What can you rev a 3.2 to, with ARP rod bolts ?

[slow car]

What would be the max safe revs for a 3.2 -3.4 with std rods and ARP rod bolts/nuts.
Balanced engine je pistons.
Ti retainers GE80 cams, stronger valve springs.
PMOs
It is suggested that i should be changing gears at 7500RPM with the GE 80 Cams
Thanks

[r lane]

Maybe you could go to 8, but with the smaller diameter rod bolts in the 3.2 rods, I would be happy at 75. Bob

[cmcfaul]

How much additionally HP are you making with that set up? Single plug? I am told Porsche did not leave a lot on the table with the 3.2. Don't like the standard 6k redline.

Chris
89 Carrera

[911pcars]

At that operating range, I'd also opt for lighter and stronger connecting rods. At elevated engine speeds, loads are increased on every engine part - more so if operating for extended periods of time, as in racing. Decreasing reciprocating weight is good. Structural integrity in those conditions is quite important.

The rev limit recommended for those cams is for max power. Repeat less often and engine longevity increases.

Sherwood

[Jeff Alton]

We never go beyond 7400 with a stock 3.2/3.3 rod, even with the ARP fasteners. Could we? Maybe, but why risk it. Most of the motors we build we are creating a VERY wide power band and the need to rev beyond that is not needed. Now, different if we were building higher revving motors with more narrow power bands, but area under the curve.....

Cheers

[stownsen914]

Based on your other thread, if the hp peaked at 6850, I think you’d be getting everything out of the motor by shifting at 7300.

Of course some good aftermarket rods would be better than stock, but if your stock ones checked out and you’re using ARP rod bolts, I believe the conventional wisdom is that you’ll be ok revving in the mid 7’s.

[Walt Fricke]

Previous generation 911 stock rods were good easily to 8,000 RPM with the better bolts. I'd expect the 3.2 rods would be also - they are forged, are they not? Some super bolts are superer than others, too.

Optimum upshift RPM is based on the torque curve the engine actually makes, combined with your gearing. Once you have the motor on the dyno, easy to see where the rear wheel torque curve in the lower gear equals the same RW torque in the next higher gear. That's your optimum upshift point. Typical stock gear boxes have the gears fairly well spaced, so generally you can upshift at the same RPM if you are on the track and optimizing acceleration. Never in 1st there (any amateur organization do standing starts in the US?), as you always run out of 1st before some optimum point unless you have installed a tall 1st, and it isn't really worth it.

My 2.7 and 2.8 race motors with a slightly shorter and closer box have worked out at around 7,600 - 8,000 for upshifts. But you really need the torque curve - that's what is the decider. If you are really good at engine building (not just assembling, like guys like me), you can fairly accurately estimate the torque curve, and adjust your specs to get it to where optimum upshifts are at lower RPMs. At some loss in HP, but for street motors stock is basically beyond what anyone really needs to begin with.

[slow car]

Thanks for the feedback here are the dyno figures and ratios(46mm PMO 1.5/8 headers)
The motor is running plus 105 octane, Twin plug all in at 3000rpm 30 Degrees.

[slow car]

Re Gear Ratios, Theoretical gear map.
Rev Drops as follows, shifting at 7000
1st to 2nd = 4400 RPM
2nd to 3rd = 5000
3rd to 4th = 5500
4th to 5th = 5770

[stownsen914]

Originally Posted by slow car

The motor is running plus 105 octane, Twin plug all in at 3000rpm 30 Degrees.

I think I've heard that some builders prefer less timing on twin plug race motors, like 26 degrees total advance. Curious to hear the logic in going with 30.

[911pcars]

Actually, the particular engine build determines the maximum spark lead. If an engine detonates with 30º spark lead, then that's too much despite the builder's preference.

In general, engines with twin plugs require less spark lead due to shorter flame fronts. Tuners can graduate the spark lead at various engine speeds depending on operating conditions.

Sherwood

[Neil Harvey]

Originally Posted by 911pcars

Actually, the particular engine build determines the maximum spark lead. If an engine detonates with 30º spark lead, then that's too much despite the builder's preference.

In general, engines with twin plugs require less spark lead due to shorter flame fronts. Tuners can graduate the spark lead at various engine speeds depending on operating conditions.

Sherwood

A little off the original topic, but care needs to be taken with ignition with these air cooled engines.

The old saying goes, "that was good so more must be better" is the death of these engines.

Ignition lead should always be monitored by plug checks and if possible knock sensing.

With these air cooled engines, we always run at least 2° away from knock. With elevated head temps, they tend to knock easily. But how do you know where the knock limit is. You run the engine into knock.

Listening for knock is the best more effective way. But many do not have the devices to do this. A very good device and not an expensive device is the knocklink. It simply will tell you if the engine is knocking and you get your foot out of the throttle. It doesn't pull timing, its just warning light. I think we sell these for under $ 300.00 with a sensor.

Another way when tuning is to reverse the advance. If you feel you have reached the limit, remove 2° and see if the torque drops any. If it doesn't. then 2° advanced will make no difference to the torque but could push the engine into knock. You should always check the spark plug to see how the temperature looks and how the plug reads for good ignition advance too.

[Jeff Alton]

Further, too much advance can be hard on rod bearings as well. Not sure on your particular aircooled motor, but having the spark ignite too early while the piston is still on the rise can hammer the bearing... This may or may not happen before pre ignition depending on your motor specs....

Cheers

[winders]

Originally Posted by Neil Harvey

A very good device and not an expensive device is the knocklink. It simply will tell you if the engine is knocking and you get your foot out of the throttle. It doesn't pull timing, its just warning light. I think we sell these for under $ 300.00 with a sensor.

How do you determine what frequency(ies) to listen to for knock? And how does the device deal with other engine noises in that frequency range?

[Neil Harvey]

Originally Posted by winders

How do you determine what frequency(ies) to listen to for knock? And how does the device deal with other engine noises in that frequency range?

Simple answer to your question, its smarter than I am.

Actually, in any sort of EFI system, if you are using a listening device, you the tuner have to determine what is normal mechanical engine noise and what is assumed to be detonation. You make the assumption that any noise above a certain noise threshold is knock. Knock has a specific noise when it occurs as a well. It sounds like a crackling noise over the harsh sounds of the engine running. You can have noise cancelling head phones as well. They help.

You run the engine up to its read line, at somewhat retarded timing, known where it would not knock and establish the engines normal noise level. This becomes your threshold number you program and the system then triggers a warning and or retards the timing as you have programed.

The knock link has some smarts built in and you do the same when first setting it up. You run the engine to its redline and the little light assy measures the noise level. Then anything above this it sets off the warning light. It gives a running green when everything is ok, changes to a yellow light when it gets close to detonation and red when it hears knock.

Its a simple warning light not a tuning tool. Would you tune an engine with this, NO!. You should use something more sophisticated. Like I mentioned above. But if you wanted something to warn you of any changes, this is a great little tool.

[Neil Harvey]

Did not mean to get off the original topic. Apologize for doing this.

[cmcfaul]

How does one listen for knock?

Chris

[john@poolcovers]

We are very lucky in Australia to have very good fuel ( and expensive)
I have been running this motor on 98 with je 10.5:1 pistons twin plugged with 30 degrees advance in 100 degrees plus for 5 years.
Now going to 12.5:1 I am running on 105 fuel. Early days I will do some dyno runs and pull out some timing and report.
Jeff what fuel and advance are you running.?
Re race rods are any better than others??
.

[john@poolcovers]

We are very lucky in Australia to have 98 octane at the pump.
I have been running a twin plug 3.4 with 30 degrees total advance with je10.5 :1 pistons for 5 race seasons in temperatures above 100 f with no signs of detention.on 98.
Now I’m using JE 12.5:1 with 105 octane race fuel.
The next time on the dyno I will see what removing 2 to 4 degrees does to the outputs.
Jeff what fuel and spark curve are you running on your builds?

[safe]

I think my 964 engine runs 38 degrees at WOT... If I remember correctly.