Hey all. Been a while since I posted so I thought I'd update you on the progress we've made with power adders on my '06 G coupe. I just posted a suspension story about the KW coilovers and Stillen camber arms over in the suspension and brake section if you're interested in handling, but for you power geeks here's how our Stillen headers and high-flow cats test worked out.



We bolted my G up to the U2Ndyno.com Dynapack hub dyno, which reads about 10-15whp lower than most of the Dynojets we've used in the area. Anyway, as some of you know, swapping headers on these cars is a serious PITA. Not a fun job at all. Took us at last 8 hours, most of it miserable with our hands jammed up in the engine bay trying to get at the header bolts. But Sasha at SG busted his *** to get the Stillen headers swapped on and here's how they compared to the stock units:





As you can see from the dyno plot, we lost a fair bit of horsepower and torque below 5800 rpm, but gained a good chunk of power from 6000 rpm to redline. At first I wasn't too happy about this trade-off, but when I drove the car on the street I felt like I'd gain 1,000 rpm of useable powerband up top, where the engine now really rips when it used to fall flat on it's face over 6k rpm. So for a track ***** like me who frequently abuses this engine to redline, the added performance up top after gaining so much mid-range from the Motordyne mods and Stillen intake/exhaust (reviewed in separate threads in this forum), I was actually really happy to have gained so much up top in the rev range.

Then we installed the high-flow cats and blammo, we gained all that mid-range hp and torque back and picked up some more high end power.



I was really pleased to see how the cats served to bring the mid-range back to life while enhancing the top end of the powerband even further, giving us a new peak whp value of just under 260whp. The other thing the cats gave the G is a new and more aggressive exhaust note. With the stock cats the engine sounded typically VQ, just enhanced a bit by the Stillen cat-back. But with the high flow cats the engine now sounds really mean and nasty, but in a good way

Next up in the power department is a Haltech Platinum ECU and a Technosquare L-spec reflash to address the throttle-by-wire issues. After that, who knows...maybe a big nasty turbo??? Haha...

 

Good job on doing the before and after testing. It's unfortunate how much power is lost with the headers. In the 1/4 mile, the car will be slower because the midrange power is totally wrecked and midrange power is where most of all the 1/4 mile acceleration comes from. However, like you were saying, on a road course, these upper rpm gains would help since you're spending 95% of the race above 5000rpms and the race is over a much longer duration of time.

It's really good to see that the HFCs do make some decent gains and reaffirms to me that they'll probably be my next mod (Berks).

 

those are major gains considering u don't have any type of ECU mod.

 

Very nice gains! I was waiting on someone to do this before i did. I have the stillen exhaust and have been looking at the stillens headers and the somewhat new stillen HFC's for about a year now.

How does the car sound? Would it be to much of a pain to get some sound clips up? I want to do this so bad, but everyone has said the stillen exhaust sounds like poo with headers and cats.

-Sean

 

Depends on what you consider is a gain. Doing a simple calculation of average HP from 5000-7000rpm (the powerband), you'll get roughly the following numbers:

Stock 228whp
Headers 230whp (+2whp)
Header/HFCs 241whp (+13whp)

Seeing that this is a Dynapack and will usually see 20% higher numbers than a Dynojet 232, you can knock those total gains down another 20%. It's been my experience, that for every 10whp gain spread across the powerband, the car will drop about .1 second and gain 1mph to 1.2mph. So with headers alone, the gains are a wash. With headers and HFCs, the car is probably solid .1 second quick in the 1/4 mile. On a road course? I really don't know because I don't do that kind of testing or racing.

 

Well im 6mt every gear following redline lands close or above 5k rpm. That being said, from 5500 rpm to redline he has a very nice gain over stock and at ~6300 rpm his gain peaked over 15hp. I would consider that significant considering the car is running stock ECU parameters. The beauty about tuning the car he can actually see gains starting from 2500rpm instead of 5k and i won't be surprised if he gained another peak 10hp after the a tune.

Yes headers did not do much alone but HFCs/test pipes have been proven to do good things on our cars. Maybe that major gain is a combination of HFC/headers but headers alone are not that effective.

 

DaveB, not sure what you're basing your Dynapack to Dynojet conversion on. If your experience is with the Church Dynapack, then I understand since that Dynapack does read higher than most Dynojets. But the U2Ndyno.com Dynapack reads lower than the Dynojets we've tested it against up here in Toronto by about 10-15%. We've also seen that the UMS Dynapack in Phoenix, AZ is dead nuts even with the Evolution Motorsports AWD Mustang dyno, which are known to read lower than Dynojets. So the gains we saw on the U2Ndyno.com Dynapack would have actually been bigger on any of the local Dynojets we use for testing, not lower as you've suggested.

In any case, the OE headers are quite good and deliver solid low to midrange torque and hp, but the Stillen headers have a superior merge collector, which is key to the high RPM gains we saw. I also believe that with proper ECU tuning (coming up next with a Haltech Platinum) we'll really see what this group of bolt-on mods is capable of, since we'll be able to optimize fuel, ignition and cam timing for these changes. But even without a retune, I think the headers and cats combo is pretty impressive overall. Real world acceleration is definitely considerably improved, as demonstrated by the higher straight away speeds on our test track compared to the OE setup. We gained 5mph on the front and back straights, which is a huge amount given how long it takes to accelerate from 95mph to 100mph (the car is hitting a pretty strong aerodynamic wall at those speeds, so gaining 5mph is really quite huge).

The engine note is quite a bit raspier and more aggressive with the HFC's. With the headers and stock cats, the sound is really quite mellow and buttery sweet, just like you'd expect from a VQ. Very street-friendly, but still sportier and sexier than stock. With the HFC's, the engine sounds much more like a race car. It's louder, more aggressive, and more metallic sounding, almost like a sports bike kind of sound. I really like it, but it may be a bit too aggressive for some people's taste.

I've got a sound clip from the dyno with the headers & cats combo that I'll post up later. I think I also have a sound clip of the car with the stock cats, so I'll post that up as a comparo for you if I can.

 

I think you mean "knock these peak numbers down". Because no matter what type of dyno it is, a gain is a gain. Whether its from 220 to 240 on one dyno, or from 260 to 280 on another type of dyno.

Besides, like Modified Dave stated, there are times where Dynapacks are calibrated to read really low. For example, my stock baseline at Church's Dynapack was 265hp/245tq. And a dyno run at Precision Z's dynapack, which I had already installed an exhaust, test pipes, & 5/16 spacer, read 252hp/240tq.

I love the fact that Modified Dave is trying to keep the variables down by using the same dyno and doing before/after runs almost immediately. Comparing the powerband to this stock baseline he posted a few months ago, his gains are really impressive.

I can't wait to see how a tune improves his powerband & peak numbers.

.

 

I'd be interested to see results after a tune... I think people will be quite surprised

 

this would be a good thread to link in the "Intake/Exhaust" area too...

 

Modified Dave. Great work. Wonderful post.

What did you A/F ratios look like?

 

I'd be real shocked if it wasn’t lean... which is why I think a tune (including adding fuel) would show significant improvement.

 

I was always the impression that dyno packs read a lot lower...

-Sean

 

My thoughts as well but I didn't want to say anything. I bet if he can up his timing, that would help get alot of his lowend back as well. I don't know if a/f correction is good for regaining low end (even if it is lean)?

Have any experience with a/f and how it affects low/mid/high? I know if it's dog rich, it kills performance all around. Maybe if he's lean, it's making the knock count go up and kicking the timing back (aka loss of power)?

 

it;s Dynapack...

they normally read higher because it’s mounted directly to the hub - so you don’t have the loss from slippage or the weight (roational mass) of the wheel/tires to account for...

It's all how they are calibrated though... some probably pusposefully calibrate to be close to a dynojet near by...