NineMeister

Getting close to finished with this project now. We have had a problem with engine parts supply this year which has frustratingly delayed the build of the engine, so to get the car running we had little choice but to fit the 4.0 litre engine & gearbox out of my 993RS (after the end of the racing season I must add). This has obviously allowed us to do all the necessary chassis checks: set up the suspension, testing the 4 channel RS brake system, oil system, electrics & the like (which all works perfectly I'm pleased to say). More on this later.

So, with respect to the motor, we decided from the early days of the project that ultimate hp was not the primary goal and that the engine was to be built from known technology with zero risk, thus ending up at the following specifcation for a 3.82 litre "Race" engine which should make around 425hp (i.e. more than a 996GT3RS) on our dyno:

M64/20 993RS base point engine
Stock 993RS crankshaft with 132mm Carrillo rods
996GT3R two chamber oil pump
CNC Ported cases
9m 103mm short skirt slipper pistons & cylinders
9m Billet cylinder heads, valves, springs, retainers
9m Race Cams, chilled iron billets
9m ITB intake system
9m header & twin silencer exhaust system
Motec Engine management

The engine build started some months ago, in retrospect the crankcases could have been tumble polished for a more pleasing finish but I'm loath to strip apart the bottom end again just to make it pretty. Assembling a bottom end is not exactly cutting edge, so here are the photos of the assembly from the cases up which I did over the last few days. I'll post more of the cylinder head assembly later.

mr_bock

Lookin' Very Nice. I love the pistons. Can't wait to see the dyno results.

Good Luck with your project!!!!

FLA997

Beautiful!

Cactus

pr0n

Bill Verburg

Nice, can you compare the weights of the recipricating assembly w/ stock 993RS?

Are those head studs
993.101.172.02
or
993.101.170.51
or
other?

NineMeister

The studs are the late model 993 version, don't know the part number off the top of my head. We have found that these work fine in combination with the 9m sealing rings - look closely at the cylinder top you can just make out the hardened & ground steel sealing ring located in the rebate of the top of the cylinder.

The 103mm pistons are the 2618 upset billet 9m Race versions that I have been running in my 3.8 & 4.0 litre engines for the last 4 years, the current version weighs in at 418g without the pin, slightly heavier than the earlier versions due to the increased dome volume (and hence increased compression ratio). The pistons run a 22mm pin with the 132mm centres connecting rod (5mm longer than stock), with the standard 76.4mm stroke it gives a nice rod/stroke ratio of 1.73.

Here are some more photos of the billet heads assembled onto the cam carriers and subsequently fitted to the bottom end.

droy3

...engine ****...

NP993

Ridiculous. Mark my words: in 60,000 miles (or who knows how long), when my engine needs a full rebuild, I'm going to do the full 9m business. It's still cheaper than a GT3.

DJF1

drool....

droy3

Hi Colin,

Given that this is a "race" build, would you vary the build for a street only build and if so how? I really like the idea of short skirt pistons but wonder if a daily driver would be adversely impacted. Could the Varioram be retained in such a case or does it prohibitively inhibit adequate volumes of air? Which brings up another point...is their a point/size engine whereby the Varioram can no longer be used (i.e. 3.8 or 4.0l)? Sorry if these questions have already been asked...

Thanks in advance,

Doug

chris walrod

Very cool indeed Colin!

One thing I never understood is why Porsche threaded those head studs the length they did. Just seems like a waste of material and manufacturing time even if they are rolled threads. I am curious how hard those studs are? That, and alloy.

Tour18

Waaaaaaaaaaaaaaay Cool.

NineMeister

[yoda=on] You ask question of excellent value, Mr Doug, indeed, a question that is not often answered adequately by those who should know enough to tell, but to those who truly understand is often replied in one word: synergy. [yoda=off]

In all seriousness Doug, you have asked two questions, I'll answer the piston question first.

For a pure street car that has occasional track use, at this time I would specify the standard length rod & skirt over the short slipper version purely on the grounds of longevity and noise. Reduced high rpm friction is the advantage of the longer rod and short piston, which is not as important a requirement for a street engine as a race engine which spends all its life above 6500rpm. Similarly, because the slipper piston is short it has to run thin rings in order to fit them into a smaller space, unfortunately the rings we can (currently) buy don't have the same life expectancy as regular ring packs. Geoffrey's engine is a case in point where the original Mahle pistons and rings lasted comfortably for 100 hours, whereas the expectancy of the slipper ring pack will be half that.

The second question is the more complicated one. The simple truth is that when you are designing any engine from a fixed set of components you have to evaluate the full potential of each component in the "system" that affects the efficiency of the engine, then design the engine around the limitations that you discover. In the case of the stock 993 Varioram manifold, with a few simple porting modifications we have found that it will comfortably support 3.6 and 3.8 engines at up to 360hp (with billet heads and sport cams). From my experience with the non-Varioram system I would say that, even after fitting a better exhaust system, to take these engines further would require longer duration cams and at this point you will probably hit issues with idle stability should you choose to run with more overlap (which is the usual approach), hence why I recommend ITB's as the next step. I dare say that given enough time and money we could design & develop a cam to max out the performance of the VR manifold but from what I can deduce the current 9m Sport cam is not too far away from ideal.

Does this answer your questions?

NineMeister

One reason why Porsche changed to fully rolled threads was to increase surface area, hence speeding up heat transfer during the warm up phase of the engine.

Juha G

Colin, great work! Thanks for the updates, I'm following this build very closely as I have similar plans for my 993 (GT2 body conversion + engine to match).
I will be racing next season in another car so I have plenty of time to plan this thoroughly.

When you say 100hours above, are you talking about stock engine or something else?
If one drives 100km/h for 100 hours, it equals 10,000km's. That isn't alot is it?

What kind of life expectancy would a completely rebuild 993 engine (stock bottom) with a healthy 9m top package (billet heads, cams etc.) have if driven 70% track 30% street?

Thanks!

Juha