Ok, so I'm building a "twin charged" setup with a turbo feeding a Magnuson TVS1900 roots type supercharger. It's a project I've always wanted to do, so I decided to do it. The setup I have is on My truck which is already turboed with a Masterpower T76 on a forged 346 LS1 with 6l heads at about 9.2 to 1 comp. I want to run a total of about 15 psi of boost.

Before you tell me this is dumb idea, or waste of money, don't bother cuz if you think that, then your not the kind of person i want to hear from, cuz this build is happening. I want the low end grunt of a root supercharger to get the heavy truck moving, and the pull of a turbo up top. And its cool

Here is the truck its going on.

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This is how the turbo will most likely fit.

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If that doesn't fit, it will fit like this

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I had a little discussion with another member on here and he came up with if the blower runs at about 7 psi, then I need the turbo to support about 75lbs of air at 1.4 PR (6psi) to get the 15-18psi i want to run on this motor. Here are a couple maps of the current turbo, and the turbo I'm thinking of trying next.

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Looks like the t88 would fit the bill if he is correct, but I really don't know how a turbo or blower is going to react with each other. I will have some temporary gauges hooked up to monitor the turbo to blower boost and the exhaust back pressure.

Tell me what you think from a TECHNICAL aspect

 

Seeing as you already have a MP-T76 why not get a matching one, run twin, into a dual inlet, single outlet a/a cooler and go into the blower from there. Then you could at least drop the intake air temp, and keep your total cost down? And I think dual .96's would be big enough for what you want to do.


Ryan

 

I think its a great idea since we all know that turbo's don't make any low end torque.

 

Looks like someone didn't get the memo.

 

Adding a second MP T76, 38mm WG, manifold and down pipe would cost as much or more then a used PT88 and building a bigger dp, and I'm a turbo dealer, so I get even better deals then most. Plus would be a lot of labor too and there isn't much room on the driver side of the truck with out moving a bunch of stuff.

As far as Just running a T88 buy itself, ya that would make the "peak" power, but would have a TON of lag to get it spooled. That's why I want to do the compound setup. I want near zero lag and a HUGE power curve to move this heaver truck from off idle to red line. This truck is a daily drive that will see some track duty once in awhile.

As far as intake temps, I don't think they will be a big deal, as the blower has a large L/A intercooler under it in the tub and I have a large heat exchanger in the front of the truck as well as a large reservoir tank I can put ice in at the track. I will also be spraying meth between the turbo and blower.

Any more options on possible other turbos I should use???

 

Well, Just found out MP is making a T88 and I'm a dealer for them so I should have known that, lol. My distributor never told me about them till just now. Looks like that might be my next turbo depending on what the specs are on it

 

Looks like a Garrett T-88 would be perfect, with room on both sides. Here is the map from squirrel perf.

http://www.squirrelpf.com/turbocalc....2&airflow6=66.1&airflow7=67.5&product_id=132

 

Your calculations are off probably from the input data. Here is how you have to think about this since it is a compound setup.
1. The pressure ratios of the two boosting devices multiply. Since 15psi (2.02 pressure ratio) is the desired end result and the blower is creating 7psi (1.48 pressure ratio) the turbo will supply 2.02/1.48 = 1.36 pressure ratio (5.36psi).
2. With the blower at a 1.48 pressure ratio the turbo will think it is supplying an engine that about 1.48 times larger. In this case that is 1.48 X 346 = 512cid. The engine/blower combo is consuming 1.48 times the air that the engine alone did.

 

So my question is this, what is going to happen with a 15psi spring in the WG with the T76? Is the turbo going to flow the air, just heating it more? or will it just be a restriction to the blower and won't make 15PSI of boost? I mean its supplying such a low boost pressure, but a large volume, it surly can't heat the air that much. Or finely it will suck its self into a black hole and create a new universe, lol

 

I don't think anyone can answer that with any certainty unless they have experience with this particular setup, or at least one that's damn close to it. Probably won't make more power than the truck did without the blower though.

You're worried about spool with the T88; why? What's going to spool faster, a T76 on 346cid, or the 88 on 512cid?

This has my curiosity totally piqued, so please run both turbos on it when you get it all back together.

 

I'm not expecting more power with the blower, I'm wanting a big, fat, torque curve that looks like a table top from just off idle all the way to red line.

 

Here is what will happen.
1. At 3000rpm the air requirement is half that at 6000rpm. The T76's compressor can supply this no problem.
2. The engine/blower combo will certainly supply enough exhaust for the turbo to be at full boost by 3000rpm. Likely long before 3000.
3. Assuming you reference the wastegate to the manifold (a must) you will have 15psi in the manifold at some insanely low engine speed.
4. At some point long before 6000rpm the 38mm wastegate and .96 A/R will not be large enough to control boost. This will want to increase boost beyond your desired 15psi; however also at some point the compressor will not be able to supply the volume of air needed to create boost. Also the high back presure will tend to cause the boost to fall off. It is difficult to say which will happen first and whether the boost will start to "run away" or it will choke the motor first and boost will fall off at medium engine speeds. It could be that the boost increases for a while and then begins to fall off.

 

Don't look at the plotting. Look at the map. And yes I would use a T-88 on a 512 cid motor.....and it would work very well, thanks.

 

I was looking at the plotting. Looking at the map I certainly agree and would add that a bigger gate is in order also.

 

OK, I got this up and running and ran into a pretty big problem with it. I am having really bad boost creep and super high EGT's, like 1650*, lol. It's making 11-15 PSI on just a 7psi spring in the waste gate. Drive pressure must be through the roof! lol. Doesn't pull at all past about 4000. This tells me that the exhaust side of this turbo and WG are WAY to small. Also, my converter is way to loose and trying to put it at around 4000+ rpm, so I can't even take advantage to all the low end boost the Blower is making. It will build 10 PSI from an idle in about 1 second!

So what I'm thinking is replacing the WG with a much larger one I have, a 50mm synopsis. I think I'm gonna try a S475 BW turbo because of it's HUGE hot side, I think the blower will like that and I can get one of those pretty cheep. I can fab up an adapter to fit my manifold, and have a 3 1/2 DP with a cutout at the end of it ready to be fitted also.

Tell me what you guys think, The S475 with have the big T6, 1.32 a/r with 96 trim turbine to help with the flow for the blower.

Here is some pics of how it came out, and I did end up with the a/a intercooler between the turbo and blower, but will probable be removing it and just spraying a meth M3 nozzle pre turbo and keeping the current M15 between the turbo and the blower.

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You need a very large exhaust for it. I would consider getting an S480 or a TV8101 for this, but even the S475 would be a huge improvement. Anything T4 based like a PT88 is a big mistake IMO. I don't think the TV8101 would have any issue spooling and with a larger turbine housing it would flow better.

 

Agreed. Maybe you can get by with a 3.5" down pipe if you don't run the wastegate dump back into the exhaust. Run the good sized pipe (like 2.5") from the wastegate all the way out the back of the truck.

 

It would have a 3 1/2 down pipe to under the truck, then a cutout. From there, I all ready have it splitting into 2, 3" all mandrel bent tubing through 2 Magnaflow offset mufflers. I picked up 2-3psi of boost creep in 3rd gear when I put that exhaust on, lol.

 

I think that a 350ci motor with 15psi should never have a single 3.5" DP. A 4" DP is about 30% more area than a 3.5". I would go 5" if at all possible out of an S400. There are some companies that sell 4.5" exhaust parts which is about equal in flow to the two 3" tail pipes.

 

If the blower is pullied for for 7 psi by itself, it isn't going to be contributing any boost when compounded. Say you're enigne is moving 50 lbs/min at 7 psi with just the blower. Now you put on the turbo and up the total boost to 15 psi, and the engine is now moving 70 lbs/min. Since the blower's speed is fixed, it's pressure ratio must drop to move the additional volume, maybe even going negative (ie, the blower is a restriction). The speed lines for the TVS1900 are pretty steep! http://www.eaton.com/ecm/groups/public/@pub/@eaton/@per/documents/content/ct_127899.gif

So, the turbo should be sized for around 70 lbs/min at around 2.1 PR, so the T76 compressor would still be around 72% efficiency. A T88 would get you to 80%, the S475 also around 72%. I do agree that you need the biggest hot side you can get!