Exhaust Merging options and Scavenging

BigSteve

Member
Ok here's a quick question for our exhaust guru, JBrady. Answer may help a few others.

My exhaust (2.25 dual with balance pipe)my original exhaust guy suggested putting a small balance pipe in my twin exhaust setup and due to lack of research, I let him go with the balance pipe instead of the X-pipe I asked for.

I regretted not doing enough research first, the slap/cackle is rather annoying and there was no noticeable increase in performance, felt more like a loss in response (Which I have no doubt that was the exact result).

So I'll be changing the setup to a merged system. Either a Y pipe into 1 straight through muffler and then split back into 2. Or a dual in/dual out Muffler with internal x-pipe.

I was pretty set on using a dual in/dual out x-piped muffler because they sound nice and smooth. But the question is about scavenging.

What are the scavenging differences between Y pipe (2.25 into 2.5) into single muffler then split back into 2, dual in dual out x-piped muffler (not sure how the perforated pipes affect scavenging), and possibly even a dual in/dual out straight through muffler with separate x-pipe?

The current exhaust would be an awesome sound on something old school, but it doesn't suit the car.

Note: stock y-pipe isn't an option. The entire old exhaust was thrown out.
 

JBrady

Moderator
The stock Y as noted is excellent but since it is gone you have to fab something.

The SHAPE of the merge is important as are the tubing sizes used. The internal X muffler is interesting but I haven't used one so can't tell you what to expect from performance.

You PM'd me that you will be running Kelford 264 cams. I am not sure about those cams with your system but generally more overlap will reduce low end torque and response.

You also say your goal is 200rwkW / 270hp even if it takes nitrous.

I would recommend running dual 2.00" pipes off the factory cats outlets. Buy and fab these from mandrel bends. Merge them into a 2.50" single center pipe. Replicate the factory location of the merge point. Slightly squeeze the 2.00 pipes and slightly stretch the 2.50" pipe to form your merge. Do not worry about reducing flow by squeezing the 2.00" pipes down to about 70% of their round area.

Run the 2.50" section the way the factory did. You may want to try it without any center muffler and you can always add a straight through 2.50" muffler later. Then split it back into your existing 2.25" system.

This will give you slightly more flow capacity than the 300hp/325tq rated 2001 GS430 has and should give you back most of the lost low end torque and response. The factory 1.97" into 2.36" stock Y pipe has supported 270rwhp on a NA GS400 running headers and a tune. Your crush bent 2.25" pipes probably flow less than mandrel 2.00" pipes. The crush reduces the area that increases pressure before the bend and then pressure drops after the bend. Each bend has this same pressure up and down costing efficiency of flow. Properly constructed the design I have recommened may outflow your current pipes and give you back response and low RPM power.
 

BigSteve

Member
on that note though, how much difference in power do the think that flow would equate to when comparing 2" mandrel and 2.25" crushed. If the difference is minimal enough then wallet efficiency has priority over volumetric efficiency I guess.

Still would be interesting to find out exactly how the Dual X-piped muffler performs compared to an x-pipe/dual muffler setup.

I haven't found a single 1uz with that setup. Might submit myself to be the guinea pig
 

JBrady

Moderator
At peak power the difference is likely within 5-10hp.

At low to mid RPM the mandrel merge system I describe creates much more scavenging and therefore power/torque/response than the crush bent 2.25" system. It is the first section from the cats to the Y that has the biggest impact. This is especially important with these relatively small engines in relatively heavy vehicles with low stall torque converters.

Also, it will sound much better.
It will fit better.
It will weigh less.

Mandrel bends are easy to find online.
 

BigSteve

Member
Hmm, I hadn't known the mandrel bends would make that much difference. I was under the impression there's only 1 or 2 hp between mandrel bend and crush bent given the exhaust is identical in setup, which is why I didn't ask for mandrel the first time.

If they in fact make a much greater difference I'll look at mandrel bends instead, which will pretty much mean a whole new exhaust.

(Edit: Added question)

Would anyone have a clue as to if the PPE Headers would fit a right hand drive '90 Celsior.

And Jbrady, what are you opinions on this design.. http://www.castleauto.com.au/ch85.htm

Castle Autos claim they will fit the Right hand drive Celsior but as yet it seems no one has tried.
 
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samsdad

Member
I've actually got Bigsteves car in my shop ATM and have just fitted some in old school speak "Fast road cams". With the exception of the exhaust manifolds and the Magnaflows on the back of it the rest of the system really needs to go by way of the bin as I'm pretty sure that my 4yo son could make a better one (no flanges and leaky welds). The man to talk to here in Perth is on leave ATM and away for another 2 weeks (he does all our custom Hilux extractors) so if you wanted to go with fitting extractors a "Tri Y" design would be best with hi-flow cats given your use of the vehicle with an "X" pipe rather than the balance pipe that is fitted (those went out with VL Commodores) running 57mm tubing to a pair of resonators then 63 to the magnaflows should do the job nicely. As she sits ATM wait until you hear it with the new cams. It makes a worked LS1 sound like something that Granny drives to the shops on pension day
 

BigSteve

Member
Yeah I've been doing a lot of reading up on exhausts as that's probably going to be the next job after I get those tyres sorted. After I sort my bills and rego, I'll have to make do with that exhaust for a bit.

Im going to get rid of those Magnaflows, they're nice mufflers but way too big. Which means I'll have it merge in the middle with a muffler and most likely 2 resonators somewhere near the back and have the tips tucked up nice.

I've been listening to a heap of exhausts on youtube and I fear an x-pipe as well as 2 mufflers will be a little bit quieter than I'm aiming for.

That exhaust guy was recommended by a Local ford forum, we all make mistakes huh.
 

JBrady

Moderator
I've actually got Bigsteves car in my shop ATM and have just fitted some in old school speak "Fast road cams". With the exception of the exhaust manifolds and the Magnaflows on the back of it the rest of the system really needs to go by way of the bin as I'm pretty sure that my 4yo son could make a better one (no flanges and leaky welds). The man to talk to here in Perth is on leave ATM and away for another 2 weeks (he does all our custom Hilux extractors) so if you wanted to go with fitting extractors a "Tri Y" design would be best with hi-flow cats given your use of the vehicle with an "X" pipe rather than the balance pipe that is fitted (those went out with VL Commodores) running 57mm tubing to a pair of resonators then 63 to the magnaflows should do the job nicely. As she sits ATM wait until you hear it with the new cams. It makes a worked LS1 sound like something that Granny drives to the shops on pension day
PLEASE do not take what I am about to say as an insult because I have great respect for individuals such as yourself that are building these or any engines to higher output.

Your exhaust recommendation above is way better than most but I respond to give further insight for readers here.

The stock Y pipe (which Big Steve does not have) is a very good part. MUCH better than what most think. It has twin 50mm tubes (1.97") feeding a single 60mm center tube (2.36") using a very effective collector design.

I built a very nice 57mm (2.25") into 63mm (2.50") merge collector (see image below) and donated it to the very first S&S header install on a GS400. A shop built mandrel bend 2.25" tubes off of the catalysts outlets into this merge collector. The peak power changed by ONE horsepower but the engine became mushy and lost response.

The Y pipe above was a direct stock bolt in replacement so the owner was able to swap back a stock Y pipe and all the response and low end came right back. He was also able to run a GS430 Y pipe which has identical dimensions except has a catalyst in the 60mm section instead of the resonator in the GS400 pipe. Power and response identical between the two stock pipes.

Another S&S header user built a 2.50" into 3.00" Y pipe using a quality merge collector from Dr.Gas. His car seriously lost low end response and power. After discussion with me he had a 2.00" into 2.50" pipe constructed and was AMAZED at how much low end came back and even felt the top end was stronger (subjective as no dyno was done).

These events occured about 6 years ago and made me reconsider all my thoughs and now recommend the STOCK GS400 size Ypipe for all motors up to 275rwhp (205rwkW). SC400 and LS400 Y pipes neck down to about 55mm in the center section so those are more like 250rwhp pipes. For power from 275rwhp to 300rwhp (or if you have an SC or LS) simply change the 60mm section for a 63mm section (2.36" to 2.50") ... AFTER THE MERGE... DO NOT CUT OFF THE MERGE... which gains nearly 13% in flow area (using .065" wall thickness tubing, standard 16 gauge). You can use either open tubing or use a perforated resonator to reduce sound. Do NOT use a resonator that has less than a TRUE 2.50" center with SMOOTH flow. Some cheap ones have louvers punched into the flow area reducing flow capacity substantially and would be worse than stock. Go with a quality part like Magnaflow or Dynomax.

It is good to consider that the flow area of a 16 gauge 50mm pipe is 2.65 sq/in... so two of them have 5.3sq/in of flow area. The stock 60mm has only 3.9sq/in so the two smaller pipes have more total area than the center pipe making the center pipe the restriction. That said some 400rwhp supercharged GS4xx cars have ran that stock pipe. Increasing the center to 2.50" gives you 4.4sq/in of flow area STILL less than the twin pipes feeding it.

Now, I am not saying the stock pipe cannot be improved upon BUT I am saying it is harder than most believe.

FURTHER complicating the above is the RATIO of the Y pipe. The stock pipe has 5.3sq/in accelerating into 3.9sq/in for a ratio. Now MANY things come into play other than strickly area but this is a good way to visualize things. The stock twin tubes have 26% more area than the stock single tube.
If you look at the same for a 2.25" into 2.50" pipe the twins are 38% larger. This requires more energy to accelerate the gas than the stock sizing. If you want to use 2.25" tubes you need a 2.75" single to have a similar to stock 24% ratio. You DEFINITELY want acceleration in the Y section as this creates scavenging but too much creates unnecessary back pressure and reversion at lower RPMs and flow.

NOW, since the single tube has less area than the twin section you MUST decide when you need more than 60mm, then 2.50" before upping that size to 2.75" (70mm). Consider how much power a 3.00" (76mm) pipe can support on a turbo engine like the 2JZ-GTE which is upwards of 700rwhp... so how much do you think a 2.50 can support? Well over half for sure. 2.50" STRAIGHT pipe can support 350rwhp. So, before increasing the size on the single section consider how much you NEED.

I have had many PM me requesting that I build proper replacement Y pipes. I have been close to doing so on a number of occasions and I am once again getting close to doing so.

Hope this helps.
 

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samsdad

Member
None taken and in fact a big thanks for all of that.. So when are you moving to Perth and opening a shop here? I'll make the first bookings with my own UZ powered Surf being the first in the door.

Where I do have to make a system which due to economics and time constraints I now rarely do I make up collectors or "Y" pipes as you've explained and shown and not due to the math involved (aside from practical math e.g quotes and bills I can't do math to save myself yet I can do prop sizing for boats PDG.. Go figure), Why? Because quite simply it is the easiest and most efficient way to make them when you do not have proper forming gear especially when merging the front pipes to a larger size for the rear if running a single system. My own is Crown log type (Engine strangler) exhaust manifolds with twin tuned length 57mm front pipes, single hi-flow cat with 63mm single system and Walker Super Turbo muffler, All bends in the system are formed sections with the "Y" pipe exactly as you've shown..

Perhaps if you have time to do so an exhaust tutorial from you would be a major benefit to all of us. I personally go with what I've tried in the past and found "works for me" plus keeping a pleasant exhaust note with also "keeping the cops away" yet without access to a dyno or time to experiment I honestly cannot say for sure what is the best system to run. Just to let you know JB my comments in this instance were based on the fact that I had the car in the shop, saw what was there and heard it before we put the cams in (Sorry Steve but it really did sound rude... Too much crackle) and was what I'd do if it were mine. Yet the new cams certainly changed the whole persona of the vehicle for the better. All I can say is once it has a properly designed system on it and is able to be correctly tuned it will for want of a better phrase have "Great big hairy nuts"!

Again many thanks for your comments.
 

BigSteve

Member
Ah yes, very much agree it was a rather rude sounding system. Didn't really like it since the moment I drove out of the exhaust shop, but at nearly $1500 for that exhaust I wasn't in any hurry to replace it straight away.

When I pay off my bills and put together funds, exhaust is going to get redone. Needs to be moved away from whatever it's hitting on now anyways.

I was thinking maybe 2.25 into 2.75 (for the length of the old middle pipe) and leave room for if I decide to supercharge down the track (Was considering Nos eventually, but problems with legality and insurance are most likely not worth it)
I haven't seen a 2.25 into 2.75 y pipe available so Im guessing that'd need to be custom made.

With a tune and exhaust the thing should sure be rather exciting to drive.
 
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BigSteve

Member
Ok after some thinking, I think I have come to a final conclusion.

When I get around to revisiting the exhaust, I'll probably Go with replacing the front section with 2" Mandrel bent then A Magnaflow Y pipe 2" into 2.5" (http://www.magnaflow.com/02product/displayapplications.asp?partnumber=10735)

Ill run the centre 2.5" down to join up with the rear pipes for now. So I need to find a Y section to split from 2.5" into Dual 2.25" to weld up to my rear pipes. (Edit: Found one, but not sure how the flow would be on this design http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=9784)

Then further down the track if It needs to be louder Ill take off the 2 rear mufflers and put 1 in the 2.5" pipe.

Should give good scavenging and sound a lot cleaner at least.
 
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JBrady

Moderator
None taken and in fact a big thanks for all of that.. So when are you moving to Perth and opening a shop here? I'll make the first bookings with my own UZ powered Surf being the first in the door.

Where I do have to make a system which due to economics and time constraints I now rarely do I make up collectors or "Y" pipes as you've explained and shown and not due to the math involved (aside from practical math e.g quotes and bills I can't do math to save myself yet I can do prop sizing for boats PDG.. Go figure), Why? Because quite simply it is the easiest and most efficient way to make them when you do not have proper forming gear especially when merging the front pipes to a larger size for the rear if running a single system. My own is Crown log type (Engine strangler) exhaust manifolds with twin tuned length 57mm front pipes, single hi-flow cat with 63mm single system and Walker Super Turbo muffler, All bends in the system are formed sections with the "Y" pipe exactly as you've shown..

Perhaps if you have time to do so an exhaust tutorial from you would be a major benefit to all of us. I personally go with what I've tried in the past and found "works for me" plus keeping a pleasant exhaust note with also "keeping the cops away" yet without access to a dyno or time to experiment I honestly cannot say for sure what is the best system to run. Just to let you know JB my comments in this instance were based on the fact that I had the car in the shop, saw what was there and heard it before we put the cams in (Sorry Steve but it really did sound rude... Too much crackle) and was what I'd do if it were mine. Yet the new cams certainly changed the whole persona of the vehicle for the better. All I can say is once it has a properly designed system on it and is able to be correctly tuned it will for want of a better phrase have "Great big hairy nuts"!

Again many thanks for your comments.
Thank you for your respectful response. I almost always try to do the same.

Hey, we are all and always learning right?

I have posted quite a lot here and on Club Lexus so some seaching under my name will turn a fair amount if anyone is interested.
 

JBrady

Moderator
Ok after some thinking, I think I have come to a final conclusion.

When I get around to revisiting the exhaust, I'll probably Go with replacing the front section with 2" Mandrel bent then A Magnaflow Y pipe 2" into 2.5" (http://www.magnaflow.com/02product/displayapplications.asp?partnumber=10735)

Ill run the centre 2.5" down to join up with the rear pipes for now. So I need to find a Y section to split from 2.5" into Dual 2.25" to weld up to my rear pipes. (Edit: Found one, but not sure how the flow would be on this design http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=9784)

Then further down the track if It needs to be louder Ill take off the 2 rear mufflers and put 1 in the 2.5" pipe.

Should give good scavenging and sound a lot cleaner at least.
The first Magnaflow part you list, 2.0" inlets, 2.5" outlet, PART # 10735, will work just fine in both postions, front and back.




However for the front Y the narrower the merge is the better so if you can find someone to build one like I posted you will get a slight improvement.

The second Magnaflow is a poor design that I do not recommend for either front or rear Y. The main problem is the large plenum area at the transition that allows the gasses to slow WAY down and when that happens pressure goes UP... only to be forced to speed back up again... not efficient.



You want the least possible "plenum" area in a transition and you want the smoothest shaping to take the least energy from the flow to make the transition.

Use the first Y you pictured, PART # 10735, to split the center back into your duals. It does not matter that it uses 2" outlets, simply slide your 2.25" pipes right over those 2" sections. The combined flow area of the two 2" pipes is greater than the flow area of the single 2.5" pipe so no restriction occurs.


Also, build your front Y pipe with the Y in the same location as the factory right after the transmission. You may find it best to cut most of the 2" extensions off and weld on 2" mandrel bends to get the Y placed as the factory did. This will give you a shape closer to the factory that looks kind of like this Magnaflow part (not recommended due to its using the same 2.5" for both the inlet and outlet sizes).



Of course once you have gone to this much trouble you may consider rather than buying two Magnaflow Ys instead cutting the 2" mandrel bends at an angle to create the above pipe in the proper 2.0" into 2.5" size.
 
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BigSteve

Member
Yeah, that is what I was thinking about with the 2nd Y-pipe having that plenum sort of design.

Thanks heaps for the very informative posts, I have done a fair bit of reading on reversion and scavenging (for intake side as well) and it's all making quite a bit of sense. Only wish I had read up on it before going the standard "Bigger exhaust for more noise" in the first place.

As for the Y-pipes it might be more cost effective to modify the magnaflow Y-pipes as I can probably get 2 on ebay from the US for around $175 shipped. The front section in mandrel bends shouldn't be too expensive either. Will be happy to have some low end torque back. I just hope it doesn't get too quiet!
 

BigSteve

Member
Another question Jbrady, had much experience with electronic Cut outs?

Only thinking of it as an option to go in my middle pipe rather than trying to make it loud by reducing mufflers, leaving the system sounding quietish and pressing a button to open up a a cutout in the middle pipe.

I have no idea how the cutout itself would affect flow while closed, or open since there will be an extra chamber to fill with exhaust gas with it closed.

But I guess if I'm trying to drive around town quietly with it closed the exhaust flow won't matter quite as much.

1uz would sound very ballsy with just 2 cats and Y-pipe
 

Bushwhacker

Member
What about this merge design ......Would it be effective on the 1UZ?
http://planetsoarer.com/pdf/xfactorcolour.pdf

Simple enough to make in a shed. :D


On my Hilux conversions, I use the stock LS400 exhaust manifolds into 2.5" down pipes (about 12" long) then the rest of the system is all 2" pipe with a 'H' pipe where the 'Y' pipe would have been on the LS400, then a Flowtech Raptor muffler on each end with polished 3" tail pipes. No Cats. Nice sound to the exhaust at idle and light throttle and an 'I take no prisoners' bellow at WOT!:D
 

spf_lexus

New Member
I've been listening to a heap of exhausts on youtube and I fear an x-pipe as well as 2 mufflers will be a little bit quieter than I'm aiming for
When I built my 2.25" dual I ran a magnaflow X pipe and magnaflow mufflers with mandrel bends and the sound was very clean and throaty up top but at idle/low rpm it was exactly the same as stock. I was not amused! I ended up ditching the magnaflows while keeping the X and ended up with two 2.25" id w/ 4" tip canisters and im in love with the note. The canisters would be obscenely loud but the X cleaned up the sound a lot. Very throaty at all speeds w/o the "big pipe raspiness/harshness".

Now for your truck application im guessing canisters are out of the question as for as asthetics :p. If I wanted to mimic the same note but for a truck app, I would go with a pair of glasspacks + the X.
 

BigSteve

Member
I don't know if that X-pipe kinda setup you linked would have any sort of decent scavenging Bushwhacker, the idea is to get each exhaust pulse from one bank to "draft" the pulse of the other bank by ramming them into a merge, that design is more just like a chamber to mix the gas from each bank to balance the noise, would be a heap of turbulence in there (My guess)

What I was hoping to do was because my merge will quieten it down a lot, is run an electronic cutout at the End of my merge just before it splits again so I can have a loud button. Just not sure the flow through these "e-cutouts" is any good. Plenty of dyno results out there saying they pick up power across the board. But I'm thinking that might be because it's reducing power while it's closed rather than gaining power while open lol.

Just been thinking about it, and I might speak to the exhaust guy Samsdad knows sometime to see if he's willing to try and make a a W-pipe I guess you could call it. A Y pipe with a middle piece that is valve, so that the flow shouldn't be interrupted much (The 2 splits coming off at a greater angle) And also when it's open MOST of the gases will blow through the middle section rather than past the cut out (Making it sound like an exhaust leak rather than cut off exhaust).

Could work well for times when you want extra loud and some extra flow, like at the track.

Something like this so to speak (Excuse the picture, Microsoft paint and bad mouse pad)


open the valve and the flow will go straight out the middle of the Y pipe (Most of it)

I guess you could even make it a bigger valve
 
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