X-Force v others and header sizes.

[ducker85]

Be nice if the OP would reply with his thoughts.

Frustrating when people post a thread but never reply to it. I'm sure Their reading this after all

 

[Not_An_Abba_Fan]

No, you were saying driving style and I said driving style suited to car, not every condition the car will meet. Yes you can have an exhaust better suited to your car and driving style?! More torque near stock torque convertor stall speed versus mang.

The main reason people change the stock system on ANY car is predominately performance gains. Some just do it for sound, but in my 25 years of doing this, the majority want more go. With this in mind, they generally drive the car harder to take advantage of the exhaust, or more to the point to extract the most out of the improvements made by the exhaust upgrade. (pun intended). So by this reasoning, bigger is generally better.

Enough to know that's a simplistic explanation, and only one of several key forces affecting header design... of course I know how they work. The reason for exhaust gases "banking up" right back into the fricken intake is that too large an exhaust exit CSA doesn't work for stock CFM because the exit velocity is too slow.

Header companies have spent a lot of time, money and thought into header design. With the exception of a few copies, they are made that way for a reason. There is a reason the primary pipes are a certain diameter and length, where the collector is and how it is designed, even the length of the collector. In an ideal world, you would order an exhaust system tailored to your engine and how you drive it, but that would be cost prohibitive. So header manufacturers make their products to cover a broad range of circumstances to give a better increase over a larger cross section of consumers. Yes, exhaust design for the general public is a commercially based decision. In short, what is available, works.

Not noticeable at OP's stock engine exhaust CFM.

Without trying to sound like a smart arse, do you have evidence to back that up?

Yes, by its nature, but still flows adequately for stock engine's exhaust CFM.

And this is the statement that hits the nail on the head. Adequately. Yes, the stock system does indeed flow "adequately", but we don't want adequate, we want optimum. Fitting a better header and free flowing exhaust will inherently increase performance because is flows better than "adequate". You WILL increase velocity, so you WILL increase performance.

Possibly, not because of removing restriction to his current weak CFM but because it promotes flow thereby increased velocity (within the parameters of stock tune). Definitely not up scaling from 1 1/4 to 1 7/8, that's backward.

Just doing some calculations, the best header primary pipe for a 6.0L is indeed 1 7/8". That is what will provide a torque boost at around the engines peak torque RPM. If you are talking tuning an exhaust to an engines peak torque, then 1 7/8" is pretty much bang on.

Mate it's the headers which are suited to the stock tune! Putting on 1 7/8 is for a totally different state of tune!? Remove the torque ring at the flange (like I did) and see what happens.

Because you are removing a restriction....

Not quite like that with AFR feedback from the bungs, put the 1 7/8 on and see how a stock tune likes dem apples!!

Engine lights generally come on after fitting new headers because the coating on the headers contaminates the sensors.

Well yes, if it will even run untuned without limp mode, warning lights etc., and ECU compensates AFRs ideally for new bung placement then it may produce a smidge more with tits screaming... ie not the most practical improvement for the OP who is careful about cost, no scavenging gains nor torque gains in his stock CFM tune every day driving.

It will run quite well, just the annoying chimes.

 

[WazzaVN]

I got some hurricane 1 7/8's, 200c cats after I got my oxforce put on. Stock tune still.

Feels to me like it goes harder, especially after about 3500 rpm. Placebo? Might be, it feels faster to me though. However I've got no proof. If I could be bothered I'd bolt my stock manifolds and cats back on and do some 0 - 100's.

Anyway, fking love the sound they make! :thumbsup:

 

[PIR4TE]

The main reason people change the stock system on ANY car is predominately performance gains. Some just do it for sound, but in my 25 years of doing this, the majority want more go. With this in mind, they generally drive the car harder to take advantage of the exhaust, or more to the point to extract the most out of the improvements made by the exhaust upgrade. (pun intended). So by this reasoning, bigger is generally better.

Sure, I accept the logic of an upgrade path rationale, just saying the jump from stock to 1 7/8 is a doozy, and a 3" is purely for noise.

Header companies have spent a lot of time, money and thought into header design. With the exception of a few copies, they are made that way for a reason. There is a reason the primary pipes are a certain diameter and length, where the collector is and how it is designed, even the length of the collector. In an ideal world, you would order an exhaust system tailored to your engine and how you drive it, but that would be cost prohibitive. So header manufacturers make their products to cover a broad range of circumstances to give a better increase over a larger cross section of consumers. Yes, exhaust design for the general public is a commercially based decision. In short, what is available, works.

True. But 1 7/8 are not made for the stock engine with a stock tune, it works, but not anything like optimal for everyday driving.

Without trying to sound like a smart arse, do you have evidence to back that up?

What, the exhaust flow of his stock engine being between 126 and 136.5 CFM (divided by two for each cat/bank is less than 70 CFM per cat), much less than cat flow… or do you mean evidence that comparing flow from a low output engine like this has negligible effect re flow/restriction vs high output?

And this is the statement that hits the nail on the head. Adequately. Yes, the stock system does indeed flow "adequately", but we don't want adequate, we want optimum. Fitting a better header and free flowing exhaust will inherently increase performance because is flows better than "adequate". You WILL increase velocity, so you WILL increase performance.

Optimum is not two stages oversized.

Just doing some calculations, the best header primary pipe for a 6.0L is indeed 1 7/8". That is what will provide a torque boost at around the engines peak torque RPM. If you are talking tuning an exhaust to an engines peak torque, then 1 7/8" is pretty much bang on.

See results table in post #12, of stock 270kW L98 @ 5300 rpm 0.480 lift, showing exit speed in feet per second at given cross sectional areas of primary exhaust pipe.
These results are from calculations performed by Pipemax 3.95, where the complete intake system flow for this specific engine (right down to the valve stem diameter) to produce that output is 175 CFM actual.
If it were my car, with an output of 370kW @ 6100 0.525 lift, yes… 1 7/8 single primary pipe in 4-1 configuration is ideal for low to mid range TQ and HP, and possibly larger for mid range TQ to higher rpm HP. However in two-step equal length tri-y 1 3/4 gives better low to mid range TQ and HP.

Because you are removing a restriction….

Yes, if you look at it in terms of flow, but that is sometimes as in this case at the expense of exhaust port velocity, so no. If you remove the torque ring it makes more noise, slows down velocity resulting in reversion and less scavenging.

It’s there for a reason, have several pics and videos to prove said reversion effect on intake chamber / runners as I have spent a lot of time investigating improvements to strike a balance between exhaust system flow and header velocity within the physical confines.

 

[Jecs]

thread cleaned. keep it on track. im enjoying reading the discussion between naaf and pirate.

its relevant to OP and teaching me a thing or two about systems.

 

[BERNIE_VP]

I have been away and I got a bit of a shock with the amount of reply's to my OP lol. So sorry for the late response ducker85.

Frankly I'm impressed with the advice and appreciate it. PIR4TE and ABBA, holy smokes batman, very technical but excellent info guys it has helped a lot. I believe in doing things properly the first time. So I will probably end up going with my original plan of getting the cat back first. Then I will save for the CAI, Headers and Tune to get done at the same time and to get the most out of my car for the money.

Taking on board PIR4TE’s comments about being too large of a step up above standard header size and considering that I won’t be getting the headers until I can do the tune at the same time I’ll probably go the 1 7/8” 4 into 1 headers so I can be set up for further mods later on if I so wish to go down that path. Plus both you guys, ABBA and PIR4TE are running these in your no doubt weapons. And considering ebay prices on the 1 3/4” and 1 7/8” are not that different the cost isn’t really a factor. In saying all that though I wonder, what is the difference in mid range TQ between the two sizes? Or does this have any bearing upon being tuned?

I just lashed out and upgraded the speakers and subs so whilst the back seat was out I had BAMM and Dynamat put in on the parcel shelf and along the wall of the rear seat all the way down the floor plan. This was pre-empting the installation of the exhaust a little later in the year. I have noticed a definite reduction in exhaust noise coming through into the cabin (kinda but kinda ). So I reckon the 3” might be the way to go, however I might see if I can go listen to the sound of a car with one fitted to see if I like the sound (as discussed this being totally subjective and everything). I can live with a possible drop of economy without a tune until I can afford to get one done.

Now all I have to decide is if I go MAF or MAFLESS as it’ll depend on the CAI setup that I order lol. I know that this will be a bit off in the future for me at the moment but how much of a power difference post tuning am I looking at if I go MAFLESS over a MAF tune?

 

[07GTS]

in the VE either maf or mafless will be extremely close for end results, just depends on what u want from your tune and what mods u may be doing in the future...

 

[ducker85]

Then I will save for the CAI, Headers and Tune to get done at the same time and to get the most out of my car for the money.

I looking at if I go MAFLESS over a MAF tune?

I thought you implied that you will be doing a tune but wasn't 100% sure

There's really no point in going MAFless with a 6L or larger LS motor. There was gains to be had on 5.7Ls But the 6L got a huge MAF upgrade factory that flows faster then the manifold! Personally I'd get a VCM MAF cold air kit on and have engine tunes to suit once the headers n cats are done.

 

[BERNIE_VP]

There was a thread on here about exhaust myths.

The test car was a silver 6 speed 317 Senator. The tested every combo of exhaust and the 1 7/8 primary 4 into 1s with 3" 200cpi cats and 3" cat back made the most power before tuning.

They tested it with;
stock exhaust,
HSV front, 2 1/2 cat back
HSV headers, hi flow cats, 2 1/2 cat back
1 3/4 tri Ys hi flow cats 2 1/2 cat back
1 3/4 4 into 1s etc
And finally the 1 7/8 4 into 1s with cats n 3" back and it made the most power on a stock motor (no CAI, no tune)

The video was from a workshop called garage I think

Just watched this video and it was excellent. It helped a lot and explained pretty much everything PIR4TE and NAAF talked about in this thread. Thanks bud.

 

[BERNIE_VP]

I thought you implied that you will be doing a tune but wasn't 100% sure

I'm confused bud. Yeah the plan is to do a tune once the headers are fitted as it'll need to be done to combat any pesky engine lights from raising their heads. I believe this to be caused by moving the location of the Oxygen Sensors, but I dare say there are other reasons also. Tuning obviously also to get the engine to be most effective for the mods added.

I have heard good things on other threads about ORSSOM and Duspeed OTR's, both do MAF or MAFless. One bloke said the VCM ended up cracking and he ended up having to throw it away. Do you have one fitted?