V8 Performance Exhaust

[JBrady]

I am new to this board but not new to Lexus or internal combustion performance.

A site member just joined another forum that I participate in and based on his comments I thought I would check out LOC. Good site from what I have read so far.

Now, with regard to the performance potential of the Lexus exhaust system. I have seen a couple of posts here suggesting larger exhaust pipe size... DO NOT use larger than necessary exhaust pipe unless you want LESS low and mid RPM power. 2.50 pipe is TOO LARGE. Stock is 50mm (1.96") feeding a single 60mm (2.37") center pipe. I am currently working with a few members with both headers and either 2.00" or 2.25" pipes feeding a single 2.50 pipe before splitting back into duals. The Lexus dual Y pipe design is very effective for low RPM torque and is quiet.

Another consideration is what year engine and what mods you plan in addition to exhaust. 1990-1994 LS400s and 1992-1995 SC400s are rated 250hp/260tq but IMO are actually over-rated and produce more like 230hp/240tq. 1995-1997 LS400s and 1996-1997 SC400s are rated 260hp/270tq and are fairly accurately rated. If anything the SCs are still a bit down on power due to the single tube exhaust manifold design vs. dual tube on the LS. The 1998-2000 GS400s are acurately rated 300hp/310tq. The 1998-2000 LS400s are accurately rated 290hp/300tq with a more restrictive cat back exhaust. The 1998-2000 SC400s are "slightly" overrated at 290hp/300tq again due to relatively poor exhaust manifold design.

All models benefit from the S&S Headers especially the SC400s and early LS400s.

[SKperformance]

I stoppped following your thread on the headers a long time ago as it got full of wasted space from others asking dumb questions.

So where are you at with it now?

Do you have them on your car?

Did you finally dyno them and release the results?

[Toysrme]

The best exhaust.... is no exhaust. Unless it's having to make it's way throguh a turbine.

[JBrady]

I stoppped following your thread on the headers a long time ago as it got full of wasted space from others asking dumb questions.

So where are you at with it now?

Do you have them on your car?

Did you finally dyno them and release the results?

Yes they are now available.

I have my set but have not installed them. Ironically, they are bolt in for the GS400, GS430, LS430 and SC430 but on my LS400 I must fabricate a new Y pipe. I had flanges cut and pipes ready but donated them to the first GS400 header install. I have just begun welding up a new Y pipe design called a "nozzle" collector based on what was learned on the GS above. Time restrictions dictate I will probably not install until spring.

Dynos have been few so far. I have not personally dyno'd them. Results have been 15rwhp and up with a supercharged GS gaining 40rwhp at one point with an average of 25rwhp on the otherwise stock pipes. Here is the update thread. http://www.clublexus.com/forums/showthread.php?t=181544

[SKperformance]

Hmm not bad.

I remember seeing you Y's you first made a while ago but not one makes a nice merge with low angles. I am just going to be using 2 borla 2-1 mufflers for a full length variable diameter and smooth merge for the manifold and exhaust ends.

As for toys comment , i don't even know how to logically respond to that.

No exhaust?

[JBrady]

Hmm not bad.

I remember seeing you Y's you first made a while ago but not one makes a nice merge with low angles. I am just going to be using 2 borla 2-1 mufflers for a full length variable diameter and smooth merge for the manifold and exhaust ends.

Actually, I make the 2 into 1 nozzle and merge collectors between 20 and 30 degrees total merge angle. I assume you are looking at the Borla 40670 with dual 2.25 and single 3.00. http://www.borla.com/products/product_mult...rbo+XL+Mufflers

I personally would not recommend a 3.00 center pipe. 3.00 will support huge power and is way larger than needed on a N/A Lexus running stock camshafts. You are also looking at substantial weight, questionable allowable space and over $500 for just those 2 parts. I have shipped 2 sets of the nozzle collectors. Once set to be used on a 93 SC400 running the SS headers. He wanted to go back to 2.00 into a 2.50 center after trying dual 2.50 into 3.00 and lost low end torque.

http://lextreme.com/forums/showthread.php?t=4388

The other is trying the 2.25 into 2.50 pipes after trying dual 2.25 merge collector X pipe on his 1998 SC400 (vvti model, 290hp) and also loosing low end power. Here is a link showing his design: http://www.performance928.com/cgi-bin/page...ass_parent=1128

Notice both are nicely formed designs. The problem is TOO much volume for the needs of our small 4.0 liter little cam engines.

My nozzle design should restore the lost low end power and still provide sufficient high rpm flow for max power.

One more interesting note. Another individual installed the headers with dual 2.25 pipes and stock rear mufflers and NO crossover and his impression was dramatic improvement in low end AND top end power. So, while crossovers are good for virtually all systems they must still be designed correctly to get the desired results.

[JIBBBY]

I read on the Lextreme forum one guy is running headers with three inch straight pipes all the way back to the highflow mufflers with no X or Y's needed, he said no loss at lowend just roaring power which I argued about based on the former posts.. I agree you definetly will lose low end with larger tailend exhaust pipes but you will also gain top end torque and allow the engine to breathe better at higher rpm's. The larger exhaust pipes being used will cause torque loss at lowend but that can be countered with a stronger torque converter. Engine will perform better with faster running times.

JBrady, I hope I am not irritating you with my come back posts that is not my intention but I tell you my 1992 sc400 flows better with the larger tailend pipes and I would not go back to the smaller stock piping just to gain back a little lowend which I don't need and lose my top end. My car still bolts off the line with rude lowend torque and even with the Supra LSD my rear wheels still spinout in first gear at full throttle without the use of my nos system.. With nos a traction nightmare. See ya, this just my show of events that happen from hands on experience with my car.

[JBrady]

I read on the Lextreme forum one guy is running headers with three inch straight pipes all the way back to the highflow mufflers with no X or Y's needed, he said no loss at lowend just roaring power which I argued about based on the former posts.. I agree you definetly will lose low end with larger tailend exhaust pipes but you will also gain top end torque and allow the engine to breathe better at higher rpm's. The larger exhaust pipes being used will cause torque loss at lowend but that can be countered with a stronger torque converter. Engine will perform better with faster running times.

JBrady, I hope I am not irritating you with my come back posts that is not my intention but I tell you my 1992 sc400 flows better with the larger tailend pipes and I would not go back to the smaller stock piping just to gain back a little lowend which I don't need and lose my top end. My car still bolts off the line with rude lowend torque and even with the Supra LSD my rear wheels still spinout in first gear at full throttle without the use of my nos system.. With nos a traction nightmare. See ya, this just my show of events that happen from hands on experience with my car.

Well, when I make a post on a public forum I open the subject up to comment and discussion. What does concern me is when someone makes a statement not based on fact and thereby cluttering and confusing the discussion. As a long time Lextreme member/mod I do not recognized your above reference. I did post above regarding SRQ400s 99 SC400 with headers, dual 2.25s, no x or y pipe and stock mufflers reporting very strong low end power... is that maybe what you are thinking about? If you are certain about the other post please provide a link as I must have missed it.

Regarding your own experience, did you ever TRY 2.25" pipes as a comparision or are you just guessing that they would reduce your power? You may recall jp430 at CL installing headers on his supercharged GS430 and gaining as much as 43rwhp through the STOCK 1.96" pipes. There may well be another 20rwhp in 2.25" pipes but after that I do not think the gains would be dramatic if at all going to 2.50 or larger.

If you are familiar with David Vizard, he writes technical exhaust papers, was involved in the design of the Dynomax Super Turbo muffler (probably the most successful muffler produced) and was involved in the flow testing and subsequent power rating listed for many of the Dynomax mufflers.

Check these links quoting Vizard: http://www.houston-f-body.org/tech/exhaust/exhaust.htm

http://www.houston-f-body.org/tech/exhaust/exh4.jpg

The second link shows a chart that basically indicates at 2.2 CFM flow per horsepower produced there is no significant gains to be made by adding capacity. You can argue other details but going with this you can then check out the dynomax website to compare their mufflers flow capacity and power supported.

Go here: http://www.dynomax.com/documents/ultrafloss_specs.pdf

look at muffler part numbers: 17291, 17292 and 17293

These 3 are the same size EXCEPT pipe size. Power supported based on their list and above Vizard info is:

2.00" = 364hp

2.25" = 455hp

2.50" = 544hp

Now, honestly I am suspect of these numbers BUT it is worth noting the twin turbo Pontiac outlined in Engine Masters that made an outrageous 2800+hp (two thousand eight hundred) had only 2.50 primary collectors.

So, again, when I suggest using the SMALLEST pipe that supports you needs I say so with a reason.

[JIBBBY]

Received and understood!!!!!!! The only comparisions I have made to your statements was in regards to my 1992 sc400 exhaust first hand adventures. So to answer your question I did have the stock exhaust piping running with a high flow cat and high flow mufflers, then I only changed the rear section of exhaust piping to the 2 1/2 inch piping from the cat to the mufflers, and I noticed very little change in performance with lowend torque and just noticed a little more highend that is why I have been suggesting the larger piping along.

I can say I have researched alot on the exhaust setups, read many of your posts over the past year and others, and actually purchased a set of your designed S$S Headers and completely respect your knowledge and understanding of exhaust flow, however I know what worked best on my 1992 sc400, and keeping in mind your talking about newer sc cars and my old car is a 1992 sc400 and is also not stock - with an ecu piggyback, LSD dif, Intake, runs rich with nos, and perhaps runs different then others sc's. So John, I will assume you are right and I am wrong for suggesting the larger piping in the rear sections. I would love to link this stuff I talked about prior to this post but I have not yet figured out how. I will work on that to validate my claims in the future, but as you can see I can provide pictures and am running the larger pipes..

I also suggested in prior posts that changing out the Cat converters on pre 96 lexus's is a good idea, as I have witnessed first hand the stock cats truley clog and become very restrictive over time. I changed my original stock cat converter to a magnaflow highflow cat which is fitted and designed just like the stock and wow did I notice a difference at top end, suprised the heck out of me I was expecting nothing big. My car had 105,000 miles on it when I did that change out.. Anyway that is all, you are the man on exhaust....

I am just trying to offer my 100% honest opinion to help others that is it.

[Jgordon0893]

Is there a cat back system that you recommend to work well with the S&S headers on a GS430 car? I was looking at the GREDDY EVO2 but after reading your post am concerned the pipe size may be too large. The piping is 60 - 70 mm (2.36" - 2.75"). I plan on leaving the stock Y pipe.

Thanks