Porsche Enthusiasts Club Forum

Unfortunately no AFR plot and the graph is a touch clunky as per previous versions.

Hi guys, many many years ago when I worked for Aldon Automotive we used to look after a hillclimb 924 Turbo where the top of the inlet manifold had been cut off and rewelded on with the inlet/throttle housing joint facing the N/S of the car, this made plumbing an intercooler much simpler and also improved the air flow as the air didnt have to go through a 180 turn to get into the manifold this set up in some ways reflects the GTS set up but at a lower and far easier cost.......it also had nitrous which was fun......

Nitrous would be interesting I remember seeing a 924 Turbo for sale with a nitrous kit...

I've just realised I haven't really done any kind of update on this thread regarding my own car for some time now...

I managed to get the bottom-end built-up last year. Everything was measured and blue-printed. I even machined the oil pump end plate back into tolerance and got hold of some Molybdenum Disulfide spray to coat it with. ARP rod-bolts were fitted to stretch. Ring gaps on the forged Omegas were all redone by hand with a diamond file allowing for big boost.
This engine is now sitting on the stand...
Here are various shots of the bits n' pieces...

So, after the bottom-end I began modifying the cylinder head. The head is experimental with the idea of increasing the combustion chamber volumes to deshroud the valves and reduce CR but retain all the quench pads and lose the remaining squish. This works on other cars so thought I would try it with this.
The head is still not finished but the combustion chambers are almost there, just needing a radius or chamfer machining around the edges of the chambers to get rid of the remaining sharp edges. You'll notice that the small rectangular indentations on the standard turbo head are gone completely...

This is what I started with...



Chamber roughed out...



Template showing crown area of the Omegas...



Chamber almost finished...



The head still needs porting. After this I have some 44mm inlet valves and 37mm exhaust valves along with corresponding new seats, heavy duty springs and the rest of the valve train

These are some pics of my standard Turbo cam compared with my own spec custom cam made by AGAP in Sweden...

Standard cam - notice how pointed the lobes look...



New AGAP cam...





New cam was originally designed with the OEM log exhaust manifold in mind and so I went for a reverse split spec with longer duration on both but less so on the exhaust side to minimise reversion and overlap. This was ground on a 112LSA. This should still work nicely with a tubular exhaust mani and help spool the turbo.

Now on to Turbos.
Originally I had obtained a K27 with 3070 compressor and intended to use it with the original 931 turbine housing and exhaust manifold.
This shows the K27 alongside the original K26, K27 on the left...



The plan is now to go with a custom stainless tubular exhaust mani, possibly with split pulse for the Holset HY35 I have with 10cm turbine housing.
Here is a pic of the Holset with the K27...



Common T3 turbine housing fitting and V-band turbine outlet...

This gets me just about up to date. I've been bogged down with house renovation etc. since September last year and have to fit a new bathroom before I can resume with the car.

On top of that I acquired a race-prepped standard S1 turbo motor at the end of last year. Bottom-end has been heavily prepped, lightened and balanced etc but still uses standard S1 7.5:1CR cast pistons with OEM rings. The deck is 'O' ringed and it has the alloy 911 pressure plate with uprated clutch.
The head is fully ported with 42mm inlet valves and 38mm exhaust valves.

I'll be getting the car back up and running with this engine along with a new inlet, charge-cooler and the Holset/new exhaust system.

This will allow me to sort out the new standalone ECU and tuning without worrying about flooding the newly rebuilt engine etc.
This engine last made ~280hp with a hybrid KKK/Garrett - using the smaller KKK hotside.
With low CR and the Holset, I'm confident of being able to run decent boost with this bottom-end and keep inlet temps reasonably low. Should be very 'oldskool' turbo to start with but fun... I will upload more pics in due course.

Thats clean internals Wes. Too nice to soak in boiling oil or pour petrol over and set fire to them!!

looks great wes, good to see another 924t being built properly!

if you feel like selling one of your built engines/turbo get in touch, i have a good stock 924t engine but want some power!

look forward to more updates from any of the current 924t projects. im currently massively busy at work and so my progress will slow up a bit for a while. also collecting parts atm

Cheers Guys.

I doubt my build will match the quality of yours but as long as it all works I'll be happy.

The reality started to sink in last week when we started to offer parts up in the engine bay with an engine in place and realised it's going to be a hell of a job getting it all to fit

The turbo in general is much longer along it's shaft axis and has a much larger compressor cover than something like a GT28 which many people have used on these motors. Fitting it in a sensible place and leaving room for things like alternators and chargecoolers will be interesting!
It also needs proper support as the turbine housing is heavy...

I have a feeling things will turn out completely different to what I have planned but that's the way these things go I suppose.

Anyone with experience of testing the overboost switches and their accuracy. FSM suggests they cut out the fuel supply circa 1.1 to 1.4 bar, a pretty wide target. I'm going to test my relatively new switch and find out when it cuts, but I think I may have hit it by accident already when messing around with boost shortly after fitting the new dizzy at 1.1 bar. A large misfire and stutter for a nano second. Is there a more accurate option? Surely having the fuel cut at full boost and WOT can't be a pleasant experience for the pistons/rings?

IIRC mine used to work at ~1.3-1.4bar. I remember this happening a couple of times when I was setting up the electronic boost control.
I disabled mine after fitting the boost controller - the controller has its own boost limit and alarm settings so I used that instead.

If its anything like mine was you'll know when you trigger it as the car attempts to lob you through the windscreen

Got an update about this car, so here is some info for people interested.

It appears that the engine had a tendancy to develop some kind of stumbling/loss of power issue after it had fully warmed up and being run hard on the track. The current owner brought the car to specialist Reiner Telkamp as the people he had handled the car to before supposedly couldn't figure out what was causing the problem.

It turned out that the issue was caused by an incorrectly adjusted K-Jetronic, a blocked breathing system, an in-tank fuel pump not working as it should and a curious fuel system set up consisting, amongst others, of 5 (yes, FIVE) fuel pumps.

Just went for a drive with my new exhaust set up. The front pipe has been replaced with a Hayward & Scott custom exhaust with the bore off the turbo opening up to circa 3.5''+ before tapering back to 3'' for the tail section. I fitted the straight through tail section and its far too loud sounding like there's no exhaust fitted at all. So the Dansk went back on. The wastegate is now open to atmosphere with a short screamer pipe.

So first observation is the turbo whine whilst spooling is louder and boost appears to come on far faster from 0.5bar to 1.0bar, in fact it overboosted to 1.1/1.2bar a few times before winding back the boost controller. The boost feels like it comes on stronger, more aggressively, however this may be noise related rather than fact.

The wastegate is venting to atmosphere so when the max boost is reached a lot of the noise which was suppressed by the turbo/exhaust back box is now coming straight from the manifold, through the wastegate and on to the road under my feet. I'm not 100% convinced by this right now and probably need a second opinion on it. The sound of the exhaust set up without the wastegate open is just fine. In fact I like the improved turbo whine.



Other jobs done was to improve the swirl pot location and mounting. This has now been welded to the thermostat upper housing and is far more secure. I've also improved air intake/air filter placement rather than using cable ties and now again far more secure. All aqua blasted to tie in to the other ally parts. The only job I forgot this week was aqua blasting the stainless inlet to intercooler and lose its shiny over bling status in my engine bay.