Custom HPF type exhaust and custom downpipes

[Beasted]

Local Longlife garage has agreed to custom build a cat back 3.5" straight HPF copy exhaust with a 1792 vibrant resonator and flexi pipe, plus downpipes for £550- fitted. Absolutely chuffed with the price.

Just a quick question, as I'm having 3.5" cat back, should the downpipes also be 3.5" or should I ask for 3" downpipes going into the 3.5" cat back?

Cheers all.

[dtla1]

How much power are you making? 3.5" is too much cross sectional area if I remember my previous calculations correctly.

[Beasted]

Originally Posted by dtla1

How much power are you making? 3.5" is too much cross sectional area if I remember my previous calculations correctly.

Currently about 350-400hp, but, I am going to be going above this up to 550bhp.

So your saying 3" all the way? Because I see someone did 3.5" from downpipes. So wasn't sure. This is how the exhaust will look when done to give a idea! Pictured.

[dtla1]

I'm sure 3.5" would work, whether it is ideal, I'm not sure. A friend of mine that works for a very reputable Nascar racing team is the one that actually has done various calculations etc. It all depends on power, engine type, number of bends etc. If you think 3.5" is best then go ahead.

[Beasted]

Originally Posted by dtla1

I'm sure 3.5" would work, whether it is ideal, I'm not sure. A friend of mine that works for a very reputable Nascar racing team is the one that actually has done various calculations etc. It all depends on power, engine type, number of bends etc. If you think 3.5" is best then go ahead.

Well that's what I'm not sure about hence why I've posted the questions mate. 3" or 3.5" downpipes or not? Then 3" or 3.5" cat back too?

Want to get the best option before I go ahead and book in.

[lowbudgethero]

3.5in downpipe hands down, it's still slightly less area than the n54's 2x2.5in downpipes, turbo cars like less back pressure on boost.

I guess the other question is do you have an n54 or n55 car

[Beasted]

Originally Posted by lowbudgethero

3.5in downpipe hands down, it's still slightly less area than the n54's 2x2.5in downpipes, turbo cars like less back pressure on boost.

I guess the other question is do you have an n54 or n55 car

Mine is the n54 mate.

So are you saying get two 3.5" downpipes going into a single 3.5" cat back? Cheers

[lowbudgethero]

dual 3" into the 3.5 should be fine, i think you would have a hard time fitting 3.5 in without it touching somewhere or reducing it somewhere else.

[Beasted]

Originally Posted by lowbudgethero

dual 3" into the 3.5 should be fine, i think you would have a hard time fitting 3.5 in without it touching somewhere or reducing it somewhere else.

Excellent been a great help, I'll go 3" downpipes to 3.5" HPF mate. What about the resonator 1792 I heard was the best sounding, I don't want it tinnie or farty more meaty! Cheers

[lowbudgethero]

now that I don't know, I'm only running stock exhaust from the midpipes back

a resonator always sounds good on these cars though, because the muffler deletes tend to be droney

[Beasted]

Hopefully someone can help there to get the best sound

[iminhell1]

Don't pay any attention to any exhaust size calculator.
Anything after the collector is basically irrelevant. Exception is pipe that's excessively too small.

My little 4cyl car came with 1 7/8" pipe. I built it up and now it has 3" pipe. No loss of power or TQ. And I actually loose power with 2.5" pipe. It defies all exhaust calculators ... because you have to research how the calculator was built. Many are based on the cylinder offset timing for a V8. Once you deviate the formulas break down and will be wrong.

[Beasted]

So can anyone confirm the resonator and sizes?

[dtla1]

Originally Posted by iminhell1

Don't pay any attention to any exhaust size calculator.
Anything after the collector is basically irrelevant. Exception is pipe that's excessively too small.

My little 4cyl car came with 1 7/8" pipe. I built it up and now it has 3" pipe. No loss of power or TQ. And I actually loose power with 2.5" pipe. It defies all exhaust calculators ... because you have to research how the calculator was built. Many are based on the cylinder offset timing for a V8. Once you deviate the formulas break down and will be wrong.

I wasn't going off of an exhaust Calculator, I was going off calculations done by a good friend of mine that works for TRD building their Nascar engine, and also does work on the side, of his own tuning cars etc. But like I said, its hard to pin down the true "best method".

[Beasted]

Ok so going to get the exhaust done Friday. Can any one please advise me, I can't get 3.5" straight catback now it will be 3" cat back keeping stock downpipes "for now" will be changing them for 3" ones in a month or so do bare that in mind. I'll also be running a resonator and a flexi part going into a Y pipe for exits. Finally using single 4" tips either side or quad 3-3.5" tips.

Let me know if it will all be ok for performance and anything else exhaust effects

Thanks guys

[ShocknAwe]

You could literally run a cut out directly after the turbo and that would be best. Not that you would WANT to do that, but on this car, it would be fine.

That said, N54 is great with 3" downpipes to dual 2.5" mids, axleback whatever you want. It's going to be next to impossible to fit larger than 3" directly after the turbos, and if you go too big on the midpipe section you'll have issues with the middle brace.

Pay attention to the different diameters of those resonators as well, make sure they use the right size for your piping.

[Beasted]

Originally Posted by ShocknAwe

You could literally run a cut out directly after the turbo and that would be best. Not that you would WANT to do that, but on this car, it would be fine.

That said, N54 is great with 3" downpipes to dual 2.5" mids, axleback whatever you want. It's going to be next to impossible to fit larger than 3" directly after the turbos, and if you go too big on the midpipe section you'll have issues with the middle brace.

Pay attention to the different diameters of those resonators as well, make sure they use the right size for your piping.

Thank you mate.

Just finished speaking with him and its booked for 9am tomorrow morning.

For now it will be stock downpipes into, 3" straight stainless mid pipe with a flexi part, then just before the Y pipe a 3" resonator then quad 4" exits.

P.s. Later in the line will be custom 3" downpipes

Hope that sounds good

[ShocknAwe]

Originally Posted by Beasted

Thank you mate.

Just finished speaking with him and its booked for 9am tomorrow morning.

For now it will be stock downpipes into, 3" straight stainless mid pipe with a flexi part, then just before the Y pipe a 3" resonator then quad 4" exits.

P.s. Later in the line will be custom 3" downpipes

Hope that sounds good

Good luck! Post up some pics of the routing for folks once you get it done!

Also, I believe there are some aftermarket manus that do 3" DPs that will work for RHD.

[Beasted]

Originally Posted by ShocknAwe

Good luck! Post up some pics of the routing for folks once you get it done!

Also, I believe there are some aftermarket manus that do 3" DPs that will work for RHD.

Will do mate just waiting for them to open up the shutters. Then work starts on it. Pics by the end of the day!

[ErvGotti]

Originally Posted by Beasted

Thank you mate.

Just finished speaking with him and its booked for 9am tomorrow morning.

For now it will be stock downpipes into, 3" straight stainless mid pipe with a flexi part, then just before the Y pipe a 3" resonator then quad 4" exits.

P.s. Later in the line will be custom 3" downpipes

Hope that sounds good

Just curious why don't you just buy downpipes from the vendors on here? The fabrication for custom ones I think will cost you more than the 550 pounds quoted. If you're looking for perfect fitment AR Dp's are around $800, on the other end VSRF has them cheaper, but fitment might not be as good. DP's for the N54 aren't easy to fabricate. N55 yes N54 no.

[rod.bearings]

BlackMarketRacing has a 3.5" single mid-pipe exhaust for sale. It has a dual 3" collector going into a 3.5" y-pipe. For reasonators 1792 is too small as it is only 2.5" you would need the vibrant 17970 3.5" resonator. Also I wouldn't do a single 3" since it has less surface area than the stock dual 2.25" mid-pipes unless your doing it for weight savings. I'd personally buy downpipes from a vendor then make a custom catback.

[Beasted]

Well it's done, 3" downpipe back system with a 3" resonator, going onto 2.5" y-pipe to quads.
Sounds nice! Seems to run well with it.