Vilhuer

Works fine as long as weight is cut down to same as GTS rods. 968 rods have little more material in other places also besided width of bottom end. Specifically at bottom.

slate blue

Thanks for the info Errka, I just have to make this cost effective too, when you can buy brand new billet rods, for $1200 I would want to get these second hand and fitted for no more than $500 to $600. Can that be done I don't know.

Greg

GregBBRD

The early rods are indeed weak. They are suitable to hold up paper towel rolls in your garage's bathroom. I have disassembled several engines with bent rods. We refuse to re-assemble any engine with these rods. Porsche's technical information on these rods states that if two or more rod nuts are loosened, all the rods must be replaced. Porsche does not like to print "technical bulletins" like this....it makes them look like idiots.....so I would not take this information lightly. I certainly would not consider a supercharger with these rods. The rods pictured are indeed, early rods.

We rebuilt/replaced a 944 turbo engine (that had less than 8 hours on it) that someone had installed a set of early 968 rods. All were bent and one finally broke...which turned most of the engine into scrap metal. The 968 rods are almost the same, BTW. The 928 version has a offset to compensate for the piston to crank angle. The 968 rods will not fit in an any 928 engine that I'm familiar with.

I indeed have a box of these rods....which is where they need to stay. I have no idea why I have saved these pieces.....pack rat. The bent ones are indeed a curio. Just as the 5.4 pistons without the oil return holes drilled are fun to laugh at. I actually have no idea what Porsche was thinking when they built the GTS engines....must have turned the project over to a "rookie". In my opinion, the GT's will turn out to be the collector car and the GTS will not be as desireable, just because of the engineering flaws in the engine.

BTW. The later GT engines used a "forged" rod that looks completely different than any other 928 rod. They are not the same as the S-4 rods.....they are very, very strong. If anyone is building a track engine from a 5.0 base, it would be worthwhile to search out a set of these rods.

Greg, I'll pass along your offer, although I would not suggest that you hold your breath. These pieces are very rare and have high value here and in Europe....which is where this car lives. (We can never find used late 5.4 rods and always end up buying new ones from Porsche). Perfect used cranks are....unobtainium. I do have a used 5.4 crank with a damaged thrust bearing that needs to be repaired, which might better suit your budget, BTW.

gb

Vilhuer

Just for clarification. Any and all 924S, 944, 951 and 968 rods can be easily modified to fit any and all stock 928 cranks.







S3 is 968 and 5,4 is GTS. Both are early '92-93 MY style rods and have exact same casting number IIRR. Same measurements apply to all 928 engine family (928, 924S, 944, 968) engines.

27,0 mm rod lower end width, 928
29,0 mm rod lower end width, 944 & 968
55,0 mm rod lower end opening (obviously not same as crank conrod journal diameter which is little under 52 mm)
24,0 mm piston wrist pin size
30,5 mm width of opening for conrod in piston
26,5 mm rod upper end width

2 mm rod lower end width difference is all away from one side. On 928 two rods are next to each other and 4 mm total needs to be taken away from two rods because of this. In every other way they are identical except that 4 cylinder rods have more material as shown in pics for balancing purposes.

slate blue

Again Errka, you are the man when it comes to the pics, are you sure you're not Japanese? How is your build coming along? Boy aren't those early rods skinny!

Greg

SwayBar

Now this is a kick-*** thread!

Vilhuer

Thanks Greg. 968 pistons will go to machinist on Monday for valve relief cuts to exhaust side and crank for 2mm removal from counterweight outside edge. Weights are just barely too big when piston is at BTC and they rub skirts. After those mods I'll do final trial fit into block. If all looks good then crank etc are at last ready for balancing. Still long way to go though. Next summer its finally on the road if nothing major comes up. About time.

Mike Simard

Does your crank have enough counterweight meat to be able to turn the OD down? Do you know if you'll have to add heavy metal for the final balance or still have enough cw to drill?

Vilhuer

No idea at all if CW's are over or underweight for heavy rods and pistons I'm using. Could not give exact weight info for Moldex as pistons are still not in their final form and thus crank is unbalanced. Largening exhaust valve cuts will lighten pistons a little. Also at the time of the crank order I didn't have exact rod weights since wrist pin holes were not yet modified for Porsche stock 24mm pins. So I gave Moldex unmodified parts weights rounded up a little in hope that crank would end up little too heavy. They seem have made weights as large as possible.

Now I have to make a choice between modifying pistons or removing material from crank. At the moment crank modification seems better choice even though it could mean much more mallory metal is needed. I do have option of using S3 wrist pins instead of 968 pins. They have abroximately 2mm larger hole and are noticeably lighter. Nothing is final yet. It could be that I end up dividing the problem and remove material from both crank and pistons. A lot depends on what machinist says next week.

slate blue

Errka thanks for the update, I'm sure you know this but make your machinist does too, the pin offset which is what I presume you are addressing by sending them there in the first place? It just that 968 pistons are made for a 4 cylinder so I would hate to see an error like that. Also make sure they equalize the piston volumes. I'm sure you have this covered, you have been very thorough to date.

Greg

Vilhuer

That is exact reason for the valve relief mod. I'll do fine tuning on pistons once those cuts are done. This includes measuring CC's for all tops and taking them down to same +/-1 gram weight. CC value is especially interesting as piston top will be only variable which will determine CR. Aim is little under 11:1 and it looks like its going to be close to 10.7-10.8:1. Just perfect for local high octane fuel I think.

slate blue

What is the Octane in Finland? I realise that everybody uses different standards, the U.S uses a hybrid type rating, I think our 98 octane is the equivalent of there 95? What is the rating for Shell V power in the States? Here, there is 98 which is everywhere, also 100 octane which has a 5% Ethanol added, it is called V power racing. I know that the premium is much more expensive in the Nordic countries. I would have thought that if you have a 98 rated fuel, 11 to 1 would be the minimum you should aim for.

My euro two valver is 11.1 to 1 that has never knocked to my knowledge however I was fussy with the piston deck height.

Greg

Greg

Vilhuer

Very good quality 95 and 98 is available everywhere. Shell sells 100 also on some stations in here too. I think rating style in Europe is exact same as in Australia.

Fastest928

Errika...perfect assessment!!!


Cheers,
Marc

Charley B

Well, I'm certainly glad we got this cleared up. :>)