No Cat=Sluggish Takeoff?

[TooFastTooG]

Hey guys, just had a question for ya.

I recently drove my friends girlfriends car which was a 97 GST, completely stock. The car felt so much better when leaving from a stop. Now im not talking wot, just normal driving. Basically, it felt alot more "torquey".

Now my 95 GSX which is lightly modded:K&N Air Filter, DejonTool MBC, Autometer boost and A/F gauge, 2.5 Exhaust, Dejon Tool UICP, 1st Gen BOV, Aluminum Intake Pipe, and NO CAT.
My car feels like I need it give it alot more gas to take off and it just feels "sluggish". It feels great top end though. The exhaust was done before I bought the car, and I think it was done cheap, becuase after my downpipe its all 2.5" and no cat.

So to sum it up im thinking that this is mainly becuase I have no cat? I searched and people have problems in midrange but I just want to know if this also effects you from a complete stop too. Thanks in advance!

Edit: I did do a boost leak test a while ago and I found a leak in the biss screw and my stock intercooler piping, both fixed.

 

[Sivad87]

This is very reasonable. However, when I had my civic I know there was a noticeable power difference in the low end between having an exhaust and running an open header with nothing else done to the car. Does anyone else have any TECHNICAL insight?

dont worry i come from an econo box NA background also

the biggest thing i see on lower hp NA engines (and most likely hgh output ones also) is not really the backpressure but the flow.

think of it this way if you run open header once the exhaust gets out of the header what happens to it? it decides to eo everywhere! causing, you guessed it turbulence just outside the header, which can in turn cause backpressure, and poor flow on the header, causing performance problems.

now that is why after a certain rpm usually the air outside the header starts to resemble a flow which is why you get the better high end.

that is why a nice 3" exhaust helps out in all areas, because it keeps a constant flow at lower rpm, and has enough volume to support the engine at WOT.

Make sense?


also again, take my word as you wish, im not neccisarily right or wrong.

 

[4BangR-x]

I think we can draw the conclusion that in general, turbo or n/a, will gain top end and lose bottom end from no cat, based on everything else being equal.

About 2 strokes, yes if they dont have enough backpressure the motor will suck fuel out of the intake stroke.

 

[PieEyedPiper]

I think we can draw the conclusion that in general, turbo or n/a, will gain top end and lose bottom end from no cat, based on everything else being equal.

I don't think we can reasonabley draw that conclusion based on the information at hand.

 

[RyanJ]

I'm sorry to upset all you "back pressure" guys out there but back pressure does not help at the low end. it never helps as a matter of fact. It's somehting else called scavenging, its like drafting for your exhaust. Read this http://dsmtuners.com/forums/showthread.php?t=168578


Edit: fixed spelling mistake

 

[ilikespeeding]

There is a reason for backpressure in NA 4 strokes. When exhaust leaves a chamber, it is pushed. Behind this cloud of exhuast there is a vaccumm. When other exhaust 'drafts' behind this vaccumm, its not as hard for the engine to push the exhaust. Which is why there is a limit on piping size. No cat would not hurt the turbo cars and the only thing I can think of is checking the front 02 sensor.


No question about it tho, the GSX should feel more torquy due to more traction on from a stop. The higher horsepower FWD should unload traction on a launch and a GSX should hold therefore more power to the wheels. During highway acceleration tho, the GST should feel a bit better. Since you dont have any fuel mods but some intake mods you might be running a little lean...but IMO not enough to cause all of that. Try compression testing. What are the odo readouts on the cars as well? How much boost are you getting?

 

[TooFastTooG]

Wow, im really suprised at how this thread is going back and forth.

Like I posted earlier today, I did put on a high flow cat today. And I very pleased with the difference, and just EXACTLY like DSMCrazy3 said above, it feels alot better now from a stop, but I do notice a little, and I mean a little hesitation now in high rpms. Not nearly enough though to make me want to take it off.

And to answer your questions ilikespeeding, the gst had 90,000 miles and I have 120,000. The gst was all stock, and my gsx is running 15 psi. I have not done a compression test, but plan to soon. But like I said earlier, I think my issue has been solved by the cat.

 

[RedTurboEclipse]

I ran my car with no cat and another time with my 3" HF cat. I didn't feel any difference in the low end, but having no cat was noticibly faster.

 

[ilikespeeding]

Id suggest getting a datalogger and AFC. Tuning is big around here and slapping bolt ons only flys but for so long before you gotta get your hands really dirty.

Oh, check your plugs and think about running some sea foam. Any knock?

 

[TooFastTooG]

Id suggest getting a datalogger and AFC. Tuning is big around here and slapping bolt ons only flys but for so long before you gotta get your hands really dirty.

Oh, check your plugs and think about running some sea foam. Any knock?

A datalogger is something I need to get, consider im planning on a turbo upgrade soon.

This may sound stupid but i dont have a clue on how to use it, or what i need to get, any links to help me out? Or advice?

 

[ilikespeeding]

A datalogger is something I need to get, consider im planning on a turbo upgrade soon.

This may sound stupid but i dont have a clue on how to use it, or what i need to get, any links to help me out? Or advice?

Plug it into the OBDII port usually.

http://pocketlogger.com/instructions/install.html

That'll give you a readout on a palm.

 

[Sivad87]

There is a reason for backpressure in NA 4 strokes. When exhaust leaves a chamber, it is pushed. Behind this cloud of exhuast there is a vaccumm. When other exhaust 'drafts' behind this vaccumm, its not as hard for the engine to push the exhaust. Which is why there is a limit on piping size. No cat would not hurt the turbo cars and the only thing I can think of is checking the front 02 sensor.


No question about it tho, the GSX should feel more torquy due to more traction on from a stop. The higher horsepower FWD should unload traction on a launch and a GSX should hold therefore more power to the wheels. During highway acceleration tho, the GST should feel a bit better. Since you dont have any fuel mods but some intake mods you might be running a little lean...but IMO not enough to cause all of that. Try compression testing. What are the odo readouts on the cars as well? How much boost are you getting?

actually no you dont need backpressure. what you are talking about is scavenging, which is a result of high velocity gasses. this is a direct result of pipe sizes, not backpressure. backpressure is a side effect from smaller pipe and other restrictions.

If you take the time to read the thread posted above it explains everything i have been saying but in more detail.

also this is starting to be like beating a dead horse. can we like move along, it seems as though the thread starter got his questions answered allready.

 

[Spoolin4Ever]

AWD cars are known to "Bog" when starting from a stop because all 4 wheels provide so much traction, the engine works harder at first (so does the transmission). It's just when you first start letting out the clutch (unless you launch it or ride/slip the clutch alot, and even when you slip it it still bogs a touch). I mean mods help, but this is just a tendancy of AWD in general.

And this is all AWD cars, not just DSM's. But then the extra traction makes up for it once you get spooled.

I know you got a cat and it helped, but still...something to keep in mind.

Also; keep in mind just general maintenance and other stuff that might need done, as a silly example: My car seemed kinda slow, I hadn't checked the air in my tires in a long time, I only had 20 lbs. of air in the front. I aired them up and it was quite a bit faster, especially from a stop. (Yeah I know that's lame I let them get that low)...

 

[No_Skillz]

Read this http://dsmtuners.com/forums/showthread.php?t=168578

That writeup is da bomb.

 

[jongreene]

Agreed, basically puts everyone who says backpressure is good for turbo cars in their place...in a professional manner

 

[No_Skillz]

Also puts everyone who says backpressure is good for n/a cars in their place.