Decreasing Valve overlap

[john.p.clegg]

Dear All
In my search for better low end torque,at the expense of high end power would it be safe to decrease the overlap by 4 degrees...ie moving the MOPs from 110 to 112....

Thanks in advance

John

P.S. just removed the 420 cam from the inlet as this was not much good for street use and having a five speed box,wanted to move the power band lower down the rev range...

[rgh0]

If you had QED 420 cams and were unhappy with the torque. i would have spent some time on a dyno first to make sure it was setup right as the torque is not much different to a Sprint cam set up. If still unhappy with the torque then try replacing the exhaust cam with a Sprint cam and keep the QED 420 inlet.

Yes reducing the valve overlap like you propose will increase torque at the expense of top end power

cheers
Rohan

[john.p.clegg]

Thanks Rohan,that is what I did have,QED 420 inlet cam and sprint 360 exhaust cam,am going for both sprint cams but would like a little more low end grunt,just worried if reducing the overlap might cause the valves to clash...

Thanks
John

[ecamiel]

Those cams should give more than adequate torque. The problem is elsewhere as Rohan suggests. Get a proper dyne tune. I have .440 cams at 102 timing with new Webber 45's, tall close ratio first gear and find the car totally street drivable. Maybe you have early carbs?
The Twink is very sensitive to back pressure. Strangely, I found the large diameter racing headers helped low and mid range torque. Increase the the diameter of the exhaust system all the way back.

Eric
64 S1/2

[rgh0]

Hi John
Reducing the overlap increases the space between the valves on overlap. If you increase the overlap as you typically do with high lift long duration race cams this is where valve head to head clearance on overlap can get very very close!

cheers
Rohan

[john.p.clegg]

Thanks All

Eric, " Maybe you have early carbs?"...they were ditched for EFI approx 2009..
"The Twink is very sensitive to back pressure"...straight through slightly big bore...

Rohan Thanks for that,haven't got my head round the overlap period yet...

John