1725 Camshaft Question

[Tim R]

I took the car out for it's first proper run since fitting a brand new 1592cc camshaft and followers today. Everything else such as valves, rings etc is unchanged I did everything from the bottom of the engine and didn't disturb the top. Compression is up across the board. All cylinders hit 100-110 on first 'pump' and 155-165 after four rotations. I am more than happy with that, this is a massive improvement.

The car started immediately and drove smoothly and powerfully. At motorway speeds the revs were massively down. Previously the car was screaming at over 5,000 rpm with just over 60 showing on the speedo. Today we had 80 showing on the speedo which is probably about 70 -71mph on this car and it was showing 4,000 rpm. Much better all round.

It took an awful lot of finding but if you ever experience unexplained low compression and the valves and rings are fine, don't discount the camshaft as a possible cause.

Tim R

 

[todd reid]

Tim,
Glad your car is running better. I don't understand how your speed to rpm relationship could change if all that changed was the cam.

 

[alpine_64]

Tim,
Glad your car is running better. I don't understand how your speed to rpm relationship could change if all that changed was the cam.

Agreed, the acceleration could improve... The car may feel less strained ... But the rpm to MPH is purely related to the gearing .. so unless the gear ratios, tyre and wheel diameter or rear end ratio changed there should be NO change in rpm vs speed

 

[spmdr]

Re, gearing/RPM/speed...

One little fact was missed/forgotten...

Tim's Alpine has an AUTO trans...

DW

 

[todd reid]

so your theory is he didn't have enough power to get out of 2nd gear?

 

[Bill Blue]

Maybe a matter of torque convertor stall. TC's are strange beasts with mysterious response to load/input changes.
Bill

 

[Tim R]

The car is engaging all three gears in the auto box correctly and has been throughout. I don't claim to know HOW the revs to mph are different but they certainly are. The only thing that has changed is the camshaft but the engine is turning less revs to deliver a higher speed, it is like a different car now. We have had this car for over 20 years, it ran well until the problematic camshaft was fitted during a full engine rebuild about 8 years ago. Now that that camshaft is out and changed back to a standard one the car is running well once more.
Tim R