When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Very nice design, getting away from stock bearings is a good idea IMHO. As a point of interest, Nascar engines use the same design but less grooving in the mains although I have seen then vary the length of grooving and where it starts. From what I have seen they seem to use anything from 140 to 180 degrees but this is not right up to date information. Current spec is as you would imagine, secret.
Originally Posted by GregBBRD
I'm assembling a 5.9 liter engine, with one of my custom crankshafts and thought I'd share some pictures of what my latest crankshafts look like.
Actually, to casually call this a crankshaft, might be a sin against all things mechanical. This is pretty close to art.
Starts life as a vacuum formed solid billet chunk of steel and ends up like this:
This crank has a stock stroke of 85.9mm (stock GTS) and weighs 54 pounds, versus a stock GTS crank at 62.75 pounds. 4 Kilos less total weight!
It's an 8 counterweight crankshaft (the 928 GTS cranks have 8 counterweights also), with the two center counterweights slightly smaller (Nascar Style Counterweights....which have the exact same function, without the mass.)
The rod journals are hollow to reduce mass.
Pendulum cut counterweights (lighter) and center drilled all the way through (lighter and stiffer.)
I use 2" rod journals with these crankshafts to make them stiffer and allow us to use a much stronger rod bearing than the stock 928 bearings, plus reduce the bearing speed.
High speed oiling (each connecting rod is fed individually from a main bearing. No blind holes, no plugs, no shared oil passages.) Oil passages are "surface drilled", not center drilled, like in the stock 928 crankshafts.
Greg thats a work of art , like most of the stuff you make
you should make some nice posters for garage art.
I hope it works perfectly in your engine build.
Very nice design, getting away from stock bearings is a good idea IMHO. As a point of interest, Nascar engines use the same design but less grooving in the mains although I have seen then vary the length of grooving and where it starts. From what I have seen they seem to use anything from 140 to 180 degrees but this is not right up to date information. Current spec is as you would imagine, secret.
Current spec apparently changes from race to race, engine to engine, depending on what is needed to turn the rpms they turn, at individual tracks, according to one of the biggest dry sump pump builders in the country.
It's been explained, to me, that a given engine may work fantastic with one crankshaft/bearing oiling design and then may fail with a 250-300 rpm change, requiring a change in design. People way smarter than me say that a crankshaft is constantly flexing and twisting. You can have the correct clearance on a rod bearing at 8,000 rpms, but if the crankshaft changes the way it twists at 8250 rpms, that same rod bearing may get pinched and require additional oil to keep it from failing.
Way beyond my pay scale....
I've been using this same oiling design for the past 4-5 years and this design oiling works great for me, at the rpms I'm currently turning these engines.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
All fair enough and makes sense to me, I understand there has been resonance issues also, this mainly occurs on the ovals where the engine speed band is very narrow. Porsche on its GT3 engines doesn't generally even use dampers, personally I will use the damper I got from you in the group buy for the mini stroker 5.9 litre engine and then on my bigger engine I have bought the bigger damper used for big blocks and I will change the snout design on the crankshaft to be more in keeping with the big block design and make my own crankshaft adaption piece as I recently bought a CNC lathe for this kind of work.
All fair enough and makes sense to me, I understand there has been resonance issues also, this mainly occurs on the ovals where the engine speed band is very narrow. Porsche on its GT3 engines doesn't generally even use dampers, personally I will use the damper I got from you in the group buy for the mini stroker 5.9 litre engine and then on my bigger engine I have bought the bigger damper used for big blocks and I will change the snout design on the crankshaft to be more in keeping with the big block design and make my own crankshaft adaption piece as I recently bought a CNC lathe for this kind of work.
Cheers GG
I changed the oiling to the bearings on my cranks because of the constant rod bearing failures I've seen on both 944 and 928 crankshafts, over the past 30 years Seems like everything works pretty good with the stock oiling system, until someone raises the rev limit even a few hundred rpm, where both the 951 engines and the 928 engines will start spewing rods at an alarming rate.
I'm not sure why Porsche decided to not oil the rods through the #3 main bearing.....however I see that as a major issue.
Seriously, its a real gem to look at. Thanks for the insight Greg. This is just good stuff.
Thanks!
I thought everyone would enjoy seeing the current technology we are using to improve the 928 engines, in order to make the vehicles have power like modern cars.
The more I work and refine, the better things seem to get.
This shorter stroke crankshaft does some amazing things with the proper piston and rod combination (I'm running a connecting rod well over 6", in engines using this crank....and the change to a longer rod makes an amazing difference.)
I'm in the "middle" of building four of these engines...with stock heads, cams, exhaust, and intake (so the engines appear to be completely stock), which is a little bit different approach , for
me.) I just finished the first one for a GTS and are in the middle of breaking it in....with completely stock brains, at this point (no tuning.)
It hasn't been above 5,000 rpms, so I have no idea what the higher roms feel like, but the amount of torque it makes is amazing. It pushes us back into the seats, while finding mind numbing speeds, as much and as quickly as any modern car I've been in.
For those of us that like to plan ahead, what is your lead time for building a stroker, say if one wanted to get in the queue today? A year, two, more?
For those of us that like to plan ahead, what is your lead time for building a stroker, say if one wanted to get in the queue today? A year, two, more?
Depends....on parts. And how many engines I have backed up to build.
The longest lead time is waiting for crankshafts. Right now, that is about 6 months from start to finish. I try to anticipate what I am going to need ahead of time, to keep me from having $30,000 worth of crankshafts gathering dust on the shelf versus not having a crankshaft anywhere to be found, but this proves to be very difficult, at times. However, since rebuilding/building an engine is a process, I'm not stuck sitting around for crankshafts, very often.
The rods and pistons are faster to get....they take about 6 weeks, each.
Once I have pistons in hand, the machine work on the block can start.
Right now, I'm about a month into building the next "batch" of crankshafts.....which gives me some room to build the current engine waiting for me to get to and start the process on the next engines.
Long answer short....6-9 months for the entire process, once I know the exact direction we are headed. ("Direction" can change, during a rebuild. For instance I took apart a GTS engine, for a freshening. The client wanted a completely stock GTS engine. Turned out the bores were badly worn, but Porsche had ( or has) no oversize GTS pistons. Complete change in direction required....and the time required to do the rebuild instantly doubled.)
Depends....on parts. And how many engines I have backed up to build.
The longest lead time is waiting for crankshafts. Right now, that is about 6 months from start to finish. I try to anticipate what I am going to need ahead of time, to keep me from having $30,000 worth of crankshafts gathering dust on the shelf versus not having a crankshaft anywhere to be found, but this proves to be very difficult, at times.
Right now, I'm about a month into building the next "batch" of crankshafts.
I've got a customers car here that wants one, just need to talk to you about $$ and timeline.
@GregBBRD
I want to build a beast. I've had multiple BB Chevy
nitrous inj, twin turbo etc... My current addiction is the 928. I have the Garage queen Ihave the purest driver I have the DD. Now I'M wanting to build the beast. What do you want me to send you for my build year model etc. I could go an LS route but I just don't want to be that bastard step child
@GregBBRD
I want to build a beast. I've had multiple BB Chevy
nitrous inj, twin turbo etc... My current addiction is the 928. I have the Garage queen Ihave the purest driver I have the DD. Now I'M wanting to build the beast. What do you want me to send you for my build year model etc. I could go an LS route but I just don't want to be that bastard step child
Truthfully, I'm not the guy to build the "beast" with turbos, supercharger, nitrous, etc. Hacker recently made a list of all the engines that make the most horsepower, have the best 1/4 mile times, go the fastest on the salt flats, etc. I'm no where to be found on that list....because I don't care about any of those things (and I live in California where none of those things are remotely legal.)
I'm the guy that builds state of the art naturally aspirated engines that make up to 600hp and last as long as a stock engine lasts. My goal is always the same: Increased power and efficiency that is streetable and reliable. I've got stroker engines running with 80,000 miles on them that have had only regular service work performed, which make 500hp and look completely stock.
10-12-2018, 06:26 AM
