Engine of unknown origin

[Briana]

So when I purchased my car the PO also included an engine. Supposedly it was a 2.8 of some variety. With the help of Chris Bennet we are slowing uncovering what this engine really is. I'd like to post what we have discovered so far and ask for you opinions, observations or just general comments. My plan is to use this engine in my RSR wannabe, which we be used primarily as a summer street car. Maybe a couple of DE events, but no serious track useage. case - 1970 E stroke - 66mm bore - 90mm Mahle RS heads - 2.4 heads with 35mm exhaust bore and 38mm intake bore cam - a "warm street cam based on the following measurements taken at 0.1mm 0 deg Both valves closed, crank at TDC 123 deg Exhaust Opens 322 deg Intake Opens 386 deg Exhaust Closes 604 deg Intake Closes Single plug ignition Induction - currently none, plan is to use a set of Weber/PMO 40s Thoughts?

[Briana]

One of the things I'm looking for advice on is what jets and venturies to use.

[Scott Clarke]

Pretty large intake ports for a 2.5. With the RS pistons compression will be quite low. How about finding a 2.7 crank and rods? Then you can get up to 8.5:1 CR and have the displacement to use those intake ports. Has the case had piston squirters installed? A must for those nikasil cylinders. Case savers would also be essential. Check, also, for the oil bypass modification. Which oil pump does it have? I don't know about the cam. I don't have specs handy.
-Scott

[2.7RACER]

Using the cam you have, 90mm x 66mm, CR 8.5/9.5:1, 40IDA Webers, 32mm venturies, 150 mains, 180 airs, 55 idles, F3 emulsions, will make a nice quick, pleasant to drive, street 911.
For track use hotter cam, higher compression, maybe 34mm venturies, 155 mains, 200airs. These are starting points, subject to change based upon dyno readings, plug readings, etc. Have fun.

[Scott Clarke]

With RS pistons and a 66mm crank CR will only amount to 7.5:1 or thereabouts, hence my recommendation for more stroke.

[kenikh]

There's always forced induction. 7.5:1 would be ideal for a small roots charger.

[ChrisBennet]

Originally posted by Scott Clarke
With RS pistons and a 66mm crank CR will only amount to 7.5:1 or thereabouts, hence my recommendation for more stroke.

I CC'd the motor and got 8.3:1.



-Chris

[Scott Clarke]

Chris-
Could you run the same figures for a 70.4mm stroke? I thought that there was about a 1 point difference with the stroke change.

[kenikh]

I remember this being the case as well; looks like it should be about 9.5:1 which is still fine for single plugs.

[Scott Clarke]

I thought that Mahle RS pistons were 8.5:1 @ 70.4mm stroke. Is this incorrect?

[ChrisBennet]

Here's a spread sheet with a few combos. For the 66m stoke I tried the measured deck (.85mm) and a 1mm deck (probably stock).

I did the same for a 70.4mm stroke.

I programmed the spread sheet and worked up the CC method from scratch so there is plenty of opportunity for mistakes. If you can review my figures (maybe using your own compression calcs) that would be helpful.
thanks,
Chris

[Scott Clarke]

Chris-
I don't have any data available to compare against your numbers, but it is surprising that your information suggests that the common notion that:

1) All other things being equal, change in stroke from 66mm to 70.4 mm will change the compression by one point.

2) Mahle/Porsche CR claims are optimistic, and that measured results will reveal lower numbers.

are both false. I'm completely open to the idea that the common conceptions are incorrect. I't wouldn't be the first time!

Is it certain that the pistons in question are RS, or are they the more recently designed "sport" pistons?

[ChrisBennet]

Originally posted by Scott Clarke
Chris-
I don't have any data available to compare against your numbers, but it is surprising that your information suggests that the common notion that:

1) All other things being equal, change in stroke from 66mm to 70.4 mm will change the compression by one point.

2) Mahle/Porsche CR claims are optimistic, and that measured results will reveal lower numbers.

are both false. I'm completely open to the idea that the common conceptions are incorrect. I't wouldn't be the first time!

Is it certain that the pistons in question are RS, or are they the more recently designed "sport" pistons?

I'm leaning towards some sort of error in my process. I just got another set of "9.5:1" JE's that measure out to be 10.5:1 and I'm really concerned that I'm doing something wrong.

The piston was ID'd by YTNUKLR in this thread: Piston Identification
"Looks like a 2.7 RS factory Mahle to me."

-Chris

[Briana]

Here's the piston in question

[Briana]

So what's the most economical way to get some hp out of this puppy? Does it make $ense to go with a 70mm crank to increase the CCs and CR or would I simply be spending and extra $1,000 or so for another 5hp?

[Scott Clarke]

Briana-
Note that the 2.4 motors (70.4mm stroke) made 10HP more than the 2.2 (66mm stroke) motors, and due to changes to the pistons had LESS compression. In your case, given the 90mm pistons, large ports, and low CR, I would think that the difference in power due to increasing the stroke might amount to something on the order of 15 HP. Also, I'd think that some careful shopping could net a crank and rods for a little less than $1000. Remember that along with the HP will be added bottom end torque that should really be useful for a street driven car. It seems like the obvious way to pump up the motor to me.

[Briana]

Thanks Scott. That's the kind of input I'm looking for.

Anyone else have a thought they'd like to share?