S&S Headers on 1998-2000 LS400

[JBrady]

I recently received a PM from a new member in Panama on the S&S headers for 98-00 LS400s. I had posted my recently plans a few months back on CL and thought I had done so here as well but for some reason no. Here is the posting I did on CL followed by new member thjakits PM (reposted with his permission)


Well gang, believe it or not I do NOT have the S&S headers.

The 98-00 LS400 manifolds are longer and the cat flanges are rotated relative to the GS400 manifolds that the S&S headers were designed to directly replace.

My set of headers is currently at Jet Hot and should be in my hands in about 2 weeks. I have decided to modify the headers rather than the Y pipe. This keeps the car serviceable with factory parts at any time. I will also be creating a new Y pipe but it will be a direct bolt in fit to the factory.

Modifying the headers requires that I jig the stock manifolds, cut the cat flange off the S&S headers, extend and re-weld the then extended flange in the correct position for the factory installation.

By doing this I will have the ability to modify headers (by request and arrangement) for any one else that is interested in this same approach.

I will also post pictures and progress as I move through this project.

The headers should generate the same HP and TQ increases that the GS400s see roughly 15-20 RWHP and RWTQ and improving engine response, power under the curve, feel and the fun factor.

For a Y pipe upgrade I plan on building a direct bolt in replacement that will replace the stocker which unlike the GS has a bottleneck resonator and ugly cut and slash sections at the cat outlets. The plan is a part that will be a direct replacement. I also plan on a second Y pipe that will replace the center muffler section and bolt in and use the stock rear mufflers. These parts will give a number of options for power and noise levels. I will build them to suit my taste for relatively quiet operation, preserving low end power/torque and allowing peak possible power/torque.

Depending on how hard this project turns out to be I may consider making other copies.

Stay tuned.

 

[JBrady]

Here is thjakits PM. It is a GREAT example of someone doing the personal work required for a well planned project AND in asking good and pertinent questions:

JB-SS headers and then some .....

--------------------------------------------------------------------------------

Hi John,

how are you?

For starters: Don't have any L yet, but if everything checks out, I will be the owner of a '98 LS400 within 2 weeks - or some '01 to '03 LS .....
(most likely the 98)

Took your suggestion/advise and read through EVERY jbrady-started thread on ClubLexus, with special attention to AirIntake mod, JBSS headers + other exhaust mods.

BOY, does that get confusing with all the different car-models!!

"Well gang, believe it or not I do NOT have the S&S headers!" - What tha .....??!

Can't believe what you went through for the community and then the things don't fit on your own car!

Now from all the posts I understand the following (please correct me if I am wrong!):

The JBSS headers are shorter than the original 98-02LS headers and the cat flanges are 180° rotated??

I also gather that you will cut, rotate and extend your set of headers.

Questions:

a) Will you be offering that service?
a1) I assume you would get non-coated headers and send off for coating after your mod?

b) How much is the difference in length EXACTLY?
b1) Reason for this question: Would it be possible to weld up a connector to bolt between the headers and stock cats?
Looking at the JBSS flanges and the cats it seems it will not be a problem to fit bolts 'n nuts as the triangular flanges would be "out of each others way".
If the difference in length is only 1/4" a 6-hole adapter plate might do the trick.
1/2" and up, welding 2 flanges 180° rotated - same idea.
At this time just wild guessing - you are the man with the insight - literally!!
b2) Can you confirm the "180°" rotation for the LS?
b3) Is the angle of the JBSS-flange to the LS cat flange okay or is this off too? (Except for the 180° rotation and distance, are they parallel?)

c)Did you talk to Loren Barnes about the possibilty of making LS-"perfect fit" headers?
It seems if he works off a jig the setup change should be minimal and to order production not any more expensive than the present series - should (I have no idea! I may be way off here...)

d) My main concern here is, that I live in Panama, no NOT FL, but literally a stones throw besides the Canal (Panama Canal). So ordering a non coated set, modifying it locally and send it back for coating is wishful thinking at best! (No jet-hot or even regular powder-coating in Panama!)
If I want to use the existing JB SS headers and the original y-pipe (until you have your super pipe ready ....) it will only work if I can adapt the headers without cutting them.
I would not mind to notch the header and cat flanges if the adapterplate idea works .....

e) I need your help on this!! Actually seeing the original headers is a frustrating, sad experience - if you actually have an idea about exhaust flow!!

f) some of my other interests are experimental/homebuilt aviation and alternative engines (aviation again - basically car engines modified for aviation use, especially mazda rotaries!!)
f1) I did not build anything yet, but read up and study everything I come across. Especially when it comes to aerodynamics - aircraft dynamics, cooling dynamics, intake/exhaust, etc.
f2) Based on the above I have some questions/suggestion (again - pure theory at this point) to muffler, y/x pipe, venturi, venturi pump, etc. - design.
However I don't want to bother you with this if you are too busy at this time.... - the details I asked you about the JBSS and cats will do for now!

Thanks for your time!

Best Regards,

Thomas Jakits,

PS: Please feel free to post/edit this PM any way you want - if you feel this would be interesting for others!

 

[JBrady]

Hi John,

how are you?

For starters: Don't have any L yet, but if everything checks out, I will be the owner of a '98 LS400 within 2 weeks - or some '01 to '03 LS .....
(most likely the 98)

Took your suggestion/advise and read through EVERY jbrady-started thread on ClubLexus, with special attention to AirIntake mod, JBSS headers + other exhaust mods.

BOY, does that get confusing with all the different car-models!!

"Well gang, believe it or not I do NOT have the S&S headers!" - What tha .....??!

Can't believe what you went through for the community and then the things don't fit on your own car!

Now from all the posts I understand the following (please correct me if I am wrong!):

The JBSS headers are shorter than the original 98-02LS headers and the cat flanges are 180° rotated?? I also gather that you will cut, rotate and extend your set of headers.

Yes, est 1-2 inches shorter and rotated roughly 180`
My plan is as you predict, cut, rotate, extend and reweld.

Questions:

a) Will you be offering that service?
a1) I assume you would get non-coated headers and send off for coating after your mod?

Actually, welding coated headers is not a problem. I ordered my set coated with the cat flanges only tack welded in place. I will weld them to the correct dimension to fit the stock Y pipe.

b) How much is the difference in length EXACTLY?
b1) Reason for this question: Would it be possible to weld up a connector to bolt between the headers and stock cats?
Looking at the JBSS flanges and the cats it seems it will not be a problem to fit bolts 'n nuts as the triangular flanges would be "out of each others way".
If the difference in length is only 1/4" a 6-hole adapter plate might do the trick.
1/2" and up, welding 2 flanges 180° rotated - same idea.
At this time just wild guessing - you are the man with the insight - literally!!
b2) Can you confirm the "180°" rotation for the LS?
b3) Is the angle of the JBSS-flange to the LS cat flange okay or is this off too? (Except for the 180° rotation and distance, are they parallel?)

b) I do not have a measurement yet.

b1) possible but bulky and there are clearance concerns.

B2) roughly 180` as I have not made specific measurements.

B3) no data yet

c)Did you talk to Loren Barnes about the possibilty of making LS-"perfect fit" headers?
It seems if he works off a jig the setup change should be minimal and to order production not any more expensive than the present series - should (I have no idea! I may be way off here...)

Loren will require a stock set of LS manifolds in order to jig. I may send him mine once I have done the swap and see about this option. It will cost more and he may require an order of 20 sets to build an new part. Hard to say for certain without confirming with Loren. It will be on my list but no promises of timeline.

d) My main concern here is, that I live in Panama, no NOT FL, but literally a stones throw besides the Canal (Panama Canal). So ordering a non coated set, modifying it locally and send it back for coating is wishful thinking at best! (No jet-hot or even regular powder-coating in Panama!)
If I want to use the existing JB SS headers and the original y-pipe (until you have your super pipe ready ....) it will only work if I can adapt the headers without cutting them.
I would not mind to notch the header and cat flanges if the adapterplate idea works .....

I understand your concerns. As I stated above welding coated headers is not a problem. I am actually leaning towards using 2.25” to extend the collector on my headers. This will require expanding it again to 2.5” for the collector flange to catalyst connection but will give a higher velocity collector and the 2.25 will fit inside the stock 2.5 collector. This will require careful attention on my part to smooth the inside flow at this junction by beveling and expanding if necessary the 2.25 for a snug internal fit.

e) I need your help on this!! Actually seeing the original headers is a frustrating, sad experience - if you actually have an idea about exhaust flow!!

f) some of my other interests are experimental/homebuilt aviation and alternative engines (aviation again - basically car engines modified for aviation use, especially mazda rotaries!!)
f1) I did not build anything yet, but read up and study everything I come across. Especially when it comes to aerodynamics - aircraft dynamics, cooling dynamics, intake/exhaust, etc.
f2) Based on the above I have some questions/suggestion (again - pure theory at this point) to muffler, y/x pipe, venturi, venturi pump, etc. - design.
However I don't want to bother you with this if you are too busy at this time.... - the details I asked you about the JBSS and cats will do for now!

Thanks for your time!

Best Regards,

Thomas Jakits,

PS: Please feel free to post/edit this PM any way you want - if you feel this would be interesting for others!

Please feel free to add your theories, insights and experiences…

 

[JBrady]

Here are the only pictures I have of S&S headers on a 98-00 LS.

These are courtesy of a less than happy Howard Katz who using my at the time (2006) misinformed assumption of direct fitment had them installed. The installed did a decent job of custom fabricating the Y pipe section to work.

Howard was upset at the additional cost. He also did the cold air mod I posted and complained that the car bogged. He went back to stock on the intake and was VERY happy with the headers and even reported beating a G35 coupe to 60mph.

While I cannot understand how or why his intake mod would have a negative effect (I have ran it for 6 years now with great results) the headers do seem to work well even with tight clearances. Now there is a member from Puerto
Rico that did the headers and claims poor performance. What exactly is going on with his situation is unclear. With AFAIK 100% positive performance results on GS400s, GS430s, SC430s, LS430s and even at least on 1995 LS400 and knowing the stock manifold design... I can't theorize on how the S&S would loose power PERIOD.

Anyway, here are the pictures:

Driver side SS compared to passenger LS showing flange rotation. Notice on the SS the single bolt is in the "UP" position and on the LS in the "DOWN" position.


Here is the SS mounted with cat showing the mismatch vs. the Y pipe.


Here is the very tight fit around the steering requiring heat wrap around the steering to protect it.

 

[thjakits]

Hi all!

JBrady:

a) 98-00 LS400:
The header seems AWFULLY close to the steering components!
Keeping the cat in this position doesn't look right at all - see the PS-lines?
(I thought about the same - bolt the cat to the header as is and fix the fit with the y-pipe. .....change of plans!)

b) Please read the following with the understanding, that I have NEVER built any exhaust system, ...yet - theory learned from reading only and transfered from other disciplines of aero dynamics!
quote jbrady "I am actually leaning towards using 2.25” to extend the collector on my headers. This will require expanding it again to 2.5” for the collector flange to catalyst connection but will give a higher velocity collector and the 2.25 will fit inside the stock 2.5 collector. This will require careful attention on my part to smooth the inside flow at this junction by beveling and expanding if necessary the 2.25 for a snug internal fit."

I am sure it was posted somewhere - it just doesn't want to be found by me - it seems:

What is the inside diameter of the SS-header collector?

If you want to do exactly what you recommended not to do - wrong direction for slip/socket fit - you probably need a rather meaty piece of tubing, so that the intake part can be properly beveled - I am not sure (need to search for the paper on this...) but IIRC the bevel starts at about 30° to the centerline and (optimally - ...but at this small size just wishful thinking) then follows a parabolic curve to parallel the centerline of the tube.

Depending on the actual inside diameter of the collector tube you might even be able to have this piece turned on a lathe ......
Turning a definite outside edge on both ends to seat the plug into the collector and a piece of mandrel tubing on the other to meet the cat (on the y-pipe), you could even make the inside smaller - if you care to try a propper venturi.
From the looks of the pic in your previous post you should be able to insert this plug 1.0" - 1.5 " into the collector and therby reduce the collector volume some.... (as you elaborated in another thread - nozzle collector?)

The important item here is to avoid turbulence at all cost. The smallest protrusion causes a vortex that effectively reduces cross section area.
That's why I thought about a lathe turned plug....

At this part of the exhaust, flow speeds are still extremly high and a disturbance will cause major drag. You even want to reduce the cross section on purpose which should increase speed even more....

However, considering that inertia increases exponetially with speed - if this venturi is porperly made the gains could be incredible!
(inertia goes up 4 times when you double the speed ......)
That inertia will want to keep the exhaust going and then pull more out of the venturi.....

quote: "This will require expanding it again to 2.5” for the collector flange to catalyst connection but will give a higher velocity collector..."
Not - the way I understand the venturi principal:

If you expand again to the initial diameter you will also slow down the flow.
Furthermore it will be even slower than before as it cooled off during the passage of the venturi - energy that went partially into the venturi and leaves the system via the exhaust tubing - radiating into the surroundings.
Coming back up to the same diameter the gas will want to return to the same state as before the venturi. As there is some friction loss and now less heat energy available it will get the needed energy out of its inertia - resulting in a lower speed than before the venturi.
Instead keep the reduced diameter and "jet-nozzle" it into the cat!
see below.... (and the article mentioned below somewhere)


(Check google/wikipedia for more on venturi. There is also a great Venturi Tube calculator here: http://www.pipeflowcalculations.com/venturi/index.htm
or here: http://www.efunda.com/formulae/fluids/venturi_flowmeter.cfm )

If you choose to turn a plug you also can really sharply cut - even back cut, the exit from the venturi tube - into pipe/tube to the cat. That should ensure a clean separation without turbulence produced by exhaust gas back flowing around the exit from the "nozzle" ....


c) Here is a great article on proper exhaust design, repeats a lot of what jbrady preaches: http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/index.html

Messages from this article:
- "Bigger is better" - NOT!
- "A properly designed exhaust system does not loose power!"
- "A properly selected muffler has no more restriction than a pipe of the same length!"
- "Do your homework and select mufflers just big enough for your engine and get good noise reduction!"






'nough said - of the box.



Cheers,

thjakits

 

[spdrcr771]

So john if my thinking is correct,in reading this thread, then the LS seems to have alittle bit more fitment issues than the pics you posted on CL "no more s&s headers" ex: steering rack, short on length, header flange rotated in wrong position. VS the SC, where as the sc's are alittle longer than need be. the pics look like if you cut the cat flange off & rotate the cat to correct position & maybe shorten up alittle it would work just fine, thats where im @ on my plans. Im getting them tomorrow. thanks again for your help.