10,000 rpm

[seafeye]

I know it's not a S2000. But what can be done to raise the RPM limit?
I have a 2.7L Twin Plug. Weber 40's. Is another 1000 RPM possible?

[Trackrash]

A thousand RPM more than what?

What cams are you running?

Your maximum safe RPM is determined by your valve springs, cams, weight of your valves, and the strength of your rods and crank. Now, other factors like your carbs, cam timing, port size and and exhaust will determine your maximum peak power PRM.

[Flieger]

you'll need a different crank- at least a 66mm stroker.

actually, 10,000 rpm might be past the torsional resonance for the 70.4 but you still need go through it.

[Tippy]

I'd love to hear a sound clip of 10k RPM. Dang...

[Steve@Rennsport]

9K is possible with a LOT of money, 10K, not so much.

[faapgar]

Hi,I have built a number of motors in the 9-9500 range.Built a 64 x 98mm that was sweet & ran to 9500 rpm years ago.Power & breathing has always been in the heads and induction.The right exhaust,the I.D and the distance to the collector is the key to make it happen.I am starting a new build of 66 x 98mm with a new hi-flo piston design that I will share with a post as it happens in the next few months.A hint to builders.I only use IRL Valve springs because they work.Infinite combos.A buddy of mine Mike Bavaro from Bodymotion ran his GT-3 car to 10,000 RPM in Club Racing and won a lot.Fred

[txhokie4life]

I think I surpassed 10K RPM.... Once -- wasn't very happy with me...

I'll settle for about 7500-7800 with my current build :-)

Mike

[chris_seven]

Originally Posted by Flieger

you'll need a different crank- at least a 66mm stroker.

actually, 10,000 rpm might be past the torsional resonance for the 70.4 but you still need go through it.

Max,

Where do you think the torsional resonances are on a 70.4mm motor?

If there is a critical resonance in the running range then without some form of damping I wouldn't think there is much chance of running through without the crank failing.

The old V10 F1 motors had a critical at around 1800rpm due to inertia and they used air starters that spun the motor to 2500rpm before the ignition switched on and then anti-stall etc that always kept the revs high.

There are also the high order gas torques to consider as these could eat into the cranks fatigue like.


Do you know if anyone has produced a Holzer Table for this crank?

It would be interesting to look at the mass-elastics and try to estimate what is happening.

The gas torque may be more difficult to add in without some costly software.

[tharbert]

Originally Posted by seafeye

I know it's not a S2000. But what can be done to raise the RPM limit?
I have a 2.7L Twin Plug. Weber 40's. Is another 1000 RPM possible?

The starter's mounted wrongly...

[seafeye]

I'm going for light weight. I may just forget the whole starter altogether. Park on a hill whenever I can.

[m42racer]

The later GT3 engines have a resonance around 2200 RPM. There is a damper available for this engine. I believe this same company has done research on the earlier cranks as well.

I find it hard to believe that known physics and gas laws are redefined in the Porsche world.

Short stroke engines results in a smaller cylinder volume with a given bore. This requires a head that flows really well and a wide lobe separation angle. One of the ways around the separation angle on new engines is the ever changing cam positions unavailable on these early 2V engines. The head design along with the plug positions limit the ignition timing and CR numbers possible. Even with race fuel, you have to have air before you can add fuel, whatever type.

With lightweight parts its possible that these engine could run at a higher RPM but I cannot understand how any would make any power up there? You need air to fuel, and these engines just cannot maintain sufficient air volume to carry any torque. All you do is increase the stress level on the parts for zero gain. There are limitations on valve size, port volumes etc that determine what is possible. Most of the typical parts found inside these 2V engines would limit the RPM talked about.

The weight of the valve train, even with Titanium Valves would require spring forces that would be double what they are typically. Valve spring rates would be a lot higher, with wire diameters and coils numbers limited to a retainer length limited by rocker geometry and coil bind distance. This limits valve lift which works against the engines pumping ability.

But some have found ways around this it appears.

[chris_seven]

Does the GT3 have a dual mass flywheel?

Does the damper work with the Dual Mass of is it only fitted when the flywheel is replaced by a single mass unit.

I would imagine that if an undamped crank was run at its resonant speed it would almost certainly break the crank.

70.4mm cranks are not generally fitted with dampers and their resonant speed must be above running speed or you have to pass through this speed fairly quickly.


How would you determine the gas torques?

Do you calculate from gas pressure estimates as this will change substantially with load.

We used to measure the speed variation within the combustion cycle on a single cylinder engine test rig and then estimate its effect on the whole engine by adding the influence of the extra cylinders into the model.

We used to carry out a significant amount of torsional analysis on a fairly wide range of engines when were manufacturing drive shafts and torque measuring systems for use in anechoic test cells.

[faapgar]

I love the technical talk.66mm is like Henry said the motor Porsche should have built.I have built more than 15 of 66 x 95mm.I ran one in my 914-6 more than 80,000 miles with no problems.When I started to exceed 9,000 I had to pin the 6 bolt flywheel as the check paint on the bolts was cracking.You have to make sure you lap the flywheel to the crank & use light oil for a lubricant & torque to 110 lbs like we did with the RSR 70.4 Crank.What every one misses is the exhaust is the black art that compliments the heads for flow.Every engine size needs a percentage of the total displacement in cc to the collector.Then & only then is the motor free.Otherwise you are like Rawknees with a cork in the wrongplace which is a hinderence to the motors lifestyle.Waiting for TI Rocker arms from Chris in the UK.I am your 1st customer for 2 sets.I am down to my last two sets of forged rockers.Thanks Fred

[bickyd]

I had to look up"anechoic".... thanks.

[Flieger]

Originally Posted by chris_seven

Max,

Where do you think the torsional resonances are on a 70.4mm motor?

If there is a critical resonance in the running range then without some form of damping I wouldn't think there is much chance of running through without the crank failing.

The old V10 F1 motors had a critical at around 1800rpm due to inertia and they used air starters that spun the motor to 2500rpm before the ignition switched on and then anti-stall etc that always kept the revs high.

There are also the high order gas torques to consider as these could eat into the cranks fatigue like.


Do you know if anyone has produced a Holzer Table for this crank?

It would be interesting to look at the mass-elastics and try to estimate what is happening.

The gas torque may be more difficult to add in without some costly software.

I believe it is around 8000-8500rpm, or at least that is where it starts. I'm talking about the resonance that caused RSR's to shed flywheels and which prompted Metzger to design the 917's engine with the central power take-off.

[m42racer]

Doing some "quick math" on those 98.00 x 66.00mm engines, at 10,000 RPM you will lose approx 41HP to friction, the piston speed would be over 4300 ft/min and you would need over 40 degrees of Ignition lead. This would be the best case engine, so any de tuning to get the engine to live would lower the output values.

Without knowing any of the actual engine spec's the HP is impossible to calculate.

However, knowing the air flow limitations of these early 2V heads, I would estimate peak power around 6500- 6800 RPM and by 10,000 RPM you would have lost about 100 HP.

[boosted79]

Max piston speed for 98 x 66 at 10k would be close to 6900 fpm. A quick calc of max piston acceleration gives about 45600 m/sec^2 or about 149600 ft/sec^2. That is getting close to what the Cosworth F1 CA did at 10k and they went to 20k. But, the Cosworth CA piston package weighed about 300g total (98mm bore). A JE will weigh about 425 g I think. The CA Ti rods came in about 290 g vs. a Carillo at 575 g. So you can see where this is heading..

[faapgar]

Well,I am just a country boy who builds these for fun so I have to wonder how my 2.8 made 374 H.P at 9300 & 249 ft.lbs of torque from 4400-9000 RPM.I just dug up some parts in the barn & voila a hayseed miracle happened.I just used TI Rods,valves & some old 3.6 heads & slide valves,Motec the tractor did not need anymore.I took the stainless 1.75 I.D tubing from the still to make the exhaust.Damn I miss that still.I have to dig around in the chicken coop as there are probably some better cams to spin my newest abomination to 10,000.That will wake the cows up.Fred

[boosted79]

Yes, Ti rods and valves, he doesn't say what he has now and how long he wants it to last or what it's use is. Hot street that may see 10k now and then or a track car that hits the limiter on every shift.

[m42racer]

To understand what you achieved, you made 374HP with a 66mm stroke 2.8L engine when most 993 3.8L RSR engines struggled to make 400 HP at 8000 RPM?

Is that "still", still is in operation and you're testing its product, maybe???