We were dyno testing Ryan's twincharged 06 SS today and decided it would be nice to record some concrete data concerning the blower bypass.

We made two dyno pulls with the only difference being the blower bypass position. Pull number 1 shows the standard configuration with the blower bypass opening as the turbo spools. Pull number 2 had the bypass valve closed the entire pull.

In pull number 1, the bypass was set to open at 26psi and full boost was set to 30psi. Pull 2 was set to 30psi for the whole pull. Boost was slightly higher on pull number 1(less than .5psi difference), while peak horsepower was 46whp higher! While coolant temps as well as initial IAT2 temps were consistent for both pulls, peak IAT2 readings were 115 on pull number 1 and surpassed 140 degrees on pull 2.

For another test, we put Ryan's twincharge setup up against my 08 LNF with turbo upgrade.

This is not an apples to apples comparison based on the mods of each vehicle, but I still found it interesting.

Differences between these two vehicles-

Twincharge setup has Bullseye S362et turbo, LNF has Bullseye S256et turbo.

Twincharge setup has standard fuel injection with 80lb injectors, LNF has direct injection with stock injectors and raised fuel pressure.

Twincharge setup has stock head with 78lb springs, LNF has zzp ported head with 78lb springs.

Twincharge has stock cams and fixed cam timing, LNF has stock cams with dyno tuned variable valve timing.

Twincharge setup was run at 30psi, LNF was run at 25psi.

Both cars have full length ZZP 3" exhaust.

Note- the twincharge dyno made less power early in the pull because the blower was bypassed at 26psi. Had we regulated the blower to maintain 29psi, then the twincharge setup would have made more power than the LNF all the way to 7500rpm.

 

nice work as usual

 

1. Is the Twincharge Kit set to open the bypass valve on the SC at a set psi or a set rpm?

2. I don't think this a fair comparison of a typical Twincharge setup VS a Compounded Twincharge setup. Your using a turbo that is a efficient to the boost level your testing. I would like to see you guys try this same comparison with the turbo that comes with the Twincharge kit. Try to get 30psi out of that by opening up the bypass valve.

I am not hating. Just commenting.

 

1. On Ryan's setup, we have a regulator set to open the bypass at a certain boost level.

2. The 256 ET made nice gains going from 28psi to 30psi on our original twincharge Cobalt. While you are correct that there would be a difference, I think the gains would be within a few hp with an S256et turbo in place of the 362.

 

to me, it makes perfect sense.

with the bypass open, you have much larger flow area in witch the turbo can push its flow, while leaving it closed is forcing everything thru the blower.

that becomes the bottle neck, and bam, power drop +IAT jump.

ps, nice comparison of the cars, if you ever get the boost up that high on the LNF, it'll be interesting to get a good luck at the area under both the curves.

 

Cool.

Well it is clear that the SC is robbing hp with the by-pass valve closed. What size pulley is on the SC?

 

While this is the way it appears at first glance, it's not really what's happening. If the blower is moving more air than the motor would naturally aspirated, then it will move more air regardless of what the turbo is doing. Consider the pressure ratio difference above and below the blower. This ratio will remain the same even when the turbo is feeding compressed air to the blower inlet. In other words, no matter how much air the turbo moves, the blower will still increase the flow. While it may seem like opening the bypass valve allows compressed air from the turbo to enter the intake manifold more easily, this is not what is happening at all. When the bypass valve is open, the rotors are still moving air to the intake. However, now the charge is able to avoid being compressed further as air flows through the bypass valve back into the blower inlet. When air pressure remains equal above and below the supercharger, inlet temps are also somewhat equal.

So, where do the gains come from?

1. Parasitic loss from driving the blower is mostly eliminated. With a stock pulley on the blower, I would estimate this to equate to a 20-25whp gain.

2. More efficient use of the turbo compressor. If you look at the 362et compressor map at 58lbs/min and a 3.1 pressure ratio, it falls within a very efficient range. When the blower bypass is closed, however, 30psi in the lower intake means that you have about 12.5psi in the blower inlet. At a low 1.85 pressure ratio and still flowing 58lbs/min, the 362et falls into a much lower efficiency range on the map.

3. Intercooling. While the factory water/air IC is better than nothing, it really is not a very good IC. With the bypass valve closed, the large FMIC on Ryan's car is going to waste. While temps going into the blower are near ambient, the factory IC struggles to cool the charge heated while the air is compressed by the blower. He is much better off compressing the air prior to the FMIC due to it's significantly greater cooling capacity.

 

It would be interesting to see the result of a compounded Twincharge setup when the Tubro is in its optimal efficiency range. I think the overall HP differences would be less but the compounded system would still be lower because of the parasitic hp loss from boosting the blower.

 

I agree that there would be some turbos out there better suited to a compound turbo/blower setup. You would want a turbo that works well at lower boost on a larger motor such as 10-15psi on a V6. I would want to run a better intercooler under the blower as well.

 

i want to see 2 compounded superchargers...

 

understood.

this actually sparked a good conversation between myself and a few co-workers today.

we were going out to cut down some tree's, while talking fluid dynamics. one hell of a way to start the day.

the only thing i could see, thats not covered by your post, is the fraction of a second drop in manifold pressure you'd get during the change over(opening of the bypass) but the dyno chart shows this.

 

great comparo. Thanks for posting this up.

that actually sounds very interesting. I'm not quite sure how that'd work on a 2.0 4-banger though.

 

Lumberjack engineering, interesting combo.

Yes, there was a decent pressure drop on this dyno pull. It can be eliminated by opening the bypass valve slowly while the turbo wastegate controls the overall boost pressure. We had it completely seemless at 25psi, but as we turned it up, the transition became obvious once again.

 

is that guy's engine sleeved or not? seems like a crap load of power through a block that seems to blow sleeves at much lower power levels

 

no sleeves

 

I believe they are being more conservative with the a/f and timing than most. See, most people are pushing the limits on the stock blower, tvs, or something like a 20g. Where as ZZP is using big turbos right in their efficiency range, and they don't have to push the tune hard to make power.

That's the difference between a company(lots of money all to build/test/race cars) and an individual(car is just a hobby).

 

Stock sleeve's hold up fine in the absence of detonation. Once we surpass a certain boost level, we make the switch to race gas. While it's expensive, it's still a lot cheaper than replacing a motor. We also use good thermal management to avoid detonation. Hobby or job, people need to understand that you can't just beat the crap out of a motor ten times in a row running high boost and pump gas.

Of course this doesn't mean that we aren't pushing these cars close to engine failure. Eventually parts just break regardless of the tune.

 

do you know if the forging process for the LNF crank is different than the LSJ crank? or if they use diferent sleeves. If not, then yea, you're definitely at the brink of a few breaking points...lol

hey, somebody's gotta find the limit though

 

im curious if you dont mind sharing, at what level psi do you cross over to RG and what oct?

 

Good ******* work guys! I am impressed!