Hey gents,

Couple of questions regarding the topic: I know there have been built alot of high hp race engines but which different actions would be necessary to build a reliable and driveable smooth high power and revving street engine? High revving as in what levels could be reached 8-9k? Say power levels north of 400 crank hp.
From an open checkbook point of view. Think Singer DLS style :-D

If we look at the different parts involved, what would be needed to be done to each?

Cylinder block - Add volume and other necessary mods?
How big bores/sleees are possible?
Crankshaft, what would be needed to do here? Balanced, knife edged, lightened? Offset stroking and how much is possible? Custom profile billet? Think RS 4,0 crank for the 911 guys.
Rods, steel or titanium as some high revving exotics came with from factory?

Cylinder head - What sort of magic can be done here?
What sort/spec of cams would be best suited?
How big valves can be put in there?
Titanium/steel valves?
Titanium springs/retainers?
Solid lifters, titanium?
Porting/polishing?
Variocam, keep or not?
Balance shafts, keeping for smoothness or plug em?

Intake system - To match above? Increased cylinder volume and high flowing head.
ITB system what size throttles and plumbing?
Runner lenght short or long with the added cyl volume?
Plenum dimensions and design?

Oil system - Obviously dry sump but what more to secure enough lubication, more squirters, other parts?
Will drysump cure the second bearing issue?

Fuel system, ignition and ECU for the above updraged mechanicals?

There need to be a system design off course many good parts dont necessary make e good engine but surely come a long way.

So how exotic can we make it!? Cool And no V8 transplant! Keeping it Porsche!

 

I think the simplest and easiest solution for 400hp would be something like a mildly built vw 5 cylinder 07k swap with forced induction (see boost brothers garage for the swap, as well as their youtube channel). I dont think 400+ hp is achievable for an NA 968 build (but maybe I am wrong).

To go to the extreme such as what you are suggesting above for the 968 engine will put it more into the race engine category, and the cost for doing all the work (including forced induction if you want 400+ hp) you could probably do two 07k swaps. Much of the work you are suggesting is also going to have to sacrifice a lot of street ability and drive ability for such a build. For instance, removing balance shafts is going to introduce a lot of NVH, and typically something like dry sump is for a full race build (to maintain oil pressure in high g forces). The "second bearing issue" is typically only a problem in full race applications, aggressive cams will make your idle very rough, etc etc. If just doing the occasional track day, probably not needed.

Simply building the 968 internals (turbo rods, forged pistons, potentially sleeves) and turboing it, will probably get you there without needing to do much of the other work you are suggesting that will affect driveability. Using a 2.7L 8v head, a converted LR 8v head (in both cases using the 951 turbo and piping setup), or do a 16v head with custom turbo and piping. If you want to keep it NA I would adjust my expectations to 250-275hp range with some aggressive cams (requires disablement of variocam) and/or ITBs. In both cases youll want to convert to standalone engine management in order to ditch the restrictive AFM and have full tuning control.

 

A classic engine builder's mantra is that RPM stands for Ruins People's Motors. When you start getting piston speeds into the stratosphere basically every moving component in the engine is stressed exponentially harder. Something like 400HP from a NA four cylinder would sure be exotic but probably not very streetable and you'd be in rebuild territory pretty often. There's a reason famed high-revving NA engines like the BMW S54 need rod bearings replaced at regular intervals.

wallfreydo is right in that forced induction is really the true answer as far as getting the power more reliably and with a lot less investment.

 

Just add a V-8. Plenty of people have done it!

-Yogii
AKA 968 Novice

PS there is an outfit in Australia that purpose built an engine for the 968. Do a google search and you will find them.

 

Most realistic IMO is a 944 turbo engine swap, 350HP with some mods. 400HP could be done with a stroker or 3.0 Turbo. 450 on a 16v 3.0 turbo, maybe try to get some more displacement from an offset ground crank. The block will probably need to be sleeved or plated anyway for decent Turbo pistons in anything other than the 100mm bore. The engines won't rev and that's fine as I do not feel high RPM is suitable for a 944 street engine.
This more-or-less already fits in the chassis and would not require extensive fabrication which is not only expensive but takes time and leads to multiple revisions and fixes down the line. Only realistic if you are the fabricator and you want to invest the time.
IMO it would be a lot cheaper and less frustrating to get a 996 or 997 Turbo and just drive it around.
I get wanting to upgrade a 924s/44/68 but it's very easy to mod the car to the point where it's an obnoxious, always broken, money pit that never gets driven. Particularly once you buy a decently fast mostly stock car you can just drive around.

 

Guys, were my instructions not clear already? No transplants, no turbos, no superchargers, no Audis, no fabrication There is already a GT2 in the stable and a 2,7 head, 3,0 block and 951 engine sitting but they will not be participants in this dream.

I understand that its a slippery and expensive route and maybe we only get to 400 stressed hp but its been done before and with some other exotic ingredients we might up that a bit? https://rennlist.com/forums/924-931-...r-400hp-3.html

There are plenty of street cars with originally equipped ITBs. Why would they not work in this build?

Sure we can set the bearing change interval quite regular as well. I dont know what intervals Singer DLS has on those parts but sure they need to do some maintenance every know and then?

Would it not be able to spin to 8k with all moving parts lightened/lighter materials and in sync?

What gives the most change? Adding cylinder volume or working with cams/head?

 

OK you can have a refund for what you paid for my advice even though you didn't say "no turbos" originally (your instructions were clear but apparently incorrect) [edit- OK I see it in the title.]

No way can you get near 400HP with an NA Porsche engine that'll fit without fabrication. It'd be hard to do with 4.0L of displacement, and hard to get over 3.5L in a 968 engine.
Having only 4 cylinders is a big obstacle. Maybe figure out the gas speed of the engine you want and see how much you'd have to flow in order to achieve that.

 

If you really want to go down this road, you should start a conversation with @michaelmount123 . He's provided some really interesting threads over on another forum on his approach to building N/A engines, and has a ton of the kind of experience that I think you're looking for.

I'm interested to read about what you come up with. I have no ability (or the pockets of required depth) for something like what you're looking for, but I love living vicariously on these things.

Cheers

 

That's right, he already built one, the thread is on here somewhere and IIRC it was a 16v 104 bore 94 stroke 400hp at 8000rpm. Not sure if this qualifies as -street-


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I would say yes to both, but if only one choice, then getting as much flow as possible through the head is first priority over displacement.

 

The easies way is to swap in a V-8. Everything else will be a PITA...

-Yogii
AKA 968 Novice

 

Could you go ahead and elaborate on this “easiest way”….. Inquiring minds want to know.

 

a GT3RS is 4.0L and 500hp. 125hp/L

a 968 is 3.0L. so say 375hp target. you would need a hell of an induction system and big cams and ~9000rpm to get there. adding displacement will bring the RPM target down for the airflow needed.

928 blocks have been taken to 108mm with wet sleeves in the past. 968 has bigger barrels so that should be doable too.
you will want a deck plate made to hold the cylinders in place relative to the block.
i would have a custom crank made rather than modifying an old one. the price really won't be too far off but you'll have a NEW piece which is worth something and you can revise the oiling.
IIRC about a 95mm stroke is possible using the 45mm Mitsubishi rod bearings but for the RPM i would not think of using smaller rod journals. a 2" journal or slightly larger will be much stronger and has a lot of bearing options (NASCAR etc). you would want custom conrods with a narrow profile to fit into the block still. stock stroke is 88mm so maybe target 92mm. titanium rods probably good and very light pistons will be needed.

108x92mm bore/stroke = 3.37L

dry sump - yes

stock 968 cylinder head is very good already. Michael Mount probably has a porting plan to get a little more flow out of it. but you will really want mega camshafts to make this work with solid lifters. no variocam.
stock valves are 39mm iirc. could probably go to 40-41 with a big enough cylinder bore but may not be entirely necessary.

ITB not necessary but they make runner length tuning much easier. you could hit the power target with ITB or a well-designed single-TB common plenum. short runners since this is a max-effort kind of thing. the displacement will go a long way to making the torque curve liveable.

balance shafts - they are made to match the stock crank/rod/piston components and all that is out the window so i would ditch them. they spin at 2x crank speed so that could be 18000+ rpm...

 

Well there was a guy on here a few years ago who did it. I believe he sold it on Being a Trailer. Check there...
At my first track day a team from Gozoo Racing was working out the bugs on their V-8 powered 968 race car.

-Yogii
AKA 968 Novice

 

www.renegadehybrids.com

Very well-supported and documented swap.