2.5 16v Turbo?

[George Elliott]

Has anyone ever heard of such a project among all the turbo engine projects which have been carried out?

I am aware that the 8v head is simple and strong, and that 16v is perhaps not so important when the engine is turbo'd, and Porsche used the 8v on their 968Ts which was either convenient, or a vote of no confidence in the 968 16v head. The 951 Cam profile was never state of the art either.

WUF proved 2.5 litres could produce 400hp with incredible attention to detail, so if it could breath easier....?

The 3.0L or 3.2L produce serious power/torque I can imagine, but the sheer swept volume creates challenges in itself, such as cooling capacity, inlet/exhaust flow rates, intercooling capacity, butterfly constraint, engine management perhaps. I have noticed more recent 3.0L or 3plus turbo projects have started to appear with 16v heads. They seem to have strong performance but perhaps at the expense of reliability?

So, 2.5L 16v turbo, smaller turbo, quicker spool, easier water cooling, easier I/C, better breathing, less windage, lower rotating mass, better fuel atomisation and swirl, better Cam profile?? with lower compression could it run more boost??

I realise the 944 parts bin will not have turbo compatible manifolds, but the 16v 3.0L engines have special components to get around this.

George
944T

 

[nick_968]

Never come across one....but it could certainly be done. But why would you go to the expense of making a 2.5 16v turbo when you could spend the same money and end up with a 3.0 16v turbo? They 3.0 16v do not have reliability issues if the install is done right i.e. proper intercooling, oil cooling, water cooling and a good tune. The reason Porsche used the 8v head was for simplicity combined with the low down torque of the 8v and the power limits of the series they wanted to race in. So they went for low hp with the fattest torque curve making 369lb/ft torque at 3000 rpm.

 

[Lowtimer]

I we take Baz Hart's 16V 3.0 Variocam turbo project as the ultimate in sophistication (as opposed to the ultimate in sheer high boost brute force), and the standard 8V turbo as the stone-axe dependable low-cost thing, a 3.0 8V turbo and a 16V 2.5V turbo would both represent different sorts of half-way house.

For everyday road use, of the two, I would take the 8V large capacity engine every time. I can't see why you would not want to have the capacity increase as the enhancement of choice, given that it does such wondrous things to the spin-up of the turbo, and greatly enhances the power and responsiveness in the normal 2000 - 5500 RPM range where we spend 99% of our time driving.

It might be that there could be more ultimate strength in a 2.5 16V Turbo meaning you could run higher ultimate boost pressures, and of course rev it higher, which in a race application might mean you could bet more ultimate top-end power. But that is only speculation.

If I were doing a complete engine build, spending my own money, for a road car, I would always choose to get to a given overall performance level by first using extra capacity to both minimise off-boost lethargy and bring the boost threshold lower down the rev range, and then focus on other enhancements e.g. the boost control system, trick modern turbo etc, to maximise the tractability and predictability of the throttle response and the size of the area under the power curve. A 16V head would be about the last thing I would try because I wouldn't have any reason to want to rev past the low 6000's anyway.

Beyond 400 HP in a race setting things might be different, I accept. But my guess is you would not get much from putting a dumb 16V head on a 2.5 turbo. Putting a smarter variocam 16V head on (968 gear, basically) surely has a lot of potential in terms of extending the top end whilst keeping the bottom end and midrange usable.

 

[George Elliott]

Nick, all good points, just wondered if the 3.0L approach was excessive and perhaps causing side issues but it is effective none the less.

Simon, I follow your logic, and agree the 6k limit, but just wondered if a high boost smaller capacity short stroke might rev out nicer than the monster capacity unit. I don't know, - what I do like however is your suggestion of the varioram being included. How compatible is the 2.7 block (with the big waterways) with the 3.0 16v v/r head, or I guess a relined 2.5L block giving 104mm bore with that head?

thanks for comments
george
944t

 

[nick_968]

As a rule of thumb the 16v head on a 3.0 adds about 100cfm and 100hp with nothing else changed. However it will make its torque a little later although those retaining the variocam have been able to cancel most of this out enabling them to have their cake and eat it! There is little downside to a 3.0 16v with variocam other than the cost to do it properly and keep everything cool.

 

[944Turbo]

9ff built one with 2 turbos

Though that was probably a 3 litre


Tony

 

[Lowtimer]

How compatible is the 2.7 block (with the big waterways) with the 3.0 16v v/r head, or I guess a relined 2.5L block giving 104mm bore with that head?

Dunno, but I bet if you call Hartech they will tell you/

 

[nick_968]

It is compatible as it is the reason the 2.7 8v head is used on the 3.0 block i.e. its the same block design with the same waterways. If you fitted the 968 head you would have a 2.7 16v but you would still need pistons, rods, custom intake, custom exhaust manifold, engine management, etc etc so why leave out the 3.0 crank?

 

[TTM]

As far as I have gathered, the combustion chamber of the 16V head is better shaped than on the 8V head and the detonation threshold is located higher on the ignition advance map, meaning it should allow to run a higher "dynamic compression ratio" (=static compression ratio + level of intake pressure) than on the 8V head, for the same given map of ignition advance.

The 16V head shines in higher revs and I'm sure would allow running "insane" amounts of boost, let's say more than 1.5bar, for a static compression ratio of 8:1 and ignition advance settings similar to those of an old Guru Racing chipset, provided the pistons are modified to suit the volume filled by the moving pattern of the 4 valve per cylinder set up.

It may well perform like an high output turbo engine from the early 80s though, gutless low down, barely driveable up top with a particularly brutal transition when the power kicks in... Not sure I would want that in a small-sized GT like a 944.

 

[Lowtimer]

That's exactly what I was thinking. The standard 2.5 16V is pretty much dead from the neck down but nice and fizzy when you rev it hard. Put a turbo on it, inevitably you would have to reduce the static compression (even you you could get away with a smaller reduction than for the 8V engine). You would thus emphasise both the main characteristics of the NA 16v 2.5 - it would be even more flaccid below 4000 rpm, but it would go like a mad rat on serious performance-enhancing drugs at high revs.

 

[TTM]

Yes, and as the dynamic compression ratio can be set higher with the 16V head, it would make most sense to run pistons with a CR higher than 8:1.

Duke's 3.0 16V engine build in Sweden illustrates that point pretty well, as his engine is apparently making a terrific amount power at only 1.0 bar with a CR I think of 9.5:1, without detonation.
However the thing is apparently so fast that he doesn't seem to run more than 0.6 bar of boost on the road.

Perhaps a 2.5 engine would actually be more driveable than a 3.0, a bit less power and less torque but well enough to get busy at the wheel.

George, you know what's left to do now, source a 944 S engine, a set of high CR pistons, some good rods and you will be good to go ...[]

 

[Lowtimer]

For my purposes, sounds like a low-boost 3.0 16V with variocam, say about 320 to 350 bhp ,would be just about heaven for the road.
Well, I suppose it's a lottery project.

 

[barks944]

Its probably not worth using the 16V head for that kind of power output. A 3.0 8V would give more bottom end and you can just use the turbo to compensate for the drop in VE.

 

[333pg333]

Shame that 9tt project didn't use dry sump and lower the engine saving the gouge in the hood.

 

[333pg333]

Oh, plus there are quite a few 2.6L 16v racecars in the US.

 

[Diver944]

ORIGINAL: Lowtimer

For my purposes, sounds like a low-boost 3.0 16V with variocam, say about 320 to 350 bhp ,would be just about heaven for the road.

I think you'd really struggle to make power that low with a 16v variocam head

My own 3.2 8v made 350bhp at the factory level of 0.8bar boost

 

[944Turbo]

ORIGINAL: 333pg333

Shame that 9tt project didn't use dry sump and lower the engine saving the gouge in the hood.

Is there space to lower the torque tube if you lowered the engine? The hood was in its unfinished state wne the pictures were taken. Havent seen any pics of it finished though.

Tony

 

[333pg333]

Having been in a couple of turbo'd S2s recently I have to say that they certainly didn't lack in low rpm thrust. Plus these are 8:1.0 c/r motors. I think the whole idea of 3L 16v motors being weak down low is not necessarily true.

Tony, yes, it's been done. In higher budget track cars the engine has been both lowered and positioned further back. Sure it's custom work but so is hanging 2 turbos off the exhaust side. []

 

[Jonny944CS]

Has anyone ever heard of such a project among all the turbo engine projects which have been carried out?

I think the first ever public outing for the 944 engine block was at Le mans in 1980-ish.

The famous block was in the final stages of production sign-off at the time. What better way to test - than strap it in a race car.... [8D]

924 GTP - only 2 cars built + ~ 10 engines

2500cc with a prototype 16v head

around 1.1bar boost

400-440hp depending on torque curve

 

[George Elliott]

Folks, I appreciate all the info and views, the question originated from my 15yr old son who suffers from an unhealthy interest in 951's, I blame his mother. (for allowing his father to waste time and hard earned on 951's [8|])
I can see the logic in the strong 3.0L argument, but Jonny, when I saw your bombshell, I am glad I asked. Really interesting that the boys at Stuttgart did that way back then, the marketing dept obviously did not have any say in LeMans racers.
Thom, I wish I had the time and budget, and yes it would have a temperment like the 1985 swb Quattro (see Walter Rohrl In Car video[])
Paul, perhaps if we run it on diesel..[]
Nick, why leave out the 3.0 crank......I'm struggling, your going to suggest Porsche would likely have used a less stressed 3.0 in 1980 if it had existed, and that is reasonable. What I would say, and its the reason I asked this question on the forum, is a 2.7 Carrera drives nicer than a Carrera 3.0. A lower inertia engine, with lighter internals, more top end boost, faster turbo dynamics, variocam to assist off boost performance, just wondered if it was worth considering, then you point out a 3.0 16v adds 100hp and Im thinking....blimey[].
Tony, the 9ff project, bit too 80's Yugo look for me, can you imagine the heat, I'd say the osf strut/damper needs to be watercooled[>:]
Simon, perhaps Baz will chip in here, or perhaps he is too busy keeping the nations m96'z in one piece.
Patrick, was not aware of the 2.6 cars, that would be a 944s turbo I guess.
George
944t