Discussion
Yet another posting......
I have always suspected an air leak on my 4.3 after the rolling road session at Mech Repairs when Mark Adams though there might be one. However we ran out of time and the car made quite good power anyway albeit with a large fuel coefficient on the Tornado chip.
I have recently adjusted the base idle and the screw was almost closed to achieve the 500rpm. Not the usual 2 turns. I appreciate all engines are different but it is hardly open.
The car runs well and ticks over fine but I was wondereing about the servo hose and vent cansiter hose etc might have a small leak. So today I squeezed the pipes closed with a large pair of pliers. When I closed the small bore pipe that joins the large crankcase breather pipe from the manifold the engine almost died. It is connected to the large pipe via a T-piece.
How "closed" is the crankcase breather circuit and should this be affecting the amount of air entering the manifold at all?
Basically does anyone know if this is normal?
Many thanks in advance and happy New Year to you all.
Cheers
Ed
I have always suspected an air leak on my 4.3 after the rolling road session at Mech Repairs when Mark Adams though there might be one. However we ran out of time and the car made quite good power anyway albeit with a large fuel coefficient on the Tornado chip.
I have recently adjusted the base idle and the screw was almost closed to achieve the 500rpm. Not the usual 2 turns. I appreciate all engines are different but it is hardly open.
The car runs well and ticks over fine but I was wondereing about the servo hose and vent cansiter hose etc might have a small leak. So today I squeezed the pipes closed with a large pair of pliers. When I closed the small bore pipe that joins the large crankcase breather pipe from the manifold the engine almost died. It is connected to the large pipe via a T-piece.
How "closed" is the crankcase breather circuit and should this be affecting the amount of air entering the manifold at all?
Basically does anyone know if this is normal?
Many thanks in advance and happy New Year to you all.
Cheers
Ed
Does sound like you have a slight air leak on the induction side.
This will make no difference at all to the peak power figures, since there's no manifold depression at full throttle. Depending on the severity, the unmetered air from the leak might make it a harder to achieve a steady tickover and crisp throttle response. But you haven't mentioned this as a problem so I assume its OK.
When you adjusted the base idle using the set screw, are you sure you had the pipe to the stepper motor completely blocked off? If this was still letting air past it would raise the idle speed and give you a false base idle.
The breather pipe you're referring to should have quite a small restrictor to limit the amount of air sucked out of the crank case. If you have clear access for air into the rocker covers (filler cap off, or more flow than normal able to get past the ventilator on the NS rocler cover, and the small breather is unrestricted, you could get more air out of the breather than normal at idle. Normally the amount of flow is very small at idle.
This will make no difference at all to the peak power figures, since there's no manifold depression at full throttle. Depending on the severity, the unmetered air from the leak might make it a harder to achieve a steady tickover and crisp throttle response. But you haven't mentioned this as a problem so I assume its OK.
When you adjusted the base idle using the set screw, are you sure you had the pipe to the stepper motor completely blocked off? If this was still letting air past it would raise the idle speed and give you a false base idle.
The breather pipe you're referring to should have quite a small restrictor to limit the amount of air sucked out of the crank case. If you have clear access for air into the rocker covers (filler cap off, or more flow than normal able to get past the ventilator on the NS rocler cover, and the small breather is unrestricted, you could get more air out of the breather than normal at idle. Normally the amount of flow is very small at idle.
Peter
Thanks for the reply. I have only just got around to reading it.
Where is the restrictor and is it possible it is missing?
I did have the bypass hose clamped shut when setting the base idle and the idle is a litte lumpy. Mark Adams put this down to a possible non-standard cam due to a TVR Power engine rebuild documented in the service history (but it makes no mention of the cam used).
Would you expect the engine to die when the small breather hose is clamped shut? it seems a little unusual to me.
I take your point about peak power
oh well.
Cheers
Ed
Thanks for the reply. I have only just got around to reading it.
Where is the restrictor and is it possible it is missing?
I did have the bypass hose clamped shut when setting the base idle and the idle is a litte lumpy. Mark Adams put this down to a possible non-standard cam due to a TVR Power engine rebuild documented in the service history (but it makes no mention of the cam used).
Would you expect the engine to die when the small breather hose is clamped shut? it seems a little unusual to me.
I take your point about peak power
oh well.
Cheers
Ed
Can't say I've ever tried it but this breather is effectively bypassing the throttle just as the normal idle adjuster does. So it seems reasonable that it would affect the idle. Might be interesting to see whether you get a similar effect when you block the bigger breather upstream of the throttle?
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