Compound drive pressure

Joesixpack said:
A fairly easy concept is back pressure after the turbine in the case of a single charger can be a huge detriment to power. This is the same case in what the secondary turbine is seeing as back pressure or primary inlet pressure.
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If I understand this right, it is a pressure differential.

If I had 100psi on the manifold and 50psi in the hot pipe (2:1), I'd move more air than 70psi manifold and 50 hot pipe (1.4:1), correct? Less pressure in the hot pipe means more volume of air can pass through the secondary turbine and into the hot pipe.

Or do I have that wrong?
 
oldestof11 said:
If I understand this right, it is a pressure differential.

If I had 100psi on the manifold and 50psi in the hot pipe (2:1), I'd move more air than 70psi manifold and 50 hot pipe (1.4:1), correct? Less pressure in the hot pipe means more volume of air can pass through the secondary turbine and into the hot pipe.

Or do I have that wrong?
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In general you want the least pressure on the backside of the turbine as possible but obviously some pressure is needed to drive the primary.

I think what he was saying in the first post is that gas expansion occurs across the manifold turbine. You're taking a smaller volume at higher pressure/density before the manifold turbine and expanding it to a larger volume at lower pressure/density. Like compound compressors in reverse.


I still think something is a miss. HE351/72/83/1.10 is an excellent set of twins on a 12v. They should run very cool with 5x.012s even with a maxed 215 pump. The gate on the 351 is jammed or there is some boost leak in the cold pipe or piping from the HE351 into the engine. Or garage delivery valves hidden in that pump.
 
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I have checked the cold side for leaks with none found. The gate is working because when I open up the boost elbow it will open the gate and I can boost around 20 - 30 psi max. Truck is obviously a dog and gets very hot.

I have to run my gate loose in order to combat my drive pressure and egts, but this takes away my bottom end. So to make it light faster I run the preboost screw in a touch farther than I'd like. Isn't an issue until I'm towing. Then it leaves a puff at every light during take off and that's annoying.

Dvs are stock as far as I know. And I have no smoke or even haze under boost.
 
My previous compound setup on my street truck was HX35/12cm internally gated compounded with an HT60/super tight 20cm turbine housing. That setup seemed to choke out just over 500 HP, it did just 518 on the dyno but over 1200 ft lbs showing the fast spool and great low-end but terrible topend.

I then swapped out the newer technology HT60 for an older technology HT3B/26cm and I picked up a solid 50 HP but lost considerable mid-range torque, in fact, there was a slight plateau or lull in power in the middle of the power band as the wastegate opened on the HX35 and the HT3B wasn't fully lit.

I agree that too tight on the big turbo can create drive pressure issues and make the small turbo's turbine perform poorly.

I then built a new setup using an HE351cw over S480/96/1.32 still internally gated. Makes 80-85 psi at full boost and power went up about 50 HP over the previous HT3B setup with the same fueling. I then stepped up to 7mm DV's and picked up another 50+ HP.
 
Will I was reading your thread earlier. About the only difference in our turbos is your larger primary. In your opinion should I go larger turbine housing on my 472 and keep the 351 as is or gate my secondary and hope for the best
 
Have you given any thought of running a new style Borg 63/74 or 66/74 in a T4 x .91 housing?

I know I hated the clipped 73mm turbine wheel in the Silver Bullet I ran for all of 50 miles...but my little v8 6.0L doesn't have the "Push" of the straight 6 cylinder exhaust.
 
Mechanical fuel injection isn't my thing but I can tell you late timing on a common rail in the upper rpm's along with not enough injection rate will inflate boost/drive and egt's. So while it will seem to be inline at that 3000rpm and less its that 3000+ where it starts to show.

On an injector change alone at the upper limits of rpm I lost boost and drive and also egt's while making more power.
 
Joesixpack said:
Mechanical fuel injection isn't my thing but I can tell you late timing on a common rail in the upper rpm's along with not enough injection rate will inflate boost/drive and egt's. So while it will seem to be inline at that 3000rpm and less its that 3000+ where it starts to show.

On an injector change alone at the upper limits of rpm I lost boost and drive and also egt's while making more power.
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After reading this I was thinking the same thing for the egts. 5x.012's seem small to me for the setup. Granted my setup is with a 175hp pump. 63/68/12 over a s476/83/1.10.. Switching from a 5x.012(plate full forward) injector to a 5x.016 and moved the plate back. With the 2nd setup the truck picked up 2 mph in the 1/8th and on my WOT runs the truck ran 300 cooler on egt's. Maybe from less duration??. I did not have a drive pressure on the first setup. 2nd setup boost to drive was 1:1.1 Boost:68psi Drive:75psi to 3400 rpm
 
Extended Power said:
Have you given any thought of running a new style Borg 63/74 or 66/74 in a T4 x .91 housing?

I know I hated the clipped 73mm turbine wheel in the Silver Bullet I ran for all of 50 miles...but my little v8 6.0L doesn't have the "Push" of the straight 6 cylinder exhaust.
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I've given it quite a bit but not sure what to go with.

My present setup doesn't come out of the hole like I think it should and I'd sure hate to make it worse.

Ideally I'd swap secondaries, put a little larger exhaust housing on my primary and step it up to a t6. Sounds like I need a larger set of injectors also?

I don't need more power than what this truck should dyno at, working correctly, which I feel is 600-650. The 5r is factory with a dpc converter, no need to press my luck.
 
Bumpin this back up.

So I am assuming that once I finish installing this new 69/74/.91 as my new secondary...I will lose pretty much all the bottom end response I had from the 66/68/.84...

I guess a gear swap, say 4:10's...or a very loose converter, say 2500...is what is going to be required to run this on the street...or am I just blowin smoke?

Just thinking that I have made the exhaust side of the compound system less restrictive throughout the whole path, and now I think it's going to take a lot more velocity, and volume, to get everything spinning.

I'm guessing here, but based on the older facts of when I ran the T3 x .70 housing on the 66/68, I could spin the tires off the line...no brake boost...and driving down the highway, cruising at 70 mph, I had 10-12psi of boost. (But extreme drive pressure at WOT.)
So now, with less restriction on the secondary, it's going to take even more to get this tub moving...but will have less drive pressure issues at WOT.

The quest for more POWA continues!
 
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