Twin Turbo selection guidelines?

[kumba]

So I read through all 5 pages of the Turbo SHO sticky and I understand what was posted there regarding comp/turbine selection. What I didn't see was how you choose for a twin (paralell) turbo set-up.

Say I have a 3.2L and want to plan to make 450chp. According to what I read I would want a p/r around 2.0 with 45 lb/min of airflow and a turbine a/r somewhere around .70-.80 (whatever I can find), all hopefully making upwards of 15psi. But from reading that post, that is a single turbo guideline. While useful, and simply illustrating the points that needed to be made, I don't see much mentioned about how twin turbo selection should be handled.

Using what I know, and assuming quite a bit, my first inclination is to roughly halve the airflow and turbine numbers since only half the engine is driving/driven-by any one turbo. The PR should stay the same.

Am I correct in assuming this?

I tried some google-fu but all I could find were youtube videos with bad music and crappy video on a windy day in the dark, someones set-up specs with dyno sheets, or what looked like a infomercial script from the oxyclean guy telling me to buy some book I've never heard of.

As far as what my plans are I'm looking to acquire an '87-88 turbo-coupe 5-speed and put a twin-turbo SHO in it. Also want to keep the cold-air scoops on the hood functional as well (always liked the look of those). Since it's a fox chassis, and the engine bay is huge (longer then a fox mustangs), I should have lots of room and selection of parts to cram in there.

All I'm at right now is the research phase. I want to get my game-plan formulated so that when I do move on it there isn't a bunch of ad-lib going on (except the fabrication parts).

Thanks and any help, URL Links, or reading suggestions are much appreciated.

 

[LOUDSHO92]

Get some Turbo Books Like Maximum Boost and Street Turbo Charging and read up. You will need it.

 

[kumba]

Oddly enough, a relevant site (www.turbobygarrett.com) turned up when googling for LB/Min calculations. Busy reading through all of the info they have over there and collecting formulae for later. I'll look into those books you suggested once I'm done.

Once I get enough stuff together I will probably program a simple PHP graphing calculator that will allow me to just plug in numbers and see what kind of maps I should be looking for. Then I can start looking at turbo options.

 

[NEp8ntballer]

it'll require the same amount of boost to make the power but the work will be done by two smaller turbos as opposed to one larger one.

 

[luigisho]

That sounds like alot of work and an excellent project. You might want to consider upgraded internals on your build for that power level. Not saying you can't get there stock but I don't know how long it will last.

 

[rubydist]

You are on the right track w/ using the pressure ratio of around 2+ and approx half the airflow for each turbo. Then, you need to select turbo size and air ratio based on those numbers.

 

[Racer X]

That sounds like alot of work and an excellent project. You might want to consider upgraded internals on your build for that power level. Not saying you can't get there stock but I don't know how long it will last.

You can get to those levels safely on stock internals, however your margin for error in regards to fueling and timing are incredibly slim.

This sounds like it's going to be a fun build. In for the pics, good luck with it.

 

[SuperchargedSHOguy]

That sounds like alot of work and an excellent project. You might want to consider upgraded internals on your build for that power level. Not saying you can't get there stock but I don't know how long it will last.

The stock engine has been proven to handle 450 if properly tuned and not beat on all the time. Put your money into the car and all necessary parts and then if you need to upgrade the pistons in the future you can without holding up your build.

 

[luigisho]

The stock engine has been proven to handle 450 if properly tuned and not beat on all the time. Put your money into the car and all necessary parts and then if you need to upgrade the pistons in the future you can without holding up your build.

I totally agree. I would build it without forged internals for a variety of reasons. If I had optimal time and money I would put the stuff in. I would start getting wary of stock internals after I double the hp and really bump the tq #s. That's just my comfort level.

Then again, I bought just about every bolt on around thinking I was going to get somewhere. So take it for what it's worth.

Oh yeah. I second the pics please if this thing gets off the ground!

 

[NEp8ntballer]

The stock engine has been proven to handle 450 if properly tuned and not beat on all the time. Put your money into the car and all necessary parts and then if you need to upgrade the pistons in the future you can without holding up your build.

sounds like a poor investment only to have it fail eventually.

 

[kumba]

I was planning do take a stock 3.2 and do a full rebuild with forged pistons. From all the searching on this forum that seems like the best investment inside the engine for what I'm trying to do. I also like to slightly over-build if at all possible.

I'm currently looking for a reasonable workshop or just moving to a house with a garage in it. That is the biggest thing holding me back right now and is also the reason I sold my last '85 T-Bird with a 400hp 5.0L. Still miss that money pit. Once I get around that I'll make sure I update this thread as I progress.

I should have a turbo calculator up in a week or so that you can all play with. Hopefully you will be able to plug in your displacement, peak-HP RPM, peak-torque RPM, single or twin, and a few other things and it will give you some interpolated map points and values that you can use to shop for a turbo. Not sure how useful it'll be but it'll help me learn what's going on.

 

[SuperchargedSHOguy]

sounds like a poor investment only to have it fail eventually.

Once you grow up a bit you will learn that it is not necessary to beat the crap out of your car all the time. Building any SHO is a poor investment anyways.
In fact, any car is a poor investment with that attitude-they all break if you constantly beat on them.

 

[HotRodKid]

Do yourself a favor and dont throw to many mods at the car at one time, break it into stages and youll be much happier, for example:

1) swap motor, set up teh driveline, maybe throw in a turbo ready fuel system, make sure it runs properly
2) build the turbo setup, enjoy the car for the summer @ maybe 9 - 12 psi, as you might find that your maf hates being where you put it or something.
3) swap in a built motor, break it in at low boost, then when its happy @ 9 psi turn the wick up to 15+ psi

Dont be like me and somedude, with gutted chassis that are getting the summit catalog thrown at them all at once just so we can sort AAALLL our glitches out at the same time, its a great way to wind up hating your project car, lol

 

[kumba]

Well my plan was pretty much as you have listed except step 1 involved that 3.2 rebuild with forged pistons. I can't really bring myself to just put in an engine without at least tearing it down and putting bearings, gaskets, and rings on it. If I am already that far into the engine I might as well slap pistons on it as well. I already know that if things go as planned I will need these pistons, and worse case scenario I have an N/A block that makes a little less power. As far as bugs go the different pistons should be pretty trouble-free as long as the machining is good on the block.

 

[HotRodKid]

that works too, its normal to build the motor for boost, drop it in and add a fuel system thats ready for boost at the same time.

you may have to do something about the exhaust manifolds when you put the motor in, i know you cant use a stock manifold on the drivers side of a sho powered LT1 style camaro. sho manifolds are swapable side to side, but neither will clear the camaro steering shaft. you may or may not have the same prob.

 

[kumba]

Well I no longer have access to the TIG welder I used to but I still have quite a few friends who do. I was planning to make some manifolds and then have my buddy do the seams. I'm just going to do the mock-up and tack them together.

 

[illSHOyou]

Once you grow up a bit you will learn that it is not necessary to beat the crap out of your car all the time. Building any SHO is a poor investment anyways.
In fact, any car is a poor investment with that attitude-they all break if you constantly beat on them.

What he said...Plus NEp8ntballer , do you know how cheap you can get SHO motors? Who cares if you blow one up, just slap in another, but on a serious note if its tuned right the engine will last. 90% of the time engines blow up because of bad tunes, not hardware problems.

 

[SHOtime2511]

twin (paralell) turbo set-up?
Like a stock twins Supra?

 

[kumba]

Parallel as in both turbos make boost simultaneously, instead of sequential (like some diesels) or in series (one turbo feeds another turbo). So yes, probably like a supra. The 2010 SHO uses a parallel set-up. The 6.4L Powerstroke Diesels use a sequential set-up. I was told by a Mazda guy a while back that some of the early turbo rotary's used a series turbo set-up.

Parallel is what most cars are. From what I've been reading it's the simplest and easiest way to do twin turbos.

 

[Toolman]

I always found that the easiest way to do twin turbos was to leave one off.