sublimate

I'm posting this here because this is the most knowledgeable group of engine builders I know. But this isn't for a 928 (anyone have a link for a good engine builders forum?).

My question is, what's the latest thinking on aluminum rods for a street engine? I've always heard it was a no-no, but I'm reading some things which say that's just a myth. For example, BME says:
But, on the other hand, Howard's says: Which sounds like they don't really recommend them for the street.

The reason I'm asking is I found someone selling a short block which looks ideal for what I want. I'm looking more for throttle response than absolute power. This car will be a weekend/track day toy. It'll have ITBs, a lightened flywheel, and a dry sump. Now I'm looking to get the rotating/reciprocating weight as low as possible.

This short block already has the pressed in liners, a stroker crank, and the 12:1 ratio I was looking for. The crank has been knife-edged too which should help it rev, but has me a little concerned about it's longevity. But my primary concern is the aluminum rods. He built it for the street and thinks it'll last, but I'm not so sure.

Any opinions?

fst951

I always hear not for the street. And I also have a machinist who always said that who has driven and all motor 450ish horsepower 5.0 liter....probably about 5.6liter now mustang LX for about 200000 miles since installing aluminum rods. In a good street application, I think it will work fine. They are tough. In many engines, the clearances become an issue with the oil pan etc.

Good luck.

svp928

Aluminum vs steel- Aluminum has 3 times the thermal expansion rate of steel. The very best aluminum has about half the tensile strength of normal steel rod, about 1/3 of racing steel rod. Aluminum loses strength rapidly with temperature (drag engines don't ever get as warm as a street car). Aluminum stretches and fatigues much more than steel. Aluminum rods are generally nearly twice the section thickness of a steel rod, making for clearance problems everywhere. Aluminum rods are relatively soft, and absorb detonation forces well, which is why you find them in Nitro class engines, but they change them between rounds.

So, armed with this knowledge, the decision is yours....

hans14914

Aluminum has very few advantages over steel. The primary use of aluminum rods are motors that are rebuilt multiple times per year: drag engines... etc. When used in this application, they are cost effective, as they last long enough for the runs, and are cheaper than steel. One of the better aluminum rod manufactures is near me, http://www.rrconnectingrods.com/ I talked to them several years ago regarding an audi build-up, and they told me to use steel or titanium. The new rod technologies from manufactures like carillo, pauter, and cunningham weigh less than before, and offer better lubrication and strength. I would steel, and try and save the rest of the weight in the crank/pistons.

sublimate

Thanks for the advice everyone.

I'm not sure if I can swap out the rods for steel ones since the crank has already been balanced with the aluminum rods.

So if I can get the short block for cheap enough to consider it disposable then I may grab it. Otherwise I'll pass.

hans14914

I would investigate titanium as a middle ground. In my experience Arrow makes some of the best TI rods, here is a link:

http://www.arrowprecision.co.uk/titanium.html

RyanPerrella

what the hell is this engine for? Why would you pay 3x-4x the cost of very good custom steel rods for Ti ones? if your buiding an all out race motor perhaps, But if thats the case, I suggest you look for a lighter, more compact, more modern engine then one from a 928 which was designed over 30 years ago. If your not planning on racing the 928, then why use Ti rods? I think good forged H Beam rods will run you $1800 or so. I think Ti is $4,000-$6,000 depending on who you use.

And aluminum rods are used ONLY in drag racing. Thats the only motorsport that i know of that uses aluminum. Keep in mind those engines go 1/4 mile distance and are then torn apart. Do you really think thats suitable for a road car?

hans14914

FYI, last time i had a totally custom rod quoted, it was $180/rod in steel and $450/rod in titanium.

180x8=1440
450x8=3600

Prices above included hardware. As voiced by several members, steel is just the better choice. It is also more reliable/durable than the titanium. There are several methods for removing the mass in a steel rod. Call a couple of the manufactures, and see what they can do for you. Everyone has a rod manufacturing preference, i have had good service from Cunningham and Pauter, and found the prices to be reasonable from both (although neither of which are benchmark manufactures). Arrow/Carillo are where i would look for the ultimate in lightweight steel rods.

Tampa 928s

I finally convinced my wife to allow me to use my lap-top in my hospitial room. The first place to go Rennlist so I must be a little crazy. This weekend I had a Heart Attack but am doing pretty good so hope to be back in the seat in a little while. As soon as Murf gets his 86 running a SC is in my future, no need to wait life is too short and can throw you a curve before you know it.

RyanPerrella

****! BAD NEWS

GET WELL SOON!

928SS

carrillo makes an "A" series for about $1100. pauter makes some nice steel alloy stuff for about the same...

RyanPerrella

Rob,

Where do you get 8 Carillo rods for $1100. Thats cheap, How long is their turn around, 3-4 week? That sounds like the way to go. I always figured they were $1800, but i guess thats retail. They had to be cheaper though, i mean you cna buy eagle rods for fords and stuff for $400 or so. And as far as i know they all come from just a few blanks and are all machined down.

RyanPerrella

also, if anyone still wanted aluminum rods, NEVER buy a used one, they are just a paperweight, you would have to have NEW only. They sell used ones because they are over their duty cycle.

928SS

there's a dist. in texas... I'm sure there are other places too.. just gotta shop around... I think I listed the supplier in another thread a couple of years ago... I'd have to go digging for the info now.. if you can't find it, pm me and I"ll go hunting for ya.

AL makes good beer cans and body parts, imo... if you tell moldex your piston/rod specs they'll cut your cw's down to make balancing a breeze.

sublimate

Sorry if there's confusion. As I said in the OP, this isn't for a 928.

It's a one-off mid-engine car that uses a FWD drivetrain mounted in the rear like the Ariel Atom or Noble M12. Mine uses a 2.2 litre Honda VTEC four-banger (H22). However I haven't been able to find any Honda engine forums where the average age is over 15, that's why I was asking here.

The blocks are cheap and plentiful enough that I wouldn't bee too upset if the AL rods failed in spectacular fashion. Although maybe I need to be concerned because the engine sits just a few inches behind my seat? I've seen rods punch a hole through a block, but it didn't seem like it threw parts like a flywheel does when it lets go.

I ran the numbers on this guys shortblock (it's unused - I'd never buy used AL rods) and the rod-stroke ratio isn't so good. The better stroker motors weld on a deck plate which increases the deck height by up to 1.5" to improve the R/S ratio. It's certainly not worth custom Ti rods.

Getting back to 928 content:
Has anyone decked a 928 like this when they've made a stroker? Since I don't think you can get a longer timing belt I guess you'd have to shorten the path a bit to make it work. Maybe take the troublesome waterpump out of the loop (replaced by an electric water pump) and mount an idler in it's place a little higher up?