I spoke with one of their head Tech guys at HKS and the reason that they don't offer a full cat back on the 2k is that they couldn't produce any more horsepower than with their muffler section (dynojet +8).

 

ummm...have you looked at the 2k exhaust?

right after the resonator there is a section of pipe that is completely crushed to about 1/2"...
if replacing that with a 2.5"+ pipe doesnt increase flow then I don't know what would!!!
if you ask me...that crushed section and the stock y-pipe are the most restrictive areas....
the stock rear section looks fine on a 2k.

 

My contact at HKS said that they would've loved to have made a full cat-back (ie, charge more $$$$) but it didn't produce anymore than just the rear section. So I don't why, b/c I've seen the pix of the crushed pipe.

 

I think all of you guys should not really worry about your exhaust to much. All these expensive mufflers and cat-backs will get you limited hp. Why? Remember when the 2000 max came out, Nissan said how they optimized it a lot ? It yielded 32 additional hp with diffrent exhaust modifications. Remember , this exhaust is almost as tuned as you can get it. So why try to put another cat-back on just for hp? I think the engineers knew what they were doing when they tweaked the hp to 222.

Theres another key thing to remember. If an exhaust is too open, it will kill your performance because lack of backpressure. I mean nissan has already given you 32 hp just from tuning the exhaust. ( I know not all 32 hp came from exhaust. Some came from lighter pistons, etc..) Even some of the exhaust systems knew let you gain high end , but loose low end. If you racing off the line to 60, that could be really bad.

Bottom line: I think the maxima exhaust is 94% optimzed as you can get. Paying 400 - $600 bucks for 6-7 horsepowere is not worth it. Get intakes ( not if your in Florida though) torque converter if your auto, and Y pipe. If you have an expenditure of money, buy a SC. Then you could even open your exhaust up a lot( even get the fake dual exhaust that are on the grand-ams)

 

HKS has never made a catback for the Max because there stupid. That is why Greddy has always made the most power, its a full-catback.

 

what is the problem with an intake in FL? I need to know 'cause that's where I am.

 

Cold Air Intakes have a habit of sucking in water (from deep puddles, hurricanes, etc) because they are so low to the ground.

 

Yeah but they are in a sealed compartment. You guys get as much rain as we get in Texas, and we get bad rains here. We never had problems.

 

As I recall, a cold air intake replaces the stock air box with a tube that is routed down close to the ground. This allows the intake to grab air passing underneath the vehicle instead of the engine bay. Hence the ease of the CAI to grab water instead of air (just put an AEM bypass valve in the intake to solve this problem).

 

Correct close to the ground but in a sealed compartment. Obviously you have not installed one. It goes in the compartment behind the foglight. It is almost 95% sealed except for a drain hole. I had it, and no water got in there. Until you have owned one or installed one, please don't act like you know everything about the CAI and think its that dangerous when about 75% of the people on this club own one.

 

It's close to the bottom of the car, but there's still about 2 inches from filter to liner... plus, you have clearance from liner to ground. So I estimate about 10 inches of clearance.

If you get floods... the CAI is not a recommended mod.

 

A few things:

1. The main modification that got the 2k+ another 32 hp was the addition of variable intake runners. If you look at a 4th gen dyno, hp falls off after about 5400. In the 5th gen it goes UP after 5400. There were other tweaks but that is clearly the big one.

2. Intakes are fine in Florida. You can have a pop charger. Or you can have a CAI. I went with the pop because of water concerns with the CAI. However, I have since learned about the AEM device for the CAI.

3. HKS confirms research that madmax2k and I did. Specifically, we dyno'd with the rear section after the cat DETACHED. We made approx. 3hp to the wheels more. That was with a y-pipe and intake. There was no appreciable drop in torque so we aren't dealing with too little restriction. Rather, the restriction in the cat is probably almost equal to the restriction anywhere on back. The result - expect very modest gains from a cat-back on the 2k.

Perhaps a cat-back plus a high flow cat would yield a better result. I know others have experimented far more than me, so I'll defer to them.

As for any after market parts manufacturer's estimates of hp gain - well, all I can say is look at Stillen. They claim mid-20s from the y-pipe and 6 from the SI (IIRC). In testing on my car, combined they made 13 to the wheels or 15 at the crank.

 

Actually, the biggest change isn't the intake runners. The 2k has a different CAM, that is why it makes more power all the way to redline compared to the older gen. That is the biggest difference.

 

Thanks Russ. That's interesting about the cam - well I guess it would be cams (aren't there 4). First time I've heard that but it certainly makes sense. Where did you find that info?

Do you know for certain where the extra hp comes from on the 2001 AE? I've heard muffler, exhaust, intake but never seen a confirmation for certain.

 

Whoa…Hold on a minute. Yes, I do understand that I don’t know everything. I decided to go with a Weapon R intake on my car because a good rainstorm will back-up the sewers and leave a few good size puddles in my neighborhood. I was concerned that I would suck in water (even with the compartment) with a CAI. I am just trying to tell people to “look before they leap.”

 

For a naturally aspirated car this may be true...
But DEFINITELY not for a Supercharged/Turbo'ed car...
I pulled off the exhaust from after the cat and my car picked up 4/10ths and gained 4 mph in the 1/4 mile....now that is ALOT more than 6hp.
I'm expecting even better gains with my 3" cat, 3" mandrel piping, and 3" APEXi N1 muffler that's going on tonight.

I agree though that on a basically stock (boltons) 2K Maxima you wont see *that* much of a power increase with a catback exhaust.

 

max gator...i talked to a guy at a local performance shop about your and mad max's exparament w/ the exhaust...basically by taking off all of the piping and muffler at the cat you are yielding no backpressure which does gain hp, but if you put a good straight through muffler w/ full catback piping w/ the right amount of backpressure for that vehicle, usually the numbers jump up from that 3hp that you dyno'd to about 18 (he showed me dyno plots on his celica gts...they tried this on his car and the results i just told you are just about the results it yielded...15hp gain after they put a new catback and muffler on)...he said the only cars that this would help a lot on are supercharged and turbo'd cars because the backpressure really doesn't matter on those

 

That's interesting. I think he is correct as to the difference in super/turbo charged cars. But I don't think there is any way you'll see 18 hp from a cat back on our maximas.

On our test, there was a nominal drop in torque (less than 1 ft. lb) which, I think (and I'm no mechanincal/engineering genius here) means that there was sufficient backpressure. I really don't know. But if anyone could show me an 18 hp gain from a cat-back system on our maximas - I'd buy it in a heartbeat. Show me the dynos.

 

I've got to agree with Gator and disagree with Russ. Almost ALL the new found power in the 5th gen VQ came from the variable runner intake manifold. The 5th gen manifold has two stages, a long runner and short runner. Long runner develops big torque and short runners develop good hp. Not until the early 90s having the best of both worlds wasn't possible in a street car until the SHO came out (varible runner design). Once the 5th gen VQ hits 4500, the short runner butterflies open and the engine is allowed to breath deep. Any gearhead knows that increases in useable rpms means you increase hp (ie hp is directly related to rpm). The 4th gen VQ has really long runners which gives it big torque, but hp falls after 5600 rpms. This design is very much like the L98 350 used in the 97-92 F-Body. It made huge torque, but killed the topend. Then the LT1 came out in the 93 F-Body (92 in the Vette). The LT1 had a short runner design which made good torque, but a ton more topend power (power was produced till 5700 vs 4900 rpms). Then the LS1 F-Body came out with a short/long runner design (doesn't have butterflies though) and it blows both these motors away. It makes BIG torque and hp everywhere. The 5.0 Mustang has long runners and the aftermarket setups use a shorter runner to develop more topend power. The 96 Cobra incorporates a long/short runner setup which allows it breath to 6800 rpms.

The new cams and exhaust used on the 5th gen VQ aren't much different from the 4th gen. The cam specs on the 5th gen are actually less aggressive and the catback setup is more of a gimick than anything.

The "crushed" pipe you guys talk about on the 5th gen isn't as bad as you think. I've seen it and it looks EXACTLY like the flattened Y-pipe on the LS1 F-Body. After lots of experimentation, it was realized that the pipe wasn't a restriction. Why? Because the pipe still had the same internal area as the rest of the pipe.

As for back pressure and torque loss. Back pressure IS NOT A GOOD THING and you don't want it. Adding a large diameter catback doesn't loose back pressure, instead it looses exhaust velocity. Adding the large pipe doesn't allow the exhaust gases to accelerate out of the ports, therefore the gas becomes very turbulent, therefore a drop in torque happens. The best setup would be a full 2.25-2.35" setup from the y-pipe straight out the muffelr. You want the system was uniform as possible. Bigger is not always better. 3" catbacks are good for cars producing 350-450hp. 2.5" catback are good for cars producing 250-350 hp. See where I'm going with this?


Dave

 

Loren figured this out a while back while comparing parts between teh 4th and 5th gen, and the 5th had different part # and specs for the cams...

 

How deep? I drove fast through some puddles where it spashed the water way over the top of the car, no problems.