F/I with Single pipe HKS, with or without Cats....??

R

raymond

Member
Location
Netherlands
Car
FX35 RWD
Hope i don't bother you guys but have so many questions and so little intell around here :embarrassed:
The turbonetics kit i bought is a NON-Catalystic version. So with test pipes or such....
I have the HKS Legamax exhaust wich i like and want to try to keep/use in this set-up.
Now i know a lot of you guys suggest a dual system when going F/I and maybe in time i know i need to get it but for now want to keep this :wub:
My thought is ( but please correct me if i'm wrong ) that the legamax will give more
resistance then a dual system.
Therefore it might be better to keep the cats out of the system.
OR is it better to keep them and just create a bit more resistance for lower torque...??

BUT i also read here on the forum that test pipes would create far more noise the oem Cats. AND i do need them for the yearly inspection. Now the last i can work a bit around but what you all suggest.But i do not want to go any louder then it is now already.

Going Cat or Non-Cat, cause i need to purchase new down-piping if i do :tup:
 
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Do not get rid of your cats...

Your ride will be twice or even 3 times louder with the FI and the test pipes.

If you want someone to hear just at idle and want to sound like an American NASCAR race car do it. If not go in another direction.

IMO I like my fx to sound a bit tamed and quiet at idle
 
Believe it or not Bert, a turbo suppresses exhaust sound some. Example: twin turbo'd FX with nothing but straight pipes after the turbos going out the back end would be quieter than the same FX with no turbos and just straight pipes coming from the headers and going out the back.

That being said, the cats would be a good idea, you'd get annoyed by the volume after a few months going without them.

When it's time for my TBE I will be going with high flow cats because the difference in power is not significant enough to me to warrant the extra noise. I had resonated test pipes on my FX for a long while and day 1 I didn't love them. I just thought the sound was eh, not better, not worse, just different. After a few more months it was annoying, and as the FX is now the exhaust is stock from the cats back, but aftermarket headers up front and I think that's leaps and bounds better than when the test pipes were on.
 
Cats won't give you low end torque. Everyone likes to think that cars need exhaust backpressure. Not really true, it's all about exhaust velocity. With N/A cars, an exhaust that's too big results in lower exhaust velocity, and lower power. But with F/I, it's all about removing resistance. No exhaust would make more power than an open downpipe with a turbo.

Having said that, I'd get some high flow cats or something. Test pipes are great and you'll make more power with them, but the sound is atrocious. Plus it gets old smelling gasoline fumes. Although the ability to shoot flames out of your exhaust is rather amusing. On my old Maxima with a custom turbo, and a VQ30DE, I went from a 2.5" exhaust to a 3" and gained ~20whp. When I swapped to a test pipe from my stock cat, I gained 12 whp. But the sound became much more buzzy and raspy.

It's true that turbos do cut down the exhaust noise. But it's dependent on the size of your turbo; the bigger the turbo, the less noise reduction. My wife had a turbo integra, we ran a smallish T3 on it. The car became much more quiet after the turbo setup even though we were running the same exhaust. On my Maxima with a much larger 60-1, the noise didn't really change much. I believe you plan to run a GT35R which is approximately the same size as a 60-1, so I wouldn't count on too much noise reduction.

raymond said:
Hope i don't bother you guys but have so many questions and so little intell around here :embarrassed:
The turbonetics kit i bought is a NON-Catalystic version. So with test pipes or such....
I have the HKS Legamax exhaust wich i like and want to try to keep/use in this set-up.
Now i know a lot of you guys suggest a dual system when going F/I and maybe in time i know i need to get it but for now want to keep this :wub:
My thought is ( but please correct me if i'm wrong ) that the legamax will give more
resistance then a dual system.
Therefore it might be better to keep the cats out of the system.
OR is it better to keep them and just create a bit more resistance for lower torque...??

BUT i also read here on the forum that test pipes would create far more noise the oem Cats. AND i do need them for the yearly inspection. Now the last i can work a bit around but what you all suggest.But i do not want to go any louder then it is now already.

Going Cat or Non-Cat, cause i need to purchase new down-piping if i do :tup:
Click to expand...
 
Yes, I definitely would not want to be running test pipes on the FX all day long. Would be fun to be able to just swap them in and out for the track though. The noise and gas fumes is something I would not like to have on a daily driver.
 
Thanks guys this helps me a lot....!!

Shadow, my HKS is 2.5" but love the sound of it. The guy before me made a bigger downpipe for the GT35 to fit he told me. 20Hp is quite some......but would my HKS hold up you think...??

Further i hear many stories about these High Flow cats.....Some say there aren't that better then the OEM onces and always the story of warranty and cracking of them......so in the end are they really that better then stocks....??
 
HumbertoCALI said:
Great to know that there are several experts to help you Raymond in your decision process.

Let us know what direction you take.

Mod on.
Click to expand...

Thanks Berto...!!

I'll make a topic of it when the "Projekt" starts. Hope it 'll be in the winter time,but need a lot off stuff wich i wanna get all first before i begin. So hope my wallet allows me to do this in the winter as well :wink:

Keep you all posted. But man what many questions pop up. To little intell here in the netherlands. Lot off people say this and others say that. Just want to be sure of it all before i begin.
 
Raymond, your HKS will hold up just fine and if you love the sound, there's no problem keeping it. But just know that you'd make more power with a bigger exhaust. Also, the sound will likely change after the turbo install.

I'd say that you really should consider HFC's for a turbo setup. The stock exhaust size is ~2.25"? I'm not really sure; so that's likely the size of your cat. The downpipe is going to be larger than that (you didn't list the size). So the stock cat will be a disruption to flow; going from a 2.5" or bigger downpipe to a ~2.25" cat isn't ideal. It will work of course, but it will cost power. If I were doing a turbo setup, I'd get whatever size HFC needed to match the rest of my exhaust system.
 
shadow191 said:
Raymond, your HKS will hold up just fine and if you love the sound, there's no problem keeping it. But just know that you'd make more power with a bigger exhaust. Also, the sound will likely change after the turbo install.

I'd say that you really should consider HFC's for a turbo setup. The stock exhaust size is ~2.25"? I'm not really sure; so that's likely the size of your cat. The downpipe is going to be larger than that (you didn't list the size). So the stock cat will be a disruption to flow; going from a 2.5" or bigger downpipe to a ~2.25" cat isn't ideal. It will work of course, but it will cost power. If I were doing a turbo setup, I'd get whatever size HFC needed to match the rest of my exhaust system.
Click to expand...

I'll look into that as i'm not sure myself. A collegue of mine has a few lying in his warehouse so i'll messure some of his first.
I know the pre-owner increased the size of the downpipe as well i thought for the GT35 turbo so need to see what is what.

Are there any HFC with a bigger diameter available in the market....??
 
I think most of the bolt on HFC's are 60mm; I know that's what the Berk is. If that's not enough, you could just have one custom made. You can buy the Carsound catalytic converters (same as magnaflow) in just about any diameter you want up to 4". Then have a shop fabricate the piping; any decent shop can do this as it's just welding flanges onto some piping and fitting an O2 sensor. That's basically all Berk and Kinetix and any other HFC maker is doing.

Random Technologies (they used to be the only HFC company around) is in my town and essentially all they do is take a universal core and weld flanges/bungs to it to make it fit a certain application. The universal cats can be found for as low as $40 (Random would of course charge $250 for each "custom application")

That's what I ended up doing on my old car. They didn't make a 3" HFC, so I just bought a 3" Carsound universal cat and had a friend's shop weld on flanges and the O2 bung. Total cost came in under half of what the off the shelf 2.5" HFC would have been and the actual cat was the same.


raymond said:
I'll look into that as i'm not sure myself. A collegue of mine has a few lying in his warehouse so i'll messure some of his first.
I know the pre-owner increased the size of the downpipe as well i thought for the GT35 turbo so need to see what is what.

Are there any HFC with a bigger diameter available in the market....??
Click to expand...
 
raymond said:
I'll look into that as i'm not sure myself. A collegue of mine has a few lying in his warehouse so i'll messure some of his first.
I know the pre-owner increased the size of the downpipe as well i thought for the GT35 turbo so need to see what is what.

Are there any HFC with a bigger diameter available in the market....??
Click to expand...

Ok update on this. I'm really going fast forward on this projekt right now. Bought a catalystic conversion pipe from turbonetics wich they offer.
I gues it is all 2.5 inch diameter. Has a straight single pipe toworths the back so a dual exhaust wouldn't be an option for me anyways.

Thing is the downpipe is still stock wich is also 2.5" i'm doubting if i need to change this to a bigger diameter. Thing is that to make that custom isn't easy as the downpipe also contains 2 connectors ( one from each header ).....

I'm deff running the GT35R, so the main question is will the 2.5" downpipe be enough to get rid of the fuses...........
 
I'm running a single 3" turbo-back exhaust with no cats. I don't know for sure, but I would think you would be ok with a single 2.5".

Yes it is louder - but the engine sounds have drastically changed now that I have built internals, the Pathfinder cooling mod, routed exhaust manifold in front of the firewall... there are a lot of factors contributing to noise and sound. I don't think removing the cats impacts the system that much in terms of volume.

Also - I really don't know too many custom turbo builds that keep the cats. It's just not done very often. I'm sure people do it, but to me it's one more thing that can go bad and need to be replaced.

To help with sound I would recommend isolating the exhaust with rubber mounts - no hard connections to the car. Also, insulation in the interior. Dynamat changed road noise for me in a very positive way. Doing the trunk, back seat and door panels will help the most.
 
jumbosrule said:
I'm running a single 3" turbo-back exhaust with no cats. I don't know for sure, but I would think you would be ok with a single 2.5".

Yes it is louder - but the engine sounds have drastically changed now that I have built internals, the Pathfinder cooling mod, routed exhaust manifold in front of the firewall... there are a lot of factors contributing to noise and sound. I don't think removing the cats impacts the system that much in terms of volume.

Also - I really don't know too many custom turbo builds that keep the cats. It's just not done very often. I'm sure people do it, but to me it's one more thing that can go bad and need to be replaced.

To help with sound I would recommend isolating the exhaust with rubber mounts - no hard connections to the car. Also, insulation in the interior. Dynamat changed road noise for me in a very positive way. Doing the trunk, back seat and door panels will help the most.
Click to expand...

What about the Downpipe.....you recan my 2.5" will do well also...??
I didn't bought the cat for noise issue honestly.But we have a yearly check up here in the netherlands and when my A/F is to high they won't give it a green light and i'm screwed and cannot drive the car anymore.
So that is a bit the case.
I've read up on your dynamat tread as well and amd thinking about it......another cost...that is what i ment in my Pm :wub:
 
The downpipe should ideally be as large as you can make it. You are routing exhaust gasses from all six cylinders through the turbo and downpipe, then splitting them to the cats. If you can stay with a 3" downpipe, that would be better.

The major cost of Dynamat will be in the installation. If you can do it yourself it is not very expensive - maybe $300 US for 6.6 square meters (72 sq ft) and that should cover almost the whole car.
 
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