Porsche Enthusiasts Club Forum

starting to think about the engine build in my 924 turbo, and as the project seems to keep getting slightly more involved, im starting to think i want to hike the power substantially to match the rest of the car.

when looking about before i found some parts are not the easiest to get hold of these days!

whats the deal with the bearing shells which are/were unavailable, and what to do if when i strip the engine i see it requires a new set?
also arp bolt sets?

the main thing i want to be able to do is run a bit more boost without worry of blowing the cast pistons?

i can fabricate a custom exhaust manifold so as to run a modern turbocharger etc, i just want to ensure the engine can cope!

best pistons and rods to use?

really i want 350-400bhp? realistic? if not what sort of power levels can i expect without going crazy?

other areas of attention the 924 turbo engine will require? i will be getting rid of CIS and running standalone management

this question is purely regarding the actual engine build itself only, all the supporting mods/management etc i can take care of, just need some more detailed info on the engine and its capabilities/downfalls at higher levels of tune.

not a huge amount of info i can find out there

i have a few updates on shell prep progress to come soon! cant wait to get the panels for the front end, and show you all the updates to the shell work, aswell as a few other interesting 944/924 projects we have on the go for customers!

many thanks
nick

Some of your asks and some can be found here viewtopic.php?f=25&t=13106&hilit=Modifying+924+turbo

Bearings - bloody hard to find. There was a group by on 924board.org but that's well delayed
ARP rod bolts need another group buy. They make 10 sets to order. A must on high boost build
JE have made lots of turbo, GT, GTS forged pistons from 7.5:1 to 9.3:1. CR. Take your pic subject to overall engine plans and spec. I'm running Omega forged.
Check out Wes's build for manifold fab, Holset turbo, EFI etc. That will be a monster once he pulls his finger out and gets it finished

cheers! so is the group buy still active on 924 forum? if bearings cant be found whats the solution? there must be companies who can knock a set up from scratch? albeit at a cost!

i suppose it might be hard to find 10 people all wanting arp sets for 924 turbo? although tbh 10 isnt really that much of an ask is it?

is there no demand for these parts, surely there must be people building carrera gt/gts/gtr cars around the world? how do mittlemotor go about rebuilding a 924t engine, or freisinger when re building race cars etc?

i really want to keep the car 924t at heart as its a rare car now! but at the same time i want to use the thing! and if i cant get parts i may feel like putting another engine in! plus point is i have time to find the parts as im concentrating on shell build and getting it to rolling shell stage. engine can be last thing to worry about, but i want to make a plan and start sourcing parts!

hows your car? i have seen wes build looks interesting and i will be going down a similar route with efi and modern turbo setup etc

cheers
nick

Mittelmotor have lots of parts but have run out of bearings when last asked. Friesinger also had none.

Dan at ideolasgarage.com does try to keep some NLA parts and collates interest in group buys

Hi Nick, the guy who put the liners in my block also casts and machines bearings up for the pre war aston martin engines he builds. He would need your block and crank I would imagine. I will pass on his number when i drop turbo and engine mount of later today.

on my phone...
350-400 a lot to ask of stock pistons/rings. 280hp has been done but YMMV
Whats the budget hehe

Forged pistons are around 650usd plus shipping and tax etc.
Crower rods around 1000usd plus shipping and tax. They're I-beam and virtually indestructable and include ARP hardware.
ARP will make sets of 5 but they go up in price then to more than 300usd.
Even 10 sets cost more than 200usd.

Alternative approaches:-
Stock rods can be prepped down to 815g each IIRC with typical balancing machining shotpeening etc.
A good machine shop should be able to modify them for non standard larger rod bolts.
Throw away stock piston rings and get some total seal rings. Place in York sells them.
You could then get the cast piston crowns ceramic coated to help with heat tolerance along with all the other heat management.

Or get Mittelmotor to crate you a brand new GTS spec engine. No idea of price but their GTS spec car still running CIS, K26 turbo and electronic dizzy puts out 343bhp. How much more do you need from a well balanced 1000kg chassis? You have to get that power down

Mittelmotor supply 931, GT and GTS pistons http://www.ebay.co.uk/itm/Satz-Rennspor ... 2a33bb58ee contact directly as their ebay price includes ebay and paypal fees.

They also do rods http://www.ebay.co.uk/itm/Satz-Rennspor ... 2a33af510a

I'm sure £10-15k could easily be sucked up into an 'ultimate' 924 turbo engine build.

I agree with Steve that ~343hp is more than enough in a light 931.
Even 250hp and 1000kg is quick.

There is also more than one way to 'skin a cat'. Do you want all out power at the expense of some response or do you want torque from the word go?
I believe it's possible to get a genuine 300hp+ and retain good response but it needs careful planning and turbo-matching etc.

I'm not even sure anymore what the ultimate 931 engine build would be - probably defined by the individual.
I've changed my mind many times.
'Ultimate' to me would be an engine that's usable in any situation, with 100% reliability, whilst providing enough torque and power to scare the s*** out of me

It's a very simple engine at the end of the day. Relatively speaking, and I stress RELATIVELY, a monster engine spec could be put together for reasonable money in the grand scheme of things.
I'll build you a nice engine for £10K but I'm sure you're quite capable yourself.

Answers on a postcard for the ultimate 931 engine spec...

thanks for all the input guys, i agree im sure anything over 300hp will be plenty quick enough, but this is an all out race car, which will be running 12/13j rear wheels and slicks/semi slicks etc so i want enough power to keep things interesting. i don't want what i had before from another track car which was to much grip that overcame the power of the car and made driving it a doddle and bit boring!

with regards to driveability im never going to use the car on the road, and so it will only ever see the track, and therefore peaky engine is not so much of an issue.

whats the head like on the 924t? will it need attention or flows well as stock? i see there are big valve kits available. how about the valvetrain, what sort of revs can it cope with?

dry sump system available? or custom build setup

any downfalls/weaknesses with this engine?

many thanks

13j slicks and all-out race car... I'd go the whole hog then.

Dry sump system is supposedly available from Pace but not cheap.
I'll be back on later to post properly.

Do we need two 931 engine threads? This is when discussions get lost in the search function/memory banks. Can we merge with the link above?

I see what you mean Steve. I can post in either or both?
The 'Modifying/Improving the 924 Turbo' thread isn't really limited to the engine though.
I think Nick is after something quite extreme and as we know 350-400hp is easily in reach with a modern turbo and ECU.

So here's my thoughts on a race engine build:-

The block is about as strong as it gets so doesn’t need any special attention.
I considered changing the main cap bolts for studs but it’s really not necessary.
The cranks are also strong and personally I wouldn’t remove loads of weight from it. A typical race prep finished by hand is enough along with getting the rotating assembly dynamically balanced.

The standard rods are strong but in a race engine I’d go for some aftermarket, lighter rods with their own ARP hardware. Take your pick with those from such as Carrillo, Arrow Precision, Crower etc.

The pistons are said to be an achilles heel but no more so than any cast piston but are unsuitable really for a 300hp+ build.
Omega, Wossner, JE, Diamond will all make suitable pistons. Get them to base the spec on the S2 turbo piston.
The ultimate would be a piston crown that mirrors the head chamber which you can get from the likes of Omega, for a price of course.

People have different views on the head gasket which is also seen as a weak point as on many turbo’d cars.
On a car that sees serious abuse on track I would go with the ARP studs and a Cometic gasket.
The heads can deform after longterm sustained abuse with the standard OEM gasket and the bi-metal nature of the engine does the gasket no favours.
It’s not that much of an issue on a road car but your engine will be more than double standard power…

I would definitely go with a dry sump. Not just for lubrication but also for crankcase breathing/oil control and better combustion.
Mark has the Pace system on his GTR replica.

The head is nothing special, just an average 8 valve head.
The design is old and suffers by modern standards.
Even a well-developed head struggles to flow more than 170-180CFM.
The valves even as standard are shrouded by the combustion chamber and the bore limits. Boring the block out helps alleviate this to a degree.
Head mods are as any other 8 valve head - don’t take much material out of the ports just smooth. Make the small radius in the valve throat larger and get a decent seal on the valves.
Ideola can source you a big valve kit that comes with everything you need including heavier duty springs which you’ll need for higher revs and boost.
Sourcing other valves on your own means trawling through catalogues then maybe getting them modified by a machine shop.
Whilst you’re ordering the kit, order a set of Sten Parner followers with some Manley shims. The standard followers won’t be up to the abuse and have been known to break up.

Cams are always an arguing point. Catcams do some turbo specific ones.
http://www.catcams.co.uk/acatalog/Porsche_924.html

My opinion is that unless you’re making a proper split pulse twin scroll manifold then stick with something mild.
A truly divided twin scroll system would get some benefit from a hairier cam.

Which turbo are you thinking of using?
As an example, a GT30 has made 384hp on this engine, even with the stock exhaust manifold. The same engine has seen lots of track abuse since 2003.

cheers for all that! all very useful!

is the car running the gt30 one from abroad? i remember seeing videos of something like that on youtube but cant seem to find it again! what sort of spec engine is he running to achieve those figures?

i was thinking of a gtx series turbo which give good power and awesome spool, 3071/3076? depending on final power goals etc.

any recommended engine builders for these motors if i was to get someone else to do it? if i have time would do it myself but time is scarce atm! so maybe something i source out.

clutch options on this engine for 400hp ish?

how is your project coming on wes? did i read somewhere u had a built spare engine? want to sell it lol?

thanks again
nick

384hp engine is Swedish. It’s the highest power 924 Turbo I know of.
Photos and details are page 2 of the other thread:-
http://forums.tipec.net/viewtopic.php?f=25&t=13106&start=15

It would be very interesting to see what a GTX could do. There’s a guy from Holland who has converted a standard NA 924 engine to turbo with a crossover pipe like the 951.
He’s achieved 307whp (~350hp crank) using E85 fuel and the engine is completely stock apart from a new head gasket. That’s at 1.5bar using a GT3071R with a 0.86AR turbine. The NA head is different and probably a bit more knock prone compared to the 931 head.
It shows the strength of the stock engine but also that you’d easily achieve 400hp with the GTX and correct supporting mods.
This is the thread:-
http://www.924board.org/viewtopic.php?t=38765&postdays=0&postorder=asc&start=0

Don’t know any decent engine builders but maybe someone else reading this does?

Regarding the clutch, all I’ve done with my own is upgrade the pressure plate to the alloy Sachs Sport 911 version used on 911’s with the 915 transmission (72-86). This gives greater clamping and is lighter. You need the S1 flywheel to do this, not the S2.
The plate is just a standard genuine Sachs. I think for racing you may need something a bit heavier duty but I’ve not done much research into that.

My own project has stalled since May due to various reasons. I’ve built a bottom-end with forged pistons but since then bought a complete S1 engine. It’s stock with cast pistons but everything has been race-prepped. The idea is to get the car running with that first as I’m not experienced with standalones. This will allow me to tune the standalone and get used to it whilst hopefully ironing out any problems with all the new/custom parts.