Turbo Header Qs

[Anonymous]

Ok. Addo has sewn the seed in my head, and got me thinking on this possibility. Good thing too, since I was about to get started on collecting the tubing.

What was suggested, was to take up the Porsche flat six exhaust profile, of having a common header for 1,3,5 and 2,4,6 cylinders respectively, and installing a 45 trim T03 at the collector on each header group.

I'm thinking the main advantage of this setup is that it'll sound cool. I dont really think that the turbos will spool up faster, although I may be wrong on that, since three cylinders will exhaust into the turbo one after the other. Perhaps splitting up the intake manifold into two groups, and feeding the intake charge into the plenums (Plenii?) will be good for ram tuning.

Oh, and another thing, is there such a thing as a harmonic for a turbo exhaust header? What I'm getting at, is there a rough formula out there to calculate the optimum header length while under forced induction conditions, or should it be treated exactly as it is treated with naturally aspirated engines?

Thanks

 

[StrangeRanger]

To duplicate the Porsche firing order, you need to collect an inline 1-2-3 and 4-5-6 which is almost too easy. Splitting the intake is the same thing, you end up with (2) 3 cylinder engines joined at main bearing number 4. Exactly what Ford did with the EFI 300 except they included a balance port between the pleni.

As to the harmonic, it exists, but it probably won't work quite the same because you're unlikely to get a significant negative port pressure in a manifold with a turbine mounted on the outlet. The longer tubes required for low RPM boost would also allow more heat loss offsetting any gains they might allow. I'd venture that for a turbo shorter is better.

The turbo should dampen or remove any pulsation from the downstream pipes, so tuning them is probably going to be of little value

 

[addo]

SR, are you sure about the Stuttgart firing order? I mean, if you look at a plan view of the crank journals, you will see 1,3,5 occupying one side's bores. Similar for a WRX.

AFAIK, the Porsche fires 1-5-3-6-2-4 in crank order, but this equates to one side, then the other in the plan view. Exhausts didn't used to cross over, from memory. (Do they now?) The Rexy is 1-3-4-2 in plan. Same scenario.

(Brief pause while cat pukes on floor and Adam cleans it up.)

I think there would likely be benefits from spooling the turbos this way. Three sequential impulses to one turbine may mean changes in A/R or trim. If the effect was detrimental, they would have a way around it - as for the induction, that's different...

A wild guess based on popular theory , but the current split system of first three, second three would be good to maintain. Anyhow, as it's all on one side, it's be easy to experiment a little. Worst case? You'd spend more for the same level of turbo performance. Best case? Whoooom! "What the heck was that?"

Regards, Adam.

 

[MustangSix]

SR is correct. Porsches fire on alternate banks with the order 1, 6, 2, 4, 3, 5 with this cylinder numbering.

front
3 6
2 5
1 4
rear

 

[addo]

That I didn't know. But what about the Subi?

 

[Anonymous]

Ok, back to the bank arrangement I was considering before.

Good to know that I don't have to worry about harmonics now. It seems a little hard to mimic the exhaust banking of the Porsche now, seeing as to exactly replicate it, i'll have to drag a pipe from the rear of the engine to the front, and vice verca.

However, three sequential pulses into a turbo still sounds rather promising. My idea on this is to have the turbos fired off like that, and have a common plenum chamber for the time being. If I feel like experimenting, I think I'll install a pair of air-water intercoolers (they'd be easy enough to make up, just get a pair of aluminium coolers, and weld some plate around where the air would normally go. Pump water through it using Holley Blue or similar solution, and have an a/c condenser cool the water for me), and have the opposite bank of cylinders feed into the engine, for instance, 1,3,5 would feed into 2,4,6. I don't think I'll be needing to change the housings or anything, since I believe Turbos work on a flow of gas. It'll be getting a little more than 2 litres of gasses flowing through it (for a turbo intended for a 3.0 I6). Some of the R31 GTS Skyline folk out there are quite happily running a 45 trim T03 on their RB20DETT motors (boost comes on at around 2000 rpm) The turbos will be idle for 50% of the time its running.

Has anyone got any further comments on this idea?

 

[rbohm]

8) if you want to run two turbos then SR is right, you want to gang cyl 1,2,3 to feed one turbo and 4,5,6 to feed the other. that way you have the turbos being fed alternately.

 

[MustangSix]

Six cylinder Scoobieroos, Corvairs, Lycoming, and Continental aircraft engines have the same firing order as the Porsche.

 

[StrangeRanger]

Disco
I'm getting confused here. Are you putting the twin turbo setup on an inline or on a boxer? Either way, the principal is the same, keep evenly spaced pulses in each collector. In the case of a boxer, you collect each bank separately, however numbered; in the case of an inline, you collect the front 3 and the rear 3.

The idea of crossing the turbos over to the opposite inlets may provide some balance in the case of one of them not functioning properly but if everything is working as it should it may not be worth the complexity vs. a single intake.

 

[Anonymous]

I wonder...
What if you split the exaust like you said and put two small turbos like for the little rice rockets(Something about half the size of yours). If I'm not mistaken wouldn't that make them spool up really fast and since there's two of them supply more then enough air to the engine. What engine is this for, the 200 or what?

 

[StrangeRanger]

They're only boosting half the engine but they're only being powered by half the exhaust. The smaller turbine and compressor are going to have a lower inertia so they will spool up somewhat more quickly but a properly sized for the street turbo is going to spool up pretty quickly anyway

 

[Anonymous]

Thanks for the insight SR

Ok, this is for a 250 EFI Crossflow, on Propane...

And yes, the turbos I'm using are known to be found under the hood of ricies..

 

[Anonymous]

I like your plan, Disco, though I am using a single turbo off the stock exhaust manifold. Anybody who is interested in knowing whether this plan can work needs to check out the story below...

http://www.truckworld.com/4x4-OffRoad/9 ... illys.html

 

[XFlow_Fairlane]

just use a log about the size of a stock six manifold. you migh teven be able to cut a stock six manifold and a stock 2.3L manifold and have them furnace brazed together...or just make your own log setup.

nick