993 connecting rods

Pio72porsche · 10-06-2022, 07:42 AM

I recently posted a question about putting a 993 crankshaft into an old aluminum case. Anyhow, someone mentioned that I would have to use 993 rods due to the crankpins being narrower, and that their are two versions of such rods. Okay, here is my question, which rods are the ones to steer away from? Also, how do I decipher which is which?

MoreGAS · 10-06-2022, 11:57 AM

Weigh them without bearings but yes Bolts I assume.( 993 Spec book does not say it just says complete rod)
Def. do not use stock bolts but buy ARP'S.
The weight groups go from 508-514 (6 grams difference max in a group) up to top group roughly 564-570 grams.

If this is a tbo engine (you noted Tbo case) don't even consider using these but go w a Carrillo or Pauter rod w a much stronger beam.

For a non Turbo streeter I would go for the stoutest 993 Rod set I could find like the top group.

Good luck
Kevin
GAS Motorsport

Pio72porsche · 10-06-2022, 01:40 PM

So I weighed one and it weighs in at 555 grams. The pauter and carillo rods are a bit out of my budget. I’m building a street driven natural aspirated motor but I am considering the molnar rods since they come with arp bolts.

pocv0 · pocv0's Garage

I think you would be OK with the rods if they are close in weight like Kevin pointed out. You're building a long stroke engine using a 993 crankshaft ( 76.4mm) The 3.2/3.3 liter engines were 74.4mm , and the 3.0 70.4mm. You will have other problems related to the 76.4mm 993 crank stroke. The 993 rods are too long , or you need custom pistons with the wrist pin in a different location otherwise your piston crown will be too high making contact with the heads. You could however shim the cylinders up, but now your deck height is off and you would have to shim the chain housing up as well. Lots of little problems. SO, back to the rods.......you may need custom rods depending on what your plan is, to account for the additional stroke of the 993 crankshaft. Lots of builders have made this conversion. J&E or CP can make the customs pistons, but it in the $12-1500 price range. Custom Carrillo rods probably the same.

Howard

Pio72porsche · 10-07-2022, 10:20 AM

Howard, thanks for your input, I was planning on going with JE pistons regardless, that way I could get the correct wrist pin height. Also, I was thinking of going with 9.5 or 10:1 compression ratio. So I guess my question is, if I do a gross weight of the stock rods that I have and they within a gram of each other, would the $1000 for Molnar rods be money well spent? Carillo and Pauter are $2500 for 993 application.

pocv0 · pocv0's Garage

In my opinion you are better off going with the stock 993 rods. Get new Porsche rod bolts, or if it's in the budget ARP or Raceware rod bolts. You could send the connecting rods out for refurbishing and weight matching, not expensive. If you were building a race motor, yea, go with Carrillo or Pauter, but the Porsche rods will be fine for a street motor.

Good luck !

pocv0 · pocv0's Garage

I've never heard of anyone using Molnar connecting rods in a Porsche engine. Stick with what's been proven to be reliable parts- OEM Porsche , Carrillo, or Pauter, J&E, CP for the internals and you'll be ok.

917_Langheck · 917_Langheck's Garage

https://molnarrods.com/porsche-964-connecting-rods

https://molnarrods.com/porsche-944-968-connecting-rods

https://forums.pelicanparts.com/911-engine-rebuilding-forum/1112015-molnar-rods.html

Black 993 · 10-14-2022, 09:13 AM

Overall this seems like a needlessly complicated engine build. To each his own of course, but there are so many tried and true ways of building a 911 engine, what is the point of blazing a new trail here?

917_Langheck · 917_Langheck's Garage

Quote:

Originally Posted by Black 993

Overall this seems like a needlessly complicated engine build. To each his own of course, but there are so many tried and true ways of building a 911 engine, what is the point of blazing a new trail here?

Because, that is how innovation happens. Plus it spreads a big pool of money through the system when replacement parts are purchased after the kablammo...

Pio72porsche · 10-15-2022, 06:52 PM

I was under the impression that it was a relatively common build, putting a long stroke crank into a 3.0 case.

917_Langheck · 917_Langheck's Garage

Quote:

Originally Posted by Pio72porsche

I was under the impression that it was a relatively common build, putting a long stroke crank into a 3.0 case.

Indeed, that is what the 3.2 Carrera is - a 4mm stroked SC. Some people, however, don't see past what others have done. Fortunately, there are "Smokey" Yunicks and Jim Halls every once in awhile.