Awesome

 

WOW! now that's what I'm talk'in bout Props to you John now there are some definitive #'s before and after. Thanks to you Ken also
Since far more GS400 are getting the headers we should be seeing some comparo #'s for the non FI's dying to see where the power curve is w/ supercharger and header.

OK JP430 "drive it like you stole it now" LOL

 

Hey JP that's one GS not to be messed with ! Congrats. I would like to know about your exhaust system behind the headers. Are you still running stock cats and Y pipe ?

 

Hell yes, that's what I'm talking about!! Now I'm even more excited about dropping the car off this week for my headers to be installed- time to see what it can do for the 'ol RMM SC kit!! Thanks for sharing Ken

 

Ken how much did the headers increase the noise factor?

 

It's really hard to tell because when the car is on the dyno, the dyno makes a "jet noise". It gets loud inside the shop... I would have to let John answer that question once he drives the car for a day or two. Since the cats are still attached to the car, I don't expect the noise to be that much louder.

 

Thanks guys. I was running JIC CB exhaust for those numers posted. I am having the tanabe hyper,super,whatever medalion exhaust installed tomorrow. The noise did not really change at all with the headers (maybe just a little) thats what LMS told me. Ken made a good point about the noise in the shop, I know exactly what you are saying (those chargers suck in some air (big time). My exhaust was louder before I got the SC. I am just so happy with the results. Here are the dyno sheets.

 

Hey John, A few questions did they dyno your car in 3rd or 4th gear.
Looks like the blue line in the dyno chart is HP, the red is TQ but what does the black and green line represent??

 

Look at the bottom one is the A/F and one is the boost. I do not know what gear, I know he does not really get on the gas. I think he just takes it slowly through all the gears. He went up to about 120mph.

 

Excellent information. The drop in boost indicates an improvement in exhaust flow. Remember, this car still has the stock Y pipe with a single 2.36" center pipe. Even so there is some interesting data to be gained. Power and Torque are up accross the board starting at 66mph (RPM?) with 9hp/7tq and going to 117mph with a gain of 28hp/24tq.

Peak numbers are one thing but the spread is more revealing. Biggest hp gap was at 111mph with 43hp/34tq. Solid 20-30 power and torque gain from 95mph to redline. This was with less boost. With a larger center pipe this engine would probably pick up another 10-20rwhp.

One further observation, the header dyno has a dip in the last bit of the RPM range. I would think that is a glitch and will probably clear up and give back 10+hp and tq. Of course a leaner A/F ratio could easily give 20rwhp.

Nice to have some solid dyno numbers. I am certain these will not be the last for this car or the headers.


MPH----HP1----HP2---TQ1---TQ2---HP><---TQ><
66---151---160---205---212---9---7
67
68
69
70
71---205---205---266---266---0---0
72---206---206---267---267---0---0
73
74
75
76
77---225---235---290---305---10---15
78
79
80
81---241---254---301---316---13---15
82
83---244---258---291---313---14---22
84---245---259---290---312---14---22
85
86
87
88
89---252---267---286---305---15---19
90---253---267---285---304---14---19
91
92
93
94---264---283---283---303---19---20
95
96---267---287---282---304---20---22
97
98
99
100---277---300---278---303---23---25
101
102---280---301---279---301---21---22
103
104
105
106---281---307---265---296---26---31
107
108---278---312---263---295---34---32
109
110
111---281---324---260---297---43---37
112
113---295---327---264---295---32---31
114---292---323---257---287---31---30
115
116
117---311---339---258---282---28---24

 

There's got to be a even better gain losing the 2.36" center pipe.
X pipe Dual, or 3" pipe with Dynomax Straight thru Muffler for Noise control. I say at least a 18 HP gain , maybe 25 HP right there. And then some A/F tunning. WOW !

 

John,

Your Tanabe is no problem. Next chance you get measure the pipe where the 2 Tanabe tailpipes join together. Most aftermarket systems like the Carson Tuned exhaust have a much larger than stock diameter at this point, looks to be 75mm / 3.00".

Your stock system has dual 50mm pipes that feed a single 60mm center. 60mm = 2.36". I havent had the chance to test various sizes and there is definitely an art to getting optimum exhaust configurations and sizes. Too small restricts power. Too large hurts low speed response and power.

Consider that a 60mm pipe has 47% more internal flow area than a 50mm pipe. The stock 60mm center pipe has less capacity than the two 50mm pipes feeding it. Now this sounds bad at first but is actually part of the scavenging effect of the exhaust. I intend to experiment with 2.125" and 2.25" primary pipes. Actually I already have data on a twin 2.25" system feeding a single 2.50" center pipe and the gains were very minor on a stock engine and the response was decreased.

Twin 2.250" pipes feeding a single 2.75" center pipe may work very nicely but I haven't tested that combo yet. Keeping your twin 50mm primaries and increasing the center pipe to 2.50" may increase your power. I cannot comment on sound or droning as I haven't done this yet but would expect a slight to moderate increase in exhaust loudness.

Bottom line the stock pipes are marginal at 300hp. You are making around 435hp. That is a bunch of flow through a single 60mm pipe. Of course you either have to build a full exhaust or you must cut your existing pipes. Cutting your existing pipes makes it tricky to go back if you do not like the result. This is call R&D. I can make reasonable theoretical suggestions but it really needs to be tried.

If you decide to cut your stock Y pipe... I would cut it right where the two primary pipes join. I would keep the twin D shaped section and keep the weld holding the 2 together. I would then add a 2.50" pipe from there back to your Tanabe Y pipe. The 2.50" pipe has just under 13% more flow area than the 60mm pipe.

To build a full system you will need a 2-into-1 merge collector dual 2.25" feeding a single 2.75" (the design IS important and this NOT an off the shelf part). Two oxygen sensor fittings, three 2 bolt flanges (one for each cat with a 2.25" opening and one at the Tanabe with a 2.75" opening). Either a mandrel bending machine and pipe or pre-bent mandrel tubes. A skilled craftsman to build the system. Form the system just like stock but with the larger tubing. Maximize the center pipe length (hard to do on the GS).

It is difficult to give power estimates for each of the above systems. The larger may only have an extra 10rwhp over the smaller example, but then again, who knows until it is tried, it may have much more. The smaller system may be an excellent compromise but then again may cost easy power. If you cut the stock system and decide to go back to stock you can weld it back together if you have a competent craftsman.

Wish the answer was quick and easy. Some would say simply stick dual 2.5" pipes on it. Personally I believe that would be a mistake as I believe the low RPM characteristics would suffer. You can buy off the shelf X pipes (quality and performance differ GREATLY depending on design). It takes a trained eye to spot the correct design. Burns stainless build the best. Stainless Works offers a different design that is still effective. Unfortunately neither will work well with the Tanabe of other center pipe systems like it.

A third option would be to use a 2.75" pipe with your stock dual 50mm pipes. 2.75" has 38% more flow area than the stock 60mm. This ironically may be too big for the stock 50mm feed pipes and hurt scavenging. 13% may not be enough increase (2.50") and 38% may be too much (2.75"). I am unaware of any easily available pipe sizes between these 2 sizes. So, a solution to achieving say a 20-25% increase would be to start with a 2.75" pipe and flatten it to about 2.25" this should widen it to about 3.00" and give a 22% flow areas increase over the 60mm stock pipe.

So you see, to optimize the exhaust is not a quick simple answer. I personally would try the 3rd option with the oval pipe first.

 

John,

There is no off the shelf bolt in option. If it were my car I would purchase 2 feet of 2.625" (2 5/8") 304 stainless from Burns Stainless part number ST-263-16-304
http://www.burnsstainless.com/304tub...raight304.html

This will cost about $40.

Have the stock center pipe and resonator cut from the Y pipe at the point where the 2 feed pipes join. Cut right after the weld where the the 2 feed pipes join. The inside should look like 2 "D" shaped pipes. Cut the flange off the center pipe and have the hole cut open to the 2.625 size. Fit the correct length of 2.625 pipe between the Y and the Tanabe. Weld the flange on in the correct location and weld the 2.625 to over the two feed pipes. You may have to expand the 2.625 pipe slightly to fit over the feed pipes but you definitely want it OVER the pipes slighlty.

Good luck.

 

Hey, you haven't given us your driving impressions with the headers...

 

I believe John is picking up his car tonight. LMS had to do some final stuff to the car...