New Y Pipes

[JBrady]

Ironically I must build a custom Y pipe for my LS400 to work with the GS400 headers I helped design. That is ok as the stock pipes leave a lot to desired. People are also constantly asking me where to find correctly design Y pipes. I am going to build a few of these in very limited quantities so if you are in need of them send me a PM.

For our applications I have designed them to maintain or enhance low and mid range power while enhancing top end. 2.25" feed pipes and 2.50" center size. Design I suggest is stock configuration using two Y pipes to enhance torque. This allows for a single 2.50" center resonator and then dual resonators and then dual mufflers for high flow and good muffling.

Unlike anything else I have seen I have modified the front Y for maximum response and torque with a velocity/one way modification to the somewhat familiar racing merge collector design. This is only for the front Y with the rear Y maintaining a standard racing merge collector design.

 

[Lextreme II]

John,

So the SS headers require modifications on the Y pipes? What about the Cats? Will they work on the SC400?

 

[JBrady]

David,

The headers are a direct fit that work with the stock parts on the GS400s and all the 430 cars that I know of.

The 1998-2000 LS400 and SC400 require a different Y pipe.

The earlier cars will require modified cats or relocated cats as the header to cat flange is different in size and moves the cats farther from the engine. Obviously a new Y pipe.

High flow exhaust is advisable on all models but not a requirement.

 

[doey]

What pipe diameters would you use on a supercharged engine?

 

[Lextreme II]

John,

So the earlier models will require cats and Y pipe modifications. Secondly what about EGR?

 

[JBrady]

John,

So the earlier models will require cats and Y pipe modifications. Secondly what about EGR?

Yes, the cat to header flange is different with the newer style having a wider spacing on the 3 bolts. The new style manifolds and therefore the headers will also place the cats lower and farther from the engine. The vvti engines do not have EGR so there is no place on the headers for this feature.

Solutions include relocating the cats to under the car or reworking the cats with new 3 bolt flanges. S&S has extra flanges available so you can build downpipes or weld to the cats. If you choose to rework the cats you must shorten their overall length. I have not tried this and do not know how big (long) the core is so this would need to be considered. If you reworked the cats you could re-use your stock Y pipe but that is a restrictive part and I suggest replacement anyway.

An EGR flange can be added to the inlet side of the cats or to the downpipe and then with proper flex pipe connected back to the stock valve on the back of the engine. Not hard to do and S&S has the EGR flange for cheap.

 

[JBrady]

What pipe diameters would you use on a supercharged engine?

What type of supercharger? Centrifugal or positive displacement? Power level? For centrifugal I would keep pipe size similar or same NA build up (small as possible to support expected power). HIGHLY recommend headers though. For positive displacement you can get away with larger diameters but honestly it depends on your goals and most critically the design of the system.

Properly designed a single 2.50 pipe will support 350hp. On the stock GS400 vvti engines the single center pipe is 2.37"/60mm and supports 300hp. On my LS400 rated 290hp the center pipe actually shrinks down to 2.2"/55mm. Exhaust sizing is ALWAYS a compromise between ideal power curve and peak power. On a street driven vehicle response and low to mid power is very important for driving enjoyment. Peak numbers are nice but not at the expense of drivability.

Dual 2.25" pipes will easily support 400hp and more. The Y pipes I have pictured above can easily be modified to either a 2.75" or 3.00" center pipe. The magic really occurs in the merge area. I also have dual 2.25" into single 3.00" available for higher powered applications.

I am also planning on building dual 2.50" into 3.00" and maybe even high velocity X pipes as well. Again, the magic is in the way the merge functions. I have modified this to increase velocity and decrease reversion over a standard racing merge. Standard racing merge collectors are light years ahead of standard swaged of production Y junctions. So these are a step up from the step up.

 

[Lextreme II]

Nice John,

Great info. Do u think its a good upgrade for the earlier models? Do u seen any problem with fitment or installation dificulties on the first gen SC and LS?

 

[Hiccup]

Unlike anything else I have seen I have modified the front Y for maximum response and torque with a velocity/one way modification to the somewhat familiar racing merge collector design. This is only for the front Y with the rear Y maintaining a standard racing merge collector design.

Interesting. How is your design different from the racing merge collector? Have you seen or tried the y-pipes from Dr. Gas? (www.drgas.com) If so, what do you find lacking? I ask because I just used one of them.

I installed the S&S Headers on my 1993 SC400 about 2 weeks ago and used 2.5" downpipes/secondaries into a 2.5" x 3" Dr. Gas y-pipe, a 3" converter, and merged it back into the STOCK Y P.O.S. at the rear. Everything from that point rearward remains stock. The sub O2's were relocated aft of the converter. The EGR pipe was cut off next to the header and blocked at the intake manifold. A 10k resistor was spliced into the harness next to the EGR gas temp sensor.

At first the CEL would not go out, but I figured that was because I did not have the sub O2 sensors hooked up yet. I was disappointed with the low end, which was MUCH WORSE than stock. I say I was disappointed, but I sorta expected it with the sotck rear Y left in. Anyway, once I hooked up the sub O2's, the CEL still wouldn't stay off. It turned out one of the main O2 sensors was hacked so I fixed that.

WOW! What a difference! While there is still a problem with the low end, it's not much worse than stock, and the rest of the RPM band is very powerful. I did not expect such an improvement from just having the O2 sensors working.

I am considering fitting another Dr. Gas for the rear Y (3" x 2")to eliminate the restriction, but I'm also considering rebulding the whole thing with 2" downpipes/secondaries and a 2.5" cat/center section.

The noise is very loud with the throttle open, very quite with it closed, and varies according to the throttle opening. Not good. This is another reason I'm considering smaller pipes. The question now is 2.25" or 2"? I don't want to have to rebuild it a third time.

Anyway, here's some pics.

 

[JBrady]

Interesting. How is your design different from the racing merge collector? Have you seen or tried the y-pipes from Dr. Gas? (www.drgas.com) If so, what do you find lacking? I ask because I just used one of them.

I installed the S&S Headers on my 1993 SC400 about 2 weeks ago and used 2.5" downpipes/secondaries into a 2.5" x 3" Dr. Gas y-pipe, a 3" converter, and merged it back into the STOCK Y P.O.S. at the rear. Everything from that point rearward remains stock. The sub O2's were relocated aft of the converter. The EGR pipe was cut off next to the header and blocked at the intake manifold. A 10k resistor was spliced into the harness next to the EGR gas temp sensor.

At first the CEL would not go out, but I figured that was because I did not have the sub O2 sensors hooked up yet. I was disappointed with the low end, which was MUCH WORSE than stock. I say I was disappointed, but I sorta expected it with the sotck rear Y left in. Anyway, once I hooked up the sub O2's, the CEL still wouldn't stay off. It turned out one of the main O2 sensors was hacked so I fixed that.

WOW! What a difference! While there is still a problem with the low end, it's not much worse than stock, and the rest of the RPM band is very powerful. I did not expect such an improvement from just having the O2 sensors working.

I am considering fitting another Dr. Gas for the rear Y (3" x 2")to eliminate the restriction, but I'm also considering rebulding the whole thing with 2" downpipes/secondaries and a 2.5" cat/center section.

The noise is very loud with the throttle open, very quite with it closed, and varies according to the throttle opening. Not good. This is another reason I'm considering smaller pipes. The question now is 2.25" or 2"? I don't want to have to rebuild it a third time.

Anyway, here's some pics.

First of all WELCOME to Lextreme.

To answer your questions... yes, I am aware of the Dr.Gas Y pipes, much better than most. Now, I have preached here and at CL that 2.5" pipes are WAY too large for the NA 1UZFE. Properly done I think 2.25" is a very good choice but I also think 2.00" is acceptable if done with mandrel bends and CAREFUL attention to detail. With crush bends I would go 2.25 for sure.

The modification I have made is internal and has several very nice impacts. First, the function of a merge collector is to reduce collector volume and use the gas velocity and energy to reduce reversion. However, you will notice that the feed pipes have greater combined volume than the receiving pipe. In your case dual 2.5s feeding a single 3.0. My example above is dual 2.25s feeding a single 2.50. Stock is dual 50mm feeding a single 60mm. So, the gases must be accelerated at the junction. In a stock merge collector this acceleration occurs as the combined gases leave the collector. This means that as the gases converge in the collector they slow and with that pressure increases. This pressure is seen by both pipes and at low speed can allow reversion or the pumping from one feed pipe to the other. As the gas leaves the collector the gas must speed up going to the smaller volume. This extra velocity is created at the expense ofl increased backpressure in the collector and therefore in each primary pipe. My modification actually places the increase in velocity in the feed pipe just prior to the collector. It also directs the flow downstream. This means that when the two gas columns merge they are already accelerated and do not revert into each other. One of the main things a merge collector is designed to do is create a scavenge effect on the adjacent pipe(s). My modification enhances this effect without compromise at these power levels. It directs the energy better and it makes reverse flow extremely unlikely (one problem with low speed power on most systems) I call it a nozzle collector.

BTW, thanks for the pictures. Other than the pipe sizing you selected a decent design. Now, I take it you deleted the stock cats in favor of the single cat, correct? Anyway, if it were my car I would go with dual 2.25 and a 2.50 center although with your cat location you do not have much center pipe.

For the record un-merged dual pipes are more prone to reversion at low to mid rpm than a proper X or Y or even H pipe. The Y and some X pipes work similar. The X pipe may also work like an H pipe. The H pipe and Y pipe do not have the same effect.

 

[Hiccup]

Thanks for the reply.

Yes, the stock cats were deleted for a giant single, and yes, it didn't leave much of a center section.

As for the pipe sizes, you're preaching to the choir! I have been following most all your post here & on CL. I don't want to make an extensive post, so let's just say I had my reasons for going with the 2.5" x 3" and I still think it MIGHT work well at the low end IF the rear y-pipe restricition is removed and the ECM given time to adjust to it. But Even if it does restore low end, it is too loud. I'm considering the 2" pipes because they will still be larger than stock, but small enough for discrete WOT. I'm wondering how much louder 2.25" pipes would be because if it's much, I'm not interested.

Anyway, I'm now more interested in your internal modifications to the y-pipe. Is it anything you would care to divulge? I might be interested in aquiring it for the next rebuild it if I knew more about it. You've described what it is supposed to do, but what is it? Also, with an open y-pipe, have your tried taping small pieces of tissue paper or the like on the open end of one of the in-pipes, and pulsing air at various velocities through the other? This may be very informative. I tried it with mine before installation and could not get visible reversion, but that may be because the large end was open. Hooked up to a cat the reversion could be significant, but again, only an experiment will tell. Had I thought more about it I would have done this as well before installation.

 

[SCV8]

Those large, 2-1/2" pipes, not to mention the added volume of the headers, are going to make your engine want a huge accelerator pump shot(initial enrichment), and you will continue to have a tough time with the stock ecu.
I would just get smaller pipes and make life easier, unless you have plans for a supercharger, fuel mods in the near future.

 

[Hiccup]

Those large, 2-1/2" pipes, not to mention the added volume of the headers, are going to make your engine want a huge accelerator pump shot(initial enrichment), and you will continue to have a tough time with the stock ecu.
I would just get smaller pipes and make life easier, unless you have plans for a supercharger, fuel mods in the near future.

I am planning on 2" pipes into a center 2.5" converter & pipe. You're right on with it wanting more fuel: it just started throwing a code 25 (too lean) yesterday.