1969 911T 2.0 Liter Iron Cylinders for Track Use

[greg79s]

Hello. I am putting together a 2 Liter Track engine and plan on utilizing the standard 911T iron cylinders. Has anyone had experience with these cylinders for track use?

The plan for the set up are as follows:

9.5 to 1 compression JE pistons 80 mm

911E or late Solex cam

Webber Carbs

Standard 911T Crank Shaft

Oil Pressure fed tensioner upgrade

Standard 1969 combustion chamber with 42mm intake and 38 mm exhaust

Tearing down the motor.. I noticed there are shouds between the cylinders. Are these neccesary for the air flow?

Thanks for your feedback.

[tadd]

Yes, the 'tinware' is very important. There was an update made in the mid 70s to a few of the pieces that can be done with snips that improves cooling.

The solid cast iron cylinders are typically prefered for the 356/912 people rather than the birals since they dont distort as badly. THe modern twist is to coat the iron cylinders with the nickel silicon carbide coating used on the all aluminum cylinders for a significant improvement in friction, hence cooler running. Need to add squirters though, if you go with the nickie coating.

If this is truly a track car, you will want more cam. An S isn't really as 'peaky' as everyone thinks. If you keep the 32 mm T ports, it will choke it a bit anyways for improved low end, but the top end will be much nicer. You may want to look into 67S heads since that will keep the valve size but give you 36mm ports. The carrera 6 motors (906) become very streetable (read rally) when they kept all the race parts (including hot cam) but used the 69S heads (36 vs the 38 mm 906 ports).

The non-counterweight cranks will spin to 7-7.5k if you keep an eye on them (and the case). The lower moment will let it spin up nice and quick.

t

[ix0ifan]

Originally Posted by tadd

The non-counterweight cranks will spin to 7-7.5k if you keep an eye on them (and the case). The lower moment will let it spin up nice and quick.

I have been interested in the T crank debate for some time now and realising you have a strong engineering backgound would be inerested in looking at some of the arguments in more detail.

I can agree that reduced inertia does allow the engine to spin up more quickly as the torque needed to accel the inertia will be reduced but does it make any practical difference when accelerating a car?

I think that the main benefit of lower inertia is with downshifts as the only torque available for decel is engine friction and low friction motors need very low inertia to slow effectively.

I don't know the difference in inertia between the S and T cranks to try to do some first order calcs but it must be small.

I also feel that to build a 2.0 litre race motor that will only rev to 7.5K is a bit limiting and will struggle to be competitive.

I think E Cams or even Solex cams will be a long way behind these days and even the S cam is not enough.

I would think a competitive 2.0 litre needs to make a minimum of 200BHP and run to at least 8500rpm.

[greg79s]

Thank You for your input. I am now leaning toward more cam and some mild porting work on the cylinder heads. The goal of this motor is going to be realibility/longivity. The club I plan on driving with I was told does not need HP as a priority since they only run at Sears Point and Thunderhill.

[tadd]

Well my Phd is in physical chemistry, so my engineering background is from Holiday Inn Express . Thanks for the kind words.

Ok, I agree the largest benifit will be in a quicker downshift. That said, there is a 1.4# (0.63kg) difference between the two - and that's all 'outside mass, in a competive field with a 10-20 hp difference maybe that's an accleration edge? Note: the CW crank is a 2.7 and the NCW is a 66. So the 'apples to apples' NCW would be lighter.
I've thought about taking this further though. My forever 2.8 build will use some Ti rods from crower, 340g each. 250g is rotational mass. A typical 2.4 rod is 760g total. So assuming roughly the same distribution, that's a 250g savings. Add in the difference between the 57 and 53mm SC journal and you end up with ~2 kilos! In my mind that's non trivial.

Finally I have to admit that I wonder about the 200 hp number... Not saying your wrong, observation is sometimg one cannot ignore. But I have seen 912s wax 2.0s. There should be an easy 40-50 hp between them for a 1720 616. 'he who gets the power to the ground best wins' perhaps?

[tadd]

Greg:
seriously... Porsche did a great job on there ports. Use 67/8 S head (or 69s if you can find and actually run them) and get a heavy breathing cam.
If you check out opinions on the 906 grind, it's considered 'very safe' since Porsche wanted high rpm operation with the spring metalurgy of the day. Flow into the cylinder is simply flux times time. In the 60s lift was limited so they upped port size. This costs velocity and low end suffers. Smaller port, new cam with more lift, almost the same top end but now the bottom and mid fattens up. What once sucked on the street ain't too bad. On the track, much more flexability.

Just don't fall too far down the hole... It does get expensive quick .

[BURN-BROS]

Originally Posted by ix0ifan

I also feel that to build a 2.0 litre race motor that will only rev to 7.5K is a bit limiting and will struggle to be competitive.

I think E Cams or even Solex cams will be a long way behind these days and even the S cam is not enough.

I would think a competitive 2.0 litre needs to make a minimum of 200BHP and run to at least 8500rpm.

Well said, depending on where you run, you will can be easily be left behind.

A proper solex cammed twinplugged 2 liter may put you in the top ten, but outright wins you will not get.

The flip side is that you will have a low maintenance build, so the cost to go racing is not as bad.

[neilca]

Greg,

I think you are asking the wrong question. The cylinder in the picture looks to me to be a birel. Put a magnet to the fins to verify.

[ix0ifan]

Tadd,

If the T crank were worth 20 HP of accel this would be equivalent to an effective weight loss of 200lbs in first gear (assuming the old 10lbs/HP Rule of Thumb) and less with every upshift.

This seems a bit too much for a 1.4lb weight difference as this will only reduce inertia by about 10% when the flywheel is considered.

I think extra torque available for accel is only about 2 lbsft which would relate to around a 30lb weight loss in first gear.

I would agree that using Ti rods is a great idea and the new JE Piston (FSR) looks very good and would be a great help.

[tadd]

Ix0ifan:
Please don't miss understand, I was not suggesting a 20hp increase. I was just saying that there could be sometimg useful in a tight field. The forumla V guys would squbbile over one or two. Just swapping cranks for 'something' might be worth while. Added in with resized journals and Ti pankels could be interesting.

[ix0ifan]

Tadd,

I did misunderstand but do agree that even a couple of HP must be beneficial particulalry in a tight field.

I do like Pankl Rods and Arrow in the UK also make good Ti parts which seem price competitive.