So, I want to use a roots-type supercharger......19-21psi....goal is 1,100 RWHP.

I've been told that if I spin SC'er too high on the top end which will is great....max power.......It will be spinning too fast down at the low rpms when driving normally around town.

Is that true.....?

Say use a 70mm upper and a 10% lower, it'll spin at 22,700rpm at 7,000 engine rpm. Will that drive perfectly normal at idle, cruising at 30-40-50-70 mph.

Is there any problem like this with roots-type SC'ers.....?

Thanks....

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If you run one that has the built in bypass valve, it's not going to make boost just cruising around. From personal experience though I wouldn't spin the blower higher than the manufacturer rating. They become inefficient due to heat and turbulence, not to mention most bearings aren't rated for more than 20k rpm.

 

Check the rpm rating with the manufacturer.

 

Roots type blower probably isnt the best idea with your power goals. They arent meant for crazy high hp builds unless your running fuel that dont have to worry about knocking and high Intake air temps. Spinning too fast creates a lot of heat and can really kill high rpm power. Most cars that come with them stock are already at max efficiency out of box. Not that you cant get more HP out of them by putting on smaller pulleys, exhaust, and headwork but usually have diminishing returns. Roots blowers are way better at providing instant and reliable power over wide rpm ranges. Your power goals may be possible but i would suggest diff form of boost.

 

How about full time E85
10:1 compression
Large Intercooler

 

Id start with a forged ls3 shortblock and cnc ported Ls9 heads from GM performance. Then at least a 2900 or larger blower with the biggest air/water intercooler you can make work. Custom blower cam with E85 and see how fast you can spin the blower till the air gets too hot.

 

 

Can you explain the reason you say 10:1 isn't high enough?
I have a 408 that made over 900hp on the dyno with a 10-71 old school roots blower on E-85 at 15lbs of boost and compression is 8.5:1, Lower compression and more boost is better than more compression and less boost unless something changed that I didn't hear about?

He's not going to get those numbers with an LS3 bore and stroke or LS3 heads unless they are heavily ported but a stroker combo with good heads should get him there.

 

Why not go turbo?

 

 

But it's not the old school way of thinking, You can still pack more fuel and air into the cylinder with lower compression ratio and in turn make more power. There are other benefits like less valve shrouding and wider tuning window and so on. It's not just a theory but has been proven over the years. It may not be a lot but it's there and it's free power.
The main reason people say otherwise is usually because they are running a turbo on the street and don't want it to be a dog off boost, Roots style superchargers don't have that problem.

Aren't you running a centri not a roots? A roots blower doesn't suffer from low end power loss with lower compression like a turbo and centrifugal supercharger does. They make boost from idle and make tons of low end torque.

 

 

I'm not very knowledgeable, but Leah Pritchett's super stock Dodge Demon makes up to 1,300hp with a 2.9 Whipple. Randomly came across a video yesterday. It's a factory 6.1 Hemi that's bored 60 over, so it isn't very big.

 

Looks like they can get much bigger......ModelDisplacementMax Continous RPMMax Peak RPMMax CFMMax M^3/HRMax PSIPeak VEPeak AESC Blueprint (PDF)W100AX1.6 Liter/rev18,00020,00011201902309981100AXW140AX2.3 Liter/rev18,00018,00014302430309980140AXW140R2.3 Liter/rev18,00018,00013892360309577140RW175AX2.9 Liter/rev18,00018,00017202922309978175AXW200AX3.3 Liter/rev16,00018,00021403635309978200AXW200R3.3 Liter/rev16,00018,00020303449309476200RW245AX4.0 Liter/rev16,00018,00025184278309978245AXW305AX5.0 Liter/rev18,00020,00034625882309877305AXW305R5.0 Liter/rev18,00020,00032505522309375305RW510AX8.3 Liter/rev11,00012,00034625882309877510AXW510R8.3 Liter/rev11,00012,00032505522309375510R

 

Fountain Racing Engines.......made 1150 FWHP with a Harrop 2650 Supercharger last month on a 416 LSA engine with LSA 8-Rib drive................15psi and E85. NW 102mm TB.

That was NOT with the larger 10% lower pulley.

 

I guess looking back at his post I'm not so sure he's even looking at a roots style blower, You don't turn a roots 22,000rpm, A centri maybe. If he was looking at a true roots style then he can easily find a blower that will support the power he's looking for.

 

So....Eaton recommends a max rpm of 18,000. So how much further can you take it before it gets inefficient?

 

 

A 2.3L TVS is good for ~650 rwhp at 15000 rpm. I've had two of them running that speed. No heat problems at all. Doing a little cyphering, a 2.65L blower should blow enough air to hit ~750 wheel running similar blower speeds. Run the 2.65L blower up to 18000 rpm and you're in the 860 wheel hp range. I haven't heard how good the intercooler/heat exchanger system is on the 2.65L TVS. That could be a limiting factor. Plus, you'd need to be sucking through a bigger throttle body (or a pair of throttle bodies) to help this thing breathe. A big cube engine would certainly help too. By far, not the easiest way to get four digit power numbers. It would be a fun ride getting there though.

 

The Harrop 2650 technically has made 1,000 RWHP. A shop in Florida made 1150 FWhp at 15psi.

Another guy in South Florida made 803 RWHP with a basically stock Chevy SS engine....no mods except for the Harrop 2650 and a new cam to accommodate the blower. Ran 9.84 @ 142 mph.

Here it is at the drag track and doing highway pulls: ((just about the ugliest car possible....but it shows what the Harrop can do on the LS engine))