sizing turbo headers

[rebelce]

Howdy Gents,   I'm building up a friends car and it's time to upgrade the header system on the turbo. Right now it's a simple log Ack Miller had made up for us 15 years ago. We always hear the sayings, go smaller for bottom end, larger for top end power.  To me that's a little too ethereal. We're talking a 330 CI six and 45# of boost. It has 3 inch tubes running to and from the charge cooler, which is rated at 1300 HP and I want to tax it! I've built up low angle merge collectors but the tubing size has me stumped.  Any ideas?

[Dynoroom]

What size turbo & how many?

Is this for Bonneville or Mile events?

What engine speed do you run?

Is this a gasoline or diesel engine?

Do you currently monitor turbo back pressure? If so what is it?

At what engine speed do you start to make boost now?

Is 45 lbs. how much boost you run or what you think you want to run?

What do you think you will gain by running tubes vs. a log?

[rebelce]

Hello Mike, thanks for stepping up to bat. This is my friends drag car and we are in the process of upgrading the package.  The car is up in Boston right now and and I don't have all the information right off the top but I can answer many of your question from memory. I can be more detailed when it's back.  I don't generally mess with drag racing but felt the answers here could be used on LSR engines as well.



What size turbo & how many? - T4, the AR's will be coming.

What engine speed do you run? -  Because it's a straight 6 with a long, cast 292 Chevy crank, we limit RPM to 6,000 for now (trying to stay out of harmonics.

Is this a gasoline or diesel engine? - Alcohol via Ron's injection

Do you currently monitor turbo back pressure? If so what is it? - No we don't have a data acquisition system but it's in the plans. It's the only way we can know what's really going on in the car.

At what engine speed do you start to make boost now?- It comes up to 20# @ 3,000 RPM at the line

Is 45 lbs. how much boost you run or what you think you want to run? - This is a target, it currently runs 25# with the waist gate cranked down. Jack has sent us another turbo, it looks (from memory here) like a T3/T4 hybrid.

What do you think you will gain by running tubes vs. a log? - It's my feeling the least restrictive, most direct path from the engine to the turbine will gain more power than a turbulent log. Sort of like the last page on your link.

Here's what it looks like now

[Dynoroom]

First, NONE of my answers are meant to discourage you and your friend in this endeavor BUT…..

The turbo you are running does not flow enough air to make 1300 hp although two of them can.

You are also most likely running waaayyy  off the compressor map, at least at 45 psi you would be. Many maps for this type of turbo with all it’s variations are on the internet so you can check for yourself. You might start at the Garrett/Honeywell site or Turbonetics as they both post turbo maps for the unit.

I would never run that much boost with that turbo (although I know much of your competition does) When you start running above a 2.5:1/3.0:1 pressure ratio all you do is make more hot air (less density) for the chargeair cooler to try to convert back to a usable range.

The engine speed you are running for durability makes it somewhat tough to make hp you want too. 900 lbs/ft @ 6000 rpm is just over 1025 hp & 1000 lbs/ft @ 6000 rpm is ~1150 hp. Can your crank & bottom end stand this?

You can and should (IMO) check current backpressure as this will also help you determine IF it is worth the time and effort to build tube type exhaust. Backpressure is mainly a result of turbine size, turbine housing size & design then lastly exhaust system.  When backpressure gets ~2 times over boost you will start to see diminishing returns on performance VERY rapidly, although this is less of an issue in drag racing than endurance racing much like the boost pressure issue above. You can easily do this by drilling and taping a hole in the turbine inlet side of the exhaust manifold and running a pressure gauge that works in 1 pound increments for the driver to see. Peak pressure as all you need to know. I use a piece of copper tube about 3 feet long coiled up to act as a heat sink and a Freon filter (Graingers or Mcmaster-Carr) to help protect the gauge.

If you were going to run a divided turbine housing to try and get “pulse” tuning don’t waste your time unless you feel you are giving up low speed performance. It didn’t sound like that was the case as you stated 20 lbs @ 3000 rpm. This is the starting line stall speed correct? If so you won’t see any improvement (IMO) trying to pluse tune.

Okay, I know I haven’t answered you original question on tube size and length yet….
The real reason is I don’t think you will see any measurable improvement in your system until you deal with some of the other (IMO) shortcomings. If you must have tube exhaust don’t forget to allow for system expansion with either slip fit tubes or bellows. If you don’t do this your pipes will only last a short time <2 years IMO.

That being said I do use a formula to calculate tube diameter & length but need a few more specs from you:

Bore & Stroke. I already have the engine speeds I need.

[Blue]

Howdy Gents,   I'm building up a friends car and it's time to upgrade the header system on the turbo. Right now it's a simple log Ack Miller had made up for us 15 years ago. We always hear the sayings, go smaller for bottom end, larger for top end power.  To me that's a little too ethereal. We're talking a 330 CI six and 45# of boost. It has 3 inch tubes running to and from the charge cooler, which is rated at 1300 HP and I want to tax it! I've built up low angle merge collectors but the tubing size has me stumped.  Any ideas?

First, the turbo size needs to be increased significantly for what you propose.  Dynoroom is right, and you may look at a pair of 3-into-1's and small turbos or a larger single turbo.

On the header, there is absolutely no question that a header is better in every area of the powerband than a log.  40 years and literally billions of dollars of experimentation in drag, indy, and F1 have proven this.

Sizing?  I'd let Burns tell me.  As a guideline, size the header as you would for a normally aspirated power plant then correct for the higher EGT, pressure, and flow (fatter and shorter).  2x compressor pressure in exhaust back pressure is certainly too much, 1.5 is a better planning figure;  although you have to look at trades in 4000 vs. 6000 RPM for your current plan.

As to harmonics, remember that a properly balanced I-6 has no balance or moment issues and can spin faster at higher power than an equivalent V8.  I don't think the bottom end of this mill is up to this, I would spend some time on tall main caps with sleeves and a girdle.  What are your rod and b/s ratios?

[rebelce]

Much to think about and absolutely no discouragement issues!!   The turbo can be changed as well as anything else that needs it. That's the nature of racing. Though going to the car owner and telling him the shop's suggestion was off on turbo sizing. I don't think they were aware of the horsepower we are making or where we want to go. Right now the car has ran 9.48 @ 139 MPH.  Which ain't half bad for a straight six. Estimated HP based on those speeds is apx. 600 Hp. We will need every bit of 45#'s if we are to attain our hopes. The turbine housing isn't divided, though the old one was. The mounting flange for the two are the same. Yes, 20# up against the trans brake.  We will change what we need to, it may be one bite at a time, it's a big elephant, but it has to be done! That's our mantra, knocking out weak links and trying to stay one step ahead of Murphy. The log manifold was extremely bad at sealing on both ends. The bolts would loosen every round, expansion no doubt, that's diffidently a place to be aware.

One good thing about the late sixes, is the seven main bearings. With copious amounts of nitrous, they have lived at well over 1400 Hp. There is an all aluminum Duggan block sitting at the shop for the next round and it is the engine I described. The Duggan has a bore and stroke of 4.125X4.120.  This engine has an additional set of main bearings for a total of 28! The bearing size is the same as a 350 Chevy. We use two small block Chevy heads, cut and welded to form a straight six, the block is re-tapped for the new pattern and Falconer's laminated head gaskets go right on.

In all due respects Blue, even though the straight six is in perfect static balance, it's length and firing order make harmonics extremely bad. One friend measured 16 degrees difference between the front and back of an older GMC when it got going. Broken cranks and flywheel bolt loosening are two of the most common areas but timing gears and cams have been know to go away as well. As far as I know, the only two ways around it is the best dampener and /or staying out of the ranges. We are running 7 inch aluminum rods with a stroke of 4.120.  It will live or die trying!

[Blue]

Respect to you, for pushing the envelope;  we're all here to learn.  Forgive my lack of knowledge of this series of I-6, is the firing order 1-3-5-6-4-2?  And the next question, is it fully counterweighted at each crank throw?  I ask this because BMW and Toyota I-6's are famous for their incredible smoothness and are able to take obscene levels of specific power (>8 HP/ci) without shaking. 

That's one of the reasons for the r/s question.  There's a lot of debate right now about how low to go, I tend on the higher side of 2.

[rebelce]

Morning Blue, you're absolutely right, we're all here to learn and everyone brings something to the table. Straight 8's and 6's suffer from torsional vibrations.  I think the three greatest reasons these engines tend to brake cranks is 1) the length of the crankshaft, 2) The lack of torsional rigidity and 3) A firing order that tends to exacerbate the natural frequencies.   For the 6's it's 153624,  One and six fire 360 degrees apart on opposite ends of a long springy crankshaft.  One main reason the BMW, Toyota's and other small sixes run so well is the diameter of the main and rod bearings. It is the amount of overlap between the two that helps establish the rigidity of the crankshaft.  Our old truck 292 engines have a main bearing that's 2.3" in dia. and a rod journal of 2.1". When you add that to a 4.12" stroke there is only .095" of overlap between them. The 12 counterweights actually add mass to this and make it worse!  Though they do make your bearings last a lot longer and the engine much smoother. lightening and polishing the crank, running a good harmonic dampener, a light flywheel and staying out the offending RPM ranges is about all we can do. Don't you hate compromises! Hope this helps as you have helped so many of us understand airflow.

[1 fast evo 2]

First things 1st I the car is pretty badass.
Next I totally agree with Blue on the header. Back a long time ago I when switched from muscle cars to imports no one ran tubular headers and I thought that was extremely weird. Now after alot of experimentation we know that a good header is worth quite alot of power over a log style or stock ex. manifold, is it worth having In a 3-400 whp car no not really unless you are trying to push that setup as far as you can. I think it is without a doubt a needed upgrade to your system.

I think we need the exact size of the turbo, cam specs, head flow(this will help decide if you need a low or high pressure turbo), you said you are looking to make around 12-1300 crank hp rite??
I also agree the turbo will need to be either bigger or 2 smaller ones installed I highly rec. 1 larger turbo especially as it's a race car, and costs involved will be much less with 1 large turbo i.e. piping, waste gates, fittings.

[rebelce]

Well, I kind of lost a portion of this round.  I finally got the cars owner to step up to a tubular/pulse style header but after designing a merge header system for it using 2 inch tubes, we dropped it off at the header company.  The car owner and header company owner decided to re engineer my headers and now we have a set made with 1.75 tubes into so-so collectors.  He's also decided to run the T4/T3 turbo for this season.  I personally think he wasted a lot of money for minimal results.  A six this size is equal, cylinder for cylinder, to a 440 V-8.  I'm kind of bummed out but maybe I'm out to lunch on this one and it will kick ass.

[SPARKY]

Would love to see picts of finished product and how it differs from your choices   

[rebelce]

Will do!

[RidgeRunner]

     Thought I had a handle on forced induction systems after having worked around them for a bit, Roots since '65 and turbos since '69 in marine and locomotive applications.  Recently I picked up a copy of "Turbo Real World High-Performance Turbocharger Systems" by Jay K. Miller ISBN 978-1-932494-29-7.  For me it has been more than worth the purchase price and has again validated the old theorem "the more you learn, the more you know how little you knew".  I recommend it highly to anyone thinking of or running a forced induction system.

     Was also taught [and experienced in '67] that every engine crankshaft has a critical speed, usually above or below normal operating ranges.  If unavoidably within the range, the application is usually engineered to pass through that range as quickly as possible.  In my opinion, for performance applications, harmonic balancers are a viable band aid but balance shafts border on an inefficient crutch/cover up.

                                Ed

[Rick Byrnes]

I have been under the impression that balance shafts affect only shaking forces, not torsionals, which is why they are found primarily on large 4 cyl engines that have quite high secondary order shaking forces.
I wouldn't use them in a 4 cyl "race only" engine.  Wasted energy, increased friction, increased complexity etc etc.
With the long inline 6 cyl crankshaft, torsionals are the most noticeable and of course most destructive.

God said any 4 cyl over 2.0 liters  shakes like hell.

[mtkawboy]

It was 40 years ago, but I had serious problems with flywheel bolts on a drag race 300 Ford 6. No matter what I did they broke or backed out, even tried safety wire, stronger bolts and tacking bolts to the flywheel. At then time there were no trick harmonic balencers made so maybe you wont have that problem today. Good luck with it, especially against the V8s