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6 cylinder 4.0 liter turbo choose

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Hello, I need some pieces of advice from more experienced engine builders. I am building a 6-cylinder 4.0-liter boxer engine (Porsche natural aspirated in stock modified to accept a turbo). Target is 650-700 hp and spool as sooner as possible even if I have to sacrifice top-end power. I have chosen to go single turbo (more manageable with fewer parts) and an EFR-9174 for that engine with a 0.83 vband turbine housing. I was between 0.83 and 1.03 housing, considering the long turbo manifold needed over a meter maybe a meter and a half. I am afraid that the housing will be too small for that size of engine. What you think any one more experienced in same size engine?

this might be off topic but if you want power as soon as possible and willing to sacrifice top en power. a supercharger should work much better for what you want to do. much better low end power but on top end it does reduce a bit. turbos are mainly built for top end power and reduced low end power in the form of lag.

you might also want to mention what engine you have no two engines are the same. one 4.0 V6 in a Porsche might be completely different from a 4.0 V6 in a BMW for example.

also in what conditions do you want to run it? track drag drift or weekender?

now if your concern is the intake might be too long. at 1500mm yea it might be. however you need to look at the shape of it.

flow rate Q = mV x A Q1 at one point wil equal Q2 at other point. in other works lots of flow though a small area wil be high velocity air but that same air will slow down as the cross section increased. we had a 1200mm intake in our FSG car back in 2011 with 20mm air intake restriction. to get around the problem we expanded the chamber leading to the manifold and exchanged velocity for pressure. further we injection molded the intake manifold with internal runners so that opposing cylinder runners would face each other inside the intake. air has momentum and these runners would act as a pressure battery and feed the next intake stroke in the opposing cylinder

in short it all comes down to the design that you use. smaller diameter intake usually has higher airstream velocity but its how you use it that matters

Enzo, it's a flat 6, 4valve, quad' cam' engine.

As you said, it's going to depend on exactly what he is wanting. It also depends how much emphasis he's putting on where it starts to produce boost, and how critical lag is going to be?

If it has an 8k red line, some may consider "as sooner as possible" as being from 2k, others from 4k and others maybe higher, for the engine to start producing boost. With lag, some may want it to respond as soon as the pedal is smashed to the floor, others can accept that slight delay as it spools up and develops boost.

I would agree, for what he seems to be looking for, a supercharger may be a viable alternative, a centrifugal may even be easier to integrate than the turbo', when you consider the additional plumbing and heat control that would require.

I'm assuming from your avatar and the description you are dropping a 911 GT engine into a Cayman/Boxter? Ceramic coating/wrap & heat shield the manifold/cross pipe to maintain energy. Should still be impressive.

If it's cammed more like factory turbo (peak power under 7000rpm) it should make ~ 650whp at 2.2bar absolute, 1.2 bar boost at sea level, over 700 at 2.5. If response/boost threshold is your priority EFR8374 is probably your best bet, with an engine that size and decent gearing I would probably run housing around 1AR but it might be worth trying both to see how you feel. If it's cammed more like GT3 I would be tempted to go EFR8474 with the largest Vband housing or step up to the larger turbine.

Might be worth looking at final drive ratios too, although with that displacement and boost the criticism of the bixter/Cayman final drive ratio might be moot.

The supercharger solution is not on the table there is no free space in the engine compartment in a Porsche Boxster.

Dear Michael Howes,

Unfortunately, I don't have a gt engine, I fitted a 997 c2s Carrera engine (naturally aspirated in stock form) 3.8 sleeved to 4.0 liters with dartons mid, JE forged pistons, k1 rods, arp bolts almost everywhere, and a Maxx standalone ECU. The camshafts will be kept stock at the moment.

So you think the 9174 will be too big? better go to smaller hmmm. Between 8474 and 9174 I think there won't be so big a difference in spool and response because they use the same turbine shaft 74mm. the turbine housing ar will play the most critical role. If I choose to go with 9174 which turbine housing should I go for concerning the AR?? But I will take a second thought about switching to a smaller turbo...

As far as gearing I have many options on a Boxster I will do some tests and choose the right for my application but considering the low weight and the power output, the stock long gearing seems ideal.

It's probably a personal preference thing on how you like the power band, either compressor will flow enough air for you, the 84 might be easier to package being smaller OD, you don't have a high pressure ratio target for that power so the 91 wheel is probably wasted in your application.

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