Porsche Enthusiasts Club Forum

just looking into engine options, have considered v8's but tbh im only really interested if its twin turbo, and fitting it all in seems like it could be a lot of work. plus tbh Im more of a fan of revvy engines with boost, and as mentioned in my other thread I would prefer to keep the engine Porsche if its feasible. I am considering audi 5cyl 2.2 20v turbo aswell, but want to compare costs etc to a 16v turbo Porsche engine

my main questions are, will any of the 16v heads fit onto a 2.5 turbo bottom end? or would it need to start as a 2.7 16v engine with low comp pistons etc, or s2 engine with similar internal mods.

if you do need to start with a 2.7 or 3 litre bottom end, which is the stronger block to start with?

the other option to think about, is which displacement is most suited to turbocharging? a 2.5 16v turbo, 2.7, or 3 litre (or larger!)

I don't only want decent power of 450-500bhp+, but I want it to be reliable, and revvy to ensure a larger turbo can be used and boost held to the redline. which to me says sticking with a 2.5 or 2.7 bottom end would make more sense? the larger 3 litre engines and above I think may give to much of a diesel type power delivery, a big chunk of mid range/low end torque, and not so much top end and revs?

a 2.5 of 2.7 will mean a more revvy engine, and a more linear power delivery, as well as keeping the torque down a bit so traction is better and things break less!

obviously a 3 litre will require less boost to make as much or more power than the smaller engine options, but I think it maybe overkill?

people can quite easily get 6/700 bhp out of a 2 litre 16v engine, so 500hp is easily achieved with a 2.5 or 2.7, I am thinking this smaller capacity will give me an engine I prefer rather than a torque monster from the 3 litre or larger?

I am currently carrying out work for a customer building a 3 litre 8v turbo, who is also building a 16v version to replace once its all up and running, and I also had a long conversation with another customer today who wants to build a 3 litre 16v engine, so I have 2 customers both either in the process of building a 16v turbo engine, or wanting to do one. if I wanted to do one aswell it means 3 sets of parts can be fabricated/modified to get the engines working and turbos setup, which means costs will be much more manageable than building a one off! hence my interested starting to slide to this engine configuration.

be interested to hear thoughts, and suitability of each engine block for this application

thanks
nick

The 2.5 16v head bolts onto the turbo block I believe. The 2.7 and S2 blocks are practically the same.

I can't offer any opinion but am looking forward to hearing from some of the guys that know better, as turbo charging the 16v engine is something I may consider in time. I can't really understand why there is so much mystery around it, if it's just down to the fact that you need some extra fabrication over using the 8v Turbo head and ancillaries, then I don't see that as too much of a problem. Not really any different to all of the other NA to FI projects that go on outside of the Porsche circles!!

Although I'm sure I did once read that as far as forced induction is concerned, a 16v head doesn't offer any benefit over an 8v head.

Pretty sure, as Pauly says, that the 2.5 16v head will fit straight onto the 2.5 Turbo bottom end, so then it's just a case of exhaust and inlet fabrication, and then deciding on what to do with fuelling/ignition. Me personally, something like MegaSquirt would make sense here.

Look forward to seeing how the project pans out!

well that's good if a 16v head will fit straight onto the 2.5 turbo bottom end, I don't feel I need any more capacity than 2.5 litres. it will make for a nice revvy engine that has linear power and good torque that isn't silly and just breaks components and traction all the time.

a 16v head will show its benefits at the top end where an 8v will start to choke, much better if you want to run a big turbo and keep power to the redline. bigger turbos need more revs as they kick in later and so in turn require more revs to produce peak power.

the fabrication side of things is fine, and I have 2 customers both after inlet and exhaust fabrication anyway so it would just mean making another set!

like you say decent engine management setup will be required, with this you can also bin the distributor and run coil on plug, and wasted spark etc.

best ways to strengthen the bottom end? where can I find forged rods/pistons, and do I run steel liners?

I would only go 16v if you wanted to seriously increase the rev limit, say to 9000 rpm or beyond, but to go much beyond 7500 rpm you need to dry sump the 944 engines, otherwise the oil pump turns into a cavitating foam making machine.

Then, if you want high power, I would recommend turning the block into a closed deck design.

From experience, 16v bellow 6000 rpm improves torque but little on top end, but with the 944 engines you get surplus amounts of torque anyway, I have always found torque easy to get from turbo 8v engines, to the point where traction is an issue anyway.

Beyond 6000 rpm I have found that 16v in turbo (or non turbo) configurations begin to make sense, but going dry sump can be expensive.

16v heads have one benefit which also makes them work at high rpm, which is the ignition point being more central to the bore, which especially on very large bore sizes can become a problem on 8v designs, for the 3.2 turbo engines I had planned and carried out much of the leg work to develop a twin plug conversion to the 8v engines, but everyone who had a 3.2 found they had way too much power anyway and didnt want for more, so the engines never realised their potential.

For a real screamer engine, I would also be tempted to destroke the engine, which might seem counter productive, but it reduces some of the harmonics which build at higher rpm on these engines, while reducing the moment of inertia on the reciprocating mass, which then allows you to go even further in RPM while also improving response.

In any case.... Money.. Lots and lots of money is required

The 2.7/S2 block has the better supported cylinders and windage ports so if you want to go 16v an S2 engine with a 2.5 crank would be a logical starting point. Turbotim has gone this route so it will be interesting how it goes when he gets the engine in his car. Maybe the stroke/bore (rod) ratio was more favourable with this setup too.

I don't have my heart set on going 16v, im just looking into options etc, and if it doesn't make sense then I wont go that route.

I just thought putting a 16v head onto a 2.5 turbo bottom end could make it breath a bit easier and make it a bit more revvy.

if there is minimal gains then that may not be the best route to take.

it has been seen that 400bhp can be done without to much hassle on a 2.5 8v engine, and so I didn't think the jump to 500bhp would be as large as having to go dry sump, closed deck, fully forged etc! I know that's the best route to go in an ideal world where money is no issue, but I find a lot of engine builders overthink and over build engines to be safe. I have customers who go against the grain and all the advise given to them and run big boost and big turbos on totally stock engines, and they actually outlast the fully forged built engines and cost them a 5th of the price! yes one day they might blow up, but then you just buy another stock engine and chuck it in!

when people spend 10k building an engine, when you could buy 10 stock engines for the same price, you may find the stock engine lasts 2 years before it blows up! going on that scenario you could run stock engines for 20 years before you had spent the same money as one forged engine, that might only last a year or 2 more? or have build issues and blow up before even the stock item!

you can pick up 944 engines for cheap so it makes sense to try and see what happens!

the more simple option is to just stick with a stock setup and push the boundaries a bit and see if it lasts?
for example take a 2.5 8v, supporting mods, big turbo, and aftermarket management, and run it at 450bhp ish and see what happens?

im willing to take the risk of blowing an engine up in the process to see how it lasts when pushed a bit

Depends where you intend to use it, on the road where it's under full load for seconds at a time it could last for ages, on a track with long straights it may be found out quite quickly. Start asking for 450 bhp from old engines with cast rods and you'll probably have an engine like Fen's at some point.

that's the only downfall, I intend to use the car on track, although I would be installing a very large intercooler, and radiator/oil cooler etc. I don't mind cutting the shell about to house decent cooling setups and full front mount intercooler, maybe water injection aswell?

what are the main issues caused by track use on these cars?

I suppose mainly heat management.

I don't mind chucking rods and pistons in 2.5 bottom end if needs be

so my next question would be what sort of engine spec would be required to see 400-450bhp reliable on track? either with 8v or 16v head

im not bothered about going 3 litre etc, I don't think its necessary myself, you can have 500bhp and 500ft lb or torque from a 2 litre 16v with ease, so a 2.5 will be fine for my goals

main concerns and issues for track use?

if that's not achievable easily, then what sort of level of tune can be had an have a reliable car on track (and road occasionally)

if the 944t engine cant be made reliable on track, that's when I need to think more seriously about an engine conversion!

I've never tracked one so I'm just repeating years of internetting I think it's oil flow starving No.2 big end, cast rods and head gaskets mainly. That and too much boost/heat and revs for extended periods.

Are any of those engines cheap and have they got a old alloy block ?

does the 924 turbo engine take to modification and track use any better or does it have similar issues??

if you binned the cis injection, went for injection management, big turbo and forged engine could the 924 turbo engine be made reliable at 400-450 bhp (or more) without issues that the 944t engine suffers from??

Golden rule for these engines: You only need a 16v head if you already have a very expensive bottom end.

If decent power can be made from the 8v Turbo engine without spending an absolute fortune (i.e. forged bottom end, etc), then surely, at the very least, it would be an interesting example to bolt a 2.5 16v head to the 8V turbo bottom end, and to see how it turns out?

For me it would be about trying something different, that so many say is pointless, just because it's easier to start with an 8V Turbo engine.

I'd have thought the better ignition positioning on the 16v head would yield some improvements at the least?

Although, if a 16v head would mean a higher rev limit, surely in that sense it would be less suitable to FI as you will never get a turbo that performs well across a very wide rev range? You'll either have something that boosts low down and starts to become a restriction at the top end, or something that works well with the new rev limit, but will be laggy - or is there a way around that?