roots and turbo

S

stothew

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Oct 23, 2009
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i run a 3.9 cummins and was thinking of running a turbo and a eaton m90 i got from a tbird. how would you plumb it? like a compound having the turbo feeding the supercharger? would i need to bypass the s/c once turbo is spooled/ how would it need to do this? thanks and sorry if this is strictly for 6cyl. cummins.
 
thanks Forrest. i was thinking that but just didnt know. should i worry bout the heat of the eaton and try and run it through the charge cooler? or just cram the cooled turbo pressure thru it and into the head? thanks again
 
it will run better if you run it through a cooler, but it's not necessary by any means.

what are your power goals or is it more of a "let's build something neat" thing? just curious
 
thanks again. its in an early bronco and it just doesnt have any power till the turbo gets going and ive tried all kinds of different combos including compounded hx 30 and 40. it was good on spool up but the 30 was too small to flow all the air the 40 was giving it. and when im out crawling im having to put into low range when it isnt needed just to get itself out of the way. so thought a roots would really get it. power wise somewhere in the 300hp range ultimately. yeah and something cool. currently im running the he341, good turbo once its spooled but takes too long with the 3.9 for my tastes.
 
Just read member MIKA posts, he have Chevy with roots and twins:rockwoot:
 
if you're crawling at altitude and only looking for 300hp, I would go smaller than the 64 feeding the blower.

I think you're definitely on the right track.

Those T-birds were only rated at like 225hp or so... say you're going to be making ~175hp at 15psi w/ the blower, you'll probably want a turbo designed to make 325hp at 25-30psi... I'd do something wacky and try an HE351. I would get the truck running with just the blower untill you get the pulley combo figured out to where it'll make 10-15psi, and then hang the turbo on it, and see what you end up with :D
 
awesome, thanks Forrest. yea was thinking the 351 would just bolt onto my current header and exhaust and flow more than the 341. and the 351 would flow enough to get me 350hp or so.
 
I've been looking for a 3.9 for my Jeep and was wondering how it would be for crawling...this sounds like a lot of fun!!!

what other mods or on the 3.9??
 
why does everyone say have the turbo feed the blower? why not have the blower feed 12-15psi into the turbo, where the blower is atmospheric and the turbo is secondary. im just thinking it would be easy to plumb this way.

is one more efficient than the other?
 
I suppose you could do it either way. It would probably be best to look at the compressor map for the blower, but that particular blower came on a 3.8 liter V6 making about 215hp... he's looking for ~300hp, so you'd need a blower designed for a ~300hp application feeding a turbo designed for a 150hp application, and all your exhaust has to squeeze through that little turbo.

with the turbo acting as the primary, the turbine will be correctly sized for the overall power level of the engine
 
doing some quickie math, it looks like the blower should work well... 150hp at 10-12psi it's looking pretty good.

very cool project IMO!
 
getblown5.9 said:
why does everyone say have the turbo feed the blower? why not have the blower feed 12-15psi into the turbo, where the blower is atmospheric and the turbo is secondary. im just thinking it would be easy to plumb this way.

is one more efficient than the other?
Click to expand...

The reason is the blower is positive displacement, each rotation moves a given amount of air. A turbo or centrifugal turbocharger is not, therefore if you had the blower feeding the turbo, once the turbo spooled up you likely run the risk of running out of air with the turbo. The blower just simply cannot supply more air without more rpm, at which point the turbo needs more also.
The turbo feeding the blower can compress the air entering the turbo therefore compounding it like twins, and would never run out. Might be out of its map but would at least not be out of air.
 
you mean the blower would be out of its map? i was thinking that but would the turbo pressurizing the blower help with the map?
 
They both have a map, feeding the blower with a turbo makes a altered map. But blowers create alot of heat because they don't move air that gets pressurized downstream, they compress it internally. So, and I may be talking out my azz here, I would think you would reach the edge of your map sooner when compressing the blower inlet.
 
Nrose has the jist.. No reason to put a positive displacement device before a variable displacement one...

Using my super/turbo compounding spreadsheet the 4BT with an MP90 on it will have to be overdriven 3:1 to make 18psi @ 100% VE (which is impossible). You'd want to throw a 66/73 on there to make some good numbers. It only needs to make 20-25 psi to produce 55-60 compounded.

I have one in the works as well. Looking at the Eaton TVS2300 or whipple 3.4L... Not a 4BT though ;)


Brayden
 
i see what you're saying nrose. what would you suggest for plumbing this combo for my little 4banger Brayden? yeah those chargers you talk about are great ones but im not needing that kind of volume and yeah like you said not for a 4cyl. would an m112 be better suited and help with the map and heat? tia

scott
 
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