Spinning a 3.2 to 7500
 

What needs to be done?
Do I need aftermarket rods?

I know the 3.2 rods are weak because of the 9mm rod bolts, but I saw a set of carrillo rods for a 993 engine and they had ~9mm bolts as well or is my "measurement skills" that bad?

Could I just use my stock rods with some trick Arp rod bolts?

7500 for how long?

I believe most engine builders will tell you that a sustained 7500 rpm requires
1. oiling mods to the crank and bearings. There's different ways to do this.
2. recommended also to have a turbo or gt3 oil pump upgrade
3. aftermarket rods, carillo, pauter, R&R etc. The carillo rods you saw may have had same size stud in an upgraded material (higher tensile strength) than the OEM.
4. If you just want insurance against over revs, then stock rods with aftermarket studs is probably OK. But any sustained action at 7500 requires upgrades.

When we build an engine using a 74.4 stoke crank that is intended to sustain high RPMs we grind the crank rod journals from 55mm to 53mm. During this process we increase the fillet radius.
Now you can run a stock 911 SC rod with ARP bolts or any number of after market rods. This configuration was a staple for all big bore 911 factory race engines including the GT3 engines found in modern racers.
We also cross drill the crank (grooving the bearing and enlarging the oil passage in the case), install cam feed line restricters and any number of upgraded pumps.
At that RPM reducing the fan speed is also recommended.

Yes, I mean sustained rpms of 7500 or more. I'm gathering information for an upgrade to take the engine above 300 hp.
The carillo rods had Arp bolts. But if its only the original rod bolts that suck, arp bolts would do the trick. But that cant be the whole story?
R&R rods is supposed to withstand over 8000 rpm they say.

Crank oiling modifications:
Cross drilling, what is that really?

That would improve stroke to rod ratio, but the rod would be to long. So you would need some custom pistons, right?
Would an SC rod with ARP bolts handle 7500 without any problems?

The SC rod is only .032" longer so shimming the barrels or minor piston dome surgery will remedy that issue. Of course a custom piston mated to a GT3 Pankl is the coolest option.


It's not the best option but they seem to survive quite well.

Wouldn't you need better valve springs too?

I've got a race engine in pieces the will need some new pistons (maybe jugs)
it has carrillo rods.

I was thinking of upgrading the valve springs and considering what else I would need
to push a 964 crank with 3.8L pistons above 8K sustained.
There is a nice article in Popular Mechanics this month about PPI Valve Springs.

Was figuring better bearings were needed. lighter pistons.
In my case it's a hybrid 964/993 engine.

Mike

I would need new pistons anyway... as well as a bunch of other stuff...

When you grind down the rod journal, is the larger fillet a bonus or the primary reason?

You're right, valve springs should be upgraded for sustained 7500 rpm.

There's also aerodynamic mods, mooning the case and knife edging the crank. When you go to even higher RPMs, there's other mods and maybe necessary work. Mods like shuffle pinning the case, necessary work like line boring the case, maybe better spec component balance, lightened components, top quality bearings, etc,etc.

The higher in RPM you go, the more necessary it is to work with a top quality shop. Their experience in building high RPM engines is invaluable. Do your homework, educate yourself, but in the end it's the experience that counts. Guys like Henry can tell you what works and what you shouldn't waste your time on, but you also want that advise coming from your machine shop...not from a forum....at least this is my opinion.

Those are VERY true words,.......:)

Making reliable power at those RPM's requires a systematic and thorough approach with a host of modifications and parts specific for that purpose.

Shortcuts can be quite expensive. :) :) :)

I will stick on whatever Henry says,he is a tru master.,cheers.,Stefan.

We have many top notch guys like Henry, Steve W, John Walker, Aaron Bruns, Chris Carol and many others. All I'm saying is that ultimately you will need to have a machine shop do the work for you. It is better for that top level of advise to be coming from your machine shop (i.e. deal with a top notch shop) than to get your information here on the forum and convey to a shop that is not familiar with the work, especially for the higher tuned engines.

I have great respect for all the guys above, thats why I'm asking these questions here.
I want to know myself before I take my stuff anywhere what should be done. I don't want to be tricked in to getting stuff I don't need or the other way around....

I take parts to a machine shop to be machined. I don't understand the connection between the machine shop and the build. I don't know of a machine shop in Houston that would know enough about a 911 to make an informed build. There are several engine builders local that could make that call (William Knight, Sam Sabala) but they are no different than those who chime in here.

This is the proper attitude.
When you have a dream, you first express that dream (you want more ?), find an architect to help conceptualize the dream by isolating information pertaining to the specific project (establish a realistic goal) and then you find the personnel to execute the process.

There are often overlaps but each step needs to be addressed.

Asking a machine shop to design an engine is like asking a carpenter to design a house. Sure, some can but generally you look to the specialist in his/her field to help you through the process.

When it come to this type of engine build you would be hard pressed to find better counsel than Henry's. It's offered freely without expectation and it's backed by years of engine specific experience.

Not directly related to the 7500 rpm question, but related to the line of conversation dealing with having a solid dialogue with the shop doing the work:

I am in the middle of a fairly stock 3.2 rebuild and I have been farming out all the machine work etc to a very well respected local Porsche specialist (Brent Hunter: Hunter Motorsports - The Shop ) He has been great in walking me though each stage of equipment selection and his view of the best options and methods. Concurrently, I have gleaned a ton of useful knowledge here. Henry in particular has influenced my thoughts (and choice of head studs). What was great was being able to have Brent provide independent feedback and advice particular to my needs. I found that Brent's and Henry's (as well as other people here) views were essentially the same. If I was doing an "unusual" build, I think this validation would be even more beneficial.

Great people and advice here, but it is hard to convey the total start-to-finish body of knowledge over the internet (and how if pertains to a unique set of goals). And, unfortunately, with the internet there are always people who "sound" much more knowledgeable than they actually are (not referring to anyone here, just a general observation).

Good luck with your build!

Sorry, I think I muddied your thread a bit. I apologize.

Here are some threads that you might find useful:

http://forums.pelicanparts.com/911-engine-rebuilding-forum/230656-cross-drilling-crank.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/204047-case-crank-mods-they-worth.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/383178-two-inch-nascar-bearings.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/310463-cam-oil-line-restrictor-adapter.html

http://forums.pelicanparts.com/porsche-911-technical-forum/67789-oilpump-modification.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/207800-intermediate-shaft-bearing-weirdness.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/617117-crank-cross-drill-necessary.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/570213-grooving-main-bearings.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/159484-crank-hardening-2.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/527825-cross-drilled-crank-bearing-question.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/469439-cross-drilling-crankshaft.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/447676-case-crank-work-summary.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/140066-high-rpm-pulley-upgrade.html

AlfonsoR...you just saved him a TON of potential pitfallsw/ those very important threads he needs to be up on...nice job...!!

Another one to add is the "ultimate case sealing" thread I believe it is called, where all of the "goops" are listed for the different area's of the motor that need sealing compounds...

Yeah well, i went back and read my input and realized I was not helping my Pelican brother Safe. Instead i got his thread going on a tangent. So to make up for it, I did a bit of homework, that's all.

Re ultimate sealing, very good thread. There is a ton of really information on this board.