Quote:Only make your pocketbook $200 lighter. It won't help performance at all. Dual-valve springs only help high-RPM camshafts (higher than 6000 RPM).

Building a custom manifold to use quad carbs of a bike could be an option if you can weld. Adding a plunum on the inake side of the carbies will tend to reduce the over all peak HP of a tuned system, bring it down the rpm range, spread it out and add a second peak lower down. The smaller the plennum the more this effect, the other extreme of course is no plunum or infinite volume.

If you're not doing anything else forget the springs, you only upgrade them if you're having trouble closing your valves.

If you're on a budget start by port matching, deburring, reducing any restriction on the intake side (air filter etc.) and ducting up cold air induction. That'll make the most of what you've already got.

If i fit springs into the original ones will that do anything?

In that case then all you can afford is higher compression.
You can shave your head :) or get high comp pistons or
taller cheap pistons you can machine down to avoid valves
hitting them which is more pricey but worthwhile in the end
as you can also gain extra CCs by going up to 77.5mm bores.

No major Upgardes atm,I really want to see how the stock a15 has more power over the a12.
I cant even afford a 32/3/6 weber Right now,I will have to do some saving.
What a Lseries ones could i get them off ?

ITB (Individual Throttle Bore) setups like twin Mikunis can gain substantial HP. I'm told it can double the HP on an A-series engine. But the runners need to be very long (about 23 inches long) to be effective at 6000 RPM. And it tends to be extremely peaky as in normal power above and below the tuned RPM range.

This is not long enough

Lots of things you can do and depends on your countries limits laws etc.
do you want all out power or just good torque for daily use?

All out power you cannot go past boost with SU carb.

for just extra oomph and Torque you need good ignition and the mentioned above goodies

Massive torque and driveability without sky high revs.

You will need a custom Headgasket made for full sleeved block
like renault 5 to 83mm using milled tops on ca18de pistons,
mild cam, ignition, headers and IDA single 36mm carb should
be a stump puller with big valve head and ported inlet mani.
1775cc but youll need deep pockets and gearbox to suit.

twin carbies?
porting?
oversize bore?
lightened flywheel?
cam (reground?)?
dont expect any to be more economical... what kind of engine are u looking for? ie. big top end power, very torquey, mild streeter with lumpy cam etc?

Agreed, the springs on their own won't bring any performance gain. They will only allow the A15 to rev more than 6,400 RPM.

If you really want this, just buy A-series dual springs, only $100 brand new from USA cam vendors.

If everything else is stock then you would be better off upgrading the ignition or the camshaft. Even extractors/headers.

The springs on their own won't bring any performance gain.