Newer Rod's Strength info, assessment

[Guest]

http://www.superchevy.com/technical/engines_drivetrain/shortblock/1510sc_howards/

Above is an article I found while researching the efficacy of the new rod manufacturing process using Powder Metal. The newer rods are in theory lighter, easier to make and inherently stronger from what I gather. The significance here is that some of us appreciate the racy formula 1 sound of the V6 as it climbs in RPM. As much as I hate to admit it, the 350 Z and probably one or two other V6 imports, Infiniti and maybe a Lexus, sound very impressive at wide open throttle if you've had the chance to hear one, I have.

What I have found to suggest that maybe the rods in the 3500 and 3900 are strong enough to push beyond 6000 rpm to 7000 rpm to take advantage of camshaft upgrades for max power is the following:

GM manufactures two kinds of PM rods, powder metal & forged powder metal, unless there are several typos across the engines that only list straight PM.
Then there are Sinter Forged rods found in the 3.6L which may only differ by a heat treatment or maybe not at all, their literature also stated the 3.6 has forged pistons but I've found no human being to support that.

Peak horsepower output for both engines (3.5, 3.9) is at 6000 rpm, fuel shut off is at 6400 rpm for the 3500 & 6000 for the 3900. Is the difference due to valve float and larger valves in the 3900? I don't know. Would stronger springs make a difference?

There are a few engines that either have higher output or higher fuel shut off rpms with very similar bore and stroke combinations to the two engines above, that are listed as having powder metal rods with no forging;

3800SC, PM rods, 6K fuel shut off, which is stated to have rods stronger than the old chevy pinks in the article above.

4.6L Northstar, 6700 rpm Fuel shut off, PM rods, same stroke as the 3.5 & 3.9
4.4 SC Nstar, 6700 rpm F-shut off, heat treated PM rods no forging. 469 hp.

There is a very good possibility that the rods across all of the engines with near the same stroke exception being the 3.8, have a lot in common, the 3.6L rod might even be the same as that found in the 3.5 & 3.9. All of these engines are safely rated for 6000 rpm, a level considerably higher than the older engine ratings and many of us have consistently run the older apparently weaker parts well into the danger zone without a problem.

This is somewhat self serving in that I intend to make 7K the mark, and needed to find information or experiences suggesting I'm asking for trouble if I do so, I haven't found it. And since in some cars the 3.6L has a 7k fuel shut off and uses a rod that in a picture looks nearly identical to that found in the 3.5 & 3.9, I have actually been encouraged, though heat treating and then cryo treating might not be a bad idea.

[geoffinbc]

Don't ever take the fuel cutoof point as a reference for rod strength. We all know that good old forged 660 rods were rated to 7000RPM but most older 660's couldn't make it to 5000RPM. The new PM rods could be pushed further since they are lighter with the same strength.

All told with a precise balancing job and a light reciprocating mass you could go beyond 7000RPM with no trouble.

[Joseph Upson]

I chose fuel cutoff because GM has to take into account extended drivetrain warranties in which case they have to set limits that will insure that they have very few warranty pay outs due to pushing the drivetrain to its upper limit frequently.

I have heard of 7k rpm ability on the older rods, but never saw any factory specs that suggested it was possible based on its operating specs. Here the engine is rated at a HP level that would require you to be able to reach the documented rpm to validate the the engines ability produce the stated HP as well as actually spin that high. Nearly all of them are dyno certified so they should be able reach the peak.

The 3.4 DOHC was rated at 210hp @ 5200 rpm and the guys here run them to 7K, so I suspect you are right in that the 3.9 particularly that is rated at 240hp @ 6000 rpm can probably stand to go higher still than 7K and still stay together. At least the better rotating assembly would suggest that. Since the pistons in it are floating I just might look into a rebalance.

[Superdave]

I have the rev limiter set to 7K on my 3500, the cam supposedly makes power till 8K but i don't want to push my luck... I've only taken it to 6K so far. It would be nice if we could confirm the actual strength of these rods. Knowing my luck i'll be the first to snap one

[sharkey]

its in the gm powerbook that the older forged rods can take 7000rpm in stock form. with some work (better rod bolts, beam polishing and shot peening) they will take much higher rpm.

the fuel cut has nothing to do with the rod strength. you have to remember that the larger the stroke, the lower the peak power will be. in stock form, the 3900 doesnt need to rev about 6000, peak power is lower, and it just isnt needed

[Joseph Upson]

its in the gm powerbook that the older forged rods can take 7000rpm in stock form. with some work (better rod bolts, beam polishing and shot peening) they will take much higher rpm.

the fuel cut has nothing to do with the rod strength. you have to remember that the larger the stroke, the lower the peak power will be. in stock form, the 3900 doesnt need to rev about 6000, peak power is lower, and it just isnt needed

Peak power for the 3900 is not lower than 6K, it is at 6K where GM advertises it and has also dyno certified it on their spec page. Autotrader also lists it at 240hp @ 6000 rpm. The fuel shut off is not being used as a measure of rod strength but a measure of likely stability/dependability at that rpm because GM is allowing it to rev to that level in the wake of the lengthy drivetrain warranty which it would be a foolish thing for a manufacturer to do if the part can't handle the stress at that level repeatedly mile after mile of everyday use characteristics. The stroke for the 3900 is the same as the previous 60 degree engines except the 2.8 of course.

Since some cushion is usually incorporated the rods should be able to safely handle more rpm than the fuel cutoff limitation allows.

[Joseph Upson]

This is what it's all about for me,

http://videos.streetfire.net/video/6F1EF2A1-8042-4A19-A8B5-53C95B0C3293.htm

http://videos.streetfire.net/search/f1/8/ff0c3901-0b0d-4912-9bc3-761051efd4b3.htm

http://videos.streetfire.net/search/f1/2/wm/3049C1A6-C6CA-4BB4-A069-4FD474074313.htm

HIGH REVS, I can't get enough of the sound of those engines at the edge but still producing a harmonious exhaust note.

[ForcedFirebird]

This is what it's all about for me,

http://videos.streetfire.net/video/6F1EF2A1-8042-4A19-A8B5-53C95B0C3293.htm

http://videos.streetfire.net/search/f1/8/ff0c3901-0b0d-4912-9bc3-761051efd4b3.htm

http://videos.streetfire.net/search/f1/2/wm/3049C1A6-C6CA-4BB4-A069-4FD474074313.htm

HIGH REVS, I can't get enough of the sound of those engines at the edge but still producing a harmonious exhaust note.

Did you notice in the second video, the driver was stick-shifting - no paddle!

Was the car/boat/bike race a surprise?

Back to topic:

I am on the understanding that the bolts are a weak point on the rods, in fact I saw a picture the other day of a bent 660 rod (actually bent in an "s" shape), the car was still running! He got water in the cylinder from a blown gasket...
http://www.putfile.com/pic.php?img=5496910
http://www.putfile.com/pic.php?img=5496909

[geoffinbc]

Still the fuel cutoff has ZERO to do with the rods ability to take the RPM or Power. The valvetrain is going to float long before 7000RPM and the power will also drop off before then especiall if the valvetrain is floating. Hydraulic lifters also start to pump up and completly ruin engine breathing. Also take into account the accessories bolted to the motor. And remember that several people on this board report that they cannot get there Getrag 282 to shift with any reliability over 6000RPM. I know the 282 has nothing to do with todays motors but I am using it as an example.

On a stock engine the rods are the least of the worries when setting a fuel cutoff limit.

[PCGUY112887]

Wow you guys are in depth. I planned on either leaving my 3500 at stock or to 6500. I'd be afraid to do 7k

[Joseph Upson]

Still the fuel cutoff has ZERO to do with the rods ability to take the RPM or Power. The valvetrain is going to float long before 7000RPM and the power will also drop off before then especiall if the valvetrain is floating. Hydraulic lifters also start to pump up and completly ruin engine breathing. Also take into account the accessories bolted to the motor. And remember that several people on this board report that they cannot get there Getrag 282 to shift with any reliability over 6000RPM. I know the 282 has nothing to do with todays motors but I am using it as an example.

On a stock engine the rods are the least of the worries when setting a fuel cutoff limit.

I probably should have stated that I have LS6 springs and a 6 speed transmission for my swop.

No problem, it's not an issue I intended to debate more than evaluate, just a risk management assessment. This is a blanket safety issue, obviously the weakest link is setting the limit and none of us believes it is the rods.

Of course the valve train plays a big role in the rpm limitations and that goes without saying, I indicated that in the first post by asking that very question when addressing the different rpm limit between two of the engines.

The valves are the same for 07, 04-06 3.5 has a 6k limit & smaller valves.

To add a twist to the subject, the 07 3.5 & 3.9 differ by: a 400 rpm cutoff, stroke, and piston pin location. If the valve train was the limitation, how is the extra 400 rpm possible with the same valve train for both engines when piston pin location and stroke has no effect on its strength or weight?

Maybe the camshafts are different and because the engine has VVT, valve float may allow for contact with the piston. I have read of one bent valve incident on the G6 forum however it was not stated how it was done, but some difficulty with shifting at the time it occured was suspected and suggests a possible over speed leading to valve float if it's possible in these two engines at 6k, that hasn't been proven yet to my knowledge.

The rods also have a larger diameter big end equaling more bearing surface which should reduce engine failure due to bearing wear which was the biggest killer of V6 Fieros.

The oil squirters on the 3.9 must remove a tremendous amount of heat from the pistons. I have an engine oil cooler to take advantage of that as well. That's where the weakest link is, we just don't like to talk about it because it's the toughest area to address due to expense.

I don't like one off critical parts where in damaging one calls for an astronomically priced replacement. Can you buy one custom piston? It's more practical to test the limits of stock when a set of custom pistons costs almost as much as a complete low mileage replacement engine. The newer pistons look pretty strong and I intend to find out.

I have a video of a dyno run on a stock turbocharged late model GP 3800, 438hp 429 lb/ft at the wheels but they cheated by spraying nitrous into the turbo inlet. Still good numbers for a 200hp 230 lb/ft base engine at the crank. I think they chipped a piston at some point but that's due to detonation I believe.

I can live happily with those numbers at the wheels with the ZO6 making less than that at the crank. Heck the stock 3800 only has 10 more lb/ft than the 3500, with a cam I'm sure it can lay down those numbers. If mine had oil squirters on all 6 cylinders I would use it instead of opting for the 3900.

For those who are not aware of my junk pile here is a link to what I'm doing, the engine in the picture will be replaced with a 3900:

http://www.fiero.nl/forum/Forum2/HTML/077718.html#lastpost

[Superdave]

sorry to go off topic, Joseph, where did you get the flange for that front manifold? we need a pair of them for a little project in a sunbird...

Thanks

/offtopic

[Joseph Upson]

sorry to go off topic, Joseph, where did you get the flange for that front manifold? we need a pair of them for a little project in a sunbird...

Thanks

/offtopic

I purchased a burnt 3900 and specified that I needed them to cut the exhaust below the flanges during removal. They are not easy to come by because almost as soon as the engines are removed from the cars they are crushing them, and some over paranoid places will not even do that because it's illegal to sell a used catalytic converter in some states and the flanges are almost directly connected to them so many will not bother to do it for that reason.

They do come in handy especially if you have to remove your turbo for some reason.

[Superdave]

well, it's official.. the 3500 rods will take 7K RPM. I bounced mine off the 7K rev limiter in 1st and 2nd gear earlier...

[Joseph Upson]

I'm not surprised, what all have you done to your engine?