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Increase redline?

Hello, I just got my 964 C2 back on the road after a big engine rebuild (with a strong assist from this forum in working out an oil pressure issue). Given the parts used in the rebuild, Iím contemplating raising the redline. Anybody have any experience/insight on this? I think stock is 6700, and Iím thinking 7300? A couple caveats; this is a street car that Iíd like to keep reliable, and Iím currently running a varioram intake which I know isnít ideal for high revs. Here are the relevant specs on the engine:
- 102mm bore, Mahle cylinders
- 80.4mm stroke, billet crank from a vendor who shall remain nameless
- Custom Mahle pistons, 11.15 CR
- Web cams with a grind from Steve Weiner
- Carrillo rods, 130mm
- ARP rod bolts & head studs
- Turbo squirters in case
- Heads reworked by Extreme with good springs & retainers
- Billy Boat exhaust
- 993 injectors, fuel rails, harnesses
- Gt3 oil pump

Thanks,
Sam


Old 03-12-2019, 06:11 AM
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Need more info on the cam grind being used. Looks great!
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Old 03-12-2019, 06:39 AM
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I would ask Extreme and Steve what they recommend for your valve/spring/cam setup.
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Old 03-12-2019, 01:03 PM
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Here is another take - put your car on a chassis dyno, and get a torque curve up to, say, 7,500. The engine is mechanically strong enough (rods, rod bolts, oil supply)for this. In older engines, with smaller valves, the stock valve springs can take 8,000 rpm for a while, and 7,500 just fine.

Then use the ratios of your gears to determine the optimum upshift points. You are, in essence, creating a graph of thrust in each gear - the torque curve is the same, and is RPM dependent, for each gear. Thrust is the vertical axis, speed the horizontal axis. Speed depends on tires and R&P, but those are constants, so you can include those or not - the shift RPMs will be the same. The thrust gets lower as you go up through the gears an the car goes faster, an the thrust curves get much flatter..
You will see that, at least for maybe 1st to 2d, that there will be an RPM for each upshift where the thrust in the lower gear is the same as the thrust in the higher gear. That's where you want to upshift. It has nothing to do with the mechanical redline. These upshift points may vary a bit depending on the gearing split, though Porsche's gears tend to be pretty good about this.

You want to use your own engine' measured numbers for this. Luckily, using a chassis dyno is just fine here, as it is the torque delivered to the rear wheels which counts, and you don't have to wonder what the flywheel figures are.

Sounds like this is a street car? On those, there is never a good reason to upshift above the right RPM for the gear, as you reduce your overall acceleration by shifting too early or too late. On the track, running over the optimum upshift point sometimes is useful if you can stretch it and avoid an extra upshift shortly before a brake point. But this isn't the deal on the street.

My stock motor/transmission SC race car has shift points from 6250-6,000. Other SC motors pencil out at slightly different shift points. Nominal factory redline for these motors is 6,700-7,000 depending on year.

If you look, you should be able to find an Excel spread sheet you can use to calculate all this once you have your torque curve. Start at 3,500 rpm, and use the torque there and at 500 rpm intervals up to where you shut off the engine on the dyno. That level of granularity is quite adequate to interpolate where these crossings are. Or you can do it by hand on graph paper - there was an article long ago in Up-Fixin showing how Porsche race engineers did just that.
Old 03-12-2019, 01:43 PM
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Thanks to all for the replies.

Walt - am I understanding your suggestion correctly; do some chassis dyno runs, determine the optimum shift points, then see if a higher redline would even be beneficial given these shift points? I like the point you made about race cars having a need to string out rpms in order to avoid extra gear changes, but this being mostly irrelevant in street cars (which mine is).

Another thought, should I expect any problems with vibrations/harmonics at high revs as Iím now running a pulley without a damper? For what itís worth, I think this billet crank is supposed to have better intrinsic balance than the stock 964 crank.

Also as suggested, Iíve included cam specs below.

-Sam
Old 03-13-2019, 05:47 AM
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nice cam! I would say 7000-7300 is safe, but I'd get it on a dyno and see what's what to be certain.
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Old 03-13-2019, 06:27 AM
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I would like to learn more about your crank. 80mm billet? Nice.

Again, what does your camgrinder recommend for your cam/spring set up as max RPM? Seems to me that would be the limiting factor.
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Old 03-13-2019, 10:09 AM
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[QUOTE=Moriartyhlms;10387252]Hello, I just got my 964 C2 back on the road after a big engine rebuild (with a strong assist from this forum in working out an oil pressure issue). Given the parts used in the rebuild, Iím contemplating raising the redline. Anybody have any experience/insight on this? I think stock is 6700, and Iím thinking 7300? A couple caveats; this is a street car that Iíd like to keep reliable, and Iím currently running a varioram intake which I know isnít ideal for high revs. Here are the relevant specs on the engine:
- 102mm bore, Mahle cylinders
- 80.4mm stroke, billet crank from a vendor who shall remain nameless
- Custom Mahle pistons, 11.15 CR
- Web cams with a grind from Steve Weiner
- Carrillo rods, 130mm
- ARP rod bolts & head studs
- Turbo squirters in case
- Heads reworked by Extreme with good springs & retainers
- Billy Boat exhaust
- 993 injectors, fuel rails, harnesses
- Gt3 oil pump

Thanks,
Sam


Why???

Someone had to ask!
Old 03-13-2019, 11:16 AM
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Neil - for some, these are our babies, and we want to do good things for them. Me, I thought I'd died and gone to heaven when I got my 2.7 back when, transitioning from VW bugs and busses - accelerate so fast up hill that you have to brake for corners? Heat going down hill? My 07 Turbo has a lot of basically wasted HP (though I love it). So, other than for reliability - which is pretty good at street driving levels - hard to see why one would need all this stuff unless for the track or autox.

I guess that is why it is called discretionary income? Driving around in twisty circles as fast as possible is kind of a crazy way to spend time, but it sure is addictive.

Sam - you don't hear about the 9 bolt cranks shedding flywheels. If this were a stock Porsche crank, I'd say not to worry - especially since you aren't going to see high RPMs often anyway on the street - only so many freeways to enter, stoplights where you are first in line to leave, etc. I'd ask the maker of the crankshaft what they know about its harmonics and their affect on flywheel fasteners, or a need for a harmonic balancer.
Old 03-13-2019, 12:41 PM
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[QUOTE=Neil Harvey;10389268]
Quote:
Originally Posted by Moriartyhlms View Post
Hello, I just got my 964 C2 back on the road after a big engine rebuild (with a strong assist from this forum in working out an oil pressure issue). Given the parts used in the rebuild, Iím contemplating raising the redline. Anybody have any experience/insight on this? I think stock is 6700, and Iím thinking 7300? A couple caveats; this is a street car that Iíd like to keep reliable, and Iím currently running a varioram intake which I know isnít ideal for high revs. Here are the relevant specs on the engine:
- 102mm bore, Mahle cylinders
- 80.4mm stroke, billet crank from a vendor who shall remain nameless
- Custom Mahle pistons, 11.15 CR
- Web cams with a grind from Steve Weiner
- Carrillo rods, 130mm
- ARP rod bolts & head studs
- Turbo squirters in case
- Heads reworked by Extreme with good springs & retainers
- Billy Boat exhaust
- 993 injectors, fuel rails, harnesses
- Gt3 oil pump

Thanks,
Sam


Why???

Someone had to ask!
Rhetorical question? There is a lot of demand for Singers. Do we ask why?
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Old 03-13-2019, 01:04 PM
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Quote:
Originally Posted by Walt Fricke View Post
Neil - for some, these are our babies, and we want to do good things for them. Me, I thought I'd died and gone to heaven when I got my 2.7 back when, transitioning from VW bugs and busses - accelerate so fast up hill that you have to brake for corners? Heat going down hill? My 07 Turbo has a lot of basically wasted HP (though I love it). So, other than for reliability - which is pretty good at street driving levels - hard to see why one would need all this stuff unless for the track or autox.

I guess that is why it is called discretionary income? Driving around in twisty circles as fast as possible is kind of a crazy way to spend time, but it sure is addictive.

Sam - you don't hear about the 9 bolt cranks shedding flywheels. If this were a stock Porsche crank, I'd say not to worry - especially since you aren't going to see high RPMs often anyway on the street - only so many freeways to enter, stoplights where you are first in line to leave, etc. I'd ask the maker of the crankshaft what they know about its harmonics and their affect on flywheel fasteners, or a need for a harmonic balancer.
We look after customer engines as if they were our babies too.

But the question should be asked, "why do I want a higher red line"? There has to be a valid mechanical reason to do this. More top speed, love to hear the engine scream, tall gearing etc.

If you have a valid mechanical reason, then you would look at the parts of the engine that will allow or inhibit a higher RPM limit. Complete intake flow numbers, camshaft spec, exhaust restriction etc.

Easiest way would be to find where the torque starts to fall off when remapping the engine. Then as you increase the engine speed, see where the HP hits its peak number. I suspect with this setup it to allow the engine to run above 7000 RPM but the peak HP to be below 7000. Still should be a great street engine.

I expect this engine will need mapping/remapping if its using the stock/aftermarket EFI.

I can guarantee you will need a damper for this engine.

Two major failures will occur. The scavenge gears will break across the keyway groove and the cam timing will go all to hell. We designed along with ATI several years ago, dampers for these longer stroke engines.

The damaging harmonics do not necessarily happen at the higher RPM's. The 4.0L water cooled engines have their highest harmonic below 5000 at normal driving speeds. All depends upon the crankshaft design, how much it twists, the masses rotating etc.

Dampers will help even the stock engines keep their cam timing in check.
Old 03-13-2019, 02:41 PM
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Again, many thanks to everybody for responding.

Quote:
Originally Posted by Neil Harvey View Post
Why???

Someone had to ask!
Iíd say that if it makes sense to raise the redline, my intent would be to achieve some untapped performance. That said, if itís damaging to the engine or if power has already peaked by the stock 6700 redline, then itís a bad idea for a street car. Mainly, Iím just curious if anyone on the forumís had experience with raising redlines.

Today I got some very helpful feedback from Steve Weiner who provided my cams: ďthose cams are over the power curve peak by 6800 RPM so there is no point on going past that.Ē

So, in my case, it sounds like the smart move is to keep it at the stock redline. That said, it will be very interesting to see what the actual power curve looks like during dyno tuning.

As a point of reference; it doesnít look like either the Singer or Guntherwerks engines run dampers, and they redline at 7300 and 7800 respectively (somebody let me know if I got that wrong). Iíd be very interested to learn what sort of tricks those engines are working with...aside from the obvious wealth of experience at Ed Pink and Rothsport.

Quote:
Originally Posted by Neil Harvey View Post
I can guarantee you will need a damper for this engine.

Two major failures will occur. The scavenge gears will break across the keyway groove and the cam timing will go all to hell. We designed along with ATI several years ago, dampers for these longer stroke engines.

The damaging harmonics do not necessarily happen at the higher RPM's. The 4.0L water cooled engines have their highest harmonic below 5000 at normal driving speeds. All depends upon the crankshaft design, how much it twists, the masses rotating etc.

Dampers will help even the stock engines keep their cam timing in check.
Neil - Youíve got me scared about not having a damper now. I went with Rothsportís non-damper pulley over their damper one because I want air conditioning. Are you talking about the scavenge gears in the oil pump being at risk? Is it all a function of the specific design/harmonic response of the crankshaft?

Quote:
Originally Posted by Trackrash View Post
I would like to learn more about your crank. 80mm billet?
Yeah, the crank is a billet piece I had sized for 997 cup rods. It has a stroke of 80.4mm and a gt3-format snout. I had some major issues with the vendor, so I wonít endorse them here (although you may recognize them from the picture below). It does seem like a nice piece though. If anybody needs specifics on my ďcrank experience,Ē send me a PM.
Old 03-13-2019, 11:25 PM
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Ask Steve Weiner as he gave you the cam specs.

The cams have some of, or the most impact on RPM capability of an engine.
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Old 03-14-2019, 05:10 AM
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That motor should be a beast. Can't wait to see dyno numbers.

As a data point. My recently built 3,0 L is rated to run safely to 7500 according to Camgrinder here. However my power drops off after 6500 due to my "Conservative" cam so on the track (DEs), that is usually where I shift. During an auto cross I will occasionally hit my limiter, which is around 7300. It pulls well from 3500 to 6500 which is what I wanted.
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Last edited by Trackrash; 03-14-2019 at 06:56 PM..
Old 03-14-2019, 07:11 AM
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[QUOTE=Moriartyhlms;10390082]Again, many thanks to everybody for responding.

Neil - Youíve got me scared about not having a damper now. I went with Rothsportís non-damper pulley over their damper one because I want air conditioning. Are you talking about the scavenge gears in the oil pump being at risk? Is it all a function of the specific design/harmonic response of the crankshaft?


Did not mean to scare you. Just warn of what typically can happen.

Should also make it clear to all, we sell dampers for these engines. Was not trying to sell you anything either. Was not the intention or motive here.

All engines suffer from harmonics, as all engines create torque pulses. These pulses twist the crank back and forth at very high frequency. The more mass in the crankshaft at certain places does help. The fact you have 53.00mm journals helps too. This gives more overlap between the rod and main pins. The steel the crank is made from, design, its strength etc all play a huge role here. There are different levels of pulses too.

Can you feel these when driving. Usually not as the frequencies are too high. If the pump gears break, what normally happens, oil starts pouring out past the rear main seal if a reverse seal is installed, or the case fills up with oil and the oil tank runs empty signally an oil pressure issue.

The gears in these pumps are sintered and very brittle. The scavenge gears bang into one another all the time as they suck air and oil. Why Porsche designed a gear with the key way groove at the gear root baffles me.


The later 80.00mm long stroke engines suffer from these harmonics. Pump gears breaking and in the 997 engines the cam actuator gear assemblies rattle loose. Its all from the noise that emanates up from the crankshaft, through the chains into the cam assembly. There goes the cam timing. Air cooled engines suffer the same cam timing fate.


I cannot tell you where your engine will produce the highest level of noise. Each engine built with different parts and with different levels of compression forces will act differently. Just be smart and aware of these dangers.
Old 03-14-2019, 09:14 AM
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