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ARP Rod Bolts Group buy?
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safe  



Joined: 18 Mar 2017
Posts: 163
Location: Sweden

PostPosted: Thu Dec 12, 2019 8:40 am    Post subject: Reply with quote

Its NEVER cheep to properly rebuild an engine, regardless the cost of the vehicle.
This is the downfall of the 924, it costs $1000 so the hillbilly who owns it doesn't want to by 4 new good tires, he buys 3 different kind of used tires. A relay fails, that costs money, he has a switch left over from a tractor. Lets put that in, lets drill a hole in the dash for it... etc.
Soon this car is a pile of junk tons of "customisations" that gets left in a field to rust away.
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kondzi  



Joined: 02 Jul 2018
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Location: MZ/Poland/EU

PostPosted: Thu Dec 12, 2019 9:46 am    Post subject: Reply with quote

If I was rebuilding an engine, I'd use the less expensive use-it-once OEMs.
For heavily modded engine / race engine, I'd go with reusable ARPs.
To put it on the shelf (current situation) it's just too much.

That's my (and not only mine) point of view.
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tyfighter123  



Joined: 19 Jan 2010
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PostPosted: Thu Dec 12, 2019 1:05 pm    Post subject: Reply with quote

I am in for 2 sets!
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peterld  



Joined: 10 Dec 2006
Posts: 771
Location: Noosa Heads QLD Australia

PostPosted: Thu Dec 12, 2019 11:49 pm    Post subject: Reply with quote

There is a certain feeling of deja vu about this whole discussion......very similar comments to the first round of ARP bolt buys.

So first up, let's be very clear about one thing. Unless you have a cherry unmolested, unmodified Toofah, commercially it makes little sense to spend too much on anything. Although prices are rising (less so in the States), it will probably be at least another 10 years before we see any real value in them....and that will be for the cherry examples.

If you're in it for the short haul, the above applies. However if it is an emotive issue, AND there is the probability you are going to track it at any time, then only the best MUST suffice.

30 minutes of track time in a running group is approximate to a regular race (without any wheel banging).......same time frame, same revs, same braking stresses, etc. Repeat that twice more on that day and you have now subjected your car to the same stresses as a normal race weekend!

Realistically, your Toofah was NEVER designed with that in mind, certainly not to continue to do so repeatedly; and if you are going down that slippery road then upgrades for the whole car will be necessary.
A decent motor alone will cost easily $5,000.......machining/balancing/blueprinting/pistons/bearings/valves/etc, etc.

For a nice road car motor, one time use bolts are more than sufficient. For any sporting application where there is a chance you will have to pull down and reuse, the ARP is a no brainer.

The first bolt buy originated from discussions Dan and I had back in the 2000s after I had posted seeking new rod bolts, having had a catastrophic engine failure due to a sheared rod bolt at a race meeting. And yes the bolts and nuts had been crack tested!
It transpired that Dan had technical drawings of the bolts, and he approached ARP and a group buy ensued. I said I'd take 5 sets and away it went. So thanks to Dan we now had an alternative. And then along came the Cometic deal, which saved me from O-ringing a block, and so on.

The take-out is: you get what you pay for. If you are running higher revs (and boost) you need to spend up. Is it worth it....only you can determine that.
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TJC  



Joined: 04 Apr 2010
Posts: 751
Location: Central-ish Arizona, USA

PostPosted: Fri Dec 13, 2019 2:08 am    Post subject: Reply with quote

I'm just going to throw this out there.
Considering what the potential cost of the bolts are going to be and then, at a minimum, have them installed and have the subsequent machining done to make the rod useable, (magnaflux and resizing at a minimum, but may as well re-bush, perhaps flash grind and shotpeen plus rebalance, etc.), one could have a pretty tidy sum wrapped up in basically stock ~40 year old rods.

If I were to build a serious engine I would have to consider that fact very carefully and start looking for an alternative such as a purpose built rod or adapting a newer rod from some different engine. To potentially have $500-600 or more wrapped up in 40 year old rods for a high output engine doesn't make a lot of sense to me.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Fri Dec 13, 2019 3:44 am    Post subject: Reply with quote

Define "high-output"... it's very not easy to build such a beast out of the NA. That's why I got the ARP bolts for my Turbo first...

Super-easy to swap out the bolts on the rods, if that's all you're doing.

Regarding upgrades... grinding down flash, lightening, and balancing are easy, just a little time needed. Anything beyond that, yes you'd be wise to price out some aftermarket rods.
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TJC  



Joined: 04 Apr 2010
Posts: 751
Location: Central-ish Arizona, USA

PostPosted: Fri Dec 13, 2019 5:11 am    Post subject: Reply with quote

924RACR wrote:
Define "high-output"... it's very not easy to build such a beast out of the NA. That's why I got the ARP bolts for my Turbo first...

Super-easy to swap out the bolts on the rods, if that's all you're doing.

Regarding upgrades... grinding down flash, lightening, and balancing are easy, just a little time needed. Anything beyond that, yes you'd be wise to price out some aftermarket rods.


Let's start at 225+ HP and mostly dedicated track use but still somewhat streetable.
You are in the business and connected, much like myself, so what may be easy for us may not be so easy for others as they may have to rely on outside sources to perform the work.
Also as most are well aware the connecting rod is only one facet of an entire build and all components must be designed and assembled to work in harmony to achieve the best result. Without getting into technicalities we know from the outset that the connecting rod is subject to tremendous abuse under race conditions and the extreme cycles based on engine speeds constantly changing is a lot to endure.
Under mild conditions the story changes and there may not be any reason to change out the bolts at all in which case a simple rod reconditioning is all that's required.

I'm following this particular thread to get as much information as possible to help me make a decision as to which route I want to go with the '80 924 Turbo that I have. A couple of my main priorities are of course cost and possible failures and downtime. My goal is to have a fun, light and reliable little car that I can enjoy on the mountain and canyon backroads near my home so I am not necessarily devoted to any one platform although I am fond of the 924. As I continue my "due diligence" I continue to have these little angel-devil on the shoulders debates as to what I may do !!!
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safe  



Joined: 18 Mar 2017
Posts: 163
Location: Sweden

PostPosted: Fri Dec 13, 2019 7:13 pm    Post subject: Reply with quote

Correct me if I'm wrong and if so explain why.
I don't see a need for stronger rod bolts on a boosted engine. The tensile strength of the rod/rod bolts is an issue when the crank is yanking the piston down on the intake stoke. As long as you don't rev the engine higher you don't get any higher loads.
If anything the boost will push down on the piston and lessen the force on the rods.
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CÚdric  



Joined: 27 Aug 2004
Posts: 1975
Location: Sweden

PostPosted: Fri Dec 13, 2019 8:07 pm    Post subject: Reply with quote

safe wrote:
Correct me if I'm wrong and if so explain why.
I don't see a need for stronger rod bolts on a boosted engine. The tensile strength of the rod/rod bolts is an issue when the crank is yanking the piston down on the intake stoke. As long as you don't rev the engine higher you don't get any higher loads.
If anything the boost will push down on the piston and lessen the force on the rods.


No problems with std bolts in real life, they hold up fine with the standard rev limit, regardless of what type of racing you do. As you say, rpm is the toughest factor. I think the difference between new std ones and ARP is negligible for most of us, the biggest risk is the reuse. They arent stretch bolts, thats what porsche told me at least, but reusing old bolts is always a risk on a fairly critical part. I dont think the risk is big at all, but the consequences are of course.

Still no prices on the ARPs?
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1972
Location: Somerset, UK

PostPosted: Fri Dec 13, 2019 10:13 pm    Post subject: Reply with quote

Carrera RSR wrote:
Juho wrote:
Might be intrested in a set, how big of a upgrade they are and are they worth the price?


On a stock NA, they are recommended to be replaced ..... but are not always needed and you could reuse the old. Depends on your state of risk aversion.

On a stock turbo, recommended to change bolts on rebuild, but if you are feeling lucky, don't over rev or overly boost, you may get away with reusing. Not the best advice.

On a high revving NA or over boosted turbo you must replace the bolts or internal damage may ensue.

Stock bolts would suffice but they are long time NLA. So ARP is the only option except they are not a stock item and have to be bought in minimums of 10 sets direct from ARP. Not necessarily seen as an upgrade.....but ARP does sell themselves as superior to OEM. No idea if this is true on rod bolts spec? But they are your only option.....so you have to pay the price of new bolts and nuts. Think I paid circa $200 on the last set I bought with nuts.



To boost order numbers, may be worth contacting Mittelmotor who stock them but do run out of supplies. I think EBS Racing also do/did?


The advice above came from emails with Mittelmotor during my engine rebuild some years ago trying to source some OEM or ARP bolts. If you feel lucky, re use. If not, then you have a choice of OEM and ARP now subject to ARP minimum set purchase. You pay your money, you take your choice.......

I am happy with ARP that I have a second chance if I have to rebuild. I also like the confidence that when I very occasionally red line it I'm hopefully not going to hear a large bang

Or re use your stock bolts on a stock engine. For me its like re using a condom. Sometimes it works, sometimes its doesn't ........
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Fri Dec 13, 2019 11:28 pm    Post subject: Reply with quote

Yeah, again, stock motors and even more moderate builds on NAs I think it's no issue using stock bolts; even re-use can be OK. But there is risk with re-use, especially if you're not as experienced to notice that the bolts are stretching (as I did, in my case).

Once you get into multiple builds etc on the same block, ARP turns into a cost-saver... but that's probably maybe 5% of the crowd here.
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safe  



Joined: 18 Mar 2017
Posts: 163
Location: Sweden

PostPosted: Fri Dec 13, 2019 11:44 pm    Post subject: Reply with quote

Lighter pistons would be better over all for the engine. If you build a race engine you probably would do this and then there is a lot less force on the rod bolts.
I would say that on most rebuilds, stock or not, the pistons are "more junk" than the rod bolts anyway.
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Fifty50Plus  



Joined: 28 Feb 2008
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PostPosted: Sat Dec 14, 2019 1:52 am    Post subject: Reply with quote

Years and years ago I raced a 2 liter 911 with stock rod bolts. I consistently revved over 8000 RPM with never a failure. Later I switched to a 2.4 liter engine with a longer stroke and factory rod bolts began to fail above 7500. ARP finally came out with their version and no more failures.
I've now been racing 924s over 4 years with Dan's bolts and no problems. The induction and cam pretty much limit revs to 6500 - 6700 which I've done, but more importantly, torque pretty much quits above 6000 so I now shift there. I like the feeling that I'm using bulletproof parts and never need to worry about a failure. Rod bearings are more of a concern but I run an AccuSump and record oil pressure. With the AccuSump, there is no oil pump cavitation and subsequent drop in pressure in sweeping high speed turns.
I'm not saying that stock rod bolts are a problem but I like the extra insurance that technology upgrades provide.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Sat Dec 14, 2019 4:15 am    Post subject: Reply with quote

Yeah, I think the Accusump is critical for these engines. I don't log pressure - don't even want to open that can of worms, and I know the engine is good since Build 1 lasted 15 years of racing.

I did used to wind mine out to 7000rpm, when it'd save me an upshift (since 5th is a dog)... and it was fine as long as I didn't get overzealous on the downshifts - around 8000rpm the lifters tended to come apart.

That was on used stock rod bolts, but with an engine making maybe 135hp crank. Barely more than 100rwhp on the dyno. And I'd have ARP bolts in there now, if I'd had them last time I built the engine (September).
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Sat Dec 14, 2019 11:10 am    Post subject: Reply with quote

safe wrote:
Lighter pistons would be better over all for the engine.


My problem is that I would need bolts in order to change the pistons in any 2.0 shortblock.. Be it my current block, or more likely the replacement when I finally blow mine up..

Might be cheapest just to find another 931 engine to blow up, or a 2.0 shortblock if my head survives the inevitable catastrophy, but would need the pistons replaced, thereby requiring new rod bolts $$..

This just seems ridiculous money for some bolts.. Head studs are half the price..

We already know a lot can be ground off our rods to save weight and they are still plenty strong..
Why can't we find some more available and sanely priced bolts to do the job, and possibly even modify the rods to work with them?



The rods could possibly be reemed to take a slightly larger diamiter bolt?
The rods could possibly be modified where the head of the bolt meets the rod?

ideola wrote:
M10x1.0 Porsche Rod Bolt


They are 10mm dia?

What is so complicated about finding bolts to fit these holes?

BMW M10 rod bolts are 10mm
https://www.summitracing.com/parts/arp-201-6304/overview/
$108

Too short? Take some material off the rods so they fit?

10mm=0.393701"
7/16"=11.1125mm
Ream the holes out to 7/16?

49 results of cheap rod bolts in 7/16..
https://www.summitracing.com/search/part-type/connecting-rod-bolts/thread-size/7-16-in?N=thread-size%3A7-16-in&SortBy=Default&SortOrder=Default

ARP has all sorts of 10mm bolts..
https://arp-bolts.com/kits/bulk.php?PL=89&M=2&W=*&D=8&P=15&WS=13

Can't make anything fit?
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