Big whipple

[Empty Pockets]

Chevy has been able to get more efficiency out of a smaller unit. 1.7 vs. 2.3. Spun a lot faster. Curious how that translates to heat generation.

Me too.

It's a mystery to me how a smaller blower spun faster is somehow more efficient overall. 'Far back as I can remember, the 'engine gurus' have always opined that, generally speaking, for any given boost level desired, the blower that can produce the desired boost level at the lowest blower rpm will produce the most h.p. in part because it generates less heat (and shouldn't take as much engine h.p. to drive it).

But, that said, one can't argue with G.M.'s results.

'Too darned 'deep' for me...

 

[Fast Freddy]

Going bigger would be the wrong direction for a road racing track with heat concerns.

not to metion all that extra weight with a high center of gravity....

 

[SMOKDU]

Me too.

It's a mystery to me how a smaller blower spun faster is somehow more efficient overall. 'Far back as I can remember, the 'engine gurus' have always opined that, generally speaking, for any given boost level desired, the blower that can produce the desired boost level at the lowest blower rpm will produce the most h.p. in part because it generates less heat (and shouldn't take as much engine h.p. to drive it).

But, that said, one can't argue with G.M.'s results.

'Too darned 'deep' for me...

I have over the years changed blowers 5 times and every time I went faster with a bigger blower. The problem is with a bigger blower it takes more HP to turn and that means to make the same power you need more fuel and with our cars this is a problem because of the pumps we have. more power more fuel. bigger blower robs power so again to make more power the engine works harder to get fuel. Meth inj could help with some fuel issues but until we have bigger pumps I would pass. It is also harder on the crank snout and you will need double keyway or a pinned on balancer like I did.

 

[Indy GT]

Chevy has been able to get more efficiency out of a smaller unit. 1.7 vs. 2.3. Spun a lot faster. Curious how that translates to heat generation.

Gary, I would opine the heat generation from the higher compressor speed would place more emphasis on the intercooler to remove that additional heat-of-compression. If the 1.7 output pressure is higher the exit temperature has to be higher as well. Just no way around the Perfect Gas Laws. And I would be a little hesitant in saying the smaller 1.7 Chevy blower is more “efficient” than the 2.3 unit. Depends on how you define efficiency.

It's a mystery to me how a smaller blower spun faster is somehow more efficient overall. 'Far back as I can remember, the 'engine gurus' have always opined that, generally speaking, for any given boost level desired, the blower that can produce the desired boost level at the lowest blower rpm will produce the most h.p. in part because it generates less heat (and shouldn't take as much engine h.p. to drive it).
But, that said, one can't argue with G.M.'s results.
'Too darned 'deep' for me...

EP agree with your comments!

It is also harder on the crank snout and you will need double keyway or a pinned on balancer like I did.

Interesting that you bring this up. One of the engine design challenges the FGT 5.4 engine team identified was the original front snout of our crank needed to be strengthened from the machined shape they wanted to use. Various strengthening attributes were added to this region of the crankshaft (I am sure you know them well) to address the increased stress in this area. Increased strength was especially needed for crankshaft harmonics at the 4th engine order which is the dominant excitement mode for our crank. Swapping non OE elastomeric heavier/lighter harmonic dampers (in lieu of the viscous OE damper), additional key ways or holes in the shaft snout all change the vibrational characteristics of the shaft and could lead to snout fatigue failure. The design team spent quite a bit of development time in this area.

 

[SMOKDU]

additional key ways or holes in the shaft snout all change the vibrational characteristics of the shaft and could lead to snout fatigue failure. The design team spent quite a bit of development time in this area.

until

I used to run a stock GT40 create motor from ford racing and ran 18 psi with a 2,2 kbell for years and everyone told me I could not do that. Even ford racing. I did and proved them all wrong. I also ran 9,s with stock 8,8 4 lug and slicks for years (also could not be done) . Some things just work even though they are not suppose to. I drive my car and have these changes so ask me after I put them to the test on my combo. We have proved things work and not just said they would not.. if not you were right LOL

 

[Xcentric]

I define efficiency as getting the same boost out of less capacity. Might not be more efficient if it takes more hp to do that. That's what I don't know about the Chevy 1.7l Eaton.

I certainly never thought that way before about the dominant excitement mode for my crank, but I'm digging the harmonics. Thank you for that!

 

[Fubar]

I can't speak to engine harmonics, that topic is WAY over my head. However, I have looked at the efficiency curve of the roots style blower, trying to decide if bigger is better. There are trade-offs but the main reason to go bigger is a higher boost capacity but because all of the componets are bigger (therefor heavier), it takes more energy to spin. Therefor efficieny is lessened at lower power levels but as higher boosts make more energy, the effect is a net gain at the wheel. If you need 30-35lbs of boost, then the 4.5L is a good option. Obviously keeping in mind that compressing air generates heat, and compressing it more, makes more heat. If you just want cooler temps at the track, race with torque not HP (ie: lower RPMs).

 

[Indy GT]

I can't speak to engine harmonics, that topic is WAY over my head.

LOL. That’s OK Mark it is a rather esoteric topic. Vibrational dynamics either harmonic (where various modes combine at a given rpm/frequency) or non-harmonic where they occur without superposition with other modes is quite complicated. But very important for engine life. All the OEMs have engine dynamic programs based or tweaked by testing experience to design reliable rotating systems which will minimize NHV and provide target life goals. Safety margins (but often not that much) are built into the programs which some post-sale modifiers use up with “their improvements” to the OE design. The days of just “building and busting” engines trying different designs to see what works and what does not is an artifact of the past. Engine systems are just too costly to fund an engine development program based on this philosophy. Sadly, let the individual owner pay for his misunderstanding of engine design aspects.

However, I have looked at the efficiency curve of the roots style blower, trying to decide if bigger is better. There are trade-offs but the main reason to go bigger is a higher boost capacity but because all of the componets are bigger (therefor heavier), it takes more energy to spin. Therefor efficieny is lessened at lower power levels but as higher boosts make more energy, the effect is a net gain at the wheel. If you need 30-35lbs of boost, then the 4.5L is a good option. Obviously keeping in mind that compressing air generates heat, and compressing it more, makes more heat. If you just want cooler temps at the track, race with torque not HP (ie: lower RPMs).

All true, and the Ford supercharged 5.4L was very well matched for the design cycle of our FGT. A BIG note of gratitude goes out to John Colletti at Ford who lobbied successfully for this powertrain option in our cars. Other configurations were considered. But it appears the OE’s at least at Ford recognize there is a thermal and weight penalty with supercharging and maybe normally aspirated engines are more favorable in a track environment. Witness the successful Mustang Boss 5.0 Coyote/Roadrunner engines and the yet to be revealed Mustang GT350 which is rumored to also have a normally aspirated engine. Each design has attributes and negatives which much be weighed.

 

[Cobrar]

LOL. That’s OK Mark it is a rather esoteric topic. Vibrational dynamics either harmonic (where various modes combine at a given rpm/frequency) or non-harmonic where they occur without superposition with other modes is quite complicated. But very important for engine life. All the OEMs have engine dynamic programs based or tweaked by testing experience to design reliable rotating systems which will minimize NHV and provide target life goals. Safety margins (but often not that much) are built into the programs which some post-sale modifiers use up with “their improvements” to the OE design. The days of just “building and busting” engines trying different designs to see what works and what does not is an artifact of the past. Engine systems are just too costly to fund an engine development program based on this philosophy. Sadly, let the individual owner pay for his misunderstanding of engine design aspects.



All true, and the Ford supercharged 5.4L was very well matched for the design cycle of our FGT. A BIG note of gratitude goes out to John Colletti at Ford who lobbied successfully for this powertrain option in our cars. Other configurations were considered. But it appears the OE’s at least at Ford recognize there is a thermal and weight penalty with supercharging and maybe normally aspirated engines are more favorable in a track environment. Witness the successful Mustang Boss 5.0 Coyote/Roadrunner engines and the yet to be revealed Mustang GT350 which is rumored to also have a normally aspirated engine. Each design has attributes and negatives which much be weighed.

Nicely done - Bill!

 

[PeteK]

I define efficiency as getting the same boost out of less capacity. Might not be more efficient if it takes more hp to do that. That's what I don't know about the Chevy 1.7l Eaton.

I certainly never thought that way before about the dominant excitement mode for my crank, but I'm digging the harmonics. Thank you for that!

Well, as the say, "it's complicated." Let's break this down. Let's define the supercharger efficiency as the amount of boost output, divided by the HP input. Thus, more HP input for the same amount of boost is less efficient.
As the RPM of the supercharger increases, the pumping losses increase, due to just thrashing the air around as it goes through the blower. So, one might think that a larger blower, operating at lower RPM (at the same boost), would be more efficient. And it is, to a point. But, if you spin the blower too slowly, you lose boost due to leakage around the rotors. Even though we call this a "positive displacement pump" (unlike turbochargers), the rotors don't seal perfectly. There is some gap between the rotors and the housing, and the slower the RPM and the higher the boost, the more air squeezes through the gap, reducing the boost and thus efficiency; and larger blowers have more total gap than smaller ones; and of course, they weigh more and take up more space.

So, the efficiency of the supercharger depends on RPM and boost. I went to Whipple's web site to try to find the efficiency curves, but they weren't posted publicly, otherwise I'd put the link here. But, what you should take away from this discussion is that choosing a blower is, like almost everything else about engineering, a process of choosing trade-offs. For the Chevy application, that 1.7 l. blower operating at higher blower RPM might be the most efficient way to go. From an efficiency point of view, a smaller blower might even be more "efficient" for our FGTs, but it won't produce as much torque and power at WOT and high engine RPM. And I sorta suspect that the vast majority of us are not too concerned about EPA efficiency.:rofl

Adiabatic heating: This is the heat of compressing the air. The heating of the air as it passes through the supercharger is almost entirely due to the compression in the supercharger, and not to the waste energy of thrashing the air through the supercharger. The size of the supercharger makes little difference in this heat increase, but higher RPM has a small influence.

 

[Indy GT]

Thanks for weighing in Pete.

Nicely done!

 

[Hollowpockets]

Id be interested to hear your thoughts on my example, I found that while out on circuit here in the UK in July my car was getting too hot after 5/6 laps due to the heat from the supercharger and would flash a warning at me, so a cool down lap later and its good to go for another 4/5 laps.

I already have SPAL cooling fans and extra ducts on my front bumper to get more air over the rad but I have just ordered an upgrade to go from the 3.4 whipple to the 4.0 and the fuel booster pump, I am concerned that it may create more heat but as I'm only doing the 4" pulley to go from 720hp to 780hp (UK Horses) with boost going from roughly 16psi to 18psi, the charger body itself is the same size and it will have a larger volume of air flowing through, I am thinking that it may actually run slightly cooler but not sure.

I presume getting weight out of the car would be the best way to reduce load and heat but not sure what could be removed from it

G

 

[fjpikul]

The GTGuys offer a different radiator direct replacement if I remember correctly. The most usual cause is in air in the coolant system. The suction apparatus does very well in this instance. A Search will find the links to overheating and limp mode.