Larger than 3'' on the N54 is a PITA. my 3'' J pipe from IC to CP barely fits. The n54 is great but it has it's limits and there definitely is a sweet spot for power and $/hp or bang for your buck.
Yeah I'm a pretty big fan of the acf kit, there's room for a smoother downpipe on the doc race kit with more diameter. Relocating the dme im forsure not gonna want to do there's some viper syle side exit that @Glassreflectionzn54 did on his car that im gonna do with mine as well im thinking.
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