The Only 3300 lb. Buick V6 in the 8s using...

[Street Lethal]

A given compressor will definitely be more efficient when there is X amount of boost rather than Y amount of boost. That's why that number on the gauge does truly mean something. At the same time time, two turbos that both make the same X amount of boost on a given engine can make much different power numbers, even if the inlet temp is similar. In my previous example, both the GT42-76 and the S88 that replaced it were making around 20psi on that good 370. The power difference was HUGE. As Dusty mentioned, some of that may well be due to back pressure, but I know for a fact some of it was due to compressor size. When I picked that turbo for the 347, it was clear we'd be riding the edge of the map....

To be honest here, we are essentially saying the same thing, although your referring to the boost pressure as being the integral part of the compressor map, whereas I am referring to the airflow (and the velocity of that airflow). It is essentially the relationship between the pressure ratio and mass flow rate that gives us our operating range, but when (if) being fully maximized throughout the RPM band, the larger one will always make more power because it can follow through up to, and a tad beyond, the RPM scope. It soon becomes a matter of either building the engine around the turbo, or selecting a more suited turbo for a particular engine application. Again, in the perfect world, all turbo's wouldn't lag, and would spool instantaneously, and if that were the case, then it is obvious for us to build the engine around the largest turbo that is able follow through up to, and a little beyond, the RPM scope, as that will fully maximize the air charge, while keeping it most efficient. If your focus is on selecting a turbo based on a particular application, then I can see your argument of which turbo would be better, including a smaller turbo. But in Don's case, although he may be able to run a similar number with less turbo as you are suggesting, that would just mean that there is more in his existing setup....

This is not exactly true. If you run a turbo outside of it's range on a compressor map (bigger or smaller) you can have issues with surge or low power....

This is why it is imperative to build an engine around the turbo, and not select a turbo off of the shelf based on an approximation of horsepower. Surging happens with too small a volume flow, and too high of boost pressure, as the flow cannot adhere to the suction of the compressor blades, interrupting its' discharge. This is where the velocity, rather the speed of the volume becomes a major factor in reducing surge...

Also there is a huge difference in rotating mass with superchargers, and especially with the big prochargers. I know of two different cars that were quicker with the F2 than the F3 at similar boost levels....some of the reason may be rotating mass, some of the reason may be the compressor itself. Both were small block cars....a large big block probably would have acted differently.

It is hard to say without knowing the internals of both engines, but if both engines were identical, then the larger supercharger would be able to flow the same amount of cfm much earlier in the RPM band, then carry through well beyond afterward, using slightly less boost pressure than the smaller supercharger. Larger compressors will always flow more cfm than a smaller compressor at the same boost pressure because the charge is more dense, and unlike turbo's, the supercharger's are already spooled at idle, so it becomes more of a matter of controlling volume with a wastegate than it is controlling boost pressure, because boost pressure can be reduced at any time, with volume increasing at that very same time....

 

[Dusty Bradford]

Also there is a huge difference in rotating mass with superchargers, and especially with the big prochargers. I know of two different cars that were quicker with the F2 than the F3 at similar boost levels....some of the reason may be rotating mass, some of the reason may be the compressor itself. Both were small block cars....a large big block probably would have acted differently.

I see the same thing here, very often. The compressor wheels are huge. An F3 can be anywhere from 123mm to 139mm. A small block will run faster with a 123mm than it will with a 139mm because of parasitic drag. The 139mm is just too big for a small block. Also the larger the engine, the more hp the car will put to the tires with the same 139mm. A 565ci with a 139 can not compete with a 706ci with a 139. That's why it's so hard to keep the blower rules fair for everyone. They aren't like a turbo engine where a small block and big block can make near the same power with 88's.

 

[Dusty Bradford]

I was told directly from an Honeywell engineer that came to our facility for testing about 7 years ago that you would always be better with one big turbo than two small turbos. His reasoning was that you double the ineffiencintcies(don't know the spelling) of the system. I don't have any experience to agree or dissagree but it made sense at the time. Turbo technology has changed over the years so this may be outdated.

Allan G.

It's hard to say what he was testing. But for drag racing a set of twins will always make more power. The key is sizing everything properly to get the car to accelerate. If the twins are too large, you need alot of rpm to get them spooled and accelerating the car. That high launch rpm can lead to traction issues..etc. There are so many variable into putting it all together to run fast on the track that you could never cover them all in these discussions.

 

[Street Lethal]

These turbo discussions remind me a lot of camshaft discussions, as we all try to tailor the correct map for a specific application. But then variable valve timing was introduced, and then perfected, changing how we look at camshaft specifications entirely. The same can be said with turbo chargers of course, but has anyone here actually played with a variable turbine geometry turbo like a Holset found on a diesel...?

 

[Alky V6]

The argument of twins vs single becomes much more involved where nitrous is in the picture.

 

[Fryguy]

If you compare two turbo's with one equally matched turbo (exhaust housing, flow ability, MAP, etc.), run two 2 1/2" downpipes on the twins, and a 5" downpipe on the single, how exactly do the twins make more peak power at a given RPM (note that twins will obviously make more power under the curve)? Please explain, as I am very curious....

Just one more small point.....if you do the math, dual 2.5" pipes flow considerably less than one 5" pipe. That's why when we wanted dual exhaust on one of my current cars, I split the 5" down-pipe into dual 4" to maintain flow.

 

[Alky V6]

Here is the S510 compressor map.
You can see that I'm running smack dab in the middle of the 76% eff island at 3.0 PR and 1200 hp. At 4.0 PR, I would still be at 70% eff.

 

[Fryguy]

These turbo discussions remind me a lot of camshaft discussions, as we all try to tailor the correct map for a specific application. But then variable valve timing was introduced, and then perfected, changing how we look at camshaft specifications entirely. The same can be said with turbo chargers of course, but has anyone here actually played with a variable turbine geometry turbo like a Holset found on a diesel...?

The drag racing application simplifies things quite a bit, because we can use the trans brake and other things to bring up the turbo, and with the proper torque converter we can use a narrow RPM range to get the car down the track. For an OEM, all that stuff gets pretty crazy. It kinda makes my head hurt.

 

[Fryguy]

Here is the S510 compressor map.
You can see that I'm running smack dab in the middle of the 76% eff island at 3.0 PR and 1200 hp. At 4.0 PR, I would still be at 70% eff.

How much air are you saying your 224 CID engine with mild heads is consuming??

 

[Fryguy]

Here is a consumption chart for a stock V6 buick:

231 air consumption

 

[Alky V6]

How much air are you saying your 224 CID engine with mild heads is consuming??

If we look at what's already been discussed in this thread, my bhp calculates out to be a minimum of 1180, up to this point in time. I know some will calculate 10 hp per 1 lbs/min. Some will use a number a little over 10.

 

[Alky V6]

Here is a consumption chart for a stock V6 buick:

231 air consumption

You're link was blocked. Something is wrong with it.

 

[Street Lethal]

The drag racing application simplifies things quite a bit, because we can use the trans brake and other things to bring up the turbo, and with the proper torque converter we can use a narrow RPM range to get the car down the track. For an OEM, all that stuff gets pretty crazy. It kinda makes my head hurt...

The tuning aspect is what makes me hesitate with a VGT turbo, although there is obviously software out there that simplifies it tremendously, like the new Holley HP Dominator system. Always wanted to explore the GM Northstar w/VVT engine running a VGT turbo, w/fueling controlled with the Holley system, and just shoehorn it all into an '81 Regal, but I digress...

 

[Dusty Bradford]

The argument of twins vs single becomes much more involved where nitrous is in the picture.

For someone racing themselves nitrous is an option. For class racers, it's not even in the picture.

 

[TURNEROFFROAD]

How much air are you saying your 224 CID engine with mild heads is consuming??

a quick question, is this a generic chart for 231 cubes or would a series II (heads are better stock than the older heads) flow better I was just kinda curious

 

[Fryguy]

It's just a generic chart. They have a few more for some of the popular engines. Obviously these are rough guesses, as heads/cams/etc can change the numbers:

Turbos, Turbo Selection 101

 

[Alky V6]

For someone racing themselves nitrous is an option. For class racers, it's not even in the picture.

I race plenty of V8s during my testing at the track. They know they're in for a whoopin' when I come up against them. No rules.

 

[Alky V6]

It's just a generic chart. They have a few more for some of the popular engines. Obviously these are rough guesses, as heads/cams/etc can change the numbers:

Turbos, Turbo Selection 101

My particular situation demanded more creativity when I picked out a turbo.

 

[Fryguy]

My particular situation demanded more creativity when I picked out a turbo.

I know it, you were going for the slowest 91mm turbocharged and nitrous oxide injected vehicle on the planet. I can't find any math for that.

 

[Alky V6]

I know it, you were going for the slowest 91mm turbocharged and nitrous oxide injected vehicle on the planet. I can't find any math for that.

How much did you guess my heads should have flowed using your chart?