Twin ( parallel) turbos--redux

[Michael Fowler]

I have searched this topic, and found that all the threads seemed to die off with out resolution.

It seems that a single small turbo on each exhaust manifold would make for relatively simply plumbing, and fabricating. If this is true, why has it not been done?

Assuming junk yard shopping, what turbos would be the easiest to use?

What I do not know about turbos would fill several books, but it seems that a small turbo would limit its boost w/o a wastegate just due to the volume of gases it can pass ( unlike some members on this forum ...) Is that not the principle behind the pulse turbos?

Also assume that the the goal here ( at least in my hypothetical case) would be to improve towing ability; not smoking corvettes etc.

To maintain engine longevity what boost levels would you recommend? I am thinking 6 to 10 psi would provide enough power to maintain speed on the hills with my 7000 lb fifth wheel.

Is the power from a boosted engine simply a ratio of boost pressure to what is normal atmosheric pressure? In other words, if an engine produces 100HP naturally aspirated ( 14.7 psi more or less) would it produce about 150 HP if the turbo was set to 7.35 psi, or an additional half an atmosphere? Assuming perfect efficiency, would it then produce 200 HP if the turbo was set for 14.7 psi? Also assuming that there is sufficient fuel available for combustion.

If you swaped the exhaust manifold side to side and flipped them upside-down you would have the exhaust exiting at the rear of the engine and turned up toward the hood. Would it be as simple as fabricating as short elbow to carry the turbo for each side and then fabricate a down pipe for wach side.
It seems this simple--What am I not seeing? If it were as easy as am imagining somebody here would have already done it, and posted the pipe dimensions, or even offer them as a kit.

 

[Exekiel69]

Specially if You are using this for towing one turbo charger is enough. This trucks can take safely 13psi and max at about 15psi but that is not proved to be safe yet . If You read one of Darrin Tosh post's He posted the results when He put He's truck on the dyno, I believe the # where 202hp at the wheels.

 

[Al_E]

I have been considering offering manifolds simillar to the ones I built, for you guys that want to try something different.

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[jauguston]

Michael,

Unless you just have a LOT of time and money on your hands to experiment a Hypermax turbo kit will give you all the boost your engine will like and it is a bolt on deal. Sometimes it is better not to try reinventing the wheel (-:

Jim

 

[RLDSL]

I have been considering offering manifolds simillar to the ones I built, for you guys that want to try something different.

You must be registered for see images

That is one sweet ride

----------Robert

 

[Al_E]

I agree Hypermax will give you all the boost you need and they have exelent tech assistance with whatever you decide to do. Thanks for the compliments on my truck.

 

[82F100SWB]

A pair of properly sized parallel twins would give near instant boost, and wouldn't over boost at all, but, I'd want to intercool, as with the quick spooling, you will make more heat towards the high end of the rpm range, and it'd need to be a wastegated system. Definitely could be sized to make for zero lag. I've thought about this, but, I haven't yet put any research into it. I know a pair of turbos from a 2.3T with a stick work very well on a 351w that turns say 6500-7000 rpm, so, they may work nicely on a 6.9, or they may be too large. I need to dig out my books and refresh my memory on this stuff.

The Hypermax system, and my Banks non gated, basically have the turbo oversized, so that it takes lots of exhaust volume to make it spool, and you'll run out of RPM before you move enough volume to make too much boost.

 

[FordGuy100]

A pair of properly sized parallel twins would give near instant boost, and wouldn't over boost at all, but, I'd want to intercool, as with the quick spooling, you will make more heat towards the high end of the rpm range, and it'd need to be a wastegated system. Definitely could be sized to make for zero lag. I've thought about this, but, I haven't yet put any research into it. I know a pair of turbos from a 2.3T with a stick work very well on a 351w that turns say 6500-7000 rpm, so, they may work nicely on a 6.9, or they may be too large. I need to dig out my books and refresh my memory on this stuff.

The Hypermax system, and my Banks non gated, basically have the turbo oversized, so that it takes lots of exhaust volume to make it spool, and you'll run out of RPM before you move enough volume to make too much boost.

All the stuff I'm about to talk about is what I have gathered, and might be true, or completly false, so correct me if I am wrong.

To pick the right turbo's for a parrellel twin-turbo setup, you have to look at what CFM's they flow. I dont know what a 6.9/7.3 needs CFM-wise at say 3300rpm, so I cant really say if those turbo's off of a 2.3t would work. But lets say if those turbo's are only flowing say 300 CFM appiece at the wastegated limit, then I would think they wouldnt be good for a 6.9/7.3, but two turbo's that flow maybe 450 CFM's apeice at their wastegated limit would probably be better.

Another things about turbo's, I think, is that boost is just the preasure measure above sea level of the intake manifold, and that the CFM's are more important. So if you have 15 psi of boost thats coming out of say a hypermax system, that is flowing say 900 CFM's (I'm guessing that is what a 6.9/7.3 IDI require CFM-wise, but I'm probably wrong) that would be a better system than a turbo that put out 100 psi of boost at only 100 CFM's. So I guess what I'm saying is that if your going to custom make a twin-turbo'ed IDI, you should look at the CFM's they flow, and not the psi of boost. Because you could be using two turbo's off of that 2.3 liter, and they could have a boost level of 25 psi apiece, but they flow less CFM than a properly sized single turbo that has been matched to the 6.9/7.3 IDI by Garrett and used my banks, ATS, ect... So if a hypermax system designed for a 6.9/7.3 IDI running at 15 psi of boost can blow out your headgasket, two turbo's off of a 2.3 running at 25 psi, but less CFM might not blow out the headgaskets, just because they are flowing less CFM's

But not nowing what a 6.9/7.3 IDI requires as far as CFM's go, and what kind of CFM's a turbocharger system from banks, ATS, hypermax, and those turbo's off of one of those 2.3's, I cant really say if they are a good match.

 

[Michael Fowler]

Thanks all, for the replies.
I gather that, in spite of the previous threads on this topic, no one has actually done this and made it work.
Too bad--that is probably the only way it would be cheaper than the hypermax kit.
Lets keep the discussion going, maybe someone at the IDI 4th of July camping trip can contribute when they get WiFi connection, or therwise back in touch.

 

[shorthair]

if you know the volume of the area where you are measuring boost at then you should also know the cfm of said area by converting boost to volume =cfm?

 

[ttman4]

All the stuff I'm about to talk about is what I have gathered, and might be true, or completly false, so correct me if I am wrong.

Well correct me too because I don't remember doodly squat, much less 1/2 what I should!
And I certainly don't remember all the lefthanded Chineese Algebra arithmetic formulas, but this would have some round-about way of having a bearing on air requirements & up'ed horses.

IIRC, the required number sticking in my mind (not sure of #) of 242 CF of air at 14.7#(1 sealevel atmosphere) to burn 1# of diesel factored along with, lets say, the 7.3liter converted to CF, along with how much fuel is crammed into these C/feet...., now fuel weighing approx 8#/gal X 242CF = the C/feet of air required to burn said gal of fuel.... WHEW! big numbers hurts my brains....

And IIRC, a C/foot is approx 7.5 gal, 231 C/in per gal.....,
Then there's Cetane#'s, BTU's converted to horsepower per gal of fuel.....,
Then there's figuring whether 'ya at sealevel,or at, let's say 3000' altitude....,

Now, if 'ya gonna cram 1 (one) gal of fuel in there per mile at, lets say 60MPH (1 mi/minute) 'ya got lots of C/feet of air to cram in per mile per minute.....

At 10# boost on a 7.3 getting 20 MPG at 60MPH......
At 15# boost on a 7.3 getting 10 MPG at 120 MPH....
If 'ya gonna leave lots of smokey 11's in the street 'ya need lots of air....& seatbelts
But even a 6.9/7.3 NA needs lots of air!!!

Man! Looking back over what I just said, I don't even know what I said!!!
siggghhh....I sure like my turbo.....

 

[72f2504x4390]

If the smaller turbo won't push the amount of CFM needed in a 6.9 then it won't develop boost. It has to be able to push excess CFM in order to pressurize. Otherwise the motor will be sucking all that it has quicker than it can supply it(restriction)

They will work just fine. Think about it, gas or diesel makes no difference. It is more about engine size(cubic inches) and rpm.

I know the stock 94 turbo is just barely bigger than one from a 2.3. A pair of them I bet would push 20+lbs if you wanted them to. I intend to try this myself since I am good at fabrication and have a mandrel tube bender at my disposal. Not enough time this summer so maybe I will do it next summer.

 

[jauguston]

Michael,

Your two turbo idea is interesting but don't think for a minute that it might actually be cheaper than a regular old tried and tested Hypermax turbo kit. I am willing to bet when you were done building it you would have way more money in it and you would have less boost and more trouble. Those kinds of projects can be fun but there are so many unknowns the odds of it working well are not very good. If you just want to do something off the wall different go for it but if you want boost go with Hypermax.

Jim

 

[Michael Fowler]

Jim,
I reluctantly agree with you. However,its easier for me to spend $100 here and there over time and have the experience of fabricating it than to drop well over a grand at one time. And so I hope for a magic pill to avoid spending the big bucks for the over-the-counter, tried-and-true, kit.

 

[82F100SWB]

A pair of those 2.3 turbos will make 14 psi on a W, no problem. 351 CI @ 6500 rpm = 1320 CFM
420 CI x 3750 rpm(my engine turns that) = 911.45 CFM, so, those turbo should be more than big enough.
They may be a bit on the large side, a 2.3(140 CI) @ 7000 rpm moves 567 CFM, which is more than half the volume a 6.9 moves., I'll have to dig out my books and re-educate myself on how to read a turbo map to see if the exhaust side is small enough on those units to spool properly on a 6.9, I'm thinking it probably isnt.