Well - I put over 100 track miles on it last night and didn't really hold back. Henry's creation held together:)

I haven't had a chance to analyze my data yet but I know I was hitting much higher terminal speeds - I have some driver adjustments to make due to the higher rpm limit allowing different gear choices.

Also being on the track gave me a good chance to really try to listen to mfi mixture - think I need to work on some gross adjustments to make sure I understand changing characteristics.

Don

Shift points
 

Don

If you have a dyno sheet on this motor, you should use that plus your gearing to determine optimum shift points. If you don't, a quick pull on a chassis dyno will give you what you need for that purpose.

For most motors the rev limit has nothing much to do with where optimum shift points are. Those limits are to avoid overstressing engine parts, or to extend service life, or both.

You want to upshift at the point where the delivered torque at the rear wheels in the old gear equals the delivered torque in the new, higher, gear. This torque (or, if you will, thrust) is what accelerates the car.

As a practical matter, you can discount tire diameter and ring and pinion when doing these calculations, since they are constants, but it is convenient when creating a graph (delivered torque on the vertical, MPH on the horizontal is the usual, with a curve for each gear set for a total of five intersecting curves, each one lower, flatter, and more to the right than the last) to include these.

With a race motor this might be different. My long stroke 2.8 (I bought it - not a real RSR - from a friend) has a torque curve which says I should be shifting above 8,000 rpm, which is where I stopped things on the chassis dyno run.

But my 2.7 race motor, which revs freely up to and over 8,000, turned out to have optimum shift points at 7,600. My stock SC should be shifted at 6,250 or so even though those engines can run happily to 7,000 without problems.

Of course, on a track sometimes you may want to run up beyond optimum if it will save an upshift just before a braking point. What you save by not upshifting usually more than compensates for what you lose in diminished acceleration.

Yes I was speaking more about the later - at my home track the increased rpm gives me a corner or two where the likely fastest route is to run it up on entry rather than grab another upshift. The data will tell.

Henry

That looks like one of the factory racing MFI pumps if its not how do you get it to look like that?

I want to try to create a 2.5ST engine not only internally but one that looks right visually compared to factory, and pumps, if they can be found, cost more than a house in parts of Florida!!

Hello Henry,

That is a fantastic motor!

I am in the midst of a 3.2 rebuild, and I plan on using Supertec head studs. However, I was intending to re-use the case through bolts. I noticed in your fourth picture that the acorn nuts and bevelled washers appeared to be zinc or cad plated. Did you also plate the through bolts? If so, was it zinc or cad and did you have the platers do a post-bake?

Otherwise, if you did not plate them, what would be your recommendations for preparing the through bolts for re-use?

Thank you!!

Thanks for the kind words.
Yes, we plate the hardware. It's called Cad II by the platers but it is a zinc process. All the parts are heated after plating to prevent nitrogen embrittlement.

Hello Henry, thank you very much for the reply, that is exactly what I wanted to know. Take care!

Allan

How on earth are you yielding appropriate intake flow for that kind of BHP for 2.8L? I'm not so much of Porsche builder, but I am a Ferrari engine builder of the equivalent vintage. For instance, an equivalent cammed and compression carbureted 3L 308 motor with appropriately ported heads is very difficult to get north of 280bhp. If the porting and cam timing and tuning is just right, they can touch 285-290bhp on a DTS flywheel dyno but again, very difficult for a streetable engine.

Boxer and Daytona engines are very much the same situation in that yielding greater than 95bhp per liter in a street engine is remarkably difficult. I have seen it done, but never with Weber carbs. I suppose the best example would be the NA 328 engine with a interesting and very custom ITB arrangement which made around 105bhp/Liter.

These are not carbs....

Henry please call me William Knight