Porsche Enthusiasts Club Forum

Hi Jon. Thanks for contributing so much to this thread, and the forum in general - you must spend quite a lot of time replying and helping people out on here. It shows your enthusiasm for Porsches, that's for sure.

I didn't realise you could get away with running that rich but I suppose extreme forced induction calls for extreme measures to keep temps down.

I've taken in the other advice you've given on quench distance etc. and I'll be cc'ing the chambers and making sure the quench distance is spot-on. I've had the block re-surfaced to ~30Ra and the head will be the same so I can choose from different head gasket thicknesses.
Would you go for something like 0.050" cold quench clearance, taking rod stretch and thermal expansion into consideration?

My plan at the moment is to get the engine up and running on EFI and wasted spark using the original exhaust manifold and the K26/K27 hybrid.
Later on I'd like to improve the exhaust side and run a modern turbo like one of those BorgWarner EFR's or maybe a Garrett GTX, though the Garretts don't seem to have quite the map width of the EFR. I almost bought a Holset but I think they're just too large for a 2.0L road engine (at least the Holsets that are plentiful). They'd probably be great for a track car though.

For a road car engine with a rev limit no higher than say 7000rpm do you have any tips for boosting torque over outright HP?
I remember you saying the Omega piston design may help torque. The more I get into the build, the more I think usable torque should be my ultimate aim - to tune it like a WRC rally car. I think it will probably make the car faster in the real world and possibly more fun to drive?

I played around with that Matchbot for ages and it looks as though the smallest 6258 would make boost as low as 2000rpm and make a fair amount of torque over a wide area, at least up to the standard 6500rpm redline. Looking at the Audi TT's etc that have used the same turbo, it also seems more than capable of 400hp+. I suppose the flip-side is that higher cylinder pressures at low revs mean more chance of detonation, so careful tuning is in order. I'm still not quite decided on what CR to target now it's using a stand-alone.

If my numbers come up on the lottery I'll throw 20 or more grand your way so we can see how much power a 924 Turbo can make. A completely standard-looking 924 Turbo with 600hp+ under the bonnet

By the way, I visited your website and really enjoyed reading some of your articles on tuning the 944 Turbo. That was some awesome stuff you did with the 3.2 engines - a proper engineering exercise.

It's been a year since it was all in the engine bay when we started but if I remember right it will need circa 50 to 80mm section of silicone to link up the FMIC to duct and similar for the turbo to FMIC.

Progress has been delayed significantly by my engine guy. Hoping to have the motor back next week, installed the week after, run in and shake down tested and down to you shortly after for tuning.

600hp in a 924 would be awsome!!

did you still have the intercooler setup for sale carrera rsr?

been doing some work on my 924 turbo and keen to get it sorted and out on a trackday soon, interested in your intercooler kit if u still have it

thanks

I do. Its still up in Scarisbrook (I'm in Somerset!). A modified 944 turbo IC and all pipework including a DV for a bargain price of £60 collected. It gave 198bhp on the car it came from with no other modifications. In fact the engine was a series 1 running lower CR than a series 2, but sat in an S2 car, so may just break the 200bhp mark with all things being well with yours. I think 210-220bhp would be achievable pushing boost up from the S2's stock 0.63 bar to circa 0.75/0.8 bar. That would be quite quick in a lightening race chassis.

steve i will take it! im in no rush, and tbh i am located on south coast so its a massive drive for me to collect it! if you are able to package it up, i can arrange a courier to collect, weight is not an issue! like i say im not in a massive rush. let me know
cheers (does it come with an air filter?)

thanks
nick

I will see if we can box it up. There was a Pipercross cone as well if its not gone walkies. I'll let you know when ready for collection, address, paypal etc, via PM/email.

that would be great if u could mate. it would cost me as much in fuel to come get it lol! if it has a cone filter aswell that would be helpful!

can u increase the boost without having to tune the fueling? will the car adjust for extra boost up to a certain point?

i dont want to have to go massively involved with this car, tbh i just want it running right, reliable and good fun!

i spent a day last week playing with the car, sorting out little niggles, changed the rear caliper that was seized solid, bled the brakes to gain a pedal, so now the car drives and stops like it should again!

i also modified the rollcage which was quite simple, and added some extra tubes to further reinforce the cage. added some gussetting down the a pillar to add some more strength aswell as make it look nice!
added a rear diagonal and harness tube, and a cross brace into the main hoop, aswell as x type doorbars both sides, and some triangulation tubes in the rear section to tie the main hoop back into the rear legs, aswell as intersect with the doorbar and cross brace junction. so the cage is now quite substantial and looking good, just need to paint it now!

also lowered the drivers bucket seat as much as possible as it was very high and my head was hitting the cage! added rollcage padding in all the areas anywhere near my helmet.

doesnt really need a lot to be race/track ready now, just a good service. will be replacing the brake fluid with high temp stuff, aswell as replacing one front caliper as the bleed nipple broke off when bleeding to gain a pedal. change the coolant, oil and filter, fuel filter, spark plugs, drive belt and probably change the cambelt aswell as its very simple and cheap to do. i know its a non interference engine but it will still ruin your day if it snaps on the first lap of a trackday, so will change it for piece of mind!

will also do a gearbox oil change and just give the car a thorough check over and replace anything needed, although looking at the car its very clean and i dont think it will need much if anything really!

engine also seems to run very nicely, starts from hot or cold on the button, fan kicks in, nothing gets to hot, no funny noises etc, and drives well on the limited 1st and 2nd gear speeds i can drive about the ind est at! good oil pressure from cold approx 4/5bar, which drops to around 2bar once oil is hot. the car has a boost leak off valve installed which has been locked wired, so will need to check boost pressure to ensure no one has gone to mad winding it up! it has a boost guage installed but it isnt working so need to replace that.

looking forward to getting it all up together and driving it, it looks a well setup car, very clean, no underseal, signs of seam welding in areas, leda coilover suspension all round in very good shape, holes in the rear 1/4 for reindexing, i imagine it will be very light, although i could save a fair bit more by replacing the bonnet with fg item, and the rear hatch for perspex, and like you say with over 200hp will make for a great little track car that should surprise a few things!

will start a thread at some point for anyone who is interested
thanks
nick

This IS an interference engine and it WILL ruin your week/month if you knacker the head and pistons if a £20 cam belt snaps!! Several of parts are now NLA if you had to rebuild!

oh ! im sure i read it was non interference! sorry my mistake, like i say im changing the belt for piece of mind anyway!

cheers for the heads up

nick

If you so much as look at a 924 turbo engine (or any CIS engine) you will need to change the fueling.

A combination of adjustments at the fuel metering head, a two way adjustable warm up regulator and if need be fitting larger capacity fuel injectors from another CIS and some experimentation on a rolling road will allow you to increase the boost safely, but I would still be worried about the standard pistons, in particular the area above the compression ring land beyond 0.9 and 1.0 bar used in anger.

The sky is the limit with CIS if you know what you are doing, including fitting a second bank of injectors further up the intake with a 928 or mercedes V8 fuel metering head.

You can also use a fuel injector between the system and control pressure lines with some cool electronics and a map sensor to increase fuel pressure relative to boost by a variable amount via a knob or keypad, which we do on 911 turbos made from the 70s through the the early 964 3.3 turbos to increase fueling at several rpm points relative to boost which pushes the envelope further still.

But all of this is involved.

Probably the single best mod would be a dual port wastegate, or at very least a decent improvement to the boost control plumbing to stop wastegate creep and the front mounted intercooler, anything more gets to be involved.

Jon, I'm currently cc'ing the head and working out some other details on the engine build.

What quench distance would you aim for with standard steel con rods and 2618 forged pistons?

Most of what I read says no more than 0.050". I can get 40, 45, 46, and 51 thou gaskets.
The thing I'm unsure of is the safe minimum, and I'm a bit worried over pistons hitting the head if the clearance closes at high temp/revs.

I would be tempted to stick to between 0.039" and 0.050"

Less than 0.039" and you stand a risk of high rpm rod stretch causing a collision, especially if you build up any carbon on the top of the piston and on the head face, as the pistons will not remain bright and shiney forever... Although, aim for a nice close quench/squish area of 0.039 to 0.045 and you will never get any carbon on those surfaces anyway.

Above 0.050" and you will loose quench while retaining squish, which can be bad for detonation resistance, which a lot of people do not seem to understand.

Ok what are quench and squish???

It is a zone of the combustion area designed to squeeze out the air fuel mixture when the piston hits the top of its stroke, to aggitate the mixture (make it well mixed) just when (or interestingly when ignition is already in progress) and to cause an area which is excluded from initial combustion, which creates an area in the combustion chamber and bore which is cooler for the expansion of combustion to move into and so reduce the chances of the burn turning supersonic (nasty type of detonation)

Extra especially important on a turbocharged engine.

So there always has to be room for initial expansion in an ignition stroke? Is that a loss of power or does it allow power generation over the expansion time?