42 vs 44 valves

[nicolas]

Oh sure, a 70 idle is huge, I would guess 60 would be the go, it should cut the cylinder  with about 1/4 turn remaining to go in, and kick it back in by 1/2 to 3/4 out from fully in, 1 turn out should be all smooth, then give it 1/4 turn, all this with the linkage off obviously.
If your porting and manifolding are correct, you can run up to valve size on the choke, I come down 2 mm for circuit racing where we need the best possible throttle responses, so with 44 inlets, I'd run a 42 choke, don't forget 42 inlets use the same seat  as 44,s  so you should be good with a 40 choke, assuming you don't want to leave power in your pocket, I run big squirters again for throttle response,  you may not need 60 squirt jets but it will be a starting point and about were you want to be, 50 sounds to small, so maybe 55, also 3 hole IDA' can use a size down on mains over the 2 hole ones.

took this quote from a different post, but it got me thinking about the valves. why even bother with 42 inlets if the 'hole' (seat and area just behind it) is the same? or are they cut differently? in which case you always can upgrade a 42 seat to a 44, but with a port job as well? is this difficult to do?

[neil68]

Since no one is responding, I'll contribute one comment.  I had K-Roc work on my  42 x 37 mm 044 Ultra Mag Plus heads a few years ago and I recall him mentioning much the same thing about the seats.

Darren removed the original 42 intake valves, installed 44's and did some porting.  In back-to-back dyno tests, I gained 11 WHP

[K-Roc]

Actually what I did was recut the same seat out to 44 mm  with a 3 angle grind and radius the bottom into the 42mm throat size and reshape the chamber.

Cheers

[nicolas]

everyone can chime in Neil!  if it is a personal experience it is always welcome in my opinion. if it is a story about i heard of a friend of a friend's uncle who's cousin from alaska did this, i am a bit more reserved in believing it. 

but back on topic. so the seat is the same, and the seat is radiused into the existing port and rest of the head. what reshaping of the chamber is needed? enshrouding around the valve? or was this a chance to 'upgrade' the heads some more?

[spanners]

It's horses for courses, for a throttle response engine required for circuit racing, or even street,  for pure gas speed, not volume,  you won't want a 44 valve in a small cylinder when a 42  gives more torque, the bigger valve can hurt cylinder filling, the gas has to go around a bigger obstruction, for example, I use 42mm in my circuit 2.1 with 94mm bore, but 44mm in my 2.5 with 98 bore, the seat is thinned for a far bigger port which would hurt gas SPEED ON THE 2.1, the 2.5 motor has a short con rod for huge 'suck' on intake, so can support a big valve and port, tho There is plenty of meat still to come out for a forum photo port job, but that don't cut it for variable rpm racing, The same analogy applies to exhaust valves and ports.
drag motors are a different animal, and I've also done 1641's with 40 mm intakes and ports bigger than I now use and know work better for the job I do, but it needed flat shifting for the whole race to not lose that gas speed, the clutches had to be massively vented to cool them,,,
Exceptions can apply with fuel injected/ electronic ignition controlled motors, but my comments cover carbed non turbos of the old Skool circuit racing type,  any other input on an interesting subject welcomed.

[cnfabo]

My circuit/hillclimb 1916cc motor has 44 intakes on kroc ported  SE's.I'm not sure why the size ,but a very very good engine builder here in Australia uses smaller valves in his built 1916's and makes good power not to mention his cams are 1.1 ratio cams and only lift low 400's at the valve....spouse its not always biggest better....

Thanks
Fabo....

[fish]

Hey Fabo, whos this Australian engine builder you speak of?

Valve size and porting is a bit of a science as is the correlation of cam to inlet track shape and length, as pointed out you can reshape a 42mm seat to fit a 44mm valve but do you really need to, weighing up the positives and negatives outlined above.

ben

[cnfabo]

Hey Fabo, whos this Australian engine builder you speak of?

Valve size and porting is a bit of a science as is the correlation of cam to inlet track shape and length, as pointed out you can reshape a 42mm seat to fit a 44mm valve but do you really need to, weighing up the positives and negatives outlined above.

ben

Pobjoy

[fish]

I respect the guy, but I don't agree with $6.5k engines producing 65whp.

Putting together a blown 2387cc atm with 44mm inlet Fred Simpson heads, ports are large in comparison with 42s because as outlined previously the large valve just gets in the way of the charge if the port is left alone.

[K-Roc]

My circuit/hillclimb 1916cc motor has 44 intakes on kroc ported  SE's.I'm not sure why the size ,but a very very good engine builder here in Australia uses smaller valves in his built 1916's and makes good power not to mention his cams are 1.1 ratio cams and only lift low 400's at the valve....spouse its not always biggest better....

Thanks
Fabo....

Displacement and RPM required, dictate the min. Intake port cross section, ( could be the seat throat in some ports...)

The throat dimension dictates the valve diameter...... ( the throat is a percentage of valve head diameter as well )
 
You can get away with a smaller valve sometimes ....on a blown or turbo, but  in a normally aspirated motor  if you size the valve too small your port will choke, if you size it too big it will be lazy.

Cheers

[cnfabo]

My circuit/hillclimb 1916cc motor has 44 intakes on kroc ported  SE's.I'm not sure why the size ,but a very very good engine builder here in Australia uses smaller valves in his built 1916's and makes good power not to mention his cams are 1.1 ratio cams and only lift low 400's at the valve....spouse its not always biggest better....

Thanks
Fabo....

Displacement and RPM required, dictate the min. Intake port cross section, ( could be the seat throat in some ports...)

The throat dimension dictates the valve diameter...... ( the throat is a percentage of valve head diameter as well )
 
You can get away with a smaller valve sometimes ....on a blown or turbo, but  in a normally aspirated motor  if you size the valve too small your port will choke, if you size it too big it will be lazy.

Cheers

What he said,my heads not lazy