2.2 race motor rod bolts...redline

[speedo]

I am about to begin assembly of a 2.2 motor for the track. All machining is done, parts tested , polished and balanced. I am planning on using the 2.2 Porsche factory new rod bolts as I learned that both ARP and Raceware no longer make a 2.2 bolt. I just read an article in a 2004 Excellence by Bruce Anderson responding to a readers question concerning rev limits on a rebuilt 3.2 using ARP bolts....and he adamantly states that the stock bolts should not be rev'd over 7000 rpm. He told the reader that with the ARP bolts that 7700 ought to be redline for his specific motor.

My local shops assured me that the stock bolts would be fine for my 2.2 motor....but I am concerned nonetheless.

Here are the specs...
Cosworth 10.5-1 pistons
fresh honed aluminum biral mooned cylinders
S ported heads with heavy springs, single plug
Ge 80 cams
balanced rods w/in .5 grams
noncounterbalanced 2.2 std/std polished crank
40 IDAs
4R case with squirters, timecerts, oilbypass, linebored etc

I had planned on the motor starting to pull at 6000rpm to an 8500 redline....aiming for 200+ hp.

So obviously Bruce suggesting a 7000 redline limitation for the stock bolts makes me wonder??

[andrew15]

Hi Speedo - Two things:
First - The suggested 7,000 RPM limit is for stock bolts on a 3.2. The 3.2L engine went to a smaller diameter rod bolt vs the 3.0 and there were some problems at higher rpms - this is not an issue for your 2.2. The 2.2S used the stock bolts and had a 7,300 RPM redline.

Second - If you want the peace of mind of a stronger rod bolt, Henry over at Supertec uses a modified ARP 928 bolt on the 2.2 Rods. Give him a call - he's quite helpful.

Regards,
Andrew M

[speedo]

Thanks Andrew....

I will give Henry a call....

Speedo

[Eagledriver]

With your short throw crankshaft and large rod bolts you should be fine but I'd hope that Henry or Steve will chime in on this. I know that Bruce Anderson mentions an RPM range for the 2.4/2.7 race engine of up to 8000 or maybe it was 8500 but I forget and I don't have the book with me. Your engine with the 66mm stroke should be good for at least the numbers for the 2.4/2.7

-Andy

[eapcpa]

There is some harmonic vibration issue with the flywheel bolts on the six bolt crank. Might ask Henry or Mike Bruns about it. Seems like 8000 is the RPM that causes problems but I am not positive.

[356RS]

Ed,

The harmonic vibration issue started with the 70.4 mm stroke crank. The short 66 mm stroke crank was sweet at 8000 RPM.

[Henry Schmidt]

For racing applications we use 2.4-3.0 rod bolts on 2.2 rods. This gives us an effective rev limit of 8500 rpm. To do this you must modify the rods. We do this modification in house.
The 928 rod bolt thing is an error. We use Porsche 928 rod nuts on all 10mm rod bolt applications because we believe they are a better nut.

[andrew15]

I'm extra dumb today. Thanks for correcting me Henry - I don't know why I though 928 bolt!

AM

[Walt Fricke]

By all means go with Henry's bolt system. I ran my 66mm 2.3 up to 8,000 all the time with stock bolts. Seemed fine for quite a while until a rod bolt failed. Had that classic necked down pattern at the point of failure. This was before anyone made high strength bolts (at least that us ordinary folks knew about) for the rods for that crank. I bet the factory replaced those bolts after every race weekend on their race motors if they didn't use

If you use red Loctite very carefully, and torque the flywheel bolts on a 70.4 crank to 150 lbs/ft (not easy with that short headed Allen bolt), I don't think you'll shake the bolts loose up to at least 8,200 (as high as I generally went, though I saw 10,500 once on the memory tach). I don't think such heroic measures are needed on the 66mm crank (something about where the nodes of the 4th harmonic are or are not). But that's a different matter than rod bolt strength.

Walt Fricke

[speedo]

Dang it! The rods have already been rebushed , peened and balanced,new std/std bearings and I have the stock bolts. Case is cleaned, bored and modified , crank is magnafluxed and polished . Oil pump (3.0) is cleaned and everything is ready to assemble . Argh!

Henry , I have PM'd you to learn more.