Replacing stock equipment with Hotshot Header and BRM Exhaust

[BadMojo]

So...as you may have guessed from the title, I'll be replacing the OE exhaust manifold with a Hotshot Header and the OE exhaust with a 2.5" BRM unit.

I'm getting ready to do this job and am trying to think of any other hardware I should be replacing at the same time. I'm working under the assumption that anything under the car is going to be pretty corroded.

Right now, I've got new gaskets, new exhaust hangers and will get new washers and nuts to attach the header to the block.

For those of you running aftermarket catbacks, did you retain all or any of the heatshields at the cat or at the manifold?

Thanks!

[InsanityInc]

The manifold heatshields won't go on the header. I would also recommend replacing your cat with a 2.5" unit as well. The heatshielding realy just causes rattles, I'd take it all off.

[BadMojo]

The manifold heatshields won't go on the header. I would also recommend replacing your cat with a 2.5" unit as well. The heatshielding realy just causes rattles, I'd take it all off.

Sorry, forgot to mention that I got a Catco high flow cat from Greg also. The old one was way past its prime.

So, you'd omit the heatshielding on the cat too? I suppose other than a few smouldering leaves and a warm floor, there wouldn't be much downside.

[InsanityInc]

I've never set anything on fire. Probably the only downside is you could burn yourself on the exhaust pipe if you're working under the car when it's still hot. Just don't drive through fields :P

[skatanic28]

get all stainless steel hardware if you can. youll thank yourself later.

[slipnfall]

Unless you have decent ones already, I'd suggest buying OEM cat/DP gaskets. They are far superior to anything you'd find at an autoparts store. Multi-layer metal, with each layer sorta 'twisted'(think of a lock washer).

Yes, stainless nuts/bolts would be ideal. But for any other bolts subjected to high heat, I would at least use an anti-sieze compound on the threads. As the last poster mentioned, you'll thank yourself later.

I didn't think high-flow cats were rec'd for NA applications(?)

[InsanityInc]

How are high-flow cats not recommended for NA applications? Read my signature, it speaks the truth.

[BadMojo]

How are high-flow cats not recommended for NA applications? Read my signature, it speaks the truth.

Yup, I agree...less back pressure is always good. I would have gone with larger pipe for the exhaust if I didn't think the noise on an NA application would have been unbearable.

Besides, an OE cat is extremely expensive, and a new cat (high flow or not) will perform much better than the old one I've got now.

So, as for the gaskets...do you all really think the OE ones are a better bet than the ones included from Hotshot and BRM?

And, yes, there will be use of some anti-seize compound on all the exhaust hardware.

[slipnfall]

Regarding the backpressure: I was just under the assumtion that backpressure is OK for NA, but forced induction is where it really hurts.

Anyways, keeping with the thread topic: I'm no expert on gaskets, but after seeing the OEM, I wouldn't bother with a normal metalic. All I know is it closed my cat leak, where an auto-parts store version wouldn't.

[InsanityInc]

Regarding the backpressure: I was just under the assumtion that backpressure is OK for NA, but forced induction is where it really hurts.

Anyways, keeping with the thread topic: I'm no expert on gaskets, but after seeing the OEM, I wouldn't bother with a normal metalic. All I know is it closed my cat leak, where an auto-parts store version wouldn't.

Yay I get to explain exhaust dyanmics once again. Really, we should have a sticky for this.

The way a properly tuned exhaust system creates power is via something called the Bournelli Effect. Basically, it states that the faster a fluid (gases are fluids) is moving, the lower the pressure is in that gas. Your exhaust system is filled with gas, and in order to get good exhaust evacuation you want a low pressure in your exhaust pipe. The first (and obvious) way to get a lower pressure is to reduce backpressure. You could put a 7" pipe on your car and probably wouldn't lose anything over stock (unless your stock exhaust system is really good), and you'd probably gain a bit on the higher end just from reducing the backpressure. Now, say you put a 3" pipe on your car instead. Not only have you basically reduced backpressure to 0, you've also increased the velocity of your exhaust stream (PV=nRT, and all that loveliness). Now, remember the bournelli effect? So, not only do we have no more backpressure, we have an even LOWER pressure because our exhaust is moving more quickly. If you have backpressure and good velocity you're basically just shooting yourself in the foot.

[centralcoaster33]

Maybe this is the place to add some questions I have. I'm doing a similar upgrade. I have sourced the rare and discontinued GReddy header for 95-98 240SX's. Unfortunately there are no specs on the product from distributors, installers, or the manufacturer. It should arrive within a week. I will need to buy a cat and a cat back exhaust. Because of noise levels, I will be looking for an affordable 2.5" stainless steal exhaust. I'm waiting for the header so I can measure the pipe and what cat will fit that end (hopefully also 2.5"). So far I've learned I should purchase some stainless hardware, to be sure to use an anti-seize compound, new hangers, and that the heat shields will be tossed. Should I replace the sensors also? Now what I don't understand... My exhaust is like this (sort of) header with sensor (type?), then coffee can looking thing (supposed cat) with pipe out and second sensor (type?), then normal looking cat (supposed cat), then pipe with cat shape (supposed resonator), then kinky pipe, then muffler. Which sensors are what? Which parts are real converters with an actual catalyst inside? Please refer to coffee can cat, normal cat, and cat resonator for me to understand. So, since my header replaces the coffee can cat, and the sensors on both sides will be on the header, if there was a real cat there, won't the second sensor be sending screwy info to the ECU (or whatever it is)? Now, the cat looking cat probably is a real catalyst, so, if the coffee can one is gone, is a high flow cat still a good idea? If the third one is a resonator like I suspect, is that what many are calling the fake second cat? Are they not aware of the coffee can cat? Am I going to have to relocate a sensor or have my ECU reprogrammed to be sure my engine isn't running lean or rich? Is bolting on the exhaust enough to get horsepower or does it require real tuning? It's all metal, so aren't there ground wires somewhere? Finally, with engines vibrating and roads being bumpy, I image some level of movement or flexibility is needed in an exhaust system. How do I make sure that's achieved? After I've done all this, should I look at an aftermarket intake? Is there anything else I'm not thinking of?

[pr240sx]

all those cats make me confused!!

In a S14, the stock system is like:Exhaust manifoldO2 sensorCat (real)some sort of downpipeDummy catO2 sensorresonatormuffler

[mmm240]

um.... detonation = bad

exhaust velocity is good, you don't just want the exhaust banging around in there, it should flow smoothly