Standard size or 2 1/4

[White ls400]

At the moment i just have the 2 rear mufflers swapped for hot dogs, but i am planning on upgrading further. What i was thinking was swapping the y pipe and single muffler for a x pipe that runs straight to the centre resonators but replacing these with higher flowing items...
Then i sort of had a change of heart thinking of just going 2 1/4 back with x pipe two high flow resonators and two high flow mufflers... Which would sound better in your opinions and is going 2 1/4 going to make that much more power to justify the price of redoing the whole lot again..
Also im still yet to inspect my cats but i am guessing they are stuffed after early issues i had with the car is it worth getting high flow cats or just grabbing ones similar too whats there now. Any suggestions on brands that are available to australia would also be greatly appreciated
Thanx for your time...

 

[JBrady]

At the moment i just have the 2 rear mufflers swapped for hot dogs, but i am planning on upgrading further. What i was thinking was swapping the y pipe and single muffler for a x pipe that runs straight to the centre resonators but replacing these with higher flowing items...
Then i sort of had a change of heart thinking of just going 2 1/4 back with x pipe two high flow resonators and two high flow mufflers... Which would sound better in your opinions and is going 2 1/4 going to make that much more power to justify the price of redoing the whole lot again..
Also im still yet to inspect my cats but i am guessing they are stuffed after early issues i had with the car is it worth getting high flow cats or just grabbing ones similar too whats there now. Any suggestions on brands that are available to australia would also be greatly appreciated
Thanx for your time...

Australian imports often have aftermarket cats installed as part of the certification process. Find out what you have. Why do you think they are stuffed? Stock cats are not bad flow wise, at least the 2 at the manifolds. The center cat or resonator is another concern. Again, determine what you have.

Otherwise on a stock car the stock 50mm (1.97") pipe is fine. Keep the front Y section and replace the center with a single 2.5". Buy or have a good merge Y pipe made to split it back into 2" pipes. I would NOT use the Magnaflow X pipe as it is too large internally. If you need new cats I would use the metal substrate cats available as they flow very well.

Here is an example I have never bought from this company so this is NOT and endorsement but rather an example

http://www.performance-curve.com/index.asp?PageAction=VIEWPROD&ProdID=1180

The metal substrate cats are have very thin almost a foil that is spiral wound creating the holes for flow. This is opposed to ceramic cores that are have rows in a line cast into the ceramic "brick" that is a rectangle shape rather than a true round shape with a metal core cat.

Here is a stock 1999 Lexus metal substrate cat internal picture (retail $1000+)

 

[razzer]

As far as i knew the front y pipe was the biggest restriction escpecially on 1st gens. So if you were going to change all this plus the 3 middle resonators it may as well be worth going 2.25 in for the extra power. Also from the sounds of the other post of yours you have torched your cats and changin them over will probally net you a massive gain, Just have a grinder ready when you inspect the cats mine didnt come off with out a fight

 

[White ls400]

Its an Australian delivered 1990 Ls400 so it doesn't have a compliance cat. The day i bought my car the previous owners pressure washed the engine bay and during the 2 hour drive home the leads shorted out dropping the car too 3 or 4 cylinders cant remember exactly, anyway the cats got hot enough too melt the tar below the car so i'm guessing there screwed. I also heard that the y pipe was the biggest restriction in the ucf10's?... Plus i just noticed the two hotdogs iv already got just manage too be glass packs so i guess ill piss them off anyways, So now i guess the question is 2" or 2 1/4" pipe for best performance and exhaust note and 2" cats or 2, 2 1/4 or 2 1/2" cats

 

[JBrady]

As far as i knew the front y pipe was the biggest restriction escpecially on 1st gens. So if you were going to change all this plus the 3 middle resonators it may as well be worth going 2.25 in for the extra power. Also from the sounds of the other post of yours you have torched your cats and changin them over will probally net you a massive gain, Just have a grinder ready when you inspect the cats mine didnt come off with out a fight

Who says the front Y is a big restriction. Peter Scott of Planet Soared did some makeshift flow testing on his Soarer (SC400) exhaust and the front section was the LEAST restrictive of the 4 sections. The back mufflers were the worst, the center mufflers next, the cats next and the least was the front Y section.

See his tests and notes here: http://planetsoarer.com/V8exhaustmeasurements/Soarer_v8_exhaust_measurements.htm

When the first set of S&S headers were installed on a more powerful GS400 we tried a VERY good 2.25" into 2.5" merge Y that I donated and found NO power. Both his stock Y with a resonator and a GS430 with a catalyst were just as good peak power but had much better response.

Also worth noting his 10 year old cats outflowed a new cat and were only slightly worse than a high flow cat.

So, as I recommended, keep the front Y section. I would cut it right after the 2 pipes are welded together and replace the rest with 2.5". The stock center is 2.36" (60mm) and has an internally necked down center resonator or on some models a catalyst.

Here is that actual Y pipe I donated for the S&S header test: (on the right, the other is a 2.25-3.00")

 

[JBrady]

Its an Australian delivered 1990 Ls400 so it doesn't have a compliance cat. The day i bought my car the previous owners pressure washed the engine bay and during the 2 hour drive home the leads shorted out dropping the car too 3 or 4 cylinders cant remember exactly, anyway the cats got hot enough too melt the tar below the car so i'm guessing there screwed. I also heard that the y pipe was the biggest restriction in the ucf10's?... Plus i just noticed the two hotdogs iv already got just manage too be glass packs so i guess ill piss them off anyways, So now i guess the question is 2" or 2 1/4" pipe for best performance and exhaust note and 2" cats or 2, 2 1/4 or 2 1/2" cats

Well, if the cats did overheat and break down then yes you will want to replace them. Stock or the ones I showed would be my choices. Size on cats is only pipe inlet/outlet size as the core size which determines peak flow are usually the same regardless of in/out pipe size. On an otherwise stock engine go with 2" mandrel or if not available or good workmanship go with 2.25 crush bent.

 

[White ls400]

Ok heres were my minds at now correct me if im wrong (highly likely). New cats only if old ones are stuffed, Keep the y pipe the into a 2.5" pipe then branch out into a new y pipe (standard 1 useless due to pipe angle i guess), after the new y pipe two new high flow resonators (perforated steel the best i gather?) then into 2 high flow mufflers similar to that guys soarer? Glasspack mufflers are useless from what i know?

Jbrady do you happen to be a exhaust specialist or you just know your S@#t real well

 

[JBrady]

Ok heres were my minds at now correct me if im wrong (highly likely). New cats only if old ones are stuffed, Keep the y pipe the into a 2.5" pipe then branch out into a new y pipe (standard 1 useless due to pipe angle i guess), after the new y pipe two new high flow resonators (perforated steel the best i gather?) then into 2 high flow mufflers similar to that guys soarer? Glasspack mufflers are useless from what i know?

You got it correct.

I would cut the front Y pipe just after the 2 pipes join. You will end up with a small ring left over from the stock 60mm (2.36") center pipe. Inside this ring each of the two 50mm (1.97") pipes are stretched and formed into a "D" shape each making up 1/2 of the inside of the 60mm pipe. This creates a low restriction nozzle for each pipe. This nozzle works like the narrow section of a merge collector and accelerates the exhaust gas flow and therefore minimizes any reversion. I have not had a chance to test the stock pipes to maximum flow but at over 300hp they were not a restriction vs. the above Y pipe I have pictured.

Here is the way the stock pipe with the back-to-back "D" looks inside. Remember each feed is 50mm so they have to be stretched WIDER to fill the inside of the 60mm pipe. Total area of the "D" is slightly less than the cross section of a single 50mm but the shape is aerodynamically good and is a very good one way flow transition that creates minimal backpressure.

 

[JBrady]

Here is what the stock Y merge looks like on the outside. Look carefully and notice the the single 60mm is actually streched (swaged) to fit over the 2 "D" shapes formed by each 50mm pipe.

 

[JBrady]

The above picture shows the detail under the heat shields. Here is the Y pipe with the heat shields on.

 

[White ls400]

Ok i know this is going against what you said and all iv read on here, But i went and visited the local exhaust "guru" thats done my friends skylines and forresters and such and they have all been very exceptional sounding and performing, And said he's done alot of 1uz exhausts and he explained with the first one he did he tried several setups held together by v-band clamps to see the results, He said the best sounding was and performing was running both sides separate with no crossover. So in all realism how much power could this cause the system too lose, as this guy is the only guy i trust for quality work, and i dont want to piss him off by pretty much saying no your wrong do it this way

 

[JBrady]

Ok i know this is going against what you said and all iv read on here, But i went and visited the local exhaust "guru" thats done my friends skylines and forresters and such and they have all been very exceptional sounding and performing, And said he's done alot of 1uz exhausts and he explained with the first one he did he tried several setups held together by v-band clamps to see the results, He said the best sounding was and performing was running both sides separate with no crossover. So in all realism how much power could this cause the system too lose, as this guy is the only guy i trust for quality work, and i dont want to piss him off by pretty much saying no your wrong do it this way

Well, I have done my best to help you. It is so HARD to GUESS what your guy actually tested. Most would simply rip off the entire system and start building "something" and go from there. I have no idea what he actually did or tried. If he "tried" a set of big pipes (2.5") with and without a crossover (X, or H or Y) and decided no crossover was best... what does that say? Not much. What I am suggesting is actually CHEAP. Cut slightly after the Y and add a single 2.5" section. From there you are mainly trying to quiet things down otherwise continue with 2.5" pipe and no mufflers.

If I were you I would simply ask him to build a system AFTER the stock Y section starting with a 2.5" single pipe. Otherwise, good luck.

 

[White ls400]

I am very confused as from what iv heard he knows his **** apparently but from the et your 1700-1800 kg ls is running im leanin in your direction(whats your exhaust setup atm), I do believe you, and i really couldnt tell your how he really tested it either i wasnt there so for all i know its probably a waste of money so to tell you the honest truth i may have too look elsewere if he doesnt like this idea...Just too get a better idea in my mind only one bank is firing at one time so exhaust flow through the y pipe is intermittent so flow will not be restricted through this area, but as only one side is firing at a time it creates a vacuum on the other pipe to scavenge the remaining exhaust gases, where as without a crossover of some sort the exhaust gasses will remain in the pipes untill the next time that bank fires which causes unwanted back pressure at low revs? is that right or missed by a mile.... Sorry about the dumb questions as iv only played with carbied straight motors in the past

 

[JBrady]

I am very confused as from what iv heard he knows his **** apparently but from the et your 1700-1800 kg ls is running im leanin in your direction(whats your exhaust setup atm), I do believe you, and i really couldnt tell your how he really tested it either i wasnt there so for all i know its probably a waste of money so to tell you the honest truth i may have too look elsewere if he doesnt like this idea...Just too get a better idea in my mind only one bank is firing at one time so exhaust flow through the y pipe is intermittent so flow will not be restricted through this area, but as only one side is firing at a time it creates a vacuum on the other pipe to scavenge the remaining exhaust gases, where as without a crossover of some sort the exhaust gasses will remain in the pipes untill the next time that bank fires which causes unwanted back pressure at low revs? is that right or missed by a mile.... Sorry about the dumb questions as iv only played with carbied straight motors in the past

My exhaust is STOCK! My car is a 1999 Vvti 1UZFE and I have ran many low 14 second passes at high 95+mph with the 14.2 @ 99mph my best pass (3 other 14.2s) That is one of the hard facts that I use to support my recommendations. Why would your 225hp engine need more exhaust than my 300hp engine?

Your crossover question is not so easily answered but you are starting to understand.

Consider at peak power and at 6000rpm each of my 1.97" pipes is supporting 150hp of flow.

So, how much flow is needed at peak torque? Peak torque is at 4000rpm and is around 310tq. That equals ( 310 x 4000 / 5252 = 236 ) 236hp. So, at 4000rpm each pipe is carrying 118hp. So if each pipe can support 150hp how much backpressure would that size present at 118hp? Virtually none.

Lets cut this back further to a very common street RPM of 3000rpm. My engine should make around 270tq at 3000rpm which is 154hp which means each pipe is now only supporting 77hp of flow.

What happens to velocity? At lower RPM it is dramatically slower. This allows more time for the gases to reverse and flow back into the engine. This is the real reason for the low end losses with bigger pipes as they completely kill low RPM exhaust velocity.

Ideally you would have a system that would be much SMALLER to increase low to mid RPM power but of course too small will hurt high RPM power.

A crossover can either act as a merge collector like the stock Y does or more like the end of the pipes like a box H or a window X which will create a secondary tune. Of course placement of this tune is important and is best at one RPM and hurts at another. I like the collector style as it has more range and function. The stock one is pretty good especially at your power levels. Helps cancel noise also.

 

[White ls400]

Dear Jbrady, I have come to trust your advice, and while enquiring about insurance Zuffen has reminded me to do so, My dilemma is my cats rattle and now i have dented my y pipe after an altercation with a ditch carrying extra passengers than i normally do, I went to see another exhaust shop for a second opinion from the 1st (idiot) shop i seen, He said go 2.25" metal hi flow cats, into a merge pipe (its 2 2.25 pipes into a sealed oval then back out into 2 2.25" pipes and is about 8" long) out into two stainless pack resonators or mufflers depending on noise level then back into two oval mufflers. Now i know you said only go 2 inch pipe but my dilemma is mandrel bending is out of the quetion due to being an apprentice and shops here charging the earth for mandrel bends

 

[JBrady]

Dear Jbrady, I have come to trust your advice, and while enquiring about insurance Zuffen has reminded me to do so, My dilemma is my cats rattle and now i have dented my y pipe after an altercation with a ditch carrying extra passengers than i normally do, I went to see another exhaust shop for a second opinion from the 1st (idiot) shop i seen, He said go 2.25" metal hi flow cats, into a merge pipe (its 2 2.25 pipes into a sealed oval then back out into 2 2.25" pipes and is about 8" long) out into two stainless pack resonators or mufflers depending on noise level then back into two oval mufflers. Now i know you said only go 2 inch pipe but my dilemma is mandrel bending is out of the quetion due to being an apprentice and shops here charging the earth for mandrel bends

Where is your Y pipe damaged? Got a picture? If it is in a straight section you can simply replace that section.

Otherwise, the play you outline will work. I am unsure about the H shape section and cannot predict its effect on low end but is a part you could change out if it is unacceptable.

Have you checked the wrecking yards on the price for a stock Y pipe?
You can of course cut the flanges off your existing damaged cats and weld them to the metal core cats to replace in stock location.

 

[White ls400]

Ls's in wrecking yards around here are very uncommon and i found a celsior today but the exhaust was gone.. The y is damaged right were the 2 pipes merge. The exhaust shop said he has used the merge section on a couple of soarers and the owners were pleased with the lowend. Basically the merge was 5" id (i think) and about 8" long pipe pressed down into an oval then they use a bit of round bar top and bottom to press in a divider for the 2 pipes, they then fully seal the section of pipe off with a bit of plate then holesaw the 2 inlets and 2 outlets then the 4 pipes were tig'd into the holes

 

[White ls400]

Would that work well in your opinion or too hard to tell

 

[JBrady]

Would that work well in your opinion or too hard to tell

I remember reading about that style of a merge. The dynamics of the gases flowing into the merge are probably similar to having no exhaust at all after the merge. I do not like your description of cutting 2 outlets with a hole saw as that is not an aerodynamically good design exiting the merge.

If you have a picture of the damaged section of your stock pipe I could give better recommendations. Personally I would try to salvage it OR even use the stock second Y to fix the first Y.

The best bet is limiting the total volume in the merge section. If, as I suggest above the created merge is seen by the engine as the "tailpipe" IE no pipe after... then it becomes a question of where to place it. I see no reason to rebuild the pipe from the catalyst with crush bent 2.25" pipe when that would have questionable dynamics vs the stock mandrel bent stainless 2" pipes (1.97").

 

[White ls400]

Havent got a pic yet, but i did take a closer look and i reckon i could pry it back out if i cut the single pipe out, or i might get one of the older more experienced guys at my work to heat and cool it see if that works but im a bit doubtful on such thin ss