Ben26
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Posts posted by Ben26
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Fuel system price drop - $200
Blitz front pipe - $50
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Nistune sold.
Price drop on fuel system to $300.
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- R32 gtr standard fuel pump, rail and injectors all working and in good condition. Just pulled off my gtr making 410rwhp with these items. $400 for all 3.
- Nistune chip on standard ecu, was running with standard fuel system, -5s etc making 410rwhp. $250
- Blitz front pipe, damaged. Still works fine but as you can see in the pictures there is a fairly large indent. $100
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1 minute ago, Dose Pipe Sutututu said:
I read all that and my conclusion is that a proper equal length twin scroll manifold, single turbo with a divided rear housing and a pair of external waste gates will be better.
haha agreed Dose Pipe!
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6 minutes ago, GTSBoy said:
Yes you are. The Hagen-Poiseville equation ignores entry and exit effects, etc, as I said before.
Pressure and pipe resistance are basically equivalent to voltage and electrical resistance. You get a reasonably simple relationship where the flow is directly proportional to the driving force and inversely proportional to the resistance. The H-P equation just wraps up the diameter to area relationship along with the other factors in one equation. It actually hides a lot of thinking. R^4 for example, is actually R^2, just mentioned twice. One of them is the pipe area considering its effect on the flow capacity (the bigger it is the more it will flow). The 8 comes from a number of divide by 2s. The L is only the bottom line of the equation because the longer the pipe, the higher the resistance to flow. But as I said, the pipe does not exist in isolation.
Ok yea, Im not sure on the entry and exit effects so I don't know how that would impact flow in a manifold. Yep that makes sense what you are saying, thanks for explaining!
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13 minutes ago, GTSBoy said:
Read my reply above, then stop. You are trying to work with just one element in the middle of a system. If you don't consider the whole system, you come to the wrong conclusions.
Pressure drop (loss of energy) in pipe flow stems from internal friction (viscous effects in the fluid flow) and from wall friction. Add fittings (bend, tees, orifices, changes in section, etc) and you get more of each of those. All governed by some ridiculous equations (Bernoullis, etc) that are effectively insoluble for real people with calculators. We don't even solve the real equations when we're doing CFD unless it's a simple problem and you have an enormous computer available. In CFD we use dramatically simplified models to do the turbulence calculations
I am considering the whole system. I understand what you are saying and I do not think that in the circumstance of an exhaust manifold, halving the length would double the flow rate, because the other variables in the equation of fluid flow are also changing. My point was that length does have an impact on fluid flow, and that if all else stays that same, there is an inverse relationship.
Yep I have done a little CFD and understand what you are saying!
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4 minutes ago, GTSBoy said:
Oh heck! I didn't even read that.
It's absolutely not true. Not even close. The length of the manifold runner contributes a TINY percentage of the total resistance to flow in the inlet-engine-exhaust-turbo-exhaust flow path. Even if you ignore everything upstream of the exhaust valve, the fraction of the resistance coming from the runner length is almost nil.
The only time that the quoted statement is remotely close to being true is when there is the pipe and nothing but the pipe. Like a pipe on the outlet of a fan. And even then it's not true, because there are fixed entry and exit pressure drops associated with any pipe. Time for a thought experiment. Blow through a 6" long drinking straw. Measure the flow. Now do it with a 12" long straw. You won't have half the flow rate.
Hey gtsboy. Im not talking about resistance, only what the hagen-poiseuille equation says regarding flow rate and length of a pipe.
Of course I was assuming all else is remaing constant, as I previously mentioned, so if there are other variables in the formula changing than that would affect the relationship between flow rate and length of the pipe.
Hmm thats an interesting example but something that to me cant be quantified without measurement in my mind.
Awesome that we can have this discussion!
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7 minutes ago, MBS206 said:
Yes, but pressure differential can be regarded as 0, there flow flow rate regarding pressure change = 0 change in the runner.
If the pressure differential was 0, wouldn't that also mean the flow rate is 0? That's what that equation says.
I'm happy to be wrong and learn something new, but going by that equation and researching pipe flow vs length, thats what im reading!
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I disagree mate, if you rearrange for Q
. Ie they are inversely proportional if all else stays the same.
Maybe I'm missing something but I just typed pipe length vs flow rate into google and this was the answer as well "Flow rate varies inversely to length, so if you double the length of the pipe while keeping the diameter constant, you'll get roughly half as much water through it per unit of time at constant pressure and temperature."
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This is the hagen-poiseuille equation. Am I interpreting wrong?
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23 minutes ago, Lithium said:
So what benefit do you think there may be in having a lower flow rate?
And yeah, very interesting stuff. Hoping we can try some stuff out with a design on a car we're doing, but the problem is there won't be any comparisons - it will just be part of an overall setup so hard to know what will contribute to what.
I don't think there would be a benefit from lower flow rate, although im not sure. However lengthening the runners may have a benefit via timing exhaust pulses and scavenging?
That is the trouble most of the time right, we try different modifications but dont always have the time or money to do direct back to back comparisons! It doesn't work comparing different cars with different setup, because there are far to many variables.
Ah well, hopefully one day someone will on here and post the results for all to see!
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Yep, understood and agreed with both of you, diameter of the runners has more influence on the pipe velocity, however flow rate varies dramatically with length of the pipe. Half the length of a pipe and expect double the flow rate.
All very interesting, now who has the budget and time to test all of this with different length runners and pipe diameters on the same turbo setup and see what happens!
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11 hours ago, Lithium said:
Hmmm not sure how the runner length would affect the turbocharger's efficient speed? Some of those other things I can see interacting with each other to a degree but compressor efficiency and optimal turbine speed I don't really see the runner length doing much.
I very much understand choosing things which deliver sound etc that you dig, though... like realistically nothing is ever going to be perfect performance wise so if there are things which are going to make it more fun to you then by all means. Does my head in when people try to justify their preferences arguing until they are blue in the face when "I just like it this way" is a perfectly acceptable reason for choosing their own mods
I am pretty sure I didn't say exclusively heat. A lot of it is theory but I feel there is quite a bit of reason to assume it has plausibility to it - not least that we have data already provided in this thread showing very carefully designed and nicely built manifolds with smooth curves and nice merges showing that it would be generous to say that it didn't gain... realistically that's probably charitable when I would guess in some instances like this if the "stock manifolds" result was the "after" in the comparison then it could have been arguably called a great success.
Like anything it will come down to various variables, what the target is etc. If I had seen these headers before this test with what I've seen now (excluding this test) before this test was done and asked what would perform better overall I wouldn't be confident in much other than the tubular ones would likely sound cooler....
Well the velocity of gas coming out of the manifold drives the turbine right, so you would think different velocities of air would have a different effect on the turbine in my mind?
Yea im not going to pretend that some modifications I make are for aesthetics or sound haha. Most are functional but hey the whole experience is not just about perfection otherwise we wouldn't own skylines!
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12 hours ago, GTSBoy said:
Heat loss can probably be more than sufficiently mitigated with ceramic coating though.
I think beyond that, the question is not really amenable to thought experiment. The variables are non-linear and it's not really possible to say which one has the bigger effect at the exact conditions in play. Would make a lovely episode of Engine Masters though.
Yea ok, interesting. Agreed, trialling a few different length runner designs and thicknesses with the same turbo setup would make an interesting comparison.
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Yes me too, its great learning from other people experiences and trying to put together your own understanding to then test in practise.
Ok, that definitely makes sense, but I wonder if the runner length determines the optimum speed the turbine will operate at, ie alter where the turbo chargers are at peak efficiency, and therefore tune the runners length depending on turbine size, rpm limits, cam sizes and boost pressure. This is something I would like to play with.
It makes sense what you are saying based on how a turbocharger works, and definitely when your only collecting three cylinders per turbocharger as opposed to 6 with a single turbo manifold.
A somewhat important part of the runner length / shape to me is also sound however, and I have found that the longer the runners, the more I like the sound. Maybe not something everyone cares about.
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Interesting, what did you find Lithium / what are your thoughts on twin tubular manifolds?
I recognise that modern singles with an equal length manifold will likely out perform 99% of twin setups, however I love the idea of twin manifolds for the racing nostalgia to group a etc
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Hey Mat,
Did you ever get a video or up the boost / make any more changes?
Cheers,
Ben
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Yep, on my car I also measured them at 210mm and my length I set at 217mm, the sweet point for me was between 215mm and 217mm so it seems as if we are on the same page even if setups are a little different. Thanks again gts boy.
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Nice, all great ideas !!! Thanks for everyone's input !!
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Ah yes I have also found decent bump steer measuring devices online for a few hundred dollars so I think for next time I will certainly either build a better jig with dial indicators or purchase an already made rig.
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Hi Andy I have adjustable camber arms as well, so I set the camber roughly where I wanted it to be to begin with, then started playing around with the traction arm length. I measured my stock ones at 210mm middle of bolt hole to middle, and I ended up with a traction arm length of 217mm so it seems we have a similar result. Yea Im aware that the combination of the two upper arms has an effect on the toe curve of the rear suspension, But I was just trying to get a ball park figure of what people were getting.
Yea that makes sense, so you think that if you get a ratio between the length of the standard traction arm and camber arm, and maintain that ratio, you would achieve a good result. I might have to test that, sounds like it might be a good starting point for future cars / set ups.
Thanks for your insight my friend.
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Ah ok, yep Im aware that you change toe using the tie rod but to me it looked as if adjusting that arm had little to no effect on the traction arm or upper camber arm. I will remember that for next time, thanks for your advice
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Hi Gts boy, thanks for your feedback, ok I can understand why the upper control arm length and different cars are going to affect the relationship with the traction arm, but why does the static toe influence toe under bump ? I guess my thinking is setting static toe doesnt really affect toe under bump, thats the traction rods job, whether you set you toe at 2mm out or 2mm in for the rear, doesnt it just matter than its not changing under bump ? Or am I looking at this the wrong way ?
Yep ok thats another neat method of measuring toe change, as you say and Carroll smith says in his books, we dont care how much bump steer we have quantitatively, only that we eliminate it !!
. Ie they are inversely proportional if all else stays the same.
R32 Gtr Standard Injectors, rail, fuel pump, ecu with nistune chip and blitz front pipe
in For Sale (Private Car Parts and Accessories)
Posted
Ok no problem. Feel free to PM me details.