camshaft timing

[handyguy]

My BANTAM  has a 1937  English Austin  48 cu. in. 4 cyl.  flathead that I have upgraded to Turbo , ( 5 lbs so far ) and port injection , ( siamese intake ) with batch fire .  The cam I started with has .320 lift , ( won't flow  anymore beyond that with 1 1/8" intake ) and 300 degrees duration seat to seat with intake closing at 82 degrees  ABDC ,  108  center .. Paul , my English engine guy did this cam for carbs , ( 1 1/8" S/U  X 2 ) ..   Now I  need Turbo  profile , maybe 112 / 114 center and more exhaust duration ..   ANY THOUGHTS  / INPUT    STEVE

[wobblywalrus]

The Dynomation engine design program has modules for forced induction. 

[Dynoroom]

In VERY general terms the reason you move the lobe separation angle further apart helps reduce the overlap period. It has been found that turbocharged engines respond well to this with mechanical or batch type fuel injection. Port timed or sequential fuel injection seems to show less influence in this area.
Another thing that tends to happen when you spread the separation angle is the torque curve gets broader which is a good thing in an application such as yours.
Regarding adding duration to the exhaust side. My feeling are in an engine like this (flathead) the added duration will just add heat to the turbine side and cause potential valve & valve seat issues. Remember the exhaust side is under pressure & not free flowing.
I'd go to at least 112 lobe separation & keep the duration you have currently. But what do I know, I never did a flat head engine.   

Good luck with your project.

[fordboy628]

The Dynomation engine design program has modules for forced induction.

x2


Spend the time to do an ACCURATE model in one of the simulation programs available.    Dynomation, Engine Pro, whatever.

OR, pay a good camshaft specialist, to do the model and provide your cam.   Somebody like Mike Jones of Jones Cam Design, Denver, NC.    Or Bret Bauer, etc

BTW, "over lifting" beyond the max flow lift value, is a common way to control valve train motion factors, especially velocity, acceleration and jerk.    The decision to not lift beyond the max flow lift point is simplistic in that it does not consider these other factors.   AND, just to keep it as complicated as it is, valve train mass, spring force available, spring packaging dimensions, etc, etc, all need to be considered.    It all comes together as a "compromise".    You want the best compromise for your particular "application" . . . . . . . . . .

All of the above guarantee that forethought put into your valve train design initially, will pay off in the finish.

Wide "ish" LCA is usually the way to go with any sort of supercharging.   Do the model.

JMO
Fordboy

[handyguy]

Pics of engine  hosing , blue water , red oil , black fuel , (gas now , alcohol next)

[manta22]

I like your color coded hoses idea, Steve.

[handyguy]

AND , its not totally correct ..  The air from turbo is blue , you can't get yellow for air ..  The water alcohol injection into the air hose is red ..  Every Winter I  redo things .. Last year the oil to front of the crankshaft got direct oil from the engine pump , ( originaly the crank to rods oil was from oil jet on side of the block at 15# oil ) ,,  everything else got secondary oil , ( cam bushings , lifter galley , turbo )..  This time all secondary oil will be 30# isolated from crank oil at 75# to 90# ..  Should water from the tank behind seat go to the head first and out the side block opposite of now routing ??  This engine is 2 main roller brgs , now pressure fed to rods through front of crank , ( crank and rods now billet steel , counterbalanced , mains mist fed )..   STEVEl

[wobblywalrus]

The dynomation program models forced induction but it does not model flatheads.