Another hot rod

[andyjboy]

Wonderful !!!

[CamBiscuit]

Bloody hell, nice sound Tom!

[Cornpanzer]

Tom,
What were the ignition advance numbers that they settled on?

[blue72s]

You can listen to the Olive Tart give her very non-pc version of the 2,9L flat six shriek,

Is that 93mm bore x 70.4mm stroke in mag crankcase?

[Flunder]

Now is a good time to catch up with some correspondence. First off, Blue72S, thanks for your questions.

1. What's the weight difference between steel and alu door skins? On the Cayman R the difference weighs out to al little more than 30 lbs and I suppose that would be in the neighborhood for the 911. The doors feel extremely light with the alu skins, plexi windows and simplified door panels.

2. Without heat exchangers, how do you demist the windshield? Crack a window and have a roll of paper towels handy! Some rally prepped cars would have had Webasto gas heaters, but not the project car.

3. Is that 93mm bore x 70.4mm stroke in mag crankcase? Yes, ANDIAL built this engine on a mag case. The case went back to Ollie’s to be freshened up. Images of the case halves are attached.

Cornpanzer, thanks for your post.

4. What were the ignition advance numbers that they settled on? Here is what the guys at the shop had to say about the advance: “It was 28 degrees. The timing is currently set at 27-28 degrees and this gives the power of the middle line. I feel this is safe for pump fuel with the AFR where they are. We have not road tested it yet, so there may be further adjustments.” I looked back at the original ANDIAL dyno sheet dating from 1982 for this engine and noted that for their runs they set the advance at 28*

5. Marco had this commentary regarding the cam timing: "When I first read the spec sheet from Andial that you posted earlier it said cam timing was set at 6.2. Having just timed my 906 cams prior to reading the post I was naturally very curious as the spec sheet on 906 cam timing puts them at 6.8. I'm not aware - of a lot of things - but I'm not aware of any factory cams that time to 6.2. If the cams in Andial 129 were, in fact, 906 parts then I wonder if the slightly retarded cam timing was something that was reached through testing on the dyno. I do know that adjusting the injection pump timing can yield substantial gains in HP as well as altering the drivability of a car; it naturally follows that altering cam timing would produce similar results but, due to the headaches involved in testing/tuning cam timing, it's something that is/was rarely done. As we know, Porsche has been using VarioCam technology for quite some time to increase bottom-end torqe while retaining the car's top-end HP. Perhaps this 6.2 906 cam timing was Andial's compromise; their way of delivering the most HP and torque for the given engine configuration and its intended use. Maybe I should set mine to 6.2 ..." Here is what we did for the rebuild: The cams are set to 6.2 on overlap, this is straight up. Scott found this to be the best all around setting for low and high speed drivability. He has set them at 6.0 on track only cars and picked up top end power.

6. A message received from a reader off-line inquired about the non-linearity of the torque curve on the 1 Jun 11 dyno sheet shown above in post number 683. Scott’s explanation makes for some interesting reading:

“The car makes good torque at lower rpm so it shrinks the graph thus making the dips appear more pronounced, because they are a greater percentage overall.

If the torque started out at 100 or less then the dips would not appear so great, as they are actually only 10-15 ft lbs.

That being said, they are still dips. They are caused by a combination of things.

First, the fuel mixture is going rich and causing a loss. The car needs to be tuned to its leanest point and this causes some rich areas.

With programmable injection we have the ability to tune this out but not with the mechanical pump.

This is not always the pump’s fault.

On this engine I would say that the rich spots have to do with the RSR cams “working” with the R muffler exhaust system.

If we were to run straight pipes, it may clean this up.”

Well, I think we all know what Rolly would do to address this issue!

[blue72s]

On the Cayman R the difference weighs out to al little more than 30 lbs and I suppose that would be in the neighborhood for the 911. The doors feel extremely light with the alu skins, plexi windows and simplified door panels.

Thanks but I meant just the door skins, not including glass or interior panels.


BTW, I believe that the doors on the Cayman R and 911 GT3 are all aluminum (not just the skins) as there are no rivets on these.

[Mr9146]

The cams are set to 6.2 on overlap, this is straight up. Scott found this to be the best all around setting for low and high speed drivability. He has set them at 6.0 on track only cars and picked up top end power.

So you did end up timing the cams to 6.2? The cams in 129 were spec'ed out as 906 grind, and you chose to go with the RSR "Sprint" cams you already had, right? How was the 6.2 cam timing decision reached? Did you try a few different settings and then compromise? Or is 6.2 standard cam timing on the "Sprint" cams (I've never had a pair so I don't know this info).

This is very interesting data to me ... The final engine size is 2.9L w/twin plugs and high butterfly, running 28* total advance and it made roughly 265hp and 200ft/lb of torque @ 7400RPM on pump gas? VERY impressive numbers.

[Flunder]

Hi Marco:

Thanks very much for your post. I hope the following helps to answer your questions.

We used factory RSR cams.

We did not use the RSR Sprint (it was pure conjecture that ANDIAL 129 had the RSR Sprint cams; in fact it turned out that it was fitted with 906 cams).

For comparison sake, here are the factory specifications for the 906 grind as compared to the factory RSR grind.

906 Lift I/E: 11.73/10.24; Duration I/E (deg crank) 281/251; Lobe Center (deg camshaft) 95; Intake Valve Overlap 6.7*-6.9*
RSR Lift I/E: 11.79/11.43; Duration I/E (deg crank) 278/267; Lobe Center (deg camshaft) 101; Intake Valve Overlap 6.1*-6.3*

Again, the RSR specs set out in the above table are for the factory RSR cam, not for the Kremer/Schrick RSR Sprint grind. As you can see in the above data, the factory spec for the RSR cams calls for 6.1* to 6.3* overlap.

Scott installed the cams in the engine for project car “straight up” at 6.2* (the midpoint in the range). Based on prior experience he feels this is the best compromise for all-around drivability and power.

For clarification, the engine is 93mm bore, 70.4mm stroke for “2,9L” displacement and the 2,5L ST heads are twin plugged with 41mm ports for both intake and exhaust.

The engine made the big numbers on race gas. With timing set at 28* total advance the engine made 200 ft lbs and 264 hp at the wheels at 7342 rpm on 110 leaded.

However, on 93 octane pump gas the engine made 182 ft lbs and 248 hp at the wheels at 7342 rpm.

Please ask away if you have more questions. Thanks again for your post.

[Mr9146]

Okay, now I see where the cam timing came from. I was under the impression you were using the Sprint cams.

What diameter headers are you running?

[Mike_Moore]

so if I run it to 82-8400 we would get some more power.

Fantastic stuff Tom, tried looking back over this great thread but couldn't see the head details, are you running solid rockers?