Whipple Gen5: Why 3/4 rotor pack?

[Meatball]

When Whipple designers the Gen5, I know they went with an upside-down design to clear the 18+ hood and improve cooling with a 2-pass IC, but does anyone know why did they chose a 3/4 rotor pack vs the 3/5 from the gen 4? I can’t find any info on advantages.

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[Angrey]

When Whipple designers the Gen5, I know they went with an upside-down design to clear the 18+ hood and improve cooling with a 2-pass IC, but does anyone know why did they chose a 3/4 rotor pack vs the 3/5 from the gen 4? I can’t find any info on advantages.

https://www.enginelabs.com/engine-tech/next-gen-boost-testing-whipples-gen-5-cobra-jet-supercharger/

Like all fluid mechanical systems, it involves efficiency "curves" and they looked to improve or maximize the curve under the most useful areas where the blower is employed.

Basically, you might have a pump that operates REALLY well in one area, but has limitations in another area, so you attempt to shift that over into the areas where you'll be operating it.

They made a bunch of other improvements beyond the rotor ratio, but I'm guessing it was adjusting the ratio that either increased or allowed them to make other supporting changes (like the length to diameter, etc).

At the end, the result is a blower that for a minimal increase in volume (.1 L) they're able to maintain performance at lower rpm conditions but improve flow at higher rpm conditions. This means basically you get a blower that makes more peak power without sacrificing good low end flow and power and torque.

 

[Meatball]

Thanks, makes sense. That article looks like a good read.

since you seem to be knowledgeable on this stuff, do you know what the inherent adv/disadvantages are with TS vs roots? I think at this point in development there’s a hell of a lot of overlap between the tvs and Whipple/KB capabilities for a street car. Seems like in the old days the roots were maybe slightly more efficient (less power to turn the sc) in the low-mid rpm range and the TS slightly more on the high end. Besides cost and mass production availability considerations I think this is why Ford chose roots for the 07 GT500 and TS for the Ford GT of the time. I’m guessing there’s v little difference these days but I haven’t seen an unbiased comparison and am just curious.

 

[engineermike]

I find it interesting that the TVS increased the helix angle (still less helix than Whipple but closer) and added lobes (4x4 now) in the latest gen, while Whipple subtracted a lobe (3x4 now) and further increased the helix angle. Air enters and exits in virtually the same location in each. They both compress using the same basic principle and are both morphing into essentially geometrically the same thing. I bet by about the 10th gen they will be identical....

 

[Meatball]

I find it interesting that the TVS increased the helix angle (still less helix than Whipple but closer) and added lobes (4x4 now) in the latest gen, while Whipple subtracted a lobe (3x4 now) and further increased the helix angle. Air enters and exits in virtually the same location in each. They both compress using the same basic principle and are both morphing into essentially geometrically the same thing. I bet by about the 10th gen they will be identical....

It definitely looks that way. But it might be coincidence...for sure, the performance seems to be converging. They seem so similar but the operating principles have some pretty big differences..the roots compresses in the post-blower manifold (like a centri), the TS does at least some of it within the compressor itself. And it seems the TS designs always had different male/female lobe count, roots the same. But yeah they both seem to want to increase the helix angle, etc.

The only (maybe) unbiased description I found (I didn't look very hard) was an interview with a Ford product manager back when the 07 GT500 came out, explaining why they chose the roots over the Lysholm. He said the roots had a little advantage down low-mid, the Lysholm up top...but otherwise, it came down to production feasibility (no mass production for the TS, but Eaton (who has a license to build TSs, incidentally) was ready to provide lots of roots blowers. A little bit of a cost difference as well, but not much. These weren't a problem for the Ford GT. But for the performance targets, I guess for the track, the GT got the TS, for the street/track, the GT500 got a roots. But I bet the differences are smaller now.

 

[engineermike]

Another interesting bit when comparing the two is to look at the theoretical ACFM of each design as it is offered in kits. This would be calculated by using the pulley ratio and the volume/rev the respective compressor moves.

For instance, at 7500 rpm:

Roush stage 1 and 2: 1540 ACFM
Edelbrock stage 1: 1480
Edelbrock stage 2: 1580
Whipple stage 1: 1360
Whipple stage 2: 1410

This makes me wonder what the hp and torque curves would look like if they were pulleyed to move the same volume of air.

 

[Meatball]

Another interesting bit when comparing the two is to look at the theoretical ACFM of each design as it is offered in kits. This would be calculated by using the pulley ratio and the volume/rev the respective compressor moves.

For instance, at 7500 rpm:

Roush stage 1 and 2: 1540 ACFM
Edelbrock stage 1: 1480
Edelbrock stage 2: 1580
Whipple stage 1: 1360
Whipple stage 2: 1410

This makes me wonder what the hp and torque curves would look like if they were pulleyed to move the same volume of air.

That would be interesting, although I don't really understand ACFM well. Interesting that the 2.65L TVSs have a higher ACFM than the (2.9 or 3.0) Whipple. I guess if these are from the standard kits, could look at the pulley sizes to see what actual rpm each is running at at 7500 engine rpm. I assume the whipples are turning more slowly since they displace more.

HP & torque on a Coyote would be interesting to see with all of these moving the same "ACFM". I'd also like to see the supercharger kits, fully assembled, on a test stand where power consumption and post-IC air temp could be measured vs rpm, for the superchargers at the same ACFM. This would never happen but would be a true apples-to-apples comparison. I'll bet the sc manufacturers have that data but would never share.

 

[engineermike]

Yes, the higher ACFM from the TVS kits is due to being spun faster. For instance, the roush kits include an 80 mm (3.15”) top pulley and use the factory balancer. Edelbrock S 1 supplies a 3.25” top pulley. Edelbrock S 2 includes an overdrive balancer and spins it faster still. Whipple includes 3.875” (S 2) or 4” (S 1) pulleys for use with the stock balancer.

 

[Angrey]

Yes, the higher ACFM from the TVS kits is due to being spun faster. For instance, the roush kits include an 80 mm (3.15”) top pulley and use the factory balancer. Edelbrock S 1 supplies a 3.25” top pulley. Edelbrock S 2 includes an overdrive balancer and spins it faster still. Whipple includes 3.875” (S 2) or 4” (S 1) pulleys for use with the stock balancer.

It's an interesting look, but honestly, not very valid in the real world. Pulley size gets a vote and where even a 2.65 eaton or Odin starts to really fall short is the upper end against a 3.0 whipple.

If the Odin costs as much as a gen 5 whipple, and we compare them (even though the whipple has a volume advantage) I've seen 1300 rwhp out of a whipple gen 5. You couldn't find a pulley small enough or spin it hard enough to get a 2.65 into that arena.

Efficiency gets a vote, but not at the expense of belt slip and pulley size. I'd rather have an oversized blower (positive displacement) and spin it at mortal levels and deal with less belt slip issues. Belt slip is resolved mainly 2 ways, crank more on the tensioner or go more ribs, one is expensive and the other is risky and both have limits themselves.

I think Whipple hit it out of the park on the gen 5 3.0 They have a kit that's competitively priced to make easy 800 rwhp and can be cranked up to make 1300 rear if you need room to grow.

 

[engineermike]

@Angrey , you are correct theoretical volume and speed are only two components and several other things do matter. For instance at low rpm, slip comes into play and at high rpm, volumetric efficiency starts to matter more.

However, if you take the air flows I calculated above and compare them to advertised boost levels, it actually matches up quite closely:

Roush stage 1 and 2: 1540 ACFM, 12 psi
Edelbrock stage 1: 1480, 13
Edelbrock stage 2: 1580, 16
Whipple stage 1: 1360, 9
Whipple stage 2: 1410, 11

If you believe the majority of dyno numbers, I think think most agree that the Whipple stage 2 makes the most power of the group even though the volume of air moved is less than all of the TVS kits. This can only lead to three possible conclusions: 1) the TS rotor pack is just that much more efficient at high rpm or 2) the inlet tract (filter, MAF, duct, TB) has less restriction or 3) a combination of both.

 

[Angrey]

@Angrey , you are correct theoretical volume and speed are only two components and several other things do matter. For instance at low rpm, slip comes into play and at high rpm, volumetric efficiency starts to matter more.

However, if you take the air flows I calculated above and compare them to advertised boost levels, it actually matches up quite closely:

Roush stage 1 and 2: 1540 ACFM, 12 psi
Edelbrock stage 1: 1480, 13
Edelbrock stage 2: 1580, 16
Whipple stage 1: 1360, 9
Whipple stage 2: 1410, 11

If you believe the majority of dyno numbers, I think think most agree that the Whipple stage 2 makes the most power of the group even though the volume of air moved is less than all of the TVS kits. This can only lead to three possible conclusions: 1) the TS rotor pack is just that much more efficient at high rpm or 2) the inlet tract (filter, MAF, duct, TB) has less restriction or 3) a combination of both.

Front feed is obviously way more efficient. VMP's only real claim to fame is what amounts to be a glorified "porting" effort of the TVS platform that everyone uses for roots kits (Roush, VMP, Eaton who makes them, etc). They also work on all the other intake side restrictions to make it suck as much as possible.

And you are correct, efficiency becomes much more apparent at the upper limits of use. a difference of 5% efficiency at low utilization might look trivial, but as load increases, that 5% divergence becomes more and more apparent.

 

[Meatball]

@Angrey , you are correct theoretical volume and speed are only two components and several other things do matter. For instance at low rpm, slip comes into play and at high rpm, volumetric efficiency starts to matter more.

However, if you take the air flows I calculated above and compare them to advertised boost levels, it actually matches up quite closely:

Roush stage 1 and 2: 1540 ACFM, 12 psi
Edelbrock stage 1: 1480, 13
Edelbrock stage 2: 1580, 16
Whipple stage 1: 1360, 9
Whipple stage 2: 1410, 11

If you believe the majority of dyno numbers, I think think most agree that the Whipple stage 2 makes the most power of the group even though the volume of air moved is less than all of the TVS kits. This can only lead to three possible conclusions: 1) the TS rotor pack is just that much more efficient at high rpm or 2) the inlet tract (filter, MAF, duct, TB) has less restriction or 3) a combination of both.

So if the same engine, at the intake ports of the heads and everything downstream, sees the boost levels you show above, and let's say they all make the same power (I know there are differences in peak power, but Whipple is not one of the low ones in their claims or people's posted dynos), it seems like the Whipple is consuming significantly less power to spin the rotors and/or heating the air less during compression. I know I'm neglecting IC efficiency and especially differences in the tune (spark adv and cam phasing), and also differences in flow restriction in the post-sc intake manifold. But back to that Ford product guy and the decision to use the roots in the 07+ GT500 in part because of low-mid range advantages, maybe the roots design inherently makes more power (beter efficiency) down low. That's why I'd love to see a comparison of SC power consumption vs rpm on a test bench.

 

[Burkey]

So if the same engine, at the intake ports of the heads and everything downstream, sees the boost levels you show above, and let's say they all make the same power (I know there are differences in peak power, but Whipple is not one of the low ones in their claims or people's posted dynos), it seems like the Whipple is consuming significantly less power to spin the rotors and/or heating the air less during compression. I know I'm neglecting IC efficiency and especially differences in the tune (spark adv and cam phasing), and also differences in flow restriction in the post-sc intake manifold. But back to that Ford product guy and the decision to use the roots in the 07+ GT500 in part because of low-mid range advantages, maybe the roots design inherently makes more power (beter efficiency) down low. That's why I'd love to see a comparison of SC power consumption vs rpm on a test bench.

The last point you made seems to have merit IMO.
If we think of it like a turbo, where we can very specifically pick the point of maximum efficiency to suit the application, this isn’t that vastly different.

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