RPM limit?

[Prophead]

Wanting to mark a red line / gear change limit on my new tach before I take the car to the track for the first time (by track I mean circuit not drag strip). Done a bit of web searching but cant find a consistent answer so I thought I would sanity check with you guys.

What I know about the engine:-
1. SD1 block (at least thats the closest match for the block number) but is also stamped CR 9.75:1
2. Its supposed to have come from a TVR 350 (Wedge)
3. It is running Edelbrock 1404 CFM 500 carb, with Edlebrock performance intake manifold
4. It has a very large and loud exhaust

What I was told, but have no proof of:-
1. It has performance cam (dont know which one)
2. Its had head work done (but what exactly I dont know)

As for pistons, crank, rods ect ect I have no idea, but am making the assumption that they are 'standard'.

The engine revs very easily to 5,000rpm and there is a deffinite step up in performance above 3,000rpm and not so happy pottering around in the low 2,000s (it will just a little stuttery).

I have provisionally marked the Tach at 5,500rpm but as yet haven't take it over 5,000rpm.

[Ian Anderson]

6700

I was advised that the Rover Hotwire system had a cut off at that point to save the engine.

But in order to get there you have to have everything right so valve train does not pump up, hopefully balanced or it will damage itself etc.

Now if you have it in a light car you will find it more fun to drive on torque and probably live in the 3000 to 5000 range which will pull like a train and keep it away from the damage end of the Rev range.

Safety at 5500 would seem fair.


Ian

[sidecar]

The first 'mechanical' thing the limit the RPM one these engines is the valve train. Obviously the heads have to flow enough and the cam has to be right or the engine just won't rev even if you want it to. I'd say that the standard valve train would just about go to 6k if you are lucky but if the valve springs are weak the valves might start to bounce at 5500 RPM, what happens then is that the followers start to pump up which hold the valves off their seats, this causes the engine to misfire and crackle in the inlet manifold. This was Rovers way of telling you to change up a gear.

My old 3.5 had stage III heads and it would rev to 6500, I only take my 4.6 to 6000, it uses the same heads as my 3.5, the heads don't flow enough to allow the larger engine to rev any higher which is fine by me anyway as the bottom end is more or less standard.

[DaveEFI]

Standard tappets will pump up and stop the engine exceeding a safe maximum.

It sounds like you have a Vitesse unit by the CR. So peak BHP is at 5280 rpm and max revs nominally 5500, although a different cam may change these.

[Prophead]

Thanks all. From these replies seems like 5,500 is a good red line to use and target gear changes 5000 to 5250.

I am hoping to get the car dyno'd in the near future, will hopefully shed some light on the truths of the 'performance' upgrades.

[mgbv8]

Thanks all. From these replies seems like 5,500 is a good red line to use and target gear changes 5000 to 5250.

I am hoping to get the car dyno'd in the near future, will hopefully shed some light on the truths of the 'performance' upgrades.

You would be better off getting the car on the rollers sooner so you can get accurate data to see where you need to shift gear for best effect rather than just guessing at a redline figure?

[Prophead]

I'm going to a 2hr track session Thursday evening and won't be able dyno'd before that. Wanted to mark something sensible beforehand.

[SimpleSimon]

6700

I was advised that the Rover Hotwire system had a cut off at that point to save the engine.

But in order to get there you have to have everything right so valve train does not pump up, hopefully balanced or it will damage itself etc.

Now if you have it in a light car you will find it more fun to drive on torque and probably live in the 3000 to 5000 range which will pull like a train and keep it away from the damage end of the Rev range.

Safety at 5500 would seem fair.


Ian

Ian think you will find the Lucas Hotwire EFI cuts off before that more like 6200 on the RV8 and that was raised to this level by TVR stock LR I think is lower still TVR owners have often bragged of pulling to over these RPM's no problem with factory spec engines but then the TVR instruments are seldom accurate inc the tach

[Ian Anderson]

I have a standard Hotwire ecu and it will go to 6720.

Number from tachometer at two different dyno operators

But then again my engine is far from standard!

I still change up about 5500 and love the kick in the back with the torque.


Ian

[SimpleSimon]

I have a standard Hotwire ecu and it will go to 6720.

Number from tachometer at two different dyno operators

But then again my engine is far from standard!

I still change up about 5500 and love the kick in the back with the torque.


Ian

Then you may have a chipped ECU Ian i.e Tornado chip etc because that's certainly not the norm IMO nice

[Prophead]

Mission successful! Had a good 2hr track session at Knockhill, car didnt miss a beat for the drive there, 25 or so laps and the drive home. Shifting at about 5000rpm actually felt about right, there was still some more there but the pull from the torque in the next gear worked out very nice.

Was a very good shake down session, learnt a lot about the car and what needs to be tweaked next. That said the car works very well as an overall package. The balance is very neutral, excellent traction out of the corners coupled with the smooth delivery of power was very pleasing, not to mention the noise on WOT and in the down shift (very grin inducing).

Now I just have to get through the MOT next week, might have just enough tread left on the tires