Mixing camshafts.....

[Matt Elan]

I should be getting my (stromberg) head back from having some helicoils, plus new valve guides and recut valve seats soon, and will be building it up over the Christmas holiday - its a standard (i.e. not Sprint) one. I've got an assortments of cams, 3 SE (one ring) and one Sprint (two ring). When I bought my current head it had the SE on the inlet side and the Sprint on the exhaust side which seemed a bit counter intuative. Now when I build the head I'm tempted to put the Sprint cam on the inlet side and one ofthe SE's on the exhaust on the premise that you want help to get the best charge sucked in, but it is not so critical getting the gasses out as they'll be pushed out anyway. So is this a correct assumption and has anyone tried any combinations of cams, and if so what was the result?

[RogerFrench]

you want help to get the best charge sucked in, but it is not so critical getting the gasses out as they'll be pushed out anyway

I have no experience of mixed camshafts, but I thought you might like to know that the above is very close to a quotation, albeit in English, from Ettorre Bugatti.

You are not alone...

[Harvey]

Matt,

In my opinion, after speaking with some people who know more about engines, particularly the Lotus twin cam, than I do, your belief is correct. I have been successfully running a sprint cam on the inlet side and an SE on the exhaust side for the last 8,000 miles since my engine was rebuilt. In fact, I am getting ready to build a stroker motor and, with a Stromberg head, I am going to try a Dave Bean 114 cam on the inlet side for more lift (.413) and move the sprint cam to the exhaust side.

Lee

[rgh0]

Non symetrical cams are a common modification for race setups. The higher lift and / or longer duration cam going on the inlet side always. Putting the sprint cam on the inlet and SE cam on the exhaust should give an outcome in terms of top end power very close to the same as you would get with 2 sprint cams and you may even get a better torque curve than you would with 2 sprint cams as the twin cam especially in stromberg form has to much exhaust flow compared with inlet flow capability which tends to put a hole in the torque curve.

cheers
Rohan

[GrUmPyBoDgEr]

Non symetrical cams are a common modification for race setups. The higher lift and / or longer duration cam going on the inlet side always. Putting the sprint cam on the inlet and SE cam on the exhaust should give an outcome in terms of top end power very close to the same as you would get with 2 sprint cams and you may even get a better torque curve than you would with 2 sprint cams as the twin cam especially in stromberg form has to much exhaust flow compared with inlet flow capability which tends to put a hole in the torque curve.

cheers
Rohan

Hi Rohan's post has reminded me of a race 1300cc twincam engine that I built for my 23B way back when & the camshaft set up was as Rohan has suggested, albeit not Lotus cam profiles as the car was purely for full throttle racing.
The cam profiles did give a hint of tractability to what was in essence a screamer & permitted me to release the clutch at 4000 RPM if needed.

Sounds like you have an interesting project; good luck!
John

[Matt Elan]

Thanks for the replys and the validation of my thoughts

I'll keep the forum informed; but the Restoration is a bit long term!