Fisher, Yes, you are correct, if the dyno shows a nice increase in power I am certain the line will grow longer.

That said, MANY if not most do not understand what dyno testing REALLY tells you about a part.

Most people want to know one thing and one thing only... how much power did it gain? Of course they are refering to PEAK horsepower (or killowatts in some reqions). While it is always good to gain peak power what is actually more important is power/torque under the curve AND responsiveness of the engine. These numbers are partially shown in dyno runs but the nature of an inertia chassis dyno (dynojet) does not lend itself well to measuring transient response.

Lets compare an actual situation right here. gawd had a 2.25" Y pipe welded up with parts that I donated to him. (these were for my car but I felt the GS400 needed them NOW) Unfortunately the person that welded it up did not have a lift and therefore bench welded the system and it did not fit correctly. BUT, the main problem is that there was not enough pipe length after the collector. gawd immediately noticed the car felt sluggish accross the power range (compared to the stock Y pipe) and he didn't like the sound. (sound turned out to be the misfitting pipe rattling and an exhaust leak). He dyno'd the bigger pipe against the stock pipe and found that the bigger pipe actually gained 6tq and the power was within 1hp.

So, what do we have? A gain in torque should indicate that this part is better than the stock pipe. HOWEVER, it FELT lousey. How many people would spend money on a part that made their car FEEL slow? Even when the dyno said it helped?

Now, gawd has had the bigger pipe reworked, fit corrected, 6" length added after the merge. He did not have a chance to test it before the header install but he reports it feels at least as good as stock if not better

He intends to dyno with both pipes so that additional info will be helpful but for now it looks like a good idea to upgrade Y pipes on header equiped cars. Based on the data so far I am actually working on a different Y pipe design that should further improve power AND response. If effective it should be a good upgrade for all GS400s with or without headers.

Back to the Headers....
Many posts back I described the "feel" of 20+rwhp as more or less the "feel" of a stock car in hot weather vs. cold weather. My LS400 runs a solid 2 to 3 tenths quicker in cold air than hot air. Drag racing dyno charts will tell you it takes about 10hp for every tenth quicker for a car in the 14 second range. So, is my car ACTUALLY gaining and or loosing up to 30hp??? On ONLY air temperature???

YES

How is this possible?

The answer lies in the fact that colder air is denser air. This means that there is MORE actual molecular weight in any given VOLUME of air. Engines pump volume. Density determines MASS at any given volume. Mass determines power NOT volume.

Also, our engines have highly sophisticated electronics and both the fuel flow and the ignition timing is altered as air mass increases and air temperatures decrease.

Even though this is LONG and BORING to some... it is actually a simplified tiny fraction of information intended to make a POINT.

The POINT is the FEEL of you car when you drive it.

My previous estimation appears very accurate. gawd's car FEELS to him like it does in very cold air when in fact it is around 100 degrees and very humid in Houston. So, the car FEELS like it picked up 20-30hp. This means several things. The car is more fun to drive. The car is almost certainly quicker, much quicker, than without the headers. This also means that it will be QUICKER still in cold air.

Now, what will the dyno numbers say? We do not know yet. But WHATEVER it shows we already KNOW these headers are working and working very well at that. This means at the very least we have nice gains in responsiveness. This will USUALLY be seen as increased mid range torque. gawd is reporting a noticeable gain from 2600rpm up. The problem is that it is very hard to dyno these automatic transmission cars from low rpms. They will try but we may not get that data.

I guess the best way to describe the headers improvement is as I did above. Your car will FEEL like it does in very cold air when the air is actually hot. It will FEEL even faster in cold air. I would be HAPPY to race a GS4xx with only headers against another GS4xx without them. I would not need a dyno sheet to be confident in placing a wager

So, again, I am sure that a nice increase on a dyno chart will sell more headers. That actually is not helpful or hurtful to me. I do not get a cut off the deal. But, as I have tried to illustrate above it is not always the car with the bigger peak dyno number that is the quickest. In the Corvette and Supra and other hi-po car world it is VERY COMMON indeed that it will be the "weaker" of 2 cars (based on dyno charts) that WINS the RACE

 

jbrady- sorry for a rookie question, as this is probably been covered, but the thread is so long I can't find it- what modifications will be necessary for a gs 430?? I follow about how a gs430 should respond better to the headers than the 400, but what do I need for the actual install procedure? unfortunately I'm not mechanically inclined- i was proud i changed my sparkplugs- but if I call a shop and ask if they will install these headers, what else would I need to ask about? I assume I would need a new y pipe like the 400?? anything else?? thanks for all your time and effort on this

 

well, this tread is tooo looong!~ I gues a lot people are already in....well, once the result is out and some members installed them, I will be in to order one too... maybe a GB?!

 

John:

You stated that so eloquently, and educationally...Props...

Ryan

 

I do believe the $600 is the GB...Read back in the beginning of this thread...

Ryan

 

I'm also getting a 3.92 rear too. Might be in before the headers not sure.

I am going to do 2x 2.25 ypipe, running as separate pipes as far as possible till I get to near thae cat back which ill have the 2x 2.25's run into a 2.5" tapering into a 3" then I'll taper to the 2.5" cat back flange IIRC. No Cats. If it's too loud I'll add a free flow 3" periforated race resonator instead of the 3" expansion area.

I will be dynoing on a mustang dyno w/ 94 octane gas.

 

I agree that you cannot rely on dyno numbers alone for something like this. It is certainly a useful tool (if the dyno runs are done correctly) but your advice is well taken!
If you add in other factors such as a high stall TC and different gearing and then consider the different types of dynos, weather variables, other mods to the car etc. it becomes VERY difficult to use the dyno numbers as an absolute standard.
That said, dyno runs can certainly be beneficial for comparison purposes on the same car and same dyno taking into account weather etc. As they say "Use for comparison purposes only, you mileage (or HP) may vary".
I am looking forward to gawd getting some good pulls on the dyno now that his ECU has had some time to compensate for the headers.
I like what I'm hearing so far though!

 

Yes, dyno numbers are a usefull tool IF DONE CORRECTLY and if USED CORRECTLY. That said consider the many many conditions that are NOT measured on a dyno pull.

Part Throttle Tip in Response: This is how responsive the engine "feels" under normal driving conditions. Does the engine "feel" crisp and powerful even without using full throttle? This is a BIG part of the joy of day to day driving.

Fuel Economy: While a dyno that takes A/F readings will tell you the BSFC under full throttle it does not tell you the part throttle efficiency and that is what determines fuel economy.

Off The Line Power: On a stock torque converter this is the torque available at 1800-3000rpm. With a 2800 stall TC this is 2600-3500rpm (both are target ranges and not absolutes). This is how well the car responds from a standing start.

RPM Drop Recovery: This is how the engine response during gear changes. How much torque is available when the next gear is engaged AND how well the engine accelerates going from a high RPM and then abruptly dropped to a lower RPM while still under WOT.

Part Throttle Balance: The peakiness or lack of when maintaining part throttle 50-80% load. Definitely effects how "driveable" a car is during driving manuevers (hint, the throttle is a variable control not an on/off switch).

And many other part throttle/load/response conditions that make up the very complex mapping needed in an ECU controlled engine.

Now, looking at what a dyno DOES measure it is important to understand HOW to interpret the information.

Peak Power and Peak Torque are what almost everyone wants to know for "bench racing" discussions. These are fun numbers and worth knowing BUT the IMPORTANT full throttle dyno information is the POWER UNDER THE CURVE. This is the average power (torque and HP) for the RPM range used. Of course "Off The Line" is important for drag racing type competition but once underway the engine will never drop below a certain RPM. The average power between say 4000 and 6300rpm is more important than peak numbers. While still laking the responsiveness data this AVERAGE power under the curve is the best data available from a dyno. When was the last time you heard someone compare power under the curve data?

Like I have said before there is MUCH more to the story than simplistic measurements. Considering the above driveability conditions let me pose a couple questions:

Would having a much more responsive car that gets better mileage AND performs better be worth spending money to achieve even IF peak numbers were not increased on a dyno?

Would you spend money to gain peak numbers on a dyno even if the driveability and in fact real world performance went down or didn't improve?

 

Lotsa people do it when they buy an intake....Peak HP and Peak TQ seem to improve at a cost of low end performance and driveability....LOL So what was it you were trying to say?? LOL

 

I LOVE easy tests!!

1.) YES
2.) NO

All of the different characteristics you mentioned-call it "throttle response" or "driveability" are what I love about my GS! Especially with the TC and lower gears, the car is just amazing for the power to weight ratio (approx. 12 lbs/HP). I am confident the headers will only enhance the driving experience, whatever the actual dyno numbers are...

 

Jbrady.....so what is your overall take on the SRT intake? Is this a must for our V8 GS400's if interested in power?

 

The SRT addresses the fact that the factory MAF is restrictive. They do it by placing the MAF element in a larger diameter housing. The increased flow relative to the factory MAF calibration makes the car run VERY lean. This requires a correction to the signal to the ECU. SRT calls this part their Race ECU. If you tune the ECU to run a slightly leaner mixture than the factory setting under full power you will gain power. However, each application tends to be slightly different as the factory OBDII programing is dynamic and even resetting it tends to produce a variable in the relearn. gawd ran a baseline dyno on his 3.77 LSD and SRT intake equiped 99 GS400 prior to the header install. His torque was good at 260 but the power was on the low side at 230rwhp. A/F ratios were too rich at 11.5-to-1. His ECU needed a leaning to closer to 12.5 or 13 to 1 for best power.

So, to answer your question, IMO the SRT is currently the best aftermarket peak power intake for the GS400. There are some other tuning considerations including tapered pipe and resonator chambers that could improve the intakes performance and possibly regain any lost low RPM power. Since no one is making this theoretical part YET... the SRT is the best choice for PEAK performance but not low end performance. When in comes to confrontations such as the one gawd had in the street stories section of CL... the SRT was definitely helpful.

 

jbrady / DaveGS4 - Just a suggestion to avoid the same questions being asked and answered over and over and also the problem of it not being feasible for most people to read through 53 pages of posts... perhaps the *first* post in this thread could be updated with an up to date FAQ? The first post is now 19 months old.

 

Hi,
Thanks again jbrady for all of you have done; I was #5 on the header order by the way!

Based on what you have written, I can tell you posses an extraordinary knowledge of exhaust system construction. I think I have read through all of the exhaust posts so I hope that I am not asking questions that have already been addressed but that I missed. I know you have recommended 2.25" tubing for the system with a "Y" pipe having 45 degree inlets. Do you recommend the same degree for the outlet "Y"? Also, what diameter tube do you recommend for the center-pipe? Finally, what type of mufflers do you recommend?

 

Great idea but yet another task. If you want to go through and get a basic outline started and populate a few questions maybe we can do exactly that. For starters:

Common questions pertaining to all models:
GS400 specific:
GS430 specific:
1992-1997 SC400 specific: