Compound boost question?

what about twin vortechs

I don't see why you couldn't. But I imagine avoiding belt issues (belt slip, chewing up belts, throwing belts, etc.) would be a challenge.

You could but it wouldn't work too well. A single turbo would make more power..

I would argue that most of the time, a properly sized single blower/turbo is more efficient than compound anything. Larger compressors tend to be more efficient than smaller ones. You simply need to choose a correctly sized compressor wheel for the boost and flow your engine will make.

BTW, I can't even image the power required for a positive displacement blower to run as the last stage. It must be a HUGE power draw.

IMO, the only reason to run a compound boost setup is if you plan on making 40+psi... which is absolutely not necessary on a gas/alky engine. A diesel on the other hand may see these kind of numbers.

Noobz347 said:

The only reason I can think of why someone would do a Pos Disp blower and centri would be to get all that down low torque from the Pos and top end from the centri.

I can't think of a singe reason to run two centris unless both are tiny and spool up very quickly.

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Agreed.

One day, I want to build a compound boost 03 Cobra (with the Eaton and twin turbos). Port the blower to the max, and leave the stock size pulley on it. That way, it would be as efficient as it could possibly be, and should help keep the IATs down. Hit it with some methanol if needed to keep the IATs down.

I remember a BIG argument over on SVTP (or might have been HPJ or YellowBullet, don't remember) a couple years back about compound boost. One argument was that compound boost is dumb because it's inefficient, and you can make more power with the turbos, and it's too complicated, and blah blah blah. The other is that the peak power isn't that big of deal, and that there will much more low end torque with the blower, and that it really isn't more complicated in the end, and that it will be more fun on the street.

Well someone actually took a twin turbo Cobra and tested it with and without the blower. In the end, it only took 4 more pounds of boost on the compound setup to make the same peak power as the turbo-only setup; in other words, it was only 4 pounds of boost worth less efficient. To me, at 30+ pounds of boost, that's not a whole lot, especially when we're talking street car. What was a whole lot was how much more torque the compound setup made before the turbos spooled. And it was a LOT. 150+ ft-lbs of torque kind of lot.

My opinion/conclusion: sure, the Heaton adds a lot of inefficiency to the setup. At the same boost level, the turbo-only setup will make more power. No one can debate that. BUT, is that slightly better efficiency worth the lack of torque before the turbos spool? I guess that's up to whoever owns the car, but to me, the answer is no.

You can look at Hellion's website at the GT500. The have dynos of both a TT with a stock blower and TT only. The TT only made about 50-100 hp more at the top end showing the restriction the blower causes. But the compound setup had crazy low end torque, something like over 700 ft/lbs to the wheels at like 3k rpm and up.

I was told that tuning is more difficult with a compound setup. Not even getting into the which compound setup is best or efficient, but how do you plan on running a vortech and an eaton? I'm assuming the tork tech kit which has a full pulley bridge with the vortech bracket? Sounds like a migraine of belt routing and modifying both brackets to work. You might be able to do twins with the tork tech kit. Your setups are limited by fitment.

Noobz347 said:

I can't think of a singe reason to run two centris unless both are tiny and spool up very quickly.

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Small centrifiguls don't spool up faster.. the boost curve is linear. Shelbys that use the twin turbo compound boost hellraiser kits gain alot of power up top after removing the blower..

turbogt said:

Shelbys that use the twin turbo compound boost hellraiser kits gain alot of power up top after removing the blower..

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And they lose a ton down low, too.

Here is Hellion's own video of a GT500 with their twin turbo kit, both with and without the stock blower. Skip to 1:28 to see the difference at the same boost level, with and without the blower.


Sure, without the blower, it made about 100 more horsepower at peak RPM. But look at 2000 rpm....3000 rpm.....4000 rpm.... There's a 150+ ft-lbs of torque difference through that range, as much as 250 around 3500 rpm. Say what you want, but the car with the blower is going to SMOKE the other car on the street. And be a ton more fun to drive. And if I was really concerned about the peak power, all I'd do is up the boost on the turbos just a bit. I'm sure 5-6 extra pounds of boost would make up that peak difference.

This was also on the STOCK blower. I'm sure that if you ported it (i.e. greatly increase it's efficiency), it would easily pick up 50 rwhp at 6k rpm, and a plenty down low as well.

sneaky98gt said:

And they lose a ton down low, too.

Here is Hellion's own video of a GT500 with their twin turbo kit, both with and without the stock blower. Skip to 1:28 to see the difference at the same boost level, with and without the blower.


Sure, without the blower, it made about 100 more horsepower at peak RPM. But look at 2000 rpm....3000 rpm.....4000 rpm.... There's a 150+ ft-lbs of torque difference through that range, as much as 250 around 3500 rpm. Say what you want, but the car with the blower is going to SMOKE the other car on the street. And be a ton more fun to drive. And if I was really concerned about the peak power, all I'd do is up the boost on the turbos just a bit. I'm sure 5-6 extra pounds of boost would make up that peak difference.

This was also on the STOCK blower. I'm sure that if you ported it (i.e. greatly increase it's efficiency), it would easily pick up 50 rwhp at 6k rpm, and a plenty down low as well.

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The only thing its going to smoke is it's tires

I love compound boost cars. The 5.4 with compound boost is pure sex.

I have a couple buddies here in Houston doing it. One is a 1200rwhp terminator with the stock blower, twins and a built auto. The setup is nice and hits farely hard and dead hooks with his suspension setup. Makes 1200-1300rwhp through an auto. Here is another buddy running around slowly at the track last week with his 5.4 Ford GT with the stock blower and a Hennessey twin kit. It makes 1150rwhp. Still has stock cams.