Dual mandrel "X" OR single "Y" Better?

[spf_lexus]

I have been trying to knock off as much weight as feasibly possible while maximizing power. So far my sc400 is down to 3100lb with a couple gallons of gas. I realized my exhaust layout was not optimized for my goals. I have 2.5" rush extractors feeding dual 2.25" mandrel pipes and a magnaflow x pipe and dual magnaflow mufflers.


I figure by running a "single" exhaust thats fed by a well engineered merge collector "Y" pipe, I can elimninate 1 muffler and 6 feet of exhaust piping. This would mean another 15lb of weight savings.

Is it possible to exploit some extra HP by running this setup?:

-Rush 2.5" header collectors feeding...
-2.5" Burns stainless "Y" into a 3" main pipe. (3" too small/big?)
-Mandrel pipe (straight as possible) to a single 3" ID Canister with 4" out?



Right now the system is very mellow, and downright silent at idle and low rpm. I dont mind it getting a bit louder but I want absolute uninterrupted flow and maximum hp. I plan to tune this motor N/A with adaptronic once I get a loom from Neil. Here are a few pics of the current setup (phone pics, sorry):

 

[spf_lexus]

Just thinking out loud but I know magnaflow mufflers wont flow as much as a straight through chambered design. What about swapping mufflers for straight through Blitz canisters -OR- replace my maganflows with flowmaster chambered mufflers?

 

[cribbj]

OT, but in looking at the pic of your gas tank, and knowing that the SC and Supra share a common platform, I'm now wondering if a SC tank would fit a Supra or vice versa.

Supra's are normally single exhaust, exiting on the left, but I've been thinking it would be kinda cool to have a dual exhaust on it as & when the 1UZ goes in. Problem is the gas tank effectively blocks the whole right side.

What's the capacity of your gas tank Sean? The Supra is about 16.5 gals IIRC, and the fill door is on the right rear fender. Where's yours?

So maybe a Supra gas tank would fit your single exhaust goals better, and perhaps an SC would fit mine

 

[JBrady]

Just thinking out loud but I know magnaflow mufflers wont flow as much as a straight through chambered design. What about swapping mufflers for straight through Blitz canisters -OR- replace my maganflows with flowmaster chambered mufflers?

Actually the magnaflows are straight through and out flow chambered mufflers.

A single system will save weight and will support the power if sized correctly.

What is the power goal here?

BTW how much do your speedy 19" wheels weigh?

 

[spf_lexus]

OT, but in looking at the pic of your gas tank, and knowing that the SC and Supra share a common platform, I'm now wondering if a SC tank would fit a Supra or vice versa.

You can see the tank? I cant see it . On the SC, its inside the trunk, directly above the rear sub frame. Identical to the early LS400 tank. And my filler cap is on the right rear fender. As far as capacity, I want to say its 18 gallons? I always run just a couple gallons but i'll try and remember next time I fill it for a long trip.

[QUOTEWhat is the power goal here?

BTW how much do your speedy 19" wheels weigh? ][/QUOTE]

As far as hp goes, I decided to stay strictly N/A. Down the road I want to try 11:1 maybe 12:1 ross pistons, Lex's stage II cams, large valve upgrade and mild-medium head port and a straight runner manifold. Once I get the adaptronic tuned I should expect 330BHP or so. I guess my final goal is 400BHP w/ 6-speed swap.

29lb w/o tire. I know I can save some weight here but I couldn't afford gram lights or volks so i swapped these off project LS470. A bonus is that the low profile tires will add a little stiffness overall and thats what im shooting for.

 

[spf_lexus]

Im just curious if a single canister style exhaust off a Burns stainless Y pipe can net me any more hp. Im thinking 2.5" merging into a single 3" all the way down? Would this be too big or small? I have a high stall TC already and my low end is decent.

 

[JBrady]

Im just curious if a single canister style exhaust off a Burns stainless Y pipe can net me any more hp. Im thinking 2.5" merging into a single 3" all the way down? Would this be too big or small? I have a high stall TC already and my low end is decent.

Peak power? Power under the curve?

While both the S&S and the Rush/Tex headers have 2.5" collectors I do not believe that 2.5" is a good size for half this 4 liter. The stock 300hp GS400/430 uses the same 1.97" pipe as the early much lower HP 1uz engines. Many have built 2.25" system but I would suggest 2" or 2.125" as a better size for up to 175hp or so (per side) for making power under the curve. Your torque converter certainly helps but why use heavier pipe with less ground clearance than you need?

The stock ratio on the Y pipe is twin 50mm into a single 60mm. This gives an "acceleration ratio" (area of feed pipes minus the area of the receiving pipe divided by the feed pipe)((FP-RP)/FP ) area of 26%. This is a good target. By accelerating the gas a one way merge is encouraged. This helps keep the flow away from the engine. Dual 2.25s feeding a single 2.5" is a ratio of over 37% and this is faster which requires more backpressure. The opposite looses acceleration so dual 2.25s feeding a single 3" pipe only has an excelleration of 8%. I suggest the factory is a good target. So dual 2.25s would need a single 2.75" to get a rate of 24%.

The internal shape of the Y is important. This and the above and more are why I continue to recommend the stock Y pipe up to 300hp and even more. A better pipe is possible and I intend to do more testing with 2.125", 2.25" and 2.5" pipe along with testing but for now anything built is more or less an attempt to better the stock pipe... and I have yet to see convincing evidence of anyone doing that for most street engines.

 

[spf_lexus]

Thanks Jbrady. So it looks like I can keep my 2.25" pipes and somewhere fit a burns stainless. I plan to add cams + larger valves so 2.25" into 2.75"? Would a 2.5" better fit my current setup over the future modded version?

 

[JBrady]

Thanks Jbrady. So it looks like I can keep my 2.25" pipes and somewhere fit a burns stainless. I plan to add cams + larger valves so 2.25" into 2.75"? Would a 2.5" better fit my current setup over the future modded version?

I am unsure how the Rush headers will react without catalysts and with smaller than collector size (2.5"?) tube. On stock manifolds or shorty headers the catalysts work somewhat like one way valves where the high pressure blowdown passes downstream but the lower pressure reversion pulse is buffered. Without cats the buffering is lost. With the longer tube Rush headers going down in size after the collectors it is hard to predict the dynamic. You are down to 2.25" already. 2.125" is probably a better size but not necessarily with the Rush pipes.

So, I would stay with my suggestion of 2.25" into 2.75" (75mm) single although that size is not the easiest to find both in tube or in mufflers.

 

[spf_lexus]

Thanks for the ID reccomendations. Once I get the burns Y pipe I will start this project. I have heard burns products are unparalleled so im staying strict to this part of the system. As for the odd pipe sizes, I have a friend that can enlarge pipes with his hydraulic mandrel bender. I'll ask him if I he can make "in between" sizes. I figure if I run a smaller ID like 2.5" for the straight shot, replacing it with larger ID down the road will be much easier/cheaper than upgrading a dual system.

 

[spf_lexus]

Hey Jbrady,

Just curious but what are your feelings on the Magnaflow hydroformed X pipe versus the bruns stainless X pipe? I paid just under $80 for the magnaflow so im sure the burns is 2x that.

 

[JBrady]

Hey Jbrady,

Just curious but what are your feelings on the Magnaflow hydroformed X pipe versus the bruns stainless X pipe? I paid just under $80 for the magnaflow so im sure the burns is 2x that.

There are multiple designs called "X" pipes. Burns builds theirs as twin Y pipes to create an X. This accelerates the gases and then cleanly divides them to have dual paths. Otherwise the first Y into a correctly sized single works nearly identically.

Magnaflow makes two styles: the older style that you have and a newer style similar to a Dr.Gas which is two mandrel bends touching with a "window". This works more like an H pipe. An H pipe has very little cross flow but creates a plenum at the point of the crossover. This also happens with a Dr.Gas but with maybe a bit more cross flow.

The Burns style merges all the gases as does your Magnaflow but your part does not control the gases in the same manner and is less efficient.

The factory Y pipe is similar to a Burns but changes the point acceleration. I have studied and really like the way the stock Y works for optimizing low and mid range response with exhaust velocity. I call it a nozzle collector. Most would think it is restrictive but other than size it works very well. Heck some supercharged Lexus V8s have the stock Y and make nearly 400rwhp. I am not suggesting doing THAT but using it as an example that it is not completely choking flow even at those levels.

I have built a few prototypes using the nozzle principles. Yet to install on my engine but one who did was pleased with the responsivenss. IMO the nozzle style is superior even over a burns for full range responsiveness needed on a street engine.

 

[spf_lexus]

Its really decieving when you see those 1.9" pipes pinched together. After looking at a lot of high end y pipes and their use of the "d" seperators, I really understand why the stock one is so efficient. Im going to go with the 2.25" merging into 2.75" just so I have some building room in the future. N/A gains take a lot more work/cash to get so i cant forsee 2x hp levels and time soon. What about 2 burns merge collectors with a home made d shaped seperator? I have access to a full machine shop at school.. if you can send me couple pictures of how it SHOULD be designed, i'd like to follow it.

 

[spf_lexus]

edit:

forgot burns sells pre-made y's hah. If you can give exact dimensions i'll try and cut it out and weld it up with the help of my shop manager.

 

[JBrady]

Its really decieving when you see those 1.9" pipes pinched together. After looking at a lot of high end y pipes and their use of the "d" seperators, I really understand why the stock one is so efficient. Im going to go with the 2.25" merging into 2.75" just so I have some building room in the future. N/A gains take a lot more work/cash to get so i cant forsee 2x hp levels and time soon. What about 2 burns merge collectors with a home made d shaped seperator? I have access to a full machine shop at school.. if you can send me couple pictures of how it SHOULD be designed, i'd like to follow it.

Where have you seen other D shaped collectors. I would like to check out that work.

Not sure on how to properly describe the "dimensions". Might be easier to build you a couple pipes and send them unwelded. Maybe I can get around to that.

What size are your current Magnaflow mufflers: 2.25? 2.50? Since the exhaust cools you may be able to effectively use a single 2.5" muffler at the bumper.

 

[spf_lexus]

Im at school right now but tonight i'll try and post some examples.

What size are your current Magnaflow mufflers: 2.25? 2.50?

Its 2.25" in/out.

Since the exhaust cools you may be able to effectively use a single 2.5" muffler at the bumper.

Can you elaborate on this? Is 2.7" piping too large? It seems like 2.5 is the perfect size for what i'm running right now but with my adaptronic and any future head work I will be undersized at that point.

 

[JBrady]

Can you elaborate on this? Is 2.7" piping too large? It seems like 2.5 is the perfect size for what i'm running right now but with my adaptronic and any future head work I will be undersized at that point.

I haven't had the chance to test a 2.25" into 2.5" nozzle Y pipe. I did test a 2.25" into 2.5" merge Y pipe. Now, there are MANY variables but on a GS400 it gained 1hp peak on the dyno (statistically unchanged) but the driving "feel" degraded and no longer felt crisp. The owner reported if felt mushy. The "crisp" response is a BIG part of the joy of throttling an engine so why trade that for no gain?

Since a GS430 with 300hp and 4.3 liters comes with the same 1.97" duals into 2.36" OD center pipe I would think a single 2.5" center will give crisper feel than a larger pipe while still supporting at least 300hp (your stock engine is IMO 235hp) leaving 65hp upside at LEAST.

BUT... you have long tube Rush headers with 2.5" collectors that you have connected to 2.25" duals. So... what happens when you accelerate the flow with a 2.5" single? My test above would suggest twin 2.25" feeding a single 2.5" may be too much and hurt throttle response and low end power.

BUT... with a nozzle collector it may get BETTER!!! Hard to say without testing and WHY I no longer make simple pipe diameter suggestions and WHY I also suggested a 2.75" single to go with your dual 2.25" pipes. I suggested that with this 2.75" single that you could probably run a single 2.5" Magnaflow with very little loss due to exhaust cooling and placing the muffler at the end of this system. I would not think a single 2.25" would be the best choice. I was trying to get you most of the way at the lowest cost since you already have mufflers.

Now I had one person install S&S headers on his SC400 with dual 2.5" into a single 3" using a very good merge Y pipe. He was very dissapointed. I suggested dropping to dual 2.25" and he decided to drop to dual 2.00" into a single 2.5" using a muffler shop created Y pipe (less than great design) and he LOVED how it responded with great throttle and MORE power! This is one of the many reasons for my support for the STOCK Y pipe for MOST applications. If you still have yours I would cut it to fit your system and change the center resonator out for a piece of 2.5" pipe.

Understand that dual 2" into a single 2.5" creates less Y pipe acceleration than dual 2.25" into a single 2.5". The flow is slower in the dual 2.25" verses the dual 2" pipes at any given power.

I guess if it were my project I would START with dual 2" mandrel into a single 2.5" nozzle Y which is slightly larger than the stock 300hp Y pipe. Since you already have dual 2.25" you can easily go back to that system at ANY point.

If you REALLY are worried about weight... change the tires and wheels

 

[spf_lexus]

I must have read your last post 5 times over the last 2 days. I plan to just unbolt the whole system at the header collectors and go from there. Do you think if I run the 2.25" into a single 2.5" instead of your recomendations of 2.0" merging into 2.5", am I really going to notice the slight dip in low end tq, even with my high stall TC? On paper I am looking at a 50BHP deficit over the gs400/98' ls400 per say, but once im tuned, I can gain 12% WHP, which will turn into about 35BHP and with this in mind the hp difference will much smaller between the 2 systems. i would rather deal with a little low end loss temporarily, and then have it tuned to fit the exhaust size for a more complete match. This way I dont have to change the system again for a 3rtd time hehehe. thanks for your help John, much appreciated.

 

[JBrady]

Sean, do you have a stock Y pipe around? That would be the easiest way to test. You could cut and install the stock Y to the header outlets and build a 2.5" from there. The area to pay attention to would be the transition from the 2.5" collectors to the 1.97" stock pipe diameter. I would try to stretch a 4" section of 2" pipe to 2.5" (called swaging) and mate the remaining 2" section to the stock pipe paying attention to having no sharp edges hanging into the direction of flow. For the Y pipe outlet you can cut the center pipe leaving 3" or so of it still on the Y and slide the new 2.5" over that section and weld. If in the future you want to try a larger diameter Y pipe you can easily remove the stocker and replace it. You can even to easy back to back testing with your current 2.25" X system to this stocy Y based 2.5" single system.

The total length from the header outlets to the Y section should probably be 2 feet but you may not have room to place it that far back. If you can place it in the stock location and still have 2 feet (or more) of the 1.97" pipe that is where I would put it.

The ONLY concerns I have are how the headers will react with this pipe size NOT how the flow capacity. Consider my above example with a GS400 making IMO 65hp more than your stock engine did and running the same 1.97" to 2.36" Y pipe. If the extra 65hp over your stocker was creating a big restriction increasing the pipe size on the GS400 should have made more power but it did not and it in fact lost a bunch of power under the curve making response sluggish. Even trying a GS430 Y pipe with the same pipe size but WITH a center catalyst did not lower power.

 

[JBrady]

BTW, each 50mm tube (1.97" OD) has 2.65 sq/in of ID area using .065" wall thickness exhaust tube (16 gauge). So, two of these pipes have a total of 5.3 sq/in of area. The stock 60mm tube has 3.91 sq/in inside area. My suggestion above steps that up to a 2.5" with 4.41 sq/in of inside area. This gives an increase of 13% flow area over the stock system known already to support 300hp.

One further note, I pulled off all the exhaust on my LS400 after the center 60mm pipe. I was VERY loud. I did NOT notice any power increase and if anything felt a loss of low end response. I did not dyno it but feel that the mass flow through the rest of the pipe was responsible for preventing some reversion. Build the above system with 2.5" all the way to the rear muffler. You can then try it with no muffler and you can try it with one of your 2.25" Magnaflows (which flow very well). This slightly smaller size will reduce noise and may or may not change the power. Most mufflers slip OVER the pipe feeding them. Check the internal diameter (ID) of one of your Magnaflows. It may be 2.25" ID which is the same as a 2.38" ID tube... same as the stock 60mm pipe... supports 300hp. Just make a smooth transition from the 2.5" pipe which should be easy.