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John McCormack

Rev Limit

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I apply a self imposed rev limit of about 4,500 on my stock 1970 PI. It is a 50 year old engine and in today's traffic I get plenty of performance at that limit.

I just went out for a run and took her to just over 4,500 in 2nd and then changed up. It felt like it would have liked to go harder but I don't want to stress it.

What do other owners rev their engines too?

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Generally keep below 5 although  I know it will go over. But then with the supercharger  the fun is from the low down grunt and Not the top end. 

Tim

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I generally limit myself to 5.5k as per the factory rev counter, but if you keep your foot in, it will pass 6k. Has a 6-2-1 exhaust manifold and Phoenix straight through system and it sounds great when working hard. However that is on an engine that had all the rotating internals balanced as part of the rebuild process. My 2500 saloon feels much less smooth when you get to 5.5k, put it that way.

Matt

Edited by matt george

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It's a convention of engine design that the mean piston speed should not exceed 20 meters/sec unless exotic materials or special preparations are used.   This value is a surrogate for the piston acceleration, which is a much more complex calculation.

The mean piston speed of the two engines at 6000rpm may be calculated, EG: At 6000rpm, the piston travels from top to bottom of the bore in half a revolution:

Duration of stroke = 60/6000 x 2seconds = 0.005 seconds

For the 2L engine, mean speed of piston = stroke disance/stroke duration (in seconds) = 76/0.005  =15200mm/s =15.2m/s


2L, 76mm stroke
RPM        Mean speed in meters/sec
6000        15.2
7000        17.7
7500       19.0

2.5L, 95mm stroke 
6000        19.0
6500        20.84
Thus it becoms obvious why the 2.5L engine becomes unreliable at a speed at least 1000rpm lower than the 2L.

John

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I rarely take my TR6 past 5,000rpm. If I go past 5k it's only very briefly and the rev limited on my electronic ignition is set at 5.5k.

In reality a well set up PI engine delivers so much torque from below 2,000rpm, there's no need to take it to the limit on the road.

Nigel

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My 4,500 limit is conservative then. That is good but I might nudge it a bit higher on occasion.

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These engines are very robust. Currently I have a Rev Limiter at 6.100. 280 cam and C.R around 9.6. Engine #2 will go upto 7.000.

However, this all depends on driving behavior and engine config. I prefer Rev, others keep it low.....so what. 

Jochem

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On 9/12/2019 at 7:39 AM, Tim D. said:

Generally keep below 5 although  I know it will go over. But then with the supercharger  the fun is from the low down grunt and Not the top end. 

Tim

Yes, and no need to wait for the rpm to cllimb...drive the torque. I get 6 psi boost at 2800 rpm and approx 100 bhp at the flywheel, so hardly ever exceed 4000 rpm ( and ca 8psi). Peter

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