Max HP with stock 930 rods

[JoeMag]

What's max HP I can run on a 930 engine with stock rods? ...have arp rod bolts, Henry's head studs.

Also, with stock valve springs, what is max rpm I can run?

[BReyes]

You should be able to do +/- 400 with those rods, and keep a street car under 6500. Sounds like lot s of fun on the way, huh?

[sand_man]

Joe is running a race car...

[Henry Schmidt]

The 3.3 rod is a piece of crap no matter what bolts you run.

Horse power is not the real question. The real question is "what RPM can you run ?"
If you make horse power @ under 6800 rpm you can go almost as high as you want 4, 5, 600 hp. The key is that these rods (more importantly) rod bolts will stretch at higher RPMs and when they (the rod bolts) stretch, the nuts come loose and you're done.

The issue is reciprocating weight (rod above the journal, piston, pin, rings and clip) @ RPM and between 6000 and 8000 the weight almost doubles to becomes tons not grams.

[sewell94]

Henry is right about the rpm being a limiting factor. Stock 930 rods being crap i'm not so sure about. Alot of guys have make alot of hp on stock 930 rods with better rods bolts. I've seen alot of 911's make more than 600 hp hp with stock rod's(arp bolts) , they're pretty safe to about 7k, but with stock springs i wouldn't want to push it more than 7k anyays.

[JimCulp]

I just got my stock rods back from static balancing which I understand is very important on high horsepower 930's. They are balanced to within an 8th of a gram which I understand to be critical to engine longevity.

[BReyes]

Aren't the Pauter rods reasonably priced, somewhere, these days?

[JoeMag]

Interesting, thx. Yes, my car is race car and rods are balanced, by Henry ;-).

Didn't really think I could really get much more than 7k, and sounds like that's the case.

However, how much less do the pauder or carillo rods weigh?

[Henry Schmidt]

The issue is not so much the weight but the design.
The reciprocating weight will tend to change the shape of the big end. Pulling on the rod causes the a transformation to something more egg shaped than round. These deformation causes extreme bearing and bolt loading. A properly designed rod will minimize the deformation reducing bearing wear and stresses that stretch and fatigue the bolt.
The combination of rigidity and flexibility is the goal.
The joint between the two rod halves must be rigid. The rod must also be flexible enough to deform without fatiguing.
Because of the small (9 mm) bolt design of the 930 flexibility is there but not a sufficient amount of rigidity.

Titanium rods offer something else. Rigidity and reduced loads do to a significant reduction in weight. The ty rod has a problem with flexibility. They are flexible but by flexing the material will work harden and eventually cracks develop. At that point the rod becomes useless. That is the rub, $$$$$.

[WydRyd]

Juan and Mike Rombotis have very high HP turbocharged Carrera's, which they drag race often. No issues whatsoever. They do run ARP fasteners though.

[Rob 930]

My research also suggests that stock 930 rods, with better bolts (such as ARP) are fine to a very high horsepower (700+). This issue has been discussed for years on other boards. To my understanding, 930 rods are plenty strong under the compressive loads they see in a high-boost, high torque application. But as Henry suggested it's the high rev applications (7000+ RPM) were you might run into problems (where the rods start to see more significant tensile loads from centrifugal forces). But who's doing that with their 930s? That's one of the beauties of a 930; you can achieve tremendous torque and power in the 4K-6K RPM range. There's rarely a need to go beyond 6850, even for a race engine. So, in my opinion, there's minimal benefit in spending the requisite $1800 (or whatever costs) to go to Pauter or Carillo rods unless you plan to rev the engine over 7000 RPM.

[Henry Schmidt]

I wonder how many over revs are planned ? Hi hp Turbos spool up quickly and shifting to keep up can be a challenge.

Do you want to rebuild after every over rev ? If not, a higher quality rod is required.

We are talking about building high performance turbo engines. Who's going to baby that ?

[Rob 930]

If you want to buy insurance against damage from abuse, then there are plenty of ways to do that beyond just installing Carillo rods. Unzip your wallet. But with respect to the use of stock rods, many successful racers and track drivers with high horsepower turbos have not found it necessary to do anything more than add good rod bolts. It depends more on how the engine will be used than how much horsepower it's producing. The fearsome "you can pay me now or you can pay me later" philosophy sometimes makes good sense, and sometimes just costs money.

[Henry Schmidt]

Rob 930
It sounds to me that you are trying to convince yourself.
Let me guess, you have stock rods in your 930.

If you think rod failure is not a huge problem in 930 engines, try to buy a good used 930 crank.

Rod failure is by for the number one cause of 930 engine failure. Number 2 cause of damage is over rev.

Even the best drivers fall pray to the occasional over rev. That is the exact reason for telltale tachometers.

[Rob 930]

Henry,

You're right. I have stock rods in my 930. And it was a choice I made quite deliberately, on several occasions. I felt the gains from Carrillo rods were not worth the expenditure *for my application*, for the reasons I've stated above. Instead, I spent $200 on ARP bolts. And I'm happy to have spent that extra $1600 on parts and labor that I felt were better spent elsewhere.

In my experience, the most common mode of serious failure for road racing 930 engines relates to the top end and the turbochager, melted pistons, damaged turbos and the like. Bottom end failures are by comparison quite rare. And when they occur, I've seen them mostly from bearing seizures due to lubrication issues, contamination, or assembly errors. I have never seen a catastrophic rod failure that was caused purely by inadequate rod strength.

When crankshafts do get damaged, there are hundreds of reasons why it happens, and purely catastrophic failure of a rod (absent other factors)is near the bottom of the list, and even more rare with proper rod bolts. The reasons 930 cranks are not commonly available are as complicated and varied as the reasons they got damaged -- and not relevant to this debate. The rarity of 930 cranks is *not* the result of catastrophic failures of stock rods fitted with ARP bolts.

A competently assembled 930 bottom end, complete with stock rods and ARP bolts, is a workhorse. It handles big power and takes incredible abuse, including occasional, modest overrevs. If you want to regularly rev to 8000, then Carrillos are a must, but for my 6500 rpm shift point, they're a waste.

JoeMag, I don't know exactly what your application is, but I bet it's similar to mine, so I wanted to make sure you heard my counterpoint.

[Henry Schmidt]

Somehow you have interpreted my statement to mean I think you should use Carrillo or Puater rods. That is not my point. My point is that the 3.2/3.3 rod design sucks.
If you really want to build a high hp race engine I would recommend converting the rod journal to fit a 3.0 style rod. If you really want a reliable crank rod combination add an after market rod to that package.
Just a note.
I'm sure you're aware: no factory race engines were ever built using a the 3.2/3.3 rod design.
That is to say, the 9 mm rod bolt large diameter (55 mm) rod journal.

As far as I can tell, every long or short stroke factory race engine of the 930 era (73-89) was built with a rod configuration similar to that of the 3.0. 53 mm journal, 10 mm bolt and huge journal fillet.
Why do you think that was ?

As for crank failure: I can't tell you how many 3.2/3.3 engines I have disassembled that had a rod nut floating loose in the case.
This phenomenon is caused by rod bolt stretch which releases the tension on the bolt and nut which allows it to just spin off.
This is not caused by oiling issues.

[Craig 930 RS]

Call me a dogpile assbite, but I'm agreeing with Rob here.....
My engine is shifted at the same point.

[Rob 930]

Henry,

Your point, as I understand it, is that I shouldn't have used 3.3 rods in my engine. Right? I disagree for all the reasons already stated, and all those that follow. I have nothing to gain by having this opinion -- I'm not being paid by the Porsche factory or ARP to set the record straight. I had ample opportunity to take a different path, several times, and based on my research, observations over many years, and the advice of several top engine builders, this was the right path for me. I don't abide by the theory that "if enough is enough, more is better and too much is just right." Such an adage only works well for those with paranoia and a very large bank balance.

And you're missing my point. I'm saying the 930 rod, *for my application* (and likely for JoeMag too, whose thread we've hijacked), is good enough. Could it be better? Sure. Is it worth spending an extra $1600 for "better?" Not for me. Is it even worth changing to the 3.0 rod? Why should I? The stock rods works fine for me, and I own them. If the stock rod doesn't break or cause damage to the engine, for a reasonable useful life, then that's how I've defined "good enough." That's not to say that there aren't other marginal benefits to a lighter rod as well. But my primary concern was strength, especially given the relatively low-revving characteristics of a turbo engine.

Perhaps we agree on this point: horsepower does not exploit the "weakness" of the stock 3.2/3.3 design. It's the smaller, stock bolts, which become more highly stressed by forces put upon them during periods of high rotational speed, that limit the usefulness of the design. But my opinion, based on the dozens of race engines I've seen operating properly and the hundreds that I'm more peripherally away of is this: stock rods, fitted with stronger ARP bolts, or other quality bolts make the stock rod perfectly acceptable for all forseeable use and most forseeable misuse, as long as the engine is normally operated at or below the factory redline. This includes occasional overrevs of the modest variety. If there's an 11,000 RPM excursion, then it's likely that something will fail, and that the top end will be wiped as well. But the 3.0 rods and the Carrillos may fail then too.

Every design can always be improved upon. Even the Pauter or Carrillo, I'm sure, could be made stronger, lighter, and better. But the fact is, a 930 rod, with the right bolt, is plenty good enough for the majority of factory redline applications, including turbo race engines with high horsepower.

Regarding your comments about the factory never using a 3.2/3.3 rod. Maybe so. But so what? The factory never used ARP bolts either. Have you ever seen an ARP rod nut floating around in a turbo engine case? If so, are you sure it was torqued correctly to begin with? If so, how high was it overrevved? What kind of abuse did it see? I've never seen or heard of a turbo engine failing a competent stock rod and competent, properly torqued ARP bolt, even under brisk track conditions, because of a design weakness in the rod or bolt. Ever. And for that reason, I didn't see fit to spend money to fix a problem that didn't exist.

[DonE]

Me too, Craig. I shift at 6500 and rev limit at 6800 (EFI). If I miss a downshift, then so be it. I'm using the stock "crap" with ARP hardware based on a couple of engine builder's recommendation with no problems. So who's right? I'm betting the other guys....

[Henry Schmidt]

Originally posted by Rob 930
Henry,

Your point, as I understand it, is that I shouldn't have used 3.3 rods in my engine. Right?..........................

Wrong, if you read what I originally posted was that
"Horse power is not the real question. The real "question is what RPM can you run ?"
If you make horse power @ under 6800 rpm you can go almost as high as you want 4, 5, 600 hp. The key is that these rods (more importantly) rod bolts will stretch at higher RPMs and when they (the rod bolts) stretch, the nuts come loose and you're done."

Nowhere did I say you or anyone else should not use the stock rod. I just stated my opinion that "The 3.3 rod is a piece of crap" then proceeded to tell you why.

What I stated is if you don't rev it you can use it.

You and some others try to justify using the stock rods.

It's your engine, use any piece of crap you want.

My purpose with this post as with all my posts is to educate. If you choose to bury you head in the sand,
cheers.

BTW : The stock 3.3 rods is also too short, just another reason why it's crap. Try to argue with that. Please