964 Engine - What is the realistic redline for bottom end?

[Henry Schmidt]

All rod bolts are stretch bolts.

I want to offer a slightly different direction. Even with Carrillo rods the failure rate is too high.
The problem is not the rod or rod bolts. I believe the real problem is the crank design.
The 3.2, 3.3 and 3.6 cranks use a larger rod journal (than a 3.0) and that rod journal diameter and the location of the oil pump facilitated the need to redesign the rod .
The new design required a smaller rod bolt producing a weaker rod and rod bolt combination.
What we have been doing for years (with out even one failure reported) is grind the crank journal to fit a 3.0 rod.
This allows us to grind the journal with a huge radius adding more torsional rigidity.
The 3.0 rod is an excellent part / design and is also slightly longer than the 3.2-3.6 rod improving rod /stroke ration (much needed in all 3.2+ Porsche 911 engines.)
In conclusion, regrind the crank for strength and improved rod design, drill the crank for extra oiling and your good to go.
Of course it is necessary to reharden ( we use salt bath Nitrating) the crank and replace the plugs but when it's done you have the best possibility for success. Can you still choose Carrillo rods? Yes, but even with the stock 3.0 rod in this configuration you'll have a combination stronger than a stock crank with Carrillo rods. One thing I also advise is ARP rod bolts with the 3.0 rods.
It's a lot of work, but when is race prep easy?

Rev limit with this mod is 8000+. and with the longer rod the engine spins at higher RPMs with greater ease.

[herman maire]

Henry that is really intresting....... Its kinda hard to believe but I am not one to question somebody that has years and years of experience.....

If you say it works, for some strange reason I have total confidence in your set up (even thought I never met ya )

-How much would you charge to mod the crank and I guess the case stays factory right (NO MODS) ?

-Do you use stock pistons or because of the longer stroke you need custom pistons?


I am not really considering this just because I dont have the budget to but all I want is for my 95 993 motor to be a solid , a forget about kind of motor and regularly rev it to 6800-6900rpm.

Is your mod really something that should be considered with the 993 motor?

Have you seen that many 993's with blown rods ?

Would really apreciate your opinions on this... I will be tearing my motor down soon.
Thanks

[CBRacerX]

Interesting. Going to be using R&R Rods with ARP bolts - but was planning on the stock rods until piston fit forced my hand.

[Henry Schmidt]

Originally posted by herman maire
Henry that is really intresting....... Its kinda hard to believe but I am not one to question somebody that has years and years of experience.....

If you say it works, for some strange reason I have total confidence in your set up (even thought I never met ya )
Thank you

-How much would you charge to mod the crank and I guess the case stays factory right (NO MODS) ?
the total cost is around $1,500 and includes rod bearings and rod reconditioning. Remember that because you are grinding the crank, you can use a crank that needs repair.

-Do you use stock pistons or because of the longer stroke you need custom pistons?
the rods are only .030 " longer. You can machine the pistons, use a thicker base gasket or buy new custom pistons


I am not really considering this just because I don't have the budget to but all I want is for my 95 993 motor to be a solid , a forget about kind of motor and regularly rev it to 68006900 rpm.

Is your mod really something that should be considered with the 993 motor?I see no reason why it would not work. Why not?

Have you seen that many 993's with blown rods ? Supertec builds primarily early 911 engines (by choice) so I'm not the best to ask about later 911 engines. Perhaps Steve , Ralph or Grady may know better.

Would really apreciate your opinions on this... I will be tearing my motor down soon.
Thanks

[snowman]

My opinion is that FACTORY parts are best for low budget engines. For anything else Carillo rods, based on their relative low cost "difference" not total cost are the way to go. Why, because even a BETTER rod and bolt, that is not 100% tested is NOT a better part. And as far as I know none of the others out there are 100% tested.

As to the factory parts, they are very very good and almost nothing beats them. The biggest reason for using Carillo rods and SPS bolts is that they are 100% inspected. ARP is good, maybe better than stock, maybe NOT as they are not 100% inspected and consequently can have a fatal defect that will ruin you motor. Stock parts are not inspected at this level either. But the factory usually puts in a huge safty factor that prevents a lot of failures. For a race engine you cannot afford that much margin. I (choke) agree with Henry that other factors, like a poor crank design or lack of oiling can be more important, but I always assume that on a race engine those things are considered anyway.

All and all the rod bolts are still the weak link. Compare an SPS bolt to an ARP bolt, like comparing a chevy to a Ferrari, no comp, period. SPS is a $25 ea bolt for good reason and worth every penny. And the worlds best bolt isn't worth much is it dosen't work with the rod. Only Carillo rods are designed around the worlds best bolt.

Frankly I have visited many people on the race track, the ones rebuilding a broke engine, late at night. Many many have stated that they wished that they had used Carillo rods. I have only heard of ONE thats 1 person that claimed to ever have a problem with Carillo rods. I have NEVER seen a person with a broken Carillo rod at the track, but I have seen dozens of others. People, put your fking envy aside and save up a few hundred bucks more and you will not ever regret it.

[Jeff Alton]

Henry, interesting stuff. I have never heard of that approach but it certainly makes sense from a technical point of view. I would have tried this on my 3.4 had I known...

Cheers

[Henry Schmidt]

I have seen many dead engines with Carillo rods. I fact the only connecting rods I have ever seen where the small end of the rod break were Titanium rods and Carillo rods.
Let me say, when the small end goesit saws the whole engine in half.

As for bolts, ARP Hardware is the standard of the racing industry for good reason. I have never seen a failure that could be attributed to ARP rod bolt failure.
SPS on the other hand offers no Porsche specific hardware and as far as I can tell it's hard to buy SPS metric hardware.

That said, a 9 mm bolt can not offer the security you get from a 10 mm bolt and the 3.0 factory rod by design is stronger than a 3.2/3.6 Carillo rod.

If you want the best possible combination use the 3.0 Carillo rods on a 3.2, 3.3, 3.6 crank. All you need is money.

We'll do some math.
Spun rods on your 3.6 crank. throw anyway ?
By grinding it down to a 3.0 journal (53 mm from 55 mm) you have plenty of room the clean up most cranks. Remember now you get a large fillet at the web. Much stronger than stock. These price are just gestimates
Grind .................................................. ..... $250
Heat treat (salt bath Nitrating)................. $220
Replace plugs........................................... $125
Used 3.0 rods........................................... $300
Mag & x-ray used rods...............................$130
Rebuild & convert rod bushing (22-23)......$180
Balance rods............................................. $60
ARP rod bolts............................................ $280
Custom rods bearings.................................$190
Total............................................. . $1,555.00
Carillo rods ........................................... $1,600.00
If your crank is damaged
(by good used std/std one ) .............$ 1,500-$1,800
Total............................................. ..$ 3000.00+?
When all is said and done the modified crank and rod combination is stronger, better rod angularity and may even be quite a bit less expensive.


You could also weld your damaged crank back to standard then all crank cost would be the same.
Crank mods for oiling are the same for either crank

There's my case, any questions?

[TonyG]

>>>I have seen many dead engines with Carillo rods. I fact the only connecting rods I have ever seen where the small end of the rod break were Titanium rods and Carillo rods.<<<

While I don't have the knowledge of the 911 engine that you do, the statement above is a little misleading.

The only thing wrong with that implication [first paragraph] is that people that buy Titanium or Carillo rods, are people that intend to spin the engine to higher rpms, make more power, and/or run at high rpms for sustained periods of time compared to people with stock engines or that are using stock rods (apples-to-apples).

That's why people buy Titanium or Carrillo rods in the first place.

Thus it would only be natural to see more failed high performance rods compared to stock rods due to the usage.


Just my .02


TonyG

PS> This has turned out to be a very informative thread. Thanks for the info...

[Henry Schmidt]

Point taken Tony.

Here's my point: There are thousands of 911 based 2.0-3.0 liter race engines out there. Maybe tens of thousands over the years. Most are using production based rods (my opinion). I have only heard of one factory rod breaking at the small end with no other factors but rod failure. That can not be said of Carillo or titanium rods.

My point is that the factory 2.0-3.0 rods are great rods.
(also my opinion)
Stock are bolts are another thing altogether.

[snowman]

sounds like an oiling problem, not a rod problem if the small end is breaking. I am going to talk to the Carillo rep in the next couple weeks and I will ask her what she thinks about small end failures. The rod bolt is the weak link, so the failure is curious.

No you can't use the worlds best bolt (SPS) in a Porsche rod. You must use Carillo or someone who has designed their rod to accomadate the SPS bolt. The best SPS bolts have strengths of 320,000 lb vs the ARP 220,000 lb bolts, PLUS they are 100% Xrayed and tested. They have very special unique thread designs. Thats one of the weakest areas of a rod bolt. They are used to hold critical parts in fighter aircraft togather and they start at $25 ea. No way to compart it to an ARP bolt.

Henry, you forgot the cost to reshotpeen the rods if required, what about $120/set at Metal Improvement Company.

[Henry Schmidt]

If you feel that an x-ray would easy your mind on an "untested product" Critical Operations will x-ray any parts you desire, even new rod bolts.

It's my opinion that most engines builders have determined that shot peening has no measurable value, much like boat tailing cases.
Many of the race engine processes are performed as a selling point and a margin tool to unnecessarily inflate prices. Peace of mind might best describe some of the processes.

But even with the cost of shot peening the price of the 3.0 rod conversion is well worth the cost.

BTW: $120 to shot peen 6 rods seems high. But what isn't these days.

[snowman]

Most mechanical engineers have determined that shot peening critical parts is essencial, not optional. Cracks cannot propagate on a surface in compression. Shot peeing puts the entire surface in compression. I even shot peen cranks, valve springs, head and case bolts.

However if peening is done by someone that dosen't know what they are doing, ie almost anyone other than Metal Improvement Company http://www.metalimprovement.com/ , it can be very worthless. If the company that peens your product dosen't give you a bunch of curled up metal strips, about 1/2 inch wide, 1/16 inch thick and 3 inches long, they didn't do a good peening job.

[sammyg2]

Shot peen valve springs? I'm a mechanical engineer and that's a new one to me.

[Henry Schmidt]

Over the years I have done some research on shot peening and by all accounts it does offer exceptional fatigue resistance.
In the case of connecting rods, crack prevention do to fatigue seems it's greatest value. (My opinion).
Now the $24,000 question.
How many 911/930 Porsche connecting rods have you seen (this is a real question) with cracks?

I am asking this question, not to be sarcastic, but in an attempt to gather some real data.

I personally have only seen one cracked 911/930 Porsche connecting rods and we mag test them regularly.

Last question: If Porsche rods don't generally crack from fatigue, where does shot peening benefit the Porsche rod.

Although we shot peening racing production rods on occasionally, I would hesitate to call it a critical process.

Side note : Shot peening valve springs is extremely common.

[Cookie Porsche]

Now the $24,000 question.

Henry,

Firstly - the $24k will not cover the cost of rebuilding a stuffed race engine - even if the reply is correct!

Secondly - I have never had a broken (factory) rod where the cause was attributed to a 'crack'.

I have seen bent rods, rod bolt failure and rod bearing problems.

Of course I replace rods if any shows up problems when building an engine - but be it a 3.0 to a 3.8 I have used factory rods in racing whith no problem so far.

A few people have questioned the revs issue. In my experience 'some' drivers over-rev their engines regularly or do not maintain/inspect the engines and then look for answers when the motor goes bang .

Hope that answers your 'real' question, and thanks for the objective threads.

Regards, Tom

[snowman]

dosen't the factory shot peen their S rods? I know they did on the early engines.

[Henry Schmidt]

I'm not sure about shot peening they were however Nitrated.
The nitrating process was abandoned because they saw no improvement in strength or longevity.
I have never read where they were shot peened.

[Eagledriver]

Henry,

What was the reason the factory went with bigger rod journals on the 3.2 and up cranks? I assumed it was for more surface area for the bearing surface. It seems that your solution would be a better way to go just wondering why the factory made the change.

-Andy

[Henry Schmidt]

I am not an engineer so perhaps that question might be better answered by a theorist.
I would assume they were after a more rigid crank.
It may also have to do with bearing surface area or bearing speed.

[sundog]

The force/stress on the connecting rod is proportional to the square of the RPM of the engine. The fatigue life curves for the casting metals used degrade exponentially with this applied stress. This is one reason for the rev limits, and broken rods/rod bolts.

The second consideration is that the 2 surfaces bolted together remain in contact due to the force in the rod bolt. If the acceleration of the piston causes these surfaces to separate, then there is an increase in bolt stress, and an impact phenomenon. Both of these will cause premature failure of the bolts.

I would be interested in the observations of people who have had rod failures on the 3.6 engines to see if they had ever observed a rod to fail without the bolts on the big end breaking first.