RV8 - Cam shaft dialling in.
Posted: Fri Feb 09, 2018 4:12 am
I have recently built a RV8 Thor 4.6 and it is at the stage of having its final configuration completed - the engine is replacing a 3.5 carby engine.
To run in the cam I put the 3.5 carb manifold on the 4.6 and ran the engine which seems to have run fine and I covered about 10km before removing the carb manifold and putting the Thor manifold on - as yet the engine has not run in this configuration. When I ran it before ignition was provided by EDIS 8 running on default mode (10 BTDC) and the engine seemed to run OK even under load.
When I rebuilt the engine I wanted a bit more torque at highway cruising speed as around 100kph, because of the low gearing of the LR FC101, the engine is starting to come off its torque curve and lacks a bit of pulling power at higher speeds. I put in a locally made cam that is supposed to improve torque a bit higher up the rev range which is what I wanted - (no need to discuss this decision in this thread).
Here are the specs of the new cam. I was happy with all that until I read this comment on my local LR forum about the cam I had put in.
"When I did my 4.6 conversion of my D2 I fitted the Crow 371771 but was really unhappy with it. It made the car very sluggish and a 0-100 time of 19 sec . I rang Crow about it to ask if the cam had any advance or retard ground into it, and no. I mapped the cam out on a degree wheel to check proper timing and it was fine. One thing Crow said to me was "they work well in a 4.2 Commodore" so I'm thinking that the Crow cam is more a generic grind than Rover specific.
I was so unhappy with it I pulled it out and fitted a new stock 4.6 cam. Wow what a difference, back to what it should be 0-100 in 11 sec."
I also contacted the manufacturer and he said they had no issues but emphasised the need to dial in the cam. I said all well and good but with a standard engine, new single cam chain, new sprockets, new lifters etc - ad all lined up with the dots on the sprockets with nothing to adjust - what would dialling in the cam tell me other than they manufactured the cam wrong.
So as I cannot adjust anything - is there any point in pulling stuff (like the manifold and tin gasket) to dial in the cam (check its manufacturing) as the guy on the other forum did and found it all correct but not running right. I am tempted to pull this cam out and put a standard one in but then when I had the vehicle running before it did seem to run OK but I did limit revs to 2500rpm because of the fixed timing.
The reality is that going from a carb 3.5 with about 85kw to an injected 4.6 with 160kw I am not really going to know if the cam is causing issues - even if the engine is going to be down on power, it will still go better than it did.
Thoughts - comments appreciated.
Thanks
Garry
To run in the cam I put the 3.5 carb manifold on the 4.6 and ran the engine which seems to have run fine and I covered about 10km before removing the carb manifold and putting the Thor manifold on - as yet the engine has not run in this configuration. When I ran it before ignition was provided by EDIS 8 running on default mode (10 BTDC) and the engine seemed to run OK even under load.
When I rebuilt the engine I wanted a bit more torque at highway cruising speed as around 100kph, because of the low gearing of the LR FC101, the engine is starting to come off its torque curve and lacks a bit of pulling power at higher speeds. I put in a locally made cam that is supposed to improve torque a bit higher up the rev range which is what I wanted - (no need to discuss this decision in this thread).
Here are the specs of the new cam. I was happy with all that until I read this comment on my local LR forum about the cam I had put in.
"When I did my 4.6 conversion of my D2 I fitted the Crow 371771 but was really unhappy with it. It made the car very sluggish and a 0-100 time of 19 sec . I rang Crow about it to ask if the cam had any advance or retard ground into it, and no. I mapped the cam out on a degree wheel to check proper timing and it was fine. One thing Crow said to me was "they work well in a 4.2 Commodore" so I'm thinking that the Crow cam is more a generic grind than Rover specific.
I was so unhappy with it I pulled it out and fitted a new stock 4.6 cam. Wow what a difference, back to what it should be 0-100 in 11 sec."
I also contacted the manufacturer and he said they had no issues but emphasised the need to dial in the cam. I said all well and good but with a standard engine, new single cam chain, new sprockets, new lifters etc - ad all lined up with the dots on the sprockets with nothing to adjust - what would dialling in the cam tell me other than they manufactured the cam wrong.
So as I cannot adjust anything - is there any point in pulling stuff (like the manifold and tin gasket) to dial in the cam (check its manufacturing) as the guy on the other forum did and found it all correct but not running right. I am tempted to pull this cam out and put a standard one in but then when I had the vehicle running before it did seem to run OK but I did limit revs to 2500rpm because of the fixed timing.
The reality is that going from a carb 3.5 with about 85kw to an injected 4.6 with 160kw I am not really going to know if the cam is causing issues - even if the engine is going to be down on power, it will still go better than it did.
Thoughts - comments appreciated.
Thanks
Garry