Larger Turbo or 3" Cat Back?
04-21-2002, 08:06 PM
#16
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[quote]Originally posted by Luke:
<strong>
My dp was round (perfectly) inside
and in diameter of the inner tube was still larger than the diameter of the turbine wheel.
I dont think you wouldn't want the cross over pipe a larger diam. than the dp either ?!?! If you attack it with a perspective on diffusion it makes more sense. High pressure diffuses to low pressure areas.</strong><hr></blockquote>
Luke, if your exaust is stock, it shouldn't be round. It's made oval for more ground clearence.
Also, you want your downpipe slightly larger than the turbine, it's the cross over that needs to be relatively small to keep exaust velocity high.
Ahmet
<strong>
My dp was round (perfectly) inside
and in diameter of the inner tube was still larger than the diameter of the turbine wheel.I dont think you wouldn't want the cross over pipe a larger diam. than the dp either ?!?!
If you attack it with a perspective on diffusion it makes more sense. High pressure diffuses to low pressure areas.</strong><hr></blockquote>Luke, if your exaust is stock, it shouldn't be round. It's made oval for more ground clearence.
Also, you want your downpipe slightly larger than the turbine, it's the cross over that needs to be relatively small to keep exaust velocity high.
Ahmet
04-21-2002, 08:08 PM
#17
Race Director
"Something like a ball-bearing turbo can achieve both improvements, "
Actually, the benefits of a ball-bearing turbo is only in reducing turbo-lag not boost-lag or flow-capacity. Turbo-lag is when you're cruising along on the freeway and then punch the throttle. The time it takes to develop 0-boost to say... 15psi@3000 (or 10psi@2500rpm, depending upon your speed), is where the ball-bearing turbo makes a difference. This time-savings is fractions of a second.
Now boost-lag, or the shape of the boost-curve as well as minimum boost levels at low-RPM, along with ultimate flow-capacity at high-RPM is only dictated by the relationship between the turbine and compressor sizes and their housings (A/R ratios). A ball-bearing center has no 'bearing' on this at all.
That's why no one can claim (with dyno testing) any HP advantages from a ball-bearing turbo given the same compressor and turbine sections.
Actually, the benefits of a ball-bearing turbo is only in reducing turbo-lag not boost-lag or flow-capacity. Turbo-lag is when you're cruising along on the freeway and then punch the throttle. The time it takes to develop 0-boost to say... 15psi@3000 (or 10psi@2500rpm, depending upon your speed), is where the ball-bearing turbo makes a difference. This time-savings is fractions of a second.
Now boost-lag, or the shape of the boost-curve as well as minimum boost levels at low-RPM, along with ultimate flow-capacity at high-RPM is only dictated by the relationship between the turbine and compressor sizes and their housings (A/R ratios). A ball-bearing center has no 'bearing' on this at all.
That's why no one can claim (with dyno testing) any HP advantages from a ball-bearing turbo given the same compressor and turbine sections.
04-21-2002, 08:16 PM
#18
Nordschleife Master
[quote]Originally posted by over1g:
<strong>
Luke, if your exaust is stock, it shouldn't be round. It's made oval for more ground clearence.
Also, you want your downpipe slightly larger than the turbine, it's the cross over that needs to be relatively small to keep exaust velocity high.
Ahmet</strong><hr></blockquote>
I thought you were saying the dp is oval. and no my exhaust is not stock.
I picked up a stage one SFR (turbo netics)
54mm comp wheel, stage 3 trim (with the stage 3 trim, the dp's ID is still larger than that of the turbine) I'm sure that 9 in piping peice will suffice. $300 is not worth 2 cfm.
car shoudl be running by wednesday.
Just had help (lots) in bolting up the new tranny
<strong>
Luke, if your exaust is stock, it shouldn't be round. It's made oval for more ground clearence.
Also, you want your downpipe slightly larger than the turbine, it's the cross over that needs to be relatively small to keep exaust velocity high.
Ahmet</strong><hr></blockquote>
I thought you were saying the dp is oval. and no my exhaust is not stock.
I picked up a stage one SFR (turbo netics)
54mm comp wheel, stage 3 trim (with the stage 3 trim, the dp's ID is still larger than that of the turbine) I'm sure that 9 in piping peice will suffice. $300 is not worth 2 cfm.
car shoudl be running by wednesday.
Just had help (lots) in bolting up the new tranny
04-21-2002, 08:29 PM
#19
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I had a TO4E 46 trim and the transient response was much slower than a K26/6. It'd be interesting to see a time-to-boost comparison.
Yeah - I'd see full boost by 3000 rpm but the boost response was significantly worse than the K26. Food for thought.
Yeah - I'd see full boost by 3000 rpm but the boost response was significantly worse than the K26. Food for thought.
04-22-2002, 10:29 PM
#23
Race Director
[quote]Originally posted by Danno:
<strong>In general, yes turbo-lag and boost-lag are related to turbo-size and flow capacity. But we're also comparing 30-year old KKK technology vs. the latest developements by Garrett and IHI. The compressor wheels are lighter despite being larger and they are aerodynamically more efficient as well.
So you don't necessarily have to experience the age-old compromizes of lag vs. flow. Perhaps if you are comparing the same model turbo, then it would be an easy thing to show.</strong><hr></blockquote>
Exactly right Danno. Matching wheels and housings properly (requires a turbo map and some math) has more to do with making power and reducing lag than the mass of the wheels.
<strong>In general, yes turbo-lag and boost-lag are related to turbo-size and flow capacity. But we're also comparing 30-year old KKK technology vs. the latest developements by Garrett and IHI. The compressor wheels are lighter despite being larger and they are aerodynamically more efficient as well.
So you don't necessarily have to experience the age-old compromizes of lag vs. flow. Perhaps if you are comparing the same model turbo, then it would be an easy thing to show.</strong><hr></blockquote>
Exactly right Danno. Matching wheels and housings properly (requires a turbo map and some math) has more to do with making power and reducing lag than the mass of the wheels.
04-22-2002, 11:27 PM
#24
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FWIW Third, my buddy and I have identical cars and he has 3 inch all the way through.
His turbo hits HARD very early and doesn't run out of steam. Underhood temps are a lot lower on his car too, because it gets rid of the heat.
The dp made a lot of difference, the cross over I wouldn't mess with.
Sounds like the consensus is that bigger IS better for a turbo.
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
His turbo hits HARD very early and doesn't run out of steam. Underhood temps are a lot lower on his car too, because it gets rid of the heat.
The dp made a lot of difference, the cross over I wouldn't mess with.
Sounds like the consensus is that bigger IS better for a turbo.
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
04-22-2002, 11:44 PM
#25
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[quote]Originally posted by Geo:
<strong>You cannot go too large for a turbo exhaust. This is straight from a good friend of mine who is an engineer for Garrett.</strong><hr></blockquote>
Just so that we're clear, my comments about sizing are for the cross over pipe(s). Heads to the turbo exaust pipe(s) sizing is critical, after the turbo is where 'you cannot go too large'.
Rothmans, I have not upgraded my turbo but I did go with a 3 inch exaust from the turbo back... This made a very big improvement in response, reduced lag, and helped with the boost fall-off. With the stock exaust the turbo ran out of steam at higher rpms, more noticably in higher gears. Now it only seems to fall off slightly if at all @ ~7k rpm(now redlines @7250rpm, after chips). It is a bit loud for city driving for my taste though, so I'm going to put a muffler on it soon, we'll see how that effects the performance...
Ahmet
<strong>You cannot go too large for a turbo exhaust. This is straight from a good friend of mine who is an engineer for Garrett.</strong><hr></blockquote>
Just so that we're clear, my comments about sizing are for the cross over pipe(s). Heads to the turbo exaust pipe(s) sizing is critical, after the turbo is where 'you cannot go too large'.
Rothmans, I have not upgraded my turbo but I did go with a 3 inch exaust from the turbo back... This made a very big improvement in response, reduced lag, and helped with the boost fall-off. With the stock exaust the turbo ran out of steam at higher rpms, more noticably in higher gears. Now it only seems to fall off slightly if at all @ ~7k rpm(now redlines @7250rpm, after chips). It is a bit loud for city driving for my taste though, so I'm going to put a muffler on it soon, we'll see how that effects the performance...
Ahmet
