Is there any real benefit to 964 cams in chipped 3.2?

[cabmandone]

I'm in the process of having my heads redone by Craig after a mechanical over rev. The "while you're in there" bug is biting me so I started looking into some upgrades. Seems some say there's no real benefit while others say it gives a little more "oomf" in the higher RPM range. I thought if I could give the engine a little breathing room and grab a little more power I'd buy a set. I was originally considering a regrind but then I found that I could buy 964 cams and put them in my car with a slight modification to the end of one of the cams.

It would be great if anyone who has the 964 cams or John's 964 regrind would have dyno numbers to support what they bring to the table.

[Henry Schmidt]

If I read your post correctly, an over-rev in a 3.2 puts the rod bolts at risk. The 9mm bolts are too small to handle high RPM let alone a substantial over-rev.
That said: 964 cams offer very little performance enhancement.
The exhaust is the easiest upgrade. 993SS cams are what we find to out perform most other cams with stock intake. If the engine is apart, IE: complete overhaul, custom 3.4 [98mm] pistons 9.8:1 compression, longer rods [3.2 Carrera rods are poorly designed and too short] equal length headers, sport muffler.
Combined with the proper chip and bingo. With these changes, if you later decide to upgrade to ITB, you're ready to go.

The longer rods increase piston dwell and reduce piston side loading. This simple [although costly] really frees up the engine for higher RPM.

We also rebuild the rockers with a resulting friction reduction in the valve train that reduces heat and parasitic lost. [free horse power]

[cabmandone]

You read it right Henry. I was doing about 60 mph in second gear and somehow hit first rather than third resulting in poor leak down numbers on three cylinders. Someone said I hit a 10,000 rpm turn. It was only a hot second before I bumped it out of gear, but the damage was done. Upon inspection, all six exhaust valves had made contact with the pistons. Sounds like I might want to split the case and change out or at least inspect the rod bolts?

If there's no real benefit to the 964 cams, I'll stick with my stock cams. I figure that'll save me about $500 that I can put elsewhere if inspection shows something is needed.

Thanks for your input sir. Always appreciated.

[Trackrash]

Go with ARP rod bolts. You don't have to split the case if just doing the rods. Although at that point you may as well do it right.

I have known guys who put on headers and re chipped and had a good bump in power.

[Henry Schmidt]

Originally Posted by cabmando

You read it right Henry. I was doing about 60 mph in second gear and somehow hit first rather than third resulting in poor leak down numbers on three cylinders. Someone said I hit a 10,000 rpm turn. It was only a hot second before I bumped it out of gear, but the damage was done. Upon inspection, all six exhaust valves had made contact with the pistons. Sounds like I might want to split the case and change out or at least inspect the rod bolts?

If there's no real benefit to the 964 cams, I'll stick with my stock cams. I figure that'll save me about $500 that I can put elsewhere if inspection shows something is needed.

Thanks for your input sir. Always appreciated.

There is no way to be sure about the rod bolts. Even in the best of situations, the rod bolt/rod journal configuration is prone to failure. Good used std/std 3.2/3.3 cranks are like rocking horse shyt....impossible to find. They have a failure rate that far exceeds all other Porsche engine configurations.

Many years ago I had a customer in the very same situation. He ignored my advise and rolled the dice. The engine lasted 82 miles. He was so disgusted with his choice that he sold the car with the exploded engine.

[cabmandone]

Originally Posted by Henry Schmidt

There is no way to be sure about the rod bolts. Even in the best of situations, the rod bolt/rod journal configuration is prone to failure. Good used std/std 3.2/3.3 cranks are like rocking horse shyt....impossible to find. They have a failure rate that far exceeds all other Porsche engine configurations.

Many years ago I had a customer in the very same situation. He ignored my advise and rolled the dice. The engine lasted 82 miles. He was so disgusted with his choice that he sold the car with the exploded engine.

I know what you're sayin. I've been weighing that since I did this. I'm in no real hurry since the car is now parked till spring so I've got time to really dig into this.

Thanks again for the input Henry! Always appreciated.

[cabmandone]

Originally Posted by Trackrash

Go with ARP rod bolts. You don't have to split the case if just doing the rods. Although at that point you may as well do it right.

I have known guys who put on headers and re chipped and had a good bump in power.

That's pretty much where I'm at. If I'm going to the point of changing rod bolts, I might as well open the case and have a look at the bearings.

My car is chipped (Sal's tune) so it runs well. I kicked around SSI's but the gains seemed marginal from the dyno charts I've seen vs my stock HE's and cat delete with a free flowing muffler.

[Henry Schmidt]

Originally Posted by cabmando

That's pretty much where I'm at. If I'm going to the point of changing rod bolts, I might as well open the case and have a look at the bearings.

My car is chipped (Sal's tune) so it runs well. I kicked around SSI's but the gains seemed marginal from the dyno charts I've seen vs my stock HE's and cat delete with a free flowing muffler.

The header option is substantial. If dyno numbers aren't showing a marked change, I would suspect tuning was incomplete.

[mikedsilva]

I'm still relatively new at engine assembly; if you went to remove the rods without splitting the case, how would you get a micrometer in there to measure the rod journals? And if you used ARP bolts, would a stretch gauge fit in there too?

[Walt Fricke]

Mike - I think the answers are no and no.

I could see the possibility of making a set of go/no go gauges you could stick in through the spigots to check the crank. You'd have to be pretty good at fabricating something like that out of flat stock with a very precise slot in the end.

On the other hand, don't most crank journals stay within tolerance for a long time absent being run without oil, or with very dirty oil? If a rod let go, you are probably best off splitting the case so you can clean out the debris. The bearing on that rod may well have almost evaporated, with lots of small stuff in places you don't want it to be. That may have left that journal looking abused, warranting at least polishing it?

I can think of a similar way to measure bolt stretch, but it would be so tedious as not to be worth it (if even possible). The free bolt length is, of course, easy - measure before installing. But a bunch of gauges (because the new bolts vary in length)? ARP has a substitute torque spec method, which ought to be adequate, as not as definitive as measuring stretch.

Pulling the heads off is the biggest labor time consumer of a rebuild, at least if you have to deal with the valves and have to pull the rockers. Once you are that far, the extra time for splitting the case is pretty small.

[targa72e]

If you are planning to change the bolts to ARP you should probably have the rods rebuilt/resized with the new bolts as the new bolt clamping force can change the diameter/shape of big end. I have measured both stretch and torque while tightening rod bolts. I have found that the torque required for the correct stretch to be pretty consistent. I think you could bolt the rods down on the bench to see the required torque for appropriate stretch and then use the torque value when the rods are put back on the crank.

john

[cabmandone]

Originally Posted by mikedsilva

I'm still relatively new at engine assembly; if you went to remove the rods without splitting the case, how would you get a micrometer in there to measure the rod journals? And if you used ARP bolts, would a stretch gauge fit in there too?

I've been doing a lot of reading on rod bolts relating to stretch vs just torque. I looked into ARP's recommendation and found that absent a stretch gauge they recommend torqueing to 40 ft lbs IIRC. This got me looking for more information and it seems in many cases where folks checked stretch, the torque is close to the spec from ARP .

On checking the journals I'm considering using plastigage. But I haven't taken the P&C's off yet so I'm doing more reading to determine the best path forward.

I know I said I was thinking of opening the case but I'm giving that more thought. I think when I get around to pulling the P&C's and then pulling the rods and looking at the bearings I'll have a better idea just how deep I really want to go.

The good news for me is that I have all winter to do this so I have all sorts of time to drive myself nuts second guessing each step that I take

[cabmandone]

Originally Posted by Walt Fricke

Pulling the heads off is the biggest labor time consumer of a rebuild, at least if you have to deal with the valves and have to pull the rockers. Once you are that far, the extra time for splitting the case is pretty small.

For me it's not really about the time to split the case but the time it takes to get everything clean to give yourself the best possible chance of a good seal when things go back together. That and the time you have to get everything back together before the sealant tacks up. Before I decide to split the case I figure I'll have a look at the rod bearings. If everything looks good I'll just go back in with new bolts. But again I have a lot of time to read and change my mind several times between now and next Spring.

[Jeff Alton]

It is not hard to "get everything clean". You have to do these steps with the top end you are already into. If you had an actual mechanical over rev the rods are coming out, period. The question is how do you want to go about that. New bearing and bolts/nuts, resize the big ends and rebush the small ends. Check for total length. If you don't split the case you can't measure the rod journal on the crank.

I would guess very few people who install ARP bolts use stretch, most don't have a gauge to measure. That is why ARP also supplies a torque value, the same way CP does for its bolts in their rods. You will be fine with the torque method.

After an over rev choosing to do a top end with new rod bolts, why are you sweating the torque vs stretch method. You are already taking shortcuts....

A regrind to 964 or similar profile will yield some gains. But if the cams and rockers are in good condition, the gains may not be worth the expense. Only you can decide. You can't replace/grind the cams without doing the rockers.

What is your goal? Fix a missed shift? Rebuild an engine? Figure out what each entails and make a choice. Then do all of the steps appropriate for your choice.

Cheers

[Walt Fricke]

Cabmando
I mixed up your initial problem a bit in my head - somehow I thought something inside had failed. "Just" an overrev might not damage the crank, even if it overstressed the rod bolts, and maybe damaged the rod bearings. The cranks and case are pretty stout, and if you didn't lose too much oil pressure or ran too much or too long or at too high a temperature over normal, maybe the crank wasn't damaged. I can see balancing out what to do after you have the rods off and can look at the rod bearings closely, and get a decent view of the crank journal surface. If one is all dark blue and the others a nice shiny silver, that would be a problem.

Something a lot of guys who assemble their own engines (like me), or are real engine builders (for a living) , either don't realize or don't want to utilize is the fact that the orange Loctite 574 Porsche used is self-soluble. A new thin layer will soften the existing hardened layer, which means you don't have to be meticulous about scraping off the old stuff. The factory manual says just that. I just knock off any big blobs (which are outside the mating surfaces anyway), and have not had a problem.

Other sealants may not work that way, though.

Getting everything bolted together fast enough so that something hasn't dried hard before it is compressed isn't all that hard either. For one thing, you can just torque by hand (or a drill motor) for the first go around to an approximate torque a bit less than the final torque. That will squeeze out every bit as much excess sealant as the final value. Then get out the torque wrench and take your time.

But with some ingenuity, you don't need to do that. The best thing is to have someone help you at this stage, and have all the hardware clean, lubricated where you might want a bit (case through bolt O rings), and assembled (same bolts). Homemade props for three rods, plus something similar for one cam chain do make all this easier, to be sure. It goes quickly - through bolts first, then perimeter stud nuts. You've got to do this sealing the cam carrier to the heads at this point.

[cabmandone]

I appreciate the input folks. Like I said, I haven't ruled anything out. Honestly the only reason I'm even looking at doing the rod bolts is because Henry recommended it. I have searched high and low and the only real mention of rod bolt issues come from Wayne in thread here on PP and Bruce Anderson's book from what I've found. I'm not saying they aren't a weak link, I'm just saying if they are, there would at least be one thread somewhere on the internet with proof that the bolts failed.

From my searching, I've found exactly two threads where guys said their rod bolts failed. One, the engine was rebuilt and the original bolts were reused... so no real surprises there. The other, the person blamed the rod bolts but when he posted pics of his rods, there was clear discoloration showing a high heat situation which means there were oil supply issues. Other than that there's no thread with any definitive proof of rod bolt failure. I'm not saying they aren't a weak link but if they are it's a pretty well kept secret on the internet. And we all know when something fails, no one ever complains about it on the internet.

In my research related to mechanical over rev, the consensus seems to be that the top end is the concern more so than the bottom end. Most indicate that the top end is the "sacrificial lamb" that takes the brunt of the damage. Many have just done the top end, cleaned the pistons and knocked down any dimples on the pistons and called it a day. That's where I was at originally since my leak down numbers on the three cylinders that didn't have bent valves were in the 5% or less range, there were no new engine noises that would indicate an issue on the lower end, and oil pressure was still good. First thing I looked at after the over rev was the oil pressure.

I guess what I'm saying is, I'm not going to let "while I'm in there" dictate how I proceed. I'll inspect things as best I can and determine how I'm going to go forward from there.

One thing I'll definitely look at if/when I choose to pull the rod bolts is the current stretch. I think it will be interesting to see just where they are. That might be the biggest reason for me changing them, to confirm after an over rev that they stretched. I'm not sure I'll be able to find the info to determine how much they stretched but I'm going to do some looking.

Again, I appreciate all the input.

[Walt Fricke]

Nick - measuring bolt stretch calls for a) measuring each bolt before it is installed, b) measuring each bolt as you assemble the rod (i.e., measuring to see if you have stretched it the specified amount, or measuring it after torquing it just to have a measurement, and 3) measuring it after use when you have removed the bolt. It is this last measurement which allows you to decide whether to reuse the bolt. And reuse normally is only contemplated with super grade aftermarket bolts - Porsche claims all its rod bolts are one time use only.

So measuring a bolt now, without the information from before the engine ran, is of no use.

The weakness of the 3.2 bolts is, I think, relative. They won't withstand an over rev as well as the wider 3.0 and earlier bolts. So the reason to replace stock bolts with stronger bolts is to earn some extra margin for over revs. While in daily driving there ought not to be over revs (from money shifts), they certainly can happen. However, I don't think anyone suggests disassembling a well functioning motor just to replace the bolts with stronger ones. If you do have rods off, the super bolts don't cost all that much more than the new stock bolts you otherwise would purchase.

So the question here is: did your particular over rev cause plastic deformation of the rod bolts. That, I think, you can check for. With the pistons off, you can set your torque wrench to the factory torque value, and see if the nut moves. If it moves, that is an indication that the bolt has stretched but not elastically returned to its previous length. This is a bit tricky, as the super bolt manufacturers allow a little bit of residual stretch when deciding if you can reuse. And I'm not sure how well this would work with the torque then angle system Porsche adopted at some (not known to me) point.

A bolt which has entered the plastic zone isn't necessarily a failed bolt. Say a bolt can hold a tensile force of 100 (elastic limit), and it is designed to be installed at a tensile force of 90. That should mean that operating tensile forces up to 100 will leave the bolt fine. Let's say the plastic limit is 120, and it was subjected to a force of 110. It hasn't failed, but it is now permanently longer. It may still be able to act elastically to forces of 90, but it no longer has a clamping force of 90. Less margin. Plastic deformation of a bolt or stud leaves it longer and thinner (necked down) at some part of its length. That part thus has a smaller cross section.

When I first got a 2.7 in 1984, I didn't know any of this stuff. I twice got 1st when going for 3d on my second track event. I adjusted things and eventually got it running smoothly enough, and my lap times improved. A year or two later, though, a mechanic thought the engine was down on power, and a compression test showed low. I pulled the engine and gave the shop the heads. They found all 6 exhaust valves bent into a sort of S shape. They had sawed slots in the valve guides so the valves sort of seated themselves again. No harm to the rod bolts (but these were not the thin 3.2s), and the case only came apart after the head work because one of the replaced valves broke and dropped its head into the cylinder on the track. The crank itself was fine, though lots of other parts were not fine at all.

I think I'd proceed the same way with my 3.0 if I had bent a valve or two from a mechanical over rev. Not sure what I would do if it were a 3.2. Maybe pull the rods, inspect the bearings, plan on new super bolts, and take everything else from there and what, if anything, I saw.

If a rod bolt has too much plastic stretch, the mating surfaces will separate some with each two turns of the crank, increasing bearing clearance and reducing the oil pressure in that journal. Leads to heat, melting of the bearing surface material, and things get worse - like rod bolt complete failure. Results aren't pretty. A friend had a blockage in a crank oil passage, leading to no oil to a main bearing. When he realized something was amiss, he pitted, but after stopping the engine seized up. Rod bolts with failed bearings wouldn't hold up that long.

I'd not rely on what discussion you don't see on the Internet for a conclusion that something is not a problem when there is an engine accident (like a mechanical overrev).

[cabmandone]

Walt,
Your first paragraph is what I was figuring would be the case. I wasn't sure if there was a "standard" new length that I might be able to find.

I agree that just because it's not something you see on the net doesn't mean it doesn't happen. It's just that it's rare to have something that is referred to as a weakness not show up somewhere other than a limited number of threads. Example, I bought a Hyundai veloster for my son. In general searches it checked out okay... but then the cat plugged and the engine crapped out. Once I knew what to look for, there were multiple threads on blown engines due to the cat melting down.

I took the P&C's off today to have a look at what kind of pain I'll be in for if I try just doing rod bolts. It looks like it might be "interesting" to say the least.

[Walt Fricke]

Longish extensions for the socket wrench. A bit tricky to deal with pulling the cap? Magnet on a flexible stick useful. An engine stand (on which you can rotate the engine) helpful so you can let gravity help rather than hinder. There are ways of getting a nut to stick (but not too much) in a socket.

I suspect it would add more to the cost than it is worth to the end user to have rod bolts manufactured to a tolerance of 1/10,000 of an inch. A guy with machines and skills could make all his new bolts be the same exact length, but he'd probably figure it wasn't worth it. I thought of measuring the amount the torqued bolt end sticks out of its nut if you knew exact bolt, nut, and torqued rod widths along the bolt axis were, so you could measure how much bolt sticks out, but that would only be a way of measuring stretch, and it seems that for street motors, torque done right is good enough.

[cabmandone]

Got around to pulling the rods last week. The bearings looked really good so I'm not seeing much point in opening the case. Deglazed the cylinders in preparation for the "new" pistons. I received a set from my brother that we both know had less than 20k miles on them. He replaced because he went to JE pistons in his car... so win for me! I bought new rings and a ring squaring tool I checked ring gap today and all were within spec which would indicate no real issue with cylinder wear if I read Wayne's book correctly. I then put the new rings on the pistons and installed the pistons back into the cylinders.

I had four bent exhaust valves from the over rev. Craig said the intake valves should probably be replaced as well, but I don't recall exactly why, so I bought all new valves. I'm waiting on some moly coating and a sealant kit my brother is sending me. I'm going to moly coat the rod bearings before they go back in.